Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Could Einstein have been right originally?

  1. Feb 13, 2004 #1
    I was reading the other day about John Tyndall, who I believe was the first person to discover that because blue wavelengths are relatively short, they scatter and disperse more than red wavelengths. At this point I remembered that Einstein’s original theory of relativity had included a universal constant to counter-act universal expansion. If I recall correctly the main reason why this was later discarded was Hubble’s observation of red shift in cosmological bodies. So my question is this: If blue wavelengths scatter more than red, then could this not explain cosmological red shift? In fact it seems to me this would also explain why bodies that are further away, seem to be red shifting more. Or to put it another way, the farther a body is from earth, the more the blue wavelengths disperse before they reach us, leaving only the relative long and concentrated red wavelengths.
    I’m not trying to put forth that this idea might be right, in fact if I were right I’m sure Einstein himself would have thought of this. I’m simply hoping one of you physics guru’s might explain why I’m wrong. Thanks in advance.

    Shawn Wheeler

    P.S. It occurs to me it might have something to do with the rate at wich blue wavelengths disperse.
  2. jcsd
  3. Feb 13, 2004 #2
    Are you talking about the cosmological constant? If so, Einstein introduced it, then decided it was the worst mistake he'd ever made. As recently as about 10 years ago, I read a paper by Steven Hawking explaining why the cosmological constant was probably zero. Now, suddenly, we're thrust into the notion that the CC is decided not zero, because it's the only way to explain what we're seeing with the CMB.

    Personally, I don't buy the CC argument. My guess is that it really is zero, and there is something else afoot of which we're not yet cognisant. I don't go for the "finely tuned universe" theories.
  4. Feb 14, 2004 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    To answer your question about why blue-scattering can not be used to explain red-shift, I must first explain how red-shift is measured.

    The light from any body is a mixture of all the different colors from the spectrum, from red to violet. If we break it up into its component parts (say by passing it through a prism) we see the familiar rainbow pattern. If you look really close, you will note that there will be little bands where a particular frequencies of light are missing. These are called "absorbtion bands" and are caused by the particular elements the light emmiting body is made of. There are also bright bands called "emission bands", also caused by these elements.

    Each element has a particular pattern of lines located at particular points of the spectrum.

    Now when we look for red-shifting, we look for these bands. Since the redshift caused by recession effects all the frequencies of the spectrum, what we see is the that the particular bands for any given element will have "shifted" towards the Red end of the spectrum, thus we get a red-shift.

    With blue scattering what would happen is that we see a general reddening of the light due to the relative lack of blue light. As a result, the red end of the spectrum would be brighter than the blue end. However, Since this does not involve any actual shifting of the frequencies in the spectrum, the absorbtion and emmission bands for each element will not have moved.

    Thus, blue scattering cannot explain red-shift because it does not involve the the distinctive band shift that recession shows.
  5. Feb 14, 2004 #4


    Thank You
  6. Feb 18, 2004 #5
    Perhaps the book Stars and their Spectra would be a valuable introductory text to expound on Janus' response on this (and related) subject. Of course, most texts on spectroscopy would discuss these issues.
  7. Feb 19, 2004 #6
    GRQC - While janus properly explained the red shift mechanism which was the original inquiry (topic), i was curious as to your comments re the CC - I also believe the 1a supernova data has been improperly interpreted - do you have any theories?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook