Thoughts on Time Travel

[Doctor Q]

Perhaps then one would consider that if you tried to go back in time it would create a different reality from the present one. Each different reality would allow the possibility to change certain events of history. Because just going back in time at all would change past events, unless you didn't touch, see, or do anything in the past. And I think that would not be possible in and of itself.

That ascribes to us the ability to create realities. If we don't want to assume that we have so much power, we could consider another view: that different realities already exist and we can travel to them and affect them without changing our original reality. So when you travel backward in time, you arrive in a pre-existing reality rather than cause one to appear.

That might avoid the "kill yourself when you were a child" paradox, but it introduces a new problem: Wouldn't traveling back in time and always arriving in a different reality imply that your original reality was "special", when they should all be equivalent? Or allow you to make multiple hops back until you happen to arrive in your original reality again? My solution: Realities have a natural sequencing, and you can only change from one to another in ascending (or equivalently, descending) order. So you can never visit the same one twice.

Therefore, realities are like Macs, because they can be assigned serial numbers!

 

[thegoldenmackid]

But there have been several people who have claimed to be from the future and everyone just says they're nutters.

If I was from the future I would never claim to be, one could get away with so much more if they just kept their mouth shut. But then again, I'd still be confused figuring out what the "past" really is, if it is in fact that future.

 

[bartelby]

That's an interesting point. And, depending on how you can travel—let's consider that by traveling back you've created another universe via parts of quantum theory—you could create another universe and thus many of your predictions would be wrong. So, our time traveler would end up dosed in the psychiatric ward and thus be trapped. People in his universe and future would assume the machine didn't work because the traveler never returned and no instances of his trip are recorded.

John Titor is an interesting example.

 

[iBookG4user]

But there have been several people who have claimed to be from the future and everyone just says they're nutters.

For some reason, that makes me think of the Time Traveler Convention. Perhaps they would've been more accepted if they had gone there, though I don't know how they would confirm that they were from the future.

 

[hulugu]

But there have been several people who have claimed to be from the future and everyone just says they're nutters.

That's an interesting point. And, depending on how you can travel—let's consider that by traveling back you've created another universe via parts of quantum theory—you could create another universe and thus many of your predictions would be wrong. So, our time traveler would end up dosed in the psychiatric ward and thus be trapped. People in his universe and future would assume the machine didn't work because the traveler never returned and no instances of his trip are recorded.

 

[bartelby]

and indeed our own experience is that future humanity - however advanced they be - do not appear to be coming back in time to visit us. This lack of experience of time travellers appearing from the future is a powerful argument, and of course we've seen many science fiction movies that raise the various issues manipulating past time would have on the present.

But there have been several people who have claimed to be from the future and everyone just says they're nutters.

 

[hulugu]

Okay, so I geeked out a little today trying to explain some of the concepts of relativity to my wife, who is not so particularly technical.

One interesting part of the conversation was when I went into the "twin paradox," where essentially one twin travels forward in time by moving at a speed near the speed of light.

That's what got me to thinking, if this form of time travel is essentially a one-way trip, are there any means - real, theoretical, or otherwise - of traveling backward in time?

My head is spinning with all the different possibilities and paradoxes this could introduce.

Try reading about the Alcubierre warp.

Also, quantum entanglement is quite cool.

Won't your body turn into energy/light if you approach the speed of light? That would make time travel pointless if you turned into energy. You would have to find a way to put yourself back together.

No, instead you gain mass until you get to a point where you use so much energy, you can't move any faster. Theoretical models seem to suggest you could get to .99c, but that would require ridiculous amounts of energy. And, that's before you get into the whole time dilation problems.

 

[jecapaga]

My head is spinning with all the different possibilities and paradoxes this could introduce.

Watched this movie this weekend and this thread just kept taking me to this visual.

 

[jmann]

Yes, but Einstein states that theoretically time travel is possible by moving close to the speed of light.

http://scienceray.com/philosophy-of-science/einstein-on-time-travel/

To everyone else, yes, it would seem as if they were in stasis.

Won't your body turn into energy/light if you approach the speed of light? That would make time travel pointless if you turned into energy. You would have to find a way to put yourself back together.

 

[iBookG4user]

So how does the frame of reference "know" that an attempt to change past events might take place, before that attempted change happens? And if that particular time travel episode were "blocked" by this principle, what would happen instead?

