Ask Lemmy

I saw a talk on the subject about a year back. It was discussing tokamak reactors, from an engineer working on them. The small ones can't sustain a break even state, but they are affected by the inverse square law to a larger degree. I believe China is about to start/has started construction on a power station sized test reactor.

The pellet sort are a different type. They have different pros and cons.

Exceeding FTL (and breaking causality) is basically a sci fi trope at this point with about as much credibility as psychics. To have at least some credibility you need one of: a testable hypothesis, or an unexplained phenomenon. Right now we have neither. At best, we have some equations, that work below light speed, where we can extrapolate past light speed and see how the math works. The problem is: none of these equations are testable as they all contain infinities or other asymptotic features that prevent passing light speed itself. So, if there's no viable math to get from sublight to FTL, and there's no unexplained phenomena, then what we're left with is nothing.

Even quantum entanglement, which is a darling of sci fi whenever they need a plot device (hello Le Guin and the ansible), has categorically been shown to obey causality and the light speed limit in every lab test.

At some point it's like asking for negative mass, antigravity, or other things that the math would allow. Except our universe doesn't.

I've got a wormhole to sell you ;)

Basically, physics says that nothing, not even information can actually travel faster than the speed of light. It's a universal limit that shows up when you do the math on relativity. This concept is called "causality".

Because of this, FTL communication is probably impossible. Quantum entanglement seems like it could provide a loophole, but it doesn't actually work that way. To actually use quantum entanglement for communication, it actually needs a confirmation message, which would have to be delivered by a different means (every quantum message needs a non-quantum confirmation). That confirmation would be bound by the speed of light, thus preserving causality.

This is a very very rough description based on my memory, so some details may be a little off, but it should cover the gist. This article goes into more detail:

https://bigthink.com/starts-with-a-bang/quantum-entanglement-faster-than-light/

Edit: After reading, the answer is more that attempting to impart information onto the entangled particles to send a message necessarily breaks the entanglement and thus does not transmit the information to the other side. Entangling the particles makes their states related to each other, but only at the time of entanglement, and anything that changes either particle (including measuring it) will break the entanglement going forward.