# Is the wave function/packet an actual property

1. Feb 3, 2014

### batmanandjoker

Or is it a statistical calculation of where the particle could possibly be. If its a property of nature then it must have a limit, distance at which it seaces to exist. Also a second question does space time exist in QM and if it doesent then why does it exist in the classical world which it does exist doesent it? Im asking this because the wave functions/ superposition of macro objects is infentismly small but what I want to know is the wave packet/superposition of macro objects subject to classical physical space/distance?

Any help would be greatly appreciated sorry for the spelling my spell check doesent work.

2. Feb 3, 2014

### Staff: Mentor

Of course its a property, just like the probabilities of a dice is a property of the dice assoicated with each face.

Your assumption 'If its a property of nature then it must have a limit, distance at which it seaces to exist' does not follow from 'property'

Of course space and time exist.

I suspect you are still not quite up to speed on what a superposition is - its simply the vector space property of the funny kind of probability QM uses.

Rock bottom, from the formalism alone, QM is simply a generalized probability model. Its the simplest such model that allows continuous transformation between so called pure states, or, equivalently allows entanglement, again without going into the technical detail of the words I have bandied about, or even exactly what they mean. The meaning of QM is another matter - that requires an interpretation. It's like when you throw a dice - probability theory doesn't tell us which face will come up - nor even why a face comes up - its silent about that.

Thanks
Bill

3. Feb 3, 2014

### batmanandjoker

but what I want to know is the wave packet/superposition of macro objects subject to classical physical space/distance?

4. Feb 3, 2014

### Staff: Mentor

I think we have been through that before.

Superposition is not subject to such. In principle the position a particle that is in a superposition of position can be observed anywhere the wave-function says it has a probability of being - and there is no restriction on that.

Thanks
Bill

5. Feb 3, 2014

### batmanandjoker

But is the wave function infinite? Because people talk about bigger and smaller wave functions.

Last edited: Feb 3, 2014
6. Feb 4, 2014

### Demystifier

Batmanandjoker, see
https://www.physicsforums.com/blog.php?b=4330 [Broken]

Last edited by a moderator: May 6, 2017
7. Feb 4, 2014

### Staff: Mentor

Of course it cant be infinite - nothing physically realizable can be.

It is however, for mathematical convenience, is sometimes approximated by a function of infinite extent.

I haven't heard anyone talk of bigger and smaller wave functions. But if they did I would assume a big wavefunction is one where the probability of finding a particle is very high in a small region - and small where it isn't.

Thanks
Bill

8. Feb 4, 2014

### Staff: Mentor

Just a note to the OP.

This concerns the PBR theorem, which is quite important, and deserves all the praise it has garnered.

But to forestall unnecessary confusion I believe its important to know from the outset one of its assumptions:
http://xxx.lanl.gov/pdf/1111.3328v3.pdf
'The argument depends on few assumptions. One is that a system has a real physical state not necessarily completely described by quantum theory, but objective and independent of the observer. This assumption only needs to hold for systems that are isolated, and not entangled with other systems. Nonetheless, this assumption, or some part of it, would be denied by instrumentalist approaches to quantum theory, wherein the quantum state is merely a calculation tool for making predictions concerning macroscopic measurement outcomes.'

Many bare bones interpretations such as the statistical and most versions of Copenhagehn do just that - have the state as 'merely a calculation tool for making predictions concerning macroscopic measurement outcomes'. This is also the interpretation people mean when they talk about the formalism by itself with little or no interpretive assumptions.

When I talk about QM, unless I say otherwise, its what I mean, so really PBR doesn't apply to my comments.

Thanks
Bill

Last edited by a moderator: May 6, 2017