A possible way to produce a wormhole.

Well for one thing, causality is much simpler and more logical than non causality. And quantum physics calculations suggest that a particle traveling back in time would interfere with itself, essentially preventing time travel.

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,We don't see any time travelers because a "time traveler" would probably end up in an Alternate Universe almost exactly like our own (except for their presence, of course), because they "went back" and changed shit. All the Myriad Ways and all that.

Of course, this is just a theory on my part, although I think it's the most likeliest outcome.

edited 23rd Apr '12 6:38:47 PM by Ekuran

Unless You Already Changed the Past.

Da Rules excuse all the inaccuracy in the world. Listen to them, not me.

Larry Niven had a cute take on this, time travel was physically possible and the universe had been rewritten several times untill the it settled on a stable timeline where time travel had simply never been invented or used at any time.

hashtagsarestupid

So... who here would be the guy to jump into the wormhole?

How can you even tell if it worked anyway? I doubt there'd be a way to come back.

They never travel alone.

USAF: Relax no need to be so hostile. It is a speculation thread not a lets bash scientists could/should be doing thread.

I don't think using a black hole is feasible it will feed off of the stars sooner or later. There is also the assorted energy emissions from the blackhole to careful of.

Finding a way to create a stable wormhole without the blackhole sounds better. But again being able to do this sounds risky at best.

Who watches the watchmen?

Assuming that 'virtual particles' or some other cosmic rule would prevent the use of a wormhole as a timemachice, would it still be physically possible to build a transversal wormhole that don't threaten causality?

hashtagsarestupid

Any FTL travel violates causality.

Pour y voir clair, il suffit souvent de changer la direction de son regard www.xkcd.com/386/

Not nesscesily, if you only travel to outside of your own 'light cone' you shouldn't be placing cause and effect at risk.

hashtagsarestupid

@Uchuujinsan: If you move FTL, yes...on the other hand space can go FTL...that's what Alcubierre drive is exploiting...and Hubble's law is consistent with it...if all form of FTL violate casualty, then the universe itself would already done that...

And USAF, stop being so freaking hostile...you wanna argue that scientist should stop doing stupid theoretical study, go open another thread, or it'll be off-topic...

I've heard about using a lot of powerful lasers to shoot at a single point to create a black hole...not sure if that'll work with creating wormhole...but Orions Arm seems to use this method...

edited 6th Sep '11 5:11:08 AM by onyhow

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Using the movement of space to travel FTL helps against some problems (for example acceleration) but I don't see how it helps against violation of causality. If you could explain it to me, I would be interested, I got no physics degree.

To quote wikipedia:

To explain the problem as I understood it, there is no universal timeframe to determine whether two events happened at the same time. This is dependent on your inertial system - and the speed of light. Say you send a signal in one direction and travel there by any means of FTL and wait for it - you arrive BEFORE you see you sending it and that means you arrive before you sent it. That's why ANY FTL for mass and information violates causality. It's not moving faster than light that's the problem, it's BEING faster than light that's the problem. I don't see how the Alcubierre drive solves this and the wikipedia article doesn't mention that this is solved. During the expansion of the universe, nothing overtakes a signal of light, so the simple expansion alone doesn't violate causality.

Pour y voir clair, il suffit souvent de changer la direction de son regard www.xkcd.com/386/

The way the Alcubierre drive 'solves' the problem is that the bubble becomes casually disconnected from the rest of the universe, making it impossible to leave or turn off.

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I know Orion's Arm goes into a fair bit of detail about their wormhole and why they can be used for space travel but not time travel. I don't understand it myself or how plausible it is but here are the links for it.[1][2][3]

edited 6th Sep '11 11:24:46 PM by joeyjojo

hashtagsarestupid

^^^ Here's a fun thing about wormhole: you don't move at FTL speed, neither local or global...wormhole is basically shortcuts in space...but traveling through it you still need to go sublight...light will still outrun you in the path through wormhole...it's technically FTL because you arrive at the destination before light traveling yo the destination by direct path...

And, as I've said before, if space going FTL violate casualty, then the universe is already screwing itself up...Hubble's law produce linear velocity graph, which means it can go FTL with sufficient distance...also current theory on Big Bang is that there's a very short period after the boom where space expand at FTL...

edited 7th Sep '11 4:12:48 AM by onyhow

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The bits that are moving FTL away from each other are casually disconnected, hence no time travel paradoxes.

