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boy genius
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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.
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:Sempiternity said: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.
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).
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.
boy genius said: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.
JesseM said: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.
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.Rev Prez said:The problem is generating the right distribution of mass-energy. You can solve for [tex]T_{\mu\nu}[/tex] in Einstein's equation given some desired metric just as you can solve for [tex]G_{\mu\nu}[/tex] 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.
>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.
JesseM said: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.
Currently, there is no scientific evidence or technology that suggests it is possible to create stable wormholes. The concept of wormholes is based on theoretical physics and has yet to be proven in real-world experiments.
One of the main challenges in creating stable wormholes is the amount of energy required. According to current theories, an enormous amount of negative energy is needed to keep a wormhole open, which is currently beyond our technological capabilities.
Yes, there are ongoing theories and research being conducted on stable wormholes. Some scientists are exploring ways to manipulate dark matter or exotic matter to create and stabilize wormholes, while others are investigating the potential of using advanced technology such as quantum computers.
While the concept of using wormholes for time travel is popular in science fiction, it is currently considered impossible according to our current understanding of physics. Wormholes would need to be stable and able to transport matter without collapsing, which is not yet achievable.
If stable wormholes were to be created, it could revolutionize space travel and enable us to explore distant galaxies and potentially even other universes. It could also have profound implications for our understanding of the laws of physics and the nature of the universe.