
Quantum Theory Experiment Said to Prove ‘Spooky’ Interactions - finnh
http://www.nytimes.com/2015/10/22/science/quantum-theory-experiment-said-to-prove-spooky-interactions.html
======
MPSimmons
Can someone convince me that there aren't hidden variables? Because my puny
monkey brain hears "a variable can be one of two states, but in the beginning,
it's in a super-position of them. When measured, the state is determined." and
it's a relative easy thing to get. But....

"There are two particles entangled together such that when one becomes up or
down, the other becomes the opposite, and measuring either will determine
both, instantaneously, regardless of distance" is a much harder thing to
swallow.

Occam's Razor says that there are hidden variables that are pre-selecting
state, and we just don't know about them until we measure. ESPECIALLY when one
of the requirements for the system is that we can only measure, not influence
the outcome of the measurement.

So please, someone who knows more than I do - why can't there be hidden
variables being set at entanglement that pre-determine the measurement
outcome?

~~~
fizx
So the real problem isn't that "when one is up, then the other will magically
be up too." That could be accomplished with local hidden variables (e.g.
shared seeds on a PRNG).

The real problem is that when you measure A in the "up" direction, and then B
in the "10 degrees east of up" direction, then B seems to know that you
measured A in the "up" direction.

That is to say: B's probability distribution as a function of the direction
its being measured is dependent on the direction that A is measured. There's
no way to construct an "A-independent" probability distribution of B's results
for arbitrary directions. The probabilities won't sum to 1 and still match
experimental results.

It's unfortunate that "A up" therefore "B up" is a degenerate case of this
reality where classicality actually works, because it leads to confusion.

Also, follow the links others have provided for a more formal explanation :)

~~~
tomp
But doesn't this then violate "no information faster than speed of light"?
I.e. You measure A at angle _a_ , I measure B (entangled with A) at angle _b_
, and the resulting distribution gives me some information about your angle
_a_. If I repeat this with enough particles, I can be reasonably certain about
what _a_ is.

~~~
fizx
The proof eludes me at the moment, but people have thought of this.

------
finnh
I posted this b/c I was hoping someone would dive into these quotes:

 _The Delft researchers were able to entangle two electrons separated by a
distance of 1.3 kilometers, slightly less than a mile, and then share
information between them._

 _..._

 _Researchers like Dr. Hanson envision a quantum communications network formed
from a chain of entangled particles girdling the entire globe. Such a network
would make it possible to securely share encryption keys, and know of
eavesdropping attempts with absolute certainty._

This implies that entanglement allows faster-than-light communication
(transmitting arbitrary information across the entangled link). I thought that
was a no-no, and that entanglement still didn't allow FTL communication
despite FTL-like properties.

Can somebody help out here?

~~~
fizx
It's the nyt, so they are at best imprecise and at worst wrong. Entanglement
can be thought of as a resource that allows you to do unexpected things (win
the CHSH game), but sharing information isn't one of them.

A better discussion can be had at
[http://www.scottaaronson.com/blog/?cat=33](http://www.scottaaronson.com/blog/?cat=33)

~~~
weinzierl
The linked article from Scott Aaronson is quite accessible and very worth
reading. My favorite quote is:

    
    
       Perhaps the best way to explain local realism is that it’s the thing 
       you believe in, if you believe all the physicists babbling about 
       “quantum entanglement” just missed something completely obvious.
     

What I still struggle to understand is the realism part. The NYT article seems
to imply that, when all loopholes are closed, we will have the final prove to
live in a non-local world. Realism isn't mentioned.

    
    
       The finding is another blow to one of the bedrock principles of 
       standard physics known as “locality,” which states that an object is 
       directly influenced only by its immediate surroundings. 
    
    

I always thought that local realism meant one of the following:

    
    
      - no realism 
      - no locality 
      - neither realism nor locality
    

The Wikipedia article _Principle of locality_
([https://en.wikipedia.org/wiki/Principle_of_locality#Local_re...](https://en.wikipedia.org/wiki/Principle_of_locality#Local_realism))
says

    
    
       Any theory, such as quantum mechanics, that violates Bell's 
       inequalities must abandon either locality or realism; 
    

Can the result of Bell's experiment be explained when we just abandon realism
but not locality?

~~~
semi-extrinsic
Answer to your last question: yes. However, the results of these (and other)
experiments are not consistent with abandoning realism.

There is also a third option that almost no-one mentions, and that's
superdeterminism; i.e. that free will doesn't exist.

------
dang
Also the experimenters' page on this:
[https://news.ycombinator.com/item?id=10428397](https://news.ycombinator.com/item?id=10428397).

------
imglorp
> particles do not take on formal properties until they are measured or
> observed in some way

This sounds like lazy evaluation.

~~~
deepdeep
Procedural generation with lazy evaluation.

~~~
imglorp
Ah yes, procedural generation ala Wolfram's "new kind of science".

------
biswaroop
I wish they used a better title. Entanglement is not a kind of interaction,
and I wonder what a "quantum theory experiment" is.

~~~
greeneggs
It isn't just the title, the whole article is poorly written. It gives the
impression that faster-than-light communication is possible.

From the first sentence:

"[Scientists] conducted an experiment they say proves one of the most
fundamental claims of quantum theory — that objects separated by great
distance _can instantaneously affect_ each other’s behavior."

Emphasis mine. This is totally wrong.

The second sentence:

"The finding is another blow to one of the bedrock principles of standard
physics known as “locality,” which states that an object is directly
influenced only by its immediate surroundings."

Again, this is wrong. Quantum physics is entirely consistent with locality. It
contradicts "local hidden variable models." Despite the similar name, this is
different from locality. (Local hidden variable models are local, classical
models.)

~~~
tbabb
To add to that, Bell's theorem says that _either_ locality _or_ hidden
variables may be true, but not both. We could construct a formulation of
quantum mechanics that includes hidden variables, but must account for the
state of the universe at arbitrarily distant locations.

