1. Originally Posted by Noclevername
So FTL would really be EAFAL: Exactly As Fast As Light.
Well.. yes dependent on your frame of reference. FTL is only inferred by the fact that the traveller could possibly traverse a distance measured in light years instantaneously within his/her own time frame. But no matter what, when the traveller returns to the initial time frame at the end of the journey, time for that frame would have passed no less than the time it would take a signal to traverse the same journey. Hence a traveller can always traverse a large distance faster, but the consequence - never sooner (if you get what I mean)

This in my mind solves the causality paradox.
Last edited by cosmocrazy; 2019-May-29 at 02:37 PM.

2. Originally Posted by cosmocrazy
Well.. yes dependent on your frame of reference. FTL is only inferred by the fact that the traveller could possibly traverse a distance measured in light years instantaneously within his/her own time frame. But no matter what, when the traveller returns to the initial time frame at the end of the journey, time for that frame would have passed no less than the time it would take a signal to traverse the same journey.

This in my mind solves the causality paradox.
But the traveller returning through the same wormhole would also take the same amount of time from the POV of the stay-at-home observer? Or would the traveller re-enter the original time frame?

3. Originally Posted by Noclevername
But the traveller returning through the same wormhole would also take the same amount of time from the POV of the stay-at-home observer? Or would the traveller re-enter the original time frame?
I could be totally wrong about this I don't claim to be a relativity expert by any means. Just in my mind how it would work is that from the initial time frame point of view the traveller would still take at least the time it would for the signal to get to the same destination. So in answer to your question - no the traveller, from the POV of the stay at home observer, (in my example) would re-emerge from the wormhole 5 years later, For the traveller, on exiting the worm-hole back into the initial time frame, their clock would now appear to be 5 years behind, yet they would have experienced no time passing at all.

4. Originally Posted by Swift
A little more seriously, yes, I like that idea, at least for a story. Imagine that travel through the wormhole is faster for those in the wormhole, but no faster for those outside of it. So one could travel to another planet quickly, by your perspective, but years would have passed in normal space. Would solve the paradox problem and give us interstellar travel.
Not necessarily using wormholes, but I've seen various stories with lightspeed or near lightspeed drives. Poul Anderson had at least three. In one, if I recall, there was an accident and humans return to Earth about three billion years after they left. The story was called "Epilogue." There were a couple of novels, but I can't recall the story names right now. In one, if I recall, they thought they had developed FTL, but arrive back on Earth six thousand years later, with a vastly different interstellar civilization. In another, they had near light speed travel using a fictional zero point energy technology, and travelers kept coming home to radically changing civilizations.

What might be interesting with slow wormholes though is that you might use it for stealth travel. I'm not sure if I've quite seen that idea (slow, possibly far below light speed stealth wormhole travel) in stories.

5. The Forever War's travel was technically FTL, but to make it "work" required reaching near light speeds so Haldeman was able to invoke time dilation anyway. Certainly coming back to radically changed civilization is a major theme in the novel. And of course any story with relativistic interstellar travel uses the trope too; A World Out Of Time, Time For The Stars, etc.

Brin's The Uplift War mentioned "Level D" hyperspace which was many times slower than other available forms of FTL, allowing battleships to be stealthy but to arrive a century after the conflict was over.

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Originally Posted by eburacum45
The wormholes in Orion's Arm are consistent with theory, particularly so since they were revised by a physicist a few years ago; they do have issues with causality, but there is a whole subset of wormholes which do not have such issues, simply because of the geometry of space-time. Here is a diagram that should explain why this is so.
https://www.orionsarm.com/page/322
So long as both mouths of a wormhole stay outside each other's future light cone, no causality problems can occur.
Interesting idea, and yes I can't think of a causality paradox with a single wormhole - but the problems remain given there can be more than one. For example, let's take this diagram again from that page :

wormholes.png

As per Orion's Arm, time is vertical and space is horizontal. This diagram has two wormholes : A-to-H (which is allowed), and F-to-H which is disallowed - but we'll change it to instead run from F-to-A (which is allowed since A is outside of F's light cone.

