David Deutsch's "The Beginning of Infinity" Chapter 11 "The Multiverse" Part 3, ToKCast Episode 26

00:00:00.000 Hello and welcome to Topcast episode 26. We're still on the multiverse and I tend to be talking
00:00:28.000 more than I have in previous episodes. Thank you to the people who've been supporting the
00:00:31.840 podcast by the way. They're coming out more frequently precisely because of the additional
00:00:36.240 support I've been receiving via PayPal and Patreon. So thank you for that. So we're going to be doing
00:00:44.240 at least after this one one more episode. I was intending on this being the final episode for the
00:00:49.600 multiverse but just looking at the time that it's taken for each of these to complete. That's in
00:00:55.920 how long each episode running for. I wouldn't like to make one episode go for two hours and so for
00:01:01.680 that reason this one's kind of probably be about an hour and then the next one will be an
00:01:06.000 about an hour as well. And then that will be the last one on the multiverse before we move on to
00:01:12.000 chapter 12 of Physicist History of Philosophy. What we've been talking about so far in the readings
00:01:19.760 from chapter 11 is the fictional story that David is telling in order to explain aspects of the
00:01:28.160 multiverse theory which aren't often considered by people who explain the multiverse theory.
00:01:33.360 One important aspect of that is fungibility and today we're going to come more directly to this
00:01:38.800 idea of entanglement as well so we're going to have a go at explaining that. So to recap what we had
00:01:44.800 in a previous episode was that a device called a transporter had a voltage surge in it in one
00:01:50.080 universe but not the other. This is the quantum event. The quantum event happens in one universe
00:01:54.720 but not the other. And quantum events are typically of this kind. We've looked at half-silvered
00:02:00.560 mirrors for example where a photon could go through the mirror or bounce off. We've looked at
00:02:05.680 interference experiments of different kinds where for example young's two-slit experiment where
00:02:10.480 if you fire a single particle at the two-slits it could go through one or the other of the two-slits
00:02:15.600 perhaps neither. Perhaps it can take different paths through both as well but there are options
00:02:20.640 within the universe about where these particles could go. In the case of the story that David's
00:02:26.800 telling the voltage surge could have happened in the universe or might not have happened in the
00:02:30.880 universe. And then the effects of that voltage surge this quantum event are amplified up
00:02:36.240 to the point where the voltage surge where it happens jolts a particular person and that caused
00:02:43.600 them to spill coffee and the coffee spill then leads to them talking to the person that's sitting
00:02:49.840 next to them and romance ensues. So we end up with this emergent kind of stream of information
00:02:56.160 going on in one universe that didn't go on in the other. Okay let's continue with the book.
00:03:01.760 I've skipped a substantial bit now I'm about to skip a substantial amount more as I emphasize in
00:03:06.400 the last chapter this is the longest chapter in the book and I am only partially doing it just as
00:03:12.000 so you really should read the entire chapter. My videos are just to provide additional context
00:03:17.600 and exposition I suppose. All right let's continue and David writes. Now suppose that scientists
00:03:24.560 on the Starship know about the multiverse and understand the physics of the transporter.
00:03:30.400 They'll note that we have not yet given them a way of discovering these things. Then they know
00:03:35.040 that when they run the transporter an infinite number of fungible instances themselves all sharing
00:03:40.720 the same history are doing so at the same time. They know that a voltage surge will occur
00:03:46.720 in half the universes in that history which means that it will split into two histories
00:03:51.760 of equal measure. Hence they know that if they use a voltmeter capable of detecting the surge
00:03:57.920 half of the instances of themselves are going to find that it has recorded one and the other half
00:04:03.680 are not pause there just my reflection. Remember also in the last episode we moved beyond this idea
00:04:10.800 that there were only in fact two universes that in fact there's a an infinite number of universes
00:04:17.200 an uncountably infinite number of universes all of which are fungible to begin with they're
00:04:23.200 all the same and they're the same number of universes is maintained throughout any event which
00:04:31.120 causes differentiation. So the idea of the multiverse is that we have a constant number of universes
00:04:38.000 it's just that they differentiate over time they become different over time and so prior to this
00:04:44.640 voltage surge there's a certain amount of universes a certain measure of universes you can't count
00:04:50.960 them for reasons that are explained previously in the book on infinities. So instead what we have
00:04:57.520 is this idea of a measure so we have this measure of universes consider it analogous to measuring
00:05:03.440 the length using a ruler okay that's an infinite number of points between you know the one centimeter
00:05:09.760 point and the ten centimeter point even though there's only nine centimeters difference between them
00:05:13.920 there's an infinite number of points and so instead of counting the points between one centimeter
00:05:19.520 and ten centimeters we measure lengths to say that there's nine centimeters between the one and the
00:05:24.800 ten now we could divide that nine centimeters and half to two four point five centimeter sections so
00:05:30.320 we're talking about lengths rather than counting points when it comes to measuring things and so
00:05:35.440 the same thing is true here of the multiverse and analogous thing is going on where prior to the
00:05:42.080 voltage surge happening the measure of universes is such and then after the voltage surge happens
00:05:48.800 the universe differentiates into two equal proportions now it doesn't have to be equal in the
00:05:55.280 true quantum theory it can be any old proportion that you like but assuming the simplest case
00:06:01.360 here we have half of the universes in which the voltage surge happens and half the universes
00:06:07.680 in which the voltage surge does not happen and all of the well I say I'm about to say things
00:06:15.200 in those universes but remember the universes are nothing more over and above the things that
00:06:20.720 are in the universes it's not like a universe is a receptacle four things as David has said previously
00:06:27.520 and so the people in that in those universes there's uncountably infinite numbers of fungible
00:06:34.160 instances of those people as there are for you and as I've said before all that seems preposterous
00:06:39.840 what on earth would it feel like to be many different people exactly as it does now now if you're
00:06:44.880 struggling with that concept well depending upon who you are perhaps you've struggled when you
00:06:53.200 first perhaps figured out that you didn't have an immortal soul and some people who believe in
00:06:59.200 the immortal soul who are religious if they undergo a transformation in their mind where they
00:07:06.080 realize that they don't have an immortal soul now if you're not a religious person you might
00:07:11.920 very well be asked by a religious person it's preposterous to think I don't have an immortal
00:07:16.960 soul I can feel that I have an immortal soul they're feeling their mind or they're feeling their
00:07:21.840 consciousness something like that so I think it's no more of a great jolt going from believing
00:07:29.360 you have an immortal soul and you have a certain sense of having an immortal soul to no longer
00:07:34.160 believing that you have an immortal soul this is the kind of transition that I would think it's
00:07:39.680 analogous to going from thinking you're just a single instance of a person in a single universe
00:07:46.000 to you are uncountably infinite numbers of instances of people in the multiverse you're a multiverse
00:07:51.840 object I don't think this is a huge transition okay so I'll just step back a bit I'll reread
00:07:58.400 some and then I'll move forward again so David wrote hence they know that if they use a voltmeter
00:08:05.040 capable of detecting the surge half of the instances of themselves are going to find that it has
00:08:11.440 recorded one and the other half are not but they also know that it is meaningless to ask
00:08:17.520 not merely impossible to know which event they will experience consequently they can make two
00:08:23.840 closely related predictions one is that despite the perfect determinism of everything that is
00:08:29.520 happening nothing can reliably predict for them whether the voltmeter will detect a surge the
00:08:35.920 other prediction is simply that the voltmeter will record a surge with probability one half that's
00:08:40.960 the outcomes of its such experiments are subjectively random from the perspective of any observer
00:08:46.720 even though everything that is happening is completely determined objectively this is also the
00:08:51.600 origin of quantum mechanical randomness and probability in real physics it is due to the measure
00:08:57.040 that the theory provides for the multiverse which is in turn due to what kinds of physical
00:09:02.080 processes the theory allows and forbids notice that when a random outcome in this sense is about to
00:09:08.000 happen it is a situation of diversity within fungibility the diversity is in the variable
00:09:14.160 what outcome they are going to see the logic of the situation is the same as in cases like that
00:09:19.200 at the bank account I discussed above except that this time the fungible entities are people
00:09:23.280 they are fungible yet half of them are going to see the surge and the other half are not
00:09:29.920 pause their my reflection so it sounds preposterous that you are made up of all these fungible
00:09:38.560 entities that there are these many different universes but the fact that it's surprising or
00:09:45.600 astounding is not a meaning is not a reason for rejecting it nor a reason for getting
00:09:51.760 unduly emotional except to be curious and interested and fascinating perhaps positive emotions
00:09:59.120 it's just what the science is telling us but it's remarkable to be that some people have
00:10:04.160 visceral negative reactions and so I'm going to have a little diversion here and we're going to
00:10:09.680 listen to a different podcast we're just going to listen to a few minutes of the excellent
00:10:16.160 Brett Weinstein's Dark Horse podcast and this is an episode in which Brett Weinstein
00:10:24.800 talks to Sam Harris these two people are great intellects I love listening to Brett Weinstein
00:10:33.040 I think he's a fantastic thinker great biologist a person who was able to sensibly reflect upon
00:10:40.720 culture at this moment and of course Sam Sam is a great rational thinker typically measured in the
00:10:48.320 way he talks about things he doesn't get overly emotional and here in what we're about to listen
00:10:55.200 to they're discussing the multiverse now as much as I admire these two great public intellectuals
00:11:02.480 I think here they make terrible missteps in simply appreciating the physics and I think it's not
00:11:09.760 only because they're stepping outside their domain of expertise I don't have a problem with people
00:11:14.000 doing that after all this is what I do quite often the concern I have is they're not applying
00:11:20.320 the same standards intellectual standards to this theory as they would to any other theory
00:11:27.360 that a scientist might have and in particular when it comes to evolution by natural selection
00:11:32.720 all of the objections that I'm sure that Brett hears from creationists or other people who reject
00:11:41.440 Darwinism or neo Darwinism all of those objections are precisely the kind of objections they're
00:11:47.360 on a continuum with the objections that he's about to raise about the multiverse okay so
00:11:53.920 rather than going to a longer preamble than that let's just get into listening to the podcast
00:11:59.760 by the way this is episode eight of Brett Weinstein's Dark Horse podcast it can be found on
