Time travel and "The Terminator"

GreyICE said:
Aitch said:
Ah, but if there are multiple pre-big-bang universes floating around in whatever they float around in, maybe the relatively small amount of energy generated by time travel would be enough to start one of them off? Not sure how the time traveller would arrive in the right point of that universe though. :confused:
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I'm not sure the usefulness of arriving at a universe 0.0001 seconds before a big bang, except to demonstrate how to become the deadest person in all of human history.
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I don't think that's what I said; certainly not what I meant! :boggled:

Lemme explain...

Time traveler (from now on referred to as TT) blasted backwards in time. Has a certain amount of energy associated with him (some of) which boots a parallel universe. Because they are messing about with time, TT is dumped into that universe at the time they were aiming for in the old universe; however, that point is the current 'now' of that universe and TT can affect what happens in it, without messing up the old one.

Why the 'new' universe is the same as the old one is harder to explain. Hmmm... Howzabout, TT's moving from one to the other causes a link between the two universes which causes the new one to exactly retrace the path of the old one, up until the point where TT arrives.

Or something. :boxedin:
 
Another big problem with time travel is that it also involves travel in space. If I were to go back in time just 24 hours or so, I'd find myself floating in space at whatever point the Earth had been at that point...
The only author I recall to address this was Gregory Benford, who's first novel dealt with a thoroughly messed-up future world trying to send a warning message back in time (via tachyon streams) to....Us.
 
This thread could do with being merged with the 'Time Travel' topic in 'General Skepticism and the Paranormal'
 
Lennart Hyland said:
Can you explain that a little more please :)
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I take a tank back in time and use it to destroy the time machine that sent the tank back in time.

Now there's two time tanks, tank A and tank A'. This introduces some interesting problems for conservation of mass, energy, etc.
 
GreyICE said:
I take a tank back in time and use it to destroy the time machine that sent the tank back in time.

Now there's two time tanks, tank A and tank A'. This introduces some interesting problems for conservation of mass, energy, etc.
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Unless my proposal is applied; and conservation of whatever applies to/across the multiverse. :eek:
 
Aitch said:
Unless my proposal is applied; and conservation of whatever applies to/across the multiverse. :eek:
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Except for the bit where it creates extra universes (or has an infinity of spare universes lying around, all of which conveniently follow the same physical laws, for no apparent reason at all).

Spawning extra universes is a stupid theory, and will remain so until someone comes up with a very good explanation (they all just randomly happen to be lying around is a very BAD explanation, and is about 3 steps down from goddidit).
 
A lot of discussion has happened about creating alternative universes and killing off your Grandparents so you never existed to kill them. However how about if time travel is possible but whatever you did could not impact on the future? One example is reading a history book. You can imagine King Harold winning the battle of Hastings in 1066, but when you put the book down he still died on that day and history is not impacted.
 
GreyICE said:
Spawning extra universes is a stupid theory, and will remain so until someone comes up with a very good explanation (they all just randomly happen to be lying around is a very BAD explanation, and is about 3 steps down from goddidit).
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The whole idea of time travel is stupid. No one will invent a time machine, because if anyone did there would be hordes of nerds from the future seducing our women with their shiny gewgaws, and since there aren't, there won't be.

Except in fiction, where anyone unwilling to put critical thinking on hold long enough to enjoy the story should just read/watch/listen to something else.
 
parky76 said:
If time travel did exist, and we went back in time and changed things, it would create an alternate time line, with the original time line moving forward as if nothing happened...right?
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I've never been happy with the concept of time splitting into alternate timelines as changes are made.

This would imply that all the energy in the universe is somehow copied into the alternate timeline.

How is this energy being created?

Dave Everett
 
bokonon said:
The whole idea of time travel is stupid. No one will invent a time machine, because if anyone did there would be hordes of nerds from the future seducing our women with their shiny gewgaws, and since there aren't, there won't be.

Except in fiction, where anyone unwilling to put critical thinking on hold long enough to enjoy the story should just read/watch/listen to something else.
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Except that that's just a cute variant on 'if aliens existed, they'd already be here' and assumes so many very stupid things that it's difficult to number them (including the concept that future time travelers will be something we'd immediately recognize as human).
 
GreyICE said:
Except that that's just a cute variant on 'if aliens existed, they'd already be here' and assumes so many very stupid things that it's difficult to number them (including the concept that future time travelers will be something we'd immediately recognize as human).
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I think "if aliens existed, they'd already be here" is stupido supremo. I have no problem believing that aliens exist, and they'll NEVER be here, because faster-than-light travel is impossible, so getting from where-they-are to where-we-are would take centuries, even if they knew we were here, and really, why bother.

I think the most, the very most, we can reasonably expect is that one day it will be possible to have a message-in-a-bottle kind of conversation with aliens, since such communication can happen at light speed. If an intelligent civilization can be found within 100 light-years of earth, and people are willing to wait up to 200 years between our "What's up?" and their "Not much. What's up with you?" it could be interesting.
 
bokonon said:
I think "if aliens existed, they'd already be here" is stupido supremo. I have no problem believing that aliens exist, and they'll NEVER be here, because faster-than-light travel is impossible, so getting from where-they-are to where-we-are would take centuries, even if they knew we were here, and really, why bother.

I think the most, the very most, we can reasonably expect is that one day it will be possible to have a message-in-a-bottle kind of conversation with aliens, since such communication can happen at light speed. If an intelligent civilization can be found within 100 light-years of earth, and people are willing to wait up to 200 years between our "What's up?" and their "Not much. What's up with you?" it could be interesting.
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Except that generational ships take at most, a few thousand years, even at deeply sub-lightspeed velocities, and would be upkept with minimal energy consumption.

