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When the speed of an object becomes equal to the speed of light

  1. Oct 15, 2008 #1
    Dear friends,

    When the speed of an object becomes equal to the speed of light, its mass becomes infinity. Then can it be possible to an object to be invisible?
  2. jcsd
  3. Oct 15, 2008 #2

    Jonathan Scott

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    Gold Member

    Re: Relativity

    As the first statement describes an impossible situation, the question is meaningless.
  4. Oct 15, 2008 #3
    Re: Relativity


    don't be so hastey to belittle people's questions.
  5. Oct 15, 2008 #4


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    Re: Relativity

    Johnathan's answer is fine. It's short, but completely correct. I don't see how it belittles anyone.

    Tachyon's don't travel at the speed of light. Only massless particles do. Tachyon speeds are always >c, never =c.
  6. Oct 15, 2008 #5


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    Science Advisor

    Re: Relativity

    It is not "belittling" to tell someone they have made a mistake.
  7. Oct 20, 2008 #6
    Re: Relativity

    Sreeja...I can think of several situations of interest:

    As noted by others, An "object" with non zero rest mass cannot attain the speed of light as it would take infinite energy to accelerate it to "c"...but other situations arise:

    Photons (with apparently zero rest mass) travel at the speed of light and the visible portion of the spectrum IS still detectable by the human eye. So we know of at least one case where light speed does NOT make an entity invisible.

    In cosmology distant objects (masses) may be receding at greater than the speed of light from our reference frame here on earth. This is due in part to the expansion of space itself. Those are generally NOT visible to us because light from them never reaches us....distance grows faster than the speed of light. For more on this, one simple explanation is that the "Hubble bubble" limit defines our cosmological horizon...at about 15B years...

    Wikipedia talks about the Bubble bubble, Hubble limit and other cosmological horizons.
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