Wormholes....

[ThisIsMyUserName]

Ello, I am new here and have a brief question that needs clarification... please don't call me "dumb" I just don't understand this...

I recently read a book entitled "How to Build a Time Machine", by Paul Davies. In the book Paul states something along the lines of... If you were to enter a wormhole at point A and exit at point B you could arrive back at point A before you even entered... Now I know the subject of time travel, and such, is a little far fetched, but I was just curious how it was possible to arrive back at point A after you already been to B. Is the author stating that the wormhole is a two way street, or would you need a different mode of transportation to arrive back at point A faster than the travel speed to point B... like an alternate faster wormhole? I don't know... I understand with time travel you can go back and forth, but he states a wormhole would have to be created first in able to travel back into the past (theoretically)... I am sure there is an simple explanation to this but it is just confusing me. If you would like more information I will find the page(s) and quote his "theory's", but if you understand what I am talking about please comment.

- thanks

[yevaud]

Well...

As the argument goes, if you were to create a stable wormhole - we'll assume this is possible, for the sake of argument - and then sent one end of it through space at a significant fraction of the speed of light, the two different end-points would be in two entirely different times. This is as the stationary end is still in "our" time, while the end-point that has been moved has experienced time-dilation. So if you were to step into the stationary end, and travel to the end that had been moved, you would effectively travel through time.

See what I mean?

Of course, this is all terribly hypothetical, as we 1) do not know if wormholes actually exist; they're just a nifty academic exercise, 2) if they can be made stable, 3) if they can be made large enough to allow passage of any significant amount of matter without collapsing instantly, 4) if one could even survive such a journey, etc.

[ThisIsMyUserName]

He also mentions something along the lines of that... If you could capture the "antimatter/gravity/i'm confused" and bring it back from where you captured it you could essentially have a wormhole given to travel back in time the amount that was spent creating it? Wormholes (in theory) also contain no mass because of negative energy or because they cancel out all ? I am sorry about my unintelligible knowledge on this, it's all very new to me. Just curious....

[ThisIsMyUserName]

significant fraction you mean 99.99999999% speed of light or something?

[ThisIsMyUserName]

Well...

As the argument goes, if you were to create a stable wormhole - we'll assume this is possible, for the sake of argument - and then sent one end of it through space at a significant fraction of the speed of light, the two different end-points would be in two entirely different times. This is as the stationary end is still in "our" time, while the end-point that has been moved has experienced time-dilation. So if you were to step into the stationary end, and travel to the end that had been moved, you would effectively travel through time.

See what I mean?

I understand you would travel trough time like that, makes sense with time dilation, but I don't understand how he says you could arrive back at A after you got to B if A is stationary and B needs to be created - Isn't there a flaw in that?.... and B had to be built from A... If you catch my drift. (sorry i edited this a couple times, I am in a rush and i have to go I will be back shortly thanks for your time )

[yevaud]

Well, by significant fraction, at about 50% of C you begin to experience fairly noticeable time dilation, so my assumption is that this is what was meant. As far as the "arriving back at 'A' before 'B,' my suspicion is that this was misstated or you misheard it. It's kind of axiomatic with this particular effect that you're stuck with two different time frames: endpoint A and endpoint B, and one can't travel backwards any earlier than the creation of endpoint A.

Hope that makes sense.

There's several sketchy, hypothetical methods for "time travel," such as it were, but truly none of them appear to be feasible. For example, Tipler's rotating cylinder, requires a massive, infinitely long cylinder. Clearly that will never occur, for all that the math appears to allow CTC's (Closed Timelike Curves).

One wonders if these possible methods of time travel are all unfeasible due to some sort of "Cosmic Censorship" principle, in that even if they appear to be possible mathematically, in reality they can never be built or used.

[yevaud]

Ah, it occurred to me what was meant by the A/B paradox. If you created said wormhole, and sent endpoint B out and then back to it's starting point, the two points would be physically close, but in two different time frames. So you could travel through the wormhole, then cross the intervening space...and arrive at one endpoint before you departed the other.

Still unfeasible I think.

Btw, this thread, as interesting as it is, is probably not appropriate for the SS&A forum. I am going to move it to "Unexplained," but leave a link here in the SS&A forum. This isn't because your questions are "dumb" (they aren't at all), but these kind of topics seem to always go right past even the theoretical and end up in the metaphysical and beyond.

[a_lost_packet_]

Well...

As the argument goes, if you were to create a stable wormhole - we'll assume this is possible, for the sake of argument - and then sent one end of it through space at a significant fraction of the speed of light, the two different end-points would be in two entirely different times. ...

You could also park one end significantly close to a very large gravity well like a neutron star where time may flow more slowly.

[yevaud]

Yes, that'd work as well.

An interesting side-benefit of creating a stable wormhole would be in the realm of colonizing the galaxy, or at least the nearer stellar systems. If a "generation ship" had one end-point of a stable wormhole onboard, then the ship could be continually manned by people residing on Earth, until it (eventually) arrived at it's destination. No real worries about sustaining generations of colonists onboard. In fact, the ship could be fairly rudimentary, just a control cabin with requisite life-support, and all the rest engine and fuel source.

