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Old 2012-02-14, 09:19   #1
jasong
 
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Default Idiot's musings on interstellar travel and wormholes

Been thinking about the idea of the limitations of light speed on space travel.

We perceive light as an absolute limit, and from a speed limit standpoint, it very well could be. But there is also this other idea that it might be possible to connect points by going through other spaces.

So what if in the future we created a wormhole where one end is on the planet and the other is on a spaceship en-route to wherever. What happens when the spaceship accelerates to a good fraction of the speed of light? If we traveled through the wormhole, what would happen?

The spaceship and the planet are two separate reference points, but what about the 2 ends of the wormhole? People might claim it's a time travel paradox, but wouldn't one have to be able to travel to the future somehow for it to be a paradox?

I'm not capable of doing the math, but I don't think it's possible to re-unite the Earth and the ship, or even someone who went through the wormhole and traveled back to the Earth, without both going past the time when the ship left the Earth. So, if this scenario is possible, we could spread throughout the galaxy, from the reference point of the Earth, within hundreds of years rather than thousands.

I'm pretty sure I didn't come up with this on my own, I think I read about it in Stephen Hawking's A Brief History of Time many years ago, but it's a helluva thought.
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Old 2012-02-14, 10:08   #2
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Quote:
Originally Posted by jasong View Post
Been thinking about the idea of the limitations of light speed on space travel.

We perceive light as an absolute limit, and from a speed limit standpoint, it very well could be. But there is also this other idea that it might be possible to connect points by going through other spaces.

So what if in the future we created a wormhole where one end is on the planet and the other is on a spaceship en-route to wherever. What happens when the spaceship accelerates to a good fraction of the speed of light? If we traveled through the wormhole, what would happen?
Good question, to which a number of answers have been proposed. Google should throw up some of them.
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Originally Posted by jasong View Post
The spaceship and the planet are two separate reference points, but what about the 2 ends of the wormhole? People might claim it's a time travel paradox, but wouldn't one have to be able to travel to the future somehow for it to be a paradox?
But it's dead easy to travel into the future. I'm doing it right now at the rate of one second (as measured by the rest of the Earth) per second (as measured by my internal clock). If I travelled fast enough I could travel at more than one second per second.

I think you're confusing time travel into the future with travel into the past. The latter could lead to paradoxes according to some interpretations.

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I'm not capable of doing the math, but I don't think it's possible to re-unite the Earth and the ship, or even someone who went through the wormhole and traveled back to the Earth, without both going past the time when the ship left the Earth.
Fair enough. Give a heuristic explanation why you think it impossible. Quite often a thought experiment is at least as illuminating as a mathematical treatment.

Last fiddled with by xilman on 2012-02-14 at 10:09 Reason: s/rest of the universe/rest of the Earth/
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Old 2012-02-14, 20:22   #3
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Quote:
Originally Posted by jasong View Post
The spaceship and the planet are two separate reference points, but what about the 2 ends of the wormhole? People might claim it's a time travel paradox, but wouldn't one have to be able to travel to the future somehow for it to be a paradox?

I'm not capable of doing the math, but I don't think it's possible to re-unite the Earth and the ship, or even someone who went through the wormhole and traveled back to the Earth, without both going past the time when the ship left the Earth. So, if this scenario is possible, we could spread throughout the galaxy, from the reference point of the Earth, within hundreds of years rather than thousands.

I'm pretty sure I didn't come up with this on my own, I think I read about it in Stephen Hawking's A Brief History of Time many years ago, but it's a helluva thought.
I take it you mean that someone could go in one hole and come out the other (nearly) 'instantaneously' (from the point of view of the worm-holer)?

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The spaceship and the planet are two separate reference points, but what about the 2 ends of the wormhole? People might claim it's a time travel paradox, but wouldn't one have to be able to travel to the future somehow for it to be a paradox?
Could you please clarify what this means? What paradox? What do you mean 'travelling to the future'?

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I'm not capable of doing the math, but I don't think it's possible to re-unite the Earth and the ship,
again, please clarify?
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Originally Posted by jasong View Post
or even someone who went through the wormhole and traveled back to the Earth, without both going past the time when the ship left the Earth. So, if this scenario is possible, we could spread throughout the galaxy, from the reference point of the Earth, within hundreds of years rather than thousands.
I'm still not following.


As a general comment on faster than light travel, the arguments against it are valid regardless of what "universe" or "dimension" other than our own such travel takes place in. All that disproving FTL travel requires is the appearance of FTL travel, regardless of methodology. There is nothing besides the infinite energy barrier (not trivial) that physically prevents us from violating the speed of light.

