Evolution of the Universe in reverse

[javisot20]

TL;DR Summary

Question about the evolution of the universe in reverse

I have a question about the evolution of the universe in reverse. I understand that three things happen:

1- The real black holes of the universe in reverse do not accrete, they expel.
2-The universe contracts.
3-The universe reaches the hot and dense state.

Is this correct?

Points 2 and 3 are part of the consensus cosmological paradigm, so I assume they are correct.

(I apologize if this is not the correct topic, the standar cosmological model does not include black holes and I am not sure where to post this question)

 

[phyzguy]

This is one of those questions that asks, "If the laws of physics did not apply, what do the laws of physics say would happen?" The laws of physics say that entropy is always increasing. To go backwards, entropy would need to decrease. This is against the second law of thermodynamics. So we believe it is not possible for the universe to evolve in reverse, so there is no real answer to your question.

If your question is, "If I had a video of the universe evolving and I played it backwards, what would happen?", then that is a question that can be answered. The universe would contract and reach a hot dense, uniform state again, and along the way black holes would "uncollapse" into the matter that formed them.

 

[javisot20]

If your question is, "If I had a video of the universe evolving and I played it backwards, what would happen?", then that is a question that can be answered. The universe would contract and reach a hot dense, uniform state again, and along the way black holes would "uncollapse" into the matter that formed them.

In this context is the one I ask, thanks.

 

[Ibix]

Yes, the time reverse of a black hole is a white hole.

 

[javisot20]

Knowing that we are talking about the same context, a necessary question arises:

In this inverse movie of the evolution of the universe, where 1,2 and 3 happen, could 2 and 3 happen without 1 happening?

 

[Ibix]

You can have a collapsing universe (i.e. the later half of a closed FLRW solution) with black holes, yes.

 

[javisot20]

You can have a collapsing universe (i.e. the later half of a closed FLRW solution) with black holes, yes.

I understand, but I was asking about the evolution of the real universe in reverse sense, adding the detail you comment here,

Yes, the time reverse of a black hole is a white hole.

Then I don't ask about the later half of a closed FLRW solution with black holes

 

[Ibix]

I understand, but I was asking about the evolution of the real universe in reverse sense, adding the detail you comment here,

This seems simple, then. If you run the universe backwards then everything runs backwards. White holes emit matter and radiation before exploding into stars that absorb radiation to drive the fission of light elements into lighter ones before expanding gently into clouds of gas.

 

[javisot20]

Now, suppose we read the following line in reverse,

https://en.m.wikipedia.org/wiki/The_Five_Ages_of_the_Universe

Could *2 and *3 happen without *1 happening?

*1- black holes in reverse
*2- universe contraction
*3- hot and dense state

 

[phyzguy]

Could *2 and *3 happen without *1 happening?

*1- black holes in reverse
*2- universe contraction
*3- hot and dense state

Well, since we're playing back the tape of our universe, no. Our universe has black holes.

 

[DaveC426913]

Yeah I'm afraid the question doesn't make sense - in that it's trivially true.

If we (artificially) reverse time - incidentally also reversing entropy, the arrow of time and the laws of thermodynamics in the process - then everything happens in reverse.

I don't see what sense it makes to ask what would happen in your reverse universe - nothing new will be revealed from what would happen opposite of our forward universe.

If you run the film Jaws backwards, you don't suddenly get Sherriff Brody graduating from college as a Burlesque Dancer. If you see what I mean.

 

[javisot20]

If we (artificially) reverse time - incidentally also reversing entropy, the arrow of time and the laws of thermodynamics in the process - then everything happens in reverse.

I don't see what sense it makes to ask what would happen in your reverse universe - nothing new will be revealed from what would happen opposite of our forward universe.

If you run the film Jaws backwards, you don't suddenly get Sherriff Brody not going to Police Academy and instead graduating from college as a Burlesque Dancer. If you see what I mean.

Georges Lemaître never had to do what you say, the thread does not talk about universes working with different laws, it talk about the evolution of our universe in the opposite direction, simply.

I agree that my question is trivially true, but for it to be trivially true its means 1, 2 and 3 must be related, unless someone proves that they are not related and 2 and 3 can happen without 1 happening

(which makes no sense, 1 must be happen for 2 and 3 to happen, it is the assumption that builds my question)

 

[DaveC426913]

I agree that my question is trivially true, but for it to be trivially true its means 1, 2 and 3 must be related, unless someone proves that they are not related and 2 and 3 can happen without 1 happening

(which makes no sense, 1 must be happen for 2 and 3 to happen, it is the assumption that builds my question)

What does reversing the direction of it accomplish in terms of answering your question?
Why not remove the confounding factor of the reversing everything? It just complicates things.

Look at my example: forward, Brody became a Police Chief, then saved the town of Amity Island.

Reversing the film doesn't change anything about cause and effect. You can't conclude that saving the town caused him to become a Police Chief.

More specifically:

I agree that my question is trivially true, but for it to be trivially true its means 1, 2 and 3 must be related,

Why? How does this follow?

unless someone proves that they are not related and 2 and 3 can happen without 1 happening

Why do you think this?