Now, suppose your grandfather meets your grandmother at H (yes, you know where this is going ! ) Some time later at T1, you set off on a rocket ship to F, go through our newly re-routed wormhole to A, and then through the A-to-H wormhole.

You are now at H. Bye Bye GrandPa

7. Originally Posted by Ufonaut99
Interesting idea, and yes I can't think of a causality paradox with a single wormhole
A single wormhole could, if it leads into the past, still cause a paradox if the mouths are moved into the same vicinity. Arrive home before you leave.

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Originally Posted by Noclevername
A single wormhole could, if it leads into the past, still cause a paradox if the mouths are moved into the same vicinity. Arrive home before you leave.
Yes, but the premise was that "both mouths of a wormhole stay outside each other's future light cone,"

9. Originally Posted by Ufonaut99
Yes, but the premise was that "both mouths of a wormhole stay outside each other's future light cone,"
OK, I missed that part.

10. Unless I've missed it, everyone is assuming the entrances of the wormholes are stationary.

There is no reason in principle why you cannot create a bridge between points just one mile apart, and then move one end to another star system 100 light years away.

The distance through the wormhole will be one mile, but you will have traversed 100ly.

11. Originally Posted by DaveC426913
Unless I've missed it, everyone is assuming the entrances of the wormholes are stationary.

There is no reason in principle why you cannot create a bridge between points just one mile apart, and then move one end to another star system 100 light years away.

The distance through the wormhole will be one mile, but you will have traversed 100ly.
And if you move it at relativistic speeds, it potentially becomes a time machine.

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But the kind of wormholes that Kip Thorne was talking about in Interstellar are solutions to Einstein's equations, and they are indeed FTL. But they rest on two highly speculative assumptions:
1) there is a higher dimensional "bulk" that our 3D space is embedded in. The wormhole enters this bulk to cross between the black hole and the white hole.
2) there exists negative energy matter, required to stabilize the wormhole.
If you invoke those two assumptions, you have a lot of freedom as to how much distance you can cross and how quickly, I'm not sure what the possibilities are.

13. Originally Posted by Ken G
But the kind of wormholes that Kip Thorne was talking about in Interstellar are solutions to Einstein's equations, and they are indeed FTL. But they rest on two highly speculative assumptions:
1) there is a higher dimensional "bulk" that our 3D space is embedded in. The wormhole enters this bulk to cross between the black hole and the white hole.
2) there exists negative energy matter, required to stabilize the wormhole.
If you invoke those two assumptions, you have a lot of freedom as to how much distance you can cross and how quickly, I'm not sure what the possibilities are.
Would the "bulk" have a time element or would it be purely relating to spatial dimensions?

14. Originally Posted by Ufonaut99
Interesting idea, and yes I can't think of a causality paradox with a single wormhole - but the problems remain given there can be more than one. For example, let's take this diagram again from that page :

wormholes.png

As per Orion's Arm, time is vertical and space is horizontal. This diagram has two wormholes : A-to-H (which is allowed), and F-to-H which is disallowed - but we'll change it to instead run from F-to-A (which is allowed since A is outside of F's light cone.

Now, suppose your grandfather meets your grandmother at H (yes, you know where this is going ! ) Some time later at T1, you set off on a rocket ship to F, go through our newly re-routed wormhole to A, and then through the A-to-H wormhole.

You are now at H. Bye Bye GrandPa
Sorry, I missed this earlier. Your scenario assumes that you can only pass through a wormhole in one direction, whereas (as far as I am aware) a traversable wormhole is open in both directions, so the F-A wormhole is also open in the direction A-F, which is not allowed. You can't use the F-A wormhole to travel because it would have already caused a paradox in the opposite direction, and collapsed (or become non-traversable in some other way, in order to avoid paradoxes).

