1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Entropy and electromagnetic radiation

  1. May 25, 2013 #1
    I don't understand this:

    According to what modern physicists believe to be true, there is entropy that slowly converts all energy of the universe into heat that cannot do any work. Than this heat is radiated as infrared light into space. Correct?

    Besides infrared heat radiation, start also produce other spectrums of light and all that goes out into space and escapes the universe for ever, if it doesn't happen to run into planets, stars, dust or other space objects on its way out.

    Because of some phenomena (what is the term that is used for it?) the frequency of electromagnetic waves decreases over time as they travel through space and all the light that escapes stars slowly becomes infrared heat radiation. Correct?

    When frequency of electromagnetic radiation decreases, the energy is lost. Why?

    Thank you.
  2. jcsd
  3. May 25, 2013 #2

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    Welcome to PF;
    That is hardly surprising - it doesn't make sense. Where did you get these ideas from?


    Entropy is a measure of the amount of disorder in a system.
    The amount of disorder in a closed system increases over time - simply because there are many more ways for something to be disordered than ordered.

    There is a subtle thing here which may not be intended: "modern physicists" do not go around "believing" things. At least not in the sense that someone may "believe" in a God, or Astrology. That would be counter productive. But, sometimes, someone will mean "believe in xyz" as a shorthand for "the weight of opinion favors xyz as most consistent with the available evidence and most useful for building new theories from".... which is a bit tedious to keep saying.

    No - nothing leaves the Universe - that is what "Universe" means.

    Kinda - you could be talking about two things here ... dispersion of EM radiation in space, or the Hubble red-shift.

    The first is understood in terms of the field becoming more distributed in space and the second in terms of the expansion of space-time.

    Because that is how it works - high frequencies have higher energy.
    You can try it with physical objects - you have to work harder waving things back and forth at a high frequency than you do waving them at a low frequency.

    Light does not magically change frequency though ... the energy has to go somewhere.
    Where it goes depends on how the frequency change happened. eg. high frequency light can be absorbed by something which distributes the energy among its component parts, warming it up ... each part later radiates some of the energy. So you get high energy light in and low energy light out.
  4. May 25, 2013 #3

    Entropy increases over time in the Universe as start convert mass into energy through fusion?

    Isn't dispersion of EM radiation in space affected by the Hubble red-shift?

    I am sorry for asking questions like this. I am a writer.
  5. May 25, 2013 #4

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    The rule is: entropy in any closed system cannot decrease. However it can stay the same.

    The Universe is the ultimate closed system and it contains a great many processes which increase the total entropy - one of which is nuclear fusion in stars.

    Mass is also energy.
    Fusion does convert mass into other forms of energy.

    The Hubble red-shift is the effect, on dispersion, due to the expansion of space-time.

    What are you trying to figure out?
    Where are you getting these ideas from?

    There is an odd wording in your questions which makes me cautious about the kind of answers I give you.
    Last edited: May 25, 2013
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook