Hacker News Reader

Comment by mr_mitm | Hacker News Reader

FTL travel implies violation of causality, no matter how you slice it. How sacred causality is to you depends of course on your personal world view, but to me it is inconceivable how causality could be violated, so I won't be getting my hopes up about this at all, even though I can't comment on the technicalities of this paper.

View on HN

Causality isn't nearly as central to physics as it may be to your worldview. Lawrence Krauss and others who have commented on the matter have argued that FTL travel, would mostly require a re-evaluation of our perspectives rather than a re-evaluation of physics

Hmm, similar to how heavier than air flight was thought to be impossible for humans?

Interesting how the will of a few can shape humanity. I love it.

Probably a pretty good analogy! Even now, it's not known whether time has directionality in any way that is meaningful in physics. FTL travel would resolve the "Arrow of Time" question (https://en.wikipedia.org/wiki/Arrow_of_time) but this wouldn't invalidate much/any of physics because the arrow is essentially non-observable at the micro level

>> Causality isn't nearly as central to physics as it may be to your worldview

No, but locality seems to be a sacred cow in physics. They'll latch on to just about anything to explain violation of the Bell inequalities, but nobody is willing to part with locality.

Generally I'm suspicious whenever anyone seems to imply that an entire field is barking up the wrong tree

Can you give me a reference?

Here, Krauss argues in favor of Lorenz invariance when presented with the possibility if FTL.

https://www.scientificamerican.com/article/ftl-neutrinos/

He discusses it extensively in The Physics of Star Trek.

Also, supposed locally FTL travel for subatomic particles is pretty different from locally non-FTL but globally FTL travel a la Star Trek, Alcubierre drives, etc

At least at quantum level there are experiments where the outcome depends on things that did _not_ happen (according to our intuitive understanding of causality). Mostly in weak measurement research.

So I'd say while causality is real, there are still some surprises to be expected.

Perhaps related, see the Elitzur–Vaidman bomb tester [1].

[1] https://en.wikipedia.org/wiki/Elitzur%E2%80%93Vaidman_bomb_t...

Warp in this case I believe is referring to bending space time or traversing something similar to a wormhole, it’s not talking about Star Trek and tachyons and FTL. Hence the discussion points of exotic matter that exudes negative mass, which is what is required to stabilize mathematical models of Einstein Rosen bridges.

Doesn't matter, if you make it from here to the moon in less than a second, no matter if it's using a warp bubble or something else, then there is a frame of reference where you arrive before you leave.

You'd need negative mass either way. Bending spacetime is the most plausible implementation of FTL travel a la Star Trek; doesn't matter a whole lot if you're using the negative matter to keep the wormhole open or create an Alcubierre drive-style spacetime wave on which to surf

there may be a a way around that with hard determinism. at least that is one of the explanations of delayed choice quantum eraser experiments.

Reply on news.ycombinator.com