00:12:06.560 YouTube it can be found on iTunes his podcasts typically very long conversations which are excellent
00:12:13.680 you know of the length of two and a half hours or so we're only going to listen to a few
00:12:19.120 minutes just a part that's about the multiverse and it comes up in a discussion just by the way
00:12:24.800 about free will and in terms of free will Sam and Brett seem to be in furious agreement about
00:12:31.360 the non-existence of free will so let's hear what they have to say right yeah well so this could
00:12:40.160 be a semantic difference between us but let's talk about what you think that that
00:12:45.440 sintilla of freedom actually is okay so first of all it is utterly dependent on us not living in
00:12:51.200 a deterministic universe if we live in a deterministic universe then I don't understand a damn thing
00:12:55.760 and it's game over for Brett assuming we don't and I think the physics is pretty clear there's
00:13:03.200 no reason to think we do there's quantum uncertainty and the fact that there is quantum uncertainty
00:13:09.440 means that uncertainty can exist at higher levels through various mechanisms well or we live in a
00:13:14.880 universe where if you take the many worlds picture seriously which again is hard to do but
00:13:20.720 many physicists do at this point now Sam has just said there that it's hard to do it's hard to
00:13:29.600 believe in this idea of the multiverse very well many things are hard to believe I suppose almost
00:13:39.280 anything in science is hard to believe anything of interest is hard to believe the universe is
00:13:45.040 13.7 billion years old now the universe is as large as it is the universe contains as many stars
00:13:51.680 that it that it does I mean these are we have preposterous numbers to some extent when talking
00:13:57.040 about these things the number of possible organisms that could be produced using the DNA
00:14:04.720 code preposterous perhaps infinite in size now just putting aside the fact that I don't think
00:14:10.960 that the multiverse adds too much to this concept of free will I think that well the concept of free
00:14:17.200 will that I have anyway this idea that it's an emergent feature of human minds coupled to their
00:14:24.400 creativity causing them to be able to do things that are inherently unpredictable I don't think that
00:14:31.440 that's really helped by the multiverse but it's certainly not made anymore difficult I don't think
00:14:37.760 the multiverse really has a lot to do with free will to be honest but putting that aside what is
00:14:44.000 the scientific criticism of the multiverse that Sam and Brett are sort of about to get into here
00:14:49.280 that's what we need to listen out for or what is the philosophical criticism the philosophy of
00:14:55.280 science or the epistemological criticism because Sam so far has said it's simply hard to believe
00:15:01.600 but the feeling that something is hard or difficult hard to take seriously is not a reason for
00:15:08.800 rejection it could be a reason to look into things a little bit more deeply and of course I'm
00:15:16.800 not going to I'm not going to get into right now the fact that Brett clearly thinks that
00:15:20.800 determinism and free will cannot go together okay I'm not the only one who thinks that they can
00:15:26.720 donate to another person reasonable people can have differences upon this okay and often it comes
00:15:33.120 down to these silly um definitional games and if we define free will in the way that people who
00:15:42.720 say they're not compatible is to be defined well then I agree that sort of free will cannot possibly
00:15:49.360 obtain if free will has to mean something like beyond the laws of physics a supernatural force that
00:15:56.080 allows you to make choices outside of what physics permits or a an uncaused cause okay if it's
00:16:05.280 something like that if that's what free will is then I agree that doesn't exist free will cannot
00:16:10.720 be supernatural and it cannot be an uncaused cause so I'd like to preserve the concept of free
00:16:16.400 will the kind of free will that people typically who believe in it I think they think they have
00:16:22.400 or at least to come to understand it a little better and so that's the reason I think that free
00:16:27.040 will and determinism have to go together and if you don't want to call what I think free will is
00:16:33.360 free will do you want to call it something else I'm okay with that as well okay but I typically
00:16:38.320 think that when people are talking about choices and free choices it's a very simple concept to
00:16:44.400 just use the term free will I've got numerous blog posts on my website about free will anyway
00:16:50.240 we're not here to talk about free will let's go back to Brett's podcast we live in a world where
00:16:59.120 everything that can happen does in fact happen somewhere right and you don't know which one of
00:17:04.400 these worlds you're in right so it's it's a new kind of determinism in a way which is you know
00:17:11.440 every every gradation of possible difference in in in this probability space which is this
00:17:19.520 conversation between us is spawning yet another universe in which precisely that thing is
00:17:25.600 happening you know as as deterministically is one billiard ball hitting another but the uncertainty
00:17:33.120 is we don't know which one we don't know whether we're in the universe where we both start speaking
00:17:38.640 Mandarin right now for reasons we can't understand or we're in the universe I'm pretty sure we're
00:17:43.680 in the universe where we're going to stay stick with English but whatever surprises are here
00:17:51.120 are still can still be understood understood determinally deterministically in that picture
00:17:57.120 okay so I think that's great I think that's more or less correct perhaps one of the misconceptions
00:18:03.200 that people have when they reject this is that although Sam what Sam has said there is quite
00:18:07.600 true we don't know if we're in a universe we're going to start speaking Mandarin all of a sudden
00:18:12.880 even though neither of them can speak Mandarin that's a physically possible universe
00:18:18.160 some people think that it's somehow likely or common or I don't know what they think the mere
00:18:24.240 possibility that that is a possibility is a refutation of the theory but it's not
00:18:32.720 there are possible organisms that one could create using DNA that would be absolutely astonishing
00:18:45.280 but terribly unlikely no doubt there is a physically possible organism that can evolve
00:18:52.960 which is highly unlikely to ever evolve in the history of our universe
00:18:58.480 interestingly enough however bizarre the organism is if it's physically possible it will evolve
00:19:04.080 somewhere in the multiverse so these are kind of related issues to be to be honest but you know
00:19:09.200 we could consider imagine a scenario an alternative history where we never had any fossils we
00:19:16.240 never had any evidence of dinosaurs imagine that possibility it's possible I mean dinosaurs
00:19:22.000 fossils are hard to come by they only result under very very rare circumstances the dinosaur has
00:19:30.880 to fall into a you know lake of mud of just the right kinding it covered up immediately
00:19:37.120 in an anaerobic environment where the oxygen can't get to it and the bacteria can't get to it
00:19:42.160 so that the bones are preserved blah blah blah there's a lot of coincidences that have to
00:19:47.200 happen to preserve dinosaurs I can imagine a world where dinosaur fossils were far far far more rare
00:19:53.360 than what they are and it could have been the case that by 2020 we had never found any dinosaurs at all
00:19:58.800 but we may have found evidence for evolution and evidence of the evidence of the DNA there's
00:20:08.800 the thing that contains the genes which is the which is the unit of evolution now imagine
00:20:14.880 if we had very similar universe the universe is basically the same as ours but it's a universe in
00:20:21.120 which fossils had never been found if somebody like me had come along doing exactly a podcast like
00:20:27.840 this and then said well DNA allows things like DNA would allow things almost like dragons I'm
00:20:36.400 not saying these dragons can break the laws of physics I don't think they'll probably be able to
00:20:41.680 breathe fire but I could imagine a flying dragon or I could imagine a dragon that is you know 50
00:20:49.760 meters long lumbering around on land I could imagine that the biologist might very well say well
00:20:57.200 that's not possible you know the limbs are too big it's too heavy it wouldn't be able to get
00:21:03.520 enough oxygen into its lungs there's no way these things could fly but of course we know even
00:21:09.280 though people in that universe don't but the dinosaurs are eminently possible
00:21:15.120 there were terradactyls big flying things that may as well have been dragons without the breathing
00:21:20.080 of the fire there were bontosaurus and diplodocus you know there's really big huge dinosaurs
00:21:26.240 that were that that that eight trees they were physically possible they actually existed
00:21:30.800 but I can imagine a biologist being so incredulous and many people being so incredulous if we didn't
00:21:38.640 have fossil evidence as to reject outright even the possibility given DNA that such a thing could
00:21:46.160 evolve but they can and in our universe we happen to know that they can now I don't know what the
00:21:50.480 repertoire of all different organisms is it's infinite but it will be an interesting I guess
00:21:58.400 project to try and figure out you know could you evolve and animal with wheels I don't know
00:22:05.600 could a mammal evolve such that it can exist in very sub-zero temperatures or or above a hundred
00:22:15.120 degrees Celsius I don't know okay but these are things which are possible or not given the DNA
00:22:24.400 and so there are things that are possible or not given the laws of physics but I think the
00:22:29.600 same has echoed kind of what I've said in the last episode in the episode before that and the
00:22:34.320 episode before that which is something that David emphasizes quite often is that the quantum
00:22:39.840 multiverse is simply determinism it's a deterministic theory and it unlike unlike certain other
00:22:50.320 so-called interpretations which are not deterministic they attempt to introduce randomness into
00:22:56.240 the world okay let's keep going we've got the next key bit by Brett well I've never regretted
00:23:07.360 not speaking Mandarin more I do right now but so here's the thing I I resent the many worlds
00:23:15.520 interpretation so there we have it there it is he resents the many worlds interpretation it's an
00:23:22.720 emotional reaction where else in science is this a legitimate form of criticism especially
00:23:31.040 from an outsider it will be right if at one of his public lectures on evolutionary biology
00:23:40.000 to reject outright a conservative religious person who stood up and said that he
00:23:48.560 resented the theory of evolution by natural selection he would be right to reject it as a
00:23:56.240 legitimate criticism it's not it's not a scientific criticism it's a sign that the person is
00:24:03.200 having a visceral emotional reaction because they don't understand it that's all it's no
00:24:10.720 sin not to understand something but it's possibly a misstep to then get exceedingly emotional
00:24:17.280 about it to the point where you're using a word like resent now perhaps I'm reading too much
00:24:23.360 into resent until we hear the rest of what he has to say I'm actually not convinced that it's
00:24:30.160 exactly wrong but I am convinced that at best it is a very stupidly explained way of phrasing
00:24:42.240 something that nobody can seem to phrase so that it is not insane okay so we can take the point
00:24:49.520 that explanations are hard to come by and difficult to express what did Carl Papa say it is
00:24:57.680 impossible to speak in such a way as to not be misunderstood so any explanation of a fundamental
00:25:04.880 phenomena is going to be difficult at times for people to grok to understand but insane
00:25:15.360 and stupidly explained perhaps the explanations that Brett has heard have been stupidly explained
