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MrObvious
2004-Jun-09, 03:14 AM
I asked this question in another thread but it was either too obvious or not on topic so wasn't answered. I still have no clue however....

If the light from a distant star undergoes redshifting, then it arrives to us with less energy than it left the star. So where did its energy go?

Considering the amount of stars out there and that all their light is getting redshifted (uniform expansion..) thats a lot of energy going somewhere.

Feel free to point out the obvious, it seems like I'm always missing it!


Regards,

eburacum45
2004-Jun-09, 03:30 AM
I have said it before, and I'll say it again;
you can't really apply thermodynamics to the expansion of the universe...

it is just expanding and that's that; losing a little bit of energy to redshifting is trivial compared to the cosmological constant...

MrObvious
2004-Jun-09, 06:53 AM
I have said it before, and I'll say it again;
you can't really apply thermodynamics to the expansion of the universe...


I've looked for posts on this topic, before and after your reply. I haven't really found it to be addressed.

Stating that you can't apply thermodynamics to the expansion is not an answer initself. If this is the mainstream view then why does it not apply?

If one asks "why can't we travel at the speed of light" the answer "because we can't" is not sufficient.


it is just expanding and that's that; losing a little bit of energy to redshifting is trivial compared to the cosmological constant...

I did not ask if the universe is expanding or not, I asked where the energy has gone.
As for a small amount of energy, it seems to me that the entire energy produced by the stars will eventually be "lost" to red shift. Dismissing this amount of energy as trivial seems to to be avoiding the issue rather than facing it.

Gerbil94
2004-Jun-09, 09:19 AM
I asked this question in another thread but it was either too obvious or not on topic so wasn't answered. I still have no clue however....

If the light from a distant star undergoes redshifting, then it arrives to us with less energy than it left the star. So where did its energy go?


I think it's dropped out as a result of an integration time that's too short - the total energy has not changed, the energy density has.

The photon energy is still conserved, but it's spread over a larger volume of space and a longer time interval when it reaches us. If you integrated for (1+z) times longer than the original event (over all directions from the original source) you'd receive the amount of energy originally emitted, the amount expended in an inertial frame containing the original event.

Say you have a 20W flashlight and turn it on, then off after a second. Obviously, the flashlight expended ~20J. Acquire a research monkey, give it the same flashlight and place it on a galaxy at a redshift z (say). The monkey points the flashlight at your telescope*, and turns it on, and then off after a second. The flashlight has again expended 20J. As the photons traverse the intervening distance between the monkey and your telescope, they must obey the prevailing spacetime metric, which in an expanding, homogenous, isotropic universe requires that time and all three unique space intervals increase by factors of 1 + z between distant galaxies and us.

So, frequency indeed drops producing a redshift (because time intervals increase), but also the time for which the monkey held the flashlight on increases as far as we are concerned. The total energy is decreased by a factor of 1+z (we receive energy at a slower rate due to redshifting, as you point out) but then increased by a factor of 1+z (we can receive the energy for longer); they cancel, we can all go home.

I have assumed that your telescope gathers all the light available from the flashlight in the spatial directions - without this assumption (say, if you are measuring surface brightness rather than total light from your target) you expect that surface brightnesses of distant galaxies are dimmed by factors of 1/(1+z)^4 - three factors from volume expansion and one from time expansion of the universe.

I hope this helps (I also hope it's correct :) )

*This telescope is some piece of work. The flashlight's pretty good too.

EDIT (sloppy language, sorry): should be "... galaxies are dimmed by a factor of (1+z)^4" or "... galaxies are brightened by a factor of 1/(1+z)^4".

superted
2004-Jun-09, 10:07 AM
Gerbil94 - I think you're correct.

Each photon arrives with the same energy it left with, they're just more spread out when they arrive.

MrObvious
2004-Jun-09, 10:10 AM
That's a dam logical explaination if I ever heard one. :D
Yep, so obvious I missed it. Thanks.

Regards,

eburacum45
2004-Jun-09, 01:56 PM
I apologise; I thought this question was addressing the energy balance of the entire universe;

a little bugbear of mine, almost enough to make me reclassify myself as against the mainstream;
perhaps some cosmologist will give me an answer, but basically
there is such a thing as a free lunch;
the Universe is increasing in energy constantly;
how can the notion of thermodynamics apply in an accelerating expansion scenario?

(sorry about the hijack)

George
2004-Jun-10, 12:31 AM
I apologise; I thought this question was addressing the energy balance of the entire universe;

a little bugbear of mine, almost enough to make me reclassify myself as against the mainstream;
perhaps some cosmologist will give me an answer, but basically
there is such a thing as a free lunch;
the Universe is increasing in energy constantly;
how can the notion of thermodynamics apply in an accelerating expansion scenario?
The energy may have been there all along. As I understand the Higgs Field (Ocean) idea, energy is residual within the Higgs field. As the overal density of the universe declines, we see acceleration since it now has the upper hand. How much longer it will last should depend on the remaining residual energy within the field. This is just my limited understanding. Hope it's close to the actual theory. In a few years, there is a good chance for finding Mr. Higgs (assuming string theory holds up).

George
2004-Jun-10, 01:01 AM
I asked this question in another thread but it was either too obvious or not on topic so wasn't answered. I still have no clue however....

If the light from a distant star undergoes redshifting, then it arrives to us with less energy than it left the star. So where did its energy go?


I think it's dropped out as a result of an integration time that's too short - the total energy has not changed, the energy density has.

The photon energy is still conserved, but it's spread over a larger volume of space and a longer time interval when it reaches us. If you integrated for (1+z) times longer than the original event (over all directions from the original source) you'd receive the amount of energy originally emitted, the amount expended in an inertial frame containing the original event.

Say you have a 20W flashlight and turn it on, then off after a second. Obviously, the flashlight expended ~20J. Acquire a research monkey, give it the same flashlight and place it on a galaxy at a redshift z (say). The monkey points the flashlight at your telescope*, and turns it on, and then off after a second. The flashlight has again expended 20J. As the photons traverse the intervening distance between the monkey and your telescope, they must obey the prevailing spacetime metric, which in an expanding, homogenous, isotropic universe requires that time and all three unique space intervals increase by factors of 1 + z between distant galaxies and us.

So, frequency indeed drops producing a redshift (because time intervals increase), but also the time for which the monkey held the flashlight on increases as far as we are concerned. The total energy is decreased by a factor of 1+z (we receive energy at a slower rate due to redshifting, as you point out) but then increased by a factor of 1+z (we can receive the energy for longer); they cancel, we can all go home.

This is probably the best explanation I have seen. However, this seems to be more of a power explanation rather than an energy explanation. If the expansion causes the light to be received over a two second period, then, the power would be 10 watts or 10 Joules/sec. The photons would be half in number from the original emission during each second, but, why don't they have the same energy per photon as when they left. They are now half in number but twice the duration but still should have the original 20 Joules. But, they don't due to the expansion.

It is easier to understand Doppler shift with the train whistle analogy as sound waves arrive at a slower speed to your ear which lowers the pitch (frequency), assuming the train is moving away from you. Since light is not allowed to slow down from the expansion (or anything else), it seems to know to lower it's frequency instead. I do not see how a photon, at light speed, can stretch, although, it does seem to behave that way. #-o

Ricimer
2004-Jun-10, 01:04 AM
yeah, Gerbil said what I was gonna say, and a damn sight better and more thurough too.

I was just gonna say: Its there, just spread out in volume and time. And leave it at that.


And that was the result of nearly....way to many posts of debate over at space.com.

Kudos Gerbil.

Tensor
2004-Jun-10, 02:20 AM
It is easier to understand Doppler shift with the train whistle analogy as sound waves arrive at a slower speed to your ear which lowers the pitch (frequency), assuming the train is moving away from you. Since light is not allowed to slow down from the expansion (or anything else), it seems to know to lower it's frequency instead. I do not see how a photon, at light speed, can stretch, although, it does seem to behave that way. #-o

George, while I'm not knocking Gerbil explanation (Since it was a very good one), but your last paragraph does bring up a question that has been brought up before. Easiest way for me to visualize it is the following.

The energy of a wave is related to it wavelength. As the wave travels through expanding space, the wavelength is stretched by the expanding space. Producing a longer wavelength, and thus a lower energy.

A photons energy is related to it's momentum. As it moves through expanding space, it's momentum is reduced due to traveling through the addtional space caused by the expansion, and thus a lower energy.

Now I'm not claiming that this is an actual model of what is happening, just a handy visual analogy for me.

George
2004-Jun-10, 02:56 AM
The energy of a wave is related to it wavelength. As the wave travels through expanding space, the wavelength is stretched by the expanding space.
But is a photon so wimpy that the expansion "stretches" it, yet an entire galaxy can hold it's shape from mere gravity? Also, the time it takes for the photon to make it's trip is....0 sec. (as far as it sees) so it must really stretch fast from it's perspective.


...Producing a longer wavelength, and thus a lower energy.
I suspect it might be the opposite. It loses energy so it must lose frequency( f=E/h). Same is true for it's momentum. If it loses energy it is losing relativistic mass and, therefore, loses momentum (the velocity remains the same)

Maybe if we knew why the speed of light is fixed regardless of any frame of reference, the answer would pop up. I presume no one knows yet. #-o

Tensor
2004-Jun-10, 04:44 AM
The energy of a wave is related to it wavelength. As the wave travels through expanding space, the wavelength is stretched by the expanding space.
But is a photon so wimpy that the expansion "stretches" it, yet an entire galaxy can hold it's shape from mere gravity?

"Mere' is not a word I would use in describing gravity from a galactic mass. While it is the weakest of the four forces, two (the strong and weak) are only felt, approximately, across the width of a nucleus. The other long range force (EM) can be repulsive and attractive and pretty much balance. Gravity is only additive and thus can affect things the other three can't. If you think about it, even something even smaller than our moon will force its mass into a shpere, against the EM force.
And don't forget, were talking about traveling over a much larger distance than the width of a galaxy.


Also, the time it takes for the photon to make it's trip is....0 sec. (as far as it sees) so it must really stretch fast from it's perspective.

Nope, it stretches from our perspective. It would see no change in itself.



...Producing a longer wavelength, and thus a lower energy.

I suspect it might be the opposite. It loses energy so it must lose frequency( f=E/h).

A lower freqency and a longer wavelength are equivalent. L=c/f


Same is true for it's momentum. If it loses energy it is losing relativistic mass and, therefore, loses momentum (the velocity remains the same)

Try to stay away from idea of relativistic mass, it can be a confusing concept. In the Energy momentum 4-vector, mass is an invariant. It is strictly momentum that is lost, when energy is lost, and you did get that right.


Maybe if we knew why the speed of light is fixed regardless of any frame of reference, the answer would pop up. I presume no one knows yet. #-o

Yep. Sorta like why does the electron have the mass that it does? It just is. Try not to read too much into my explanation. As I said, it's the way I can visualize the difference between a how a wave loses energy through a longer wavelength and how a photon loses energy by losing momentum. It's a very simplistic analogy and doesn't mean that it actually works that way in the math.

George
2004-Jun-10, 12:45 PM
The other long range force (EM) can be repulsive and attractive and pretty much balance. Gravity is only additive and thus can affect things the other three can't. If you think about it, even something even smaller than our moon will force its mass into a shpere, against the EM force.
The problem I still have rests in the idea that a particle like a photon is somehow "stretched" while not even a galaxy, or cluster, suffer from any expansion consequence. Even more so, I do not expect the individual particles which make up these galaxies suffer some sort of stretching due to expansion. What is so special about a photon particle?




Also, the time it takes for the photon to make it's trip is....0 sec. (as far as it sees) so it must really stretch fast from it's perspective.
Nope, it stretches from our perspective. It would see no change in itself.
Apparently, this is what we observe but, physically, how?




...Producing a longer wavelength, and thus a lower energy.
I suspect it might be the opposite. It loses energy so it must lose frequency( f=E/h).
A lower freqency and a longer wavelength are equivalent. L=c/f
True. I was just wondering which was the cause and which was the effect. Is energy being drained from the photon causing the longer wavelength, or is the wavelength stretching making us see a longer wavelength? The former makes more sense as it states energy is less, whereas, the latter indirectly addresses the issue of energy depletion.



Same is true for it's momentum. If it loses energy it is losing relativistic mass and, therefore, loses momentum (the velocity remains the same)
Try to stay away from idea of relativistic mass, it can be a confusing concept. In the Energy momentum 4-vector, mass is an invariant. It is strictly momentum that is lost, when energy is lost, and you did get that right.
Since the photon's "rest mass" is 0 (assuming the little guy could "rest"), it can have no momentum (mv) unless it has relativistic mass found in m=e/c^2.



Maybe if we knew why the speed of light is fixed regardless of any frame of reference, the answer would pop up. I presume no one knows yet. #-o
Yep. Sorta like why does the electron have the mass that it does? It just is. Try not to read too much into my explanation. As I said, it's the way I can visualize the difference between a how a wave loses energy through a longer wavelength and how a photon loses energy by losing momentum. It's a very simplistic analogy and doesn't mean that it actually works that way in the math.
I think the idea of "stretching" works very well mechanically. I thought when I first asked about this photon redshift behavior that I would get hit with entropy or something complex. Now it's a deeper intrigue that might lead to a deeper space-time understanding. Or maybe I have been reading too much Brian Greene's stuff lately. :)

Ricimer
2004-Jun-10, 03:15 PM
Since the photon's "rest mass" is 0 (assuming the little guy could "rest"), it can have no momentum (mv) unless it has relativistic mass found in m=e/c^2.



