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by Tylerian
1921 days ago
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> "Moreover, such a wormhole would be unstable. If for example a spaceship were to fly into one, it would instantly collapse into a black hole—an object in which matter disappears, never to be seen again. The connection it provided to other places in the universe would be cut off." Can anyone expand on this? |
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I think it's a somewhat garbled description of the Einstein-Rosen bridge, which is a feature of the maximally extended Schwarzschild spacetime--you can see a diagram of this spacetime in [1]. Roughly speaking, this spacetime has two "exterior" regions that look like an ordinary universe with a spherically symmetric gravitating object at its center (these are regions I and III in the diagram). The gravitating object that you can actually see (as in, receive light signals from) in the exterior region is a white hole (region IV in the diagram); but if you try to fly into the white hole, you can't get inside--you end up inside the black hole instead (region II in the diagram).
The "Einstein-Rosen bridge" interpretation comes from viewing this spacetime in the coordinates used in the diagram, which are not the same as the natural coordinates of an observer in either exterior region. In the coordinates used in the diagram, it looks like you have two disconnected universes (regions I and III are disconnected at the bottom) that get connected by a spherical "wormhole" or "bridge" which starts at zero size, expands to a surface area of 4 pi M^2, where M is the "mass" of the hole, and then shrinks back down to zero size and vanishes, leaving two disconnected exterior regions again (regions I and III are disconnected again at the top). The bridge shrinks too fast for anyone in one exterior region to fly through it and reach the other exterior region; any attempt to do that ends up with you trapped inside the black hole (region II) and destroyed in the future singularity.
[1] https://en.wikipedia.org/wiki/Kruskal%E2%80%93Szekeres_coord...