00:25:22.960 or insane to him it's not the sort of language I think I've ever used about a scientific
00:25:28.880 explanation there might be two kinds of people in the world when encountering a deep subtle
00:25:35.600 explanation for the first time in fact I signed up by my mother and my father my father will
00:25:41.440 often be somewhat like Brett Weinstein he will say that's stupid and he will reject it outright
00:25:47.200 because it seems to outlandish my mother on the other hand will just say I don't understand it
00:25:52.720 I don't get it that's it so when it comes to the the multiverse explanation I think it's astonishing
00:25:59.040 and when I first heard it I thought that's astonishing that's astounding that's surprising
00:26:04.560 but as for stupid and insane they're not normally words that I tend to apply to scientific theories
00:26:12.640 Brett himself would have been in the position that some physicists in with respect to explaining
00:26:18.800 aspects of quantum theory Brett as a professional biologist has probably delivered public lectures
00:26:26.160 where there's been conservative religious people who've come up to him after the lecture or
00:26:32.320 perhaps during the questions and been unable to fully appreciate what Brett has been saying
00:26:40.080 about evolution by natural selection Brett must know what it's like to deal with a person who
00:26:45.840 has an emotional a visceral reaction to something new that simply signs it is not a valid
00:26:54.080 criticism for a creationist to say evolution by natural selection is insane I mean I can use
00:27:01.040 those words if they're like free speech is permitted but it's not a valid scientific criticism
00:27:06.400 it's not a valid philosophical criticism all it is is throwing shade it's it's insults it's not
00:27:15.360 actually seriously engaging with the theory evolution by natural selection is an explanation of
00:27:22.480 how the diversity of species has arisen it's an explanation of the similarity of DNA and the
00:27:28.880 similarity of physiological structures it's an explanation of the fossil record and as astonishing
00:27:35.600 as it might be to many people who hear it for the first time or especially religious people
00:27:40.960 who believe that it runs counter to their deeply held religious views it merely running counter to
00:27:48.560 deeply held religious views or deeply held perpetual errors that a person happens to carry through
00:27:54.800 their life is again no criticism Brett will be right to dismiss a religious person who was
00:28:00.240 criticizing okay in scare quotes because it's not a valid genuine criticism but having a go at
00:28:06.400 evolution by natural selection on the grounds that it's stupid or on the grounds that it is insane
00:28:11.040 so just because the explanation that some people have heard for neo Darwinism thus far seems preposterous
00:28:17.600 that's no reason for thinking the theory or those who endorse the theory are either stupid or
00:28:25.600 insane in fact it says far more about the person leveling those allegations against portions of
00:28:33.920 the scientific community because it's not a genuine scientific criticism it's more reflection
00:28:39.120 in the case of the religious person some kind of supernatural bias the magical thinking
00:28:45.920 and again as I've said before I find it far more astonishing to think that all of the entities
00:28:54.240 described by the equations of quantum theory including the Schrodinger wave equation
00:28:59.120 all those many many entities do not actually exist as the theory says that they do but rather the
00:29:06.400 act of observation causes them all to vanish or from science and from reality leaving only one
00:29:13.120 that we do observe that's a strange impulse to have a psychological impulse that somehow science is
00:29:20.480 about you and your personal psychology and capacity to observe things rather like thinking
00:29:27.360 that the only planets that exist in the universe are the ones so far observed that would be
00:29:33.920 observed the theory of planetary formation extends beyond what we can observe
00:29:40.000 into regions of the galaxy and the universe that we have no hope of observing right now
00:29:45.120 but we know planets are there no in the fallible sense not no in the traditional
00:29:51.280 I'm justified in believing that such a theory is absolutely true the name of the existence of
00:29:57.280 planets beyond those that we can see so far but rather an understanding that the theory of
00:30:04.000 planetary formation is deeper than what our bare observations are revealing to us so to
00:30:12.560 in fundamental quantum theory we may only observe photons striking the screen at one place at a time
00:30:20.240 but the fact that they do strike the screen at this place rather than that place means that
00:30:26.720 they've been influenced by something unobserved namely photons in other universes and we've been
00:30:34.000 through that anyway let's keep going with Brett and Sam and so it is the it is that I think on
00:30:40.880 its face the hardest thing to believe that still is seemingly believed or at least paid lip
00:30:50.320 service by it might even be a majority now of physicists made it was the last poll I heard it was
00:31:01.840 something like 35 percent but it's it's it's getting there and it's it is the the strangest
00:31:07.680 picture of reality that you could you could imagine okay the strangest picture of reality that
00:31:13.120 you could imagine why just simply disagree it's not it's not the strangest picture of reality
00:31:18.960 that you could imagine that simply a failure of imagination on Sam's part but I don't think he
00:31:26.160 actually really believes that because there are many things that are far stranger to imagine
00:31:32.720 that people have taken seriously over the years great minds David Lewis wrote on the plurality
00:31:39.120 of worlds I feel a softical defense of many worlds but it wasn't many physically possible
00:31:45.760 worlds it was all the logically possible worlds and so he endorsed a kind of realism about this
00:31:52.560 and by the way David Wallace David Deutsch David Lewis I don't know if you have to be a David
00:31:58.480 to really make breakthroughs in many worlds but it seems like it helps anyway so David Lewis
00:32:04.560 his book about on the plurality of worlds talks about how all logically possible worlds obtain
00:32:11.200 some way in reality that has to be a far infinitely stranger and therefore more difficult to
00:32:18.400 imagine picture of reality on Sam Harris's account than anything that David Wallace David
00:32:24.400 Deutsch or Hugh Everett have ever come up with because the many worlds interpretation of physical
00:32:29.840 reality represents but a tiny tiny sliver of all the possible logically possible realities that
00:32:36.080 are out there all the logically possible worlds because those other logically possible worlds
00:32:40.640 will obey different laws of physics the physically possible worlds of the multiverse all
00:32:46.400 obey exactly the same laws of physics and so the the class of all different possible logically
00:32:54.320 possible worlds that is a far far greater number and therefore a stranger picture of reality
00:32:58.640 but again I just think it's kind of a failure of imagination to think that there's nothing
00:33:03.360 strange than this I insist again that all physicists endorse something like the Schrodinger wave
00:33:12.080 equation as a serious representation of reality to some extent those who do not endorse the
00:33:19.440 many worlds interpretation say that the Schrodinger wave equation in some way represents reality
00:33:24.640 prior to the act of observation and then the act of observation consciousness whatever you want
00:33:29.120 to call it the observer effect it's a thing that causes the collapse of the wave function so all
00:33:33.360 the realities disappear but one that we observe that to me is more difficult to imagine and it's
00:33:41.360 this additional assumption that what the equation is telling us about reality is true until
00:33:48.800 the act of observation when it's the act of observation that is bringing into reality what is
00:33:53.520 true that's an additional assumption over and above what the many worlds interpretation is telling
00:33:58.640 us the multiverse just says that reality is what quantum theory what the equations of quantum
00:34:05.520 theory describe that's it we're not adding anything to it but collapse models do they
00:34:11.280 add something they add this additional assumption that observation is causing reality to be the
00:34:17.200 way that it is that's bizarre that's really bizarre and as for hard to believe that's far harder to
00:34:25.360 believe this idea that observation is the thing that is causing little particles to do one thing
00:34:32.160 rather than other it's your act of observation that causes all the realities to disappear but one
00:34:36.880 and therefore all of the electrons and photons that happen to be in your experiment to follow one
00:34:41.920 path rather than another there's spooky action at a distant distance if ever there was some
00:34:47.120 the strange woo woo force coming out of your brain and affecting subatomic particles at a distance
00:34:54.720 from you that seriously is what collapse models are insinuating about reality that makes no sense
00:35:02.080 that's a weird metaphysical jump I don't get it but I wouldn't say that people who endorse that
00:35:07.200 are necessarily insane or stupid or that's necessarily an insane or stupid theory that's not a
00:35:12.160 sign to be criticism but the criticism that you must add additional assumptions like the power
00:35:19.120 of observation causes the vast majority of reality described by the equation of physics to disappear
00:35:25.520 that that is a fair criticism that we shouldn't have such an assumption that no assumption is needed
00:35:33.360 because to introduce such an assumption is merely to try to get the theory to
00:35:38.960 comport with your biases with the biases that we're hearing expressed here that it's just too hard
00:35:44.080 to imagine that it's difficult to believe it doesn't matter if it's difficult to believe
00:35:49.280 evolution by natural selection is difficult for some people to believe but the difficulty in
00:35:53.760 believing it has no bearing whatsoever on the actual correctness or otherwise of the theory or of
00:36:00.720 the explanation as being the best explanation that we have let's get going yeah I think you're
00:36:06.640 being too nice yeah it's stupid the idea that universes are spawned to deal with the difference
00:36:11.920 between the thing I dropped hitting one carpet fiber in the next day
00:36:15.440 it's hilarious to me I mean it Brett's having an emotional reaction Brett Weinstein's having an
00:36:24.000 emotional reaction a very negative visceral emotional reaction here saying it's stupid it's insane
00:36:28.240 I mean I will get emotional about science at times like this when people are having ridiculous
00:36:34.640 reactions I mean there's no reason to say that it's stupid because it's not it's not if you
00:36:40.240 understand it and I think it's reasonably clear that he doesn't understand it or that he's been
00:36:47.440 presented with a strange version but he hasn't read the books of David Deutsch let's just say
00:36:54.480 and I would recommend to you Brett please pick up the fabric of reality in particular the chapter
00:36:59.920 called shadows and if you're not convinced after that very well but I wouldn't say that people
00:37:07.040 who write such books are stupid or insane and this is not this is not reasonable philosophical
00:37:14.960 discussion it sounds measured and reasonable and Brett under normal circumstances is a great
00:37:19.200 mind a great intellect I love listening to him is fantastic as I say in terms of biology
00:37:26.480 really original thinker in certain respects I think in terms of analyzing culture right now
00:37:32.480 both Brett and Sam brilliant of that not everyone who steps outside of their domain necessarily
00:37:38.480 makes such strange sweeping generalizations you know I will comment frequently about aspects of
00:37:45.600 economics or history that I don't necessarily have expertise in but I don't usually regard
00:37:51.520 even though with whom I have a serious disagreement as stupid or insane nor their theories necessarily
