# Can virtual particles appear ANYWHERE?

• Meatbot
In summary, virtual particles only exist in mathematical calculations. They have greater momentum than energy, meaning they would be faster than light. When people say that a particular type of force is "mediated" by virtual particles (eg, photons), they mean that those particles appear in the Hamiltonian, not that they really appear.
Meatbot
Can they appear inside a black hole? Can they appear between an electron and the nucleus? Inside a nucleus? Can two sets appear at exactly the same place? What prevents them from appearing exactly where other existing matter is?

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As another question can they appear INSIDE Of another particle?

Can you have a virtual whatever-the-hell fit inside of a quark?

I know that they keep showing up in my beer, and it's beginning to irritate me.

Hey, don't write them off so quickly! Remember Donald Glaser got the idea for the bubble chamber while watching bubbles rise in his beer.

Only real things are real

Meatbot said:
Can they appear inside a black hole? Can they appear between an electron and the nucleus? Inside a nucleus? Can two sets appear at exactly the same place? What prevents them from appearing exactly where other existing matter is?

Virtual particles appear only in mathematical calculations.
Real particles exist. That's what "real" means. Virtual particles don't.
Virtual particles always have momentum greater than energy, which means they'd be faster than light!
When people say that a particular type of force is "mediated" by virtual particles (eg, photons), they mean that those particles appear in the Hamiltonian, not that they really appear.

tiny-tim said:
Virtual particles appear only in mathematical calculations.
Real particles exist. That's what "real" means. Virtual particles don't.
Virtual particles always have momentum greater than energy, which means they'd be faster than light!
When people say that a particular type of force is "mediated" by virtual particles (eg, photons), they mean that those particles appear in the Hamiltonian, not that they really appear.

Aren't virtual particles the same as the vibrational modes of the Casimere effect - both are the zero point energy, right? If so, then since the matter of the parallel plates in the Casimere effect prevents some vibrational modes of the zero point energy (which is the same as virtual particles, right), then virual particles (vibrational modes) cannot appear were matter is. Does this sound right? Thanks.

Meatbot said:
Can they appear inside a black hole? Can they appear between an electron and the nucleus? Inside a nucleus? Can two sets appear at exactly the same place? What prevents them from appearing exactly where other existing matter is?

I believe this is the hawkings radiation... or am I wrong?

Tachyon.

Tachyonie said:
I believe this is the hawkings radiation... or am I wrong?

Tachyon.

Hawking's radiation, in simplest terminology as I understand it refers to the radiation produced at the event horizon of a black hole, wherein a virtual particle may be caught behind the event horizon however it's virtual partner escapes and is released as energy. Thus the black hole decays.

ooh so virtual particles aren't some sort of undetectable particles, they simply aren't real? so when someone refers to virtual particles, is it along the same lines as referring to distance, velocity, or force; words(or numbers) which refer to changes or properties rather then actual "things"? i know, this is a total nooby question (i JUST started reading "a brief history of time" two days ago, and it's pretty much laying the foundation for my understanding of quantum mechanics at the moment)

One thing:

According to Heisenberg: $$\Delta E \Delta t > \hbar / 2$$
(HUP)

So I have always been taught that the virtual particles "exists", but only during a time according to HUP. During that time, conservation of energy and momenta is allowed.

Cvan: according to tiny-tim , virtual particles just show up in our calculations. So either both you and me have missunderstood virtual particles completley, or else tiny-tim is wrong :P

friend: I was also about to about to take the Cashimir effect ;)

Are we physicists or mathematicians?

Don't be blinded by the mathematics!

Physicists mustn't believe everything mathematicians tell them!

We can't detect virtual particles, not even indirectly, and not even during the HUP time - they're just a convenient way of calculating fields (forces).

This radiation does not come directly from the black hole itself, but rather is a result of virtual particles being "boosted" by the black hole's gravitation into becoming real particles.

http://en.wikipedia.org/wiki/Virtual_particle
As such, virtual particles are also excitations of the underlying fields, but are detectable only as forces but not particles. They are "temporary" in the sense that they appear in calculations, but are not detected as single particles. Thus, in mathematical terms, they never appear as indices to the scattering matrix, which is to say, they never appear as the observable inputs and outputs of the physical process being modeled.
In this sense, virtual particles are an artefact of perturbation theory, and do not appear in a nonperturbative treatment.
As such, their objective existence as "particles" is questionable;[citation needed] however, the term is useful in informal, casual conversation, or in rendering concepts into layman's terms.[citation needed]

Bigman said:
… is it along the same lines as referring to distance, velocity, or force … ?

