75 | Max Tegmark on Reality, Simulation, and the Multiverse

/ Astronomy/Space, Computers, Philosophy, Physics / 11 Comments

We've talked a lot recently about the Many Worlds of quantum mechanics. That's one kind of multiverse that physicists often contemplate. There is also the cosmological multiverse, which we talked about with Brian Greene. Today's guest, Max Tegmark, has thought a great deal about both of those ideas, as well as a more ambitious and speculative one: the Mathematical Multiverse, in which we imagine that every mathematical structure is real, and the universe we perceive is just one such mathematical structure. And there's yet another possibility, that what we experience as "reality" is just a simulation inside computers operated by some advanced civilization. Max has thought about all of these possibilities at a deep level, as his research has ranged from physical cosmology to foundations of quantum mechanics and now to applied artificial intelligence. Strap in and be ready for a wild ride.

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Max Tegmark received his Ph.D. in physics from the University of California, Berkeley. He is currently professor of physics at the Massachusetts Institute of Technology. He has played an important role analyzing data from large-scale structure and the cosmic microwave background. He is the author of Our Mathematical Universe and Life 3.0: Being Human in the Age of Artificial Intelligence. He is a co-founder of the Foundational Questions Institute and the Future of Life Institute.

11 thoughts on “75 | Max Tegmark on Reality, Simulation, and the Multiverse”

  1. DisagreeableMe

    Am already a fan of the MUH, so was mostly listening to hear why Sean doesn’t buy it. Didn’t get much of that unfortunately. Otherwise a fun, enjoyable podcast.

  2. Let me know

    I found this discussion quite unsatisfying. Sean should have pushed Max more on what his theory actually is and why it even relates to our physical reality. The statement that everything that mathematically can exist also does exist is a tautology to a Platonist. What predictive power does this idea have? Does it help us understand anything at all? When Max made that joke about the empty T-shirt, I think he really admitted that his proposal (as laid out in the discussion) has simply no content.

    Another issue I have with Max’s view, is that what physicists claim to be well-established theories actually don’t stand on firm mathematical ground: many of the concepts they use (eg: path integrals) are not based on solid mathematical theories. So physicists (even very theoretical ones) do actually operate and argue using tools that fall outside the realm of mathematics (or at least mathematics’ mathematics). This may be viewed as the opinion of a rigor for the sake of rigor mathematics, but; it is exactly the delicate points in mathematics which are the basis for Max’s point that many things simply cannot exist mathematically (like the sixth Platonic solid).

    Although I think that Goff’s “everything is conscious” idea stems from a deep confusion (about why there is a hard problem in the first place), in my opinion, he at least laid out his ideas to such an extend that they become attackable. Max doesn’t bother with that. It leaves me with the uneasy feeling that he might just state this “viewpoint”, because it sounds superficially cool and might impress a bunch of people who don’t think twice to actually press him on his theory.

  3. FeepingCreature

    Digression: the true TOE may not contain the number 8, but it plausibly contains the code for DNA. 🙂

    (Note that I’m going to use “theory” in the sense of “computable description”, and the view that theories are preferred if they take fewer bits to specify.)

    Any theory of reality has to predict our sense impressions. This is easy to see by the fact that if it doesn’t, we can just write down the dovetailer (program that runs every program to completion) and be done with it – if it can be computed at all, our sense data will be *somewhere* in there. Obviously this does nothing for us. So any functioning TOE in the empirical sense will need at least two phases: first build a world model, and second predict our sense data from it. But to do that, it has to locate our position in the world data first, meaning it needs a key containing quantum branch and precise region of space of the sensor. In terms of bits, this key may be quite large – it would not be surprising if it was larger than the rest of the theory. So any additional computational rules that compress the key will lead to a strictly simpler theory. Sense data is predicated on a sensor, implying life (anthropic principle!). DNA is everywhere life is and nowhere that it isn’t, and it doesn’t seem all that hard to recognize from a fields-and-entanglements level view of the universe. So it seems quite plausible to me that the most compact theory that explains our perceptions will look something like “something something big bang something quantum gravity something and so in the area with lots of DNA molecules…”

  4. Seppo Koivula

    I liked this episode. It was interesting to hear about the recent work of Tegmark. Only thing which slightly bothered was why did Max talk so much about the universe four, although he joked that the t-shirt of the equation of it would be most likely blank. I didn’t understand the rationale of that universe; I tend to see mathematics from Platonic point.

    That part which was dealing with artificial intelligence, its possible future, and Boström simulation was especially good. There was that talk about Max’s future enquiries. I like your positive take on these matters, while not forgetting some darker tones.

