Jamie_L

I've been keeping tabs on this thread over in EoG. I want to respond more, but my quantum mechanics learning is a bit rusty (and probably out of date). So, I wanted to float some ideas over here where the serious scientific thinkers at II lurk.

It seems to me that the Normal's flaw in the above thread is to make the assertion that QM events are random, chaotic, without cause. It seems to me that because QM events are probabalistic, they are not completely random.

A general question: are QM events really completely causeless? Or are we just unable to detect the cause? Again, it seems like if there is a probabilistic nature to these things, then there is a deterministic element. If it were completely random, there's be no probability.

If others more educated than I could enlighten me, I'd appreciate it. If any of you have specific thoughts on the other thread, I'd be interested to hear those as well.

Jamie

Undercurrent

Yes, QM events are considered to be completely causeless. Or at least, if there is a cause, we can never, even in principle, detect it, therefore it might as well not exist.

I'm reading this as "the fact that we can compute the probability distribution for an event (i.e. 10% chance happening this way, 30% chance happening another, &c.) negates somehow the randomness of the result. If it were truely irrevokably random, we wouldn't be able to compute even a probability distribution."

If I read that correctly, I consider that a non-starter. The "most" random a coin toss can get is a uniform distribution with 0.5 for heads and 0.5 for tails, which is a perfectly valid distribution. There is no conceivable sequence of events that is so random we can't even produce a PDF, so the fact that quantum events obey probability laws says nothing about the determinism of the results..

Lobstrosity

According to our current understanding, QM events are really causeless in a classical sense. The reason for this is because QM tells us that no two non-commuting observables (such as position and momentum) can simultaneously exist with absolute precision. Einstein thought this restriction of knowledge derived from our inability to measure such observables and considered the probabilistic nature of QM to be a mere formalism meant to aid in calculation. He thought that there really were "hidden variables" we simply had yet to detect. This view was known as local realism. For a long time it was thought that there was no way to empirically distinguish local realism from QM, but then Bell came along and demonstrated that local realism implies certain inequalities that are at odds with the predictions of QM. In the early 80s, Aspect conducted experiments which violated Bell's inequalities by, I believe, nine standard devations. The results were perfectly consistent with expectations of QM, however. So what does this all mean? Well it demonstrates that, as far as we know, there is no local realism, and without local realism, it's sort of hard to assert classical causality. This is not a problem however, for classical causality is nothing more than an idealism--an observation of a process that seems simpler than it is to the naive, macroscopic eye. It's no more necessary for an orderly universe than "perfect, supernatural free will" is for human consciousness.

PJPSYCO

Probability distrubions never imply randomness. We actually don't even need them. Heisenburg actually independantely derived the schrodiger equation using linear algebra. It's a lot harder, however. So, we tend not to repeat it.

Lobstrosity

You seem to be a bit confused as to the meaning of the term "random." All random means is that for any one specific independent measurement, no prediction can be made as to what outcome will result from among the set of potential outcomes. Processes governed by probability distributions can still be considered truly random because they satisfy the above definition. The true "deterministic" physics arises as an average of the random nature of the components. This is just like statistics used in gambling. For any given blackjack hand, for example, it is impossible to predict with any reliability what will happen (unless you are dealt 21). Anything could feasibly happen on any hand. All you can do is tabulate odds and attempt to make use of those odds by playing many, many hands. Over time, the random nature is smoothed out by averaging to reveal the underlying probability distribution governing the cards.

Jamie_L

Thanks for the various clarifications.

I'm still not sure exactly how to respond people saying things like in the OP of the original thread, but I'm closer than I was before.

Jamie

ex-xian

I've contributed to the above referenced thread to the point of frustration. That said, I think the problem is that the english language is extremely inferior to mathematics when it comes to describing QM.

As has been said ad nausuem, QM events are based on probability. So, in a sense, it's correct to call them random. If I choose to read a random passage from a book, there's no way to know which passage I'll read, but you can be sure it will be from the book in my hand. So in that sense, QM is random, but not totally without guidelines.

yguy

There are no events based on probability, which is really a fifty dollar word for ignorance.

strubenuff

If order arises out of statistical averages of random events, does the deterministic viewpoint still hold weight?

ex-xian

I'm sorry, but both of your assertions are just wrong. Probability is not "just a fifty dollar word for ignorance." If I flip a coin, I know that the probability that I'll get a heads is .5; the probablity that I'll get tails is .5. The probability that I'll get something not heads or tails is 0. I may not know exactly how things will turn out, but I do know it will be heads or tails. I'm not totally ignorant about what will happen. The same applies to QM.

As for your first proposition, anyone who has read/studied QM knows that it's based on probability. I'm curious as to why you would say something that is totally without merit. In other words, where did you get your information?