00:37:58.480 okay let's keep going sorry that's not how nature works it's a different view of parsimony than
00:38:04.800 than I have intuitively but it's a total rejection of parsimony it is the most it is the opposite
00:38:11.680 of parsimony okay so there we go um he I guess misunderstands parsimony and I think Sam is about
00:38:18.880 to correct him on that by the way and Sam does a very very good job of correcting him on it as
00:38:24.560 well I think but parsimony it's just this idea that you shouldn't increase the number of assumptions
00:38:32.320 beyond what is absolutely necessary in order to get your explanation across now this is in my mind it's
00:38:39.280 the same as Occam's razor now I've had university lectures at some point try and tell me the
00:38:43.360 difference between what parsimony is and Occam's razor and I've never got it I've never understood it
00:38:48.400 apparently there's subtly different things parsimony versus Occam's razor but I use them interchangeably
00:38:53.680 I'm not only going to continue to use them interchangeably here for the moment unless someone can
00:38:57.200 provide me with direction on where I've gone wrong and so given that they're both about assumptions
00:39:03.280 let's just go to the fabric of reality where David writes about this precise objection that the
00:39:10.080 many world is somehow a rejection of parsimony or rejection of Occam's razor this in fact was the
00:39:16.400 criticism that Paul Davies Professor Paul Davies had all the many world interpretation that it caused
00:39:22.880 the number of universes to multiply beyond all reason in order to explain the one universe we do
00:39:29.440 observe but as Sam I think says in the next bit that's a concern about the bricks and mortar of
00:39:35.040 the theory rather than the assumptions in the theory now I've already mentioned you know the
00:39:41.600 idea of exoplanets planets that are beyond the solar system now we only found the first one I think
00:39:49.120 back in 1994 something like that but our theory of planetary formation prior to 1994 predicted that
00:39:57.680 there should be planets going around other stars now it would be a violation of Occam's razor
00:40:03.680 not a correct use of it a violation of Occam's razor to say those planets do not exist that
00:40:09.200 although the theory of planetary formation says gas giants and little rocky terrestrial planets
00:40:15.040 should be orbiting perhaps a majority of stars it would be wrong to say however to take that theory
00:40:21.760 seriously would cause the number of planets throughout the galaxy in the universe to proliferate
00:40:26.320 beyond all reason no well within reason and in fact today we can see planets out to what some I
00:40:33.440 think thousand light years going around stars here in the Milky Way galaxy but it's not it's not
00:40:40.080 very far okay the other side of the galaxy is 120,000 light years away and the next nearest galaxy
00:40:45.280 is 2.2 million light years away and we can see galaxies off to you know many billions of light years
00:40:50.000 away we have no hope at the moment with present technology of seeing planets going around stars
00:40:55.520 and other galaxies but we know there must be planets going around stars and other galaxies because
00:41:00.640 our best theory of planetary formation says that when a star forms it will form from a cloud of
00:41:05.440 gas and dust which will then have a disk of material rotating around that star some of which
00:41:11.120 will come together to form planets now that's a very simple idea with very small number of
00:41:18.480 assumptions leading to this proliferation of matter the bricks and mortar as Sam will come to say
00:41:24.160 and so proliferating the bricks and mortar is not a violation of parsimony it's an endorsement
00:41:28.880 of it it's a correct use of it so let's go to the fabric of reality okay so David in this is in the
00:41:33.840 chapter called a conversation about justification page 160 of my paperback here and David is
00:41:42.800 talking to a crypto inductor this the entire chapter is a refutation of the inductivist
00:41:48.480 picture of knowledge and he's arguing with a person about what the correct theory of gravity is
00:41:55.040 so it's in the context of what we should think out correct theory of gravity is and on the basis
00:41:59.440 of what should we think our correct theory of gravity is the correct theory of gravity so we're not
00:42:04.400 going to go into that but the entire argument that David is about to use here that I'm about to
00:42:09.360 read applies in this situation so again just to reinforce in people's minds we have certain
00:42:16.320 equations of quantum theory one of which is called the Schrodinger wave equation and the Schrodinger
00:42:21.920 wave equation explains well the Schrodinger wave equation can be used to describe all
00:42:29.280 of the positions for example that an electron has around the nucleus of an atom let's say
00:42:35.840 and so this gives us the wave function and it predicts that the electron will occupy multiple
00:42:42.000 positions simultaneously around the nucleus of an atom so the electron is not in one spot it is
00:42:48.640 physically not in one spot according to the equation now if we take that equation seriously then
00:42:54.560 we say okay so the electron is not simply in one spot it's in multiple different places at the
00:43:00.080 same time around the around the electron but when we go to observe it we only ever observe
00:43:05.280 the electron at one place and so this is why some physicists some people who look into the theory
00:43:10.240 say well it's the act of observation that causes the collapse so it's said of the wave function
00:43:16.480 to one point and we see all the possibility to disappear except for the one that we do observe
00:43:21.600 now that's an additional assumption the act of observation renders the equation invalid
00:43:31.360 prior to the act of observation the equation is a description of reality but the act of
00:43:37.040 observation causes the equation to cease to be universally valid it's not valid at the point of
00:43:42.160 observation sometimes called the observation problem but if we have equations of orbital dynamics
00:43:50.160 let's say and thermodynamics that explain how stars and planets form from gas clouds and
00:43:58.080 those equations describe how most of the mass ends up at the center as a star and the rest of
00:44:04.640 the mass ends up forming planets it would be ridiculous to say again that those equations
00:44:10.880 cease to be valid except in cases where we can point a telescope at a star and see the planets
00:44:16.240 orbiting the star you're active observation isn't the thing that brings reality into being
00:44:21.840 the act of observation is just another part in the chain of science it doesn't affect all of
00:44:27.360 reality but the collapse models which includes the Copenhagen interpretation and basically everything
00:44:34.080 except the many world interpretation the multiverse all of those say there is this weird spooky
00:44:40.000 action of distance where the act of observation causes all the reality disappear but what okay so
00:44:44.880 that's the additional assumption the additional assumption is observation causes all the realities but
00:44:51.760 one to disappear okay so now I'm going to use the fabric of reality in David's words to criticize
00:44:58.960 that and David writes so your additional postulate is not just superfluous it is positively bad
00:45:07.040 in general perverse but unrefuted theories which one can propose off the cuff
00:45:11.840 fall roughly into two categories there are theories that postulate unobservable entities such as
00:45:17.360 particles that do not interact with any other matter they can be rejected for solving nothing
00:45:22.160 or comes razor if you like and there are theories like yours that predict unexplained observable
00:45:27.840 anomalies they can be rejected for solving nothing and spoiling existing solutions it is not
00:45:34.640 I hasten to add that they conflict with existing observations it is that they remove the explanatory
00:45:39.680 power from those existing theories by asserting that the predictions of those theories have
00:45:44.400 exceptions but not explaining how okay I won't read the rest there but that's perfect okay end
00:45:52.240 quote by the way that's exactly what anyone who rejects the many worlds interpretation the multiverse
00:46:00.400 as a literal description of how reality is as best we know in favor of any other interpretation
00:46:09.600 that adds a traditional assumption that again that causes them to remove the explanatory
00:46:17.760 power from the existing theory so the existing theory being that all these possible realities
00:46:23.200 do exist that's what the equations say and to add this additional assumption doesn't make
00:46:28.800 things simpler it ruins the explanatory power of that existing theory okay so let's keep going
00:46:36.000 well actually I put this to I think was Max Tegmark in a podcast I did with him I think it was Max
00:46:45.920 and it was just a just a different view of parsimony it was not you know it was kind of
00:46:50.640 privileging the the mathematical parsimony over the the bricks and mortar parsimony I think that
00:46:58.880 that I mean it did that many worlds was not set was not the result of adding lots of assumptions
00:47:06.640 or you know epicycles or something that was jiggering a theory it was just a brave acceptance
00:47:13.280 of the consequences of what this you know they're there we should say that again you know I'm not
00:47:20.160 a physicist you know we should drag your brother in here to get into more of these details but
00:47:25.120 um there's no picture of quantum reality that tracks our common sense intuitions about
00:47:32.560 how the world should be so you're you're you're left except in something at least at this point
00:47:36.880 this seems frankly bizarre but many worlds seems as bad as bizarre as anything I could imagine
00:47:43.600 again a failure of imagination live by Sam but I think everything else he says there's absolutely
00:47:47.520 fantastic that's fantastic you're left believing something strange no matter what you pick
00:47:55.760 okay it it does seem strange on first reading in the same way that those lights in the sky those
00:48:02.400 little pinpricks of cold white light that we see when we go out into a bright night sky
00:48:08.400 I literally sums like our own with planets going around them that's astonishing that's hard
00:48:14.800 to believe when you first hear it as a child if you can remember your mind being expanded by that
00:48:20.240 but as a child people are very accepting they don't have all of these irrational hang-ups about things
00:48:26.960 some older educated people do okay myself included but we're hearing now of some what I would say
00:48:34.640 hang-ups from people um now Sam also says there um it's just of the multiverse theory it's just
00:48:43.200 a brave acceptance of the theory now that's that's telling I think that is telling um why brave
00:48:50.240 why would one need to be brave in the order to expand this theory would it have anything
00:48:56.320 whatever to do with being thought stupid or irrational or someone who endorses a stupid and
00:49:01.920 irrational theory that when you end up hearing those kind of again scare quotes criticisms those kind
00:49:09.680 of insults or dismissive gestures really um no wonder so many physicists don't endorse it or
00:49:20.160 profess not to endorse it because it's a reasonable I think fear to be thought stupid and insane
00:49:30.880 simply for explaining what the science is now biologists used to have to go through this
00:49:36.400 not as much anymore but we all know about the scopes monkey trial don't we we know that
00:49:43.760 biologists historically have been attacked as insane stupid heretics of some sort and so
00:49:55.200 rightly probably um many didn't exactly get on the pulpit and try to explain evolution by natural
00:50:00.480 selection now back then we had religious people shutting down the scientific debate now I'm not
00:50:08.800 saying the Brett precisely shutting down the scientific debate but it's in that tradition
00:50:13.280 that tradition of dismissing as irrational people who are suggesting something what not exactly
