Debrolie Redshift missing energy?

  1. I'm a college freshman at the moment, so perhaps i'm just missing something simple. But none of my professors can give me an actual answer.

    If photons of light from distant galaxies undergo redshift because of the expanding universe.
    Also since particles have a wavelength according to Debrolie's equation, then a particle's wavelength should change when it is coming from a distant galaxy.

    that is a problem for me since that suggests that the debrolie wavelength changed which means that it should have changed its momentum.

    But changing momentum is a violation of the law of conservation of momentum in this case.
    Also where did that energy go?
    speaking of which, were does the energy from the photons go in regular electromagnetic red shift?

    another problem the debrolie wavelength gives me is, if a particle like a proton has a charge it should interact with its own electric feild due to the hysterises of empty space.

    please explain some of this to me
    Last edited: Nov 12, 2004
  2. jcsd
  3. ZapperZ

    ZapperZ 29,631
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    Er... what do you mean by "change"? The wavelength and energy didn't just "change" while it is making its way from the source. These things were shifted UPON emission. It didn't just transform itself along the way. The photons were BORN that way as viewed from the observer's reference frame! So consider the drifting galaxy's motion as the "recoil" if you like.

  4. dextercioby

    dextercioby 12,292
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    Nope.Louis de Broglie said in his PhD:[tex]\lambda=\frac{h}{p} [/tex].So the wavelength varies,only if the momentum (speed) of the particle changes.In their year-long travel to our eyes,those photons do not practically interact with any other particles,so their wavelength (in their own reference system) remains the same.What we perceive,instead,is not that wavelength given by de Broglie formula,but a modified one,basically by two RELATIVISTIC factors (i'm speaking about photons):the Doppler-Fizeau effect (studied by SR) and the gravitational redshift (theoretically justified by Einstein in November 25th,1915).But i repeat,in THEIR OWN REFERENCE SYSTEM,THE WAVELENGTH IS CONSTANT AND INVERSE PROPORTIONAL WITH THE MOMENTUM,AS STATED by Louis de Broglie in November 1924.

    Nowhere,it stayed with the photon.

    1.What has de Broglie wavelength got to do with the charge (which charge,probably electric,hypercharge,isospin,color,...)??
    2.Assuming you're speaking about the electric charge,the inteaction of the proton with its electric field is stated by the laws of classical electrodynamics,so de Broglie wavelength is not in the picture...If you're speaking about the interaction between a fermionic 1/2 field and the electromagnetic vacuum,that's something else,and no mean to offend you in any way,but,seeing that simple topics like de Broglie's law give you headaches,you wouldn't understand neither the physics,nor the mathematics behind QED.I think...You're a freshman,right???So my assertion basically makes sense...

    Daniel. :wink:
    Last edited: Nov 13, 2004
  5. Thanks alot. Sorry if it was something of silly questions but all I have is chemistry at the moment and personally i'm a physics major. So i have read alot of books on physics but some things just never get cleared up. Also chemists trying to explain debrolie wavelength just ruins all the life in the topic. They never made any refrence to the refrence frames at all, but that makes alot of sence.

    and dextercioby it doesn't give me a headache cause i dont understand it, it gives me a headache because I could never find anyone to clear up the little issues.

    Thank you

    Actually on another side note.

    I know E=h/f and my older physics teachers told me frequency was always an integer(or at least in all the problems we've used F was always a whole number integer). But that never made sence to me.

    didn't make any sence because you would get harmonics with every wavelength of light over a long enough distance.
    Last edited: Nov 13, 2004
  6. jcsd

    jcsd 2,226
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    Gold Member

    One thing I think that is being missed here is that the redshift under discussion is NOT Doppler shift and it is NOT gravitational redshift it is cosmological redshift and it is not caused by radial motion.

    My answer then is a departure from the previous two answers as you've made a big assumption i.e. that energy-momentum IS conserved. Remember that general relativty allows us to treat all frames with equality and there is no physical theory (as far as I know anyway) that allows energy to be conserved in all frames, so the conservation of energy is not a general law in general relativity. Infact energy itself is not even a well-defined general concept in GR.

    So to answer your question the energy just disappears (though I quickly checked this answer and there seems to be a school of thought that this energy becomes graviational potential energy).
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