Mine is a simple question: is retro-time travel possible? — Happenstance

Travel, no. Looking, yes. By looking at the Andromeda galaxy you are seeing it as it was 2.5 million years ago. By traveling closer to the Andromeda galaxy it's change would accelerate "forward" in time until you get to it and see it in its near-present state.

If time is circular, then travelling forward in time would eventually lead to retro-time travel.

But circular time probably requires a big crunch to proceed the big bang. So the would be retro-time traveller would not be able to make it through the big crunch to the past.

Where would you fit? I mean if you travelled back in time wherever you'd want to be, stuff would already be there (from the current time) so where would all that stuff go to make room for you?

Yep, my thinking also. How do you unchange what's been changed?

Travel, no. Looking, yes. By looking at the Andromeda galaxy you are seeing it as it was 2.5 million years ago. By traveling closer to the Andromeda galaxy it's change would accelerate "forward" in time until you get to it and see it in its near-present state. — Harry Hindu

Interesting thought. Makes me think that somewhere, really advanced aliens are sharing snapshots of each others' histories!

If time is circular, then travelling forward in time would eventually lead to retro-time travel. — Devans99

I remember seeing a Red Dwarf episode in which the crew land on an anomalous planet where time travelled backward to the crews', and our point of view. This seemed like it was normal to them and our past is their future and vice-versa!

The thing about the big Crunch though is: would it necessarily be the same set of events going backwards in that the inhabitants from the rebound do the same things as us, or reverse-time as in the Red Dwarf story?.

Yes it is of course. Retroness is ever-present. As I always've said to my friends "retro is modern"

The thing about the big Crunch though is: would it necessarily be the same set of events going backwards in that the inhabitants from the rebound do the same things as us, or reverse-time as in the Red Dwarf story? — Happenstance

I think it depends if you are a finitist or not. I am so I believe there cannot have been an infinite number of big bang/big crunch pairs in the past nor will there be an infinite number of big bang/big crunch pairs in the future. So that leaves two options:

1. A finite number (but greater than one) of big bang/big crunch pairs arranged linearly in time
2. A single big bang/big crunch that repeats itself in a loop of time

The problem with 1 is what causes the first big bang? There is nothing before the first big bang to cause it. Also what happens with the last big crunch? What happens afterwards? There can't be just nothing.

With model 2, the single big bang / big crunch and circular time, the big bang is always preceded by the big crunch so it seems like a more consistent model.

So a retro-time traveller could travel forwards in time, around the loop of time and experience the past. It would be the same set of events. They only ever experience time flowing forward.

I heard of a theory that, from a fifth dimensional perspective, the big bang and the big crunch as come and gone and positrons are electrons travelling in reverse-time! In this theory, the Red Dwarf scenario maybe likely.

Anyway, did you know that the smart money is on being a big freeze due to dark matter being a constant? If we get a decrease in dark matter then a big crunch is likely and an increase would mean a big rip is more likely!

Anyway, did you know that the smart money is on being a big freeze due to dark matter being a constant? If we get a decrease in dark matter then a big crunch is likely and an increase would mean a big rip is more likely! — Happenstance

But the Big Rip does not explain the Big Bang in a neat and tidy way like the Big Crunch does.

Plus if you consider it from a metaphysical angle, each moment of time must have a prior moment else it would not exist. The only topology that fits this requirement is a closed loop - circular time.

But the Big Rip does not explain the Big Bang in a neat and tidy way like the Big Crunch does. — Devans99

I agree with this, theoretically speaking.

The only topology that fits this requirement is a closed loop - circular time. — Devans99

Measurements so far have density equal to the critical density(mass needed to stop the expansion) which should eventually slow the expansion down gradually to a flat, infinite universe. This being contingent on the observable universe being at the range of the entire universe

Measurements so far have density equal to the critical density(mass needed to stop the expansion) which should eventually slow the expansion down gradually to a flat, infinite universe — Happenstance

The expansion rate of the universe has slowed in the past (end of inflation), it could slow again and maybe reverse. I think the astronomers are not too sure on the actual expansion rate:

https://www.forbes.com/sites/startswithabang/2018/01/03/scientists-still-dont-know-how-fast-the-universe-is-expanding/

I did read somewhere that astronomers had recently reported that the universes expansion rate maybe oscillating rather than accelerating, but I can't find the link at the moment.

Also I'm an eternalist and finitist so I find it hard to accept solutions positing a future eternity.

The expansion rate of the universe has slowed in the past (end of inflation), it could slow again and maybe reverse. I think the astronomers are not too sure on the actual expansion rate: — Devans99

Yeah, I must admit that my info is possibly from five years ago. I forget that these telescopes are updated periodically.

Cheers for the read, interesting. I guess I'm in the presentism camp myself but a finitist. I also don't see space or time as substantive.

Yes, it is possible but all info about that is suppressed by the governments.

Look => Philadelphia Experiment 1943.

No it is not. Full stop. The government isn't suppressing it. It's not being conducted secretly. Science fiction movies are fictitious. It's fun to think about if you like incomprehensibly paradoxical poorly explained reading or viewing entertainment exhibited poorly using bad ideas and bad actors and impossible plots.