00:50:21.120 new here I mean we're talking about a theory that was first proposed in what 1950s something um
00:50:26.880 so it's been a while it's been a long time and as David Deutsch has regretted it's such a shame
00:50:32.800 that physics in this area hasn't moved past concerns about taking the theory seriously for fear
00:50:41.840 for fear of being thought stupid or insane and hence Sam's quite right that those who have
00:50:49.120 taken up the charge by taking this theory seriously are brave
00:50:54.320 um and they should be lauded for having done so in the face of people who are not willing
00:51:01.680 to engage seriously in the debate but instead um throwing shade one might say which is unfortunate
00:51:07.200 it's unfortunate and again I think Brett's better than this in the way he's come off here
00:51:15.040 I'd be on being a bit harsh but really stupid and insane let's keep going no you're not left
00:51:19.760 with accepting it and again I'm not rejecting it in a formal sense it may be an insane phrasing
00:51:26.720 of something that could be phrased rationally from somebody perspective but as phrased it really
00:51:32.960 is the rejection of the idea of parsimony and not for a good reason just because I mean actually
00:51:37.760 Eric does have a term for the sort of thing I hope you won't resent my applying it here I think
00:51:42.000 he would but desperation physics imagine um you know of of saying of the neo Darwinism theory
00:51:55.760 of evolution by natural selection that the unit of selection being the jane that is on D&A
00:52:01.040 and that code being universal for life forms imagine simply rejecting that on the basis of being
00:52:08.400 desperation biology that it's stupid and insane because it is remarkable to think
00:52:14.080 that whatever the organism is it has a same the same code the same DNA code and if you were to
00:52:22.240 look at to DNA strand side by side one that was for bacteria and one that was for a human being
00:52:29.200 the average person would barely be able to tell any difference so in fact I'm pretty sure you
00:52:33.280 wouldn't be able to tell the difference without properly analyzing it in the laboratory somewhere
00:52:37.440 that if you simply magnified up the DNA strand and looked at the two double helices you
00:52:44.080 wouldn't notice much difference so that's a remarkable remarkable idea that the information
00:52:51.280 genetic information can code for such two vastly different structures a microscopic organism on
00:52:57.120 the one hand and a fully functioning human being on the other many things are astonishing
00:53:04.160 I'd it'd be interesting to ask Brett Weinstein we know that for example fossils are extremely
00:53:11.360 hard to combine they are a great series of coincidences usually has to occur in order for a
00:53:18.320 dinosaur to have been fossilized so far as we know a dinosaur has to die in a shallow pool of mud
00:53:27.120 and be covered over rather quickly with more mud in an anaerobic environment without oxygen so
00:53:33.040 the bacteria doesn't eat it away too quickly so that the bones can be ossified turn to rock
00:53:38.720 over time so this series of coincidences has not happened frequently we don't have that many fossils
00:53:46.560 we could be living in a world where conditions were such that we had almost no fossils at all
00:53:52.480 perhaps none let's say we lived in a world where there were no fossils for whatever reason
00:53:59.040 the bacteria tended to eat things more quickly than what they do so there was no chance for the
00:54:06.000 bones to be ossified or we lived in a world where on planet Earth the mud just wasn't the deep
00:54:12.640 enough so all of the dinosaurs that ever died rot away very quickly and nothing ever got preserved
00:54:19.440 okay I can imagine a world like that I'm sure Brett and Sam can imagine a world like that
00:54:23.520 imagine today therefore in such a world if a biologist came along and said do you know what
00:54:31.520 I think that in the past although there is no record of it I think in the past according to
00:54:37.360 what I know about DNA and genetics there might have been hundreds of million years ago walking the
00:54:42.880 earth dragon-like creatures that flew through the air perhaps they didn't breathe five in their
00:54:49.600 mouths but their huge lumbering lizards 50 meters long or more weighing hundreds of tons
00:54:59.200 now that's a possibility in fact we know that in our world that's a reality
00:55:04.880 to reject that as desperation biology would be wrong it's it's a testable theory
00:55:11.680 that if you came up with such a theory you might if you search long enough even in such a world
00:55:17.600 find some kind of evidence of that perhaps you will find an egg preserved in amber somewhere
00:55:25.280 perhaps you will find as they did in Jurassic Park the blood inside a mosquito preserved in
00:55:32.560 tree sap somewhere and then you'd be able to figure out once you've done analysis of the
00:55:38.160 the DNA that's in there you'd find dinosaurs okay but but as it is in our world we do have fossils
00:55:45.760 and so we don't have to debate the reality of dinosaurs or not but we could be living in a world
00:55:50.560 where we would be okay let's keep going but it's not even just forget about many worlds for a second
00:55:56.560 just imagine a universe that is infinitely large you know one of the the probabilistic consequences
00:56:03.120 of that scenario is that if you just go far enough in any direction again you run to the same
00:56:10.080 problem anything that can happen will happen an infinite number of times right yeah I mean that's
00:56:16.480 how big infinity is so that there are an infinite number of identical copies of us having infinitely
00:56:21.920 similar and and slightly different conversations than this an infinite number of times
00:56:27.520 simply if you make the universe big enough and that's it that just falls out of probability theory
00:56:31.440 right I don't think the way that Sam's explained that there is correct after all one could have
00:56:39.360 an infinite universe infinite in the size that is utterly featureless we may live in a kind of
00:56:45.120 universe like that that beyond the horizon of what we can see in the accelerating universe that
00:56:52.240 the universe just keeps getting larger and larger and larger infinite though it is and more and
00:56:56.960 more sparse in the distant future if the universe does in fact last forever under this accelerating
00:57:05.200 dark energy model eventually everything falls apart and we have once again an infinite universe
00:57:11.520 on into an indefinite infinite future where nothing happens because the laws of physics are such
00:57:17.440 that you won't have anything happening you'll have the heat death of the universe
00:57:20.400 even though it's the heat death of an infinitely sized universe okay that that's possible
00:57:26.960 what Sam's talking about is something slightly different where the universe has consistent density
00:57:33.280 over time and just an infinite amount of matter I've heard of heard philosophers make this point
00:57:40.640 before and I've never found it quite convincing they've got a particular view of infinity in their
00:57:46.000 mind where all possible things happen within this infinite universe but you have to add assumptions
00:57:52.880 about what the kind of infinity is there for that to work so far as I know okay we'll keep going
00:57:58.080 that's just a little aside but here's this is my point about fractals actually and you know
00:58:04.160 I'm speaking a little bit out of my depth here but my understanding is that there's a problem
00:58:08.640 with coastlines which is that they get infinitely long the closer you measure the approach
00:58:14.720 infinity in length as you get better at measuring the nuances of a coastline right that obviously
00:58:20.320 doesn't make any sense the coastline isn't getting bigger because you're measuring more finally
00:58:24.640 well you know it it makes sense it may be your your ruler has to get infinitely thin and
00:58:32.800 small I mean you like you write the point is as you get down to the Planck scale and as you
00:58:37.520 asymptote to infinity right right you discover I screwed up somewhere and it isn't my ruler
00:58:44.240 I screwed up just not actually well this cake it sort of comes back to xeno like this this is
00:58:48.400 you've applied xenos paradox to measure in a coastline bingo but the point is there is a way to
00:58:53.040 do this and it took somebody stepping back and saying you know what math is going to have to be we're
00:58:58.480 going to need a new toolkit just the same way Newton and Leibniz discovered a toolkit for
00:59:05.200 people don't like you when I say it this way but for calculating the incalculable which is what
00:59:10.880 calculus did as I see it but anyway the point is I think the many worlds interpretation is
00:59:18.480 a best answer to a problem that is phrased so incorrectly that we can't that just as if you
00:59:31.200 asked the question about where these creatures came from 3,000 years ago nobody had Darwinism
00:59:37.360 to offer so there wasn't even a way to begin to phrase the answer credibly you could say well
00:59:42.800 then that leaves you picking between deities who might have done it and really what we're after
00:59:47.200 is figuring out which one it was when in fact it wasn't any of them it was processes that were
00:59:51.760 understandable but we didn't yet have the mechanism to do so so I think that's where we are
00:59:57.440 in that case okay so they they and I think Brett's done this a couple of times now he said he's
1:00:04.240 not formally rejecting it but he's saying it's stupid and insane then he's saying it's a best
1:00:08.720 answer to a question that's poorly phrased but then he said it's stupid and insane so there's a
1:00:14.240 little inconsistency here if it's the best answer to the question phrase poorly or not then it
1:00:22.320 can't be stupid and insane can it it's just it is the best answer it actually is the best answer
1:00:27.280 it's the best explanation of what the equations say could it be wrong absolutely it could be wrong
1:00:33.200 absolutely it could be wrong but and this is why I say I don't believe in scientific theories
1:00:38.720 the word belief shouldn't have a place here we shouldn't believe our scientific theories
1:00:42.320 but we should take them seriously that's quite a different thing that that given our best answer
1:00:48.960 take our best answer seriously and when we say take it seriously take it seriously so don't get
1:00:52.720 all emotional about it use it in order to make progress in particular use it in order to make
1:01:00.000 quantum computers and yes in order to understand the operation of a quantum computer you have to
1:01:06.640 assume that the computations are being done somewhere in reality and it's clearly not in our
1:01:13.120 physical universe because it's not enough matter in our physical universe in order for the quantum
1:01:16.880 computation to take place so it's being done somewhere and that somewhere is in these parallel
1:01:22.240 universes but we'll come to that at another point yeah it might be and it's hard to see what we're
1:01:27.600 not seeing here can't even dimly imagine but it it does seem like I mean it is it is a fairly
1:01:36.400 straightforward claim that the infinite cases is even simpler because it's just you know it doesn't
1:01:48.240 require any notion of universes splitting but it's it's hard to know where to where to bite
1:01:57.040 the bullet I think I think the thing to recognize with the these counterintuitive consequences of
1:02:04.560 infinity is just how counterintuitive infinity is I mean infinity is not just really really big
1:02:12.160 right right it is and and our intuition that that it's just really really big no the rules
1:02:18.160 change when you when you put that symbol of infinity on the on the paper right right
1:02:24.480 right right there is a very big number if we can agree that in an infinitely large universe
1:02:31.680 somewhere at some point in fact an infinite number of places an infinite number of times a
1:02:37.520 asteroid will have hit another asteroid and Ardvark will have been formed absent in atmosphere
1:02:43.840 immediately died and disintegrated into a bizarrely large patunia of an unusual color right
1:02:51.200 an infinite number of times I'm telling embers compatible with the laws of physics will have
