Thread: probability question 2

Sorry if it's a stupid question,but does a particle exist in a single defined place, and we just can't identify that defined space or is the particle actually just a probability, and doesn't exist in a defined space.The name suggests the former, but 'm not sure.

This is a physics question, not a probability question. You need to use quantum theory to answer the question.

i know, I just didn't know the right word to use. Notice it's in the physics subforum.

the particle gose back and forth in time and exsist in the same time in many places and can be stabilays on one, thanks

Originally Posted by Water Nosfim

the particle gose back and forth in time and exsist in the same time in many places and can be stabilays on one, thanks

Please disregard this post.

In reality, we have abandoned the idea of solid particles since the advent of quantum mechanics. As a result, the popular analogy between an atom and a planetary system is as wrong as it is tempting. Particles are described as probability waves that attribute a certain probability of where the particle actually is. This leads to the famous Heisenberg uncertainty relation which basically says that you cannot precisely measure both the momentum and the position of a particle.

This property is not due to the inability of correctly measuring these quantities, but it is inherent to the particles. So, no, the position is not well defined. It is a direct consequence of the wave nature of matter.

The relationship between position and momentum ( and likewise between enrgy and time ) is such that Heisenberg's Uncertainty Principle is satisfied. It follows that if you know the position of a particle exactly, then the uncertainty in the momentum is infinite. The alternate is also true. Knowing the momentum, and so the velocity of a particle, and therfore its kinetic energy exacly implies an infinite uncertainty in its position, ie it could be anywhere in the universe.


We therefore think of these observables, energy and time along with position and momentum, as being 'smeared out' in quantum mechanics such that we can never know them exactly.

Oh and this is not a consequence of the wave nature of matter since we can readily measure these quantities for water or sound waves ( difficult but possible ). It is due solely to the quantum probabilistic nature of the subatomic world.

In effect knowing position and momentum ( and similarily energy and time ) exactly is not just extremely hard to do, it is actually impossible by definition.

Dishmaster you say that the position of the particle is not well defined, it does not exist in and definate space, and MigL says that particles do exist in one defined space but we as humans can't define it.
Is that correct, or am I taking it the wrong way? Who should I believe?

Someone correct me if I'm wrong, but I think these options qualify as interpretations, in the sense that both give the same results no matter how you measure them, and so there is no scientific answer. Either works and you're free to pick which you think sounds better. (Again though, I'm no expert here, so there might be some experiment that could differentiate the two.)

Re-read my post, that is not what I said.

If mesuring one quantity exactly means that another quantity tends to infinity, that obviously leads to an impossibility. I also state3d that it is a proprty of QM and not of our measuring ability.