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Author Topic: Are virtual particles exclusively virtual, or do some exist in reality too?  (Read 9088 times)

Offline pinballed

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Hi.

I understood from a previous answer that virtual photons are a mathematical tool/description, but has no real existence.

Is it the same for all virtual particles, or do other virtual particles exist in reality?

Thanks,
Magnus
« Last Edit: 04/10/2012 09:17:50 by chris »


 

Offline lightarrow

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Re: Virtual particles
« Reply #1 on: 03/10/2012 11:13:47 »
As far as I know it's the same for all virtual particles. So the explanation of Hawking radiation which uses the concept of virtual particles it's just a simplistic description even if a valid mathematical tool. If I remember, infact, even in this case it's possible to describe the effect without using the virtual particles paradigm (but the mathematical description is much more complex).
 

Offline pinballed

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Re: Virtual particles
« Reply #2 on: 04/10/2012 04:17:07 »
That's highly irritating :-(.........so we are writing books, making tv shows, spreading an explanation that we know is not true,
just for the sake of having an intuitive explanation that mathematically would predict/solve an observation we know...but otherwise have nothing with reality to do.
I've been trying to bend my head around virtual particles, borrowing time, etc.....

But very much thanks for your answer.
 

Offline JP

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Re: Virtual particles
« Reply #3 on: 04/10/2012 04:27:50 »
But keep in mind that all particles are virtual in a sense.  They all move from a source to ultimately interacting with something else and can be described by the same mathematical tools as the short-lived virtual particles we usually talk about.

What we usually call virtual particles are those that aren't caught by a detector in their short life span.
 

Offline yor_on

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JP, if we allow virtual particles a timespan they shouldn't be called virtual, then they would be 'real' to me. If we by real mean that it contain those things we actually measure by our ruler and wristwatch. Then the 'foam' or 'virtuality' of space also should become a measurable phenomena with 'paths', as in some sort of 'recoil' and subsequent annihilation. One of the reasons why I find indeterminism' so releasing :)

And this virtuality seem to assume some sort of 'fabric', which I'm not that particular towards either. Indeterminism make no such claims, as I think of it. You could though make a argument in where what we see as a 'fabric of space' from some other point of view will not exist, making this observer dependent too, and that might be acceptable.
 

Offline JP

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Yor_on, here's how I understand real/virtual and why it's a blurry line between them.  Virtual particles are interactions between two events in space-time.  Real particles occur when one of those endpoints is far enough from the other so you can approximately ignore it and pretend the particle flies off freely.  In reality if you actually included the absorption endpoints of all particles, they'd all be virtual, but we can ignore those endpoints in a lot of cases and call them real. 

In practice this is important because some interactions happen on such a short scale that when we compare them to our detectors, we can never write the interactions as going off to infinity, so our detectors can never catch these particles. 

Anyway, I don't know much more than the basics of this, so I'll refer you off to this FAQ on virtual particles by an expert :) 

" . . . since all particle interactions occur over a finite time interval, in a sense all particles are virtual to some extent." http://math.ucr.edu/home/baez/physics/Quantum/virtual_particles.html
 

Offline yor_on

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Heh, I can, in a similar way, refer you too another guy explaining in a mathematical manner why virtual particles mathematically is a limited definition, making several assumptions by 'sleight of hand', that is if I now can find it? Been some time since I looked that one up :)

But I like the way you referred to 'paths' as events, defined as having 'paths' through/due to our local clock and ruler measuring, that is if I read you right? That's the way I see it too, but that doesn't make them virtual to me. 'Reality' is defined through your measurements, as long as we're talking scientific formalism, and also according to how I interpret it naturally:) And if it wasn't, then all scientific statements and propositions belongs to the realm where 'unicorns wander freely' as they only would be one of many belief systems, even if grounded on 'logic'. We all need a place to stand on, to turn the world.

Give me some time and I will find it JP, I think you will enjoy it.
 

Offline pinballed

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Hey,
Don't follow all what you write.....but one essence is that there are a lot of phenomenon;
interactions between particles (with "virtual particles"), electric force of an electron (that is influenced by a cloud of "virtual particles"), and many more.
They are solved mathematically, and then this solutions can be built on different "explanations" although presently no-one has been able in experiments to verify any of
the explanations (so-far at least). All the explanations has pros and cons, are mostly theoretically possible, and the future will show us the answer.