Actually a photon does have momentum, desptie that. http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/relmom.html


Here's a question for you: What makes you think a photon is cohesive?

Is there any force, within the photon, that acts to keep it together? Like the chemical bonds that hold me together, or gravity that holds this planet?


I can think of no such force for a photon.

And without that, being stretched by expansion is easy.

Ari Jokimaki
2004-Jun-10, 03:58 PM
Here's a question for you: What makes you think a photon is cohesive?

Is there any force, within the photon, that acts to keep it together? Like the chemical bonds that hold me together, or gravity that holds this planet?


I can think of no such force for a photon.

And without that, being stretched by expansion is easy.

So you're saying that photon has internal structure?

TravisM
2004-Jun-10, 04:04 PM
As far as I know the photon is described by quantum theory as being a 'wave-packet.' This is a wave electromagnetic radiation that is localized along its direction of travel. It does indeed have internal structure in the repsect that it has a defined frequency. I think that relavisticly, since it has energy, it does indeed have momentum and mass, but no 'rest' mass. It only exists in motion, at the speed of light...
I think that's where I step off...

George
2004-Jun-10, 07:43 PM
Here's a question for you: What makes you think a photon is cohesive?

Is there any force, within the photon, that acts to keep it together? Like the chemical bonds that hold me together, or gravity that holds this planet?

I can think of no such force for a photon.
If the wave of the photon did not have some sort of internal tension, wouldn't the wave itself fall apart, split, disolve or something? I do not know. I just don't see it.

Here's another little quirk. Why isn't the amplitude of the light wave ever an issue? Other waves sure have them. I presume, all light waves have the same amplitude so only it's wavelength need be known to determine it's energy. This is also a hint that the wave has some sort of inflexibility.

Where's Eta C when we need him? :)

Ricimer
2004-Jun-10, 08:52 PM
Okay, imagine the wave traveling from left to right. The E and M fields are osilating up and down, an din and out of your field of view. It has tension in those directions (of a sort, changes in the e&m field in those directions are countered by the oposing field in the opposite direction, you know, why it's self-propagating).

Now, there is no force keeping the thing together in the left-right orientation, the direction it gets stretched by expansion.

In more technical terms, I know of no mechanism that keeps the photon longitudinally coherent...longitudinal being the traditional sense, the direction of propagation.



Amplitude in Light is intensity, as it is in sound. Photons have a fixed amplitude (I think.....umm...don't quote me). The overall wave has an amplitude, depending on the strength. In particle terms, greater intensity=greater amplitude=greater # of photons.

And this is what decays, per unit area, as the light spreads out from a source.

George
2004-Jun-10, 09:32 PM
Okay, imagine the wave traveling from left to right. The E and M fields are osilating up and down, an din and out of your field of view. It has tension in those directions (of a sort, changes in the e&m field in those directions are countered by the oposing field in the opposite direction, you know, why it's self-propagating).

Now, there is no force keeping the thing together in the left-right orientation, the direction it gets stretched by expansion.

In more technical terms, I know of no mechanism that keeps the photon longitudinally coherent...longitudinal being the traditional sense, the direction of propagation.
Hmmm. Doesn't the oscillation of the magnetic field induce the oscillation of the electric field which induces the oscillation of the magnetic field, etc? The field intensity has this strength which holds and dances with it's sister field. I see the em field of the photon having a strength (flux) much greater than the strength of the gravitational field strength between two galaxies at the opposite ends of a cluster which are not stretched by the expansion. If I am right, is the photon stretched or is something draining it's energy? #-o


Amplitude in Light is intensity, as it is in sound. Photons have a fixed amplitude (I think.....umm...don't quote me). The overall wave has an amplitude, depending on the strength. In particle terms, greater intensity=greater amplitude=greater # of photons.

And this is what decays, per unit area, as the light spreads out from a source.
Assuming the space between each photon increases from expansion, the intensity would be less but it would be observed proportionally longer. If energy is not somehow drained from each photon, somehow, then each photon should have the same frequecy but the overall light pulse would be dimmer, IMO. If the expansion sneaks in between a photon's wave peak somehow, why would we suppose that this forces it to loose energy. E=hf requires this to be the case, but where did the energy go?

Curious ain't it? :o

Ricimer
2004-Jun-11, 01:38 AM
you're right, the E and M fields tug on eachother, as I said.

The thing is, they tug on eachother in a plane perpendicular to the line of travel.

And, it is along this line of travel that the stretching occurs.

I.e. the expansion occurs in the dimensiont that the E&M fields don't hold any sway.



When light is traveling, its best thought of as a big wave, as opposed to a bunch of photons. You'll get the same answer, either way, its just a lot easier to do the work via the wave in this case.

George
2004-Jun-11, 01:19 PM
When light is traveling, its best thought of as a big wave, as opposed to a bunch of photons. You'll get the same answer, either way, its just a lot easier to do the work via the wave in this case.

I feel sure I understand your point of view. Your are saying that if a road with two bicyclers traveling at the same speed were to be, somehow, streched, the two riders would be further apart. Hence, light has a longer wavelength. This does match what is observed.

However, if the two riders were connected by a rubber band, a slow and gentle road stretching would have no affect on the distance between them.

In the case of light, if it loses energy, it gains wavelength. Hmmm...I suspect SR is more at work here, or something. Since we are traveling at a fast clip from the monkey's flashlight at the time we see the light, I would expect the impact (energy) from the light to be less. Since it does not change it's speed, we will see a change in wavelength instead. If we could, somehow, stop our motion relative to the monkey at the time we observed his light, would not the light wavelength be the same as when it left?

Ricimer
2004-Jun-11, 05:57 PM
If we stopped our motion, and the streched was due solely to "doppler" shifting, then yes, it would appear to be normal.

However, expansionary redshift actually changes the wavelength in route...so it would still be different...that is until the light emitted after we "stopped" would arrive.



I understand the bike example..I'm saying there is no rubber band!! You can keep the bikes in a straight line, not getting taller, or wider (thats the E&M pulling on eachother) but there is no force keeping them from getting longer.

There is no rubber band.

George
2004-Jun-12, 01:52 AM
If we stopped our motion, and the streched was due solely to "doppler" shifting, then yes, it would appear to be normal.

However, expansionary redshift actually changes the wavelength in route...so it would still be different...that is until the light emitted after we "stopped" would arrive.
That I did not know. However, why wouldn't light emitted after we "stopped" also be redshifted. Although we (or the emiiter or both) would have to be moving to oppose the expansion in order to keep equidistance, the photon would only experience a lesser degree of redshift but not eliminate the redshift. Aren't you saying the expansion is constantly stretching the wavelength, so why would it not exhibit some even if we are not moving relative to the emitter (based on what you seem to be saying). I suppose I have the understanding that it is just Doppler shifting, so I won't be shocked if I'm wrong but I would like to get a handle on it.


I understand the bike example..I'm saying there is no rubber band!! You can keep the bikes in a straight line, not getting taller, or wider (thats the E&M pulling on eachother) but there is no force keeping them from getting longer.

There is no rubber band.
I knew that is what you are saying. Given a photon as a particle, I suppose it would be fair to think of it as a two dimensional disk traveling perpendicular to the plane of the disk. It is hard to see expansion stretching it. However, it is also a wave of em energy. Electric and magnetic fields exhibit tension internally. How does the expansion stretch them with such little effort?

Ricimer
2004-Jun-12, 04:27 AM
George: I thought your motion was entirely expansionary.

You've got it right in that last post.



As for the photon stretching: its simple really. And it helps if you think of it as a cylinder, not a 2d disk. It has a width in all directions.

E&M forces keep the photon together in a certain set of directions,a nd that's perpendicular to the line of travel.

However, expansion works along the line of travel, where E&M has no influence, and so it's stretched easily, because theres nothing to keep it to gether in that direction.

George
2004-Jun-12, 10:39 PM
George: I thought your motion was entirely expansionary.

You've got it right in that last post.

As for the photon stretching: its simple really. And it helps if you think of it as a cylinder, not a 2d disk. It has a width in all directions.

E&M forces keep the photon together in a certain set of directions,a nd that's perpendicular to the line of travel.

However, expansion works along the line of travel, where E&M has no influence, and so it's stretched easily, because theres nothing to keep it to gether in that direction.

Does this conversation sound familiar? :)

Ricimer
2004-Jun-13, 02:36 AM
....yes, as a matter of fact, I wasn't distinguishing between the two seperate posts...I thought they were the same thing!

Ari Jokimaki
2004-Jun-13, 07:44 AM
There seems to be three competing views for the cause of the redshift in expanding universe:

1. Bunch of photons form a wave with certain frequency. Expanding space then causes the distance between these photons to grow, causing the wave get longer and it's redshift to grow. This at first hand sounds quite reasonable, but I don't think that this is correct, because it lacks the explanation how single photon is redshifted.

2. Expansion of space carries galaxies away from each other, causing actual motion between them. This motion causes redshift that looks like regular Doppler shift. I don't think that galaxies would feel this motion, because, if I have understood correctly, the space in their vicinity doesn't expand (presence of mass halts the expansion). So when photon starts it's journey from a galaxy, it is emitted to non-expanding space. And when the photon arrives from it's journey to another galaxy, it is absorbed from non-expanding space. On either end, photon doesn't know that there is expanding space between those two galaxies, because the interfacing happens in non-expanding conditions. Therefore I don't think that this could cause redshifting.

3. Photons are elastic particles and can be stretched, so the expansion of space stretches them, causing their wavelength to get longer. It is difficult for me to imagine how elementary particles could change their form, but I cannot come up with any sensible arguments against this, but I have one question related to this:


E&M forces keep the photon together in a certain set of directions,a nd that's perpendicular to the line of travel.

Where does those E&M forces come from, aren't photons chargeless particles?

JMB
2004-Jun-13, 07:58 AM
There are lots of problems supposing that the whole redshift of the spectra is produced by the Doppler (or expansion) effect: The bigbang requires a lot of strange hypothesis (dark matter, dark energy for instance).
The users of pulsed lasers observe, every day, redshifts produced by a parametric effect named "impulsive stimulated raman scattering" (ISRS). The theory of ISRS applies to ordinary incoherent light, but , as the parameters of this light are very different, it takes a new name: Coherent Raman effect on incoherent light (CREIL).
The CREIL transfers energy from light beams whose Planck's temperature is high to beams whose temperature is lower (it is thermodynamics). Thus, the first beams are redshifted, the other blueshifted.
I recall that in a parametric effect, the matter recovers its initial state after an interaction, so that the exchanges of energy with the light beams are not quantified, and that the effect is coherent, so that the trajectories of the beams are unchanged. The relative frequency shifts df/f are nearly constant, so that the CREIL may be confused with a Doppler effect.
The CREIL works in astrophysics, transferring, in the practice, energy from the IR, visible and UV light to the thermal radiation (2.7K, or radiation attributed to hot dust).
The gas which works as a catalyst must be low pressure and have Raman transitions lower than 500 MHz (Roughly).
The theory of stars, which is reliable says that old neutron stars may accrete matter (accretors) , and become very visible, but no accretor was ever observed. Making their spectra with taging into account CREIL by atomic hydrogen excited to get a principal quantum number n=2 or 3, a very complicated spectrum is obtained, which is ... the spectrum of a quasar !
Therefore, the quasars are not very far, very heavy, radiating an incredible energy.

A lot of other problems are solved using CREIL : the "intrinsic redshifts" used by Halton Arp, the increase of frequency of the Pioneer probes for instance.

Why do the astrophysicists did not take CREIL, a very simple optical effect, into account ?

Tensor
2004-Jun-14, 02:59 AM
E&M forces keep the photon together in a certain set of directions,a nd that's perpendicular to the line of travel.

Where does those E&M forces come from, aren't photons chargeless particles?

Ari, Under the Standard Model, photons are the guage boson (force carrier) for the EM force. Much as gluons are the boson for the color force and the W-, W+, and Z are the bosons for the weak force.

Ari Jokimaki
2004-Jun-14, 11:32 AM
Ari, Under the Standard Model, photons are the guage boson (force carrier) for the EM force. Much as gluons are the boson for the color force and the W-, W+, and Z are the bosons for the weak force.

Yes, I knew that, perhaps I should revise my question. I was under impression that EM-field is generated by electric charges, but after I did some googling on this subject, I noticed that photons are considered to have EM-field, even though they don't have electric charge. This confuses me little. Why are chargeless particles able to generate EM-field? Has spin got something to do with this? Or perhaps this is something that is observed, but nobody (yet) knows why it is so?

George
2004-Jun-14, 02:49 PM
There appears to be now 3 threads on this topic. 8) :)
Nice post, Ari.


1. Bunch of photons form a wave with certain frequency. Expanding space then causes the distance between these photons to grow, causing the wave get longer and it's redshift to grow. This at first hand sounds quite reasonable, but I don't think that this is correct, because it lacks the explanation how single photon is redshifted.
I would think only the intesity of the light would diminish as the photons/sec are fewer. However, as you suggested, this will not increase the wavelength of each photon necessarily, IMO. I can't see how a photon would stretch. To stretch it would require doing work to it which would not lower it's energy. If it has no lognitudnal elasticity why wouldn't it just fall apart. Unless the expansion is somehow robing the energy from the photon, I do not see anything other than a form of Doppler effect. (The validity of CREIL is a maybe but my knowledge is too limited.)


