[Tony Wolff]

Is the point in time at which a particular radioactive atom decays still regarded as totally unpredictable, or to put it another way are we any closer to understanding what causes the decay to happen? If not is this an area of physics that is under investigation or is it regarded as too difficult?

[insane_alien]

it's not just regarded as random it IS random. it's a quantum mechanical event and those are about as random as you can get. we know how it happens, we just can't put a time on it. we can put a probability on it though.

[Tony Wolff]

When you say it IS random does that mean that the point at which will decay is theoretically impossible to predict and will remain so forever. How do we know that if you have two atoms one about to decay and the other not that there is not some difference between them that we at present cannot determine. I recognise that I may be being extremely naive - not being a physicist!

[insane_alien]

you don't get atoms just on the verge of decaying or not. they are either not decayed, in the process of decaying(a very short time nearly impossible to measure) or decayed.

there is no middle ground with these states. like all of QM there are a finite number of states with nothing in between.

if you had 100 atoms of a radioactive substance, say Iodine-131, you will not be able to predict which will decay first though you can estimate quite readily that after 8 days only 50 or so will be left. this is called the halflife. it is the only way to put any sort of prediction on radioactive decay. though, it is entirely possible that all 100 would still be there or that they all decayed in the first millisecond, it is just extremely unlikely for that to happen.

[swansont]

insane_alien said:

if you had 100 atoms of a radioactive substance, say Iodine-131, you will not be able to predict which will decay first though you can estimate quite readily that after 8 days only 50 or so will be left. this is called the halflife. it is the only way to put any sort of prediction on radioactive decay. though, it is entirely possible that all 100 would still be there or that they all decayed in the first millisecond, it is just extremely unlikely for that to happen.

You'd technically need to scale up the example by a few orders of magnitude to be valid; the stochastic nature of decay relies on large-number statistics. But the concept displayed is certainly correct.

[insane_alien]

well, i was trying to keep the numbers easy to comprehend.most people can understand 100 and 50 but not so many 'get' the sheer number of atoms even in a spec of dust.

i am aware that the larger the sample the more true it holds. i was origionall going to start off with 2 atoms but decided that would be pushing it way too far.

[Luminal]

insane_alien said:

you don't get atoms just on the verge of decaying or not. they are either not decayed, in the process of decaying(a very short time nearly impossible to measure) or decayed.

there is no middle ground with these states. like all of QM there are a finite number of states with nothing in between.

if you had 100 atoms of a radioactive substance, say Iodine-131, you will not be able to predict which will decay first though you can estimate quite readily that after 8 days only 50 or so will be left. this is called the halflife. it is the only way to put any sort of prediction on radioactive decay. though, it is entirely possible that all 100 would still be there or that they all decayed in the first millisecond, it is just extremely unlikely for that to happen.

Well, it has not been proven that there aren't underlying mechanics that make QM deterministic. And that is the answer that Occam's razor would lend to rather than having one set of reality deterministic (macroscopic) and another set (quantum) nondeterministic, existing in parallel.

But I'm sure this has been discussed to death before, so I'll mosey on out. :embarass:

[Tony Wolff]

I suppose that puts my question more clearly. Is it right that 'it has not been proven that there aren't underlying mechanics that make QM deterministic'?

[insane_alien]

well it hasn't been proven as QM is still based on probabilities. if it was known to be deterministic(had been proved) then we would not be using probabilities as we would know the outcome before it happened.

[Tony Wolff]

Right I think I've got it. So is anyone even attempting to investigate a deterministic basis for QM or are physicists just too lazy? :-)

[Royston]

Tony Wolff said:

Right I think I've got it. So is anyone even attempting to investigate a deterministic basis for QM or are physicists just too lazy? :-)

There have been attempts to reconcile the indeterminism of QM, pretty much since it's discovery. However any attempt has been fruitless so far, if you're interested, try googling the following under QM.

hidden variables
Bell's inequality
realism
locality

See what you come up with.

[MrMongoose]

To me it sounds like a lot of physicists are putting all thier eggs in one basket when there's no conclusive evidence that (maybe at a level beyond a level beyond a level beyond a level of complexity below the effects observed in decay) decay is not deterministic. The most recently developed observations always appear to be stocastic, and it never turns out to be the case.

Or maybe it does.. we just don't know yet!