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Why does ElectroMagnetic radiation propagate forever?

  1. Apr 23, 2009 #1
    Hey there,

    I am not a physics student, nor have I ever studied physics. I have this question though (read thread title). I have googled for an answer but couldn't find any.


    According to Einstein, we are always traveling through the universe at the speed of light. When we are still, A (speed traveling) = 0 and B (rate we are traveling through time time) = c (speed of light). Thus when we move, A increases and B decreases by the same amount.

    Since the speed of light is propagating at c, isn't it stationary in the 4th dimension? Is light not aging and thus never dies until it hits something and the energy is transferred? Is that how photons can propagate through a vacuum and never go out...

    There might be a real simple answer that physics guys learn I dunno.
     
  2. jcsd
  3. Apr 23, 2009 #2

    Hootenanny

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    Welcome to Physics Forums.
    I don't know where you read that but it is not correct. Massless particles (such a photons) always travel at c, but any massive particle must travel at less than c.
    Once again, I'm not sure where you've read this, but it is not possible to associate a [locally] inertial reference frame with a photon. Therefore, it is non-nonsensical to speak of a photon being stationary in any reference frame.
    The reason the photon (and hence the electromagnetic field) has an infinite range is because it is massless. For more information search for Gauge Bosons or Force Mediators.
     
    Last edited: Apr 23, 2009
  4. Apr 23, 2009 #3
    You misread what I said. I know 'massive particles' cannot travel the speed of light because as they do they gain mass and would fill up the entire universe in order to travel at that speed. plus an unrealistic amount of energy would be required to travel at that speed.

    What you quoted was what Einstein said about how we're always traveling through the universe at c. When we are stationary, we are traveling through the time at c and speed at 0. When we move, we are traveling through time at c - speed. When we physically move, time for us slows down. I know I have a lack of technical jargon but yeah.

    I think you misunderstood what I was trying to say in the first paragraph and it carried through to my second paragraph. I was saying because of what Einstein proposed about how we are continuously traveling through the 3rd+4th dimensions at c, wouldn't the photon never age as time wouldn't pass for that photon since it is obviously traveling at c?


    Thanks i'll research this.
     
  5. Apr 23, 2009 #4
    WHAT I SAID:

    "Since the speed of light is propagating at c, isn't it stationary in the 4th dimension?"

    WHAT YOU REPLIED:

    "Once again, I'm not sure where you've read this, but it is not possible to associate a [locally] inertial reference frame with a photon. Therefore, it is non-nonsensical to speak of a photon being stationary in any reference frame."

    --------

    I see where the confusion is now! I'll try to elaborate on my most likely uninformed thought process. What I read was that Einstein proposed that everything in the universe is travelling both through Time and Space at constant c at any given moment. When we are stationary, we are traveling through time at c. When we move, we are travling through space at the speed we are moving and through time at c - speed. So based on this since a photon is propagating at constant c, shouldn't time be stationary for this photon?
     
  6. Apr 23, 2009 #5

    Hootenanny

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    I'm 99.9% sure that Einstein said no such thing. I know that similar things have been written by popular science authors who commonly associate the notion of observers travelling though space-time at a speed c, however, I've never come across an actual citation referencing Einstein as saying such things.
    As I said above, I'm pretty sure that Einstein never proposed anything like what you have said. Brushing that aside for a minute, what is this 3rd dimension you are referring to?

    In relativity, time is a relative concept. The time between two events (think two ticks of a clock) depends on the observer. So, in reference to your question regarding the passage of time for a photon, I ask "from who's point of view"?
     
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