2. Expansion of space carries galaxies away from each other, causing actual motion between them. This motion causes redshift that looks like regular Doppler shift. I don't think that galaxies would feel this motion, because, if I have understood correctly, the space in their vicinity doesn't expand (presence of mass halts the expansion). So when photon starts it's journey from a galaxy, it is emitted to non-expanding space. And when the photon arrives from it's journey to another galaxy, it is absorbed from non-expanding space. On either end, photon doesn't know that there is expanding space between those two galaxies, because the interfacing happens in non-expanding conditions. Therefore I don't think that this could cause redshifting.
As I understand it, the expansion rate is too weak, currently or in the past, to overcome the force of gravity within a galaxy or within a cluster of galaxies. The space within them is expanding but too slowly to be very noticeable. The expandig space would give the receiving galaxy additional recessional velocity from the emitter causing a redshift affect. If expansion is accelerating, the redshift will be even greater over time.


3. Photons are elastic particles and can be stretched, so the expansion of space stretches them, causing their wavelength to get longer. It is difficult for me to imagine how elementary particles could change their form, but I cannot come up with any sensible arguments against this, but I have one question related to this:


E&M forces keep the photon together in a certain set of directions,a nd that's perpendicular to the line of travel.

Where does those E&M forces come from, aren't photons chargeless particles?
[I'm the wrong guy to attempt an answer, but, why should I start letting my lack of knowledge interfere now. :) ] Doesn't everything have a wave function? The smaller the "particle" the greater the wave behavior. Maybe a photon does have charge...positive then negative then positive, etc. :)

Ari Jokimaki
2004-Jun-15, 09:39 AM
I can't see how a photon would stretch. To stretch it would require doing work to it which would not lower it's energy. If it has no lognitudnal elasticity why wouldn't it just fall apart. Unless the expansion is somehow robing the energy from the photon, I do not see anything other than a form of Doppler effect.

It seems to be the mainstream view, that photon can indeed stretch. Another strange thought about this occurred to me: How does the atom know how long photon it is supposed to absorb? I mean that if there is stretched photon with X amount of energy arriving to the atom, why the atom doesn't cut that photon in half thinking it just got photon with X/2 amount of energy?


(The validity of CREIL is a maybe but my knowledge is too limited.)

Same goes for my knowledge. When I look that post above by JMB, I can only scratch my head. I would be very interested of it, but it seems to be so much over my head that I can't even come up with any questions about it. Well, I quess I just have to learn about it more.

Hey JMB, there is an old thread about CREIL in the "Against the mainstream" forum (it's on page 4 now), you probably would have something to say to that discussion. Here's the link. (http://www.badastronomy.com/phpBB/viewtopic.php?t=11101)



2. Expansion of space carries galaxies away from each other, causing actual motion between them. This motion causes redshift that looks like regular Doppler shift. I don't think that galaxies would feel this motion, because, if I have understood correctly, the space in their vicinity doesn't expand (presence of mass halts the expansion). So when photon starts it's journey from a galaxy, it is emitted to non-expanding space. And when the photon arrives from it's journey to another galaxy, it is absorbed from non-expanding space. On either end, photon doesn't know that there is expanding space between those two galaxies, because the interfacing happens in non-expanding conditions. Therefore I don't think that this could cause redshifting.
As I understand it, the expansion rate is too weak, currently or in the past, to overcome the force of gravity within a galaxy or within a cluster of galaxies. The space within them is expanding but too slowly to be very noticeable. The expandig space would give the receiving galaxy additional recessional velocity from the emitter causing a redshift affect. If expansion is accelerating, the redshift will be even greater over time.

I'm not quite sure, but I think that you might have misunderstood this part of my post. I meant that between those galaxies I mentioned, there is enough empty space for expansion to occur. So they are not in the same cluster. In my example, the photon travelling from one galaxy to other would travel through expanding space, and I'm trying to say that in the vicinity of those galaxies the expansion would get smaller and eventually halt completely very close to those galaxies.


[I'm the wrong guy to attempt an answer, but, why should I start letting my lack of knowledge interfere now. :) ] Doesn't everything have a wave function? The smaller the "particle" the greater the wave behavior. Maybe a photon does have charge...positive then negative then positive, etc. :)

That doesn't sound bad at all, just that overall charge should remain zero, I suppose. But, not to undermine your answer, let's hope we can lure someone in who actually knows about these things to answer this one. :wink:

George
2004-Jun-15, 02:06 PM
It seems to be the mainstream view, that photon can indeed stretch. Another strange thought about this occurred to me: How does the atom know how long photon it is supposed to absorb? I mean that if there is stretched photon with X amount of energy arriving to the atom, why the atom doesn't cut that photon in half thinking it just got photon with X/2 amount of energy?
I am still unclear on this point. When Hubble first measured the redshifts, did he not simply determine the additional redshift was due to the additional recessional velocity as a result of the expansion and not the expansion of space squeezing withing the photon's wave causing it to appear stretched somehow? If so, has mainstream added this concept or am I just confused?



As I understand it, the expansion rate is too weak, currently or in the past, to overcome the force of gravity within a galaxy or within a cluster of galaxies. The space within them is expanding but too slowly to be very noticeable. The expanding space would give the receiving galaxy additional recessional velocity from the emitter causing a redshift effect. If expansion is accelerating, the redshift will be even greater over time.I'm not quite sure, but I think that you might have misunderstood this part of my post. I meant that between those galaxies I mentioned, there is enough empty space for expansion to occur. So they are not in the same cluster. In my example, the photon travelling from one galaxy to other would travel through expanding space, and I'm trying to say that in the vicinity of those galaxies the expansion would get smaller and eventually halt completely very close to those galaxies.
Let me see if I understand your statement. You think that somehow the expansion will only "do it's thing" in regions of space between clusters, avoiding regions where galaxies subsist? I am under the impression that the expansion rate of 71km/sec per Mpc (currently) is too wimpy to push galaxies away from each other. Doesn't their gravitational attraction within the cluster simply overpower the expansion "force" which attempt to push them apart?



[I'm the wrong guy to attempt an answer, but, why should I start letting my lack of knowledge interfere now. :) ] Doesn't everything have a wave function? The smaller the "particle" the greater the wave behavior. Maybe a photon does have charge...positive then negative then positive, etc. :)
That doesn't sound bad at all, just that overall charge should remain zero, I suppose. But, not to undermine your answer, let's hope we can lure someone in who actually knows about these things to answer this one. :wink:
Are we jigging or using a cork? I'm not sure which analogy is better. :) Eta C, where art thee? :)

Ari Jokimaki
2004-Jun-16, 06:25 AM
It seems to be the mainstream view, that photon can indeed stretch...
I am still unclear on this point. When Hubble first measured the redshifts, did he not simply determine the additional redshift was due to the additional recessional velocity as a result of the expansion and not the expansion of space squeezing withing the photon's wave causing it to appear stretched somehow? If so, has mainstream added this concept or am I just confused?

I don't know about the history, but this is rather confusing matter, because those both are used in the layman level literature. I'm not 100% sure about it, but it looks to me that the photon stretching thing is the prevailing interpretation.


Let me see if I understand your statement. You think that somehow the expansion will only "do it's thing" in regions of space between clusters, avoiding regions where galaxies subsist? I am under the impression that the expansion rate of 71km/sec per Mpc (currently) is too wimpy to push galaxies away from each other. Doesn't their gravitational attraction within the cluster simply overpower the expansion "force" which attempt to push them apart?

I think that current theories say that presence of mass weakens the space expansion. But I'm not sure about this either, but I have read about this somewhere, wish I could give you a reference. One thing is that the amount of mass in the universe is said to determine whether universe expands forever or does it start to contract sometime in the future. This indicates that mass affects the space expansion in the current theories.

Also, I don't think that gravitational attraction overpowering the expansion would work, because when new space would appear between two objects, their gravitational attraction would get weaker, making it harder for the "overpowering" to keep the system together.

George
2004-Jun-16, 02:09 PM
I think that current theories say that presence of mass weakens the space expansion. But I'm not sure about this either, but I have read about this somewhere, wish I could give you a reference. One thing is that the amount of mass in the universe is said to determine whether universe expands forever or does it start to contract sometime in the future. This indicates that mass affects the space expansion in the current theories.
Evidence supports a "flat" universe so far. How it gets this balance is still being sought (especially dark stuff). No doubt, once more is known about the mechanism behind the expansion more will be explained.


Also, I don't think that gravitational attraction overpowering the expansion would work, because when new space would appear between two objects, their gravitational attraction would get weaker, making it harder for the "overpowering" to keep the system together.
It is still the net force acting on bodies that determine a bodies final position. Put two bowling balls on a trampoline and the two will go to each other even if you, somehow, stretch the surface. Depending on how fast you stretch the surface, you may or may not notice any unusual time for them to roll together.

If this view is correct, there would be a varriance in galaxy positions within a cluster due to this artificial motion. For instance, this would put Andromeda's rate of motion between us, due to expansion only, at about 60 km/sec. At a similar distance, it would have been even less in the past (assuming expansion acceleration is valid). It doesn't mean Andromeda is moving away from us only that it's relative motion is different. I think we are moving toward each other at 100 km/sec. If someone were to suddenly turn off the expansion, would we not be moving toward each other at 160 km/sec? Is my understanding contrary to mainstream? [Your suggestion as to my possible novice level thinking is not out-of-line. :) ]

Ari Jokimaki
2004-Jun-16, 03:17 PM
I think that current theories say that presence of mass weakens the space expansion. But I'm not sure about this either, but I have read about this somewhere, wish I could give you a reference. One thing is that the amount of mass in the universe is said to determine whether universe expands forever or does it start to contract sometime in the future. This indicates that mass affects the space expansion in the current theories.
Evidence supports a "flat" universe so far. How it gets this balance is still being sought (especially dark stuff). No doubt, once more is known about the mechanism behind the expansion more will be explained.

Yes, but even in "flat" option it is the amount of mass that defines the situation.


It is still the net force acting on bodies that determine a bodies final position. Put two bowling balls on a trampoline and the two will go to each other even if you, somehow, stretch the surface. Depending on how fast you stretch the surface, you may or may not notice any unusual time for them to roll together.

Yes, but the net force is constantly weakening and distance between objects would get bigger. In order to compensate this, gravity should get bigger accordingly, which it doesn't. But maybe it's possible that this happens so slowly in local scale that we don't notice it.


Is my understanding contrary to mainstream?

I think it is, but knowing my level of knowledge in these matters, I wouldn't put much weight to my thoughts if I were you. And this is also one of those cases where it is surprisingly difficult to find out what the mainstream thinks about it.

George
2004-Jun-16, 03:59 PM
Yes, but the net force is constantly weakening and distance between objects would get bigger. In order to compensate this, gravity should get bigger accordingly, which it doesn't.
Why would gravity have to get larger?


But maybe it's possible that this happens so slowly in local scale that we don't notice it.
That is my point. All the actual galaxy motion vectors include this component of expansion between any two objects in motion relative to one another.

Imagine standing in an airport terminal where two people approach you. One is walking down the hallway without being on the "moving sidewalk" and the other is going the wrong way on the "moving sidewalk", but, is walking faster than the sidewalk is moving. Both will reach you, although, obviously at different times. Expansion put everyone on the "moving sidewalk". Is this not applicable?

At some point in the future, if expansion keeps accelerating, this expansion component may exceed the gravitational component and the net vector will be away from other galaxies, then, even galaxies will break up, then,....well, it gets uglier, I suppose.

Hopefully, others will jump in on this...hint, hint. :)

Ari Jokimaki
2004-Jun-16, 05:00 PM
Why would gravity have to get larger?

When space expands between two objects, distance between them increases and gravity gets weaker. With that increased distance you would need slightly more gravity to stop the distance increasing more.



But maybe it's possible that this happens so slowly in local scale that we don't notice it.
That is my point. All the actual galaxy motion vectors include this component of expansion between any two objects in motion relative to one another.

Our points differ slightly. I meant that initially for example our galaxy is like it is now, but if expansion would occur everywhere as you say, then our galaxy would slowly fall apart. We just haven't noticed it yet, because the process might be so slow.


Imagine standing in an airport terminal where two people approach you. One is walking down the hallway without being on the "moving sidewalk" and the other is going the wrong way on the "moving sidewalk", but, is walking faster than the sidewalk is moving. Both will reach you, although, obviously at different times. Expansion put everyone on the "moving sidewalk". Is this not applicable?

Yes, it applies quite nicely to my point of view. See, that thing about walking faster than the sidewalk is moving is analogous to gravity getting larger, isn't it?

Kaptain K
2004-Jun-16, 05:38 PM
Why would gravity have to get larger?

When space expands between two objects, distance between them increases and gravity gets weaker. With that increased distance you would need slightly more gravity to stop the distance increasing more.

It's a matter of scale. Let's take a hypothetical case where the expansion at one light year is one millimeter/second. At one thousand light years it is still only one meter/ second. Therefore, at interstellar distances this so negligible as to be unmeasurable.

Even at a million light years, it is still only one kilometer/second - still within the error bars of our measurments.

It is only when you get out to billions of light years that the expansion rate (now up to 1000 kilometers/second) that the expansion becomes significant!

George
2004-Jun-16, 08:04 PM
When space expands between two objects, distance between them increases and gravity gets weaker. With that increased distance you would need slightly more gravity to stop the distance increasing more.
But you are assuming that the actual net distance between them is increasing. If two objects in space were not attracted to each, and you then turned on the magical expansion of space switch, you would then see their distance increase. If two objects are attracted to each other and are moving toward each other at a speed greater than the small expansion rate, they would still move toward each other just not as fast as before.

If the gravitational field accelerates two objects toward each other at a rate that exceeds the expansion rate, why wouldn't they stay together (including orbits)?

