Debunking the Existence and Duration of Virtual Particles

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The discussion centers around the existence and interpretation of virtual particles in quantum field theory (QFT). Participants debate whether virtual particles are merely mathematical constructs or if they have some form of reality, with some arguing that they are essential for calculations in QFT, while others assert they are not needed for theoretical explanations. The concept of existence is challenged, with claims that both existence and nonexistence of virtual particles are subjective interpretations rather than definitive scientific claims. The Casimir effect is mentioned as a phenomenon that may or may not require virtual particles for explanation, further complicating the discussion. Ultimately, the consensus leans towards skepticism about the physical reality of virtual particles, emphasizing the need for empirical evidence to support their existence.
  • #91
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  • #92
byron178 said:
are you guys arguing as to if virtual particles exist? i keep reading different respones and have read different articles one by gordon kane where he claims they are real. http://www.scientificamerican.com/article.cfm?id=are-virtual-particles-rea

Yes, this thread is about the reality of virtual particles. That article was already posted, and it is flawed.
 
  • #93
tiny-tim said:
so that an energetic enough photon can knock the W out, leaving the neutron, and someone asks him (around 1:03) whether that means the W was already there, and he replies
"your mental picture that whatever comes out of a system was in there beforehand is a little bit defective!"​

But it means that before you knock out the W, there was "something" and that "something" somehow become a real W boson. This "something" is actually what we call virtual W and it's a matter of how you define things in physics.


tiny-tim said:
the only unequivocal thing he says is (at the very start) that "virtual particles are mathematical constructs" :smile:

I think he means that virtual particles are described by mathematics (at the way they are described in perturbation theory).
 
  • #94
maxverywell said:
But it means that before you knock out the W, there was "something" and that "something" somehow become a real W boson. This "something" is actually what we call virtual W and it's a matter of how you define things in physics.




I think he means that virtual particles are described by mathematics (at the way they are described in perturbation theory).

are you saying virtual particles exist?
 
  • #95
maxverywell said:
But it means that before you knock out the W, there was "something" and that "something" somehow become a real W boson. This "something" is actually what we call virtual W and it's a matter of how you define things in physics.

That's not what he said. At first he states that it is a mathematical construct. Later he goes on to explain that even if it was really there, it wouldn't be detectable because we couldn't distinguish the detection from the creation of an actual particle.
 
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  • #96
Polyrhythmic said:
That's not what he said. At first he states that it is a mathematical construct. Later he goes on to explain that even if it was really there, it wouldn't be detectable because we couldn't distinguish the detection from the creation of an actual virtual particle.

So even if they were real we would not be able to detect them?
 
  • #97
byron178 said:
So even if they were real we would not be able to detect them?

By definition. However, I'm afraid we've high-jacked the thread from you. You'll never really be able to get a handle on what the issue we're discussing is without actually knowing physics. SciAm and science popularizer books essentially throw out damn near everything important to relate things in an "intuitive" analogy with the real world.

As for the rest of you guys, I'd re-iterate that feynman diagrams (and thus a virtual particle picture of QFT) MISS certain physics. I don't see how this doesn't seal the issue. We have an integral, we want to perform a functional integration on it. We can't, so we move to a perturbation approach, from this comes the calculational TOOL of virtual particles. Because we're working perturbatively we miss certain things (which essentially means such things are unexplainable via virtual particles). From this we conclude that virtual particles are real physics?! Where do we go next? When we don't know the ground state of the system so we try a trial wave-function parameterized by some variable lambda (i.e. a variational approach) and we minimize with respect to lambda and call the lowest state the ground-state. We then find out that our ground-state wasn't of the form we guessed but we were kind of close. From this you're saying we conclude that our variational lambda is a REAL degree of freedom of the system? If I have 3 apples do I really have 6 apples plus 3 negative-apples?
 
  • #98
maverick_starstrider said:
By definition. However, I'm afraid we've high-jacked the thread from you. You'll never really be able to get a handle on what the issue we're discussing is without actually knowing physics. SciAm and science popularizer books essentially throw out damn near everything important to relate things in an "intuitive" analogy with the real world.

