How would you create a stable wormhole and know where it leads?

[boy genius]

how would you create a stable worm hole and if it is possibele how would you know where it would go to and if you could actualy put something like a remote control car through it.

 

[pervect]

I gather that it's impossible to form a wormhole classically - it had to exist already. (I don't recall the exact source for this statement, though). I'm fairly sure that I remember that Morris & Thorne proposed finding an existing wormhole and stabilizing it in their paper
"Wormholes, Time Machines, And The Weak Energy Condition", but I don't seem to be able to find a copy of this paper online.

 

[JesseM]

Here's an article discussing an idea that small stable wormholes may exist naturally as a consequence of "squeezed vacuum states" shortly after the big bang:

http://www.npl.washington.edu/AV/altvw53.html

 

[Sempiternity]

To actually create a wormhole artifically you would probably have to be able to artificially manipulate gravity in a similar way to how you can manipulate light and magnetism.

https://www.physicsforums.com/showpost.php?p=559508&postcount=12

 

[JesseM]

To actually create a wormhole artifically you would probably have to be able to artificially manipulate gravity in a similar way to how you can manipulate light and magnetism.

It's not as easy as just creating the right distribution of matter/energy though--you'd actually need to change the topology of spacetime to create a wormhole, which the classical theory of general relativity doesn't tell you how to do, although a quantum theory of gravity might. Actually, there is a caveat to this that Kip Thorne mentions on p. 496 of Black Holes and Time Warps:

In the classical strategy, our infinitely advance civilization would try to warp and twist space on macroscopic scales (normal, human scales) so as to make a wormhole where previously none existed. It seems fairly obvious that, in order for such a strategy to succeed, one must tear two holes in space and sew them together. ... Now, any such tearing of space produces, momentarily, at the point of the tear, a singularity of spacetime, that is, a sharp boundary at which spacetime ends; and since singularities are governed by the laws of quantum gravity, such a strategy for making wormholes is actually quantum mechanical, not classical. We will not know whether it is permitted until we understand the laws of quantum gravity.

Is there no way out? Is there no way to make a wormhole without getting entangled with the ill-understood laws of quantum gravity--no perfectly classical way?

Somewhat surprisingly, there is--but only if one pays a severe price. In 1966, Robert Geroch (a student of Wheeler's at Princeton) used global methods to show that one can construct a wormhole by a smooth, singularity-free warping and twisting of spacetime, but one can do so only if, during the construction, time also becomes twisted up as seen in all reference frames. More specifically, while the construction is going on, it must be possible to travel backward in time, as well as forward; the "machinery" that does the construction, whatever it might be, must function briefly as a time machine that carries things from late moments of construction back to early moments (but not back to moments before the construction began).

 

[Sempiternity]

It's a good explanation, except that what's missing is the initiation process of creating such a wormhole. When you "try to warp and twist space on macroscopic scales," how is that done? In the process where "one must tear two holes in space and sew them together," Greene Thorne speculates this as being a part of "topology-changing transitions" consisting of 3-brane manifolds wraping around the tear.

Concerning the part about a classical method, he explains that it can possibly be done by "warping and twisting of spacetime" where "time also becomes twisted up as seen in all reference frames" and the machinery "function briefly as a time machine that carries things from late moments of construction back to early moments."

However, through all of this, how does it all occur? How do you "warp and twist" spacetime in the first place? I was speculating that it might be possible to actually do so by condensing large amounts of electromagnetic energy into a small space.

From Parallel Worlds,

The light beam becomes blue-shifted--that is, it becomes more energetic until it reaches infinite energy, which is impossible. Or, the light beam becomes so energetic that it creates a monstrous gravitational field of its own which collapses the bedroom/wormhole.

Because mass and energy can be converted into each other, black holes can also be created by compressing energy.

 

[Spin_Network]

how would you create a stable worm hole and if it is possibele how would you know where it would go to and if you could actualy put something like a remote control car through it.

You have more chance of hitching a ride on the back of a team of alien dolphins:https://www.physicsforums.com/showthread.php?t=76604

 

[jcsd]

It seems to me that if you seek to make worm holes the one thing you require above all else is worms.

 

[Rev Prez]

It's not as easy as just creating the right distribution of matter/energy though--you'd actually need to change the topology of spacetime to create a wormhole, which the classical theory of general relativity doesn't tell you how to do, although a quantum theory of gravity might.

The problem is generating the right distribution of mass-energy. You can solve for $$T_{\mu\nu}$$ in Einstein's equation given some desired metric just as you can solve for $$G_{\mu\nu}$$ given some distribution of of mass-energy. I think you meant to say that we may need a theory of quantum gravity to determine whether a superluminal topology is physical.

Rev Prez

 

[JesseM]

The problem is generating the right distribution of mass-energy. You can solve for $$T_{\mu\nu}$$ in Einstein's equation given some desired metric just as you can solve for $$G_{\mu\nu}$$ given some distribution of of mass-energy. I think you meant to say that we may need a theory of quantum gravity to determine whether a superluminal topology is physical.

No, my point was that the classical theory doesn't allow you to change the topology of space just by moving matter and energy around, and a topology change is needed to create a wormhole, aside from the method Thorne described which would require a method of time-travelling during the construction.

This post by John Baez may be helpful in clarifying the difference between the metric of a spacetime and the topology:

http://www.lns.cornell.edu/spr/2001-05/msg0032747.html

>2) To what extent does the metric tensor determine the global topology?

That's a weird question, since we normally think like this: you hand
me a smooth manifold, which is a set equipped with a topology and some
other structure - a "smooth structure", meaning a bunch of compatible
coordinate charts. Then you plop the metric tensor down on this manifold.
You can't even say what the metric tensor IS without first knowing the
topology and smooth structure! So how can we run the story backwards
and ask how much the metric tensor determines the topology?

However, there are tricks you can play to answer this question anyway!

If the metric tensor is positive definite, it determines a metric in the
other sense, and that determines a topology. This is the same topology
you started with! So in this subtle sense the metric determines the
topology in this case.

If the metric is Lorentzian - one timelike direction and the rest spacelike -
it defines a notion of "lightcone". For now, let's say the "open lightcone"
of x is all the points that can be reached from x by a timelike (not
lightlike!) path. Taking intersections of open lightcones we get some
diamond-shaped regions, and we can use these as neighborhoods in a topology:
define the open sets in this topology to be arbitrary unions of finite
intersections of open lightcones. I think this is called the Alexandrov
topology. In nice cases this is the same as the topology we started with!
I forget the exact assumptions we need, but it obviously works for Minkowski
spacetime.

>As far as I understand it the aim of the GR game is to solve for the metric.
>Once that's done your spacetime is completely determined and thus so is the
>global topological structure.

I hope you now see that's BACKWARDS from how we normally think of things:
in the simplest version of this game, the manifold comes first, then the
metric. We can try to recover the topology from the metric, but we can't
even talk about the metric without first having the topology - and the
smooth structure.

 

[Rev Prez]

No, my point was that the classical theory doesn't allow you to change the topology of space just by moving matter and energy around, and a topology change is needed to create a wormhole, aside from the method Thorne described which would require a method of time-travelling during the construction.

My bad. You're right. You do assume the manifold is connected in the desired way before calculating energy-momentum.