Observing Particles

[ukanonymous]

In quantum mechanics, particles do not have a definite state unless they're being observed.
Explanation please?

[woofgang]

If someone has a fixed belief, everything that is said or not said, or seen or experienced will, to that person, confirm their belief......

[Hypognosis]

@ukanonymous

jim may correct me but you may have under-interpreted the use of the word 'observed'. Jim did mention detector equipment and it almost goes without saying that particle physicists are dealing with things which cannot be seen by the human eye.

If a detector works by monitoring for perturbations in an electromagnetic field, say, then the particle unavoidably feels the influence of that field.

So I have often wondered whether the whole thing was just a 'truism', that it is impossible to observe (measure) behaviours at the atomic scale without deploying fields and forces which, inevitably, influence its behaviour. Whoever thought it up was just trying to get across the idea that what we *measure* has been influenced by the act of measurement and thus all behaviours observed are slightly distorted.

Hence, we can only draw up mathematical models of the "slightly distorted" behaviour, as opposed to unadulterated, "natural" behaviour.

The upshot is that some fundamental truths may be permantly beyond our grasp because we have that horrible choice of looking but blotting out the effect by doing so or don't look and miss it anyway.

But we don't require absolute truths, we only need a good working understanding of the innards of the universe and we can do marvelous things like converse over the internet.

Anyway, summing up, the observation thing is not about some mystical property of the eye, sending particles or signals out, to let a distant object know it is being observed.

Although the problem I have accepting the existence of 'gravitons' could be encapsulated in a communication setup of that ilk. :0)

[ukanonymous]

//If someone has a fixed belief, everything that is said or not said, or seen or experienced will, to that person, confirm their belief......//

unfortunately not too far from the truth

[woofgang]

well admitting the problem is a start.

[jim360]

No, that seems fine to me hypo. The only thing I might say is that despite the fact that there is essentially no way to probe the quantum world free from influencing it, this doesn't mean that the results obtained by experiment can't be trusted. It's entirely possible to take this into account -- either by talking of a vague-ish "systematic error", or by just noting that before the particle interacted with the experiment but after it was sent into the set-up, in between it must have been doing something, and you can make predictions about how things behave in the interim period between measurements.

Essentially, this is what quantum theory is. Between times, a particle evolves in this way... and then you have some idea of what the probability of a particular behaviour will be, and in order to confirm this you take averages over many hundreds of thousands, if not -- by this time -- billions of such experiments.