Superluminal communication

[Piman]

https://www.futuretimeline.net/blog/202 ... -cable.htm

To clarify this paragraph:

"Only limited by the speed of light, quantum teleportation could revolutionise communication networks, enabling near-instantaneous transfer of information across vast distances. [..] It could also enable a new, absolutely secure way to share information, wherein direct transmission between distant network users is no longer necessary.":

While the quantum state of the entangled particle is teleported, instantaneously, and can be used to detect eavesdropping, this bit is random as I understand, and any useful information must still travel at or under the speed of light — through a classical channel, some of which today are already near the speed of light. (Most have equipment hops that delay by many milliseconds, as well as light travel through non-vacuum that slows it down; these could be improved).

So "instantaneous transfer" across the solar system, say, will not happen in the future, (at least via quantum teleportation; maybe something else like wormholes will make it possible), and "direct transmission" is still necessary since information cannot be teleported, needing to be transported through classical channels to complete the quantum teleportation.

https://en.m.wikipedia.org/wiki/No-comm ... on_theorem
From https://en.m.wikipedia.org/wiki/Quantum_teleportation:

"Thus, an observation resulting from a measurement choice made at one point in spacetime seems to instantaneously affect outcomes in another region, even though light hasn't yet had time to travel the distance, a conclusion seemingly at odds with special relativity. This is known as the EPR paradox. However, such correlations can never be used to transmit any information faster than the speed of light, a statement encapsulated in the no-communication theorem. Thus, teleportation as a whole can never be superluminal, as a qubit cannot be reconstructed until the accompanying classical information arrives."

Teleportation of macro-scale objects is also theoretically possible, and will very probably occur, as this timeline and many physics experts predict. The teleportation will, however, always be limited by the speed of causality/light.
String theorist Michio Kaku on future teleportation, in an entertaining 3-minute interview.

[Piman]

(I just underlined the possible issues above).

I just happened across this engaging explanation in plain English of the first experiment to prove (recently, in 2015) that this instant communication of a single quantum state really is apparently random (not predetermined).

At 19:54 the professor tries to explain that because the passed quantum information is random (and isn't affected by any action), it's both instant and also impossible to pass or extract useful information from.

[wjfox]

Something very strange keeps happening with this thread. I keep getting notifications to approve your post, over and over again.

Anyway, I've made a slight adjustment to the blog text now.

[Piman]

It looks like the only difference is the removal of the phrase, "Only limited by the speed of light"?

Actually that part was not wrong; quantum teleportation of information is limited by the speed of causality (light).

The two underlined parts in the very first quoted post seem incorrect -- based on all the following sources.

[Piman314]

For clarity here is the current, live page that I'm seeing:

"Quantum teleportation could revolutionise communication networks, enabling near-instantaneous transfer of information across vast distances. This could drastically reduce latency in future global data exchanges. It could also enable a new, absolutely secure way to share information, wherein direct transmission between distant network users is no longer necessary.

Latency is indeed expected to be reduced ( a cool paper that talks.about it), athough this will be from reduced network overheads and not from instantaneous transfer of info.

And eavesdropping will indeed destroy the message and be detectable, unlike pure electromagnetic messages -- enabling absolutely secure sharing.

However, the underlined parts seem to be stating instantaneous transfer of non-random information (normal messages, such as the above mentioned quantumly encrypted messages) -- which will not be the case. Sharing of information (as well as teleportation of objects) will still be limited by the speed of light.

[Piman314]

May I bump this up and request wjfox's opinion on this, and anyone else who wants to? Since this is a recent article, I wouldn't want any misinformation about faster-than-light communication to sit around for very long.

https://en.m.wikipedia.org/wiki/No-comm ... on_theorem

[Piman314]

I didn't notice before that in the next paragraph also:

"The process works by harnessing quantum entanglement – a technique in which two particles are linked, regardless of distance between them."

This is true.

"Instead of them physically travelling to deliver information, entangled particles exchange information over long distances without physically carrying it."

As I understand (according to the above sources), the entangled particles deliver only their quantum state, which is randomly determined by the universe and which the sender and receiver cannot affect --

so "information": technically yes, but not any actual messages or useful information.

[Piman314]

Something very strange keeps happening with this thread. I keep getting notifications to approve your post, over and over again.

I had refined the posts a few times, for perfection and easy reading.
I'm guessing the website threw a notification on each Edit, rather than consolidating the notifications.

Anyway, I've made a slight adjustment to the blog text now.

The part that was removed, "Limited only by the speed of light", was correct , ironically.
Quantum teleportation is limited by the speed of light; physics says right now that there can never be superluminal communication.

The article is all correct where it describes the study, (and the study didn't teleport information, notice). But those two paragraphs that I described above contain misinformation in the 3-4 places where they state "instant" communication.

[wjfox]

I've updated it now, hope it sounds better.

[Piman314]

Everything's correct now.
Beautiful, thanks!