No, it's even worse - different observers can agree on the distance between two objects, or at least can agree on a formula to convert one observer's measurements to another's. In that sense, distance is "real".

But the mathematics doesn't tell you anything about where the "virtual particle" is, or when, or its velocity, or anything which could, even in principle, be measured.

Feynman diagrams, for example (which is where most people think they've seen virtual particles!), are not snapshots - they're a convenient mathematical device for calculating the coefficients of the Dyson polynomial (they make sure that you don't leave out any terms)!

Then what IS a force. IS the force mediated by virtual particles, or is it "just" mathematical formalism.

A force is "real", because it can be measured by physicists.

A virtual particle can't.

I repeat:
When people say that a particular type of force is "mediated" by virtual particles (eg, photons), they mean that those particles appear in the Hamiltonian, not that they really appear.

I read that, but you did not answer what a force is. How is the force mediated in "real" world.

Theoretically, we cannot detect virtual particles because they are inextricably bound to their antiparticles which cancel their properties. However, the Casimir force is a pretty good demonstration that they exist. For those not familiar, the Casimir force demonstrates that two neutral conductive surfaces that are situated near enough to one another to suppress the formation of virtual pairs with wavelengths longer than the gap between them, will be attracted to one another due to the reduced pressure between the surfaces.

Hawking radiation is the promotion of virtual particles to real (unbound) particles when virtual pairs arise on the horizon of a BH, and one of the virtual particles is trapped by the BH while the other goes free. This argument is not as compelling as the Casimir force because it is entirely theoretical and is predicated on the reality of gravitational singularities, which may be, after all, a product of a mathematical breakdown in GR and may not exist in reality. There are other measurable effects that point to the existence of virtual particles, however, and some Internet searching will turn up examples.

A force "is" what it "is"

I don't know "what" a force is!

As a physicist, I can measure a force.

As a mathematician, I can calculate a force.

But that's all!

Do you know "what" time is?​

Cvan said:
Hawking's radiation, in simplest terminology as I understand it refers to the radiation produced at the event horizon of a black hole, wherein a virtual particle may be caught behind the event horizon however it's virtual partner escapes and is released as energy. Thus the black hole decays.

Yeah, that's what I was trying to say using one sentence and key stage 2 english. :)

Tachyon.

I know all that tiny-tim, but:

i. Virtual and existence is not a contradiction a priori

ii. real and existence is not equivalent

i.e A virtual particle is not a real particle, but we can not a priori rule out the possibility that a virtual particle can exist. Real particle exists, that we know since we can decet them directly. Virtual particles are harder to proove that the exists since we can't measure them directly. But as the Cashimir Effect has demonstrated, (as Turbo-1 also mention) virtual particles exists.

And I would say that all physicists also are mathematicians in some sense since the language of physics is math. But not all mathematicians are physicists.

I don't "know" what time is, since I don't have taken any advanced course in General Relativty yet, but i "know" that time is strongly connected to space, so let's skip the disscussion about time from now on.

But if I got you right, you are arguing that " A force is a force. " We can only measure its properties, but we can not say what it is. As we say about the electron, that an "electron is an electron", it has wave- and particle properties, but on a very fundamental level, an electron is an electron. Nothing else nothing more. Have I understood you correctly?

tiny-tim said:
I don't know "what" a force is!

As a physicist, I can measure a force.

As a mathematician, I can calculate a force.

But that's all!

Do you know "what" time is?​
ah? A conjugate variable of mass/energy?

malawi_glenn said:
i.e A virtual particle is not a real particle, but we can not a priori rule out the possibility that a virtual particle can exist. Real particle exists, that we know since we can decet them directly. Virtual particles are harder to proove that the exists since we can't measure them directly. But as the Cashimir Effect has demonstrated, (as Turbo-1 also mention) virtual particles exists.

