Do virtual particles violate Conservation of Energy?

  • #1
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Main Question or Discussion Point

We are all familiar with the Law of Conservation of Energy:

Energy cannot be created nor destroyed

In other words, the total energy in a closed system is constant.

But if the above "axioms" are correct, how does it cope with the existence of virtual particles? In quantum physics, events are described by probability,which means the advent of an event can only be described as "likely" or "unlikely" to happen, but not "impossible". The chance that virtual particles been detected is miniscule, but it does happen, they are created due to the large uncerntainty of energy fluctuation in a very short time interval.

What it struck me is the existence of these enigmatic particles but what is more amusing is that it has negative energy and mass, and it just pops out of nowhere in vacuum and disappears in the next moment. Surely this phenomena violates the Law of Conservation of Energy - "Energy cannot be created nor destroyed", but on the other hand, it might not have for the law of Conservation of Energy also states the total energy in a closed system is constant. Since virtual particles pertain negative energy and mass in vacuum, at the instant a virtual particle appears, another "real" particle would also appear in another place in the system to balance the amount of energy in the system.
 

Answers and Replies

  • #2
Janitor
Science Advisor
1,099
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Do you have a reference on the negative mass part of what you said? I had not heard that.
 
  • #3
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Hyperreality said:
We are all familiar with the Law of Conservation of Energy:

Energy cannot be created nor destroyed

In other words, the total energy in a closed system is constant.

But if the above "axioms" are correct, how does it cope with the existence of virtual particles? In quantum physics, events are described by probability,which means the advent of an event can only be described as "likely" or "unlikely" to happen, but not "impossible". The chance that virtual particles been detected is miniscule, but it does happen, they are created due to the large uncerntainty of energy fluctuation in a very short time interval.

What it struck me is the existence of these enigmatic particles but what is more amusing is that it has negative energy and mass, and it just pops out of nowhere in vacuum and disappears in the next moment. Surely this phenomena violates the Law of Conservation of Energy - "Energy cannot be created nor destroyed", but on the other hand, it might not have for the law of Conservation of Energy also states the total energy in a closed system is constant. Since virtual particles pertain negative energy and mass in vacuum, at the instant a virtual particle appears, another "real" particle would also appear in another place in the system to balance the amount of energy in the system.

Virtual particles are created in pairs, particle and antiparticle such that conservation laws are not violated. Also even so there is energy necessary to create them (the two seperated particles have more potential particles when created than when they recombine and annihilate) and this energy is stipulated to come from the uncertainty principle, giving it meaning not just as a limitation on our measurement, but a real physical meaning that particles do not have a definite energy but that the energy is physically uncertain.
 
  • #4
arivero
Gold Member
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the *definition* of virtual particles directly implies they violate the equation relating energy and momentum, ie they violate at least one of these. Here uncertainty principle enters the game: the violation can stand only during a very small time, about h/E. Because of this, they are called virtual.
 
  • #5
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arivero said:
the *definition* of virtual particles directly implies they violate the equation relating energy and momentum, ie they violate at least one of these. Here uncertainty principle enters the game: the violation can stand only during a very small time, about h/E. Because of this, they are called virtual.
So for a very short time there can be an increase of energy/mass. Does this also work in the opposite direction? Can an already existing particle such as an electron or proton blink out of existence for a short period of time?
 
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  • #6
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So for a very short time there can be an increase of energy/mass. Does this also work in the opposite direction? Can an already existing particle such as an electron or proton blink out of existence for a short period of time?
No it cannot, because proton is not the antiparticle of electron. A positron is the real antiparticle of electron.

Virtual particles are created in pairs, particle and antiparticle such that conservation laws are not violated.
I'm not sure if this argument is valid. When you say virtual particles are created in pairs, does that imply simultaneity? But in the real world there is no simultaneity. So, can two observers in two different frame of references see a different order of events?

The above also rises the question whether the Law of Conservation of Energy is symmetrical at quantum scale?
 
  • #7
ahrkron
Staff Emeritus
Gold Member
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Quoting from http://olympus.het.brown.edu/pipermail/spr/Week-of-Mon-20030915/013538.html:

John Baez said:
[...]There's an old lousy form of perturbation theory in which virtual particles violate conservation of energy-momentum - that may be what you're thinking about.

But this only survives in popularizations of physics, not what quantum field theorists usually do these days. At least since Feynman came along, most of use a form of perturbation theory in which virtual particles obey conservation of energy-momentum. Instead, what virtual particles get to do that real particles don't is "lie off-shell". This means they don't need to satisfy

E^2 - p^2 = m^2

where m is the mass of the particle in question (in units where c = 1).

In any event, regardless of which form of perturbation theory you use, in actual reality it appears that energy-momentum is conserved even over short durations and short distances (Here I'm neglecting issues related to *general* relativity, which aren't so important here.)
 
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  • #8
arivero
Gold Member
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Mike2 said:
So for a very short time there can be an increase of energy/mass. Does this also work in the opposite direction? Can an already existing particle such as an electron or proton blink out of existence for a short period of time?
The problem, you can violate energy for a brief lapse of time, or momenta in a short extension of space. But you can not violate charge conservation, so a electron can nor blink out of existence, it only can transform in other particle for such short interval. For instance it could become a virtual W- plus a virtual neutrino, and then both coalescing to make the original electron.

Another example: a quark of charge +2/3 inside a proton becomes a quark -1/3 plus a virtual W-. Then the W-, instead of fusing again with the quark, disintegrates in electron plus antineutrino. This is called, surprise, "beta radiation".
 

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