problem with randomness and uncertainty

ravendusk

I was reading the book "the grand design" by stephen hawking and I reached the part about randomness and heisenberg's uncertainty that I didn't understand. The book seems to suggest that "Probabilities in quantum theories reflect a fundamental randomness in nature". The thing seems right to me is that we have to assume events happen randomly since we lack the ability to find the exact location of a particle(for example), not that nature does not dictate the future state of the universe, but we(humans) can't predict the future with certainty(at least for now).
Another question is that what happened when they repeated the buckyball experiment, throwing one ball at a time? and what happened when they threw photons one at a time?

thank you for your attention

arkajad

This is typical of a physicist. When a physicist can not understand some regularity, he declares it to being a fundamental law of Nature and exploits it to the max. It has proven in the past not to be such a bad idea. Think about the relativity theory and its phenomenal successes. What is bad about it is that it prevents many people from thinking seriously about something even deeper. That's human psychology at work. It may then take a whole millenium or more to get back on some alternative and fruitful path.

Demystifier

See Sec. 4 of
http://xxx.lanl.gov/pdf/quant-ph/0609163v2

arkajad

The last sentence would suffice:

"But the fact is that nobody knows with certainty whether the fundamental laws of nature are probabilistic or deterministic."

I would add to the above: or else, none of the two (probabilistic vs deterministic) applies.

unusualname

There's clearly at least one deterministic law in nature - Schrodinger Evolution. However what is evolving is a distribution of probabilistic or fundamentally random states.

This to me seems quite a simple interpretation of nature, and avoids the runaway complexity you get trying to construct purely deterministic models, which are struggling to be consistent with latest experimental results anyway.

And as well as its simplicity it naturally allows free-will into nature, which is obviously comforting.

I can't think what possible causal law there could be at the level of a single quanta anyway - what's it supposed to do? You almost need to impose fundamental randomness at this level to actually get anything to happen!

arkajad

Speaking about determinism and randomness - it presumes a causal structure. But how did a causal structure came into being? From what? From some kind of a primitive graph's structure? From arrows that organize themselves into a causal structure? What "organize themselves" would mean in such a context?

unusualname

I'm not sure we can know that, we can only observe the universe and see that events can be predicted with great accuracy according to some deterministic rule. Why that rule might apply may be a question beyond our comprehension. We're still struggling with the basics.

arkajad

We can do more than that. We can think, we can have intuitions, we can B]then[B} check whether our intuitions are helping us to get more intuitions that may have practical applications and make us happy this way.

Elephants, with their small but acute eyes also observe. But elephant's science seems to be somewhat behind human's one.

Philosophers (and also some physicists) are curious about the concept of causality. Curiosity killed the cat, but without simple and sincere curiosity what would our science look like?

ravendusk

if throwing the particles one at a time will give us similar results as the macro scale experiment(meaning they act like particles not like waves.), I would have a much better explanation. the book says that doing the buckyball experiment with two holes gives a weird result and it's like the particles that were acting normal when one hole was in the wall now know that there is another hole in the wall and they move differently. then it tries to imply that these particles take all the possible routes from the source to destination and that is why the particle knows the other hole is there(resulting in theories like parallel universes)

but this is my explanation(ok this might sound stupid): making the new hole in the wall results in a stream of buckyballs that pass through the hole. which means a stream of balls that don't reflect from that part of the wall which can mean many other balls in different directions now don't hit this stream of balls and this can mean with all the balls hitting and not hitting eachother its not that weird if the balls land differently on the other side of the wall.

this explanation may not be useful since we don't have the power to calculate the movement of all these particles but at least it doesn't rely on randomness. I know that feynman's probabilistic theory can be experimented and should be used but if my explanation is correct then it would mean that the randomness is not really random but to our limited perception it is similar to random.

please tell me if any experiment that has been done denies my explanation.

FlexGunship

Remember: there is no fundamental reason why humans should be able to grasp the universe implicitly. We are beasts of analogy, and sometimes we aren't offered an analog.