1:02:56.560 an infinite number of times yes I don't believe that has ever happened anywhere in the universe and
1:03:00.560 I believe that actually what we will ultimately come to understand is that the universe has to be
1:03:04.800 limited in a way that that actually won't have occurred ever well but one easy way to bound that
1:03:09.200 is just say that it's we don't live in an infinite universe how big it is it's just it's not very
1:03:13.840 close to being right infinite Sam Sam says here that anything physically possible that can happen
1:03:20.560 will happen and bread of jacks and the idea that he's just thought of something preposterous he
1:03:24.880 just came up with a preposterous thing Harry Potter universe type scenario as I explained in the
1:03:30.480 last episode you know this thing where two asteroids come together and and Ardvark appears okay
1:03:35.920 well yeah it's it's hard to believe and to say it's happened an infinite number of times is to
1:03:40.800 misunderstand the point that David makes about measures of the universe so I it's an exceedingly
1:03:48.880 small measure of universes where that happens infinite though it might be infinite in terms of
1:03:52.560 number okay we don't count universes that way we have a measure of universes and it's exceedingly
1:03:59.360 slim measure of universes where that happens so again this is a misunderstanding of infinity
1:04:06.160 to say that just because it happens an infinite number of times and that it seems preposterous
1:04:12.880 that that alone is a refutation seeming preposterous is not a refutation of a theory you need
1:04:20.640 to have something more than looking at a consequence of a theory having an emotional reaction
1:04:26.960 to it and rejecting the entire theory on the basis of your objection to a particular consequence
1:04:32.800 it doesn't matter how preposterous it is again the theory of evolution by natural selection
1:04:39.040 on religious understandings has preposterous consequences like an intelligent designer is not
1:04:46.240 needed to guide the evolution of species according to a religious person that that's preposterous
1:04:52.480 it's hard for them to understand so bread is in the position of being a kind of religious person
1:04:58.400 here he's religious about his own common sense I suppose that because this thing violates his own
1:05:07.760 sense of common sense he's rejecting it but not on any scientific grounds not on any rational
1:05:14.640 philosophical epistemological grounds but emotional grounds it seems to preposterous it's insane
1:05:22.080 it's stupid and so on yeah so we're not worried about this particular they're definitely large
1:05:26.560 isn't infinite and the differences here yeah yeah well I agree so all right back to free but I
1:05:31.600 I should just I'll tell you I think you if you want to close the door to many worlds or at least
1:05:36.880 beach your intuitions into shape there I think you should probably have either David Deutsch or
1:05:42.400 Sean Carroll on your podcast because they're both all in on that all in I love it when people
1:05:47.200 I already want to do is bet against it because you know I'm certain to be right and it's easy money so
1:05:51.920 okay back to free will I couldn't agree more Brett one thing you should have a chat with David Deutsch
1:05:59.760 that would be great and if you think you're certain to win your money you could have a I'll give
1:06:07.200 you a $5 bet that you will be convinced it's as long as you remain open-minded about this
1:06:14.000 yeah so I think that's where we'll end that part okay we'll end we'll end the podcast there
1:06:21.200 we'll end I've been talking about it for a long time now but I just thought this is this is emblematic
1:06:26.240 of what you do here less frequently these days with respect to the many worlds interpretation
1:06:32.640 as Sam said there might be a majority opinion I'm not sure about majority
1:06:38.320 the last survey I saw and it was only a very small survey of physicists was around the 30% mark
1:06:44.960 something like that but whatever the case this kind of criticism I did hear far more frequently
1:06:54.400 and you do hear it from laypeople very frequently that it's oh that's ridiculous that's insane
1:07:00.480 how could you believe anything like that and so on well I don't believe it as I've said before
1:07:04.720 it simply is they best the best the only literal way to understand the equations of quantum theory
1:07:12.560 the other the other attempts the other theories are the other theories are hedges and
1:07:22.400 and additional assumptions and violations of Occam's razor and so on we don't change the rules
1:07:29.200 about you know the the the equations of general relativity the equations of general relativity
1:07:34.640 describe a curved spacetime where space itself is literally curved and this is why we get
1:07:43.200 orbits having the shape that they do this is why we can have GPS but could you imagine an
1:07:47.360 instrumentalist coming along and saying oh those equations from general relativity useful
1:07:52.320 though they are that's merely a fiction they can be used to create a predictive model of where
1:07:59.920 a planet will be around a star at any given point they can be used for GPS but as for this
1:08:05.600 literally describing curved spacetime and explaining gravity as it is no I reject all that
1:08:11.760 the equations don't actually do that I haven't heard physicists really make this point I think
1:08:16.800 there are some but even though I don't think that general relativity is the final word on the
1:08:24.880 nature of gravity in space and time it is the best approximation that we have so far there is
1:08:32.320 nothing to rival it so too with the multiverse understanding of the equations of quantum theory
1:08:38.880 like the Schrodinger wave equation it's just taking that literally now do I assume that in the
1:08:46.240 future we will utterly refute utterly refute the curved spacetime model I think we're as likely
1:08:52.720 to utterly utterly overturn in almost all respects the theory of curved spacetime as described by
1:08:59.920 general relativity Einstein in the same way that we're likely to utterly overturn the multiverse
1:09:07.920 interpretation and that is about as likely to happen as the decoupling of DNA from genetics
1:09:15.760 for a biologist in the future to come along to find that DNA has absolutely nothing to do
1:09:23.040 with genetics and evolution that would be astonishing to me now I do think that the current
1:09:29.840 understanding of DNA and evolution and genetics will be overturned but not in all respects as I
1:09:36.240 think the many worlds understanding of quantum theory will be overturned and general relativity
1:09:41.200 will be overturned but not in all respects we will come to see these theories as approximations
1:09:48.240 to some still deeper theory as special cases of some deeper theory if anything maybe something
1:09:57.360 like David Lewis's model will end up being more correct in which case the many worlds interpretation
1:10:02.720 from quantum theory is just a special case but these other logically possible worlds might exist
1:10:08.720 or some portion of them might exist some universes with different laws of physics might exist
1:10:13.760 okay mixed max tegmarks written these books about the many different versions of the
1:10:19.840 many worlds okay I don't like you know enjoy joy David Lewis's book the plurality of worlds
1:10:26.320 because it is the largest possible superset of all realities like all the logically possible
1:10:33.280 things that could possibly happen and the physically possible things are just a small part of that
1:10:41.200 so indeed after all that we've got Brett and Sam really walking at the idea of the many
1:10:46.800 worlds interpretation I think precisely because it violates their common sense it violates almost
1:10:53.760 everyone's common sense the first time we hear about it but once you learn the details then it
1:10:59.040 comports with common sense and other versions of trying to understand quantum theory other things
1:11:05.280 that are a violation of common sense so let's go back to the beginning of infinity finally
1:11:10.960 among page 279 for what that's worth and I'll begin reading there and David writes
1:11:17.360 here is another situation where if we are not careful common sense makes false assumptions about
1:11:22.320 the physical world and can make descriptions of situations sound paradoxical even though
1:11:27.040 the situations themselves are quite straightforward Dawkins gives an example in his book
1:11:31.760 Unweaving the Rainbow analyzing the claim that a television psychic was making accurate predictions
1:11:38.320 and this is the quote from Unweaving the Rainbow there are about a hundred thousand five minute
1:11:43.840 periods in a year the probability that any given watch say mine will stop in a designated five minute
1:11:49.840 period is about one in one hundred thousand low odds but there are 10 million people watching the
1:11:55.360 television psychic show if only half of them are wearing watches we could expect about 25 of those
1:12:02.240 watches to stop in any given minute if only a quarter of these ring into the studio that is six
1:12:08.320 calls more than enough to dumb found an naive audience especially when you add in the calls from
1:12:13.520 people whose watches stop the day before people whose watches didn't stop but whose grandfather
1:12:18.080 clocks did people who died of heart attacks and their bereaved relatives phoned in to say that
1:12:22.640 their ticker gave out and so on and quote from Unweaving the Rainbow continuing with beginning of
1:12:28.560 infinity as this example shows the fact that certain circumstances can explain other events
1:12:35.120 without being in any way involved in causing them is very familiar despite being counterintuitive
1:12:40.960 the naive audience's mistake is a form of parochialism they observe a phenomenon
1:12:46.320 people phoning in because of their watches having stopped but they are failing to understand it as
1:12:51.120 part of a wider phenomena most of which they did not observe though the unobserved part to that
1:12:57.440 wider phenomenon have no having no way affected what we the viewers observe they are essential
1:13:03.440 to its explanation similarly common sense and classical physics contain the parochial era that
1:13:08.800 only one history exists this era built into our language and conceptual framework makes it sound
1:13:14.640 odd to say that an event can be in one sense extremely unlikely and in another certain to happen but
1:13:21.200 there is nothing odd about it in reality just pause their my reflection so this is precisely
1:13:26.640 the objection that Brett articulated in his podcast with Sam where he was talking about the
1:13:32.720 advark that apparently appears after a asteroid impact the concern that that however unlikely
1:13:39.520 it's a possibility is just an argument from incredulity some things are unlikely to happen
1:13:46.320 there is a very small measure of universes where this happens and it's not a refutation of the
1:13:51.520 entire theory to say that one struggles to accept that reality okay i'm skipping a bit and David's
1:13:59.760 talking about the spaceship still and on this spaceship spaceship he talks about how there's a
1:14:06.080 captain of the spaceship and there's a navigator of the spaceship and if we could see from a god's
1:14:10.160 i view the entire multiverse that how the spaceship is represented the multiverse we would see a
1:14:16.240 flurry of different instances of the captain and the navigator but we would notice that only one
1:14:22.640 instance of the captain ever in interacts with an instance of one instance of the captain ever
1:14:28.880 interacts with an instance of the navigator so there must be information within the instances
1:14:33.840 to tell the captain and the navigator which of them should interact with which on that point
1:14:42.160 David says the upshot is that our laws of it quote the upshot is that our laws of physics must
1:14:47.360 also say that every object carries within an information about which instances of it could
1:14:51.840 interact with which instances of other objects except when the instances are fungible when
1:14:56.480 there is no such thing as which quantum theory describes such information it is known as