Can't we "measure" virtual particles by measuring the force of the Cashimir Effect? We might be measuring multiple modes of virtual particles, but that's still a measurement, isn't it?

Yes, the Casimir effect provides good evidence that virtual particles do in fact occur.

friend said:
Can't we "measure" virtual particles by measuring the force of the Cashimir Effect? We might be measuring multiple modes of virtual particles, but that's still a measurement, isn't it?

well yes, but i really ment "we measure them in a decector", as we do with the real particles.

any actual evidence?

malawi_glenn said:
But if I got you right, you are arguing that " A force is a force. " We can only measure its properties, but we can not say what it is. As we say about the electron, that an "electron is an electron", it has wave- and particle properties, but on a very fundamental level, an electron is an electron. Nothing else nothing more. Have I understood you correctly?

Yes!

I know all that tiny-tim, but:

i. Virtual and existence is not a contradiction a priori

ii. real and existence is not equivalent

i.e A virtual particle is not a real particle, but we can not a priori rule out the possibility that a virtual particle can exist. Real particle exists, that we know since we can decet them directly. Virtual particles are harder to proove that the exists since we can't measure them directly.

I agree.

But if we ever did actually detect virtual particles, we'd probably stop calling them virtual!

But as the Casimir Effect has demonstrated, (as Turbo-1 also mention) virtual particles exists.

So far as I know, the Casimir Effect has not demonstrated that virtual particles exist.

Does anyone have a reference that says that it has?

See http://en.wikipedia.org/wiki/Casimir_force :
This is sometimes described in terms of virtual particles interacting with the objects, due to the mathematical form of one possible way of calculating the strength of the effect.

"sometimes" and "described"!

I still say it's just mathematics.

Consider the "pion cloud" of "a virtual pion" round a nucleus - it explains why, in quantum field theory, the field isn't the expected and hoped-for $$e/r^2$$.

You can say "the field isn't $$e/r^2$$, it's something else".

Or you can cling to the easy idea that the field is $$e/r^2$$, and explain it away by saying that there is one virtual pion "screening" that field.

(Same thing with Hawking radiation from a black hole, by the way.)

Mathematically, both views are perfectly valid.

But there's no evidence (to use Brad_Ad23's word) one way or the other!

So there's no reason why physicists should adopt the mathematical view which requires the invention of a totally new particle that nobody will ever detect, not even indirectly!

I would beg to differ. The evidence comes from the calculations. I suppose if you wish to get technical I will parse my language and say it provides indirect evidence since by their nature virtual particles cannot be directly observed. However, as I was taught, they arise from some of the most fundamental aspects of quantum theory, and if one uses them you can make precise (albeit somewhat tedious) calculations as to what they should do if they exist. They provide things such as charge screening, anti-screening effects for quarks and gluons, and indeed offer an explination to the Casimir effect.

To be fair though, yes, that does not mean they exist, but they seem to explain a wide variety of separate situations quite nicely and predictions using them seem to fit observations.

But that said, I can still see objection since there is no direct evidence of them. Though I am hard pressed to see how you can find direct evidence for these things, and that too has bugged me.

## 1. What are virtual particles?

Virtual particles are subatomic particles that exist for a very short period of time, typically less than a billionth of a second. They are constantly appearing and disappearing in the quantum vacuum, which is the lowest energy state of the universe.

## 2. How are virtual particles different from regular particles?

Virtual particles differ from regular particles in that they do not have mass, spin, or a definite location. They are fluctuations in the quantum field and cannot be directly observed or measured.

## 3. Can virtual particles appear anywhere?

Yes, virtual particles can appear anywhere in the quantum vacuum. However, their appearance is governed by the laws of quantum mechanics and they can only exist for a very short period of time before disappearing again.

## 4. How are virtual particles created?

Virtual particles can be created through a process called pair production, where a particle and its antiparticle are created from the energy in the quantum vacuum. They can also be created through interactions between particles and fields.

## 5. Can virtual particles be observed?

No, virtual particles cannot be directly observed or measured. However, their effects can be observed through various phenomena such as the Casimir effect and Hawking radiation.

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