Perhaps then one would consider that if you tried to go back in time it would create a different reality from the present one. Each different reality would allow the possibility to change certain events of history. Because just going back in time at all would change past events, unless you didn't touch, see, or do anything in the past. And I think that would not be possible in and of itself.

 

[Maui]

And if that particular time travel episode were "blocked" by this principle, what would happen instead?

All known attempts to go back in time have failed, with startling results. Just ask Pamela Anderson.

 

[Tomorrow]

...He neatly side-steps any problems by saying that time travel if possible it would only happen under conditions where it was impossible to actually affect past events. The probability of any circumstances developing where a paradox could develop and the past could be affected is zero.

So how does the frame of reference "know" that an attempt to change past events might take place, before that attempted change happens? And if that particular time travel episode were "blocked" by this principle, what would happen instead?

 

[firestarter]

But if they were here just to observe, and not interfere, surely we would not notice. Even if they did interfere, how would we know?

Indeed. Doctor Igor Novikov posits his "self-consistency principle". He neatly side-steps any problems by saying that time travel if possible it would only happen under conditions where it was impossible to actually affect past events. The probability of any circumstances developing where a paradox could develop and the past could be affected is zero.

 

[OutThere]

I don't think I could watch that. Je ne pas sprechen zie español.

Ask your doctor for some prescription subtitles.

 

[r.j.s]

and indeed our own experience is that future humanity - however advanced they be - do not appear to be coming back in time to visit us. This lack of experience of time travellers appearing from the future is a powerful argument, and of course we've seen many science fiction movies that raise the various issues manipulating past time would have on the present.

But if they were here just to observe, and not interfere, surely we would not notice. Even if they did interfere, how would we know?

 

[firestarter]

Einstein states that theoretically time travel is possible by moving close to the speed of light.

Moving backwards in time is theoretically possible under certain conditions of general relativity. Hawking presents a conjecture that physics prevents it in practice, stating that:

It seems that there is a Chronology Protection Agency which prevents the appearance of closed timelike curves and so makes the universe safe for historians


and indeed our own experience is that future humanity - however advanced they be - do not appear to be coming back in time to visit us. This lack of experience of time travellers appearing from the future is a powerful argument, and of course we've seen many science fiction movies that raise the various issues manipulating past time would have on the present.

 

[Tomorrow]

All I know is that Los Cronocrímenes is an awesome movie.

I don't think I could watch that. Je ne pas sprechen zie español.

 

[OutThere]

My head is spinning with all the different possibilities and paradoxes this could introduce.

All I know is that Los Cronocrímenes is an awesome movie.

 

[r.j.s]

I would have to agree with this. I think Time Travel (if it does happen) will end up being like putting a person in stasis while the world advances around them instead of them moving "fast forward" in time.

Yes, but Einstein states that theoretically time travel is possible by moving close to the speed of light.

http://scienceray.com/philosophy-of-science/einstein-on-time-travel/

To everyone else, yes, it would seem as if they were in stasis.

 

[SilentPanda]

I don't think moving back through time would be possible, since no matter what, time is always moving forward.

I would have to agree with this. I think Time Travel (if it does happen) will end up being like putting a person in stasis while the world advances around them instead of them moving "fast forward" in time.

 

[r.j.s]

Okay, so I geeked out a little today trying to explain some of the concepts of relativity to my wife, who is not so particularly technical.

One interesting part of the conversation was when I went into the "twin paradox," where essentially one twin travels forward in time by moving at a speed near the speed of light.

That's what got me to thinking, if this form of time travel is essentially a one-way trip, are there any means - real, theoretical, or otherwise - of traveling backward in time?

My head is spinning with all the different possibilities and paradoxes this could introduce.

I don't think moving back through time would be possible, since no matter what, time is always moving forward.

 

[Tomorrow]

Okay, so I geeked out a little today trying to explain some of the concepts of relativity to my wife, who is not so particularly technical.

One interesting part of the conversation was when I went into the "twin paradox," where essentially one twin travels forward in time by moving at a speed near the speed of light.

That's what got me to thinking, if this form of time travel is essentially a one-way trip, are there any means - real, theoretical, or otherwise - of traveling backward in time?

My head is spinning with all the different possibilities and paradoxes this could introduce.