### Question

Einstin believed in determinism but the quantum theory disbanded this idea. Do you believe that determinism will be revitalized by the unified field theory? Why or why not?

Asked by:
Craig Croy

### Answer

It is not really a matter of belief -- this seems to be how nature behaves, independent of what theory we devise to explain or predict nature.

Einstein in fact, published a famous paper, now known among physicists as the EPR (Einstein-Podolsky-Rosen) paper. (http://en.wikipedia.org/wiki/EPR_paradox)In the paper, he tries to refute the probabilistic nature from the standpoint of "locality", which means all interactions must occur locally, or be transmitted at the limiting speed of light (which also counts as local, when you take into account the messenger particle). He argues that, since the predictions of quantum mechanics are not in line with locality, it can not be true.

The story does not quite end there. There is Bell's Theorem which you can read about here: http://en.wikipedia.org/wiki/Bell's_theorem

Employing what we call "entangled states", Bell argues that, it is not possible to reproduce the predictions of quantum mechanics with any physical model that is deterministic. (Here, being deterministic involves hidden variables; variables that have a definite value (hence deterministic) but can not be measured before the "experiment".)

Since you can not reproduce the results of quantum mechanics with a deterministic model, this means that any deterministic model we may come up with, will say something different than what quantum mechanics says, the argument boils down to the following:

1. Quantum mechanics is correct, the universe is probabilistic, and no deterministic model may describe the universe correctly.

2. Quantum mechanics is incorrect. The universe is in fact deterministic, so we need to find the correct deterministic theory to describe it. (i.e, "God does not play dice with the universe.")

So, what do you do? Experiment of course. Experiments have been performed, and quantum mechanics has passed all tests with flying colors...

So, -unless our experiments are really broken-, no new theory is going to get us our beloved determinism back...

Toss the dice...

Answered by:
Yasar Safkan, Ph.D., Istanbul, Turkey