1:15:01.440 entanglement information so far in the story we have set up a vast complex world which looks
1:15:06.880 very unfamiliar in our minds eye but to the overwhelming majority of the inhabitants look almost
1:15:12.080 exactly like the single universe of our everyday experience end of classical physics plus
1:15:16.880 them apparently random jiggling whenever the transporter operates a tiny minority of the
1:15:21.120 histories have been significantly affected by very unlikely events but even in those the information
1:15:27.440 flow what affects what is still very tame and familiar for instance a version of the starships log
1:15:34.240 that contains records of bizarre coincidences will be perceptible to people who remember those
1:15:39.520 coincidences but not to other instances of those people thus the information in the fictional
1:15:44.960 multiverse flows along a branching tree whose branches histories have different thicknesses
1:15:50.240 measures and never a join once they have separated each behaves exactly as if the others did
1:15:56.160 not exist if that were the whole story that multiverse's imaginary laws of physics would still
1:16:02.000 be fatally flawed as explanations in the same way that they have been all along there would be
1:16:06.720 no difference between their predictions and those of much more straightforward laws say saying
1:16:12.080 that there is only one universe one history in which the transporter randomly introduces a
1:16:17.360 change in the objects that it teleports under those laws instead of branching into two autonomous
1:16:22.160 histories on such occasions the single universe randomly does or does not undergo such a change
1:16:28.400 thus the entire stupendously complicated multiverse that we have imagined with its multiplicity
1:16:33.760 of entities including people walking through each other and its bizarre occurrences and its
1:16:38.640 entanglement information would collapse into nothing like the galaxy in chapter two that became an
1:16:43.680 emulsion floor the multiverse explanation of the same events would be a bad explanation and so the
1:16:49.520 world would be inexplicable to its inhabitants if it were true skipping a small part
1:16:55.040 and David writes in quantum physics information flowing the multiverse is not as tame as in that
1:17:00.400 branching tree of histories I have described this is because of one further quantum phenomena
1:17:05.920 under certain circumstances the laws of motion allow histories to
1:17:09.360 rejoin become fungible again this is the time reversal of the splitting
1:17:13.760 differentiation of history into two or more histories that I have already described so a natural
1:17:19.120 way to implement it in our fictional multiverse is for the transporter to be capable of undoing
1:17:23.760 its own history splitting okay so now I'm I'm pausing the reading there and I'm going to explain
1:17:31.280 what David has written rather than just read it verbatim so this is almost reading but
1:17:37.120 more of a summary of what's being said here okay so here's a diagram that represents the splitting
1:17:43.280 of the universe from one state that it's in x into two states x and y and x represents the normal
1:17:52.400 voltage and y is the anomalous one but the transporter causes and this diagram represents what
1:17:59.280 interference is again we have the x and y the two different voltages they can join together again
1:18:04.240 and this is what interference is interference phenomenon David defines there as where
1:18:09.680 differentiated histories rejoin okay now read a little bit and he writes interference is the
1:18:14.560 phenomenon that can provide the inhabitants of the multiverse with evidence of the existence of
1:18:19.200 multiple histories in their world without allowing the histories to communicate for example
1:18:23.760 suppose that they run the transporter twice in quick succession I shall explain in a moment what
1:18:28.560 quick means and here we have a diagram showing x splitting into x and y and then rejoining again into
1:18:34.800 x so we've got differentiation and then interference if they did this repeatedly would say different
1:18:40.400 copies of the transporter on each occasion they could soon infer that the intermediate result could
1:18:45.520 not be just randomly x or y because if it were then the final result then the final outcome would
1:18:52.800 sometimes be y because x could split into x and y while in fact it is always x thus the
1:18:59.760 inhabitants would no longer be able to explain away what they see by assuming that only one
1:19:04.160 randomly chosen value of their voltage is real at the intermediate stage okay and then David
1:19:09.680 goes on to speak more about entanglement and the rejoining of histories and I'm skipping a little
1:19:16.960 bit there and David writes in our story just as we did not allow splitting to happen in a way
1:19:22.160 that would allow communication faster than light so we must ensure the same for interference
1:19:27.200 the simplest ways to require that the rejoining take place only if no wave of differentiation
1:19:31.920 has happened that is to say the transporter can under the voltage surge only if this has not yet
1:19:38.080 caused any differential effects on anything else when a wave of differentiation set off by two
1:19:43.920 different values x and y of some variable has left an object the object is entangled with all
1:19:50.640 the differentially affected objects and here we have a lovely little diagram explaining what
1:19:58.720 not entangled is about when you've got two objects x and y those are not entangled with
1:20:05.200 the rest of the world if x and y if the rest of the world is not differentially affected by
1:20:11.200 x and y on the other hand entangled means that the rest of the world can be affected by x
1:20:17.040 while y will be will affect the rest of the world differently compared to x and that's what
1:20:22.960 entangled is about entanglement is and David writes beneath that diagram so our rule in short is
1:20:29.280 that interference can happen only in objects that are untangled with the rest of the world
1:20:33.440 this is why in the interference experiment the two applications of the transporter have to be
1:20:38.320 in quick succession although alternatively the object in question has to be sufficiently well
1:20:43.680 isolated for its voltages not to affect its surroundings so we can represent a generic interference
1:20:48.880 experiment symbolically as shown okay and here's the diagram of that we've got x and the rest
1:20:55.680 of the world so x is in the world somewhere but it splits then it differentiates into x and y
1:21:03.200 but the rest of the world is not being affected by x and y differentially affected as he says
1:21:08.560 there and interference is where x and y can merge together again to become fungible once more
1:21:14.720 and the rest of the world is still not differentially affected by x and y opposed they just
1:21:19.280 my reflection this is the difficult part for engineers trying to build quantum computers
1:21:28.080 because we need the objects to not be entangled with the rest of the world this is the concept
1:21:34.960 of decoherence when the objects that are performing the computations within the quantum computer
1:21:41.920 become entangled with the rest of the world and therefore the information about the computation
1:21:46.320 is lost I might just go to the emergent multiverse on this for a moment this is David Wallace's book
1:21:54.880 and Wallace in the book right say a bit about entanglement but I just want to mention here what
1:22:02.720 David said about a little bit earlier about how interference experiments provide that a
1:22:09.520 well would be evidence and he's about to come to the fact that he's going to say that interference
1:22:14.800 experiments provide the main source of evidence for the many worlds interpretation for the multiverse
1:22:23.200 now there is another kind of evidence as well we don't fully have it yet this evidence but we
1:22:30.080 will when quantum computers are built and this is what David Wallace writes about David Deutsch
1:22:36.800 talking about the evidence that would come from quantum computation which of course is a form of
1:22:44.160 interference experiment but anyway and Wallace is just explaining about a neutron interferometry
1:22:54.240 which is a form of interference experiment but using neutrons and Wallace writes David Wallace writes
1:23:02.000 in his book in a sense of course this discussion of quantum computation tells us nothing philosophical
1:23:08.560 that we didn't already know from neutron interferometry the really crucial step is from one
1:23:15.040 layer of reality to no more than one and the further considerations here are just quantitative
1:23:19.760 changes nonetheless there is something rather striking about the idea of empirical proof
1:23:26.240 that such a huge number of different realities must exist Deutsch puts it this way
1:23:32.800 quoting David Deutsch now
1:23:35.520 When Shaw's algorithm has factorized the number say 10 to the power of 500 also times the
1:23:41.520 computational resources that can be seen to be present where was the number factorized
1:23:48.080 there are only about 10 to the power of 80 atoms in the entire visible universe
1:23:51.760 an utterly miniscule number compared with 10 to the power of 500 so if the visible universe
1:23:57.440 were the extent of physical reality physical reality would not even remotely contain the resources
1:24:03.280 required to factorize such a large number who did factorize it then how and where was the
1:24:09.120 computation performed Deutsch 1997 page 217 so that is from the fabric of reality
1:24:15.920 I'm going to continue reading Wallace's reflection on what Deutsch has just said there
1:24:26.080 Wallace says now if by this Deutsch means that the very fact of the calculation entails multiple
1:24:33.120 universes he has overstated the case it is unproven that there are no classical algorithms for
1:24:39.200 efficient factorization and it is not logically impossible that the calculations that the calculation
1:24:44.880 just happens by magic as if as it were without any detailed account at all there is no logical
1:24:50.640 contradiction although it goes against everything we have learned in science in the supposition
1:24:54.960 that the laws of physics must contain primitive factorization implementing processes so to pause
1:25:00.880 their my reflection on Wallace's reflection on Deutsch yeah okay the magic is not logically
1:25:07.760 impossible but we don't live in a world of magic so I think it's a fair criticism to say
1:25:12.240 that although something might be logically possible if it entails the supernatural or magic
1:25:22.000 that's and that's something unexplained a science consists of good explanations
1:25:30.560 so you can always put a god of the gaps in a and then magic happens and then a wizard did it
1:25:36.000 as David likes to say but this is not a good explanation but Wallace comes back to rightly
1:25:45.120 give Deutsch credit here and Wallace writes but to object thus is to miss the point which is not
1:25:51.440 that there could be no other explanation for the factorization but that we actually have a good
1:25:56.320 in principle thoroughly testable explanation namely it involves simple well understood algorithms
1:26:02.000 operating in a massively parallel way within a single computer it presumes that each computation
1:26:07.520 happens independently the empirical prediction is that everything will happen as if the computer
1:26:12.160 as if each computation is occurring independently and there is no way of explaining the actual
1:26:16.640 computational process taking place which does not assume that the computations are happening
1:26:21.280 independently by Deutsch's criterion then there is no way of so explaining the algorithm which
1:26:26.880 does not accept the reality of all the independent computations at least within the quantum computer
1:26:33.200 there would be many worlds and quote from Wallace there and that's exactly right it will be
1:26:39.920 and I think this is why physicists are coming around to the many worlds interpretation because they
1:26:44.080 can see all the progress and all of the energy being devoted to quantum computation and they
1:26:50.320 understand that argument putting aside other kinds of interference experiments which should