As for the rest of you guys, I'd re-iterate that feynman diagrams (and thus a virtual particle picture of QFT) MISS certain physics. I don't see how this doesn't seal the issue. We have an integral, we want to perform a functional integration on it. We can't, so we move to a perturbation approach, from this comes the calculational TOOL of virtual particles. Because we're working perturbatively we miss certain things (which essentially means such things are unexplainable via virtual particles). From this we conclude that virtual particles are real physics?! Where do we go next? When we don't know the ground state of the system so we try a trial wave-function parameterized by some variable lambda (i.e. a variational approach) and we minimize with respect to lambda and call the lowest state the ground-state. We then find out that our ground-state wasn't of the form we guessed but we were kind of close. From this you're saying we conclude that our variational lambda is a REAL degree of freedom of the system? If I have 3 apples do I really have 6 apples plus 3 negative-apples?

that's ok,what i want to know is when something travels faster than light will it start traveling backwards in time?will it travel for example today to yesterday?
 
  • #99
maverick_starstrider said:
BTW, If you want to talk about heavy-hitters and there opinions here's a lecture I was just watching by Anthony Zee (of "Quantum Field Theory in a Nutshell" fame)

http://v.youku.com/v_show/id_XMTE0OTI4Nzg0.html

Check around the 45 minute mark. He goes on to talk about how the concept of Feynman Diagrams (i.e. virtual particles) "shackled" the study of QFT for quite some time. it wasn't until people like t'Hooft pointed out that there exist phenomena (such as magnetic monopoles) that CANNOT be described through the perturbative framework that virtual particles represent, that QFT began to free itself from the "shackles of Feynman Diagrams". Putting words in his mouth a bit he's basically saying that not only are these perturbation not real things but for a 30 year stretch or so they were blinding people to the real physics by taking these things too seriously.

It's interesting to hear that t'Hooft said that. I had a quick look at Veltmann's QFT text the other day and he seemed to argue the the old-fashioned view that QFT is essentially a tool for deriving Feynman rules in the absence of a better alternative!

Regarding popularising science: when I explain what my PhD is on to people who know nothing about physics, I'll tell them that the modern understanding of forces between two interacting objects involves particles being exchanged between them. I usually won't tell them that any real physical system that bears any relation to what we think of as a particle exists only to the extent that interactions can be neglected. Popular accounts mean nothing.
 
  • #100
byron178 said:
that's ok,what i want to know is when something travels faster than light will it start traveling backwards in time?will it travel for example today to yesterday?

Nothing can travel faster than light, our theoretical framework does not permit such a process. Therefore the best answer would be "no".
 
  • #103
maverick_starstrider said:
As for the rest of you guys, I'd re-iterate that feynman diagrams (and thus a virtual particle picture of QFT) MISS certain physics. I don't see how this doesn't seal the issue. We have an integral, we want to perform a functional integration on it. We can't, so we move to a perturbation approach, from this comes the calculational TOOL of virtual particles. Because we're working perturbatively we miss certain things (which essentially means such things are unexplainable via virtual particles). From this we conclude that virtual particles are real physics?! Where do we go next? When we don't know the ground state of the system so we try a trial wave-function parameterized by some variable lambda (i.e. a variational approach) and we minimize with respect to lambda and call the lowest state the ground-state. We then find out that our ground-state wasn't of the form we guessed but we were kind of close. From this you're saying we conclude that our variational lambda is a REAL degree of freedom of the system? If I have 3 apples do I really have 6 apples plus 3 negative-apples?


These were excellent points. But, a problem still remains.

You don't often here people claiming that the variational lambda is a REAL degree of freedom of the system. Nor, do you hear people talking as if negative-apples exist in reality.

But, you always see physicists speaking (perhaps colloquially), as if virtual particles do in fact exist.

Also, there seems to be a lack of consensus on whether or not virtual particles are "real" amongst the top minds in physics, as was evident on another PF thread. The same can't be said about "negative-apples".

