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Thread: An expanding universe?

  1. #1 An expanding universe? 
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    I need some help unraveling my thoughts. I'm an amateur, so please guide me when my assumptions are wrong.

    I've heard stories about the expansion of the Universe, but there's one thing that's bugging me. Scientists have noted a particular red shift in the light they observe from distant galaxies and have concluded that the space in between us and the thing we're observing is growing further and further apart; that space is literally stretching the light as it travels to Earth. I'm fine with however this was calculated, but... Wouldn't it be just as plausible to say that since the thing we're observing no longer exists that what we're seeing is a star getting dimmer, or cooler? When the source burns out the light we see is obviously going to become dimmer over time. This would also change the colour of the light emitted from the star from higher frequencies like blue to lower frequencies like red or infrared. This would give us the illusion that the star is moving away from us when really it's just becoming cooler over time and emitting a different frequency of light.

    Some scientists also say that the greater the distance being observed the faster this effect of "growing space" becomes. To me it seems natural that the further back you look the cooler the light would appear to be, since it's been travelling longer than light closer to you... right?

    Is my idea plausible? If I've gone wrong please point out the folly!


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  3. #2  
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    The observed effect is on galaxies, and light from galaxies that are very distant. Stars within the Milky Way are not subject to expansion as the gravity within the galaxy overwhelms the effect.

    First page is blank- pdf file: http://www.mso.anu.edu.au/~charley/p...DavisSciAm.pdf


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  4. #3  
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    Quote Originally Posted by RyanF View Post
    Some scientists also say that the greater the distance being observed the faster this effect of "growing space" becomes. To me it seems natural that the further back you look the cooler the light would appear to be, since it's been travelling longer than light closer to you... right?

    Is my idea plausible? If I've gone wrong please point out the folly!
    Cooler objects redden in a quite different manner from cosmological redshift. A cooler blackbody, for example, simply has different amplitudes at the various wavelengths (with a heavier weight toward the longer wavelengths than for a hotter body), but the wavelengths themselves do not actually shift. A cosmological redshift involves an actual shift of spectral lines. Since we know where the non-shifted spectral lines of various elements are, we can watch them shift and thereby compute velocities. Btw, it was through the process of examining the lines of our own sun that helium was discovered (Helios being the Greek sun god). Only later was helium found on earth, then used to fill birthday balloons.

    You're basically invoking a cousin of the "tired light" hypothesis that has been considered -- and rejected -- for the better part of a century now. A good place to start reading about the problems with the idea is Ned Wright's Cosmology FAQ: Frequently Asked Questions in Cosmology
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  5. #4  
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    tired light, nice description.
    the difference would be that light still takes the same time to reach us.

    stand 20 meter away from someone with a flash light, then cover it with your hand, or stand 20 meter away from someone than increase then move away from the other person.
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