[MvB (OP)]

HI *,
how much time does an entangled pair need to convey info? FTL? None? Lightspèed?
And most important: How do you prove it??

Best regards

MvB

[Halc]

Hi MvB, and welcome to the TNS!

how much time does an entangled pair need to convey info?

Two things.
1) No demonstration of information transfer has ever been conclusively demonstrated, so any such information transfer is interpretation dependent. No local interpretation allows any superluminal cause/effect.
2) Due to relativity of simultaneity, the time between two events separated in a space-like manner is frame dependent, so there can be no objective time between the two events, or even an objective ordering. There's no way to tell which event occurs first, if one assumes an interpretation of time where such a concept is even meaningful.

[MvB (OP)]

Thank you for your welcome and quick answer.
Though I have some difficulties to understand the answers. Please explain why
Ad 1.) You state that there is no proof for QE. But there are several papers which show the experiment which proves it.
Like in h t t p s : //www.extremetech.com/extreme/295013-scientists-capture-photographic-proof-of-quantum-entanglement#:~:text=Scientists%20have%20successfully%20demonstrated%20quantum,visual%20evidence%20of%20entanglement%2C%20though.
Ad 2.) What do you mean by "frame dependent"? A relativistic frame like in one object's speed can only be measured in relation to another object? In that case I would assume that observer and QEP are in the same frame. Or an event horizon? Then I would say that such drastic separation is not necessary for validity of abovementioned experiment.

Best regards
MvB

[Halc]

Ad 1.) You state that there is no proof for QE.

There's no evidence for instant action (actual information transfer) at a distance. There is very much strong evidence for QE.
Evidence of superluminal information transfer ('spooky action') would consist of the ability to send a message faster than light via QE.

Ad 2.) What do you mean by "frame dependent"?

I mean that relative to one inertial frame, measurment A might occur first, and relative to some different frame, event B occurs first.  If, in all frames, one event (A) always occurs first, then the two events are not separated in a space-like manner.

A relativistic frame like in one object's speed can only be measured in relation to another object?

A frame defines which events are in the same place, and thus can be used to declare an object to be stationary in it, but no actual stationary object is necessary to define a frame. So I'd say 'one object's speed can only be measured in relation to the coordinate system chosen'.

In that case I would assume that observer and QEP are in the same frame.

All observers are in all inertial frames, or at least all nearby ones. By 'nearby', I mean that it isn't really meaningful to say you're moving at speed X relative to the inertial frame of some galaxy 10 BLY away.
The measurements of the entangled thing are events, and events don't have a speed, so it doesn't really matter if the two observers doing the measurements are stationary relative to each other or not. The experiment isn't dependent on that.

Yes, if you choose to do your experiment with both observers relatively stationary, well that defines one inertial frame, and relative to that frame, one can say that the events are nearly simultaneous.

Or an event horizon?

I don't think event horizons come into play in the simple QE scenario.

[MvB (OP)]

What do you mean by 'nearly simultaneous'?

[MvB (OP)]

PS: What, if not transfer of info, is shown by QE-experiment above?

[evan_au]

One aspect that hasn't been mentioned here (perhaps because I've misunderstood it?):
- Two observers can in theory take simultaneous (or near simultaneous) measurements a a quantum entangled state
- However, the significance of the result can only be confirmed by communicating at the speed of light.
- So ultimately, the speed of an entangled communication is limited to the speed of light.

In practise, it is extremely difficult to create an entangled state that is reliably stored for a significant time while it is transported a great distance - and then to successfully retrieve the stored state and read it just when you want it.
- Since you can't successfully measure an entangled quantum state before you store it for transport, the person at the "other end" can't tell what message the sender intended to send.

Ideas like this have prompted an increasingly sophisticated series of experiments to test "Bell's inequality".
- As I understand it, no experiments have yet shown the ability to transmit information faster than light, using quantum entanglement
- They have confirmed the predictions of Einstein's theory of General Relativity
- But they have not confirmed any of the theoretical attempts to explain quantum theory by means of "hidden variables".
See: https://en.wikipedia.org/wiki/Bell_test#Overview

[Halc]

What do you mean by 'nearly simultaneous'?

They've used atomic clocks synced in some frame in attempt to make the measurements as simultaneous as they can, but nothing has infinite precision, and I've never seen a QE experiment done where both measurement events were stationary relative to each other (remember the Earth is rotating), so there is not just one obvious inertial frame to use, and thus they're only 'nearly simultaneous'. As I said, it doesn't really matter so long as the events are not in each other's light cones.

PS: What, if not transfer of info, is shown by QE-experiment above?

What experiment? The one in the post-2 link? They apparently take a picture, a different method of demonstrating QE than the usual ways. I don't see any claim of instant information transfer.

What I do see is a delay. The first measurement is presumably taken at the right side, measured well before the photons are detected on the left branch. Much of the phase rotation seems to take place after the right side as already been measured. Hard to tell since the pictures are often not to scale. But they seem to be making no attempt at 'simultaneous' measurement. Be interesting if the phase rotation took place after the delay portion.

- But they have not confirmed any of the theoretical attempts to explain quantum theory by means of "hidden variables".

Nor have they disproved said hidden variable explanations, but I've seen problems pointed out that are not currently explained by such theories. Proponents of such interpretations are working to resolve the issues, but if they can't, then there's a falsification test that they don't pass.

[Deecart]

how much time does an entangled pair need to convey info? FTL? None? Lightspèed?

This question has been superseed by some other concept.

According to the actual specialists of the domain, there is no need any more for some information travel.
They suppose that everytime (so this is a very common phenomena) some particles interact with each other they "entangle".
Doing so they cant be considered any more as individuals, but must be considered as one whole quantic object.
Per example, when two electrons entangle, if one electron go 1000 kilometers from the other electron, they must be considered as the same quantic dual particle. Therefore whatever happen to one of the electron is instantly echoed to the second particle.
Saying this do not violate the lightspeed limited transmission of information.

[Deecart]

And most important: How do you prove it??

.
We actually never be able to proove the contrary, so it is the actual opinion.