Why exactly do Virtual Particles not violate Conservation of energy?

[raracon]

TL;DR

Even tough I read through past articles on the forum and other websites I cannot wrap my head around the fact that virtual particles don't violate the Conservation of energy.

Recently I've read more about virtual particles and at first I tought that there were only doubts that virtual particles are not interpretable with the help of uncertainty principle. Furthermore it can't be used an an "excuse" for the temporary violation of the conservation of energy.

Can someone please explain why it does not violate it and what is a mathematically right interpretaion of these particles

 

[weirdoguy]

Can someone please explain why it does not violate it and what is a mathematically right interpretaion of these particles

Did you read these articles:
https://www.physicsforums.com/insights/misconceptions-virtual-particles/
https://www.physicsforums.com/insights/physics-virtual-particles/
?

 

[PeterDonis]

Can someone please explain why it does not violate it and what is a mathematically right interpretaion of these particles

Please read the Insights articles that @weirdoguy linked to; that will be much better than trying to rewrite the same content here. Then, if you still have questions, they will at least be much more focused questions. You can post follow-up questions here once you have read the articles.

 

[raracon]

Please read the Insights articles that @weirdoguy linked to; that will be much better than trying to rewrite the same content here. Then, if you still have questions, they will at least be much more focused questions. You can post follow-up questions here once you have read the articles

Understood! :)

 

[raracon]

Did you read these articles:
https://www.physicsforums.com/insights/misconceptions-virtual-particles/
https://www.physicsforums.com/insights/physics-virtual-particles/
?

First of all thank you! I will go through them and ask away after :)
One more thing...do you know any good articles about the QED Vacuum ?

 

[weirdoguy]

Well, I don't know if that is what you are looking for, but...
https://www.physicsforums.com/insights/vacuum-fluctuation-myth/
https://www.physicsforums.com/insights/vacuum-fluctuations-experimental-practice/

 

[raracon]

I've read that stuff, but I was looking for something more specific. Say a derivation of the QED vacuum or so.

What I have noticed is that people say that the virtual particles don't violate the energy time uncertainty but they violate the conservation of momentum. But that doesn't really add up, does it?

Edit: One more thing too. In some articles it is stated that fluctuations are a result of overlaying, what does that mean?

 

[Demystifier]

I cannot wrap my head around the fact that virtual particles don't violate the Conservation of energy.

I never understood where that myth of energy non-conservation by virtual particles came from in the first place. In a Feynman diagram (either a tree or a loop diagram), energy and momentum are conserved in each vertex.

 

[PeroK]

I've read that stuff, but I was looking for something more specific. Say a derivation of the QED vacuum or so.

Re QED, you could try Feynman's book to get you started:

https://en.wikipedia.org/wiki/QED:_The_Strange_Theory_of_Light_and_Matter

What I have noticed is that people say that the virtual particles don't violate the energy time uncertainty but they violate the conservation of momentum. But that doesn't really add up, does it?

You mean that some people on the Internet might be wrong? It happens! That's why we try to confine ourselves to using textbooks and other reliable sources for discussion. If someone down your local pub says that energy conservation is violated in QFT, then it doesn't make that a worthwhile point of debate.

As @Demystifier says, energy-momentum is built into QFT, so anything to the contrary is a pure myth.

 

[raracon]

Re QED, you could try Feynman's book to get you started:

https://en.wikipedia.org/wiki/QED:_The_Strange_Theory_of_Light_and_MatterYou mean that some people on the Internet might be wrong? It happens! That's why we try to confine ourselves to using textbooks and other reliable sources for discussion. If someone down your local pub says that energy conservation is violated in QFT, then it doesn't make that a worthwhile point of debate.

As @Demystifier says, energy-momentum is built into QFT, so anything to the contrary is a pure myth.

Yeah haha
I read of the violation in a article suggested by our course master, that is why I was pretty confident that it was right. But now I know better :)

Another question of mine would be if it is correct to express virtual particles through the uncertainty principle stating that the energy of said particles is pretty high and that the duration \Delta t is extremely short and that is why the virtual particles can/should not be measured? Is this valid?

 

[PeroK]

Another question of mine would be if it is correct to express virtual particles through the uncertainty principle stating that the energy of said particles is pretty high and that the duration \Delta t is extremely short and that is why the virtual particles can/should not be measured? Is this valid?

Virtual particles appear in Feynman diagrams, where the calculation involves integrating over all possible four-momenta of the virtual particles (with energy-momentum conservation built in). It doesn't make much sense to talk about virtual particles outside this context.

You cannot measure a virtual particle by definition. The particles that are measured are the real particles that result from an interaction. Virtual particles are only an aid to calculation of the likelihood of a particular interaction taking place. The UP (Uncertainty Principle) applies to measurements on real particles.

This is an example of where popular science authors and presenters have seized on an idea that makes everything sound much more exciting.

 

[Demystifier]

Another question of mine would be if it is correct to express virtual particles through the uncertainty principle stating that the energy of said particles is pretty high and that the duration \Delta t is extremely short and that is why the virtual particles can/should not be measured? Is this valid?

It is invalid. Virtual particle have nothing to do with uncertainty relations. See also https://arxiv.org/abs/quant-ph/0609163 Sec. 9.3.

 

[raracon]

It is invalid. Virtual particle have nothing to do with uncertainty relations. See also https://arxiv.org/abs/quant-ph/0609163 Sec. 9.3.

Ay, cheers! I really appreciate you all for helping me out on this one. As a high school student I really need it haha

 

[PeroK]

Ay, cheers! I really appreciate you all for helping me out on this one. As a high school student I really need it haha

If you are serious about physics, you do need to be wary of popular science sources. It's all right if you don't take them too literally. But, there is the risk that you learn a lot of stuff that is then difficult to unlearn. Especially in QM: the real thing is very different from the popular image of it.

You can find a wonderfully insightful introduction to QM here:

https://physics.mq.edu.au/~jcresser/Phys304/Handouts/QuantumPhysicsNotes.pdf

 

[raracon]

Well right now I am trying to finish the 15 page project we are doing for school. :)

 

[Vanadium 50]

Well, you were warned that this was many, many years ahead of where you are today.

You can't really skip years of work and jump to the end with any hope of understanding.

 

[raracon]

It is invalid. Virtual particle have nothing to do with uncertainty relations. See also https://arxiv.org/abs/quant-ph/0609163 Sec. 9.3.

Ok ok I see. Now how does one express this information in like a formal manner? Any tips?