Not too long ago, I posted a recent example of this dealing with the dynamic casimir effect:

https://www.physicsforums.com/showthread.php?t=503456

If virtual particles are indeed NOT real, none of this is helping matters
 
  • #104
Born2bwire said:
No, it does not.

No doubt, we cannot send a signal faster than light utilizing entangled particles. Nature prevents that from happening.

BUT, how do we explain the apparent "instantaneous" connection between the two entangled particles?

It almost appears that some sort of "information" has traveled between the two, during a measurement. After all, a connection implies some type of information transfer.
 
  • #105
byron178 said:
ive been reading on this forum that virtual particles flat out don't exist?then why is it said they exist for a certain amount of time?

Virtual particles are real, they just exist for very short periods of time. It's a myth really to say virtual particles aren't really real, as they do contribute to real things in the outside world, such as the stability of a Hydrogen Atom.
 
  • #106
dm4b said:
No doubt, we cannot send a signal faster than light utilizing entangled particles. Nature prevents that from happening.

BUT, how do we explain the apparent "instantaneous" connection between the two entangled particles?

It almost appears that some sort of "information" has traveled between the two, during a measurement. After all, a connection implies some type of information transfer.

Or classical measurements don't exist and we join the superposition.
 
  • #107
maverick_starstrider said:
Or classical measurements don't exist and we join the superposition.

Sounds interesting maverick_starstrider. Please explain more!
 
  • #108
dm4b said:
Sounds interesting maverick_starstrider. Please explain more!

Well it's just that most interpretation have the fundamental flaw that they treat measurement as a classical event external to your quantum wavefunction. In reality quantum would suggest that when one makes a measurement one's "measurement Hilbert space" becomes entangled with the state vector/wavefunction of the system you were measuring.
 
  • #109
dm4b said:
No doubt, we cannot send a signal faster than light utilizing entangled particles. Nature prevents that from happening.

BUT, how do we explain the apparent "instantaneous" connection between the two entangled particles?

It almost appears that some sort of "information" has traveled between the two, during a measurement. After all, a connection implies some type of information transfer.

How about by starting by saying the connection was there all along previous the observation? A deterministic universe resolves the EPR paradox.
 
  • #110
Goldstone1 said:
… they do contribute to real things in the outside world, such as the stability of a Hydrogen Atom.

uhh? :redface:

how? :confused:​
 
  • #111
Goldstone1 said:
How about by starting by saying the connection was there all along previous the observation? A deterministic universe resolves the EPR paradox.

Without some higher level machinery a "deterministic" universe is non-local (via Bell's Inequalities) which gets you right back to "spooky action at a distance".
 
  • #112
dm4b said:
These were excellent points. But, a problem still remains.

You don't often here people claiming that the variational lambda is a REAL degree of freedom of the system. Nor, do you hear people talking as if negative-apples exist in reality.

But, you always see physicists speaking (perhaps colloquially), as if virtual particles do in fact exist.

Also, there seems to be a lack of consensus on whether or not virtual particles are "real" amongst the top minds in physics, as was evident on another PF thread. The same can't be said about "negative-apples".

Not too long ago, I posted a recent example of this dealing with the dynamic casimir effect:

https://www.physicsforums.com/showthread.php?t=503456

If virtual particles are indeed NOT real, none of this is helping matters

Well, in reality most physicists subscribe to the David Mermin interpretation of Quantum Mechanics which essentially consists of just one sentence:

"Shut up and calculate!"

When asked or polled they'll often just say the Copenhagen Interpretation (which is really very incorrect given the original meaning of the interpretation) because that's sort of a code word among physicists that means "*shrug* I don't really care". Similarly, a lot of physicists look at QFT as essentially the physics of Feynman Diagrams because that's how you really get any experimentally verifiable numbers out of it. So I think a lot of physicists would just off the cuff say "*shrug*, Feynman Diagram's represent real physics, why not, it doesn't really make a difference to me". And as I mentioned earlier this outlook led things astray for awhile (or so Zee claims, I'm not particularly knowledgeable about the history of QFT).

