Re: Particles and their properties

[Dr.Bubafunk]

If a meson is an antiquark what is a virtual quark/meson? I thought a virtual particle was another name for antimatter altogether is this the case? If you could provide a resource it would be appreciated.

[ajb]

If a meson is an antiquark what is a virtual quark/meson? I thought a virtual particle was another name for antimatter altogether is this the case? If you could provide a resource it would be appreciated.

 

 

A virtual particle is a particle that is not constrained to obey the classical equations of motion. They are a true quantum phenomena. Informally, they are the "internal parts" of the Feynman diagrams and are responsible for the particle exchange notion of a force.

[mathematic]

Mesons are quark-antiquark pairs. Virtual particles appear as pairs, either matter-antimatter or two photons.

[swansont]

Mesons are quark-antiquark pairs. Virtual particles appear as pairs, either matter-antimatter or two photons.

 

Virtual photons do not have to appear in pairs in Feynman diagrams.

[mathematic]

Virtual photons do not have to appear in pairs in Feynman diagrams.

I was thinking of virtual particles in a vacuum.

[SamBridge]

It seems like virtual particles from what I've gathered are almost like the invisible gears of atoms, they mediate forces, but somehow they don't exist until they are measured, it's like they are made out of math more than anything in the real world. But perhaps "real" can mean something different, perhaps literally they are coefficients of an imaginary number and thus do not contain real value until some measurement happens that corrects that, I see imaginary numbers popping up a lot in quantum physics. There's also this

http://en.wikipedia.org/wiki/Virtual_particle

"They exist for a limited time", but what causes them to stop existing? Yeah I know there's mass, but what about mass makes them stop existing? The virtual particles without mass can travel indefinitely can't they? But what is it about mass? Perhaps can a Higg's field answer that? After running into too many Higg's particles their probability becomes so localized it is considered "measured"? But then how is it's energy conserved by the parent particle?

Edited January 30, 2013 by SamBridge

[ACG52]

 

"They exist for a limited time", but what causes them to stop existing?

 

The energy they used to exist was 'borrowed' from the universe and must be returned in a limited time, which I believe is inversely proportional to the amount of energy needed to manifest the virtual particles.

 

They exist for a brief flicker of time, that's why they're virtual.

[SamBridge]

The energy they used to exist was 'borrowed' from the universe and must be returned in a limited time, which I believe is inversely proportional to the amount of energy needed to manifest the virtual particles.

 

They exist for a brief flicker of time, that's why they're virtual.

So it must be related to the potentials they travel. It takes "more" energy for mass to travel a greater distance from it's parent emitter, and mass-less particles have, well, no mass, which also makes sense in classical physics if you look at photons, I guess it answers part of the question, I still don't see completely how it works, how is the energy not stolen from the particle and how does it get back? And what is actually happening at least mathematically at the moment the energy needed to sustain their existence becomes too much? Why doesn't this effect happen with normal matter?

[ACG52]

No, it's got nothing to do with travel or motion.

 

On the quantum level, the energy of the various fields which fill space can vay wildly over very small spaces and very short times. This is due to quanutm uncertaintly. At any given point of space the energy can be high enough to manifest virtual particles, but only for the very short times allowed by quantum physics.

[SamBridge]

No, it's got nothing to do with travel or motion.

 

On the quantum level, the energy of the various fields which fill space can vay wildly over very small spaces and very short times. This is due to quanutm uncertaintly. At any given point of space the energy can be high enough to manifest virtual particles, but only for the very short times allowed by quantum physics.

I see what you're saying in a way, but it doesn't quite match up to the only possible thing that I can think of that it applies to: The Casimir effect. Certain probabilities are excluded with less space aren't they? What does that have to do with borrowing energy for mass to travel distance? It takes more "space" for a higher energy mass particle to travel, but they were still "traveling" before they stopped existing, the different fields can exist over different areas of space depending on their energy, that's what i'm getting from you, but that's all I'm getting, there's something missing from your picture.

Edited January 30, 2013 by SamBridge

[ACG52]

 

It takes more "space" for a higher energy mass particle to travel, but they were still "traveling" before they stopped existing

 

It has nothing to do with traveling any distance.

[ajb]

You can think about virtual particle popping in and out of existence as being in accordance to the time-energy uncertainty principle. John Baez talks about it here.

 

 

As ACG52 has stated, you can borrow enough energy from the vacuum to create virtual particle pairs, but only for a short time as determined by

 

[math]\Delta T \:\: \Delta E \geq \frac{\hbar}{2}[/math].

[SamBridge]

Well distance isn't the right term, I mean more like space is required for higher energy fields to exist, or for larger fields to occupy a larger area, which the casimir effect shows. I still don't see how the energy is "borrowed". There's virtual particles all around us, where is that energy coming from, why does the fabric of space need it, how does it get returned, and why isn't the fabric of space being depleted of energy exactly?

[ajb]

I still don't see how the energy is "borrowed". There's virtual particles all around us, where is that energy coming from, why does the fabric of space need it, how does it get returned, and why isn't the fabric of space being depleted of energy exactly?

Maybe borrowed is not the best term. The point is you cannot exactly know the energy of anything while knowing exactly how long it existed for. This uncertainty means that for a short period of time virtual particles can just appear from the vacuum. For a short period of time there is enough energy to create these pairs.

[juanrga]

If a meson is an antiquark what is a virtual quark/meson? I thought a virtual particle was another name for antimatter altogether is this the case? If you could provide a resource it would be appreciated.