    That was an interesting and enjoyable conversation.

  5. Vimal

    I kind of agree with “LET ME KNOW”‘s comment above. It would be good to push and develop this idea further and work out its implications.

    For example, consider concepts such as infinity (and various “sizes” of infinities, continuum hypothesis, etc.), infinitesimals, real numbers, complex numbers, and so on. Sometimes they are useful tools in predicting aspects of reality, but what does it mean for them to be real?

    Let’s take the real number and infinitesimals… There’s are a few questions that arise:

    – Concept of reals: I can imagine a length of “pi” (circumference of a circle of radius 1/2). Is it physically realisable in our universe? Does there exist a universe where it’s realisable? If it’s not realisable in our universe (perhaps because length is quantised–I don’t know for sure), but it’s realisable in some other universe, then can we work out the differences between such universes?

    – Concept of infinitesimals: If we look at calculus and reasons “why” the derivative of x^2 is 2*x, we have the concept of an infinitesimal dx that’s handy, and assume that dx^2 = 0. Why? One possible answer is that this assumption is perhaps needed for calculations to work in a way that corresponds to truths in our universe. In fact, the very same infinitesimal, dx, when dealing with stochastic integrals and time, challenges the assumption that dx^2 = 0; we substitute dx^2 = dt to “make the calculations work.” Work in what sense? Work in a sense that it helps us describe / predict aspects of our reality. Or work in the sense in that it’s the only way to not arrive at a contradiction?

    – Concept of a measure: What would a universe that has unmeasurable sets look like? Does our universe admit unmeasurable sets? Is it necessary to restrict discussion to measurable sets if we want to talk about probability, whose concepts are commonly employed in quantum mechanics, and other theories?

  6. Ken Williams

    I listened to this episode today. Always good food for thought.

    As for the discussion of “everything that mathematically can exist also does exist” – the analogy that kept coming to mind was that of a computer program and a running instance of that program. The running instance may not tell you anything new about what the program code is/does, but that doesn’t mean that the two are actually the same thing. Likewise, the fact that a program exists doesn’t mean it’s actually running anywhere.

  7. joyce luna

    Hey! I am an old lady living in a care facility though I don’t need much care. I listen often to Sean Carroll’s programme because here, in this small universe I live in, intellectual ideas are not to be found. Much /many ot the ideas are beyond my comprehension but I trust that somehow they filter into my being/self/soul/brain/mind.

    Thanks so much for all of the good thinking.!

  8. Ann Kittenplan

    Here’s a thought: there’s no general solution to the quintic because we live in a 4D universe.

  9. Ciel

    from infinity times infinity
    to division by zero and the unobservable
    with the finite human mind
    intersections probabilities superpositions
    parallel & perpendicular to mathematics & physics
    exist outside the confines of space and time
    ～ ★ ～
    Loved this episode and Max’s book Our Mathematical Universe, thank you for the podcast Sean!

  10. Fátima Pereira

    Muito interesante este diálogo!
    Até ao “nível 3”, concordo!
    Nível 4-nosso universo é matemático, eficácia da matemática…. bem, um pouco complexo!
    Se teoria simulação, verdadeira, implica super seres responsáveis criação do computador, e, nos simulando??!!
    Referente à inteligência artificial, e, seu possível futuro, gostei opinião positiva de Max Tegmark, não obstante, algumas nuances mais “negras”!
    Obrigada Sean Carroll, por seus excelentes episódios!
    Obrigada, Max Tegmark

  11. Jeffrey R Rocchio

    The ‘mathematics is real’ conjecture is interesting. Others have raised reasonable concerns with the idea. I’d like to explore, a bit, down the path of assuming it is correct. Where my head is at is this – I assume that, as tedious as it may be, all the laws of physics could be fully expressed in the english language (even if we have to invent some new words to accomodate it all). Or in the Russian language. Or any human language. If my assumption is correct then I believe that, by Max’s argument, this implies that anything I say must also be “real.” Which implies that all the way-out myths, science-fiction, and fantasy stories we have told and written are realities somewhere (or someplace in time). And then actually everything I can imagine inside my mind must then have an instantiated (or instantiable in time) actual reality. Yes?

    Let me try this as well: I invent [a hammer | a new branch of mathematics]. Is everything I can imagine building with my [hammer | new math] ‘real,’ and so really I didn’t “invent,” I “discovered?” Is it all ‘real’ even if I never build the things I have imagined?

    So it all begs the question: ‘What is reality?’ (Tho I suppose that question is *the* beg of physics anyway!)

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