If you placed two tiny objects in "empty space", cancelled all gravitational fields and calmed the quantum jitters in the vacuum, what would happen? They should move away due to expansion.

If you gave them an intial velocity toward each other, then their initial velocity minus expansion velocity would yield a net velocity either toward each other or away from each other.

The idea of cranking in additional gravity is superfluous.




Imagine standing in an airport terminal where two people approach you. One is walking down the hallway without being on the "moving sidewalk" and the other is going the wrong way on the "moving sidewalk", but, is walking faster than the sidewalk is moving. Both will reach you, although, obviously at different times. Expansion put everyone on the "moving sidewalk". Is this not applicable?

Yes, it applies quite nicely to my point of view. See, that thing about walking faster than the sidewalk is moving is analogous to gravity getting larger, isn't it?

Do you suspect gravity itself is increaseing? If so, I am even more confussed as it would behave opposite to expansion.

Thanks Kaptain K. nice post.

Ari Jokimaki
2004-Jun-17, 06:51 AM
But you are assuming that the actual net distance between them is increasing. If two objects in space were not attracted to each, and you then turned on the magical expansion of space switch, you would then see their distance increase. If two objects are attracted to each other and are moving toward each other at a speed greater than the small expansion rate, they would still move toward each other just not as fast as before.

Yes, I agree with you here, but my assumption of initial conditions before you turn that switch is that the two objects are at rest relative to each other (I mean rest in the sense of distance, they might be for example going around each other in a circular orbit).

Let's use your moving sidewalk analogy here. Initial condition is that person A is walking on a moving sidewalk and person B is just standing beside the sidewalk (B is not moving at all). A walks in the direction opposite of the direction that sidewalk moves and with the same speed as the sidewalk. So, person A and person B are not moving relative to each other. Also, the direction that A tries to walk, is towards B.

Then expansion starts, which in this analogy means that the sidewalk gains more speed. A still walks the same speed, so the distance between A and B starts to grow. If A would want to keep the same distance to B, A would have to walk faster. This would be analogous to increasing gravity.


If the gravitational field accelerates two objects toward each other at a rate that exceeds the expansion rate, why wouldn't they stay together (including orbits)?

In this case they would initially have net motion towards each other, and expansion would just decrease that motion.


If you placed two tiny objects in "empty space", cancelled all gravitational fields and calmed the quantum jitters in the vacuum, what would happen? They should move away due to expansion.

I agree.


If you gave them an intial velocity toward each other, then their initial velocity minus expansion velocity would yield a net velocity either toward each other or away from each other.

Yes, and the effect of the expansion would probably be so small that they would still be moving toward each other, just with less speed.


The idea of cranking in additional gravity is superfluous.

Yes it is, it has been my point all along. I just think that it would be needed if space expands everywhere and you would like to keep two objects at rest relative to each other when they were at rest initially. So, I wasn't saying that gravity increases when space expands, I was saying that I thought you were wrong because I thought that your line of thinking would arise the need for that kind of gravity increasing mechanism.

But if Kaptain K is correct, and I have no reason to doubt Kaptain K, then I was wrong (or at least might have been wrong) because the space expansion has locally so small effect that we wouldn't notice if space would expand also inside matter concentrations (like inside galaxies).

Has this debate been just about us not understanding each other? I know my explanations have been kind of vague, it's quite difficult to explain this kind of stuff clearly with limited English. :)

George
2004-Jun-17, 01:23 PM
The idea of cranking in additional gravity is superfluous.

Yes it is, it has been my point all along. I just think that it would be needed if space expands everywhere and you would like to keep two objects at rest relative to each other when they were at rest initially. So, I wasn't saying that gravity increases when space expands, I was saying that I thought you were wrong because I thought that your line of thinking would arise the need for that kind of gravity increasing mechanism.
I suspected that is what you meant but I wasn't sure why you felt that way.


But if Kaptain K is correct, and I have no reason to doubt Kaptain K, then I was wrong (or at least might have been wrong) because the space expansion has locally so small effect that we wouldn't notice if space would expand also inside matter concentrations (like inside galaxies).

Has this debate been just about us not understanding each other? I know my explanations have been kind of vague, it's quite difficult to explain this kind of stuff clearly with limited English. :)
I know you are not a big Big Bang fan, so I wanted to clarify your views on the expansion. Were you thinking supporters of the accelerated expansion idea should be required to accept an increasing gravity force to hold orbits together? If so, orbits will not be maintained if the expansion does not stop accelerating, but, as Kaptain K pointed out, the expansion is currently too slow.

This should support the idea that not only does the weak expasnion not bust-up galactic orbits in clusters, but it does not pull on a single photon where it becomes stretched, IMO. I still see the redshift, due to expansion, as strictly a Doppler shift as a result of our increased velocity away from the original emitter. I haven't studied any supernova reports to see if this is in line with their conclusions as I figured others who had might jump in and share their knowledge on the subject.

BTW, it is always enjoyable visiting with you Ari, and, I see no problems with your English. I do routinely find problems with mine, however. :)

[edit. For proof, look for the "edit" notation on 90% of my posts. :) ]

Ari Jokimaki
2004-Jun-17, 02:13 PM
I know you are not a big Big Bang fan, so I wanted to clarify your views on the expansion. Were you thinking supporters of the accelerated expansion idea should be required to accept an increasing gravity force to hold orbits together? If so, orbits will not be maintained if the expansion does not stop accelerating, but, as Kaptain K pointed out, the expansion is currently too slow.

No, I wasn't thinking acceleration at all, I was just trying to see if it is possible for space to expand everywhere.


This should support the idea that not only does the weak expasnion not bust-up galactic orbits in clusters, but it does not pull on a single photon where it becomes stretched, IMO. I still see the redshift, due to expansion, as strictly a Doppler shift as a result of our increased velocity away from the original emitter. I haven't studied any supernova reports to see if this is in line with their conclusions as I figured others who had might jump in and share their knowledge on the subject.

You know, we only just established that it is possible for space to expand everywhere. I still think that that is not the mainstream view. But I think I'm now going to dig some references to back me up on this one, and then get back on this subject.


BTW, it is always enjoyable visiting with you Ari, and, I see no problems with your English. I do routinely find problems with mine, however. :)

Yes, this has been rather entertaining conversation. But the others monitoring this have probably rolled their eyes once or twice. :wink:

George
2004-Jun-17, 04:19 PM
You know, we only just established that it is possible for space to expand everywhere. I still think that that is not the mainstream view. But I think I'm now going to dig some references to back me up on this one, and then get back on this subject.
I'll be surprised if it is not mainstream.


...But the others monitoring this have probably rolled their eyes once or twice. :wink:
Ya think. #-o Shoot, I figured most would'a been used to me by now. :wink:

Ari Jokimaki
2004-Jun-22, 07:38 AM
You know, we only just established that it is possible for space to expand everywhere. I still think that that is not the mainstream view. But I think I'm now going to dig some references to back me up on this one, and then get back on this subject.
I'll be surprised if it is not mainstream.

Well, I have tried searching information on this, but no remarkable success yet. Most webpages I have looked agree with you, here's a link (http://www.astro.ucla.edu/~wright/cosmology_faq.html#SS) to what Ned Wright says about this subject. There he gives a link also to a relativity FAQ, but that link doesn't work for me (permission denied). I assume that this relativity FAQ (http://www.weburbia.demon.co.uk/physics/relativity.html) is the same. There they give this explanation (http://www.weburbia.demon.co.uk/physics/expanding_universe.html), which gives mild support for my point of view by stating this:


Or you may want to alter your picture of the "expanding balloon". The galaxies are not just painted on, but form part of the substance of the balloon (poetically speaking), and locally affect its "elasticity".

Well, it's not much, but at least something I can cling on...

George
2004-Jun-22, 02:50 PM
There they give this explanation (http://www.weburbia.demon.co.uk/physics/expanding_universe.html), which gives mild support for my point of view by stating this:

Or you may want to alter your picture of the "expanding balloon". The galaxies are not just painted on, but form part of the substance of the balloon (poetically speaking), and locally affect its "elasticity".

Well, it's not much, but at least something I can cling on...

Are you saying our galactic gravity well alters the "stretching" of the expansion? I wouldn't be surprised. However, wouldn't it's effects be minor on the cosmological portion of the redshift?

Your reference is interesting but I still do not understand what they are trying to say. It seems to support what I have been saying.


In old-fashioned, Newtonian terms, one says that the Solar System is "gravitationally bound" (ditto the galaxy, the local group). So the Solar System is not expanding. The case for Brooklyn is even clearer: it is bound by atomic forces, and its atoms do not typically follow geodesics. So Brooklyn is not expanding.

It seems the variations in the effects of expansion may be a result of accounting for different omega values. Also, now that acceleration is evidenced, this gives added dynamics to the equations, I suppose. I haven't found much to convince me the cosmolgoical redshift is not simply due to the net speed difference between the original emitter and us at the time we measure the photon's wavelength.

Ari Jokimaki
2004-Jun-22, 06:53 PM
Are you saying our galactic gravity well alters the "stretching" of the expansion? I wouldn't be surprised.

Yes, that's what I have been trying to say. :)


However, wouldn't it's effects be minor on the cosmological portion of the redshift?

I don't think I can discuss this very far quantitatively, but initially I assumed that expansion would halt (almost) completely inside matter consentration. That's why I made the argument in my first post:


2. Expansion of space carries galaxies away from each other, causing actual motion between them. This motion causes redshift that looks like regular Doppler shift. I don't think that galaxies would feel this motion, because, if I have understood correctly, the space in their vicinity doesn't expand (presence of mass halts the expansion). So when photon starts it's journey from a galaxy, it is emitted to non-expanding space. And when the photon arrives from it's journey to another galaxy, it is absorbed from non-expanding space. On either end, photon doesn't know that there is expanding space between those two galaxies, because the interfacing happens in non-expanding conditions. Therefore I don't think that this could cause redshifting.

But if the effect is minor, as you say, then this wouldn't apply. Although it might make our measured redshifts some amount smaller than they actually are. But the most probable alternative is that I'm utterly wrong about all of this.


Your reference is interesting but I still do not understand what they are trying to say. It seems to support what I have been saying.

Yes, at least partly. It is rather confusing, but as I understand it, we use two different models depending the scale we are looking. FRW metric is used for large scale, and it only describes expansion. Schwarzschild metric is used for small scale, and it only describes gravity. Or am I oversimplifying this? Perhaps this quote is the best description of the situation:


The "true metric" of the universe is, of course, fantastically complicated; you can't expect idealized simple solutions (like the FRW and Schwarzschild metrics) to capture all the complexity. Our knowledge of the large-scale structure of the universe is fragmentary and imprecise.

I think that you and I are looking this from slightly different angles, and at this point it is probably not possible to say which one is correct.


I haven't found much to convince me the cosmolgoical redshift is not simply due to the net speed difference between the original emitter and us at the time we measure the photon's wavelength.

To me this would make more sense than photons stretching, but as I said earlier, it seems to me that mainstream is going for the photon stretching.

George
2004-Jun-22, 11:20 PM
However, wouldn't it's effects be minor on the cosmological portion of the redshift?

I don't think I can discuss this very far quantitatively, but initially I assumed that expansion would halt (almost) completely inside matter consentration. That's why I made the argument in my first post:


2. Expansion of space carries galaxies away from each other, causing actual motion between them. This motion causes redshift that looks like regular Doppler shift. I don't think that galaxies would feel this motion, because, if I have understood correctly, the space in their vicinity doesn't expand (presence of mass halts the expansion). So when photon starts it's journey from a galaxy, it is emitted to non-expanding space. And when the photon arrives from it's journey to another galaxy, it is absorbed from non-expanding space. On either end, photon doesn't know that there is expanding space between those two galaxies, because the interfacing happens in non-expanding conditions. Therefore I don't think that this could cause redshifting.

But if the effect is minor, as you say, then this wouldn't apply. Although it might make our measured redshifts some amount smaller than they actually are. But the most probable alternative is that I'm utterly wrong about all of this.

It sounds like you are saying the expansion might be applying some sort of force on the photon which would stretch it's wavelength. Then, as it enters our galaxy, which presumably is not expanding, the force is removed so we should not see a redshift. Is this close? An analogy might be blowing up a balloon to a certain size, then we take this balloon with us in an F-18 up to 16 km (be sure you put on your mask and secure your dinner tray :) ). Then, we watch the balloon expand as we also enjoy your view of Orion ( a noon flight). Once we return back to the ground (1 atm.) we notice the balloon is back to it's original size. Is this a fair analogy? If not, I hope you at least enjoyed the flight. :wink:

An analogy of my view would be.... my kids and I are on roller skates all holding hands (Milky Way, z=0). We are standing at the secured end of a 100 meter wide rubber band that is 100 km long and perfectly flat. At the other end, it is tied to a tug boat in the Gulf of Mexico (ignore any height anomaly). You happen to be on it at a distance of 1 km from me (z=0.1 or so) and you are holding a bowling ball I loaned you (large photon :) ). You and I also have a friend on the rubber strip 50 km from me (z= larger) and he has your bowling ball. The 1 million hp tug boat takes off at 10 km/hr. Just after you feel the tug of the tug, you decide to return the bowling ball I loaned you by rolling it back to me at 1 km/hr. At the time of your roll, the streetching of our rubber "ground" has caused you to recede from me at 0.1 km/hr (1km/100km x 10km/hr). During the time it takes the ball to return to me, it is rolling on a stretching surface so it will arrive at a slower speed than even the 0.9 km/hr (1-.1 km/hr). Since my kids and I are connected (gravity holding galaxies), we do not notice the very slow movement underneath us. Notice also, you will never get a bowling ball from our friend if he rolls at only 1 km/hr. :cry:

The reduced speed of the bowling ball can be seen as reduced energy (kinetic, mv^2). A photon is not allowed to slow down, so, it's apparent energy reduction (relative to me) is found in it's longer wavelength.

