Sunday, 8 May 2011

What's the fuss about EPR?

What is really bugging a part of the physicists about the whole EPR-Bohr discussion? The main argument of E.P.R. was:

If, without in anyway disturbing a system, we can predict with certainty (...) the value of a physical quantity, then there exists an element of physical reality that corresponds to this physical quantity. (1)

I think the issue is in fact that Bohr and his crew (Copenhagen) have eliminated a very basic philosophy in physics: the existence of causality for all the processes in nature, that every event in nature can in principle be described as a reaction on another event.

He postulated a principle randomness in nature. So he based his QM on a number of stochastic formulas that described the quantum processes, and what is worse, postulated that these formulas where a complete description of the process, leaving out any possibility of introducing subquantum theories. It's like creating a formula for the behavior of a pile of sand being dropped from a truck and claiming there is no physics beyond to describe this process.

Because of the realm of QM being the atomic scale and beyond it is very difficult to invalidate such a position, for one needs measurements on individual particles to do that. The measuring devices themselves are gigantic compared to the particle to be measured, and mostly made of the same 'stuff' (electrons, protons, photons etc), but should not disturb the measurement.

Only the last decennia scientists are on the edge of doing this: atoms can be photographed and handled individually (2), and even individual electrons can be locked and stored for a long time (3). Atto seconds lasers are starting to reveal processes at atomic scale (4). Things that Bohr held for impossible.

When one of the premises of relativity is added, that any causal action cannot be transmitted beyond light speed, the experiments with entangled particles as discussed in this blog can play a role. That is, if these can be performed without loopholes, and if Bell is correct, these experiments prove that there are correlations between particles that cannot be explained by causality while keeping up the light speed constraint.

Even if that proves to be the case, I still think one should not give up searching for a causal explanation for these processes. It might well be nature hints us about so far unrevealed features, like (only speculating here) the existence of extra dimensions in space-time, or particles that can exceed light speed limits.

Just assuming we're on the edge of what can be revealed in QM (concerning the wave function and the Heisenberg uncertainty principle), without any proof for that, is for me a very strange position, but upheld by many physicist today.

  1. Can quantum-mechanical description of physical reality be considered complete?
  2. IBM STM image gallery,
  3. Wineland and Dehmelt 1973
  4. ATTOSECOND PHYSICS: Ultrafast-laser methods reveal electrons tunneling in real time,