# Ghostly interactions?

1. Mar 11, 2005

### wolram

Please excuse an ignorant question, but does this ghostly zero point
energy have any effect on real world particles?

2. Mar 11, 2005

### marlon

what is gostly about the zero point energy ?

marlon

3. Mar 11, 2005

### wolram

I dont know i am hoping that someone can give me an insight of these
interactions.

4. Mar 11, 2005

### Sterj

A cristall latter in its ground state can be explained with the harmonic oscillator. The zero point energy of such an oscillator isn't zero like in classical mechanics. Thus, the zpe of a harmonic oscillator of for example a atomic latter is:

E=h(bar)w/2.

Now, of course there are a lot of oscillators in such a latter and the whole energy of a cristallic latter in ground state is:
E=E(oscillator 1)+E(oscillator 2)+...+E(oscillator n). (the oscillators 1 to n are all in ground state and can have diverent numbers of w).

The ground state energy of a harmonic oscillator isn't zero cause of the heisenberg's uncertainty principle.

5. Mar 11, 2005

### wolram

Please be kind to me, i am asking this question as a pedestrian, if
you can give a basic answer, something that is understander able
to the GP i will be in your debt

6. Mar 11, 2005

### marlon

Look at the particle in a box (a potential well from which it "may" not escape)

In the box the potential is zero, at the exterior the potential is infinite

If the lowest energy value were zero then we know that the momentum is zero (E = p²/2m + 0). But the due to $$\Delta x \Delta p = constant$$ the position (x) is infinite and the particle is no longer in the box because it has no specific position... You see ? Thus, the lowest energy value must be non-zero

marlon

7. Mar 12, 2005

### wolram

So the ZPE field has an effect on all "baryonic", structures, and can
not be divorced from perceived physical structure?

8. Mar 12, 2005

### marlon

Virtual particles cannot be seen since they are not "physical"
I mean, they are not on mass shell or they don't obey the Einstein energy relationship. However their effect on "real" interactions is definetely there.

As to the ZPE, the Casimir effect is a pure and observable manifestation of this virtual particle see that arises due to vacuum energy fluctuations. Check Wikipedia for that matter

marlon

9. Mar 13, 2005

### Sterj

@marlon:
mass shell: obey Einstein's energy relation
mass shell: do not obey Einstein's energy relation

You mean this equation: E^2=(cp)^2+(mc^2)^2
So a real particle does obey this equation, because it has a given momentum and mass. But why don't virtual particle (take a positron) obey this equation?
I mean they have mass, they have momentum?

10. Mar 14, 2005

### marlon

indeed

Indeed

Because such a virtual particle is an intermediate stage of an interaction between real particles. QFT teaches us that we need to integrate over all momentum-values of such particles.

marlon

11. Mar 14, 2005

### Sterj

yes, but if we work in vacuum for example a virtual photon can create a positron-electron pair. Is it right, that in this case the electron-positron pait can not be observed?

If the virtual particle is only an exchange particle, it takes its energy from uncertainty and this particle will disappear after a short while, so the einstein's energy relation isn't obeyed, because this was only there for a short while.

(sorry for such an English)

12. Mar 15, 2005

### marlon

Sterj,
i have answered these matters in the QM-section, more specifically in the virtual particles thread

marlon

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