[a_lost_packet_]

Yes, that'd work as well.

An interesting side-benefit of creating a stable wormhole would be in the realm of colonizing the galaxy, or at least the nearer stellar systems. If a "generation ship" had one end-point of a stable wormhole onboard, then the ship could be continually manned by people residing on Earth, until it (eventually) arrived at it's destination. No real worries about sustaining generations of colonists onboard. In fact, the ship could be fairly rudimentary, just a control cabin with requisite life-support, and all the rest engine and fuel source.

IIRC, doesn't time pass normally inside the wormhole? The distance might be shorter but, there'd still be time to consider and interstellar distances are pretty large. Not sure what the ratio would be there. 1:5? 1:3000?

[yevaud]

Not certain, although as I remember the ideas thrown around, propagation time via a wormhole was thought to likely be near-instantaneous. The wormhole links two regions of space almost as if space was folded; the distance, and hence transit time, would be nil.

[cameron99]

This is a possible if you had a speed of 3 times the sun power you can skip 1 day now if you had a wormhole the speed of 1 sun you can time travel a meer hour maybe but not backwards you can only go forward in time

[yevaud]

^ not a word of that made any sense. Sorry. ^

[tanstaafl76]

Don't worry, you would understand if you were from year 4100: viewtopic.php?f=15&t=20935

[decry189]

Well played, sir.

[starshipomega]

not sure if this would help with an explanation, but the plots of the novels Timelike Infinity and Ring by Stephen Baxter deals with something that sounds kinda like this, one end of a wormhole is attached to a relativistic spacecraft which is sent on an interstellar loop while the other is left in the solar system, so that when the spacecraft comes back in the future they'll be able to open the wormhole, and the people at point A (stationary end) will effectively be able to learn about the future (point B). hopefully that helped, not sure if that was what was being asked

[Primero_Sol]

starshipomega wrote-"not sure if this would help with an explanation, but the plots of the novels Timelike Infinity and Ring by Stephen Baxter deals with something that sounds kinda like this"

Awesome books and actually very insightful into theories of this nature, Baxter is pretty good at applying new theories to scifi...

[yevaud]

not sure if this would help with an explanation...

We pretty much covered that.

One wonders...I mentioned "Cosmic Censorship" - it may well be that even though these all sound fine, and may be mathematically explainable, the reason they're all unworkable is that they are prevented. Else, Causality violations would occur. An effect occurring before the cause? Absurd.

[superpaul3000]

Ok I know this is a really long post so if you just want the answer read the first part…

I'm not sure exactly what this book says but I can give you a general explanation of time travel in the context of Einstein's relativity. So we all know that time travel into the future is easy (well given a very fast spaceship anyway). You don't even need a wormhole. The acceleration (not the velocity) causes time dilation so you can accelerate to near the speed of light and travel 10 light years away and come back. The end result is you end up 20 years in Earth's future even though it only took seconds or minutes for you. So given a wormhole, you could keep one end on Earth and take the other end with you for that same ride. Now you have gates A and B next to each other. There is no cosmic censorship keeping this from happening since it does not violate causality. If I go through wormhole B, I find myself 20 years in the past but there is only the one gate A there and I am at the same time I started. So you can't keep going back in time to kill your grandfather or something. You can keep going through wormhole A though and traveling into the future at 20 year increments.

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That is only given relativity, if we throw quantum mechanics into the mix things get messy. Anyway, let us consider an alien civilization that is highly advanced and exists a few billion years ago that have all this technology. Say they leave one wormhole at their home and take the other one on a similar ride but 2 billion light years away and back. So they end up in our time and they decide to check out Earth. If we go through their wormhole we end up 4 billion years in the past and we can go to Earth and just go through our entire history right? (Using the easy form of future time travel in increments) Well according to strict relativity yes, but in order to maintain causality the time traveling versions of ourselves would have existed in our past and we should see evidence of this in the fossil record right now. But if we consider quantum mechanics, then we (the time travelers) won’t see our history as it really happened, we will see a completely different series of events since each event is just a random outcome of some number of wave function collapses (however you define that collapse, Copenhagen or MWI). So after 4 billion years you might not even end up with an Earth with life. The only way we can see what happened in our past is to go through wormholes that were made at different times in our past. But as soon as you go through it that universe starts differentiating so you only have a small amount of time to check out your past (this depends on the event you are looking at, the age of dinosaurs is a long age but the time to assassinate Hitler is much shorter). Again none of this violates causality. Even if you travel to see your grandfather before you were born and kill him. This is because as soon as you go through the wormhole that person is not exactly the same person as your grandfather, even though he looks and sounds the same.

[jmil]

I think you're talking about the Twin Paradox?

You might just be having a problem thinking of time as having an absolute value throughout the universe. The flow of time doesn't have an absolute value. The only way to arrive at a point in time prior to your starting point is to travel faster than c.

Twin Paradox (in a nutshell):
If you leave Earth travelling at a speed that is is sub-c and great enough to experience significant time dilation, then you will arrive back at your starting point younger than your (theoretical) twin who did not go on the trip. You won't arrive back prior to the time you left unless you exceed the speed of light. There's a paradox for that as well, but I can't remember the name of it.