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Originally Posted by eburacum45
Your scenario assumes that you can only pass through a wormhole in one direction, whereas (as far as I am aware) a traversable wormhole is open in both directions, so the F-A wormhole is also open in the direction A-F, which is not allowed.
Although my scenario only has one-way trips through the wormholes, for myself I’ve imagined the only logically consistent way to express the restrictions from Orion’s Arm is that for any single wormhole, neither mouth should be within the light-cone (past or future) of the other.

This would hold true since if event X is within the past light-cone of event Y, then by definition Y would be in the future light-cone of X (for flat space-time). In turn this would mean we would immediately allow or disallow F-A travel without even having to consider A-F; the two directions of travel would always agree by definition (I love symmetry!)

Upshot is , from the diagram A and F are outside each others light-cones (past and present), so my understanding of the rules is that therefore a wormhole should be allowed for both-ways travel between them.

Of course, the diagram makes it look like A and F are close to each other’ light cones, so we could imagine A as being much further to the right to emphasise that they are well outside. With that, I’d be interested in why A-to-F travel should be disallowed.

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16. If you have a configuration of several wormholes that together appear to allow a reversal of causality, that is sometimes caused a 'Roman Ring', named after Tom Roman who has done some work in this area. Matt Visser thinks that these sorts of configuration are also prohibited, but he's not quite sure how that would work in practice.
https://en.wikipedia.org/wiki/Roman_ring

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we think there are black holes by various detection's
all require the massive amount of mass to be there
not flung somewhere/when else
or the black hole would not be detected
falling into one is likely to do unpleasant things to what ever falls in

but a white hole would be hard to miss
as there is no sign of one ever detected
I see a big problem with worm holes
the exit is missing

18. Originally Posted by nota
we think there are black holes by various detection's
all require the massive amount of mass to be there
not flung somewhere/when else
or the black hole would not be detected
falling into one is likely to do unpleasant things to what ever falls in

but a white hole would be hard to miss
as there is no sign of one ever detected
I see a big problem with worm holes
the exit is missing
Black holes are not wormholes.

19. Originally Posted by nota
but a white hole would be hard to miss
as there is no sign of one ever detected
I see a big problem with worm holes
the exit is missing
Since you mention white holes I think you are talking about what is called a Schwartzschild wormhole, which would be a black hole connected to a white hole, and I think it’s true that we have never observed one. But there is also the possibility of wormholes created by strange matter, which I think would not require a white hole.

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I don't really believe in wormholes that actually work, just like I don't believe in aliens being here. I would think this is all like Fermi's paradox. If wormholes were really exploitable, we would have aliens here already.

21. Originally Posted by Copernicus
I don't really believe in wormholes that actually work, just like I don't believe in aliens being here. I would think this is all like Fermi's paradox. If wormholes were really exploitable, we would have aliens here already.
If wormholes were anywhere near us. And if aliens able to exploit them had wormholes anywhere near them. Lot of unknowable variables.

22. double post

23. Wormholes may be lurking in the universe – and new studies are proposing ways of finding them.

QUOTE: Some wormholes may be “traversable”, meaning humans may be able to travel through them. For that though, they would need to be sufficiently large and kept open against the force of gravity, which tries to close them. To push spacetime outward in this way would require huge amounts of “negative energy”.

https://theconversation.com/wormhole...ng-them-153020

24. Originally Posted by Roger E. Moore
Wormholes may be lurking in the universe – and new studies are proposing ways of finding them.

QUOTE: Some wormholes may be “traversable”, meaning humans may be able to travel through them. For that though, they would need to be sufficiently large and kept open against the force of gravity, which tries to close them. To push spacetime outward in this way would require huge amounts of “negative energy”.

https://theconversation.com/wormhole...ng-them-153020
From the same article:
We also know that negative energy is behind the universe’s accelerated expansion.
Well, no, we don't know for sure. We suspect.

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