The big crunch effect on entropy and time

In summary, the conversation discusses the idea of a collapsing universe and its connection to decreasing entropy and the arrow of time flipping. The concept of observer-dependent entropy is also brought up, along with the possibility of a prior contracting phase and a rebound in the expanding phase of the universe. The topic of nonsingular bounce cosmologies and its impact on entropy is mentioned, along with a list of researchers and literature exploring this area.
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blakej
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Assuming a big crunch theory were to be true (I know it's not too popular a theory these days) I figure a collapsing universe would need to have decreasing entropy. If entropy is decreasing, would the arrow of time flip? Also, because physics is just as valid with time moving backwards, would all the events of the universe "rewind" in a collapsing universe exactly how they played out when time moved forward? Would I live my life again, moving from death to birth? Just curious of anyone else's thoughts or any content that explores this. Thanks!
 
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As I understand it, entropy is not an absolute. It is OBSERVER-DEPENDENT. It is a logarithmic measure of how many microstates comprise the given macrostate (which affects the observer).
blakej said:
... a collapsing universe would need to have decreasing entropy...

So the question is WHOSE entropy?

A lot of cosmology research these days is concerned with no-singularity bounce cosmologies. Quantum gravity effects at extreme density cause a rebound, so our expanding phase could have been preceded by a prior contracting phase (according to the bounce models being studied.)

Some people involved: Brandenberger at McGill, Ashtekar at Penn State, Steinhardt at Princeton, Sloan at Oxford…

There are scores of researchers involved and to my knowledge none of them talk about "time going backwards" or some observer's entropy decreasing.

It may be because entropy is not defined at Planck scale, or cannot be defined continuously through the bounce. Maybe no single observer can make it through the bounce, so what the macrostates are (and what microstates comprise them) have to be redefined post bounce.

Anyway nonsingular bounce cosmology is getting a lot of research attention, by smart people who don't seem bothered by pre and post bounce entropy considerations. I'll get link to the "quantum cosmology" research literature from 2009 onwards:

http://inspirehep.net/search?ln=en&...search=Search&sf=&so=d&rm=citation&rg=25&sc=0

These are ranked by number of citations received so that the more representative/influential research tends to show up first on the list.

Loop QC tends to dominate the highly cited end of the list, so if you want to just look at the non-Loop QC here's a link:
http://inspirehep.net/search?ln=en&...search=Search&sf=&so=d&rm=citation&rg=25&sc=0

It might also be interesting to check out what you get from a search for "bounce cosmology".
http://inspirehep.net/search?ln=en&...search=Search&sf=&so=d&rm=citation&rg=25&sc=0
For some reason you don't get as many hits as you do with "quantum cosmology" even though over half the QC hits involve a bounce. It's just a peculiarity of the keyword tagging/cataloging I guess.
 
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1. What is the big crunch effect?

The big crunch effect is a theoretical scenario in which the expansion of the universe, caused by the force of dark energy, eventually reverses and starts to contract. This would ultimately result in all matter in the universe collapsing into a singularity.

2. How does the big crunch affect entropy?

Entropy is a measure of the disorder or randomness in a system. In the big crunch scenario, as the universe contracts and becomes more dense, the entropy would decrease. This is because as matter gets closer together, it becomes more ordered and less random.

3. What impact does the big crunch have on time?

In the big crunch scenario, time would also reverse as the universe collapses. This means that events would unfold in reverse order, with the past becoming the future and the future becoming the past. However, it is important to note that this is just one possible outcome and there is no evidence to suggest that time would actually reverse in this way.

4. Can the big crunch actually happen?

Currently, there is no evidence to support the idea of a big crunch. In fact, recent observations suggest that the expansion of the universe is actually accelerating, making a big crunch unlikely. However, it is still a possibility and is being studied by scientists.

5. What are the implications of a big crunch on the fate of the universe?

If the big crunch were to occur, it would mean that the universe is a closed system, eventually collapsing back in on itself. This would lead to a cycle of expansion and contraction, with the universe being reborn in a new big bang after each big crunch. However, if the expansion of the universe continues to accelerate, it is likely that the universe will continue to expand indefinitely, resulting in a cold and empty universe known as the "big freeze."

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