Poincaré Reoccurrence Theorem And Time
If time is infinite, the universe should go through all possible states eventually. A similar idea to this is Poincaré recurrence theorem:
https://en.wikipedia.org/wiki/Poincaré_recurrence_theorem
But surely some states are equilibrium states? One an equilibrium is reached, no further change in the universe is possible. Isolated systems naturally tend towards equilibrium with time. An example equilibrium state would be all matter in the universe in one gigantic black hole. Or all matter converted to energy (maximum entropy).
So because we are not in equilibrium, time must be finite?
A possible exception is if there is some mechanism that is preventing the universe from entering an equilibrium state. The only example I can think of is an endless cycle of Big Bang / Big Crunch, with entropy reset to zero at each Crunch. But that model is not compatible with current observations of the increase in the rate at the is universe expanding. Also, unless each crunch is ‘perfect’, entropy would increase on each cycle (which is not what is observed - the early universe was very low entropy - see the CMB radiation).
https://en.wikipedia.org/wiki/Poincaré_recurrence_theorem
But surely some states are equilibrium states? One an equilibrium is reached, no further change in the universe is possible. Isolated systems naturally tend towards equilibrium with time. An example equilibrium state would be all matter in the universe in one gigantic black hole. Or all matter converted to energy (maximum entropy).
So because we are not in equilibrium, time must be finite?
A possible exception is if there is some mechanism that is preventing the universe from entering an equilibrium state. The only example I can think of is an endless cycle of Big Bang / Big Crunch, with entropy reset to zero at each Crunch. But that model is not compatible with current observations of the increase in the rate at the is universe expanding. Also, unless each crunch is ‘perfect’, entropy would increase on each cycle (which is not what is observed - the early universe was very low entropy - see the CMB radiation).
Comments (20)
For the theorem to apply, the system must have constant volume. That rules out infinite universes and finite universes with changing volumes, which are the only types predicted by current cosmological theories.
Also, note that equilibrium states are only asymptotically approached, never attained. So it is not possible that an equilibrium state will be fully attained and the universe will remain in that state forever. It is however expected that the universe will asymptotically approach 'heat death' which can be thought of as an equilibrium state to any pre-defined degree of approximation.
Wouldn't this allow that the universe would eventually come back to the exact same state again, making time cyclical rather than infinite?
It could vacillate between just two states forever, or any other arbitrary number of states.
Fair point, I was only using the theory as an analogy - it does not apply directly to the universe.
The universe's long term behaviour must be characterised by one of the following:
1. expanding
2. contracting
3. static
4. cycling
Time must have a start with [1]. The universe is not one gigantic black hole so [2] is clearly not happening. The equilibrium argument applies with [3] so time would have a start.
That just leaves a cyclic universe [4] as the only possible infinite time configuration:
- The universe's expansion rate is speeding up, counting against the cyclic model
- Unless each crunch is ‘perfect’, entropy would increase on each cycle, which is not what we see
- It seems very unlikely that the 'cycle length' would be constant. It would probably decrease each time (in which case with infinite time, cycling will have stopped by now) or (less likely) it would increase with time (in which case with infinite time, cycle length will be infinite by now)
So time should have a start.
Time has gone through and is always in all states.
It is a finished thing.
But we, you and me, are like the little moving part of the bar of a video player - showing only one frame.
And we keep going and going and going and it keeps coming and coming and coming, but it is already finished.
If the video was not complete, how would you play it?
Everything is set in place - static, and everything is moving because we move.
We don't actually need to know what time is in order to work out it has a start, but I think we can say time is a degree of freedom like space; we are all moving in the time direction. You can slow your movement in the time direction by moving in the space direction.
So time is a degree of freedom so is similar to space (although you can move left/right in space, time you can only move in one direction).
Quoting Shamshir
Future real eternalism is a possibility in my view:
https://thephilosophyforum.com/discussion/5302/an-argument-for-eternalism/p1
So presentism seems impossible for this and other reasons. The main models left are fixed block universe and growing block universe. The future being real goes against common sense but that in itself is not sufficient to rule out the possibility.
When adding relativity into the mix, it becomes more complicated. It is the order of the events is dependant on observers speed, that can change. Relativity says no preferred frame of reference.
