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Anything contradicting relativity is currently out of the scope of science and not backed by any observation whatsoever, so any travel-faster-than-light theory has exactly the odds granted to it by it's own believers, and zero for everybody else.

[laumars]

Wormholes don't contradict relativity. In fact they were predicted by relativity (or rather a solution to the singularity problem predicted by relativity).

The scientific name for a wormhole is an Einstein-Rosen Bridge - named after Nathan Rosen and, obviously, Albert Einstein who conceived the idea.

There are other suggestions for "faster than light" travel, but FTL is a bit of a misnomer because the concepts of FTL aren't about having a velocity that's greater than c (the speed of light in a vacuum), it's about warping or cutting through the fabric of space in a way that makes the distances shorter. A wormhole is just one theoretical method of jumping those distances via a shortcut.

[octatoan]

IANAP, but isn't the only argument against faster-than-light-travel the fact that it contradicts causality?

[TheOtherHobbes]

I don't see a problem there. The definition of causality is circular anyway. There's no formal mathematical self-consistent proof of causality. It's just sort-of assumed, and then there are back-arguments from relativity that say "Well, that violates something we sort of assume."

The problem is that in science, if you assume things in a naive way ("What goes up must come down." "Planets travel in circles") you're almost certainly wrong - because the details of physical reality are usually counter-intuitive and unexpected.

So what we really know is:

1. Spacetime is a thing. It has bulk properties described by GR. 2. Er - that's it.

We don't know what spacetime is made of, or what you can do with the things it's made of, or what their properties are.

So I'd classify this as "definitely not known due to lack of knowledge" rather than "definitely not proven."

Proposals like Quantum Dynamical Triangulation, Causal Sets, and Loop Quantum Gravity are beginning to ask what spacetime is made of, but they're barely in their infancy.

The one thing they have in common is the idea that there's a network of - something... - and the reality we recognise propagates across the network.

If the elements are discrete - and they almost certainly are, because of the Planck limit - there will be some moment where an element changes state.

How fast does that happen? What's the mechanism? What limits the state changes? (Adjacency? Some other property?)

It's completely mysterious, and I think it's unwise to make definitive statements about it until it stops being a mystery.

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I don't know if it's the only one, but it is one Stephen Baxter's novel Exultant plays brilliantly with: the people in that universe discovered means to travel faster than light, but at a high price: causality was gone - and they had to get over it.