The exact math to determine the final bowling ball speed is a determined by the speed of the tug. If the tug goes faster [accelerates], the math gets tougher. The example above also had all of us stationary before the tug took off. Therefore, knowing the initial relative speed of the emitting galaxy is also a factor (proper motion).

Now let me hold my hand out so you can slap it. :) Here is a little problem with my analogy reflecting my view. You would see the bowling ball you rolled back to me as gaining speed. Therefore, a photon would blueshift the longer it was gone from you on it's way to me (not that you could see it). If it bounced off something and several hundred million years later, it would have redshifted more than it would have blue shifted but less than if it redshifted all the time.

Is this making any sense. #-o




I haven't found much to convince me the cosmolgoical redshift is not simply due to the net speed difference between the original emitter and us at the time we measure the photon's wavelength.

To me this would make more sense than photons stretching, but as I said earlier, it seems to me that mainstream is going for the photon stretching.
I really don't know how mainsteam sees this. Surely they can dream up better analgoies than mine. :-?

I'll try to do some googling, too. Thanks for the help and I hope you enjoyed using my bowling ball. :)

Jpax2003
2004-Jun-23, 03:29 AM
Where has all the redshift gone?
Long time passing
Where has all the redshift gone?
Long time ago
Where has all the redshift gone?
emitted photons every one
When will they ever learn?
When will they ever learn?

lyrics (http://www.arlo.net/lyrics/flowers-gone.shtml) to actual song

Ari Jokimaki
2004-Jun-23, 07:13 AM
It sounds like you are saying the expansion might be applying some sort of force on the photon which would stretch it's wavelength. Then, as it enters our galaxy, which presumably is not expanding, the force is removed so we should not see a redshift. Is this close?

It's close, but not quite there yet. In my example, I was assuming that redshift mechanism is Doppler effect (no photon stretching). Doppler effect occurs if absorbing end or emitting end or both are moving. If my assumption about mass halting the space expansion would be correct, then it would seem to me that absorbing and emitting end are not moving relative to space in their immediate surroundings. Therefore I don't see how Doppler effect could occur.

But if photons would stretch during their journey through expanding space, they would be already redshifted when they arrive to absorber, and there would be no need for Doppler effect. So I revise the last part of what you said: "Then, as it enters our galaxy, which presumably is not expanding, the force is [still there] so we should ... see a redshift."


An analogy of my view would be.... my kids and I are on roller skates all holding hands (Milky Way, z=0). We are standing at the secured end of a 100 meter wide rubber band that is 100 km long and perfectly flat. At the other end, it is tied to a tug boat in the Gulf of Mexico (ignore any height anomaly). You happen to be on it at a distance of 1 km from me (z=0.1 or so) and you are holding a bowling ball I loaned you (large photon :) ). You and I also have a friend on the rubber strip 50 km from me (z= larger) and he has your bowling ball. The 1 million hp tug boat takes off at 10 km/hr. Just after you feel the tug of the tug, you decide to return the bowling ball I loaned you by rolling it back to me at 1 km/hr. At the time of your roll, the streetching of our rubber "ground" has caused you to recede from me at 0.1 km/hr (1km/100km x 10km/hr). During the time it takes the ball to return to me, it is rolling on a stretching surface so it will arrive at a slower speed than even the 0.9 km/hr (1-.1 km/hr). Since my kids and I are connected (gravity holding galaxies), we do not notice the very slow movement underneath us. Notice also, you will never get a bowling ball from our friend if he rolls at only 1 km/hr. :cry:

The reduced speed of the bowling ball can be seen as reduced energy (kinetic, mv^2). A photon is not allowed to slow down, so, it's apparent energy reduction (relative to me) is found in it's longer wavelength.

The exact math to determine the final bowling ball speed is a determined by the speed of the tug. If the tug goes faster [accelerates], the math gets tougher. The example above also had all of us stationary before the tug took off. Therefore, knowing the initial relative speed of the emitting galaxy is also a factor (proper motion).

Now let me hold my hand out so you can slap it. :) Here is a little problem with my analogy reflecting my view. You would see the bowling ball you rolled back to me as gaining speed. Therefore, a photon would blueshift the longer it was gone from you on it's way to me (not that you could see it). If it bounced off something and several hundred million years later, it would have redshifted more than it would have blue shifted but less than if it redshifted all the time.

Is this making any sense. #-o

:o Believe it or not, I understood that. Yes it makes sense. But you forgot that there is friction between the roller skates and the rubber band. If that friction is large enough, it keeps the band from stretching between you and your kids.


I really don't know how mainsteam sees this. Surely they can dream up better analgoies than mine. :-?

Don't count on it. You seem to be quite good at this, you know, analogy-wise.


I'll try to do some googling, too. Thanks for the help and I hope you enjoyed using my bowling ball. :)

This was a first time I tried bowling, and it turned out to be much fun! =D>

Ari Jokimaki
2004-Jun-23, 07:17 AM
Where has all the redshift gone?

lyrics (http://www.arlo.net/lyrics/flowers-gone.shtml) to actual song

You know, when I saw that first line, this song (http://songfacts.com/detail.lasso?id=1477) started playing in my head.

George
2004-Jun-23, 01:26 PM
...But if photons would stretch during their journey through expanding space, they would be already redshifted when they arrive to absorber, and there would be no need for [any additional] Doppler effect. So I revise the last part of what you said: "Then, as it enters our galaxy, which presumably is not [affected by any] expanding, the force is [still there] so we should ... see a redshift."
I added the bold to see if this articulates both our points. Does it?

Since the expansion (space fabric only) is so wimpy in an area the size of our Milky Way, it has too little affect on the motions of the stars with in it. It does have some. When you rolled my bowling ball back to me, did you not alter the rotational speed of the Earth? Doesn't the Sun's solar wind push the planets further out, but the net increase is practically insignificant? Of course, I am not saying the galactic gravitational field does not alter the expansion rate itself, as I don't even know what the fabric of space is. :roll: The point is that, locally, cosmological redshift seems to only be noticeable over much further distances.



... But you forgot that there is friction between the roller skates and the rubber band. If that friction is large enough, it keeps the band from stretching between you and your kids.
So you are suggesting gravity restricts the actual expansion process as opposed to the idea the fabric of space does expand within the galaxy (for instance) but makes very little net difference to the relative motions of the stars. The fabric of space would, IMO, slide out from underneath the stars into "open space" just like the rubber would from underneath the skaters. The skating kids would still feel some pull but as long as I'm telling jokes, my kids don't even notice and we never change our distance between us. Of course, now they want me to take them bowling! :wink:
If the tug boat keeps accelerating, eventually, even skating will be a problem.




I really don't know how mainsteam sees this. Surely they can dream up better analgoies than mine. :-?
Don't count on it. You seem to be quite good at this, you know, analogy-wise.
Thanks. Hopefully, a little imagination and wit will offset my unpolished technical expertise. :)




I'll try to do some googling, too. Thanks for the help and I hope you enjoyed using my bowling ball. :)
This was a first time I tried bowling, and it turned out to be much fun! =D>
Nice start. Next time I'll set the pins up for ya. :wink:

Ari Jokimaki
2004-Jun-24, 08:57 AM
...But if photons would stretch during their journey through expanding space, they would be already redshifted when they arrive to absorber, and there would be no need for [any additional] Doppler effect. So I revise the last part of what you said: "Then, as it enters our galaxy, which presumably is not [affected by any] expanding, the force is [still there] so we should ... see a redshift."
I added the bold to see if this articulates both our points. Does it?

I don't see how it can, if you think that there is no photon stretching.

Edited: Or are you looking for a compromise? So that there would be photon strecthing and Doppler effect in cosmological redshift?


Since the expansion (space fabric only) is so wimpy in an area the size of our Milky Way, it has too little affect on the motions of the stars with in it. It does have some. When you rolled my bowling ball back to me, did you not alter the rotational speed of the Earth? Doesn't the Sun's solar wind push the planets further out, but the net increase is practically insignificant? Of course, I am not saying the galactic gravitational field does not alter the expansion rate itself, as I don't even know what the fabric of space is. :roll: The point is that, locally, cosmological redshift seems to only be noticeable over much further distances.

Yes, I think we already established this point earlier.


So you are suggesting gravity restricts the actual expansion process as opposed to the idea the fabric of space does expand within the galaxy (for instance) but makes very little net difference to the relative motions of the stars.

Yes, that's it.


The fabric of space would, IMO, slide out from underneath the stars into "open space" just like the rubber would from underneath the skaters. The skating kids would still feel some pull but as long as I'm telling jokes, my kids don't even notice and we never change our distance between us. Of course, now they want me to take them bowling! :wink:
If the tug boat keeps accelerating, eventually, even skating will be a problem.

This is the difference between our views; you think that rubber band would slide freely under skaters and I think that the friction would resist that slide and with large enough friction prevent it completely. (Of course, my thinking applies only to this analogy, in real life I wouldn't think that the friction would work like that. I quess this is not the best possible analogy to present my case. :) )

George
2004-Jun-24, 01:04 PM
Where has all the redshift gone?
Long time passing
Where has all the redshift gone?
Long time ago
Where has all the redshift gone?
emitted photons every one
When will they ever learn?
When will they ever learn?

lyrics (http://www.arlo.net/lyrics/flowers-gone.shtml) to actual song

=D> I meant to thank you for the appropriate interlude. :)

George
2004-Jun-24, 02:17 PM
...Edited: Or are you looking for a compromise? So that there would be photon strecthing and Doppler effect in cosmological redshift?
I really don't understand the ideas behind photon stretching:

1) If the expansion exerts a force on a photon during it's travel, then why would it stretch more with time? The balloon at 16km altitude will not expand more if it sits there longer.

2) Where would the energy itself go in a photon "squashing" process? If work is being done on the photon by some sort of expansion force, it's energy level should increase, not decrease, I think.

3) An alternative, and it's also a "stretch" (pun intended), seems to be the idea that expanding space is able to expand between each e-m wave of the photon causing it to stretch. This would imply that the photon has, essentially, zero resistance to any longitudinal action. I would expect the interaction of the magnetic and electrical waves, which have a mutual phase angle, to easily resist such action. Considering a photon as a particle, it should have zero longitudinal length since it is moving at the "speed of light". How would expansion slip in and lengthen it? (Just wanted to muddy things up a bit on this last point. :) )




The fabric of space would, IMO, slide out from underneath the stars into "open space" just like the rubber would from underneath the skaters. The skating kids would still feel some pull but as long as I'm telling jokes, my kids don't even notice and we never change our distance between us. Of course, now they want me to take them bowling! :wink:
If the tug boat keeps accelerating, eventually, even skating will be a problem.

This is the difference between our views; you think that rubber band would slide freely under skaters and I think that the friction would resist that slide and with large enough friction prevent it completely. (Of course, my thinking applies only to this analogy, in real life I wouldn't think that the friction would work like that. I quess this is not the best possible analogy to present my case. :) )
You may be right that gravity alters the expansion process. However, I still see no reason to believe that if mere gravity can stop expansion, why would we accept the idea (no. 3) that e-m wave can't resist it? [edit: I still think the expansion slips away with or without a little "friction"]

I hope to have some time this weekend to google for various ideas. Considering the lack of other posters on this topic, do you feel we are on our own on this one and nothing about it is well established? :) [Of course, the song was nice. :)]

Ari Jokimaki
2004-Jun-24, 03:54 PM
I really don't understand the ideas behind photon stretching:

1) If the expansion exerts a force on a photon during it's travel, then why would it stretch more with time? The balloon at 16km altitude will not expand more if it sits there longer.

2) Where would the energy itself go in a photon "squashing" process? If work is being done on the photon by some sort of expansion force, it's energy level should increase, not decrease, I think.

3) An alternative, and it's also a "stretch" (pun intended), seems to be the idea that expanding space is able to expand between each e-m wave of the photon causing it to stretch. This would imply that the photon has, essentially, zero resistance to any longitudinal action. I would expect the interaction of the magnetic and electrical waves, which have a mutual phase angle, to easily resist such action. Considering a photon as a particle, it should have zero longitudinal length since it is moving at the "speed of light". How would expansion slip in and lengthen it? (Just wanted to muddy things up a bit on this last point. :) )

I don't understand photon stretching either, but I just try to reflect the mainstream views as I understand them. As you probably know, I don't believe that space expands at all.

Confusing thing is, that both photon stretching and Doppler effect are used as a reason behind cosmological redshift in layman level literature. So it's difficult to say, which one is the "official" reason. Perhaps they are both used when suitable.


You may be right that gravity alters the expansion process. However, I still see no reason to believe that if mere gravity can stop expansion, why would we accept the idea (no. 3) that e-m wave can't resist it? [edit: I still think the expansion slips away with or without a little "friction"]

Of course you could have gravity altering expansion process and still have Doppler effect as a cause for redshift. I'm willing to accept that if you just show my argument (nr. 2 in my initial post) wrong.


I hope to have some time this weekend to google for various ideas. Considering the lack of other posters on this topic, do you feel we are on our own on this one and nothing about it is well established? :) [Of course, the song was nice. :)]

It certainly looks like we are on our own, and it doesn't feel well established when I say something (=I don't know much about this stuff). But I think that we possibly are probing things that are not well known.