Maui

There was a 37% probability that he would say that

I imagine this could become a very successful slogan on Vegas Boulevard.

$$$ "Probabilities in quantum theories reflect a fundamental randomness in nature" $$$



Events do not really 'happen', they are. Ontologically, if modern physics has any kind of ontology at all, causality can not be a fundamental feature of the universe together with the dynamical spacetime story(yes that seems to strip the universe of pretty much everything). It's not very likely that science will be able to reveal any kind of truth.

apeiron

The ontological issue here is that random~determined is a pairing that presumes a certain view of causality. One that is atomistic and mechanical rather than self-organising or developmental.

You could instead take a systems view and talk of freedom~constraint. Where causality also acts top-down, from the global scale to the local, you have a different story. The actions of the local scale are free - anything can happen - except to the degree that they are constrained, there are boundary conditions limiting what can happen.

So constraints "determine" what freedoms are "randomly" expressed at the locations of a system.

In QM terms, the "quantum realm" is itself a free potential but the classical "observing" world is a set of global constraints that then limits the freedom within exact bounds.

So it could be said - in the systems approach to modelling reality - that nature is fundamentally free (rather than random), but also fundamentally constrained (rather than deterministic) because all self-organised systems arise via the interaction of local freedoms and global constraints.

Another difference about the systems view is that it does not have to be a case of either/or (either randomness or determinism must be the fundamental principle). Instead it is always a matter of both. You need two complementary things in interaction to generate any kind of self-organising outcome. And it is not too hard to see how the unlimited expression of local freedoms will - as everything interacts - lead to the emergence then of downwards acting global constraints.

A bar magnet or spin glass is a standard example. The orientation of a dipole is free. But the orientation of a collection of dipoles becomes constrained to an entropy minimising alignment - a common magnetic field.

wuliheron

To assert that quanta are "purely random" or "utterly random" or "randomness is a natural law" is to utter a contradiction. On the one hand the statements insist something is random, while on the other they insist it is predictably random! In addition the context is so vague as to be meaningless and the irony is that such statements are apparently as meaningless as the phenomena they profess to describe.

Note also that quanta have both random and orderly behavior. Like up and down, left and right, front and back it may simply be that the random and orderly are relative concepts and one without the other is meaningless.

ZapperZ

Why is this contradictory?

For example, in classical statistics using Maxwell-Boltzmann distribution, it IS expected that each of the individual particles do have a random distribution in many of its properties. Yet, this doesn't mean that the ensemble can't have a well-defined distribution, which then allows you to measure properties representing the canonical ensemble. There is nothing vague here.

Your argument is based on a matter of taste, which isn't a valid argument against anything, really. I've described an actual physical example that counters your preference. If you disagree, I would appreciate a similar physical example that would support your argument.

Zz.

wuliheron

It is not a matter of taste, but a well researched linguistic issue.

A Maxwell-Boltzmann distribution, for example, provides a description of what is observable and is no more a metaphysical statement about the particles themselves then if I were to say I can't predict the next roll of a pair of dice. It also describes just one aspect of the particles rather than all their other properties so it provides a specific context within which we can demonstrate the meaning of "random" as something we cannot predict.

ZapperZ

Eh?

So you think a "temperature" is a "metaphysical statement"? Since when is a metaphysical quantity can actually be used in a device in which you depend your life on? Furthermore, in classical thermodynamics, the maxwell-boltzmann distribution DOES described ALL the behavior of the canonical ensemble!

Your reply has not really given any credence to your assertion about the contradiction. There are enough examples in which random individual behavior can lead to a very predictable behavior for the ensemble. This is true both for classical and quantum statistics. You haven't given any physical example to counter that. A "linguistic" argument is irrelevant, unless you want to use word-play to confuse and bury the issue. Try using a well-researched linguistic issue to make your electronics to work.

Zz.

Pythagorean

Actually, as long as you're talking about statistics.

"A random number is a number chosen as if by chance from some specified distribution such that selection of a large set of these numbers reproduces the underlying distribution."
-Wolfram.

And there are many kinds of random distributions, all having mathematical form used for prediction.

The random you're thinking of is more the experiential version "something random happened to me today". Not quite the same.