Sean Carroll - Locating Yourself in a Large Universe

Rutgers Foundations of Probability
April 16, 2018

Sean Carroll
Cal Tech
Physic Department

Locating Yourself in a Large Universe

Modern physics frequently envisions scenarios in which the universe is very large indeed: large enough that any allowed local situation is likely to exist more than once, perhaps an infinite number of times. Multiple copies of you might exist elsewhere in space, in time, or on other branches of the wave function. I will argue for a unified strategy for dealing with self-locating uncertainty that recovers the Born Rule of quantum mechanics in ordinary situations, and suggests a cosmological measure in a multiverse. The approach is fundamentally Bayesian, treating probability talk as arising from credences in conditions of uncertainty. Such an approach doesn't work in cosmologies dominated by random fluctuations (Boltzmann Brains), so I will argue in favor of excluding such models on the basis of cognitive instability.

[proteus]

I come back and watch this lecture now and again. Deeply fascinating.

[Dexerinos]

I usually listen to Sean for a good night sleep, its so comforting. However this one fried my brain more then anything else :D
I guess this is not for broad audience :)

[winkletter]

Wait, this isn't Locating Yourself in a Large University? Am I in the right class?

[phi]

I believe the solution might be that we are not as observers isolated from the world around us. Albert Einstein believed, literally, that time was a dimension just like space. It is today called Eternalism, and would imply us having a temporal body in time just like we have a spatial body in space. This could explain why we're not just random fluctuations but fundamentally connected to our world and our past.

[DrJeeps]

I'm a psychologist, not a physicist, but I often listen to Dr. Caroll's talks to broaden my knowledge of cosmology. However, I have to say I felt like a submerged Boltzmann Brain listening to this one. Perhaps this is why recreational cannabis is now legal here in Canada.

[kennysaunders]

Well thanks Sean, but I know where i am in the universe: I'm right here in my living room.

[whirledpeas]

Arguably, Sean Carol it's the smartest person on earth 🌎

[Gottfried]

We create the past from the present. We are constantly evolving and shifting timelines from our decisions in the present. Everything actually exists here and now.

[trinitrojack]

4:01 You can't stop me from doing that LOL!!!

[shpensive]

Is A really more likely than B?
A) Random fluxuation makes a brain with detailed wiring to encode memories about the past;
B) Random fluxuation makes a past, which produces a brain that gains memories normally.

(B) might require more matter to exist for longer than (A), but it also has much looser requirements on the initial configuration.

It doesn't seem obvious that (A) is more likely. It also seems hard to show. Are we assuming Boltzmann brains are more likely, or have we honestly calculated that to be the case?

[abcde_fz]

I'm no mathematician, but I keep thinking to myself, "Can you PROVE that '...in any infinite universe, all allowable configurations of (pick whatever entities you want) will occur an infinite number of times'?" My brainstorm was, "Suppose that just ONE of those entities, merely by **coincidence**, (not because it is constrained in any way), ...just one of those entities doesn't budge from its original position? Isn't that a logical contradiction? If one thing does NOT move, even though it CAN, how can you posit that "...in any infinite universe, all allowable configurations of entities will occur an infinite number of times"???

[joshuaevans]

This is a super interesting talk, but I can't deal with all these interrupting pea-brained questions. I feel like the listeners are just trying to "gotcha" Sean instead of actually getting clarification

[mrnarason]

Always seen Sean Carroll in videos talking non-technically or philosophical, want to see him talk physics rigorously and mathematically.

[travisfitzwater]

I thought it was Laurence Krauss in this video. Is the "Quantum Mechanics days are numbered." Video?

[mikerosy]

Harry Crane,

I greatly appreciate you posting this vid and opining on it from your perception/logic; tip of that hat 🎩 to ya sir.


I have questions on the derivative aspect from (multi world + add cat in box 📦 non local which way data {plus gravitational wave affect all added into one}.


Also get photons close to zero kelvin and do experiments with non locality.

Would love to hear your thoughts or send links of any lectures that can assist my curiosity.

Thanks!

[SynKronos]

11 minutes. Not quite. The universe operates on energy states and it’s differentials. Should all fall in to the same energy state then the universe instantly renews. No exponential expansion.
Further the introduction of a thermometer to test such a case is impossible as it would generate a differential. (Similar to uncertainty and the observer effect)

[stefanbanev]

Well, a chain of Boltzmann brain snapshots may very well be my brain. It includes ALL aspects of brain what constitutes me as me: my childhood memory, the hot cap of coffee in my hand right now, stars in the sky I observe, my current thinking about this text… anything what my brain perceives as reality, the reality it is part of... Apparently, it does not require the reality to actually be, it requires only Boltzmann brain to be in such state as it perceives to be part of some reality.

The assembly of identical Boltzmann brains is essentially not an assembly of many but a single sample since identical copies cannot be distinguished; therefore, the collection of different/unique snapshots of Boltzmann brain constitutes such assembly. The subset of such assembly which is a composition of “slightly” different from each other snapshots and the order on such subset may represent the time evolution of one of Boltzmann brains (for example my brain).

The open question is: in what way it should be different and at what magnitude of “slightness” and what order on subset should be to have a “sane” Boltzmann brain along its timeline/evolution???

Two Kurt Gödel’ theorems:
1) Any consistent axiomatic is not complete. (*)
2) The consistency of axiomatic is not provable within its frame. (**)

Any observation is a true predicate (observations represented by false predicates are not observable). A sane Boltzmann brain must be capable to make observations.

Some subsets of Boltzmann brains assembly and the orders on these subsets may represent the Boltzmann brains capable to have observations along its timeline/evolution; therefore, all Boltzmann brains snapshots which violate this “abilities” get excluded/extinct since they cannot constitute a “sane” Boltzmann brain.

According to first Gödel’ theorem (*) there is no way to have/predefine a complete subset & order of snapshots of Boltzmann brains which represent a defined “sane” Boltzmann brain along its timeline/evolution – such subset must be open and redefine itself along its time evolution to comply with second Gödel’ theorem (**).

This process resembles the natural selection where the environment is presented by Kurt Gödel’ theorems (*/**) and the ability to make observation represents survival.
I would call i : Gödel’s natural selection of Boltzmann brains ;o)

Apparently, the neighborhood of particular sane Boltzmann brain may represent the superposition of quantum states of macro body (shalom to Everett’s relative state).

[ronaldderooij]

That was the most elaborate way to explain that random fluctuations do not produce ready made brains or universes I ever saw. But instead that there was a beginning, time evolving and development. Philosophically, I still have problems with the many worlds hypothesis. I cannot imagine the hyperuniverse it implies.

[RobRoss]

If a Universe can be spontaneously created from random quantum fluctuations, the argument for Boltzman brains seems sound as well. But apparently there’s an argument against Boltzman brains that is accepted by most cosmologists. But I am very hazy on what that argument is, and if it’s a valid argument, why doesn’t it apply to the whole Universe as well? And also, after a Deep Time amount of time after the heat death of the universe, any random bit of space is going to be mostly vacuum. So the fluctuations that would give birth to a new Universe only have access to the energy of an infinitesimally small unit of space, which is far less than the total energy of the previous universe. So where does all the extra energy for the new Universe come from??

[nickbucanelli]

The rules change every time we come close to an answer. The moment we actually do serve an exact answer is the moment the power goes out and (soft reset)