So I think the default position amongst working physicists is to just say Copenhagen Interpretation and Feynman Diagrams are real because this is sort of a code for "I really don't care about the Ontology of physics, since that way leads to madness and no remotely appliable (or publishable) results". You'd be surprised how few physicists give any thought to interpretation at all, the reason being it doesn't really make a difference and it's not going to help your career. But at the end of the day the concept of virtual particles has its origin in a mathematical crutch which has been shown to be less than perfect. It's really directly analogous to the role of perturbation in quantum mechanics, it's only good for catching perturbing potentials, if the perturbation is large (or the x^4 term of your QFT is large) your whole perturbation/virtual particle interpretations is going to be wrong, and that's known from the get go. That alone makes the Ontological notion of taking them as real to be crazy IMHO.
 
  • #113
Goldstone1 said:
Virtual particles are real, they just exist for very short periods of time. It's a myth really to say virtual particles aren't really real, as they do contribute to real things in the outside world, such as the stability of a Hydrogen Atom.

Feynman diagrams are needed to CALCULATE the stability of the Hydrogen Atoms. Non-relativistic perturbation theory is needed to CALCULATE the Zeeman effect but people don't go around saying that in the Zeeman effect the electron-magnetic field interaction is simultaneously propagating from the ground-state to all of the infinite energy levels of the system. Yet, that's a physical interpretation of the first-order correction in perturbation theory.

When we calculate the classical energy of an electron (at r0) given another electron at say r1 we integrate from r=infinity to r0. Is the reality of this math that this electron was ACTUALLY shipped in from infinity? Did the universe like FedEx it or something?
 
  • #114
maverick_starstrider said:
Feynman diagrams are needed to CALCULATE the stability of the Hydrogen Atoms. Non-relativistic perturbation theory is needed to CALCULATE the Zeeman effect but people don't go around saying that in the Zeeman effect the electron-magnetic field interaction is simultaneously propagating from the ground-state to all of the infinite energy levels of the system. Yet, that's a physical interpretation of the first-order correction in perturbation theory.

When we calculate the classical energy of an electron (at r0) given another electron at say r1 we integrate from r=infinity to r0. Is the reality of this math that this electron was ACTUALLY shipped in from infinity? Did the universe like FedEx it or something?

I'm unsure of what you are implying here. Are you asking about the infinite energy solutions to electrons?
 
  • #115
Goldstone1 said:
I'm unsure of what you are implying here. Are you asking about the infinite energy solutions to electrons?

What? no. I'm pointing out that taking the physical interpretation of perturbation theory calculations in regular quantum mechanics as "real" is silly and no-one does it. When calculating the configurational energy of a classical EM system we "take particles in from infinity" but of course no one every takes this as "real". And those are just what I came up with in like 5 seconds of thought. So why is it any less ridiculous to take perturbation theory in quantum field theory and take its physical interpretation as real?
 
  • #116
Maverick (or anybody else, of course!), how do you know so well that 'virtual' states/ processes do not appear in non-perturbative qft?

How and why does that follow from your (kinda bold) comparison of qft with calculus?

And what physical mechanism actually forbids 'virtual' particles/ processes from happening?

How do you explain quantum physical static forces, such as the Coulomb force, without virtual particles?
 
  • #117
Virtual particles aren't required to explain the stability of a hydrogen atom. That's just nonsense.
 
  • #118
Lapidus said:
And what physical mechanism actually forbids 'virtual' particles/ processes from happening?

Conservation of energy, momentum and special relativity.
 
  • #119
Goldstone1, virtual particles are a mathematical device coupled to a particular theory, there are no virtual particles in Lattice QFT for example.
 
  • #120
Goldstone1 said:
Virtual particles are real, they just exist for very short periods of time. It's a myth really to say virtual particles aren't really real, as they do contribute to real things in the outside world, such as the stability of a Hydrogen Atom.

There is no evidence for virtual particles being real, neither experimental nor theoretical. They are purely mathematical. The stability of the hydrogen atom has nothing to do with this.
 

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