The implausibility of backwards time travel

[BridgeConsoleMasher]

This measures as of the most fundamentally invalid things conceived for consideration or speculative fiction (maybe sci-fi?). That is based on casual understanding of say Einstein but you still can't really wrap your head around QP.

What is your experience in considering backwards time travel in a rational world context?

[clearspira]

This measures as of the most fundamentally invalid things conceived for consideration or speculative fiction (maybe sci-fi?). That is based on casual understanding of say Einstein but you still can't really wrap your head around QP.

What is your experience in considering backwards time travel in a rational world context?

So here's the rub: The present obviously exists as we are sitting in it, but no one has ever been able to prove that the past or the future exists as a physical thing that you can travel to. Until they do, the very idea of time travel cannot move beyond the hypothetical. It is worth noting that TIME as a physical thing has been proven due to the time dilation effect (I don't know what the correct term is) whereby time slows the faster you go.

As for backwards time travel, I really do like the version that Banner gives in Avengers Endgame: ''Think about it. If you travel to the past, that past becomes your future. And your former present becomes the past, which can't now be changed by your new future...''
In other words, changing history is impossible due to paradox. You could say ''what about the alternate universe'' method... except for the fact that the multiverse hasn't been proven either.

My conclusion: time travel is impossible based under our current understanding of the universe.

[Jonathan101]

This measures as of the most fundamentally invalid things conceived for consideration or speculative fiction (maybe sci-fi?). That is based on casual understanding of say Einstein but you still can't really wrap your head around QP.

What is your experience in considering backwards time travel in a rational world context?

So here's the rub: The present obviously exists as we are sitting in it, but no one has ever been able to prove that the past or the future exists as a physical thing that you can travel to. Until they do, the very idea of time travel cannot move beyond the hypothetical. It is worth noting that TIME as a physical thing has been proven due to the time dilation effect (I don't know what the correct term is) whereby time slows the faster you go.

As for backwards time travel, I really do like the version that Banner gives in Avengers Endgame: ''Think about it. If you travel to the past, that past becomes your future. And your former present becomes the past, which can't now be changed by your new future...''
In other words, changing history is impossible due to paradox. You could say ''what about the alternate universe'' method... except for the fact that the multiverse hasn't been proven either.

My conclusion: time travel is impossible based under our current understanding of the universe.

What Bruce Banner is talking about more or less is the alternate universe method though, or that time-travel creates alternate universes where the past is changed (which might be caused just by the fact that you are travelling through time).

Which is consistent with how time-travel (officially) works in the Marvel comic book multiverse, which is good because the MCU is canonically a part of that multiverse anyway.

[clearspira]

This measures as of the most fundamentally invalid things conceived for consideration or speculative fiction (maybe sci-fi?). That is based on casual understanding of say Einstein but you still can't really wrap your head around QP.

What is your experience in considering backwards time travel in a rational world context?

So here's the rub: The present obviously exists as we are sitting in it, but no one has ever been able to prove that the past or the future exists as a physical thing that you can travel to. Until they do, the very idea of time travel cannot move beyond the hypothetical. It is worth noting that TIME as a physical thing has been proven due to the time dilation effect (I don't know what the correct term is) whereby time slows the faster you go.

As for backwards time travel, I really do like the version that Banner gives in Avengers Endgame: ''Think about it. If you travel to the past, that past becomes your future. And your former present becomes the past, which can't now be changed by your new future...''
In other words, changing history is impossible due to paradox. You could say ''what about the alternate universe'' method... except for the fact that the multiverse hasn't been proven either.

My conclusion: time travel is impossible based under our current understanding of the universe.

What Bruce Banner is talking about more or less is the alternate universe method though, or that time-travel creates alternate universes where the past is changed (which might be caused just by the fact that you are travelling through time).

Which is consistent with how time-travel (officially) works in the Marvel comic book multiverse, which is good because the MCU is canonically a part of that multiverse anyway.

True. It is the only way to get around the paradoxes of time travel should it actually exist.

[ChiggyvonRichthofen]

There's no consensus on what time is, how it operates, etc. The two standard theories of time are the A-theory and B-theory. I'm not sure either theory nails what time actually is exactly, and it gets... very complicated. Time travel almost certainly doesn't exist as you'd see it in most popular movies, but whether you think time travel is possible depends on how your theory of time. In my view, no, backward time travel (in any meaningful sense) isn't possible.

[Darth Wedgius]

Relativity can lead to closed timelike curves (going back to your starting point in space and time) in certain circumstances. I think most physicists consider that something that a successor to general relativity should clean up more than an indication that backward-in-time travel is possible.

The Novikov self-consistency principle might allow time travel without paradoxes. If contradictory timelines are impossible, otherwise extraordinarily unlikely things will happen instead. Try to shoot your grandfather in the head and the gun will jam. Prevent it from jamming and the bullet will miss. Ensure it doesn't miss and the bullet will tunnel harmlessly through his head. Ensure that doesn't happen, and you'll get an embolism right before you pull the trigger.

[Jonathan101]

I would like to note that in Agents of SHIELD they once had Fitz give a lecture on how time is absolute and if characters are getting glimpses of the future (as some were) then those futures were set in stone.

Luckily Agents of SHIELD did their own time travel story later that bunked that though.

[clearspira]

Relativity can lead to closed timelike curves (going back to your starting point in space and time) in certain circumstances. I think most physicists consider that something that a successor to general relativity should clean up more than an indication that backward-in-time travel is possible.

The Novikov self-consistency principle might allow time travel without paradoxes. If contradictory timelines are impossible, otherwise extraordinarily unlikely things will happen instead. Try to shoot your grandfather in the head and the gun will jam. Prevent it from jamming and the bullet will miss. Ensure it doesn't miss and the bullet will tunnel harmlessly through his head. Ensure that doesn't happen, and you'll get an embolism right before you pull the trigger.

That second idea sounds too much like God for my liking. Nature just is not as intelligent as that.

[BridgeConsoleMasher]

Yeah but the more things change the more they stay the same. So it kinda works under that principle.

[Darth Wedgius]

Relativity can lead to closed timelike curves (going back to your starting point in space and time) in certain circumstances. I think most physicists consider that something that a successor to general relativity should clean up more than an indication that backward-in-time travel is possible.

The Novikov self-consistency principle might allow time travel without paradoxes. If contradictory timelines are impossible, otherwise extraordinarily unlikely things will happen instead. Try to shoot your grandfather in the head and the gun will jam. Prevent it from jamming and the bullet will miss. Ensure it doesn't miss and the bullet will tunnel harmlessly through his head. Ensure that doesn't happen, and you'll get an embolism right before you pull the trigger.

That second idea sounds too much like God for my liking. Nature just is not as intelligent as that.

I think it borrows from the sum over histories concept where any object moving can have multiple possible worldlines, and extends it by saying that inconsistent worldlines are impossible. That leaves the idea that any other worldlines, no matter how unlikely, must be used. Quantum mechanics gets into weird things that looks like somebody (or Somebody) is playing tricks on us as it is. That's as far as I'll go because if I think too hard on quantum mechanics I'll use up all my brain before the work week starts.