 

A meson is not an antiquark. A meson is a particle composed of one quark plus one antiquark bound together by the strong interaction.

 

A virtual particle is a mathematical representation of certain terms in the equations of some formulations of particle physics.

 

http://www.mat.univie.ac.at/~neum/physfaq/topics/virtual

 

 

Virtual particles are part of the imagery of quantum field theory. They are figurative language for abstract mathematics, used by experts and laymen as imagery for giving abstract recipes for calculating scattering amplitudes an appearance of intuitive meaning. However, any attempt to take this language literally gives a very

misleading and unscientific view of the microscopic world.

Edited February 2, 2013 by juanrga

[ajb]

A virtual particle is a mathematical representation of certain terms in the equations of some formulations of particle physics.

 

 

Yes, they are the internal parts of Feynman diagrams, which themselves correspond to terms in a series expansion. They are unphysical in that sense, but they do have measurable consequences. The Casimir effect is one good example of this.

[juanrga]

Yes, they are the internal parts of Feynman diagrams, which themselves correspond to terms in a series expansion. They are unphysical in that sense, but they do have measurable consequences. The Casimir effect is one good example of this.

 

The key here is that the Casimir effect can be explained without even mentioning "virtual particles"

 

http://www.mat.univie.ac.at/~neum/physfaq/topics/casimir

[SamBridge]

The key here is that the Casimir effect can be explained without even mentioning "virtual particles"

 

http://www.mat.univie.ac.at/~neum/physfaq/topics/casimir

That just seems like it's restating the experiment, it doesn't actually explain what is going on if it's not virtual particles. You don't think scientists would have already considered every possible attempt at using gravity and electro-magnetism before being forced to consider the existence of such non-existent objects?

Edited February 3, 2013 by SamBridge

[swansont]

Well distance isn't the right term, I mean more like space is required for higher energy fields to exist, or for larger fields to occupy a larger area, which the casimir effect shows. I still don't see how the energy is "borrowed". There's virtual particles all around us, where is that energy coming from, why does the fabric of space need it, how does it get returned, and why isn't the fabric of space being depleted of energy exactly?

 

Quite the opposite, as far as that view goes. Two conductors in close proximity exclude the long wavelength EM modes, i.e. the low-energy ones (which is a way of showing the Casimir force without virtual particles — look at what EM modes are supported by the gap). Higher energy means shorter wavelengths.

[juanrga]

That just seems like it's restating the experiment, it doesn't actually explain what is going on if it's not virtual particles. You don't think scientists would have already considered every possible attempt at using gravity and electro-magnetism before being forced to consider the existence of such non-existent objects?

 

Contrary to myth, such "non-existent objects" are not needed to explain Casimir experiment:

 

http://prd.aps.org/abstract/PRD/v72/i2/e021301

 

Scientists are not forced to use virtual particles.

[SamBridge]

Quite the opposite, as far as that view goes. Two conductors in close proximity exclude the long wavelength EM modes, i.e. the low-energy ones (which is a way of showing the Casimir force without virtual particles — look at what EM modes are supported by the gap). Higher energy means shorter wavelengths.

So another possible explanation is that certain types of oscillation in light waves are excluded from existing those small places? And if so, what if the experiment was done in a room with no light in it? Let's say it was impervious to ALL light, unless I am misunderstanding you.

[swansont]

So another possible explanation is that certain types of oscillation in light waves are excluded from existing those small places? And if so, what if the experiment was done in a room with no light in it? Let's say it was impervious to ALL light, unless I am misunderstanding you.

 

Right. If you can't fit a wavelength of light between the to plates in the experiment, that photon won't exist within the plates. But it's more than that: the oscillation mode itself doesn't exist. This is true even when there is no light — when you solve the QM equations you find that each mode has [math](n+\frac{1}{2})\hbar\omega[/math] of energy. So there's energy even when there are no photons in that mode (n=0), and when you can eliminate those modes in one region, you have a pressure (or force)

[SamBridge]

Right. If you can't fit a wavelength of light between the to plates in the experiment, that photon won't exist within the plates. But it's more than that: the oscillation mode itself doesn't exist. This is true even when there is no light — when you solve the QM equations you find that each mode has [math](n+\frac{1}{2})\hbar\omega[/math] of energy. So there's energy even when there are no photons in that mode (n=0), and when you can eliminate those modes in one region, you have a pressure (or force)

But if the room was impervious to all light, would we not see the pressure? Sure modes don't exist, but if there's no photons, how can the properties of the modes be expressed by photons to cause the pressure difference?

[swansont]

But if the room was impervious to all light, would we not see the pressure? Sure modes don't exist, but if there's no photons, how can the properties of the modes be expressed by photons to cause the pressure difference?

 

A room with no light is impossible, but the issue is that there is energy even when there are no photons when you solve the particle-in-a-box problem. The zero-point energy is not zero.

[SamBridge]

A room with no light is impossible, but the issue is that there is energy even when there are no photons when you solve the particle-in-a-box problem. The zero-point energy is not zero.

Ok so there's energy everywhere, what form is it in exactly if not virtual particles or photons? Or is it all just extensions of the never-reaching-0 probability densities of atoms and photons? The photon oscillation modes are excluded, but why does that matter if there aren't hardly any photons? Isn't there a point of low energy when the casmir effect is negligible?

Edited February 5, 2013 by SamBridge