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Can a light ray be redshifted so that it contains no info

  1. Jan 11, 2016 #1
    Is it possible for a light- ray to be redshifted to an extent where it no longer oscilliates and thus contains no information? Please excuse any naivety
     
  2. jcsd
  3. Jan 11, 2016 #2

    davenn

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    it will still be there, have you heard of infra red or microwave radiation ?
    but the amount of redshifting to go that far would be pretty extreme


    Dave
     
  4. Jan 12, 2016 #3
    Maybe he intended if the resultant frequency measured here is so low that the wavelenght is thousands of light years, e.g.
    Certainly it would be such an extreme case that it can only be thought, as far as I know.

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  5. Jan 12, 2016 #4

    mfb

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    The wavelength does not have an upper limit (well, the size of the observable universe is an upper limit), but our sensors have some practical upper limit on the wavelengths that can be detected.
     
  6. Jan 12, 2016 #5
    Hmmm, if we want to detect the radiation. But what if we want to detect "the field" e.g. the electric field? An extremely low frequency e.m. radiation, in the "time region" where the field is near to a maximum or a minimum, would appear as a constant field (of very low amplitude, however, certainly).

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    lightarrow
     
  7. Jan 12, 2016 #6

    mfb

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    If the amplitude is strong enough, we have some chance to detect even very low-frequency radiation, sure.
    Such a radiation would be absorbed quickly, however.
     
  8. Jan 12, 2016 #7
    For any finite redshift the answer is no, but it does bring up some interesting questions. There are two main sources of redshift (gravity and expansion of the universe). In both cases, you can have event horizons at which the redshift goes to infinity. No information is (classically) allowed to travel from the hidden side of the event horizon to the observer. I think most physicists agree that information falling into a black hole is not destroyed, but just changed into some unrecognizable form. In an accelerating expanding universe, any information that travels too far away from the observer will be forever lost because the distance between the information and the observer expands faster than the speed of light. In this case, the information isn't really destroyed--it's just in some other place we can't see.
     
  9. Jan 12, 2016 #8

    sophiecentaur

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    If the Universe is finite (I'm not sure what is flavour of the month at the moment) then there would be a limit to the rate of recession and, hence, a limit to the amount of red shift. (Plus the time since the Big Bang would limit the distance from which we could actually be receiving EM radiation.)
    About the information carrying capacity of such radiation, there is a basic relationship between the frequency of a modulated carrier and the possible bandwidth of the data it could carry. Going as far as to red shift to 'DC' would imply that no information could be carried. But, in any case, any measurement of an 'unchanging' field would need to involve a longer measurement time than the suggested time for which it's thought to be unchanging. 1s, 1000s, 10000 years? System noise is a real problem for DC measurements.
     
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