Evidence for fading stars?
It is well known to astronomers that the luminosity of certain bodies such as cepheids and type 1a supernovae emit a nearly constant luminosity homogeneously in all directions.
Imagine a spherical shell with radius r around a cepheid star,
the emitted luminosity over the angle or (proportion in radians) the observer composes of the entire shell is equal to the observed luminosity.
Or if you wish,
{The density of light is roughly equal to light emitted / 2πr) in the case of a 2-D plane, and light emitted / 4/3πr3 in the case of volumetric space, the total observed luminosity is equal to the density times the surface area of the observer on the plane perpendicular to the propagation of the light.}
According to the Hubble constant, the redshift of distant stars should vary according to their distance, or the redshift of distant stars should vary according to it's observed luminosity - as the observed luminosity / emitted luminosity is the value of which that distance was inferred. [also taking into account effects of time dilation]
This observed redshift has been interpreted as a doppler effect of light due to the relative recession velocity of the star, thus the relative recession velocity is a function of distance.
However, if that is indeed the case, the luminosity of any observed star beyond the Hubble length should decrease with time, a function directly agreeing with red-shift values, I have yet to find observational evidence for this. Leading me to conclude that it is premature to describe the redshift values as exclusively the result of relative recession velocity between the observers and these distant stars.
I am saying that the doppler argument may not be applicable to this situation.
Imagine a spherical shell with radius r around a cepheid star,
the emitted luminosity over the angle or (proportion in radians) the observer composes of the entire shell is equal to the observed luminosity.
Or if you wish,
{The density of light is roughly equal to light emitted / 2πr) in the case of a 2-D plane, and light emitted / 4/3πr3 in the case of volumetric space, the total observed luminosity is equal to the density times the surface area of the observer on the plane perpendicular to the propagation of the light.}
According to the Hubble constant, the redshift of distant stars should vary according to their distance, or the redshift of distant stars should vary according to it's observed luminosity - as the observed luminosity / emitted luminosity is the value of which that distance was inferred. [also taking into account effects of time dilation]
This observed redshift has been interpreted as a doppler effect of light due to the relative recession velocity of the star, thus the relative recession velocity is a function of distance.
However, if that is indeed the case, the luminosity of any observed star beyond the Hubble length should decrease with time, a function directly agreeing with red-shift values, I have yet to find observational evidence for this. Leading me to conclude that it is premature to describe the redshift values as exclusively the result of relative recession velocity between the observers and these distant stars.
I am saying that the doppler argument may not be applicable to this situation.
Total Comments 6
Comments
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There's nothing special about the hubble length in this context. In the observed spatially flat (where space is euclidean but spacetime is curved), the flux of a star goes as
F ~ 1/(r^2*(1+z)^2)Posted Sep4-08 at 08:32 PM by neutralseer 
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oh, and redshift is not interpreted as a doppler effect, but instead due to the expansion of space. That is, the wavelength of light is being continually stretched as it travels towards you.
Interesting questions, cosmology is wonderful
-neutralseerPosted Sep4-08 at 08:35 PM by neutralseer
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Would it matter how it's interpreted? Isn't the effect the same?Quote:oh, and redshift is not interpreted as a doppler effect, but instead due to the expansion of space. That is, the wavelength of light is being continually stretched as it travels towards you.
Posted Sep8-08 at 11:31 AM by WCOLtd
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I thought the hubble lenth is the distance in which the redshift effect becomes nonnegligible. (Where the expansion becomes the dominant behavior of the observed body)
Posted Oct14-08 at 07:44 PM by WCOLtd
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I think it's commonly accepted that the doppler effect (relativistic doppler redshift) is good up to about z=0.1 (about 1.3 billion light years distant) and that for z>0.1, the expansion of space itself needs to be taken into account in order to calculate the correct distance to an object (cosmological redshift).
Posted Oct16-08 at 05:29 PM by stevebd1
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I still don't see the difference between saying that "two bodies are receding away from each other", to saying "The space in between the two bodies is expanding" Are they not describing the same thing? And if they are not, how can a person distinguish between the two?
Posted Nov18-08 at 04:03 PM by WCOLtd
Updated Nov24-08 at 12:06 AM by WCOLtd
