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Do quantum fluctuations come from nothing ?

  1. Nov 27, 2013 #1
    Do quantum fluctuations come from "nothing"?


    I have two questions regarding quantum fluctuations. Do the particle (and its' anti-particle) appear from nothing? I know it happens in a Quantum vacuum. But do the particles themselves appear from nothing? Where do they get their energy from, or do they violate the energy conservation law? Please be detailed about this.

    And, if a particle and anti-particle collide, shouldn't their collision produce energy instead of just annihilation?

    Thank you.
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  3. Nov 27, 2013 #2


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  4. Nov 27, 2013 #3
    I have wondered this also and I read or rather tried to read, the wikipedia article. It leaves or seems to leave more questions than it answers. Both the particle and the anti-particle produced have positive mass-energy and the only counterbalance on offer seems to be that the particles exist for a short time. On the face of it, the only period this 'short time' can be is zero - which is not the case.

    Does anyone know what drives this process? It is allowed by the uncertainty principle but is it caused by this principle? All space is filled with radiation. Is this really where the mass/energy to make the pairs comes from? What if anything, is known about the rate of pair production? How is it influenced?

    And what of the particles themselves? In what sense are they virtual? If electon-positron pairs form, these are perfectly stable particles. Is there some way in which they know they are not really supposed to exist and so destroy themselves, with or perhaps somehow without the usual gamma ray?

    In Hawkings radiation which involves virtual particle pairs arising outside the EH, the BH loses mass by positive mass/energy particles escaping and negative mass/energy particles falling in. What are these negative mass/energy particles? There are no candidates in the standard model.

    Could the principles behind these quantum fluctuations and Hawkins radiation lead to a viable zero sum universe? This would be an awesome result.
  5. Nov 28, 2013 #4


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    There's no cosmic bank account where you can "borrow energy". Even if you hurry! Energy is always conserved, that's an absolute prinicple.

    Despite all the popular accounts, the vacuum does not "fluctuate". It is a stationary state. It is time-independent. Particles do not appear and disappear. They do not "pop into and out of existence." This wording is an everyman's attempt to describe in classical terms a fundamental quantum effect, namely, superposition of states. The vacuum is a superposition of states in which various numbers of particles are (always) present. All those states have the same total energy (zero), each pair of particles making zero contribution.

    The particles in question are virtual particles, which means that they don't need to obey the usual relation between mass, energy and momentum, E2 = p2c2 + m2c4. We say they are off the mass shell. Virtual particles can have energy but no momentum, or momentum but no energy. Or they can have negative energy. In the particle-antiparticle pair, one particle (either one) has positive energy while the other has negative. Together their energy adds to zero.

    What could it mean to produce "just energy"? Not possible! Energy is a property possessed by particles, and you must produce particles to carry it.
    Last edited: Nov 28, 2013
  6. Nov 28, 2013 #5
    Thanks for the replies

    If it's a superposition of states, what will we see if we try to measure what's happening in a quantum vacuum? I mean we should measure a certain state, but how would we define a state in here? Please give me an example of a quantum state in a quantum vacuum.

    A further question, is it possible to find a place that isn't contained in the quantum vacuua? Does/can the quantum vacuum exist before the universe?

    I thought maybe photons.. like when an electron and a positron collide (not sure about this line, though).

    I await your reply.

    Thank you :)
  7. Nov 28, 2013 #6
    from nothing, nothing.
    one thing is a physics vacuum and other, nothing.
    nothing is the absolute absence of anything.

  8. Nov 28, 2013 #7


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    An electron and positron can annihilate into photons. But photons are particles, and just like other particles they have many properties besides the energy they carry. Momentum and angular momentum, for example. Plus the ability to eventually strike something else!
  9. Nov 28, 2013 #8
    When you say they have negative energy do you mean they are lower than the vacuum state? I was sort of under the impression that the energy for the virtual pairs was borrowed came from the vacuum state which has non zero energy. Is this incorrect?
  10. Nov 28, 2013 #9


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    Jilang, Yes, I'm afraid your sort-of-impression is incorrect. :wink: I meant exactly what you think I meant, and I can only repeat it all over again. Consider everything in the following paragraphs to be underlined.

    Energy is never "borrowed". Energy is exactly conserved, at every moment of time, and in every interaction. Quantum Mechanics and the uncertainty principle do not alter this fact. If one particle acquires energy, another particle must, at the same time, lose it.

    Negative energy means "less than zero". :wink: Real particles, including antiparticles, always have energy that is positive, but virtual particles do not have to obey this rule.

    In Quantum Field Theory, the vacuum state has zero energy. You've probably heard that at the cosmological level there is a small nonzero vacuum energy which is attributed to the Cosmological Constant. No one understands exactly how this value arises, or what determines it, but it is unrelated to the present discussion.
  11. Nov 28, 2013 #10
    How can anything have negative energy? Isn't energy a relative concept - depending on what you set as being zero. In QFT I thought the Ʃhk/2 term where k goes from 0 to ∞ created an infinite energy anyway which is just ignored on account of it being "virtual". Perhaps I'm totally misreading this so please excuse me.
  12. Nov 28, 2013 #11
    When I was at school I concluded the following:-

    "A particle in everyday terms, is a 'solid' object of such small radius that it may be considered as having a single x,y,z,t coordinate. A wave is more or less the exact opposite. It is entirely possible for a wave to approximate to and behave as though it were a 'solid' particle. All it needs to be is very small. It is not however possible for a solid object, regardless of size to behave as though it were a wave. The diffraction experiments do not indicate 'wave particle duality' as is comonly suggested but instead show all matter particles are waves".

