On 15/09/2015 15:32, rickman wrote:
On 9/15/2015 5:10 AM, Spike wrote:
On 14/09/2015 22:32, Dave Platt wrote:
In article ,

One of the weird things about entanglement (and what Einstein called
"spooky action at a distance") is the following paradox:

- Measurements have shown that interacting with one of a pair of
entangled particles, has a definite effect on the state of the
other member of the pair. This effect occurs regardless of
distance, and isn't affected by lightspeed delay.

If that is so, then the possibility of a communication channel must
exist, the transmission mechanism of which is being used by the
particles .

It doesn't "must" exist.

The possibility of a comms system must exist using this effect. That the
engineers haven't found a way to exploit it is a different issue.

Measuring the state of either particle
determines the state of both. So how do you gain any information at the
receiving end by this? That's the problem. There is no way to transfer
info usefully.

One needs to lard in some other factor. Imagine Hertz asking what use
his waves could be, all he could do with them is turn them on and off.

The reasons are (as I said, weird) that when you interact with
particle A, the effect on particle B is one which you can't actually
detect independently (that is, by measuring particle B alone). You
have to compare the measurement on Particle B, with information that
you can only get from the measurement that was taken Particle A, to
confirm that the effect actually occurred...

With a million Particles A in a device called a 'transmitter'' and in a
distant galaxy, a million Particles B in a device called a 'receiver', a
statistical analysis would ensure to a high level of confidence that a
change had occurred. It wouldn't be difficult to arrange this to send
data. But this is mere technology, that exploits the properties inherent
in the entangled particles.

What change exactly? How do you get *any* information from the million
particles?

The use of the words 'change' follows from a quote above, namely
"...Measurements have shown that interacting with one of a pair of
entangled particles, has a definite effect on the state of the other
member of the pair". So, something has changed, and it is measurable.
Perhaps the PP could expand on this.

A good question to ask here is: what is this change that takes place? It
is clearly measurable.

Unfortunately, all of the tests which have been done on entangled
systems keep showing that entanglement is real, but (like
"superluminal" phase velocity) can't be used to send information
faster than C.

If the effect acts instantaneously over large distances, why can it not
be exploited?

What "effect" exactly?

You'll need to ask that of the PP, as he used the word in his
explanation. I was thinking of a comms system that uses the effect
(whatever it is) to transfer information.

When the partner is observed, an entangled
particle resolves to a knowable state so that when you look at it, it is
in one state or the other. How do you know which state it will be in
until you observe it which causes the same thing, resolution to a
knowable state?

Perhaps it might help if we knew how many states were available.

--
Spike

"Nearly all men can stand adversity, but if you want to test a man's
character, give him power" - Abraham Lincoln