Quantum Entanglement

[jezter]

Ok, here is one for the boffins - Two particles that are 'entangled' are then seperated - if you look at one and detect its spin, the other will automatically be the other spin. This happens faster than the speed of light - so infomation about one particle inflences the result of the another faster than light. How can this be?

[R1Geezer]

well rov I did see that but the 2 slit experiment is a staple in this area, I've encountered it many times, not least of which in Brian Greene's book "The Elegant Universe".

You can't make sense of it, if you think you have then you haven't really understood it.!

[beso]

There is an innovative variation on the double slit experiment that shows the interference pattern is not the product of interactions between photons but the wave nature of single photons.

The setup is configured so that a beam passing through one of the slots strikes the target in a straight line at a location that is between the locations of the bright bars of the interference pattern resulting from the double slit.

A single photon can be tracked through the apparatus. The photon passes straight through when the second path is blocked but will be deflected if both paths are available even if it passed through the direct slot.

This actually has a potentially important application. A special beam splitter was designed that can be set to send an arbitrary proportion of the photons down one of the paths. Even when all the photons in the experiment are sent through the direct path it is possible to detect whether the second path was available.

Consequently it is possible for an object in the second path to effectively cast a "shadow" even though not one photon interacted with it. This may have applications when observing very cold systems where the interaction with a photon would raise the temperature.