If I'm totally wrong - bring it easy on me - otherwise my already bad self-esteem in this subject will suffer more :-)

Magnus
 

Offline yor_on

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Well :) Magnus, the point is that i personally prefer indeterminism to 'virtual particles'. But it seems most physics prefer it the other way, although if we have some pure mathematicians here I hope them to know what I mean. To me it has to do with how we grow up perceiving our universe. When we later read and experiment we try to fit those results into what we already have learnt about 'forces' 'action and reaction' and causality chains macroscopically. It's my opinion anyway, and as I put a very large relevance to Einsteins definitions I find him differing, for example when describing motion, from what we've seen it before relativity. Then a uniform motion and a acceleration described the same thing, namely 'motion'. But if you check up on relativity you will see that in Einsteins definitions a constant uniform acceleration is equivalent to a gravity, whereas a uniform motion is equivalent to being 'at rest'.
==

All of this as a locally perceived description naturally. Comparing between two objects moving uniformly relative each other that means that you are free to define any of them as being 'at rest', relative the other. And if you now will want to define a 'potential energy' to any of them you then must start by define either, which one is 'really really' moving, so also defining a preferred frame of reference, which does not exist in relativity. Or you have to define a 'system' containing both objects, uniformly moving relative each other, and define a 'potential energy' as a result of that system.

That's definitly not the same concept as we had before, and I think Einstein correct.
« Last Edit: 04/10/2012 20:30:49 by yor_on »
 

Offline yor_on

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There is the possibility though, philosophically seen, to define locality as the grounding principle from which we build, and in that motto create a 'preferred frame of reference'. But if you do so you then also have to recognize that my preferred frame, when comparing it with yours, will differ. To make such an idea fit relativity you will find yourself asking what 'degrees of freedom' really means, and also where the 'connections' between different frames of reference, as in making it possible for them to communicate, exist. Because they do communicate, and locally my definition of a time and a length will be yours too, as long as we're 'at rest' etc. But thinking that way 'motion' becomes a suspect subject to me :) although we all have access to, and see, it daily.
 

Offline Bill S

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As a non scientist, I found this an interesting explanations of virtual particles.

http://profmattstrassler.com/articles-and-posts/particle-physics-basics/virtual-particles-what-are-they/
 

Offline yor_on

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Yeah, that was a nice one Bill. And if you look at it from indeterminism then probability is what defines your 'virtual particle' as I think. You don't need something 'real' as in particles, although you do need some 'perturbation' creating a outcome, from where you observing can define a interaction as having took place. I'm still looking after the mathematical definition I used to have defining 'virtual particles' as suspect beings, the problem is that this definition was saved about three computers ago :) as a guess and although I expect to have it somewhere, and remember it as a eye opener, it will take me time to track it down. But it was good, at least as I read it.
 

Offline JP

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Offline acsinuk

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    • electricmagnofluxuniverse.blogspot.com
Yes, a great answer from Profmatt; but what is the 3D electromagnetic stuff that the field is made up of?
CliveS
« Last Edit: 13/10/2012 17:52:38 by acsinuk »
 

Offline yor_on

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A very nice link in more ways than one Bill, found my own 'old link' that i wanted to show in the comments there. http://www.mat.univie.ac.at/~neum/physfaq/topics/virtual

As for 3D EM stuff Ac :) read the comments closely and you will find descriptions of the different 'fields' assumed to exist.
 

Offline lightarrow

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Hey,
Don't follow all what you write.....but one essence is that there are a lot of phenomenon;
interactions between particles (with "virtual particles"), electric force of an electron (that is influenced by a cloud of "virtual particles"), and many more.
They are solved mathematically, and then this solutions can be built on different "explanations" although presently no-one has been able in experiments to verify any of
the explanations (so-far at least). All the explanations has pros and cons, are mostly theoretically possible, and the future will show us the answer.
If I'm totally wrong - bring it easy on me - otherwise my already bad self-esteem in this subject will suffer more :-)
Maybe, but the explanation which makes use of virtual particles it's not totally equivalent to the other which don't, for the following reason:
a free real particle with mass m, momentum p and energy E, obeys the equation

E2 = (cp)2 + (mc2)2

A virtual particle doesn't.
« Last Edit: 04/11/2012 18:51:44 by lightarrow »
 

Offline JP

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True, lightarrow, but the way I've understood it is that it's a continuum from virtual particles which can be off shell (violating that equation) to real particles which have negligible probability of being off shell.  This seems very similar to the way in which small objects show quantum-ness, while large objects don't, even though all objects should obey the rules of quantum mechanics.

Or put another way, don't the same underlying equations govern virtual and real particles?  The only difference being whether you can make certain approximations corresponding to "real-ness" in the real particle case?

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

Offline pinballed

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Thank you very much for the explanations.


Thanks,
Magnus
 

Offline lightarrow

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True, lightarrow, but the way I've understood it is that it's a continuum from virtual particles which can be off shell (violating that equation) to real particles which have negligible probability of being off shell.  This seems very similar to the way in which small objects show quantum-ness, while large objects don't, even though all objects should obey the rules of quantum mechanics.

