Mindscape 240 | Andrew Pontzen on Simulations and the Universe

Patreon: / seanmcarroll
Blog post with audio player, show notes, and transcript: www.preposterousuniverse.com/...
It's somewhat amazing that cosmology, the study of the universe as a whole, can make any progress at all. But it has, especially so in recent decades. Partly that's because nature has been kind to us in some ways: the universe is quite a simple place on large scales and at early times. Another reason is a leap forward in the data we have collected, and in the growing use of a powerful tool: computer simulations. I talk with cosmologist Andrew Pontzen on what we know about the universe, and how simulations have helped us figure it out. We also touch on hot topics in cosmology (early galaxies discovered by JWST) as well as philosophical issues (are simulations data or theory?).
Andrew Pontzen received his Ph.D. in astronomy from the University of Cambridge. He is currently Professor of Cosmology at University College London. In addition to his research in cosmology, he frequently writes popular articles and appears in science documentaries. His new book is The Universe in a Box: Simulations and the Quest to Code the Cosmos.
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Sean Carroll channel: / seancarroll
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[@sashakindel3600]

I'm pleased that this episode didn't turn out to be *about* the "are we living in a simulation?" thing. I guess the fact that title made me wary that it might be speaks to why bringing it up at the end couldn't be helped, but the actual subject of the episode is something that, in contrast, hasn't already been talked to death, and I think is way more important to boot.

[@delatroy]

Thanks Sean. Been watching you for maybe 15 years. Great physics lecture series

[@amateurrandomdude5870]

This is top notch 🥇

[@steliosp1770]

thank you for the episode Sean. love the content! i have a feeling Mindscape would blow up if it had video as well but we love it regardless!

[@seionne85]

I agree! Im here for the conversations, but I feel like this would reach a larger audience if he did something similar to Lex Fridman

[@averagehummus]

although I totally agree, I think it is just easier to produce, and I assume a lot of people are listening to the podcast while commuting or doing something like sports

[@thesilentmajority2765]

Who sits down to watch a science podcast?

[@BigZebraCom]

I was going to simulate a universe--but then things got really busy at work.

[@BigZebraCom]

@@robertnewhart3547 Maybe i could run a smiluation of our universe where things weren't so busy at work?

[@luizarthurbrito]

And I got an arrow to the knee

[@BigZebraCom]

@@luizarthurbrito Arrows have ruined many a good universe simulation!

[@luizarthurbrito]

@@BigZebraCom 😂

[@DeclanMBrennan]

Lucky God was not too busy to simulate our one. 🙂

[@luizarthurbrito]

Very interesting talk. Very much enjoyed it.

[@ashikpanigrahi]

Oh Sean please get David Deutsch already!!

[@ili626]

12:53 Ok.. I’m very confused. Didn’t the JWT recently show that the universe might not be expanding anymore?

[@paxdriver]

In my opinion every thought experiment is equivalent to any scientific simulation, so simulation can be both theoretical and experimental. I don't believe anyone would dispute logical deduction / inference can be useful to test ideas just like any experiment does. Not all experiments prove a hypothesis on their own, many of them require multiple experiments to test a single theory and simulations can be used the same way imho.

[@jasonvarney8119]

I'd like to know if we hypothetically had the TOE would it in principle be possible to run a universe simulation ab initio, albeit slowly, and would "that" be a kind of experiment.

[@dmitryshusterman9494]

No. The problem is computing power, not the precision of our fundamental knowledge.

[@jayvincent1865]

Doesn't the scale of known matter looking outward into the universe seem very similar to when we observe matter at all small scale. Just referring to the shape not the behavior of the matter.

[@ronpartridge4402]

Einstein also felt that his "calculations" established conclusions as firmly as observations would. The world's physicists felt differently. Einstein was vindicated, but only when someone went out to the real world to see if he was right. When asked how he would have responded if the observations had NOT confirmed the predictions of Relativity Theory. He is said to have replied, "Then I would have felt very sorry for the Lord God. The theory is correct." Of course, neither theory nor observation could quite convince Einstein that God did indeed "play dice with the Universe". In the end, he had to concede that, in his struggle against Quantum Theory, he may have been on the wrong side.

