

Quantum ‘spookiness’ passes toughest test yet - jcr
http://www.nature.com/news/quantum-spookiness-passes-toughest-test-yet-1.18255?WT.mc_id=SFB_NNEWS_1508_RHBox

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saurik
FQXi (39 comments):

[https://news.ycombinator.com/item?id=10130203](https://news.ycombinator.com/item?id=10130203)

Nature (1 comment) (same link as this one):

[https://news.ycombinator.com/item?id=10135260](https://news.ycombinator.com/item?id=10135260)

Scientific American (0 comments):

[https://news.ycombinator.com/item?id=10139598](https://news.ycombinator.com/item?id=10139598)

Ars Technica (0 comments):

[https://news.ycombinator.com/item?id=10141658](https://news.ycombinator.com/item?id=10141658)

Forbes (0 comments):

[https://news.ycombinator.com/item?id=10129946](https://news.ycombinator.com/item?id=10129946)

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jcr
Thanks saurik, I somehow missed the fqxi.org article submission when searching
before (re)submitting the nature.com article.

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fryguy
My understanding is that entanglement doesn't actually allow for transfer any
information faster than the speed of light but is more like having two coins
sealed in a box and given to two parties, that "God" always keeps the same way
up until they're opened. You can manipulate them by flipping the coins over,
but you don't know what it was originally. You can open your box and see that
your coin is heads, and send a conventional message to the other person that
says "if your coin is heads, then attack at dawn", but you don't know what the
coin is until you open it, so are still reliant on sending the message over
means that obey the speed of light in order to transfer the information.

Is that an accurate (given that it's an analogy) description of how
entanglement works, or does this work disprove that idea and is what was
mentioned as Einstein's idea?

~~~
dools
What you've quoted there is a good _analogy_ of an entangled state. In reality
there are several differences, and the biggest piece of misinformation is that
measurement of one system somehow "collapses a wave function" in the other
system which isn't the case.

The phenomenon of entanglement is that measurements of certain things are
either perfectly correlated or anti-correlated. Eg. Measurement of spin along
some axis on electron A will always be -1 when measurement of spin along the
same axis of electron B is +1.

The similarity to 2 coins is: if i have a 1972 coin and a 1973 coin, and give
one to you randomly, then you go a million light years away and look at your
coin and find you have the 1973 coin, you will know I have the 1972 coin.
Although this is only a simplified analogy of entanglement the important point
is that the state was prepared before we separated, and no information has
been communicated. When you try to understand this in terms of classical
physics, it's weird. But it's not classical physics. I wrote more about it
here:

[https://news.ycombinator.com/item?id=10133674](https://news.ycombinator.com/item?id=10133674)

Also check out the leonard susskind messenger lectures for a quick overview
and his stanford continuing ed lectures on youtube for the long version :)

~~~
coldtea
> _The similarity to 2 coins is: if i have a 1972 coin and a 1973 coin, and
> give one to you randomly, then you go a million light years away and look at
> your coin and find you have the 1973 coin, you will know I have the 1972
> coin. Although this is only a simplified analogy of entanglement the
> important point is that the state was prepared before we separated, and no
> information has been communicated. When you try to understand this in terms
> of classical physics, it 's weird._

If that was the case (the coin analogy) it would be perfectly understandable
by classical physics.

In fact it wouldn't even need physics to understand it, just common sense.

If that was the case there wouldn't be any EPR paradox etc.

The coin analogy is very misleading in this way -- and doesn't convey the
problems physicists have had with explaining this phenomenon.

~~~
dools
No what I'm describing is a way of understanding why entangled states aren't
spooky. It's also a direct lift from Leonard Susskind so it's not even me
doing it. The point is that the state is prepared in some way X, and the state
is such that by knowing something about one thing, you also know something
about the other thing.

The actual mechanism by which this occurs is only "spooky" if you try and
interpret it classically. But if you just accept that "hey, it's quantum
mechanics" then it's very easy to understand. Same as I can't visualise a
5-sphere but I have mathematical tools to work with one.

I can't "picture" the mechanism that allows measurements of quantum states to
be anti-correlated, but I can use maths to express that behaviour and make
predictions about how the universe behaves.

~~~
coldtea
> _No what I 'm describing is a way of understanding why entangled states
> aren't spooky._

I think that if the explanation doesn't also convey the spookiness, it's not
right.

> _The actual mechanism by which this occurs is only "spooky" if you try and
> interpret it classically. But if you just accept that "hey, it's quantum
> mechanics" then it's very easy to understand._

That's just pushing the spookiness under the carpet.

~~~
dools
The original phrase is spooky action at a distance, which has been summarised
as spookiness. Actual spookiness notwithstanding, the most important thing
really is that there is no action at a distance.

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crishoj
Can anyone explain (in layman-like terms) how one goes about transporting a
single photon over a distance of 1.3km? I really like to have a general idea
of the technology involved.

"The researchers started with two unentangled electrons sitting in diamond
crystals held in different labs on the Delft campus, 1.3 kilometres apart.
Each electron was individually entangled with a photon, and both of those
photons were then zipped to a third location."

~~~
gus_massa
They use a optic fiber. This version has mare technical details, but is still
understandable: [http://arstechnica.com/science/2015/08/experiment-
confirms-t...](http://arstechnica.com/science/2015/08/experiment-confirms-
that-quantum-mechanics-scoffs-at-our-local-reality/) (HN:
[https://news.ycombinator.com/item?id=10141658](https://news.ycombinator.com/item?id=10141658)
(4 points, 12 hours ago, 1 comment))

> _To get around this, the researchers started with the diamonds over a
> kilometer apart in two different labs at the Delft University of Technology.
> They entangled each electron spin with a photon, then sent the photons over
> fiber optic cable to a third lab somewhere in between. There, the photons
> were entangled, which in turn caused the electrons in the diamonds to be
> entangled as well._

~~~
crishoj
Another enlightening point is that there _is_ a significant loss in the optic
fibers:

> The whole process was horribly inefficient, with a success rate of 6.4 ×
> 10−9, mostly because photons kept getting lost in the fiber optic cables.
> But, over the course of nine days, the setup managed to successfully
> entangle the nitrogen vacancies 245 times.

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skarap
Every time I read something on quantum theory I can't help but notice how
close to notion of magic it feels like. And I've studied physics in college.

Some time ago I thought how strange these all would look to someone who had no
knowledge in physics at all. But then I got it: two particles in different
galaxies being entangled is not much different from calling someone on the
other side of the globe using a cellphone if you don't have prior
knowledge/beliefes about either.

~~~
stefantalpalaru
I see it as a failure of the model. When the explanation is irrational, does a
scientist stop to wonder at the irrationality of the universe instead of
trying to come up with better explanations?

~~~
adekok
Thousands of people have been trying for 50 years. Every model they've tried
has turned out to be wrong.

It's easy to say "come up with better explanations". It's not very helpful,
though.

~~~
stefantalpalaru
It's easy to dismiss criticism by complaining that it doesn't propose
solutions, but the two are distinct and unrelated activities.

The purpose of criticism is not to be directly helpful by proposing better
solutions, but to help eliminate the wrong ones.

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rhelsing
Sometimes I feel like the writers from Lost are in control of our universe,
improvising plot twists as we get seemingly closer to understanding how things
work.

