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Comment by Havoc | Hacker News Reader

I had assumed it is by definition instant?

Surely anything else would imply a mechanism with additional complexity and indirectly void the entire concept. Delayed entanglement effect doesn't quite have the same cleanness for lack of better word

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Reality doesn't necessarily agree with its model though, so it makes sense to verify?

We model reality incorrectly all the time. A lot of math was wrong, too. So, it’s always good to test the models. In security, we also tested in normal, abnormal, and hostile environments.

Einstein’s relativity theory is a model that is quite fundamental, are there wrong parts of it as well? Asking not as challenge, more out of interest.

Yes, of course, 100 year old theories start to crack, because of all new data discovered recently, but we are far from a new theory to take it place.

Pilot wate theory is slowly move in, for example. In 20-50 years it may predict reality better in some cases than existing theories.

What does instant mean in a relativistic universe? Does it imply there is a simultaneous now for both entangled things?

It would imply faster than light communication between particles, but as someone else said, models are only models. Faster than light communication is impossible for us to achieve, no reason to assume there's not a way that's inaccessible to us.

Sight correction, at least in my understanding (physics major but only undergrad) this explicitly isn't communication.

It's not possible to use entanglement to transmit information faster than light, even though the entanglement itself could be simultaneous.

It's not the speed I am interested in; it's that relativity says there is no such thing as a simultaneous now (for things in different reference frames anyway).

Well you could imagine seeing a process that causes entanglement and just trying to halt this process somehow. Before a certain time you would simply see no entanglement at all and after some time you wouldn't see any effect on the entanglement. In between something might happen, but what exactly is a bit hard to tell.

None of this is beyond current models though, so I imagine you could predict the results quite well if the calculations were feasible. And if that can be done then that's probably exactly what they did.

The simulations are investigating how long quantum entanglements take to form, not how long it takes for non-local action / pilot wave / wave function collapse (if you subscribe to these views of QM) to propagate.

(There is a theory in which non-local variables propagate at superluminal speeds, but not instantaneously, but this is a whole other matter).

Might I ask, what is this theory of superluminal non-local variables? I would love to read more about it.

It looks like they measured the time of the process where the entanglement occurred, not a time of entanglement itself. I guess they can use this to put an upper bound on the time for entanglement, which is a valid thing to do for an instantaneous process.

This seems to come up in every discussion of quantum entanglement.

It doesn't travel faster than the speed of light. Information can't travel faster than c.

No need to worry about Trisolarans.

If "it" = information, then sure. But the collapse of the quantum state is instantaneous.

Only in theories where it collapses, and nobody seriously thinks Copenhagen is correct these days.

I thought information could only travel as fast as light because that was fastest medium we're currently aware of that can carry information. But that doesn't necessarily preclude other, faster mediums from existing, no?

Not quite. There are two speeds in relativity: the maximum speed and non-maximum speeds (i.e. everything else). It just so happens that light travels at the maximum speed.

Supra-luminal signals will almost necessarily imply that it's possible to violate causality by arranging a series of supra-luminal communications. Not every supra-luminal communication violates causality, but it's hard to think of a way to build a consistent theory that would both preclude causality violations and permit at least some supra-luminal signaling.

Supersonic speed doesn't violate laws of nature or violates casuality. Superluminal speed in matter just produces Cherenkov's radiation.

At superluminal speed, we will be able to hit photons in any order, including reverse order, or emit photons and catch them later. Why this is a problem for casuality?

I know next to nothing about physics, but isn't the "It just so happens" part of what you said potentially misleading? Isn't it that light is massless, so that directly implies that it would travel at the maximum speed?

It's a distinction with no difference. Only massless particles can move at the "maximum speed", in our Universe these are photons and gluons. And maybe gravitons, if they exist.

Similarly, massless particles can't move below the "maximum speed", as they'll have no energy or momentum and won't be able to interact with anything.

Why would the absence of mass force something to travel at the maximum speed? I could understand it being able to travel at that speed; why would it always do so though?

Theoretically, a massless particle can move slower than light. But then it'll have zero energy and momentum, so it won't be able to interact with anything.

Thanks. The equations give the answer in the end, I found this explanation the best [1].

The only way to get a zero mass is if the energy is zero, or the velocity is c.

[1] https://profoundphysics.com/why-do-photons-have-no-mass-simp...

No. It's an absolute, inviolable, universal limit on any and all interactions in the universe. It was recently confirmed that even gravitational waves are limited to the speed of light. This (and the Fermi Paradox) are the strongest evidence that faster than light travel or communication of any kind is impossible.

We just call it the "speed of light" because it's the speed that massless particles (like photons) travel at in a vacuum.

Ok, but why?

Per relativity, any medium that could conceptually facilitate transfer of information or of causality (which are basically the same thing) faster than the speed that light happens to travel at would also be able to reverse direction and arrive at their source in space earlier than the time that they left. That effect is completely unrelated to light itself.

"If time travel is possible, then there is no such thing as time." — Kurt Gödel, Einstein's great friend at Princeton's Institute For Advanced Study.

Einstein once remarked that he went to his office "just to have the privilege of walking home with Kurt Gödel."

https://imgur.com/a/avUwwHk

https://archive.ph/6doQh#selection-707.279-711.1

https://www.amazon.com/When-Einstein-Walked-G%C3%B6del-Excur...

IIRC It’s not that light is a medium. It is that light goes that particular speed max (photons can go slower in fact) because that is the speed of causality.

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