[@scottsherman5262]

This is only the second time (Michio Kaku being the first) I've ever heard someone agree with me (& yes, it was my idea originally...I was going to file my paper on this but the damn dog ate it, so...) on universe simulation...that it would, of course, likely take around the same amount of effort/information to simulate it than it did to create it. Nature tends to do things quite efficiently, so to simulate the universe, you'd likely need the same or more information. This is a universe that has to pass every single test we throw at it...we don't live in some low-res/low-rent world here. This seems so obvious to me, yet nearly everyone disagrees with me/this stance. I feel vindicated, because Andrew's a smart kid.

[@kencreten7308]

Now you guys have done it.... I can usually listen to these podcasts and do other things... but I like this one too much and I have to have to hear everything. If you make your podcasts less interesting, then it's more efficient for me in getting things done.... heheheh

[@physicsprof.9639]

I'm not a huge MOND fan but your guest is very wrong to say it hasn't had successful predictions. Arguably it's done a lot better than cdm in this way. Both were inferred in large part from spiral galaxy rotation curves. Then we predict the data in many other astrophysical situations. We can try it in dwarf galaxies, galaxy clusters etc. We can predict pressure in grav bound hot x-ray emitting x-rays . There's grav lending. Mond people and perhaps random people like me have a strong impression that Mond does better with fewer parameters explaining dynamics of galaxies very different from the type from which it was derived. In particular mond predicts that it's key acceleration where things change would come out the same in all situations. It does very well at that whereas cdm has to invoke all kinds of ad hoc differences from galaxy to galaxy.

[@ili626]

What if we’re in a simulation or part of one?.. Just started listening, so maybe this question arises, but i bet it’ll be interesting regardless

[@ddtt1398]

LCDM is ruled out by absence of dynamical friction. Simulating it is a waste

[@vanikaghajanyan7760]

"The hardest thing is to get rid of the feeling that you are always right. No, getting rid is too high a requirement. Get rid of him even for a minute… Oh, how stupid, blind, limited everyone is around, and they all do not act the way (from my point of view) they should, but quite the opposite… That's why most of the time I get annoyed. There is an annoying assumption that they are as right as I am. After all, I don't see what they see, they don't see what I see… But why, in fact, should I get rid of the feeling that I am the only center of any situation?* Why fight it, since I have it innate? Firstly, to protect against boredom… Secondly, for your own safety... to limit yourself to one emotional reaction to your neighbor - negative or positive, anyway - means to cut off your path to the truth, which, alas, I suspect, does not converge on me alone.. By nature, we tend to become tyrants, but we have important reasons to refrain from doing so. Are these reasons also natural? Even if they are artificial, then a little artificiality will not hurt." (Mrozek, Short Letters, fragment). -------------------- *) - Simulation?

[@spaceinyourface]

Ones a measure of nature & the others a measurement of your ability to mimick nature. It's the future,,,& it needs a beginning,,that's where you all are right now,,,,I'd settle for that .

[@kurt9232]

👍👍👍

[@andanssas]

59:01 Sean, *Avi Loeb* pronunciation = ahh vee low ehb

[@hahtos]

Who cares, plus he was talking about Ivo Labbe....

[@andanssas]

@@hahtos those that want to know who Sean mentioned (I couldn't get it myself at first). Edit: thanks for letting me know!

[@spaceinyourface]

I can't see how AI can predict any thing you haven't told it too,,,It's use must be to eliminate the obvious errors...So It seems a bit pointless just yet,,,it needs more time

[@spaceinyourface]

I see how a programmed system can be used experimentally from an uneducated user as an experiment from the users point of view,,but not from the programmers,,. The programmers all ready told it the laws of thermodynamics for the particles to behave in an observational way..the programmers learnt nothing,,and the user only has the programmers word on it

[@c.f.3503]

First

[@adama7752]

So not even light can escape a black hole, yet everything escaped the big bang?

[@timjohnson3913]

Everything is inside the Big Bang. It happened (banged, if you will) everywhere

[@dmitryshusterman9494]

Cos big bang was not a black hole, at all

[@adama7752]

@@dmitryshusterman9494 so all the matter gathered into 1 place doesn't behave like a black hole?

[@timjohnson3913]

@@adama7752 i think you need to read about inflation

[@dmitryshusterman9494]

@@adama7752 not when that place is the entire space. It's two entirely different configurations. Also, there's inflationary potential pushing space to expand

[@jayvincent1865]

I thought the universe expanded evenly

[@hahtos]

Not very convincing reasoning why they are concentrating primarily on CDM and not even bothering to look at MOND...