Or put another way, don't the same underlying equations govern virtual and real particles?  The only difference being whether you can make certain approximations corresponding to "real-ness" in the real particle case?
Unfortunately I'm not so expert in virtual particles to provide a definite answer  :)  I see the being "off shell" of a particle as I see the electron in the H atom being prevented to stay between two near orbitals; but maybe it's you which is correct.
 

Offline JP

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True, lightarrow, but the way I've understood it is that it's a continuum from virtual particles which can be off shell (violating that equation) to real particles which have negligible probability of being off shell.  This seems very similar to the way in which small objects show quantum-ness, while large objects don't, even though all objects should obey the rules of quantum mechanics.

Or put another way, don't the same underlying equations govern virtual and real particles?  The only difference being whether you can make certain approximations corresponding to "real-ness" in the real particle case?
Unfortunately I'm not so expert in virtual particles to provide a definite answer  :)  I see the being "off shell" of a particle as I see the electron in the H atom being prevented to stay between two near orbitals; but maybe it's you which is correct.

That might be right, too.  Orbitals extend way out beyond the edges shown in textbooks--it's just a vanishingly small probability that the electron would occupy those points in space.
 

Offline sciconoclast

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Feynman diagrams usually produce a large number of probable out comes for particle collision of which only a small amount actually occur. Several scientist working in collaboration at the Hadron Collider found that they could reduce the possible outcomes to only those that actually occurred by removing the virtual particles from the process. I think this will ultimately lead to revisions in Standard Theory which will allow the transfer of force through space without virtual particles. Easy reading: Loops, Trees and the Search for New Physics; Scientific American, page 38, May 2012.  More detailed reading: Precise Predictions for w+4 Jet Production at the Large Hadron Collider. Physical Review Letters.       
 

Offline yor_on

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thanks for that one Scico.

"It turns out that the Feynman method is really an elaborate way for essentially brute-forcing a solution.  If what you're treying to calculate, the metaphor goes, is the ways that a person could get from one given station on the London Underground to another, it calculates not only the valid methods of movement through the system, but also all of the impossible ones, throuhg the solid rock or earth beneath London.  Most of the possibilities that end up being calculated end up canceling out with each other, or simplifying down, but you still need them for the intermediary Feynman calculations.  The three gentlemen who wrote this article, however, have resurrected an old idea from the '60s, and developed it into a theory that they call the "unitarity" method 

What it does, is it assumes that the total probability of every possibility will equal 100%, and it calculates things by breaking them down into smaller steps, essentially finding the probabilities that a person riding the London Underground will go through a given turnstyle next, rather than trying to calculate their entire route at once.  Not only has this method been used to refine the LHC results recently, but they've also resurrected Supergravity theory with it.  It was previously thought that Supergravity theory entailed too many ever-spiraling infinities in the quantum foam to possibly be correct, but it turns out that, upon refinement with the unitarity theory, these infinities cancel out.  They are able to calculate particle collisions that would traditionally require the calculation of 10^30 terms by only calculating a few dozen terms. They have already won several bottles of wine as bets from other physicists that they won't be able to correctly calculate things with their theory are proven wrong time and time again.  They conclude by commenting that they are on the verge of solving 7 gluon interaction, and that, if this works, supergravity may be seen as alive and well, and well on the road to finding a quantum theory of gravity.  They comment also that gravitons, under their model, are predicted to interact simply like a pair of three-gluon conglomerates." from
Advanced Science Study.
 

Offline yor_on

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So what both methods presume is causality chains existing, although they have two ways to get there from probability. And that is the question.

What makes causality chains?
 

Offline JP

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I think Yor_on's post sums it up well: they haven't thrown out Feynman's path integral method, but they've figured out ways to refine it and to make approximations to allow the computations to be done quickly and accurately.

I don't think the theory in itself will change anything about the way forces are transmitted, since it doesn't disagree with Feynman's predictions, but it might allow new techniques to be developed because it allows us to do previously intractable computations.
 

Offline yor_on

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This one should be read too. It's about 'super gravity' becoming a outgrowth/principle of 'super symmetry'. The idea that everything has a 'partner' of sorts, for fermions as 'matter' becoming some 'boson' etc. So for each new particle found at LHC it then should mean that there is some balance, a 'opposite mirror' that must exist according to super symmetry, all as I interpret it. And if you combine (Einsteins) 'symmetries' with GR you get to 'super gravity' as a hypothesis. But what it is as a 'field' I'm not sure, it doesn't seem to fit our descriptions of 'forces' at least, as something resembling a EM-field? Then again, it's all seems observer dependent if you go by Einstein. Take a look at  Viewpoint: Vanquishing infinity.
 

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