George
2004-Jun-25, 05:55 PM
Of course you could have gravity altering expansion process and still have Doppler effect as a cause for redshift. I'm willing to accept that if you just show my argument (nr. 2 in my initial post) wrong.

I am curious to see an argument favoring your No. 2. It seems to me Doppler would have to be a factor. Assume two galaxies are moving away from each other at certain speed, s1, and a photon is emitted at this point in time, t1. If expansion exists, at t2, s2 will be greater than s1. Is there any known process that would cancel a redshift if two objects are traveling away from each other faster than at the time a photon was emitted from one to another? If some force is additionally acting on the photon, it still shouldn't negate the Doppler effect on our photon.



It certainly looks like we are on our own, and it doesn't feel well established when I say something (=I don't know much about this stuff). But I think that we possibly are probing things that are not well known.
Of course, there could be 50 other threads on this subject and they are all just taking a break. :)

Ari Jokimaki
2004-Jun-26, 03:47 PM
I am curious to see an argument favoring your No. 2. It seems to me Doppler would have to be a factor. Assume two galaxies are moving away from each other at certain speed, s1, and a photon is emitted at this point in time, t1. If expansion exists, at t2, s2 will be greater than s1. Is there any known process that would cancel a redshift if two objects are traveling away from each other faster than at the time a photon was emitted from one to another? If some force is additionally acting on the photon, it still shouldn't negate the Doppler effect on our photon.

Remember that my original argument rests on my assumption that mass stops the expansion. So the galaxies are in non-expanding environment, and therefore they wouldn't know that there is expanding space between them. So galaxies wouldn't feel motion, there would be just extra space appearing between them. And if they don't feel motion, there wouldn't also be any Doppler shift.


Of course, there could be 50 other threads on this subject and they are all just taking a break. :)

I remember that long time ago there was a thread about is space expanding everywhere, but I don't remember the name of the thread. I'm pretty sure it was in this forum, but it can also be in ATM-forum. So it's pretty hard to find.

But if you want to find some info on this, there are several threads by Snowflakeuniverse in the ATM-forum, which usually at least touch this subject. I just browsed some of them, but didn't yet find anything conclusive.

George
2004-Jun-28, 01:20 PM
Remember that my original argument rests on my assumption that mass stops the expansion. So the galaxies are in non-expanding environment, and therefore they wouldn't know that there is expanding space between them. So galaxies wouldn't feel motion, there would be just extra space appearing between them. And if they don't feel motion, there wouldn't also be any Doppler shift.
If space is expanding, then galaxies will be carried with it. This will generate motion relative to galaxies where "resistance is futile". Even if gravity within a galaxy (or cluster) where to, somehow, stop expansion, you would still see a difference in motion.

Or, are you suggesting that all the galaxies are fixed in space and space is squeezing in on itself causing more stretching action on a photon? #-o

I did not have time this weekend to hunt references. I did find Brian Greene saying in his book "Fabric of the Cosmos" the redshift was "akin" to the Doppler effect.

Ari Jokimaki
2004-Jun-28, 04:45 PM
If space is expanding, then galaxies will be carried with it. This will generate motion relative to galaxies where "resistance is futile". Even if gravity within a galaxy (or cluster) where to, somehow, stop expansion, you would still see a difference in motion.

Or, are you suggesting that all the galaxies are fixed in space and space is squeezing in on itself causing more stretching action on a photon? #-o

This is how I see it:

First there is two galaxies (G) and non-expanding space (n) between them:



GnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnG


Then space starts to expand, expanding space is marked with 'e':



Gnnnnee eennnnG
eee eee
eeeee eeeee
eeeeeeeeeeeeeeeeee


As you see from my sketches, "distance" between two galaxies stays the same, but light has to travel along that curved line (expanded space). There is still non-expanding space in the vicinity of both galaxies, so the galaxies have no idea that space is expanding between them.


I did not have time this weekend to hunt references. I did find Brian Greene saying in his book "Fabric of the Cosmos" the redshift was "akin" to the Doppler effect.

He might be just using confusing terminology, I have also seen terms "relativistic Doppler effect" and "cosmological Doppler effect" being used. Also "photon strecthing" is quite popular... :wink:

George
2004-Jun-28, 05:16 PM
Gnnnnee eennnnG
eee eee
eeeee eeeee
eeeeeeeeeeeeeeeeee


As you see from my sketches, "distance" between two galaxies stays the same, but light has to travel along that curved line (expanded space). There is still non-expanding space in the vicinity of both galaxies, so the galaxies have no idea that space is expanding between them.
Ah ha! Now I seeeeeee what you are saying. :) Space has either increased it's density by squashing in onto itself or it has warped itself forcing further travel requirements of the photon. In this case, there would be no true Doppler effect, so I understand your thinking now.




I did not have time this weekend to hunt references. I did find Brian Greene saying in his book "Fabric of the Cosmos" the redshift was "akin" to the Doppler effect.
He might be just using confusing terminology, I have also seen terms "relativistic Doppler effect" and "cosmological Doppler effect" being used. Also "photon strecthing" is quite popular... :wink:
Well, "using confusing" is amusing but abusing to the assumings. :wink: I'm inclined to think he, and most, see "expansion" as the result of galaxies moving apart from each other. Hopefully, you and I can hunt the variations down. I was expecting something more articulate from his book entitled - "Fabric of the Cosmos". Still, a wonderful book.

George
2004-Jun-28, 05:34 PM
Here's one view from Cornell... here (http://curious.astro.cornell.edu/question.php?number=278)


Practically speaking, the difference between the two (Doppler redshift and cosmological redshift) is this: in the case of a Doppler shift, the only thing that matters is the relative velocity of the emitting object when the light is emitted compared to that of the receiving object when the light is received. After the light is emitted, it doesn't matter what happens to the emitting object - it won't affect the wavelength of the light that is received. In the case of the cosmological redshift, however, the emitting object is expanding along with the rest of the universe, and if the rate of expansion changes between the time the light is emitted and the time it is received, that will affect the received wavelength. Basically, the cosmological redshift is a measure of the total "stretching" that the universe has undergone between the time the light was emitted and the time it was received.
Seems "akin" to Doppler, IMO. The expansion of space would make the photon behave just as if it had left a faster moving emitter, I think. That seems to be the distinction between the two. The closer the photon gets to us, the less it is being stretched since the expansion affect is less.

George
2004-Jun-28, 05:38 PM
Ari, we might want to move over to "Evidence that Redshift is a Doppler effect" ATM thread (http://www.badastronomy.com/phpBB/viewtopic.php?t=13864)

This seems to be the area of our research.

Ari Jokimaki
2004-Jun-29, 04:42 PM
Ah ha! Now I seeeeeee what you are saying. :) Space has either increased it's density by squashing in onto itself or it has warped itself forcing further travel requirements of the photon. In this case, there would be no true Doppler effect, so I understand your thinking now.

Finally!!! :P


Seems "akin" to Doppler, IMO. The expansion of space would make the photon behave just as if it had left a faster moving emitter, I think. That seems to be the distinction between the two. The closer the photon gets to us, the less it is being stretched since the expansion affect is less.

Let me see, there are two key words there, one is "photon" and what's the other one? Oh yes, it has to be "stretching".


Ari, we might want to move over to "Evidence that Redshift is a Doppler effect" ATM thread.

Yes, I noticed that you have been moonlighting in that thread. But lately that thread has become so corny that it's about to pop.

George
2004-Jun-29, 04:58 PM
Ah ha! Now I seeeeeee what you are saying. :) Space has either increased it's density by squashing in onto itself or it has warped itself forcing further travel requirements of the photon. In this case, there would be no true Doppler effect, so I understand your thinking now.

Finally!!! :P :oops: Ok, I'm new to this stuff and there are many thoughts on it, apparently, and I have not heard this version. I suppose the balloon analogy has been blown out of proportion. :wink: [I like my bowling ball one better.]

Of course, you don't believe this is happening, but you feel this is the maninstream view. Right?



Seems "akin" to Doppler, IMO. The expansion of space would make the photon behave just as if it had left a faster moving emitter, I think. That seems to be the distinction between the two. The closer the photon gets to us, the less it is being stretched since the expansion affect is less.

Let me see, there are two key words there, one is "photon" and what's the other one? Oh yes, it has to be "stretching". But, this view seems identical to my view. The Cornell quote does not clarify. Odd, I know they have bowling up there. :)



Ari, we might want to move over to "Evidence that Redshift is a Doppler effect" ATM thread.Yes, I noticed that you have been moonlighting in that thread. But lately that thread has become so corny that it's about to pop. Wow. Shucks! There's hope for you yet! :) You're a corn-ball, too! :o

I have tried to redirect it to it's original and interesting intent.

TravisM
2004-Jun-29, 05:37 PM
Still askin' where the red-shift energy went? It's still in the photon, it's just spread out over a LONGER WAVE-LENGTH...
The packet has become less localized due to the increased length it has encountered since its journey began.

Hey, let's start a new thread:

Stone Wheel Construction : 101

I'm thinking of aquatreads... any supporters?

George
2004-Jun-29, 07:55 PM
Still askin' where the red-shift energy went? It's still in the photon, it's just spread out over a LONGER WAVE-LENGTH...
The packet has become less localized due to the increased length it has encountered since its journey began.

E = h x nu. Energy spread out over time (or length) is a power issue not an energy issue. If you change the wavelength, you change the energy, or, Planck is wrong.

bigsplit
2004-Jun-29, 11:35 PM
Here is a possible explaination of how the photon is stretched.

Galaxy A emits a photon that is heading for Galaxy B. At the time the photon was emitted, the galaxies were at a set distance with set gravitational attraction between them. As the Galaxies move apart the photon is unable to distinguish between the acceleration and an increase in gravity. This perceived increase in gravity literally stretches the photon.

Not so complicated, really.

Ari Jokimaki
2004-Jun-30, 03:13 PM
Ah ha! Now I seeeeeee what you are saying. :) Space has either increased it's density by squashing in onto itself or it has warped itself forcing further travel requirements of the photon. In this case, there would be no true Doppler effect, so I understand your thinking now.

Finally!!! :P :oops: Ok, I'm new to this stuff and there are many thoughts on it, apparently, and I have not heard this version. I suppose the balloon analogy has been blown out of proportion. :wink: [I like my bowling ball one better.]

I don't think there's any reason for you to feel ashamed. If an explanation is not understood, it's not usually the listener's fault.


Of course, you don't believe this is happening, but you feel this is the maninstream view. Right?

Right.


But, this view seems identical to my view. The Cornell quote does not clarify. Odd, I know they have bowling up there. :)

I have got the impression that you are going for pure Doppler shift explanation. If that's true, then I don't see how that Cornell quote could support your view, or have you adjusted your view during our discussion?

George
2004-Jun-30, 07:06 PM
But, this view seems identical to my view. The Cornell quote does not clarify. Odd, I know they have bowling up there. :)
I have got the impression that you are going for pure Doppler shift explanation. If that's true, then I don't see how that Cornell quote could support your view, or have you adjusted your view during our discussion?
You were right. I assumed pure Doppler would explain redshift. One component radial motion of the emitting galaxy and another component due to the expansion. Maybe I am still correct but it's tough understanding it.

This looks like a real serious approach... here (http://arxiv.org/abs/astro-ph/0310808).
GR has much to say about it, apparently. I am not qualified to tackle it. I think I will go bowling instead. :)

bigsplit
2004-Jul-01, 02:55 PM
Here is a possible explaination of how the photon is stretched.

Galaxy A emits a photon that is heading for Galaxy B. At the time the photon was emitted, the galaxies were at a set distance with set gravitational attraction between them. As the Galaxies move apart the photon is unable to distinguish between the acceleration and an increase in gravity. This perceived increase in gravity literally stretches the photon.

Not so complicated, really.

Been thinking about what I wrote here, and was wondering if this logic could be taken a step further. Suppose this phenomena does occur (to some degree and effect it must), what are the implications for the galaxies themselves....is there any conceivable way this could be the phenomena that we describe as Dark Matter? Each galaxy has a certain gravitational attraction with every other galaxy in the Universe. If the are all expanding and accelerating, what impact does this have on the Galaxy itself? Does this effect cause the galaxy to behave as though its mass is greater than it actually is?

George
2004-Jul-02, 03:30 PM
General relativity deals with this, but, I have not put that "iron in the fire" so my help won't help. I hope to learn enough about to address these kinds of issues but it is a bit "too much squeeze for the juice" right now for me. :)

bigsplit
2004-Jul-02, 03:55 PM
Waiting for some feedback on the instant we exit perihelion and is there any increase in gravitational potential? I think GPS data may show something along these lines, but it may for the moment be attributed to some other mechanics. I will let you know what I find out. If there is an increase in g just after perihelion, we may can use this to explain the stretching of photon in Red Shift, as well as dark matter.....What do others think, do you think the train of thought has any potential? Does it make sense?

George
2004-Jul-06, 03:39 AM
I've been reading more of Brian Greene's book "Fabric of the Cosmos...".

His view is the redshift is caused by photons actually losing energy to gravity. The CMB is highly redshifted as these photons have been flying around for 14 billion years so gravity has had plenty of time to drain the energy from them. In contrast, the inflaton field (on "i" intentionally) takes energy from gravity and creates negative pressue which is the cause of expansion as per modern inflation theory.

So how should I revise my analogy? #-o Ok. Let's eliminate the tug boat. As you, and millions of others, roll your bowling ball, the friction lowers the energy in the ball (large photon) and generates heat (energizes the inflaton field) expanding the rubber sheet.