No, the reason that argument fails is we have no idea if the aliens are here or not. The concept of taking an organic body inbetween the stars is so laughably stupid that it can be discarded out of hand, and the sort of digital intelligences that would travel between the stars are hardly something we could recognize. We'd have no idea if they're here or not - you could store the equivalent of every human on earth in a couple square miles of computing foam on Mercury, and monitor the slow blue planet in your leisure time.

Similarly, time travelers will, in all likelyhood, probably be adept not only at fitting in with human civilization, but be digital intelligences far beyond our ability to detect. Also, their native habitat would be Mercury, which means that we'd be looking in the wrong place on Earth. If someone did travel in time, they'd be looking for nice, toasty places to hang.
 
GreyICE said:
If we examine point A in the timeline before the time traveler arrives, and point B in the time line after the time traveler departs, we see that point A and point B have equal quantities of energy/mass.
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Umm.... why? At least in the Back to the Future version of time travel, the TT suddenly appears, thereby changing the energy. But what I had in mind is something a little more sophisticated.

Lennart Hyland said:
Can you explain that a little more please :)
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Energy is intimately connected with what's called time translation or time evolution (just as momentum is connected with spatial translation). Given the state of the universe at some time, one expects to be able to apply the laws of physics to that state and produce a new, unique state which is or will be the state of the universe a moment later. But if that future state is unique there is no time travel, because with time travel two futures exist for the same past (the one that happened "first" and the one affected by the TT).

It turns out that because of the very close connection between energy and time evolution, laws of physics which all such non-uniqueness also do not conserve energy.
 
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GreyICE said:
Except for the bit where it creates extra universes (or has an infinity of spare universes lying around, all of which conveniently follow the same physical laws, for no apparent reason at all).

Spawning extra universes is a stupid theory, and will remain so until someone comes up with a very good explanation (they all just randomly happen to be lying around is a very BAD explanation, and is about 3 steps down from goddidit).
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Aside from the fact that I did explain why the extra universes end up with the same physical laws etc as this one, we are discussing something which is probably impossible (time travel), inspired by a quartet of mediocre films. And you call my light-hearted ideas of how it may be 'explained' as stupid? :boggled:

Don't want to worry you, but I think they may be slipping something into your popcorn. ;)
 
bokonon said:
The whole idea of time travel is stupid. No one will invent a time machine, because if anyone did there would be hordes of nerds from the future seducing our women with their shiny gewgaws, and since there aren't, there won't be.
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That doesn't work because, even assuming you accepted the argument (see GreyICE's point), it only rules out one kind of time travel. By far the most plausible variety of time travel is something like a wormhole for which you play around with the velocities of one or both ends causing them to experience different proper times. If you then travel through in the correct direction, you can then travel in time. However, you can only ever travel back at most to the moment you first started moving the wormholes.

Of course, there are some minor problems with this kind of idea. To start with, we have no evidence wormholes actually exist, and even the theories that predict them tend to require a kind of matter that doesn't exist and amounts of energy that we could never have access to. However, this would mean that time travel can only happen after time travel has been invented, thus neatly avoiding any "We don't see any time travellers, therefore..." arguments.
 
Aitch said:
Aside from the fact that I did explain why the extra universes end up with the same physical laws etc as this one, we are discussing something which is probably impossible (time travel), inspired by a quartet of mediocre films. And you call my light-hearted ideas of how it may be 'explained' as stupid? :boggled:

Don't want to worry you, but I think they may be slipping something into your popcorn. ;)
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It's just that if we want to propose explanations for something, we should stick to realistic ones. Sure, multiple universes is cute, but when you come out and say "oh, no, it wouldn't create any paradox because we'd have a whole new universe" I'm entitled to say "wait a minute now."

Also Time Travel, practically speaking, is probably possible in some form or another. Certain mathematical equations suggest that a sufficiently weird object could induce temporal movement simply by orbiting it.

Umm.... why? At least in the Back to the Future version of time travel, the TT suddenly appears, thereby changing the energy. But what I had in mind is something a little more sophisticated.
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Well trivially, before any point in which time travel occured, the timeline is unchanged, thus the energy/mass is the same.

After the time travel, whatever you sent back in time is now gone from where you sent it back, but arrived at an earlier point. Tank A has traveled in time, creating Tank A', but A' (or the component parts of such) are still in the universe, somewhere. Thus A' has become A, for all practical purposes (but with extra years of wear and tear). The problem comes if A' does anything to prevent the original time travel of A. Optionally, people have proposed that you can't travel in time without exchanging energy/masses between the time periods, but that turns the universe into rather a bit of an accountant, which seems unlikely.
 
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GreyICE said:
It's just that if we want to propose explanations for something, we should stick to realistic ones. Sure, multiple universes is cute, but when you come out and say "oh, no, it wouldn't create any paradox because we'd have a whole new universe" I'm entitled to say "wait a minute now."
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Er, we are talking science fiction here; I suggest you replace 'realistic' with 'plausible'. Unless we're talking Star Trek, of course... :cool:
 
Cuddles said:
If you then travel through in the correct direction, you can then travel in time. However, you can only ever travel back at most to the moment you first started moving the wormholes.
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Oh, yeah, what was the name of that movie?

Primer.

Easily the best movie of 2004 with a budget of $7000.

Couldn't afford wormholes, though. Storage lockers...
 
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