# Time running backward (The Big Crunch) **URL:** \ **Category:** Factual Questions\ **Created:** [October 22, 2005, 7:13pm UTC](https://boards.straightdope.com/t/time-running-backward-the-big-crunch/327447 "2005-10-22T19:13:39Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [October 22, 2005, 7:13pm UTC](https://boards.straightdope.com/t/time-running-backward-the-big-crunch/327447/1 "2005-10-22T19:13:39Z")
I remember this from an episode of _Cosmos_. (Saw the original boradcasts, have the DVD. Haven’t watched the new broadcasts.) One theory is that the universe will collapse – ‘The Big Crunch’ – and experience an endless cycle of Big Bangs and Big Crunches. (Last I’ve heard, the universe will just keep expanding until all of the energy is used and it will be ‘without form, and void’.) When depicting The Big Crunch, effects preceded causes. Time ran backward. Would that theoretically happen? Or would time continue forward while the universe got smaller. That is, are time and space so intertwined that the reversal of space would cause a reversal of time? ---
**Author:** ![Shagnasty](https://avatars.discourse-cdn.com/v4/letter/s/9dc877/32.png) [@Shagnasty](https://boards.straightdope.com/u/Shagnasty)\ **Post date:** [October 22, 2005, 8:14pm UTC](https://boards.straightdope.com/t/time-running-backward-the-big-crunch/327447/2 "2005-10-22T20:14:12Z")
I read something about that too and I am pretty sure that we covered it here long ago. Time as we know it psychologically would continue to run just as we always perceive it. The universe would simply get smaller and smaller. ---
**Author:** ![jimpatro](https://avatars.discourse-cdn.com/v4/letter/j/b9e5f3/32.png) [@jimpatro](https://boards.straightdope.com/u/jimpatro)\ **Post date:** [October 22, 2005, 8:24pm UTC](https://boards.straightdope.com/t/time-running-backward-the-big-crunch/327447/3 "2005-10-22T20:24:41Z")
Right, there really is no such thing as time. Time does not make clocks run fast, slow, backwards or at all. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 22, 2005, 10:42pm UTC](https://boards.straightdope.com/t/time-running-backward-the-big-crunch/327447/4 "2005-10-22T22:42:22Z")
There are three separate Arrows of Time, or ways of distinguishing past from future, in physics. There’s the particle physics arrow of time, which is exceedingly subtle and does not concern us here. There’s the cosmological arrow of time, which says that “past” is the time when the Universe is smaller than now, and “future” is the time when it’s larger. And there’s the thermodynamic arrow of time, which says that “past” is when the total entropy of the Universe is smaller, and “future” is when the total entropy is larger (it turns out that most of the arrows of time we’re familiar with on a day to day basis are the thermodynamic arrow, in disguise). The thing is, there’s no particular connection between these three. So if the Universe were to go through a Big Crunch (as you noted, current evidence suggests this will not happen), then at some point, the cosmological arrow of time will reverse. But the other two arrows will not. So as the Universe collapsed, we’d still be remembering the time when it reversed and times before that, we’d still watch eggs fall on the floor and break, rather than re-assembling and un-breaking, and so on. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [October 22, 2005, 10:52pm UTC](https://boards.straightdope.com/t/time-running-backward-the-big-crunch/327447/5 "2005-10-22T22:52:58Z")
> [@Chronos](#): > > So if the Universe were to go through a Big Crunch (as you noted, current evidence suggests this will not happen), then at some point, the cosmological arrow of time will reverse… So as the Universe collapsed, we’d still be remembering the time when it reversed and times before that, we’d still watch eggs fall on the floor and break, rather than re-assembling and un-breaking, and so on. Makes sense this should be answered by **Chronos**. 😉 So cause will continue to precede effect, and ‘we’ will perceive ‘our’ existence as we always have – only the galaxies will be moving closer together instead of farther apart? And life will be hunky dory until such a time as increased radiation kills everything and the universe continues to shrink to a singularity? ---
**Author:** ![Nic2004](https://avatars.discourse-cdn.com/v4/letter/n/4491bb/32.png) [@Nic2004](https://boards.straightdope.com/u/Nic2004)\ **Post date:** [October 22, 2005, 11:05pm UTC](https://boards.straightdope.com/t/time-running-backward-the-big-crunch/327447/6 "2005-10-22T23:05:23Z")
I seem to recall an episode of “Stephen Hawking’s **Universe** ” in which he had come up with equations to support the “Time In Reverse” notion mentioned prior > [@](#): > > re-assembling and un-breaking to borrow from **Chronos**. IIRC, he gave his notes to a student/fellow researcher to recheck his calculations. Well, in what may have been a first, the student found him to be in error. “Check it again” he was told, several times, and each time yielded the same results. In fact, no, it would be as described above with time “flowing” in the same way we percieve it to now. Least ways according to Hawking’s, if you can believe him. 😃 Anyway, I took the Ever-Expanding Universe news very hard. I had thought it would only make sense to be a cycle. It seem the birth-rebirth idea fit into the way of things. A “Big-Crunch” that started everything anew without the remotest trace of pre-existing things was comforting to me. There was an eternal-ness to it and that this existance/Universe is just one in an infinite series streaching out before and forever after us. Perhaps there are other Big-Bang event centers out in the distant emptiness and their Energy/Matter are racing towards our universe of Energy/Matter and coalescence and rebirth is still a possibility in the unimaginable remote future. If we went from Earth-Centered to Sun-Centered to Our Galaxy is the only one and is at the center, then perhaps our BangCentric thinking is off as well. I’m just sayin’… ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [October 22, 2005, 11:10pm UTC](https://boards.straightdope.com/t/time-running-backward-the-big-crunch/327447/7 "2005-10-22T23:10:54Z")
IIRC the Hindu cosmology is based on an endless cycle of birth and destruction of the universe. So if the ancient Hindus are right and the scientists are wrong, you’ll still have the ‘comforting’ cycle. 😉 ---
**Author:** ![Nic2004](https://avatars.discourse-cdn.com/v4/letter/n/4491bb/32.png) [@Nic2004](https://boards.straightdope.com/u/Nic2004)\ **Post date:** [October 22, 2005, 11:16pm UTC](https://boards.straightdope.com/t/time-running-backward-the-big-crunch/327447/8 "2005-10-22T23:16:00Z")
> [@Johnny L.A.](#): > > IIRC the Hindu cosmology is based on an endless cycle of birth and destruction of the universe. So if the ancient Hindus are right and the scientists are wrong, you’ll still have the ‘comforting’ cycle. 😉 And ya know, religious cosmology ain’t never steered me wrong afore. 😃 ---
**Author:** ![Nic2004](https://avatars.discourse-cdn.com/v4/letter/n/4491bb/32.png) [@Nic2004](https://boards.straightdope.com/u/Nic2004)\ **Post date:** [October 22, 2005, 11:19pm UTC](https://boards.straightdope.com/t/time-running-backward-the-big-crunch/327447/9 "2005-10-22T23:19:52Z")
I just remembered that when watching that episode of **Universe** , I imagined myself in the shoes of the student doing the calc. checks. I wouldn’t have wanted to be the one to make the call; “Umm…Professor Hawkings? Um…well… I finished the checks you wanted and…ummm…uh…” 😃