Satellite sets distance record for weird "spooky action" quantum communication

Less clear after the explanations.

Great. Of all the people on Big Bang I never thought I’d be Penny…:disappointed_relieved:


Sorry. Here are some good videos that give layman explanations. If you want to go into more depth on the underlying physics, I can point you to some good pop science books written by physicists.

One small note on this video is that there’s some debate in physics as to whether quantum randomness is truly random or dictated by some underlying order. However, it’s random as far as we can tell and even if it isn’t, it may still be indeterminable due to a branch of mathematical physics called quantum chaos theory.

Also, one really cool thing about quantum encryption is that, even if an attacker got a hold of the classical signal and decrypted the quantum signal with it (the quantum equivalent of a man-in-the-middle attack), the people sending the encrypted messages back and forth would know which messages had been decrypted because the act of decryption alters the message. There’s a highly speculative hypothesis that this could be overcome with something called weak measurement, but no consensus on whether enough information could be so obtained without collapsing the quantum signal. I personally suspect that any information gained by weak measurement is mathematically required to have a corresponding corruption on the signal that could be detected, but we barely know how to do weak measurement in controlled lab experiments, let alone as an attack on an quantum encrypted signal.

The best known algorithm for quantum error correction was discovered shortly after Shor’s algorithm. There’s also some debate as to whether interference from an attacker could be made indistinguishable for environmental noise, and overcoming that noise is what originally prompted the search for a method of quantum error correction.

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How many bits per spooky are they sending?

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“the physicists are pulling a fast one with the definitions of ‘information’ and ‘communication’”, but it is very wrong to say that scientists do not understand this

As a rule of thumb the only people worse than physicists at naming things are historians. They can’t help it since the biologists stole all of the Greek and Latin.

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Oh, come on. The Defenestration of Prague? The Diet of Worms? The War of Jenkins’ Ear? Those are great names.


The Diet of Worms

See, this is just bitterness from elementary school.


That is what Einstein (and Podolsky and Rosen) were proposing - they thought the solution to the quantum weirdness is that it’s all just our ignorance making things look fuzzy, but there’s another layer under the hood where things make more deterministic sense again. What is fantastic about Bell’s work is that it can distinguish these things, because regardless of the details of a putative deterministic layer, determinism forces some properties.

In the quantum story, although this phenomenon looks like “action at a distance,” nothing actually moves across a distance. And again it’s hard to make this not seem like a shell game, you must drink deeply of mathematical cups before it can seem intuitive - because it’s not two states, A and B, it’s one state, “A x B”, where x is a tensor product. That is probably not satisfying but suffice to say, it’s very, very different than if x were a cartesian product. There’s no A and B states in different places - the observations are in different places, but nothing goes from one to the other.

If you wanted to write a deterministic story, where there is a very simple starting state - the two photons were always spin up and down from the moment of creation, and then they separated, and so that’s what you are observing - you violate observation. That would be a really lovely story, but observation wins. The way you distinguish these stories is by complicating the setup - you need two measurements of the spin, along different axes, and there is a maximum correlation that can be achieved classically, which quantum mechanics and observations both violate. Sorry boring story.

There’s another way to save the deterministic / realistic story, but that is to make things nonlocal. Then your operators do need to have spooky action at a distance. Only the deeply perverse prefer this story. It is so, so nice that in quantum mechanics, everything you want to know about observations at a point x can be determined by observations in a neighborhood of that point. If this were not the case, you would basically have to kiss the scientific method goodbye.

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I thought information WASN’T limited to the speed of light.

I knew this, but at the same time I surmise at some point one could control one end of it, such as the spin. If you can control the spin so there is two states, you have the ability to transmit binary to the other entangled particle.

Disclaimer - I am not a physicist and have an above average layman’s knowledge. I realize it is currently impossible, but it seems like one of those things that could be possible as our knowledge expands. I think it is more likely that us ever having FTL travel or anti-gravity. But yes, it could just all be science fiction. My optimistic hope was that if we could at least communicate via vast distances to the stars, we could at least keep connected that way, vs the more probable outcome of man just splitting off into other systems with multi-generational ships and more or less leaving the rest of man kind forever.

Information is very limited to the speed of light, and it’s fundamental physics stopping us from using this to communicate, not just technical implementation. There’s no way for it to be more likely than FTL - it is FTL. So the same objections apply. In particular, because there is no universal notion of “now” or “simultaneous,” any funny business you do propose to do to the local causality we have in physics is time machines levels of sci fi. Not a lot of room for bargaining.

So the optimism is best spent imagining ways for casually disconnected pockets of humanity to be pretty great. It could be pretty great!

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Unfortunately not. The fact that your cat turns out to be the tabby one means that my cat must have been the black one, but aside from that determination, you wouldn’t expect anything you can control about your cat will change anything about my cat. Entangled spins work the same way.

So far information is always limited to the speed of light in vacuum, and with the geometry of spacetime anything else means moving outside normal time. I can’t tell you not to be optimistic about finding some exception to that, if you like, but I can say you shouldn’t expect it from ‘ordinary’ physics like this.


The War of Trump’s Tweet?

I love that song. Great sax.

Actually, it would be better to call it the speed limit of information than the speed of light. It is, quite simply put, the fastest speed at which cause and effect can move through space. That’s the keystone of Special Relativity.

Humanity won’t settle the stars, machines will, and possibly uploaded humans in machines with them. Since they’ll be able to alter the clockspeed of their own perception, they may think much faster and thus even communications lag rates that don’t bother use could seem interminably long to them. Or they could slow down to where an interstellar phone call is just as fast to them as Bob in Chicago ringing up Alice in New York. I expect they’ll do both, multi-threading their consciousnesses to interact over a wide spectrum of distances.

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