1:26:55.200 always already be convincing but if we are on the verge I don't know how close we are no
1:27:00.080 notice how close we are to having fully functional quantum computers then it will be very difficult
1:27:07.280 to deny what Wallace has said there where are and Deutsch's said where are these computations
1:27:13.200 being taking place if a quantum computer is computing things that would require more than all the
1:27:18.880 matter in the visible universe operating at switching speed to the speed of light and so on if it
1:27:25.440 can't physically be done in this universe it's being done somewhere else it's being done by harnessing
1:27:30.000 the resources of quantum computers and other realities but in other physical realities by the way
1:27:36.960 this book is absolutely brilliant if you're really interested in this topic then this is the book
1:27:43.040 for you once you've read fabric of reality in the beginning of infinity but it is highly technical
1:27:48.240 I might just mention as well I've been a what Wallace would regard as a wave function realist but if
1:27:55.360 you get into the if you get down into the weeds about this he says that we shouldn't be wave
1:28:03.200 function realist so wave function realist is just someone who says well take the wave function
1:28:08.400 literally okay and the wave function if you draw a graph of it I won't bother to do that now maybe
1:28:12.400 next time but let's say you're trying to describe the position of an electron around a nucleus
1:28:21.040 then the wave function kind of looks like a a Gaussian curve the bell curve normal distribution
1:28:29.040 okay it can look something like that so it's highly probable to be in the center wherever the
1:28:34.400 center happens to represent and less probable to be elsewhere but the point is with respect to the
1:28:40.880 multiverse that it isn't in one single place the wave function maps all the different places
1:28:47.760 that it could be you square the wave function and you get the probability function so you find
1:28:53.360 it and the amplitude tells you the probability that the how high the bell curve happens to be at
1:28:59.600 any particular point tells you the probability of finding the electron of that place we would say
1:29:04.000 however it gives you the measure of universes where that electron is going to be around the nucleus
1:29:09.440 anyway I digress a little bit I just want to mention what Wallace says about that and he writes
1:29:16.880 this on page 316 of the emergent multiverse if we take non-relativistic quantum particle mechanics as
1:29:23.120 our paradigm quantum theory there is one fairly obvious possible way to make sense of the quantum
1:29:29.360 state it is typically represented as a wave function on configuration space so just take that literally
1:29:35.600 on this reading which is called wave function realism according to him quantum mechanics is not a
1:29:42.960 theory of events in three plus one dimensional space time at all it is a theory of a complex field
1:29:49.280 evolving in a very high dimensional space if we could treat the whole observable universe
1:29:53.760 non-relativistically for example the space would have 10 to the power of 80 dimensions wave
1:29:59.280 function realism was first explicitly proposed and discussed by Albert it has been criticized on the
1:30:05.280 grounds that it fails to provide the kind of ontology that can rewrite records at facts about three
1:30:10.400 dimensional objects in the behavior from this book's point of view though such concerns missed
1:30:15.040 the point all that is needed is that we recover high level ontology at a structural level
1:30:19.920 and I'm skipping a little bit and he writes that the the problems with wave function realism
1:30:24.160 his he says wave function realism misrepresents the structure of quantum mechanics by singling out
1:30:28.720 the position basis for a special treatment secondly it is difficult at best to extend it to
1:30:35.200 quantum field theory where no single basis seems to have the preferred status which the position
1:30:40.800 basis might arguably said to have in non-relativistic quantum mechanics and this position basis
1:30:46.320 means we're privileging position rather than some other physical aspect of a given particle
1:30:53.200 and so Wallace goes on to say some more here there but he says I see wave function realism
1:31:00.320 as in general an unhelpful way to think about the ontology of quantum mechanics that just
1:31:04.800 an extra end quote there this is just an extremely technical point because I have heard people
1:31:14.320 recently as I have been as well talking about taking the wave function purely literally as I have
1:31:20.960 indeed in this video especially so it's a minor technical point but this is this goes no way to
1:31:27.600 denying the fact that after all this book is precisely about the multiverse that these multiple
1:31:32.720 histories this multiple physical realities really do exist okay so I'll continue reading
1:31:39.040 from the beginning of infinity David writes quote once the object is entangled with the rest
1:31:43.520 of the world in regard to the values x and y no operation on the object alone can create interference
1:31:49.520 between those values instead the histories are merely split further in the usual way and here's
1:31:55.600 a diagram on page 284 okay so in this picture here we have an object x and the rest of the world
1:32:03.920 is unaffected by the object that object x is then split into two different copies at different
1:32:09.840 shapes into x and y and the rest of the world is not affected by either x or y entanglement then
1:32:16.400 means that object x big has an effect on the rest of the world while object y has a different
1:32:23.840 effect on the rest of the world and then the splitting can continue and as David writes in a blurb
1:32:29.920 underneath that in entangled objects further splitting happens instead of interference and it
1:32:34.960 continues to write when two or more values of a physical variable have differently affected
1:32:39.920 something in the rest of the world not going to fix typically continuing definitely as I have
1:32:44.640 described with a wave of differentiation in tangling more and more objects if the differential
1:32:49.760 effects can all be undone then interference between those original values becomes possible again
1:32:55.280 but the laws of quantum mechanics dictate that undoing them requires fine control of all the
1:32:59.600 affected objects and that rapidly becomes infeasible the process of it becoming infeasible is
1:33:05.760 known as decoherence in most situations decoherence is very rapid which is why splitting typically
1:33:11.920 predominates over interference and why interference though ubiquitous on microscopic scales
1:33:16.560 is quite hard to demonstrate unambiguously in the laboratory nevertheless it can be done
1:33:22.800 and quantum interference phenomena constitute our main evidence of the existence of the multiverse
1:33:27.600 and of what its laws are a real life analogily above experiment is standard in quantum optics
1:33:33.040 laboratories instead of experimenting on volt meters whose many interactions with their
1:33:37.360 environment quickly cause decoherence one uses individual photons and the variable being acted
1:33:42.160 upon is not voltage but which of two possible paths the photon is on instead of the transporter
1:33:47.280 one uses a simple device called a semi-sealwood mirror represented by the gray sloping bars
1:33:52.000 in the diagrams below and there we have the mark the beginnings of the marks and the interferometer
1:33:58.480 which David Deutsch goes ahead and explains in the next few pages so this is where I will
1:34:04.800 end this particular episode because we've explained that in a previous episode you go back
1:34:09.440 I think two episodes or so and three episodes perhaps now and another reason to read the book
1:34:16.960 if you're still struggling to understand any of this just a whole point of these this series
1:34:22.000 is to help us all understand the book a little better and I explain things slightly differently
1:34:28.080 to the way David has explained things but encountering the explanation in two different ways
1:34:32.320 about the marks ender interferometer is very important and you can find in fact the author of this
1:34:37.520 book David Wallace on YouTube explaining the marks ender interferometer experiment as well
1:34:43.120 so this this idea of entanglement where we have these particles unentangled with the rest of the
1:34:48.400 world this is what goes on inside a quantum computer so we have these particles interacting
1:34:54.000 inside of the quantum computer not entangled with the rest of the world if they get entangled
1:34:58.240 with the rest of the world then it's like the information is kind of I don't know if David would
1:35:02.560 like it to be put this way but the information kind of leaks out into the rest of the world it
1:35:06.160 becomes entangled with the rest of the world and then you lose you lose the quantum computation
1:35:12.960 and at the moment the engineering seems to be concentrating on how to ensure that the
1:35:19.040 particles remain coherent together they don't deco here and the common way of attempting to do this
1:35:27.920 appears to be keeping the particles at low temperature I happen to be wearing a shirt
1:35:34.000 I've been wearing for this episode I'm not sure if you can see that that's um from the
1:35:43.120 University of New South Wales here in Australia and they have a center for quantum computation
1:35:47.760 and I visited there a few times and I have this remarkable way of trying to do a quantum
1:35:52.560 computation so if I had to say the temperatures need to be exceedingly low because as soon as
1:35:56.720 temperatures can get high the particles start to vibrate too much and the information that then the
1:36:02.800 particles then become entangled with the rest of you know reality now to get the temperature down
1:36:07.600 really low um well they use liquid helium as one would expect but an interesting part about this
1:36:13.680 story is that liquid helium itself isn't cold enough for what they need to do and so then it is
1:36:18.960 special isotope so they first the first stage of cooling is to use normal liquid helium which is
1:36:25.200 expensive enough but for the second stage of cooling they use an isotope helium three I believe
1:36:31.520 and the helium three isotope then boils away from the rest of the helium that they have
1:36:38.000 and that lowers the temperature even further it's like a refrigeration effect and evaporative
1:36:43.360 cooling effect using liquid helium where a nice type of liquid helium boils away taking
1:36:50.320 additional heat with it now where do they get the the helium three from well one of the sponsors
1:36:55.120 one of the sponsors of the University of New South Wales quantum computation project
1:36:58.960 so they told me was the American army and the American army not only invested in their project
1:37:06.800 military likes to invest in computational projects but they also supply them with helium three
1:37:12.800 where would they get helium three from apparently decommission nuclear bombs nuclear weapons
1:37:20.080 give off this isotope of helium three and so they collect it and again if I remember correctly
1:37:25.760 and I'm sure someone will let me know if I get this wrong they said that a balloon full of the
1:37:30.480 gas not full of the liquid but a balloon full of the gas is something like ten thousand dollars
1:37:35.200 worth that's how much it costs for this isotope of helium three that's how rare it is and so
1:37:40.960 they use this out at the University of New South Wales in order to do quantum computation because
1:37:45.920 they need to keep things cool so that they don't deco here okay that's where we'll end it today
1:37:52.480 we'll have one more episode on the multiverse and then we'll be moving on to the next chapter
1:38:01.760 so again hope you're enjoying this if you do feel the urge to contribute to my patreon account
1:38:08.240 you can find me on patreon or paypal as well and I have a donate button on my website thank you
1:38:13.120 very much for any and all support and thank you for your comments on youtube thank you for your
1:38:20.880 feedback on twitter it's all very valuable see you next time bye