I don't see observers disagreeing on the order of events as sufficient reason for there to be no start of time? As long as the start of time precedes all other events in all reference frames, there is not a problem?
Quoting tim wood
- Inside black holes
- Inside the singularity
- Beyond the edge of spacetime
I feel the absence of time in these areas is supportive of a start of time - time can be absent in certain situations suggests time can be absent globally.
I understand, but I shall repeat myself.
All you see is what there is.
All you say is what there is.
All you do is what there is.
How do you see, say or do what there is not?
And what there is - is now.
It is always complete, but through manner of division - appears always going.
It is a static, and a man spins inside it - so the static spins.
You wrote, that 'something 'other' than only now exists'.
But if I told you that there is only now and now is eternal, to reconcile the two, would you believe me?
Now, you might ask, but if now came from nothing - nothing predates now, does it not?
It does not. There is no is, do, or be with nothing. Only nothing.
If nothing is, it is not nothing.
You may think time has a start. It does.
So, does it have an end? It does.
Its start is now and its end is now and its present also now.
That's it.
Not sure I entirely follow, I think eternalism maybe correct (past, present, future all exist). 'Now' cannot exist eternally - if it did, the things within the universe (particles etc...) would have no temporal start and without a temporal start they could have no existence.
Quoting Shamshir
I think so too. I'm a finitist so I would - if eternalism is true, the time dimension is finite. My suspicion is that the time dimension is also circular. So we lead the same lives again and again perpetually (IE the start of time is co-incidental with the end of time: Big Bang meets Big Crunch).
I will try to explain.
Past, present and future are all now. They all exist now. Regardless of their distance.
Like two ends of a rope, past and future, are the same thing viewed from angles.
Imagine there is no now. Then this moment does not exist.
If this moment does not exist, there is no past and future; the whole bridge collapses.
If there is no past, present and future.
There is no time.
And yet there is time.
So there must be now and now is all there is.
The past, present and future exist in the now and because of it.
This is why the now is eternal.
And the temporal start you seek, is 'now'.
His theory has time as an imaginary variable I think? It sounds a little far fetched, that would make the universe in effect 5D? And I believe even with the no boundary proposal, that real time still has a start (imaginary time does not)?
Quoting tim wood
I do not believe we need to know the bits and bolts of time before knowing whether it has a start or not - you find out the basic stuff first do you not?
PS Even better argument for time has a start here:
https://thephilosophyforum.com/discussion/5302/an-argument-for-eternalism/p1
There is something prior to it; a timeless first cause. There are many arguments for this. A classic from Aquinas is:
1. Can’t get something from nothing
2. So something must have existed ‘always’.
3. IE if there was ever a state of nothingness, it would persist to today, so something has permanent existence.
4. It’s not possible to exist permanently in time (an infinite regress; it would have no start so could not be), so the ‘something’ must be a timeless first cause.
I count this a logical language that leads to a logical conclusion. I think metaphysics has a role to play in guiding science towards the right solutions.
Modern physics respects the conservation of energy - virtual particles only only transitory effects - if that was not the case, matter density would be infinite by now (with infinite time).
Quoting tim wood
As far as origins of the universe are concerned, there are only two possibilities:
1. An infinite regress in time.
2. A timeless first cause that created time.
The first has no start so its impossible. The second, we know from relativity that things can be timeless like the photon so it maybe possible. As the first is impossible, it timelessness has to be possible.
As a side note I don't think the universe not being a static, finite volume is a valid argument against the conjecture. If the universe is expanding like it is today, given enough time (an incredibly large amount of it) it will surely randomly contract again and at points be completely static (assuming theres any fluctuations in the expansion of the universe at all, which it is agreed there probably is).
The only true argument I can conceive is that time must end if the conjecture isn't true. if there were some sort of 'irreversible' change that happened in the universe that meant say, that protons and neutrons can't for atomic nuclei, given an extraordinarily large amount of time surely that rule will be defied at some point or another on a large scale.
Also as one last point, if we define the laws of physics as mathematical rules describing persistent patterns in nature (that probably aren't inherently mathematical but maths is a good tool for measuring things like these), surely given enough time these patterns will also begin to change? Interested to hear what everyone thinks and if this were true, what it would mean for the conjecture.