Wolv1's questions about causality and particles

Discussion in 'Physics & Math' started by Wolv1, Aug 25, 2008.

  1. James R Just this guy, you know? Staff Member

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    A violation of causality would occur if an effect happened before the thing that caused it.

    An example would be you dying from wounds received from being hit by a bus, but before the bus actually hit you.
     
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  3. Wolv1 Banned Banned

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    do virtual particle's do this? since their speed is faster than light and don't obey law's of conservation? or am i being mislead?
     
    Last edited: Oct 8, 2008
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  5. James R Just this guy, you know? Staff Member

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    Do virtual particles violate causality?

    As far as I am aware, no they don't.

    Also, I'm not aware that they travel faster than the speed of light.

    Do you have any references?
     
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  7. Wolv1 Banned Banned

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  8. Wolv1 Banned Banned

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  9. Wolv1 Banned Banned

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  10. Wolv1 Banned Banned

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    i was told by ben that they do.
     
  11. James R Just this guy, you know? Staff Member

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    The link in post #7 does not say that virtual particles violate causality.
    The link in post #8 is a copy of the material in #7.
    The author of #9 admits he is not a particle physicist. He claims that virtual particles can violate causality, but doesn't explain.

    As for Ben, he can speak for himself.

    Tell me, Wolv1, why are you so interested in causality violations?
     
  12. Wolv1 Banned Banned

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    it's just weird to me,and hoping it's impossible.why do they travel faster than light if it's not allowed by the laws of physics? so ben is wrong?
     
    Last edited: Oct 8, 2008
  13. prometheus viva voce! Registered Senior Member

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    From a previous thread:

    "The more important property of VP's is that they do not necessarily obey \(E^2 = (pc)^2+(mc^2)^2\). The energy of the particle can be anything, even a negative value. The more the energy differs from this, the shorter the time it must last for by the uncertainty principle. Virtual particles can indeed travel faster than light as well, although it is relatively straightforward to show that they do not affect causality. For causality to be affected a pile of real particles or waves must be sent back in time."

    The fact that the energy of virtual particles is not \((pc)^2+(mc^2)^2\) is what we mean when we say "off shell." Virtual particles can never be detected so nothing would happen. We can only detect them indirectly like in Lamb shift and the Casimir effect both of which have good wiki pages.
     
  14. prometheus viva voce! Registered Senior Member

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    Virtual particles do not violate causality - it's one of the first things that gets shown in most postgraduate quantum field theory courses. As I've said a couple of time now, VP's can travel faster than light but they cannot be directly detected so they cannot affect causality. For causality to be violated, real particles would have to go faster than light, which is impossible.
     
  15. Wolv1 Banned Banned

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    prometheus,so ben was wrong in telling that virtual particle's violate causality?
     
  16. Wolv1 Banned Banned

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    what does it mean it's energy can be negative?so ben is wrong say causality is violated?
     
    Last edited: Oct 8, 2008
  17. Vkothii Banned Banned

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    It means: "virtual energy can have any value, including negative value"
     
  18. Wolv1 Banned Banned

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    can it have infinite energy?
     
  19. Wolv1 Banned Banned

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    what would happen IF virtual particle's were detected?
     
  20. Vkothii Banned Banned

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    No, it can only have virtually infinite energy.
     
  21. Vkothii Banned Banned

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    That is physically impossible, but there is a noticeable effect (noticeable now that we have the ability to notice it), from the background of VPs.

    A small distance between two 'smooth' surfaces sees a force pushing them together. This is explained as VPs that can't get between the surfaces, or into the cavity between them, because the gap is too small.
    So they can't push the surfaces apart, only together - a net force is seen between the surfaces, flat surfaces especially.
     
  22. Wolv1 Banned Banned

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    i think i heard of it,was it an experament?
     
  23. Vkothii Banned Banned

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    It's the Casimir effect.
     

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