Da Rules excuse all the inaccuracy in the world. Listen to them, not me.

And that's already the problem. It doesn't matter what you do locally - globally you are FTL, and that already violates causality (according to the theory of relativity). From the point of view of any non-local observer, you travelled back in time. That's why the method doesn't matter, and any*

^{There still might be some special tricks that address this problem, like "increasing" the speed of light}

FTL has this problem.

And as I said before, space going FTL does not have this problem, because no information or object can overtake a light signal the way the universe expands.

Pour y voir clair, il suffit souvent de changer la direction de son regard www.xkcd.com/386/

^ And you don't listen to me that even locally you're still in STL when you're using wormhole...only when you go FTL locally you run into casualty problem (argued by special relativity)...not globally...really, using wormhole is basically cut through the field instead of walking around it...

...where did you get your sources anyway? I've seen sources by several scientists of good credibility arguing that it's possible, if not pratically, to go into FTL that is no local FTL...popular science book or not, those are still written by actual scientists....Alcubierre drive has a lort of hurdles that made it nearly impoossible, but none of them are casualty related...and it's technically space expands....

edited 7th Sep '11 5:37:34 AM by onyhow

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Global FTL causes the causality disconnects, but it's true it's feasible to do that without local FTL.

Da Rules excuse all the inaccuracy in the world. Listen to them, not me.

Not really :/

You know, I'll give an actuall example. I think you know the basics of the special theory of relativity.

So let's make a little thought experiment. We have a space ship with 100m lengths. In the middle is a light emitter, on the two sides are one detector each. Let's say the spaceship flys past a space station (with 0,6c), and the moment it passes the light emitter emits a light signal in each direction. 50m to each detector - it arrives at the same time at each detector. But an observer in the space station sees the events differently. The rear part of the space ship moves towards the emitter, the front part away from it, so because the speed of light is constant in each reference frame, from the observer in the space station the emitter in the rear part gets hit first. (For reference).

So far so good, let's install some special things at each detector. At the rear detector, we install our FTL-drive(tm), at the front detector we install a huuuge bomb. The FTL drive will jump in front of the front detector once triggered. The method doesn't matter. So, from the point of view of our spaceship, both detectors get hit at once. The FTL jumps, and the bomb destroys our ship with a gigantic fireball. From the point of view of the space station however, the FTL gets started FIRST, jumping in front of the bomb detector and safely preventing it from detonating.

So what happened now? That's why FTL violates causality, independent of the method.

And if scientist say it's possible, they can very well argue "screw causality" - some do. I got my information from a little literature, but mainly from my classes on special theory of relativity in school (majored*

in physics, that "got no degree" earlier refered to a university degree like a "master")

edited 7th Sep '11 6:16:52 AM by Uchuujinsan

Pour y voir clair, il suffit souvent de changer la direction de son regard www.xkcd.com/386/

Kay, I'm a bit at fault here (although not with Alcubierre drive, someone already mentioned that inside the bubble is causally disconnected with outside, which cause problems on its own...), sorry about that...although I just did some search, and that actually Matt Visser did some research about wormhole, and actually proposed a mechanism that prevent that in the first place...(although let's not argue about Roman ring right now...)...also, I saw some people argued that there are some certain cases that wormhole does not violate causality if, as joeyjojo said, it emerges outside the your light cone...

Sorry again...but that still make certain cases of FTL possible...right?

edited 7th Sep '11 7:38:56 AM by onyhow

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Wait a second, are we talking about Wormholes, FTL or Time travel here?

Technically, FTL should violate casualty. By traveling faster than light, you would arrive at a place where (when?) you weren't in a point in time.

However, a stabilized wormhole ( Not a Black/white hole) would theoretically connect two points in time. Thus allowing stable time loops to be formed.

edited 7th Sep '11 9:47:07 AM by pokedude10

^ Not really...if the time needed to travel between 2 mouths in realspace is greater than time difference between the 2 exits, time loop will not happen...on the other hand, if you use 2 or more wormholes to do it (Roman ring) then might be possible...although some argue that if any of that happens, the wormholes will collapse...

edited 8th Sep '11 4:56:41 AM by onyhow

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