The Red Shift ```Name: ken e anderson Status: N/A Age: N/A Location: N/A Country: N/A Date: 1993 - 1999 ``` Question: Could the red shift be caused by any other phenonenon"something" other than velocity of recession. ? In other words, could the mass of all the matter beyond the source of the emitted red shifted light cause a red shift? Replies: Yes. There is also a gravitational redshift as well as a Doppler redshift. However, it is only significant for light emitted from extremely massive bodies like quasars or black holes (light CAN be emitted from NEAR a black hole, as long as it's outside the black hole's event horizon). This phenomenon can be understood if you assume that photons have an equivalent rest mass proportional to their energy, m=E/c^2=h*nu/c^2 where h=Planck's constant; nu=photon's frequency. If we let g=GM/R be the gravitational potential where the photon is emitted, then the photon loses energy = delta_E = g*m when it flies out of the gravitational potential well of the mass M at radius R. If you work out the math, you'll find the photon's changes in frequency and wavelength to be: delta_nu/nu = g/c^2 and delta_lambda/lambda = 1/( c^2/g - 1 ) In astronomy we call delta_lambda/lambda the redshift of the object emitting the photon (usually designated by the letter Z). If g=c^2, then the redshift is infinite, and this would correspond to a photon being emitted right at an event horizon. See my next response for a modest attempt at explaining COSMOLOGICAL REDSHIFT. Hawley Cosmological redshift is an OBSERVATIONAL phenomenon discovered by V. M. Slipher in 1912 when taking spectra of distant galaxies. Edwin Hubble and M. Humason later showed that the amount of redshift was proportional to the faintness of the galaxy which presumably varies with the galaxy's distance. This relationship has come to be known as "Hubble's Law" and is expressed as z=H*r/c where z is the redshift (see previous response); H is the so-called Hubble constant; r is the distance to the galaxy; and c is, as always, the speed of light. There has been much controversy surrounding the origin of the cosmo- logical redshift -- whether it is due to Doppler redshift, gravitational redshift, or something as yet unknown. Current thinking favors the Doppler explanation and is used as evidence that the universe is expanding which, in turn, led to the Big Bang Theory of cosmology. (There is other eveidence that also supports the Big Bang, e.g., "primordial nucleosynthesis." One of the main goals of the Hubble Space Telescope is to pin down the exact value of the Hubble constant (another is to look for other stellar systems with planets.) If the Big Bang theory of cosmology and Einstein's Theory of General Relativity are both correct, then the value of the Hubble constant determines whether the universe is open or closed, i.e., whether the universe will continue to expand forever or eventually collapse upon itself. Hawley Click here to return to the Astronomy Archives

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