Ari Jokimaki
2004-Jul-06, 05:52 AM
I've been reading more of Brian Greene's book "Fabric of the Cosmos...".

His view is the redshift is caused by photons actually losing energy to gravity. The CMB is highly redshifted as these photons have been flying around for 14 billion years so gravity has had plenty of time to drain the energy from them. In contrast, the inflaton field (on "i" intentionally) takes energy from gravity and creates negative pressue which is the cause of expansion as per modern inflation theory.

The expansion doesn't cause redshifting? So, what do we need expansion for? I mean, shouldn't that redshift mechanism work for static universe also?

bigsplit
2004-Jul-06, 01:24 PM
OK, during aphelion on Monday there was no discernable seismic activity once we started moving back towards the sun. I did find out that on powerful spectrometers a gradual shift from positive the neutral to negative occurs for the aphelion of the earth/moon system center of gravity. What do others think? Can the acceleration (if there is any) which without a doubt applies pressure between any 2 galaxies, generate an opposite and equal reaction where the galaxies pull back, generating more gravitational attraction than the mass would imply?

George
2004-Jul-06, 01:26 PM
The expansion doesn't cause redshifting? So, what do we need expansion for? I mean, shouldn't that redshift mechanism work for static universe also?
That's a good question. (Were you grinning when you asked? :) ) I suspect GR affects the energy drain from the photon when accelerating more so than a static cosmos but the emphasis was just on gravity iteself not the rate of change? Even if acceleration helps, what about the first 6 billion years when deceleration was dominant? (You're still grinning, right? :) )

In the case of the CMB, this light, believed to be originally in the orange portion of the spectrum (3000K), would have "felt" all the effects of not only the intense gravitational field at recombination but, I suspect, the effects from GR. The older the photons, the more gravity would have had an affect if this idea is valid. In this case, I don't see how Doppler would be a factor, so, my original Doppler idea would be wrong. Or, maybe I could make gravity the "tug boat". :)

George
2004-Jul-06, 01:36 PM
OK, during aphelion on Monday there was no discernable seismic activity once we started moving back towards the sun. I did find out that on powerful spectrometers a gradual shift from positive the neutral to negative occurs for the aphelion of the earth/moon system center of gravity. What do others think? Can the acceleration (if there is any) which without a doubt applies pressure between any 2 galaxies, generate an opposite and equal reaction where the galaxies pull back, generating more gravitational attraction than the mass would imply?
These are good General Relativity questions. Keep in mind that GR says acceleration and gravity are "equivalent". I have never studied GR so there is little I can say. I would believe elliptical orbits would allow red and blue shifts simply due to Doppler alone but, maybe, some due to change in our jerk (acceleration rate changes). The shifts would be quite tiny, however.

Ari Jokimaki
2004-Jul-07, 10:11 AM
That's a good question. (Were you grinning when you asked? :) ) I suspect GR affects the energy drain from the photon when accelerating more so than a static cosmos but the emphasis was just on gravity iteself not the rate of change? Even if acceleration helps, what about the first 6 billion years when deceleration was dominant? (You're still grinning, right? :) )

Sorry, but I don't understand how acceleration relates to this.

And yes, there was a slight grin at start, but then I became rather sceptical about Greene's explanation. Maybe he is discussing only how CMBR redshifted and not how general cosmological redshift works (if they can be thought to be due to different mechanisms)? Or, is that book about string theory (which seems to bring some strange stuff to cosmology)?

George
2004-Jul-07, 02:05 PM
That's a good question. (Were you grinning when you asked? :) ) I suspect GR affects the energy drain from the photon when accelerating more so than a static cosmos but the emphasis was just on gravity iteself not the rate of change? Even if acceleration helps, what about the first 6 billion years when deceleration was dominant? (You're still grinning, right? :) )

Sorry, but I don't understand how acceleration relates to this.

And yes, there was a slight grin at start, but then I became rather sceptical about Greene's explanation. Maybe he is discussing only how CMBR redshifted and not how general cosmological redshift works (if they can be thought to be due to different mechanisms)?
I assume it would apply to any older photons as they have had more time to give up energy to gravity. Wouldn't the acceleration of the early universe involve a significant pull on the photon based on GR? Doesn't a photon redshift slightly whenever it gets into a gravity well?


... Or, is that book about string theory (which seems to bring some strange stuff to cosmology)?
"Fabric.." is not so much on string theory as his first book "Elegant Universe". It does favor the inflaton field (Higgs) which, I think, is a favored prediction of string theory. He does speak a good bit about the inflation and how nicely it deals with problems such as CMB isotropy, anisotropy and entropy. Fairly easy reading, too.

He does not explain redshift sufficiently for us, however. Nevertheless, gravity itself may be the answer after all to taking energy from photons. I like it better than trying to sneak space between waves in a photon yet not robing its energy (defying Plancks equation in the process).

I also think the CMB would not be so isotropic using my pure Doppler approach as recombination light went all directions so we should not see such uniformity in the CMB since some of it would be redshifted and some blueshifted at this point in time relative to us. Does this make sense?

bigsplit
2004-Jul-07, 02:12 PM
The expansion doesn't cause redshifting? So, what do we need expansion for? I mean, shouldn't that redshift mechanism work for static universe also?
That's a good question. (Were you grinning when you asked? :) ) I suspect GR affects the energy drain from the photon when accelerating more so than a static cosmos but the emphasis was just on gravity iteself not the rate of change? Even if acceleration helps, what about the first 6 billion years when deceleration was dominant? (You're still grinning, right? :)

Deceleration never occured, the Big Bang was an electromagnetic chain reaction.

George
2004-Jul-07, 02:21 PM
Deceleration never occured, the Big Bang was an electromagnetic chain reaction.
We are trying to first figure out what mainstream sees, as well as, develop our own opinion on redshift. I don't see this as mainstream. I suspect the supernovae teams did find deceleration prior to acceleration about 6 or 7 billion years ATB (but I am unsure on this). Follow-up studies are, no doubt, being done now.

bigsplit
2004-Jul-07, 03:17 PM
Deceleration never occured, the Big Bang was an electromagnetic chain reaction.
We are trying to first figure out what mainstream sees, as well as, develop our own opinion on redshift. I don't see this as mainstream. I suspect the supernovae teams did find deceleration prior to acceleration about 6 or 7 billion years ATB (but I am unsure on this). Follow-up studies are, no doubt, being done now.

No, sorry it is not mainstream. The mainstream says, it blew up, slowed down and now is speeding up again and may slow down again. But, I think the only reason for this being mainstream is that the Big Bang implies it and there are other factor that support the Big Bang. Now, if it (the bang) was a hot explosion of molten "who knows what" then the Universe did cool off and slowed down and then out of "who knows where" an unknown energy is pulling the Universe apart and we are accelerating again. The debate is what went Bang and how it happened. This information is needed to understand the Universe, expansion, red-shift, galaxy formation and dynamics, QM, etc. etc. All of these ideas are dependent on this primal environment and event. If we do not get them right, all of the laws and priciples of science are limited at best and true understanding is impossible.

Ari Jokimaki
2004-Jul-08, 07:41 AM
I assume it would apply to any older photons as they have had more time to give up energy to gravity. Wouldn't the acceleration of the early universe involve a significant pull on the photon based on GR? Doesn't a photon redshift slightly whenever it gets into a gravity well?

If space expansion wouldn't cause redshifting, then I don't think that accelerating space expansion would either.

Let's do a thought experiment. For this experiment we assume that Greene's explanation (gravity, not expansion, causes the cosmological redshift) is correct. There are two galaxies nearby. You are on the other side of the galaxies and I am on the other side. You are throwing photons towards me at steady intervals so that each photon flies between the galaxies before they arrive to me. I catch each photon and check their redshift with my redshift reader, which then plots the redshifts as a function of time. You have space expansion apparatus, which has three settings: off, constant expansion and accelerating expansion. So we start our little experiment:

1. Space expansion apparatus is off. Redshift reader plots horizontal line, because gravity between the galaxies remains the same, so each photon is redshifted by same amount.

2. You change the setting to constant expansion (remember to keep throwing those photons). Redshift plot shows still a line but now the line is descending. That's because galaxies are now receding from each other and gravity between them is decreasing (at a constant rate).

3. You change the setting to accelerating expansion. Redshift plot is no more a line but now the line is dropping in non-linear fashion, amount of drop increasing every second. Galaxies are now receding from each other at accelerating fashion and gravity between them decreases accordingly.

4. You can stop throwing, our experiment ends now.

So, space expansion and accelerating space expansion both have an (indirect) effect to redshift, but they are decreasing the redshift, not increasing.


"Fabric.." is not so much on string theory as his first book "Elegant Universe". It does favor the inflaton field (Higgs) which, I think, is a favored prediction of string theory. He does speak a good bit about the inflation and how nicely it deals with problems such as CMB isotropy, anisotropy and entropy. Fairly easy reading, too.

Isn't inflation theory independent theory with no relation to string theory?


I also think the CMB would not be so isotropic using my pure Doppler approach as recombination light went all directions so we should not see such uniformity in the CMB since some of it would be redshifted and some blueshifted at this point in time relative to us. Does this make sense?

If Doppler explanation would work otherwise, then I think it would work for CMBR too. It seems to me that it would make no difference whether a photon we receive would have been emitted from far away galaxy or from particle soup of early universe. In both cases you would have expanding space between emitter and absorber. So if we assume Doppler explanation, they would seem to be moving away from each other in both cases. I don't know about isotropy, but I certainly wouldn't expect blueshifts. But maybe you didn't mean actual blueshifts, but rather some more redshifted and some less redshifted?

George
2004-Jul-08, 12:41 PM
The debate is what went Bang and how it happened. This information is needed to understand the Universe, expansion, red-shift, galaxy formation and dynamics, QM, etc. etc. All of these ideas are dependent on this primal environment and event. If we do not get them right, all of the laws and priciples of science are limited at best and true understanding is impossible.
I think complete understanding would be impossible. Fortunately, we are blessed with piecemeal understanding that does work quite well for us. Newtons laws still work fine within the scope he was applying them. GR is now much better. It's amazing scientists can ponder events at almost t=0 and still make some sense.

bigsplit
2004-Jul-08, 01:10 PM
The debate is what went Bang and how it happened. This information is needed to understand the Universe, expansion, red-shift, galaxy formation and dynamics, QM, etc. etc. All of these ideas are dependent on this primal environment and event. If we do not get them right, all of the laws and priciples of science are limited at best and true understanding is impossible.
I think complete understanding would be impossible. Fortunately, we are blessed with piecemeal understanding that does work quite well for us. Newtons laws still work fine within the scope he was applying them. GR is now much better. It's amazing scientists can ponder events at almost t=0 and still make some sense.

It is amazing, but we also must be careful not to allow the present mindset to limit our willingness to reach for more. Because the "truth" may generate models that are quite different yet, with superior predictive power. Although, what we know now may be of great use and certainly can't be abandoned without a pragmatic alternative, we cannot stop seeking what was AT t=0, and what happened there. If we can find a pragmatic possibility that can explain the EMPIRICAL evidence we have availible, at this point we can work from there and either crush it or adopt it.

George
2004-Jul-08, 06:46 PM
If space expansion wouldn't cause redshifting, then I don't think that accelerating space expansion would either.

Let's do a thought experiment. For this experiment we assume that Greene's explanation (gravity, not expansion, causes the cosmological redshift) is correct.
Unfortunately, it is not clear to me what Greene's overall picture is of redshift. He does attribute gravity as a cause, if not the main cause, as it relates to expansion.



So we start our little experiment:

1. Space expansion apparatus is off. Redshift reader plots horizontal line, because gravity between the galaxies remains the same, so each photon is redshifted by same amount.
Since the photon is going through two gravity wells, I suspect it redshifts. Also, we are receeding due to prior expansion (your meter won't read the additional expansion effects, if any, at this setting) which adds a Doppler effect percentage to the red. (Assumes we are not in the same cluster). Since there is a gravitational field in open space, albeit weak, it too robs energy from our poor little photon "balls". I still do not know if this is mainstream either, however.


2. You change the setting to constant expansion (remember to keep throwing those photons). Redshift plot shows still a line but now the line is descending. That's because galaxies are now receding from each other and gravity between them is decreasing (at a constant rate). Same as above but the expansion now makes the photon struggle longer through the gravity field of open space allowing greater redshift even though gravity field has weakened (maybe). Of course, I still think that since I am now traveling faster due to expansion, that Doppler still should be a factor but I don't seem to have much support on this. :-?


3. You change the setting to accelerating expansion. Redshift plot is no more a line but now the line is dropping in non-linear fashion, amount of drop increasing every second. Galaxies are now receding from each other at accelerating fashion and gravity between them decreases accordingly. As my wife says..."exactly the same (as above) but different". A little more redshift by all the factors.

What I can't address properly is the GR factor. Acceleration should add to the drain on the photon just as gravity itself does (my GR guess only).



4. You can stop throwing, our experiment ends now.
Can we go bowling now? :)


So, space expansion and accelerating space expansion both have an (indirect) effect to redshift, but they are decreasing the redshift, not increasing. Why decrease? Or do you see the reduced gravity being more significant than me?


