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Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: syhprum on 02/04/2019 10:45:52

Title: How long does a virtual photon exist ?
Post by: syhprum on 02/04/2019 10:45:52
We are told that the force between charged particle is mediated by virtual photons that spring into existence "instantly" and are then annihilated.
How long does this take is it less than the Planck time 10^-43 sec ?   
Title: Re: How long does a virtual photon exist ?
Post by: Kryptid on 02/04/2019 14:27:55
I'm pretty sure the lifetime is inversely proportional to energy due to the uncertainty principle.
Title: Re: How long does a virtual photon exist ?
Post by: syhprum on 03/04/2019 11:53:10
My evil doppelganger has made an identically named post but has been banished to the hogwash sector 
Title: Re: How long does a virtual photon exist ?
Post by: charlatan on 03/04/2019 13:20:46
I was of the belief that the difference between real and virtual particles is that real particles are released into the environment and consequently detectable and virtual particles are equation balancers - with an undetected direct exchange that must have happened between interacting particles for their final states to be consistent. As an analogy, passing a baton to someone is a virtual exchange, throwing it to them is real - so that the baton is capable of being detected before it is otherwise absorbed. In this sense virtual particles are instantaneously exchanged because there is no travel time.
 ;) Anyone got directions to the 'hogwash sector'.
Title: Re: How long does a virtual photon exist ?
Post by: syhprum on 03/04/2019 14:03:14
Hogwash was the answer that the bored chemist gave to a post with a similar title to mine by esquire which had been moved to the new theories section.
Virtual photons mediate action at a distance and come into play for instance when one magnet or electrically charged body attracts another hence they must have a non zero lifetime else their speed  would be infinite 
Title: Re: How long does a virtual photon exist ?
Post by: Bill S on 03/04/2019 14:13:17
Here's another refugee from the 'hogwash sector'.

Hitch-hikers’ Guide to Virtual Particles.

A virtual particle is a “particle” that is not a particle at all.  It mediates an interaction between charged particles. 

Quantum theory tells us that virtual particles are appearing and disappearing in vast numbers, all the time, in the vacuum.  They must be “something”; but what?   They are disturbances in fields that are never found in isolation.  They result from the presence of other particles, or fields.

A virtual particle mediates an interaction.  Presumably, this interaction occurs in time, but is often described as being “instantaneous”.  This must involve looking at the concept of instantaneous speed.  When the speed of an object is changing constantly, its instantaneous speed is its speed at a particular instant in time.  (Charlatan's baton handover?) This “instant” is a dimensionless point on a time-line.  It is part of the scenario of time, but does not include the concept of duration.

Is this idea of “time that is not really time” something of which we have any experience?

The present is an instant in time that is notoriously difficult to pin down; it, too, lacks duration; yet, according to Marcus Aurelius, it is the sum-total of each of our lives. “No man liveth more than that infinitesimal point of time that is the present”.

Trying to measure an instant is problematic.  Planck time is only a convenient measure, it is not a physical limit, it is not an effective “tool” with which to try to measure an instant.  In fact, there is nothing with which we can physically measure an instant; yet it occurs frequently in physics.  Possibly we should stop fretting about the nature of an instant, or the present.  Like time, itself, we all know what these terms mean, unless we try to explain them to someone. 

Time, an instant, the present, a virtual particle; they are all simplifications that are used to aid our understanding of complex topics.  Generally, trying to make them into anything else leads into metaphysics or philosophy.  “Shut up and calculate”. :)
Title: Re: How long does a virtual photon exist ?
Post by: Bill S on 03/04/2019 14:23:41
Quote from: Syphrum
Virtual photons mediate action at a distance and come into play for instance when one magnet or electrically charged body attracts another hence they must have a non zero lifetime else their speed  would be infinite