    I have never really questioned this since although I have often wondered what all this 'superposition of states' is all about. Why is this concept nessesary?

    A wave surely, is a cyclic set of states. At one instant it is in one state, later it is in another state. Just because it is impossible to determine the state until an interaction occurs does not mean the entity is ever in multiple states at the same time.

    Or have I completely lost the plot?
  13. Nov 28, 2013 #12
    This seems to me a semantic issue. I am not sold on either borrowed energy or virtual particles of negative energy. There is though, one very good and visible example of 'negative energy' on a macroscopic scale - the sudden outflow of water that can occur before a tsunami. The drained area is actually part of the wave's cross section. We see the same thing but less dramatically in ordinary ocean waves. In some regions of a wave water is above the average height (sea level) while in another region the water is depressed below this average. Something like this can apply to particles one presumes but I can think of no way the negative and positive parts of the wave could be separated. Perhaps they are not?
  14. Nov 29, 2013 #13


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    the other point that has not been raised yet is the situation where the operator corresponding to the number of particles does not commute with the Hamiltonian for the system. This is talked about briefly in the link that Phinds gave. So in this case, the energy of the system is conserved, but the number of particles is not. pretty interesting. I want to learn more about this. I'm just starting to learn about quantum field theory really.
  15. Nov 29, 2013 #14
    Bruce - yes I am very keen on learning about this whole area but I am coming from a long way behind! I had a similar problem with GR which I have now more or less got on top of. What I found was that the established concepts were largely obscured by strange language that eventually one deciphers. Once through that hurdle the whole thing was entirely logical and not weird at all. I am hoping for a similar progression with QM.

    But back to the particles. What are they and what properties are they supposed to have? And what of the virtual photons that are supposedly responsible for electrostatic force?

    I note that that much of the evolution of the standard model, is predicated on matching fields to bosons. The latest of course is the Higgs. Certain matrices did not behave themselves and this meant that some particles known to be massive, should not be. So a field was invented and a boson predicted and found.

    When I learned GR I explored all sorts of ideas but always my drive was to match my understanding to the mainstream. I was never out to disproved GR or to tout any pet theories. I put ideas in posts that disagreed with GR but that made sense and I learned a lot from people shooting them down.

    Now for the same with QM. Please refute the following wrong synopsis?

    1) Waves either propagate through space linearly at c or move 'in and out' at c around a 'stationary' point in space (eg hedgehog space). Only certain configurations and thus values are possible due to the need for resonance.

    2) Linear propogation results in the cancelling out of charge or of magnetic fields (see GR explanation of magnetisum) but with in/out propagation the charge is not cancelled. All particles (in/out waves) are charged or are comprised of sub-particles that are charged or both

    3) Charge warps space like mass does (a point implied by the theoretical existance of an inner EH in a charged BH). The difference is that charge is 'stronger' by about 40 orders of magnitude and can be negative (the spin can be in reverse but the stress-energy tensor will always be added to by the wave energy regardless of direction)

    4) Charge warping space makes chage a field. Not something that is mediated by bosons, virtual or otherwise

    5) Rest mass is inherent to all in/out waves because of the energy of the wave. There is no need for a Higgs mechanism and the Higgs boson, like the W and the Z, is just an intermeadiate wave configuration.

    Again for clarity, I am looking for refutations. This is 'devils advocacy' aimed at denying respondents from simply quoting the reference books so that they have to construct the arguments themselves (hopefully)
  16. Nov 29, 2013 #15
    What is wrong with it?
    Pretty much all of it. Have you tried reading a book? Or if you want serious answers limiting yourself to one serious question?
  17. Nov 29, 2013 #16


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    Uh ... good luck with that. You'll find that it is not generally done on this forum to waste time refuting nonsense. As Jilang said, you would be better off learning some actual physics and then ask more meaningful questions when you hit a stumbling block in your learning.
  18. Nov 29, 2013 #17
    Great posts Bill_k with lot of information, saves time

    What does it mean for a virtual particle to have momentum but no energy? .....because isn't momentum "convertible" to energy?


    Last edited: Nov 29, 2013
  19. Nov 29, 2013 #18


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    Yeah, it's good to logically press the issue of why a theory is a certain way. But your questions are maybe too wild - I don't really understand what is meant by most of them. Having said that, I'll try to answer.

    uh... I see on wikipedia that a hedgehog space is a real thing. But in quantum field theories (QFT's), there is just 3 spatial dimensions and the time dimension (unless maybe if you get into string theories, but I don't know anything about them). Some particles travel at c, and others travel at less than c. In the theory, this corresponds to particles with zero invariant mass and particles with nonzero invariant mass.

    er... again, I think standard QFT's just assume the standard Minkowski space which has 3 spatial dimensions and 1 time dimension. I'm guessing by in/out propagation, you mean the idea of the hedgehog space and other topological spaces? And I'm not sure what you mean here about the cancelling of charge or magnetic fields...

