Spontaneous Energy Loss in Light

[Les Sleeth]

Originally posted by Alexander
. . . Marcus is wrong here, energy of photon conserves, thus frequency and wavelength too (in vacuum). Redshift of distant galaxis is just due to fact that they are moving away from us due to space expansion (Doppler shift due to coordinate transformation).

Well, I wish somebody would clear this up, I am very interested in knowing. Is this a dispute that is going on among cosmologists, or is there consensus? Other opinions would be welcome.

Alexander, from my understanding of what Marcus said, it didn't seem to me that he was disputing that the reshift observed from distant galaxies is due to the Doppler effect.

 

[marcus]

Originally posted by LW Sleeth
Well, I wish somebody would clear this up, I am very interested in knowing. Is this a dispute that is going on among cosmologists, or is there consensus? Other opinions would be welcome.

Alexander, from my understanding of what Marcus said, it didn't seem to me that he was disputing that the reshift observed from distant galaxies is due to the Doppler effect.

You might get into it at the level of a classic textbook like
Frank Shu
The Physical Universe: An Introduction to Astronomy
1982

He is a senior guy in the department at UC Berkeley.

Or another guy at Berkeley, Eric Linder, since he has some
notes online called Cosmology Overview. I would take his
FAQ for the layman with a grain of salt since very popularized
but his Cosmology Overview here is OK:

http://panisse.lbl.gov/~evlinder/lcos.pdf

I don't know any mainstream cosmologists who would agree with Alexander that the cosmological redshift is best viewed as a doppler shift.

Frank Shu warns strongly against interpreting (cosmological) z as a doppler shift because it is a common cause of confusion.
He draws a couple of diagrams (pages 373, 374) and goes into a couple of pages of discussion to make sure students understand.

EM wave propagation, Maxwells eqns, takes place in space and tiny changes in metric have a cumulative effect. Shu uses the
figurative way of describing it that I do---he says it is better to think of it as wavelengths being "stretched out" than to picture it due to Doppler.

Linder takes it for granted that the (cosmological) 1+ z is simply the ratio of the scale factors a(t) at emission time and reception time----nothing to do with velocity of emitter at time of emission.

the formula he presents (a non-doppler) is the one all cosmologists use that I have ever seen

1+z = a(t_rec)/a(t_em)

a(t) is the parameter in the metric that keeps track of the expansion of space. The Hubble parameter changes with time
and is defined as the time derivative of a(t) divided by a(t).

That is, essentially the time-rate of expansion but as a fraction of current size.

da/dt divided by a

That is just how everybody defines the Hubble parameter and
the usual metric is R-W defined using a(t) and
the consensus formula for cosmological redshift (as distinct from individual motion doppler) is this ratio involving a(t) I told you.

People will say different things when they POPULARIZE but what I am saying is, I believe, very consensus mainstream cosmologists' view of cosmo redshift.

Alexander's viewpoint is highly eccentric or reflects a deep misconception. Dont understand his continual repetition of it.

Anyway he is welcome to see it as Doppler---that way is very common in newspapers and popular books because more easily understood by non-technicals.

But try to understand it as a stretching out as space expands
and eventually things will make better sense to you. Promise

 

[heisenberg]

Hi, I am new! so hi to everyone

I guess a photon could spontainiously lose energy, if it coincidentally collided with a virtual particle, that is created along its trejectory.

The photon would recoil and lose energy, in accord with the compton effect! But would be
deflected at some unknown agngle!

The lost energy of the photon, would have to create a new photon of a longer wavelength.
As it recoiled with the virtual particle. Before the virtual particle disappeared again!

 

[Les Sleeth]

Originally posted by marcus
But try to understand it as a stretching out as space expands
and eventually things will make better sense to you. Promise

Thanks. Actually as you explain it is exactly how I want to see it since it coincides with a little theory I have. I don't mind doing my homework but it is difficult for laypersons to find much discussion of such things in language we can understand.

I have a hypothetical for you, which I will ask in two parts. Part I: How far do you think light might "stretch." Say 10^100 years from now the matter of the universe has radiated away its energy, and so all that is left is a vast continuum of cosmic radiation. I realize according to what you've said light's energy could eternally decrease incrementally, but what if light has a base state where it blends into one huge subtle wave.

Part II: Now imagine this vast continuum reversing its direction, so that base state light begins to converge on a point until it reaches some critical degree of convergence and explodes. In other words, might not the universe be the result of light caught up in a cycle of convergence and divergence?

 

[marcus]

Originally posted by LW Sleeth


I have a hypothetical for you, which I will ask in two parts. Part I: How far do you think light might "stretch." Say 10^100 years from now the matter of the universe has radiated away its energy, and so all that is left is a vast continuum of cosmic radiation. I realize according to what you've said light's energy could eternally decrease incrementally, but what if light has a base state where it blends into one huge subtle wave.

Part II: Now imagine this vast continuum reversing its direction, so that base state light begins to converge on a point until it reaches some critical degree of convergence and explodes. In other words, might not the universe be the result of light caught up in a cycle of convergence and divergence?

I. Light that is redshifted enough becomes undectable. We both are contemplating this.
You came up with a nice image of it----the light is dissolving into the vacuum-----is reabsorbed by the universe.
But a spoilsport with a lame imagination might prefer to look at it as the light's energy just goes to zero---it fades out of existence---as it is progressively more and more redshifted.
All I can do here is what I always try to do----look at the same thing both ways: in a cold objective light and also in figurative imagery, and to refuse to choose between them.

II. I have not heard any evidence that the universe is slated to recompress itself and its light.

The sparsity of matter and the observed spatial flatness suggest boundless expansion.

But IF it were start falling back together all the stretched-out-to-almost-nothing light would start coming back to life.

The CMB which is now 2.725 kelvin was once upon time 3000 kelvin. This 2.725 kelvin is the basic temperature of space (now). If the universe were to collapse the basic temperature of space would rise to
3000 kelvin (less than the surface of the sun but more than the tungsten filament of a 100watt lightbulb) as it was in its beginning.

And that wouldn't even be the end of it----the CMB was emitted after the universe had existed 300 thousand years. So when 3000 kelvin were reached there would still be 300 thousand years left to continue collapsing. The temperature would keep on rising. Space would be like the inside of a star.

To be fully human I expect one must try to look at these things both skeptically and objectively
(there is no suggestion of anything but continued expansion) and also responsively.

You asked about "bounce" scenarios:
dark energy estimated to be 73 percent of the total energy density in the universe is the key to that possibility. there is not enough light. the light could not cause a collapse to "bounce" but dark energy (under certain assumptions) could cause a bounce----ive seen such scenarios plotted out but they are too speculative for me---cant find them interesting. Simply burning up is poetical enough

 

[Les Sleeth]

Originally posted by marcus
Simply burning up is poetical enough

Thanks Marcus, it has been interesting.