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(Q)
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I would like to hear some interpretations of this phenomenon, especially in regards to what happens to the energy of photons in cosmological redshift – where do YOU think it goes? Is it lost or is it conserved?
Originally posted by (Q)
I would like to hear some interpretations
of this phenomenon, especially in regards
to what happens to the energy of photons
in cosmological redshift – where do YOU
think it goes? Is it lost or is it conserved?
Originally posted by (Q)
I would like to hear some interpretations of this phenomenon, especially in regards to what happens to the energy of photons in cosmological redshift – where do YOU think it goes? Is it lost or is it conserved?
I think that Redshift is a change in the wavelength of the light reaching us, not a change in the energy of any particular photon(s) at all.Originally posted by (Q)
I would like to hear some interpretations of this phenomenon, especially in regards to what happens to the energy of photons in cosmological redshift – where do YOU think it goes? Is it lost or is it conserved?
WHAT ?! LINK, PLEASE !Originally posted by marcus
I heard a neat thing about GR. An amoeba
can move in curved space merely by changing shape.
Originally posted by Labguy
Remember, the Alien looking from the "other side" sees the same light source blue-shifted, same light source = same photon energy.
Whoa? Let's say we are here and the alien is way over there, and moving about equally relative to us. Place a fast-moving light source smack in the middle between us and the alien. The light source moves quickly away from us and toward the alien. We see a "redshift" (wavelength change) because its moving away from us. The alien sees a blueshift because it is moving toward him.Originally posted by LURCH
Not so. An alien on the other side would see the light red-shifted, just as we do. If he is the same distance away, he'll see the red-shift about the same amount, too.
Originally posted by Labguy
I am talking redshift from motion, not gravitational redshift.
Well it seems like an EXTREMELY "slow andOriginally posted by marcus
Hey drag! I do not have the URL. There is an
MIT archive of online physics goodies and I
found it there. Maybe I will come across it
again. Of course it was not a real amoeba,
I just called it that. The journal article
was about an object that can change its
shape and, by using locally curved spacetime,
can move around by changing shape thru a
cycle that leaves it the same original
shape but in a different place. If I see
it again I'll post it.
And also some things about all of the "missing energy".But this guy (Q) was talking about the COSMOLOGICAL redshift which happens from space stretching out while the light is under way towards us. this is a GR thing. It is not relative motion of source and receiver, but an effect of expansion of space itself.
Originally posted by Labguy
Whoa? Let's say we are here and the alien is way over there, and moving about equally relative to us.
Therein lies the problem - the photon doesn't change its wavelength. It is created at that wavelength because the source is moving. There is no missing energy.Originally posted by Zefram
But doesn't the relation between wavelength and energy for a photon imply that when a photon is Doppler shifted (from our point of view) that the amount of energy we measure for it has changed? So the photons reaching the alien actually have more momentum (if absorbed) than photons absorbed over here.
Is an "apparent" change in the energy of a photon different than an actual one (what is an "actual" one, anyway)?
Aether? Unnecessary. Just like sound - but now both the observer and the source are moving. And it doesn't matter what frame of reference you use (Relativity) you still get the exact same doppler shift. The frequency of the light does not change while it is traveling unless acted upon by a gravitational field.Originally posted by drag
selfAdjoint and russ, if you maintain a certain
permanent rest frame in the Universe you will
see the expansion of space-time decrease the
energy of at least photons and possibly
also the kinetic energy of all rest-mass particles
(though the rest masses appear to stay the same).
Live long and prosper.
Originally posted by (Q)
Marcus
the original post by (Q) called attention to the energy that has been lost from the universe by wavelength stretching caused by expansion of space.
Has the energy really been lost? Redshifted photons would indicate it has been lost.
But is because it is lost and not conserved or is it because our frame of reference has changed and conservation does not apply?
Originally posted by schwarzchildradius
OF course the photons are redshifted everywhere, so long as the universe is isotropic. Their energy is less, as we observe them at this Time because there is more Space now than when they were generated (from decoupling event). So the energy is indeed conserved, what is not conserved is space.
Here's one for you then: since light has no medium that it travels one, can it even HAVE a wavelength except at the instants of emission and absorption?Originally posted by (Q)
Labguy
I think that Redshift is a change in the wavelength of the light reaching us, not a change in the energy of any particular photon(s) at all.
A change in the wavelength IS a change in the energy.
Ding, ding - this is what I am getting at. The energy of a photon depends on your frame of reference. This is the same as the energy of ANYTHING. In order to know what the energy is, you have to define the frame of reference and different frames of reference will result in different (and equally valid) calculations of the energy.But is because it is lost and not conserved or is it because our frame of reference has changed and conservation does not apply?
No. Schwarz's law is a restatement of the density equation: d= e/vSchwarzschildradius's Law-----energy plus space is conserved
Originally posted by (Q)
Marcus
the original post by (Q) called attention to the energy that has been lost from the universe by wavelength stretching caused by expansion of space.
Has the energy really been lost? Redshifted photons would indicate it has been lost...
So, the Universe does not expandOriginally posted by russ_watters
The frequency of the light does not change
while it is traveling unless acted upon by
a gravitational field.
Originally posted by schwarzchildradius
OF course the photons are redshifted everywhere,
so long as the universe is isotropic. Their
energy is less, as we observe them at this
Time because there is more Space now than
when they were generated (from decoupling
event). So the energy is indeed conserved,
what is not conserved is space.
Originally posted by marcus
Schwarzschildradius's Law-----energy plus space
is conserved
Cosmological redshift is a phenomenon in which light from distant objects in the universe appears to be shifted towards the red end of the electromagnetic spectrum. This is due to the expansion of the universe, which causes the wavelengths of light to stretch as it travels through space.
The expansion of the universe causes the wavelengths of light to stretch, which results in a redshift. This means that the further away an object is, the greater the cosmological redshift will be.
The loss of photon energy in cosmological redshift is a result of the stretching of light waves as they travel through expanding space. This stretching causes the energy of the photons to decrease, resulting in a shift towards longer wavelengths.
No, the conservation of energy is not violated in cosmological redshift. While the energy of individual photons may decrease, the total energy of the photons is conserved. This is because the number of photons remains the same, and the decrease in energy per photon is offset by an increase in the overall volume of space.
Cosmological redshift is measured using a device called a spectrometer, which separates light into its component wavelengths. The amount of redshift is calculated by comparing the observed wavelengths of light from a distant object to the expected wavelengths based on its known distance from Earth.