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Comment by belter | Hacker News Reader

> c is technically the speed of causality.

How does this notion reconcile with seemingly instantaneous quantum phenomena like spooky action at a distance?

Quantum entanglement ("spooky action at a distance") doesn't allow for communication, so there's no causality between the particles.

Thanks for the answer. I had forgotten about the No-communication theorem.

This led me into another rabbit hole :-) of why c is 299,792,458 m/s and for example not 499,792,458 m/s or some other value, and the fundamental constants that bring this value. [1]

Is there a current theory that tries to justify those constants that bring the current value of c ? Are those values the ones that must be, for the current Universe to be feasible?

[1] https://arxiv.org/abs/hep-ph/0205340

I'm not sure if there is a good theory on why it ends up being this speed, but if any of the constants were even slightly different we wouldn't be in this universe to talk about it.

https://en.wikipedia.org/wiki/Fine-tuned_universe

Veritasium has a few recent videos on Action. In one of them I believe he shows speed of light expressed as one unit of action, which implies that it’s the highest “resolution” any propagation can resolve at based on the fundamentally smallest path integral anything can traverse, or something.

The speed of light is 1c and is a fundamental constant.

Humans choose to express it in metres and seconds.

A meter is huge if you compare it to the Planck length. Humans are pretty big creatures compared to fundamental particles, so we have a big basic unit of length. But seconds are gargantuan, because humans are absolutely glacial if you compare them to the time it takes light to travel a Planck length.

It's like a continental plate asking why humans zip around so fast.

> The speed of light is 1c and is a fundamental constant.

Yes, but why is the value that it is and not higher or lower? From my (basic) research it seems, it could be plus or minus 20% a different value, and the current Universe would still be feasible.

Well, it has to be _some_ value, right? I mean, if we were in a universe where it was 20% greater, you would be asking the same questions.

No, the point is that if it was 20% bigger we would not be here to ask those questions :-) Stars fusion or weak atomic interactions would not work. Maybe Hari Seldon decided....

But you said in your comment that "it could be plus or minus 20% a different value, and the current Universe would still be feasible"

That touches on a long-running very complicated debate around quantum mechanics, hidden variables, spooky action at a distance, no-communication, etc.

For various quantum effects that seem to be paradoxes by classical physics what is happening "under the covers"? Does the delayed choice experiment really send information backwards in time? Even if it appears to do so if we can't at least send information back in time with that mechanism isn't it just sophist philosophy at that point?

For my part I'm not smart enough to claim to have answers to anything but my intuition is there are no quantum paradoxes. Delayed choice does not send anything back in time. We don't experience quantum phenomena at the macro scale so our intuition and reasoning are ill-suited to thinking about it. That easily leads us to incorrect conclusions.

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