Sorry! I posted without reading this.  I'll have to give some thought to the distance/lifetime relationship to see if that blows the first hole in my "guide".  :)
Title: Re: How long does a virtual photon exist ?
Post by: esquire on 03/04/2019 16:36:29
My evil doppelganger has made an identically named post but has been banished to the hogwash sector

posted an answer to your thread. colin deemed it appropriated to remove my post from your thread and create a new thread under my name in the new theory section. advise you to take it up with colin if you have an issue. 
Title: Re: How long does a virtual photon exist ?
Post by: flummoxed on 03/04/2019 16:47:20
The term virtual particle has different meanings. From the HUP they exist everywhere, and is evidenced by the Casimir force. Other forms of Virtual particles are perhaps theoretical and just equation balancers. Feynman diagrams for instance use virtual particles, do these exchange particles actually exist. https://en.wikipedia.org/wiki/Virtual_particle and can they be detected.

Title: Re: How long does a virtual photon exist ?
Post by: Bill S on 03/04/2019 20:18:32
Quote from: Flummoxed
The term virtual particle has different meanings. From the HUP they exist everywhere, and is evidenced by the Casimir force.

My understanding is that what Casimir showed was the reality of quantum fluctuations in the vacuum, and that the wave interpretation of these fluctuations was essential to the success of the experiment.  If one chooses to describe these “waves” as particles, so be it, but there are some things worth considering.

https://www.quora.com/What-are-virtual-particles-in-laymans-terms-What-do-they-provide-What-is-their-significance

Quote
Virtual particles are, in principle, mathematical artifacts invented for the purpose of calculations of interactions between particles…………… If you don't use perturbation theory, then you don't need virtual particles at all.
Title: Re: How long does a virtual photon exist ?
Post by: flummoxed on 04/04/2019 01:03:17
Quote from: Flummoxed
The term virtual particle has different meanings. From the HUP they exist everywhere, and is evidenced by the Casimir force.

My understanding is that what Casimir showed was the reality of quantum fluctuations in the vacuum, and that the wave interpretation of these fluctuations was essential to the success of the experiment.  If one chooses to describe these “waves” as particles, so be it, but there are some things worth considering.

https://www.quora.com/What-are-virtual-particles-in-laymans-terms-What-do-they-provide-What-is-their-significance

Quote
Virtual particles are, in principle, mathematical artifacts invented for the purpose of calculations of interactions between particles…………… If you don't use perturbation theory, then you don't need virtual particles at all.

That quora link has multiple versions of what virtual particles are and one I did not know off, which might be wrong, I don't know. It claims it is the real particles that don't exist and only virtual particles exist some on shell and others off shell.

Zero point energy is another term with different meanings for people, but this is based on virtual particles/quantum fluctuations. https://en.wikipedia.org/wiki/Zero-point_energy . Even if you do not use perturbation theory, these virtual particles still exist. Hawking radiation is based on virtual particles as is the Unruh effect.
From the wiki link I posted above.
Virtual particles do not necessarily carry the same mass as the corresponding real particle, although they always conserve energy and momentum. The longer the virtual particle exists, the closer its characteristics come to those of ordinary particles.
Is this a case where the term virtual particle has changed its meaning or has been hijacked, over the years.? Can we safely use the term virtual particle to mean that which comes from the HUP evidenced by the Casimir effect, and as a math thing in pertubation theory that doesnt exist.
Title: Re: How long does a virtual photon exist ?
Post by: charlatan on 04/04/2019 13:51:41
Virtual photons mediate action at a distance and come into play for instance when one magnet or electrically charged body attracts another hence they must have a non zero lifetime else their speed  would be infinite

'Action at a distance' is a just another concept - like dark matter - whose name explains the inexplicable mechanism at work. It, dark matter and a host of other concepts, i.e. virtual particles, are waiting for scientific development to unravel their nature. They are 'apparent' concepts - meaning "it's as if the objects are interacting at a distance" or "it's as if there is far more matter in the galaxy than can be seen". Just waiting for Newton 2.0. As a matter of interest here's what he said to a friend on the matter - "so that one body may act upon another at a distance through a vacuum, without the mediation of anything else, by and through which their action and force may be conveyed from one to another, is to me so great an absurdity that I believe no man who has in philosophical matters a competent faculty of thinking can ever fall into it. - Sir Isaac Newton. I, personally, concur.