(As a note to my note, even if, like me, you do not regard causality as apropos* an axiom of our physical world, there are still other paradoxes that arise from FTL travel that are even harder than violating causality.)

(*I'm not sure that's the word I'm looking for, but a quick google did not shine any light on the subject.)
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Old 2012-02-14, 20:36   #4
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But it's dead easy to travel into the future. I'm doing it right now at the rate of one second (as measured by the rest of the Earth) per second (as measured by my internal clock). If I travelled fast enough I could travel at more than one second per second.
Being a time-travel prude, I prefer to stay 100% in the present at all times. Perhaps that explains why I've never met "the future Mrs. Mayer".
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Old 2012-02-14, 20:55   #5
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Being a time-travel prude, I prefer to stay 100% in the present at all times. Perhaps that explains why I've never met "the future Mrs. Mayer".
Your preferences don't enter into it. Like it or not, your 4-velocity is c and if your space-velocity is zero then you are necessarily travelling into your future light cone at 1 second per second.
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Old 2012-02-14, 21:10   #6
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Your preferences don't enter into it.
Appallingly bad customer service they have around here. I think I'll just take my trusty right-twice-a-day wristwatch and go. You "hasty folk" can keep chasing that tomorrow-that-never-comes thing you seem to find so irresistible.
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Old 2012-02-15, 01:01   #7
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Good question, to which a number of answers have been proposed. Google should throw up some of them.
But it's dead easy to travel into the future. I'm doing it right now at the rate of one second (as measured by the rest of the Earth) per second (as measured by my internal clock). If I travelled fast enough I could travel at more than one second per second.
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Originally Posted by xilman
I think you're confusing time travel into the future with travel into the past. The latter could lead to paradoxes according to some interpretations.
Yeah, got my thoughts mixed up.

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Originally Posted by xilman
Fair enough. Give a heuristic explanation why you think it impossible. Quite often a thought experiment is at least as illuminating as a mathematical treatment.
Basically, my thought is, from examining what people get from the math, when you accelerate you're basically slowing down your subjective experience. Someone on Earth would advance normally relative to the Earth. Now the problem is what happens if someone decided to chase the spaceship? As they accelerated their experience of time would also slow down, and since you have to go faster than the ship to catch up to it, the second ship's time would actually be going MORE slowly up until the moment they caught up to it. So the mere act of catching up to the first ship would stymie(sp?) any attempt to get any sort of time paradox.

Now when I was talking about the wormholes, I failed to mention Einstein's Spooky Action at a Distance observations. I'm basically considering the possibility that at some future date we might be able to control this and use it for space travel. Since the two ends of the wormhole would be "sympathetic" to each other, you might be able to travel through the wormhole, sort of like folding a sheet of paper to shorten the necessary length of a pencil line. So from one point of view, something may be hundreds of light years away, but from another it might be mere feet or yards. Of course there are probably restrictions(and permissions I would assume) that we are unaware of.
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Old 2012-02-15, 07:30   #8
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Quote:
Originally Posted by jasong View Post
I'm basically considering the possibility that at some future date we might be able to control this and use it for space travel. Since the two ends of the wormhole would be "sympathetic" to each other, you might be able to travel through the wormhole, sort of like folding a sheet of paper to shorten the necessary length of a pencil line. So from one point of view, something may be hundreds of light years away, but from another it might be mere feet or yards. Of course there are probably restrictions(and permissions I would assume) that we are unaware of.
As I understand you, that's a fairly complete and accurate description of travelling through a wormhole.

Note that you don't need to have a wormhole for a trip to be able to take different paths between two points, and I don't mean the trivial cases of having different accelerated motion.

In relativity, the distance between two points is that measured along a geodesic joining them, a geodesic being the straightest possible path. In Special Relativity, where space-time is flat and space obeys Euclidean geometry, geodesics are Euclidean straight lines in space and as you know, Euclidean geometry only allows one straight line to exist between two points. Light rays always travel along geodesics.

Things get very different in GR where the presence of mass, pressure, etc curve space-time. It now becomes possible for two points to be joined by more than one geodesic and for light to take more than one path between source and observer. Evidence that this occurs in nature comes from observation of gravitational lensing.
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Old 2012-02-15, 17:06   #9
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(As a note to my note, even if, like me, you do not regard causality as apropos* an axiom of our physical world,
I take this back. I found out last night while doing my PDE homework that the wave equation implies causality.
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