On 16/09/2015 17:38, Dave Platt wrote:
In article ,
Spike wrote:

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

Here's a good video-and-animations explanation of the entanglement,
how we know it exists, and why it cannot be used to transmit
classical information faster than the speed of light.

https://www.youtube.com/watch?v=ZuvK-od647c

To sum it up: it's clearly measurable, but in order to show that it's
happening at all, you need to *compare* two sets of measurements - one
taken at each end of the experiment.

You cannot "see" the effect by looking only at the measurements taken
at one end of the experiment. Due to the nature of quantum mechanics,
the measurements taken at one end look entirely random.

The measurements you take at the other end of the experiment look
equally random, at the time that you take them.

It's only when you compare the two sets of measurements, that you can
see that they're "random, but opposite". And, you can't compare them
without sending one set of measurements to the other end of the
experiment... and this can't be done faster than lightspeed.

Thanks for the video link. I wish physics had been presented like that
in my day...but it wasn't. It's interesting to note that in a couple of
places, the presenter said something like "... most scientists agree
that...", which implies that there may well be other qualities of the
particles that are not understood at this time - and which could be
exploited.

--
Spike

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