Science Forums 2

[CraigD]

Space opera, physics popularizations, and hard SF on the subject of disrupting space

Originally Posted by Theory5

Wouldn't constantly creating and closing wormholes cause some kind of disruption in space-time?

I agree with enorbet’s general point on how very speculative questions about of worm holes are.

The idea that various sorts of artificial fiddling with the vacuum can “weaken” or “break” it belong, I think, firmly in the real of space opera. It actually figures prominently in an episode of STTNG. I think it must be taken, however, as an allegorical cautionary tale (in it’s 40-some year run, Star Trek has been full of these) about wearing out the Earth’s ecosystem. Scientifically, though, it’s uncertain that wormholes are even possible, so speculation about their effect on the vacuum is … for lack of a better word, fantastic.

Thorne and Hawking are said to have an ongoing debate about the possibility of traversable wormholes, including some intimations that they might at least in some manner disrupt the space they constitute. It assumes

• A traversable – at least by very small particles, such as photons – wormhole can be found or created
• Its mouths are movable
• The usual laws of physics, including special and general relativity, apply to wormhole mouths
• The time required to traverse it is zero, or much smaller than the time needed for light to traverse the distance between the two mouths in normal space.

From these assumptions, it follows that one can build a time machine from a traversable wormhole. One way to do so is to place one mouth (B) in a strong gravitational field, subjecting it to gravitational time dilation, wait ‘til , then return it to near the other (A). Anything entering A and emerging from B, then, will appear time units in its own past – that is, it will emerge from B before it enter A, existing near it’s own past self for a duration a bit less than .

Some pretty profound paradoxes of causation arise from this, such as the grandfather paradox, ie the object of information emerging from B in its past self, preventing it from entering A, so that it never emerged from B – the core plot of countless SF stories and movies.

According to Thorne (eg: in Black Holes and Time Warps), one of the scenarios offered in support of a “cosmic censorship” principle that prevents such causation-violating setups as the above is that, were it built, at least one particle of some kind would pass into its own past, then, in its “second future”, into its past again, and so on, until such a large number of occurrences of the same particle existed in the same vicinity that, regardless of what particles are involved and how the wormhole is built, it would all just, for lack of a better phrase, get blown all to hell.

Back in the realm of SF – but in this case very hard SF – in his 1997 novel Diaspora, Greg Egan considered the possibility of traversable black holes being possible, but lacking all the qualities assumed above. Not wanting to spoil this excellent novel for folk who haven’t read it but will, I’ll say no more.