Thursday, June 2, 2011


In the context of quantum mechanicssuperdeterminism is a term that has been used to describe a hypothetical class of theories which evadeBell's theorem by virtue of being completely deterministic. Bell's theorem depends on the assumption of counterfactual definiteness, which technically does not apply to deterministic theories. It is conceivable, but arguably unlikely, that someone could exploit this loophole to construct alocal hidden variable theory that reproduces the predictions of quantum mechanics.
Bell's theorem assumes that the types of measurements performed at each detector can be chosen independently of each other and of the hidden variable being measured. In order for the argument for Bell's inequality to follow, it is necessary to be able to speak meaningfully of what the result of the experiment would have been, had different choices been made. This assumption is called counterfactual definiteness. But in a deterministic theory, the measurements the experimenters choose at each detector are predetermined by the laws of physics. It can therefore be argued that it is erroneous to speak of what would have happened had different measurements been chosen; no other measurement choices were physically possible. Since the chosen measurements can be determined in advance, the results at one detector can be affected by the type of measurement done at the other without any need for information to travel faster than the speed of light.
John Bell discussed superdeterminism in a BBC interview:[1]
There is a way to escape the inference of superluminal speeds and spooky action at a distance. But it involves absolute determinism in the universe, the complete absence of free will. Suppose the world is super-deterministic, with not just inanimate nature running on behind-the-scenes clockwork, but with our behavior, including our belief that we are free to choose to do one experiment rather than another, absolutely predetermined, including the "decision" by the experimenter to carry out one set of measurements rather than another, the difficulty disappears. There is no need for a faster than light signal to tell particle A what measurement has been carried out on particle B, because the universe, including particle A, already "knows" what that measurement, and its outcome, will be.
Although he acknowledged the loophole, he also argued that it was implausible. Even if the measurements performed are chosen by deterministic random number generators, the choices can be assumed to be "effectively free for the purpose at hand," because the machine's choice is altered by a large number of very small effects. It is unlikely for the hidden variable to be sensitive to all of the same small influences that the random number generator was.[2]

See also


  1. ^ BBC Radio interview with Paul Davies, 1985
  2. ^ J. S. Bell, Free variables and local causality, Epistemological Letters, Feb. 1977. Reprinted as Chapter 12 of J. S. Bell, Speakable and Unspeakable in Quantum Mechanics(Cambridge University Press 1987)

External links


Ulla said...

This is interesting from the aspect of free will. Also the degrees of freedoms are important. Usually we say the complexity is growing, but at the same time we go towards higher entropy (=lower energy level) for both ordinary and living matter. Matter is only temporarily living.
What makes this living capacity?

If we assume the degrees of freedoms are not infinite, but finite (no hierarchy or topology) we get also a finite amount of choises (determinism). This is the same as the quantizition of matter on-shell, so all matter is deterministic. We have not every choise left for this world. In quantum world we still have all the choises.

The question is then what directs the deterministic matter, is it a) inherent in the matter itself, or b) from the quantum world?

a) then we have finite amount of choises andIN THE END no free will. But free will is a living charachter, and we may not use every choise in our lifetime, though it sometimes SEEMS as if we would. This capacity of making choises is vanishing with time.

b) free will is coming from the infinite quantum world and is endless. Note that this alternative is free from time and distance. = Dimensionless? It is not realized maybe in a lifetime, but needs many lives? :)

Free will may be linked to consciousness in the vacuum field?

Ulla said...

I forgot!
This may be seen as an ionization energy change with iniert matter as endpoint. See decaying chains.
The energy is oscillating between the different energylevels. This is a charachter of life, (and free will?).

Steven Colyer said...

Ulla, as you get to know me better you will see I am skeptical that free will even exists, and that all talk of consciousness should not be taken seriously until the later part of this century, if not the 22nd.

Consciousness is a macroscopic property, most likely, and quantum mechanics certainly doesn't explain it, nor free will, although that was a common "thought" in the 20's when Heisenberg introduced Uncertainty. By "thought" I mean by non-physicists who do not understand the theory.

Ulla said...

In which way would consciousness be macroscopic?

Steven Colyer said...

In this way: I am macroscopic and so is my consciousness.

Ulla said...

A bad answer. There are plenty of microscopic parts in you. Not the least your receptors.

Steven Colyer said...

Not an answer so much as an opinion. So it's not really bad, so much as unsatisfying.

My basic attitude is this: I only have this thing called "consciousness" for a very short time. Or perhaps if the Hindus and Buddhists are right, forever. In any event, when I die, I'll worry about it then.

Spending the rest of my life devoting even one second to the issue seems to me, personally, a waste of my time. As a biologist, if YOU wish to pursue it, then good for you, go for it. I think the answer WILL come from Biology, not from Physics, and especially not from a Mathematician such as Roger Penrose.

And in any event, I don't think we're even close to making a significant advance in Consciousness Science for 50 years, simply because we do not have enough information now. I don't expect to be around in 50 years, so good luck to you and yours in following your dream.