(BTW, the burden of proof is on you that your claim is valid. No one has to prove anything but you.)

 

[javisot20]

Well, since we're playing back the tape of our universe, no. Our universe has black holes.

I agree, but if you notice, we are saying literally that in the reverse history of the universe, black holes (now white) must expel their contents for the universe to contract and reach the hot and dense state.

We can deny that for 2 and 3 happen, 1 must happen, but that would also require proof.

 

[javisot20]

What does reversing the direction of it accomplish in terms of answering your question?
Why not remove the confounding factor of the reversing everything? It just complicates things.

My question is strictly about the evolution of the (real) universe in reverse.

Look at my example: forward, Brody became a Police Chief, then saved the town of Amity Island.

Reversing the film doesn't change anything about cause and effect. You can't conclude that saving the town caused him to become a Police Chief.

The first time I wondered about the reverse histoy of the universe, adding the existence of black holes (white in the opposite direction), I also thought he was talking about retrocausality, but no, we are simply analyzing the evolution of the universe in reverse.

More specifically:

Why? How does this follow?


Why do you think this?

(BTW, the burden of proof is on you that your claim is valid. No one has to prove anything but you.)

I agree with you, what I am saying is that I don't know the answer, but it seems more reasonable to say "yes, in the reverse history of the universe 1 must happen for 2 and 3 to happen" than to deny it

 

[PeterDonis]

could 2 and 3 happen without 1 happening?

This question has nothing whatever to do with running our actual universe in reverse. If you run our actual universe in reverse, you get in reverse whatever actually happened. You can't get anything else.

If you want to ask about some scenario where 2 and 3 happen without 1, what happened in our actual universe is irrelevant. The question is whether there is a valid solution of the relevant laws of physics that has the properties you describe.

I think you need to make up your mind what you are actually asking about. Are you asking about our actual universe, or are you asking about whether the applicable laws of physics permit a solution that has properties different from our actual universe, along the lines you describe?

 

[PeterDonis]

it seems more reasonable to say "yes, in the reverse history of the universe 1 must happen for 2 and 3 to happen" than to deny it

It's not just "more reasonable", it's true by definition. The reverse history of our actual universe is what happened in our actual universe, in reverse. There's no way to have anything different happen.

 

[PeterDonis]

the time reverse of a black hole is a white hole.

More precisely: the time reverse of a star collapsing into a black hole is a white hole that expands into a star. But such a thing is only believed to be physically realistic in reverse, i.e., if we take an actual star that collapses into a black hole and "run the film backwards". It is not something that is believed to be physically realistic in the forward direction, because white holes themselves are not believed to be physically realistic.

 

[PeterDonis]

We can deny that for 2 and 3 happen, 1 must happen

No, we can't. What happened in the actual universe, happened. So what you get if you "run the film backwards" of what happened, will have to have 1, 2, and 3 in it. There is no way to "deny" this.

 

[PeterDonis]

for it to be trivially true its means 1, 2 and 3 must be related

No, it means no such thing. The fact that 1, 2, and 3 are in the time reverse of our actual universe in no way implies that they must all be present in every possible solution of the relevant laws of physics.

 

[Dale]

In this inverse movie of the evolution of the universe, where 1,2 and 3 happen, could 2 and 3 happen without 1 happening?

This question literally has no meaning. You have restricted the domain of discussion explicitly to the unique time reverse of the actual universe. There is no room for “could” questions. The scenario you have posed expressly forbids them. Only “did” questions can be posed within the given constraints.

it to be trivially true its means 1, 2 and 3 must be related

Sure. They are all related by the fact that they did happen. Nothing about that fact implies anything about “could” or “must”, only “did”.

1 must be happen for 2 and 3 to happen, it is the assumption that builds my question

It is fine to have assumptions. Assumptions are useful. They are also dangerous. They limit the generality of your conclusions and questions.

 

[Bandersnatch]

The OP seems to be making an assertion that if three things must always happen together in our universe, then they are necessarily physically related. The thrust is to suggest on that basis that the universal expansion is related to black holes accreting matter.
Which is an example of confusing correlation with causation.
The argument could be equally stated with any process other than black holes taking the place of '1', and it'd be equally fallacious while highlighting the mistake.
Make it e.g. biological evolution: If you time reverse the evolution of the universe, then the many species on Earth would be seen to devolve towards their common ancestry. Therefore, the OP could be saying, it's reasonable to assume that biological evolution causes the universal expansion (or/and the expansion is causing the evolution).
Or mountain formation does. Or my beard growing. The (dis)advantage in choosing black holes is in they can be thought of as existing throughout the history of the universe - and this only helps in obfuscating the leap of logic.

To wit: That all time-dependent processes reverse direction when time is reversed is - as correctly observed by the OP - trivially true. But it is a logical mistake to conclude from this that those processes are causative of each other.

 

[javisot20]

I put the question in a different way to try to solve the problems of understanding.

-We have a movie of the evolution of the universe (the real)

-But we have a movie player that only capable of playing the movie in reverse sense

-We can watch the movie as many times as we want but only in one sense.

