Entanglement

146.101.134.65 writes:

Tim

The facts, as I understand them, are that quantum mechanics (and more importantly the entire field of quantum physics) is based upon the notion of the 'quantum' (measured by us as a unit defined by Planck's constant) that is the smallest amount to which certain material phenomena can be reduced. Thus a photon is a particular quantum of energy - you cannot have half a photon.

All else stems from there - and is represented primarily in mathematical terms.

Entanglement, for instance, may be considered a particular form of the Pauli Exclusion Principle - whereby complementary aspects of a particular characteristic (electron spin, say) are seen in two particles, co-produced, that are measured at distances too far apart for a conventional signal to have passed between them.

Now from memory (I am not going all that way down to reference Zak's post), Zak claims that Bohr was for some reason wrong, because he posited the idea that the act of merely travelling, or some such, affects the behaviour of a quantum particle. My own understanding of the Copenhagen Interpretation is simply that Bohr (and others) claimed there was no point in seeking hidden variables like that - the quantum universe was uncertain (see Heisenberg's Uncertainty Principle) in its individual actions, but incredibly easy to measure and predict in statistical terms. It was probably (as they said) the act of observation that collapsed the superposed waves of quantum probability (the two-slit experiment conducted with a single slit, and so on).

More recently, Uncertainty has held up remarkably well - there is only a certain degree of accuracy we can get with regard to the sum of measurments about any given object (quantum sized or otherwise) and the limit on that accuracy is still Planck's constant. The observer-related theory, however, has takne a bit of a bashing. Many, if not most, theorists, seem now to subscribe to a notion called Decoherence, whereby the superposition of states is inherently unstable, and as soon as it has the requirements to be superposed over a larger than quantum object (say a cat in a box) then the number of varying quantum states (of all the particles in that larger situation) is too great for the superposed states to retain their coherence. So decoherence is again a statistical prediction of the possibility of superposed states being maintained. And by this notion, they collapse very quickly when they are part of a larger equation.

The notion of entanglement itself is very interesting, but at best it might allow us ways in which to 'violate' the Relativistic notion that no signal can travel faster than light. In fact, no scientist has yet posited an idea regarding how entanglement might help us do this - simply because the nature of quantum physics is such that you cannot send such a message - it is assailed by Uncertainty at both ends.

Now Zak might wish to consider entanglement the 'cornerstone' or 'essence' of quantum physics, but for me the essence (if you count the amount of money and hours spent in the research) of quantum physics is the particle table - and finding neutrinos, Higgs Bosons and the like.

The essence, if you consider commercial applications, lies in computers and microchip technology.

The essence, if you consider theoretical studies, still lies in Uncertainty.

There is no way in which entanglement (fascinating though it is) is the centrepiece of quantum physics.

Cheer

the sunshine warrior

shanks