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Virtual particles vs. speed of light

  1. Sep 16, 2004 #1

    There is a religious forum where I am posting in some evolution vs. creation threads.
    Creationists often believe that the world and everything else has not existed much longer then several thousands years. If you ask them how to explain that the light from stars millions of light years away can be seen here, they give various explenations you can usually easily show to be ridiculous.

    But now someone mentioned that the speed of light might not have been constant during the years because of virtual particles.
    Photons interact with virtual particles he says, slowing them down a bit. Well, the speed stays the same, but the photons lose some time while interacting with the virtual particle.
    Also according to him, there are more virtual particles now, then there were at earlier times, because of an increase in the Zero Point Energy.

    I haven't done more physics than the most you could do at highschool, and that only mentioned quantum physics as existing and difficult to understand, so I do not know if this person is making sense in his statements.

    Perhaps some persons here could shine their light on it?
    Do photons really interact with virtual particles? Does this interaction take time? Is the ZPE increasing?

    Opinions are very much appreciated.
  2. jcsd
  3. Sep 16, 2004 #2
    This sounds very, eeuuhh, strange

    Let me explain these virtual particles (photons can also be virtual).These particles are NOT real and you will never observe them. Then why do they "exist"? Well, they were invented by great minds in order to describe interactions between real physical particles like protons or neutrons...

    The theory in which they were implemented was the Quantum-Electro-Dynamics or QED.

    You also need to know that sometimes virtual particles can become real when there is enough energy available to give them "some reason to exist". The uncertainty-principle of Heisenberg states that when there is a lot of energy, they can become real for a very short while. In Quantummechanics the principle of energy-conservation can be violated for a very short while and this gives you also the reason why you need a lot of "external" energy in order to make virtual particles real. In classical physics this is not possible because energy must be conserved when a specific kind of forces are considered (like gravity)

    Virtual particles are not "built" out of zero-point energy, they are just a way of describing interactions and that is all. And a photon itself will not interact with a virtual particle unless this photon is considered to be the virtual particle itself. i mean this : the attraction between an electron and a proton for example can be described in terms of virtual photons. It is them virtual photons that are the force-carries that mediate this Electromagnetic interaction. Two virtual photons can interact via the socalled polarization-insertion of QFT. But let's not get into that.

    And a photon does NOT loose time because of some interaction and it never slows down. The velocity is always the speed of light

    marlon :smile:
  4. Sep 16, 2004 #3


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    I remember reading about this in some article when doing a research paper but that was a while ago so I don't really remember the facts just my impression. I'm assuming the particles were virtual particles but that there were clouds of some partical that absorbed light slowed it down during the time it was in the cloud. This still means that the star's is far away and that possibly some things are closer. But there are also photons that will 'tunnel' this causes them to skip through substances. This means they appear far sooner than they are supposed to be, they are not usually many but since a photon can be detected than these will be too. Quantum physics just complicates things.
    But since the methods they use don't involve clocking a photon from a star to the earth, but rather I believe by triangulation as when the photons reach different parts of the earth. travelling through these virtual particles wouldn't make any difference as if all travel through it then there is no difference as to their striking the earth or if they don't all then some will come through and be used and the delayed join the beam of light to the earth just as a later time.
  5. Sep 16, 2004 #4
    Welcome Jovaro !

    Don't worry about the explanations they can claim to have to backup their philosophy. It is either simply wrong, or the entire physics community is. Even if such an effect could exist, it would have to be very tiny. The vacuum fluctuations can only induce small corrections.

    Also, the far cosmos looks younger. They can certainly not account for three major achievements of the Big Bang theory : the Cosmological Microwave Background, the relative abundance of elements, and the Hubble law. See here for instance.

    I also find it sad that creationists managed to have their theories taught in some school on the same footing as Darwinism.
  6. Sep 20, 2004 #5
    Let me explain the theory a bit further.

    Photons are causing a virtual particle pair to pop into existance, and this takes a little time for the photon. Like an athlete taking a hurdle.
    According to this person on the forum the Zero Point Energy has increased over time, causing more virtual particle pairs to pop in existance, "slowing down" the photons. The speed of the photons stays the same, but they have to take more "hurdles".

    Does this make any sense or can you show me that it is crap?

  7. Sep 20, 2004 #6


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    OK, I think I can't take this much longer without sticking my nose into this.

    The question here isn't what occurs, the question is HOW LIKELY is this to occur? If I have a vase that has been broken into a thousand pieces, and I throw these onto the floor, what is the likelyhood that it will recombine back into that vase? If you asked this person on that other silly forum this, he/she would not hesitate to say that this isn't likely to happen. Well then, how likely does he/she thinks a photon, in the visible range, would collide with a zero-point field that created a virtual particle? If it is THAT likely that it has cause a significant slow-down in light that the age of the universe has changed from 15 billion to tens of thousand of year, then guess what? Our universe would be OPAQUE! It will be filled with a continual collision of photons with virtual particles!

    Again, as in the bastardization of the 2nd Law of Thermodynamics, this is a bastardization of basic QED/QFT by people who are simply taking a superficial idea of it and applying it blindly to suit their cause. Considering that no physicist in their right mind would give the seal of approval for their use of such basic physics principle should immediately rings warning bells.

  8. Sep 20, 2004 #7
    This is rubbish in QED and QFT in general. Virtual particles are a mathematical artifact that allow us to do computations to high accuracies. They have no physical existence, and they can only appear in a Feynamn diagram that represents an interaction. The movement of a free particle is not affected by these vaccum fluctuations.
  9. Sep 20, 2004 #8


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    Dressed electrons?
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