Further, 'action at a distance' violates special relativity - in that information under this premise is capable of propagating at speeds faster than the speed of light. Nevertheless, experiments are being conducted that suggest action at a distance - but there is even some debate about the appropriateness of the research methodology. Here are the 2 links from Science News;

https://www.sciencenews.org/blog/context/entanglement-spooky-not-action-distance?mode=blog&context=117

https://www.sciencenews.org/blog/context/quantum-spookiness-survives-its-toughest-tests?mode=blog&context=117

The concept of field eventually 'moved in' to replace action at a distance but with no clearer idea of the mechanisms at work. Virtual photons, themselves are controversial, and would not be required - in the 'field' example you posit - when considering the nature/structure of spacetime - which displays continuous changing (warping) structure as we move away from the mass around which it is considered and where gravitational influence is communicated in the same way, diminishing with distance. Spacetime is very much like...dare I say...the aether it replaced. It's just different nomenclature. Of course, the true nature of spacetime is no more well understood as a mechanism than dark matter but, for me at least, the less clutter, the better.

BTW - how many posts before a newbie can start a topic?
Title: Re: How long does a virtual photon exist ?
Post by: flummoxed on 04/04/2019 17:36:38

BTW - how many posts before a newbie can start a topic?

You can start a thread straight away, which should be phrased as a question. Or if you have a new theory you can start a thread in new theories section.
Title: Re: How long does a virtual photon exist ?
Post by: Bill S on 07/04/2019 12:36:43
Quote from: Syphrum
Virtual photons mediate action at a distance and come into play for instance when one magnet or electrically charged body attracts another hence they must have a non zero lifetime else their speed  would be infinite
   
I’ll try an addition to the following, to see what the experts think of that.

Quote from: Bill
A virtual particle mediates an interaction.  Presumably, this interaction occurs in time, but is often described as being “instantaneous”.  This must involve looking at the concept of instantaneous speed.  When the speed of an object is changing constantly, its instantaneous speed is its speed at a particular instant in time.  This “instant” is a dimensionless point on a time-line.  It is part of the scenario of time, but does not include the concept of duration. 

Of course, there’s a complication here. 

Virtual photons mediate action at a distance, as between two magnets.  To do this, they must have a non-zero lifetime or their speed would be infinite.  Their speed is “c”, so it is constant. A shorter lifetime, therefore, equates to a more restricted range of influence.

If the lifetime of a virtual particle is inversely proportional to its energy, it must follow that the higher the energy of the particle, the shorter its effective range of mediation would be, but, even at the highest possible energy, the lifetime would be non-zero.  It might be reasoned that infinite energy would equate to zero lifetime.  Effectively, zero lifetime would equate to non-existence; so even if the “impossibility” of achieving infinite energy were overcome, this idea would be a non-starter.

None of this serves to identify the mediating “influence” as a particle.  It is a vacuum fluctuation, and the Casimir effect demonstrates that these fluctuations must have qualities we would identify as waves.  Wave/particle duality suggests that we should also expect them to behave as particles, in the right circumstances.  This sounds very much like "real" particles; so, are virtual particles actually particles, or not?

The question: “is it a wave or a particle?” is famously difficult to answer, and often leads to the opinion that “it” is neither a wave, nor a particle, but something of which we have no practical knowledge.