    I think you mean that the electromagnetic coupling constant is much stronger than the gravitational coupling constant. I agree with that. and charge can be negative or positive, but mass only has one sign. Yes, that's true.

    not quite. In general relativity, the thing that warps space is actually the electromagnetic field. it is the electromagnetic field that has energy, stress and momentum. For example, some particle might have a huge charge. But this will not warp spacetime unless there is an electromagnetic field also. So, what I mean is that charge warps spacetime indirectly, by affecting the electromagnetic field.

    Is this in/out wave related to hedgehog-type topologies? again, I don't think that's part of the standard model.
  20. Nov 29, 2013 #19


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  21. Dec 1, 2013 #20
    links/books with more info?

    I replied to this yesterday, but apparently the post didn't take. Trying again!

    @Bill_K, I was wondering if you could provide a source that does a good job clarifying your points here. I was under the impression that quantum fluctuations produce real energy, and by equivalence, real particles. I would be curious to learn more about this to understand how that perception is mistaken.

    Here are a few links to justify my confusion.

    This paper (among others) talks about how the mass of subatomic particles comes entirely from the vacuum fluctuation energy they enclose:

    Also, it seems overly hasty to suggest that the "pop in and out of existence" phraseology is only layman or "everyman". I've come across this treatment even to very technical levels -- which is not to vindicate the claim, of course, but it does make your dismissal feel a little terse. Here is a quick example, but many text books repeat the term:

    Thanks in advance!
  22. Dec 1, 2013 #21
    Your links are just speculative papers and not peer reviewed science. I can understand why you could become confused if you take them as in any way generally accepted. :frown:
  23. Dec 1, 2013 #22
    I can't remember who it was that said I should 'learn some physics' instead of playing devil's advocate but I do accept they have a point. I have a physics degree which I just managed to pass by the skin of my teeth with the key problem being the math. My maths is good enough for engineering though and 30 years in the field has taught me to be wary of parrots - people who ace thier exams by citing all the right statements but actually do not really understand the fundamentals. Playing devil's advocate is a effective method of exposing this and at the same time, because it forces a different perspective, it is also an effective remedy.

    For me, learning something means being able to visualize it. Unless I can build a picture in my mind of what these particles look like I am lost. A load of math does not generally bring me to a visualization and frequently, the text descriptions mislead. Of course I could cite all the right things and sound clever but where would that get me? I'd rather be honest and sound like a prized dunce. Whenever I go on a course I have always found when I say I don't get something, loads of other people stand up and say 'yeah I couldn't understand that either'

    I don't currently get why it is thought that electrostatic force is 'meadiated by virtual photons' or why it is thought that virtual particles arise out of fluctuations or why particles are thought of as a 'superposition of states'. That might make me dumb but it won't make me alone, even among physics graduates!

    But my post drew a very good response and some of the replies are quite illuminating so hopefully I won't be in the dark for too long!

    In reply to DennisN regarding the neutrino. This is another thing that I don't get. Origionally this was massless until someone decided it changed flavours and therefore had to have mass. So I wonder ....

    1) Do we have any evidence whatsoever that the neutrino travels at less than the speed of light?

    2) Is there any other evidence that the neutrino is not a form of EM wave?

    3) Is the 'flavor changing' just another example of state superposition (or cyclic states) or is there something else thought to be going on? What is the rational behind the assertion that something has to be massive to change flavor? Why use the word 'flavor' instead of 'state'
  24. Dec 1, 2013 #23


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    The only thing I can help you out with there is the speed of neutrinos. It's been shown experimentally that they are slower than light, though not by much. Easily the most famous experiment is the one a year or two back that caused a BIG furor in physics because it showed that neutrinos were FASTER than light, which not even the experimenters themselves (and there were at least dozens of them, at CERN I think it was) and they checked their procedures six ways from Sunday and couldn't find the error ... until they finally did, and showed that neutrinos were just slightly slower than light. They had made a hard-to-spot error in the experiment.
  25. Dec 1, 2013 #24


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    I am definitely not very knowledgable when it comes to neutrinos (nor an expert on particle physics :biggrin:), and I know neutrinos are difficult to study. But I think there are answers to those questions, I might not be able to give good answers, but I can at least try:

    1) AFAIK they are expected to have mass. And if they have, they should travel at less than the speed of light.

    2) They are fermions (half-integer spin). Photons are bosons (integer spin). Regarding neutrino spin experiments, I don't have any links at the moment, maybe someone else does.

    3) I have no idea. None at all. Zero, nada, zilch.

    But isn't this starting to deviate from the original post #1, which is about quantum fluctuations? A neutrino discussion would be better in a new post in the particle physics forum, in my opinion :wink:. And you might get better answers than mine. In fact, I'm pretty sure you will.
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