The story of the movie is clear, there are holes (white in this case), theres is a contraction of the universe and it reaches the hot and dense state. Up to this point I understand that we must all agree. As we have said, this is trivially true.

Then we can ask a more complicated question about the relationship between those three facts, but it's a different question than the first one.

 

[Hornbein]

Now, suppose we read the following line in reverse,

https://en.m.wikipedia.org/wiki/The_Five_Ages_of_the_Universe

Could *2 and *3 happen without *1 happening?

*1- black holes in reverse
*2- universe contraction
*3- hot and dense state

Suppose the Universe were contracting instead of expanding. Would it reach a hot and dense state?

I suppose it would reach a state with a great deal of matter falling into a great many black holes, those holes merging with radiation and great gravitational waves everywhere. I'd guess the zones outside of the black holes would be very hot with all that energy blasting everywhere in close quarters. Would they all merge into a single Universe-filling black hole? I suppose so. I can't say whether or not such a black hole is hot.

If black holes are white holes instead then we can be sure it would be a hot time in the old town tonight.

 

[javisot20]

Suppose the Universe were contracting instead of expanding. Would it reach a hot and dense state?

Yes.

I suppose it would reach a state with a great deal of matter falling into a great many black holes, those holes merging with radiation and great gravitational waves everywhere. I'd guess the zones outside of the black holes would be very hot with all that energy blasting everywhere in close quarters. Would they all merge into a single Universe-filling black hole? I suppose so. I can't say whether or not such a black hole is hot.

If black holes are white holes instead then we can be sure it would be a hot time in the old town tonight.

That makes no sense and has no relation to what was discussed in this thread.

 

[Hornbein]

Yes.


That makes no sense and has no relation to what was discussed in this thread.

Oh well.

 

[Dale]

Then we can ask a more complicated question about the relationship between those three facts, but it's a different question than the first one.

Ok, what is the more complicated question? Be very clear on the question and the assumptions.

 

[DaveC426913]

I still don't get how the OP infers causation between three different events.

A comet hit the Earth 65m years ago; the Mediterranean Sea flooded around 5m years ago; the Tunguska Event occurred around a century ago. Does that mean they're causitively linked? (No.)

Can I run the sequence in reverse and infer one can occur without the other? (No.)


It especially doesn't make sense talking about cause and effect when our thought experiment invokes the reversal of cause and effect.

 

[javisot20]

I still don't get how the OP infers causation between three different events.

A comet hit the Earth 65m years ago; the Mediterranean Sea flooded around 5m years ago; the Tunguska Event occurred around a century ago. Does that mean they're causitively linked? (No.)

Can I run the sequence in reverse and infer one can occur without the other? (No.)


It especially doesn't make sense talking about cause and effect when our thought experiment invokes the reversal of cause and effect.

The mental scheme I had is:

1- Confirm as trivially true that 1, 2 and 3 happen in the reverse history of the universe

2- Ask if there is a relationship in some sense that does not imply retro-causality between those three facts

Point 2 arises from the example of the movie about the history of the universe and the movie player that can only play it in reverse. In this context, I suppose I have to explain the contraction of the universe and its reaching the hot and dense state, from this unique point of view that I have. It seems reasonable under these conditions to attribute 2 (the contraction) to fact 1.

We can also do the same exercise of analyzing that video in reverse mentally, concluding that the expansion is due to an ad hoc parameter with no more physical meaning than a cosmological constant, of course. But it is still true that in the reverse history of the universe it is tempting to assume another cause, physical, without new or ad hoc ingredients.

The problem is explaining that there is no retrocausality in this process. If some kind of retrocausality were necessary, we would rule out all this reasoning and the existence of even an analytical relationship between 1, 2 and 3.

 

[DaveC426913]

... I also thought he was talking about retrocausality ...

I'm guessing you mean Lemaître?

Maybe you should point us at a reference to give us an idea where you're getting all this from. Thatvwoyld be better than this "Broken telephone" deciphering.

 

[timmdeeg]

Just to understand your point better, would you agree that in case an egg falls on the ground and gets smashed it doesn't make any sense to rund this back in time?

 

[javisot20]

Maybe you should point us at a reference to give us an idea where you're getting all this from. Thatvwoyld be better than this "Broken telephone" deciphering.

I don't get this from anywhere, really all the information I have is the cosmological paradigm, the contraction or expansion of the universe and the hot and dense state, and the fact that black holes exist, which is more than accepted today.

Simply one day 5 or 6 years ago I started with this question, which is basically analyzing the universe in reverse adding black holes (white in reverse) to the image.

 

[javisot20]

Just to understand your point better, would you agree that in case an egg falls on the ground and gets smashed it doesn't make any sense to rund this back in time?

Yes, I agree

 

[timmdeeg]

Yes, I agree

Would you also agree that in case a star collapses to a black hole it doesn't make sense to run this back in time?

 

[javisot20]

Would you also agree that in case a star collapses to a black hole it doesn't make sense to run this back in time?

Yes, I agree