It seems that all we can say, at this juncture, is that the Universe is permeated by fields.  These fields are subject to disturbances.  We perceive the disturbances as having wave-like qualities, but we can also consider them as particles.  In some cases, we can assess these particles as showing permanence, as travelling through space and as reacting with one another. These reactions are such that the mathematics describing them is the same as the mathematics that would describe the exchange of a particle.  The mathematics is most easily understood if expressed in terms of this conceptual particle exchange, and the model can be developed from there.  Essentially, this is the process of applying perturbation theory to a quantum field. Thus, the virtual particle becomes a “representation” within this process. 
Title: Re: How long does a virtual photon exist ?
Post by: yor_on on 16/04/2019 18:09:48
As far as I know a virtual particle should be under Plank time? If it wasn't wouldn't you have to call it 'real'? Then again, maybe it can 'exist' over that threshold but then I think physics would need to define where a 'perfect instrument' will fail to measure it. It's a pretty good question actually.
Title: Re: How long does a virtual photon exist ?
Post by: yor_on on 16/04/2019 18:23:25
Syphrum. If a 'virtual particle' can be allowed a 'infinite energy' maybe a 'infinite speed' is a possibility too, as long as it doesn't violate HUP. Kryptid wrote something interesting about that I think.

Then again :)
https://physics.stackexchange.com/questions/291553/how-long-can-a-virtual-particles-exist-in-a-vacuum-state

And http://math.ucr.edu/home/baez/uncertainty.html
Title: Re: How long does a virtual photon exist ?
Post by: flummoxed on 16/04/2019 18:26:09
I'm pretty sure the lifetime is inversely proportional to energy due to the uncertainty principle.

Can we really be certain about the uncertainty principle :)

Here is what prof Matt Strasslerr has to say on virtual particles. https://profmattstrassler.com/articles-and-posts/particle-physics-basics/virtual-particles-what-are-they/
Title: Re: How long does a virtual photon exist ?
Post by: flummoxed on 16/04/2019 18:28:55
As far as I know a virtual particle should be under Plank time? If it wasn't wouldn't you have to call it 'real'? Then again, maybe it can 'exist' over that threshold but then I think physics would need to define where a 'perfect instrument' will fail to measure it. It's a pretty good question actually.


Relativistic speaking if a virtual particle can be accelerated to c it would not experience time.
Title: Re: How long does a virtual photon exist ?
Post by: yor_on on 16/04/2019 18:32:36
Now that's about 'existing 'real' photons' methinks, not virtual.  It's a time energy relationship in one way, and as long as it doesn't pass the door into what we define as measurably real it can have all kind of 'unrealistic' values it seems.
Title: Re: How long does a virtual photon exist ?
Post by: flummoxed on 16/04/2019 18:43:21
As far as I know a virtual particle should be under Plank time? If it wasn't wouldn't you have to call it 'real'? Then again, maybe it can 'exist' over that threshold but then I think physics would need to define where a 'perfect instrument' will fail to measure it. It's a pretty good question actually.

Relativistic speaking if a virtual particle can be accelerated to c it would not experience time.

OK  lets look at a magnetic field, it is explained by virtual photons. We can see magnetic field lines in kinder garden experiments with magnets and iron filings.
Title: Re: How long does a virtual photon exist ?
Post by: yor_on on 16/04/2019 18:44:52
The way 'I read Matt Strassler I sincerely doubt he being unsure of the uncertainty principles existence. What he discuss there isn't whether HUP exist, it's about how to see a 'virtual particle'.
Title: Re: How long does a virtual photon exist ?
Post by: flummoxed on 16/04/2019 18:49:34
The way 'I read Matt Strassler I sincerely doubt he being unsure of the uncertainty principles existence. What he discuss there isn't whether HUP exist, it's about how to see a 'virtual particle'.

That was meant as a joke, are you certain about the uncertainty principle. Ha Ha
Title: Re: How long does a virtual photon exist ?
Post by: yor_on on 16/04/2019 18:50:43
Actually they are 'mediators' in almost anything :) Then again, you shouldn't take that as if this is the last truth of it. Try this one and see how Martin think about it. https://physics.stackexchange.com/questions/82298/virtual-photons-as-force-mediators-in-qed-really
Title: Re: How long does a virtual photon exist ?
Post by: yor_on on 16/04/2019 18:58:20
Ah, I connected the two sentences you wrote into one statement. Sorry, sometimes I miss out on the subtleties.
Title: Re: How long does a virtual photon exist ?
Post by: yor_on on 16/04/2019 19:11:50
What is slightly confusing when using a 'field approach' instead of perturbation theory is that if you have a 'field touching a field' you would expect some time to pass before a 'signal' has been received between them. But if a 'virtual particle' indeed is 'instantaneous' (Under Planck time) then the 'fields' exchange becomes , lets call it, slightly weird :) FTL, sort of ...
Title: Re: How long does a virtual photon exist ?
Post by: flummoxed on 16/04/2019 19:14:03
Actually they are 'mediators' in almost anything :) Then again, you shouldn't take that as if this is the last truth of it. Try this one and see how Martin think about it. https://physics.stackexchange.com/questions/82298/virtual-photons-as-force-mediators-in-qed-really

