
How Quantum Randomness Saves Relativity - jonbaer
http://www.forbes.com/sites/chadorzel/2015/08/11/how-quantum-randomness-saves-relativity/
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zkhalique
I am still not so sure that Bell's theorem and subsequent experiments really
do rule out hidden variables.

After all, if I split a coin down the middle and took the two halves to
different sides of a continent, it wouldn't be surprising if one was found to
be heads and one found to be tails.

It would also not be surprising that if I then repainted one of the halves,
the other half would be independent of the repainting and the "entanglement"
would be broken.

The difference could be simply in that quantum particles behave differently
than having only TWO sides to them, like a coin. But the principle is the same
... that the FTL "spooky" communication never happens even between two
particles -- rather, they are correlated because were taken from the SAME
PLACE at the same time. We just don't understand how their states work,
because they're not just one dimensional states.

~~~
williamjennings
It is important to note here that Einstein was not being translated from
German properly into English. 'Spuk' has a meaning akin to spook in the sense
of a remote observer; Rather than 'spooky', which is an adjective relating to
ghosts.

There are also a lot of assumptions in the no-cloning theorem regarding the
nature of quantum operators: that they absolutely must be linear and unitary.
This is certainly not the case for research into invisibility or stealth
technology, where non-linear optics are standard.

Lastly, the epistemological nature of hidden variables is the property which
rules them out. They are referred to as extraneous variables in every other
field of science. This has caused problems of overfitting; Biologists can hold
excessive faith in Hidden Markov Models. When you dissect Bell's theorem in
terms of raw mathematics, it is technically a restatement of the triangle
inequality within probability spaces; So it just ensures that the transitive
property holds for the variables of a functional system.

~~~
rolux
> It is important to note here that Einstein was not being translated from
> German properly into English. 'Spuk' has a meaning akin to spook in the
> sense of a remote observer; Rather than 'spooky', which is an adjective
> relating to ghosts.

Einstein's "spukhaft" is very much an adjective relating to the activity of
ghosts. If you translate it as "magical", you're not losing much of its
meaning.

~~~
williamjennings
Spooks can also refer to watchers. There are CIA spooks, idiomatically.

Ghost is translated as geist.

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augustl
This is the best layman explanation of quantum entanglement and how it doesn't
allow FTL communication I've ever seen!

~~~
ucho
Really? For me it looks overly complicated and going in circles. After all it
boils down to: "You have two boxes that generate exact same sequence of random
bits, no mater how far away they are. How can you use it for communication?
There is no way."

~~~
mmusson
No the idea is pretty simple. You give entangled particles to Alice and Bob
who are a non-trivial distance away from each other.

Alice performs an operation to send a bit of information to Bob via the
entangled property. Bob still gets random results from his measurements. If
Bob saw a signal instead of randomness this would be FTL communication.

Instead Bob and Alice compare notes after the fact and Bob finds that if he
knows what Alice did, now he can find a signal in his data. This after the
fact comparison is what scuttles FTL communication. Bob doesn't know anything
until after the "sub-light" communication.

Alice could instead transmit her information using "sub-light" communication
to Bob at the same time she performs the entangled operation, but Bob still
doesn't know anything (measurements look random) until the "sub-light"
information reaches him.

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CephalopodMD
So wait, if you can refresh the probabilities of a quantum property by making
a second type of measurement (as described by the video in the article), why
wouldn't this work? Here's how you might send information between two
entangled particles via some property:

To send a 0 via property A:

    
    
      1. Clear your measurement of property in A by measuring property B
      2. Measure property A again
      3. If A is not in state 0, goto 1
      4. The other entangled particle should now read state 0 too
    

To send a 1 via property A:

    
    
      1. Clear your measurement of property in A by measuring property B
      2. Measure property A again
      3. If A is not in state 1, goto 1
      4. The other entangled particle should now read state 1 too
    

Maybe it would take a few more tries than expected occasionally, but if you
give enough time to loop say, 10 times between measurements of the second
particle, that's only a (1/1024)/2 = 1/2048 chance that the information is
wrong! That's probably reliable enough for reasonably good error detection
[1]. As long as the amount of time needed to get the first particle into a
given state is less than the amount of time needed to send a photon to the
second particle, it would seem that you could send information faster than c.

1\.
[https://www.youtube.com/watch?v=-15nx57tbfc](https://www.youtube.com/watch?v=-15nx57tbfc)

~~~
db48x
You've forgotten what a measurement is.

A measurement is any interaction between particles. In the case of entangled
photons, a measurement consists of allowing the photon to be absorbed by an
atom. You only get one such measurement; any new photon emitted by that atom
will have a spin which is no longer entangled with the spin of it's original
twin. (Actually, they were more like anti-twins; one was up when the other was
down, and visa-versa.)

Even assuming you had two larger particles (let's say atoms) which were
entangled, allowing you to make multiple measurements, nothing you change
about one of them is communicated back to the other. If you measure a property
of your atom you may also be able to determine the value of that property for
the other, but in doing so you change the atom. You flip the spins of the
electrons, or of the atom as a whole, etc. This is what "clearing your
measurement" means; you no longer have any good information about that
property. If you then remeasure that property, it's value is no longer
correlated with the twin particle.

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vladimirralev
This is probably inspired by the recent hype about messenger lectures by
Susskind
[https://www.youtube.com/watch?v=vDmMnSKEYnI&list=PLtpXn0nfqJ...](https://www.youtube.com/watch?v=vDmMnSKEYnI&list=PLtpXn0nfqJ7vVEy1WPm5TX5GTyAubX5Ad)

There is also more detailed lecture available here on this particular topic
[https://www.youtube.com/watch?v=OBPpRqxY8Uw](https://www.youtube.com/watch?v=OBPpRqxY8Uw)

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rootbear
The author, Chad Orzel, is the author of the book, "How to Teach Physics to
Your Dog", which I thoroughly enjoyed. The chapter in which he explains the
Bell Theorem I had to read twice, but I eventually got it.

He also wrote a sequel, which I haven't read yet, titled, "How to Teach
Relativity to Your Dog". The cover art is hilarious if you know what a light
cone is.

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easymovet
Bummer, so much so sub space communication. It does sound like it would be
useful for extremely safe encryption where the two parties would have an ever
changing shared key.

~~~
scentoni
And thus
[https://en.wikipedia.org/wiki/Quantum_cryptography](https://en.wikipedia.org/wiki/Quantum_cryptography)