I think there is some confusion here, virtual particles exist and have a life time. Virtual photons might not exist and are a thing in pertubation theory, which gives accurate results.

All things are quantum fluctuations of one kind/shape or another. It is the life time, shape, intensity, and effect of quantum fluctuations that dictate what they are.

Virtual particles as predicted by the HUP and demonstrated by the Casimir effect, and more recently dynamic casimir effect, are not the virtual photons of pertubation theories. 


Title: Re: How long does a virtual photon exist ?
Post by: flummoxed on 16/04/2019 19:19:13
What is slightly confusing when using a 'field approach' instead of perturbation theory is that if you have a 'field touching a field' you would expect some time to pass before a 'signal' has been received between them. But if a 'virtual particle' indeed is 'instantaneous' (Under Planck time) then the 'fields' exchange becomes , lets call it, slightly weird :) FTL, sort of ...
Is that called spooky action at a distance. Or is the virtual photon in perturbation theory imaginary and a mathematical construct, that just happens to fulfil what is required by observations and the math. Perhaps there is another explanation/interpretation.


Title: Re: How long does a virtual photon exist ?
Post by: yor_on on 16/04/2019 19:22:44
Perturbation theory is a approximation done by relating a complex problem you have to a similar solvable, using it as a stepping stone for the one you try to solve. https://en.wikipedia.org/wiki/Perturbation_theory
Title: Re: How long does a virtual photon exist ?
Post by: yor_on on 16/04/2019 19:24:31
And yes, maybe it is a sort of spooky action over a distance? I don't know, but I would like to know :)
Title: Re: How long does a virtual photon exist ?
Post by: yor_on on 16/04/2019 19:27:21
One way would be to define time as scale dependent. On very small scales it breaks down, in a similar fashion to the way decoherence is thought to exist.
=

Sorry, not time itself, but the clock.
Title: Re: How long does a virtual photon exist ?
Post by: flummoxed on 17/04/2019 10:43:11
One way would be to define time as scale dependent. On very small scales it breaks down, in a similar fashion to the way decoherence is thought to exist.

Here is three quick discussions and points of view on space time. I am currently interested in all things emergent, including space time, but it covers the others as well https://motls.blogspot.com/2004/10/emergent-space-and-emergent-time.html here is a slightly longer link searching arxiv throws up too many papers to read http://thediagonal.com/2012/05/02/spacetime-as-an-emergent-phenomenon/
Title: Re: How long does a virtual photon exist ?
Post by: yor_on on 17/04/2019 17:53:18
It's nice thoughts Flummoxed, But in the end there are two choices.
Something comes from nothing.
Or something needs something else

Which one do you think is more correct?
Title: Re: How long does a virtual photon exist ?
Post by: yor_on on 17/04/2019 17:56:26
Choosing the first one is defining a universe without a beginning
the second one is creating a never ending loop
Title: Re: How long does a virtual photon exist ?
Post by: flummoxed on 17/04/2019 18:06:08
It's nice thoughts Flummoxed, But in the end there are two choices.
Something comes from nothing.
Or something needs something else

Which one do you think is more correct?

There is always a third option :)

Which one of your choices is closest to space expands due to dark energy which isn't really energy because its only borrowed via the HUP. Inadvertently this causes inflation, and the hot big bang etc The universe happened because there was no alternative. It happened from nothing in a zero energy universe.