Isn't inflation theory independent theory with no relation to string theory?Yes. But, there may be a relation afterall. If string theory meets all their hopes, it may explain inflation. Specifically, according the Greene, the inflaton field (a Higgs field) can be viewed as an enrgy bowl with a rise in the middle (cakes with holes are made with these molds - hey, it rhymes :) ). This center section, "perch" as he calls it, is a unique spot that creates negative pressure which causes gravity to act opposite of normal. The shape of the perch is one reason for various inflation theories, apparently. The Higgs boson is predicted by string theory and may be at an energy range reachable in a few years (the Hadron Collider is one hope).



I also think the CMB would not be so isotropic using my pure Doppler approach as recombination light went all directions so we should not see such uniformity in the CMB since some of it would be redshifted and some blueshifted at this point in time relative to us. Does this make sense?

If Doppler explanation would work otherwise, then I think it would work for CMBR too. It seems to me that it would make no difference whether a photon we receive would have been emitted from far away galaxy or from particle soup of early universe. In both cases you would have expanding space between emitter and absorber. So if we assume Doppler explanation, they would seem to be moving away from each other in both cases. I don't know about isotropy, but I certainly wouldn't expect blueshifts. But maybe you didn't mean actual blueshifts, but rather some more redshifted and some less redshifted? I suppose I see the light from recombination as a flood that occured simultaneously around 300k to 400k ATB. If we trace back our hydrogen atoms and find "Ari" (or a centroid point in the scatter :) ) and my hydrogen scatter centroid and call this point "George", we would both see the same light at first (orange if we used a strobe....maybe). Some light would reach us shortly thereafter as blueshifted due to Doppler effects from accoustic motion and random motions in the h/he cloud. If you would have ended up in a galaxy far away, you and I would still be seeing the same thing from this initial flood, namely CMB at 2.73 K. Tomorrow, we will be seeing the light from the flood of recombination that is a day later in reaching us so it is redshifted a tiny, tiny bit more than today.

If some extreme blue shifted light ever existed at recombination, and it is, somehow, just reaching us, could it still have a net blueshift? Not likely, but, it did enter my thoughts.

I am very sure that I am very unsure of my thinking on all this. :)

Ari Jokimaki
2004-Jul-09, 06:19 AM
Unfortunately, it is not clear to me what Greene's overall picture is of redshift. He does attribute gravity as a cause, if not the main cause, as it relates to expansion.

Relates to expansion? I got the impression from your description of Greene's redshift mechanism that redshifting would be independent of expansion.



1. Space expansion apparatus is off. Redshift reader plots horizontal line, because gravity between the galaxies remains the same, so each photon is redshifted by same amount.
Since the photon is going through two gravity wells, I suspect it redshifts. Also, we are receeding due to prior expansion (your meter won't read the additional expansion effects, if any, at this setting) which adds a Doppler effect percentage to the red. (Assumes we are not in the same cluster). Since there is a gravitational field in open space, albeit weak, it too robs energy from our poor little photon "balls". I still do not know if this is mainstream either, however.

Sorry, I left something out from the initial conditions. This experiment didn't happen in expanding universe. It happened in initially static universe, and you then controlled expansion with your gadget. And my redshift meter was so sensitive that it had no trouble measuring these effects.



2. You change the setting to constant expansion (remember to keep throwing those photons). Redshift plot shows still a line but now the line is descending. That's because galaxies are now receding from each other and gravity between them is decreasing (at a constant rate). Same as above but the expansion now makes the photon struggle longer through the gravity field of open space allowing greater redshift even though gravity field has weakened (maybe). Of course, I still think that since I am now traveling faster due to expansion, that Doppler still should be a factor but I don't seem to have much support on this. :-?

It seems that I didn't think this situation thoroughly. I forgot that photon has to stay longer in the gravity field. Now it's a question about which effect is stronger, decreasing gravity causing less redshift or longer struggle time causing more redshift. So my argument is only valid if effect of decreasing gravity prevails.


What I can't address properly is the GR factor. Acceleration should add to the drain on the photon just as gravity itself does (my GR guess only).

I still don't understand how acceleration (of the space expansion) would have an effect to the photon, if we are still talking about strictly gravity caused redshift scenario. But this might be due to my feeble knowledge of GR.


Can we go bowling now? :)

Well, it's summer, nice weather and my vacation is about to start, so I would prefer some outdoor activity. 8)


Why decrease? Or do you see the reduced gravity being more significant than me?

Yes, like I explained above, I erroneously thought gravity was only significant thing.


...If string theory meets all their hopes, it may explain inflation.

Ok, it was the word "prediction" that confused me there. Predicting usually means something you do before something happens, so I got the impression that you said there was no inflation theory until string theory predicted it.


I suppose I see the light from recombination as a flood that occured simultaneously around 300k to 400k ATB. If we trace back our hydrogen atoms and find "Ari" (or a centroid point in the scatter :) ) and my hydrogen scatter centroid and call this point "George", we would both see the same light at first (orange if we used a strobe....maybe). Some light would reach us shortly thereafter as blueshifted due to Doppler effects from accoustic motion and random motions in the h/he cloud. If you would have ended up in a galaxy far away, you and I would still be seeing the same thing from this initial flood, namely CMB at 2.73 K. Tomorrow, we will be seeing the light from the flood of recombination that is a day later in reaching us so it is redshifted a tiny, tiny bit more than today.

If some extreme blue shifted light ever existed at recombination, and it is, somehow, just reaching us, could it still have a net blueshift? Not likely, but, it did enter my thoughts.

I am very sure that I am very unsure of my thinking on all this. :)

ATB = After The Bang, right? I think you would need initial speeds (many many times) greater than c to achieve large enough initial blueshifts to see blueshifts even today.

George
2004-Jul-09, 02:46 PM
Relates to expansion? I got the impression from your description of Greene's redshift mechanism that redshifting would be independent of expansion.
I am trying to separate the redshift component from the other less controversial components. Redshift by the "expansion" component apparaently is viewed by Greene as due to gravity. If he sees any stretching otherwise, he did not say (or I missed it).


Sorry, I left something out from the initial conditions. This experiment didn't happen in expanding universe. It happened in initially static universe, and you then controlled expansion with your gadget. And my redshift meter was so sensitive that it had no trouble measuring these effects.
Ah ha, I thought those photons had too little redshift. Hardly any Doppler shift. :)


[2....]It seems that I didn't think this situation thoroughly. I forgot that photon has to stay longer in the gravity field. Now it's a question about which effect is stronger, decreasing gravity causing less redshift or longer struggle time causing more redshift. So my argument is only valid if effect of decreasing gravity prevails.
We would have to know the rate of photon energy depletion for a given field and compare it to it's apparent travel time, I think. It is very unclear to me if GR also becomes a factor here assuming expansion is real. If galaxies are accelerating away from each other, does the photon "feel" more stressed from the GR issue of equivalence (acceleration is gravity) and get a little more "red in the face"? It may not be a factor afterall if the fabric is "lifting" the galaxies along. Time is not altered either as symmetry remains.



What I can't address properly is the GR factor. Acceleration should add to the drain on the photon just as gravity itself does (my GR guess only).
I still don't understand how acceleration (of the space expansion) would have an effect to the photon, if we are still talking about strictly gravity caused redshift scenario. But this might be due to my feeble knowledge of GR.
My thinking comes from the idea that if I use my wimpy wand (weak compared to your on/off expansion switch) and, suddenly, jerk a star out from under a fresh photon, wouldn't this immense acceleration cause redshifting more than the redshift it experiences as it leaves the gravity well.? If so, wouldn't a galaxy accelerating away from us have a similar, but possibly weaker, affect? You can see my conflict based on my prior statement. :)



Can we go bowling now? :)
Well, it's summer, nice weather and my vacation is about to start, so I would prefer some outdoor activity. 8)
It's a little warm over here for much outdoor fun. We brag in the winter. Now is your bragging time. :)


ATB = After The Bang, right? I think you would need initial speeds (many many times) greater than c to achieve large enough initial blueshifts to see blueshifts even today.
"ATB" is After the Bang. I suppose your right. Current z for CMB from recombination is 1089, so were not likely going to get any still blueshifted and I don't think we have. :roll:

Ari Jokimaki
2004-Jul-09, 04:40 PM
We would have to know the rate of photon energy depletion for a given field and compare it to it's apparent travel time, I think. It is very unclear to me if GR also becomes a factor here assuming expansion is real. If galaxies are accelerating away from each other, does the photon "feel" more stressed from the GR issue of equivalence (acceleration is gravity) and get a little more "red in the face"? It may not be a factor afterall if the fabric is "lifting" the galaxies along. Time is not altered either as symmetry remains.

I think that photon always continues with speed of light, so it doesn't feel any acceleration.


My thinking comes from the idea that if I use my wimpy wand (weak compared to your on/off expansion switch) and, suddenly, jerk a star out from under a fresh photon, wouldn't this immense acceleration cause redshifting more than the redshift it experiences as it leaves the gravity well.? If so, wouldn't a galaxy accelerating away from us have a similar, but possibly weaker, affect? You can see my conflict based on my prior statement. :)

Somehow I get a feeling that you are mixing Doppler effect into this. With Doppler effect it might work that way, but if we stick to gravity caused redshift, then you just take gravity field away from the photon with your wand and then there is less gravity to redshift that photon.

George
2004-Jul-10, 10:32 PM
... If galaxies are accelerating away from each other, does the photon "feel" more stressed from the GR issue of equivalence (acceleration is gravity) and get a little more "red in the face"?...

I think that photon always continues with speed of light, so it doesn't feel any acceleration.
I meant by "feel more stressed" that the an acceleration (due to expansion) by a local galaxy to the photon might rob it of more energy than if there was no acceleration by the galaxy. I sorta doubt it.



My thinking comes from the idea that if I use my wimpy wand (weak compared to your on/off expansion switch) and, suddenly, jerk a star out from under a fresh photon, wouldn't this immense acceleration cause redshifting more than the redshift it experiences as it leaves the gravity well.? If so, wouldn't a galaxy accelerating away from us have a similar, but possibly weaker, affect? You can see my conflict based on my prior statement. :)

Somehow I get a feeling that you are mixing Doppler effect into this. With Doppler effect it might work that way, but if we stick to gravity caused redshift, then you just take gravity field away from the photon with your wand and then there is less gravity to redshift that photon.
I am trying to keep Doppler out of it on this point. I am wondering that if you were a large star (pleasntly plump :) ) and I was another star (ok, plump, too) but our relativel velocity was 0, and you spit out a photon at me then, immediately, using one of your niffty magic devices, jerked yourself away at some fantastic rate, wouldn't your acceleration act to create additional "gravity" which would redshift your emitted photon more than normal as it leaves your gravity well?

bigsplit
2004-Jul-11, 05:22 PM
... If galaxies are accelerating away from each other, does the photon "feel" more stressed from the GR issue of equivalence (acceleration is gravity) and get a little more "red in the face"?...

I think that photon always continues with speed of light, so it doesn't feel any acceleration.
I meant by "feel more stressed" that the an acceleration (due to expansion) by a local galaxy to the photon might rob it of more energy than if there was no acceleration by the galaxy. I sorta doubt it.



My thinking comes from the idea that if I use my wimpy wand (weak compared to your on/off expansion switch) and, suddenly, jerk a star out from under a fresh photon, wouldn't this immense acceleration cause redshifting more than the redshift it experiences as it leaves the gravity well.? If so, wouldn't a galaxy accelerating away from us have a similar, but possibly weaker, affect? You can see my conflict based on my prior statement. :)

Somehow I get a feeling that you are mixing Doppler effect into this. With Doppler effect it might work that way, but if we stick to gravity caused redshift, then you just take gravity field away from the photon with your wand and then there is less gravity to redshift that photon.
I am trying to keep Doppler out of it on this point. I am wondering that if you were a large star (pleasntly plump :) ) and I was another star (ok, plump, too) but our relativel velocity was 0, and you spit out a photon at me then, immediately, using one of your niffty magic devices, jerked yourself away at some fantastic rate, wouldn't your acceleration act to create additional "gravity" which would redshift your emitted photon more than normal as it leaves your gravity well?

George, the acceleration would have to do something to the photon. I am not sure if this question has ever been explored, if it has, could someone please share? There is no doubt that the photon feels some effect from this dynamic.

Ari Jokimaki
2004-Jul-12, 10:32 AM
I meant by "feel more stressed" that the an acceleration (due to expansion) by a local galaxy to the photon might rob it of more energy than if there was no acceleration by the galaxy. I sorta doubt it.

I am trying to keep Doppler out of it on this point. I am wondering that if you were a large star (pleasntly plump :) ) and I was another star (ok, plump, too) but our relativel velocity was 0, and you spit out a photon at me then, immediately, using one of your niffty magic devices, jerked yourself away at some fantastic rate, wouldn't your acceleration act to create additional "gravity" which would redshift your emitted photon more than normal as it leaves your gravity well?

I'm going to try to quess your trail of thought: GR says that accelerating object experiences increased gravity field. Any object in it's vicinity would experience that too, even though they wouldn't be accelerating. This same effect would be small, but still there, further away from accelerating object, so all the photons would experience extra redshifting, because accelerating space expansion would cause acceleration to all objects in universe. Is this close to what you think?

Even if it is, it still don't make sense to me. Maybe my thinking is too "down to earth" on this subject.


George, the acceleration would have to do something to the photon. I am not sure if this question has ever been explored, if it has, could someone please share? There is no doubt that the photon feels some effect from this dynamic.

So there's two of you agreeing on this point, then maybe I should just shut up and play my guitar.

George
2004-Jul-12, 01:37 PM
Ari, Accoustic or electric? I bought my first about 8 years ago - Les Paul (Gibson). You think this will help us with string theory? :)

I bought another book, Extravagant Universe. It has a whole chapter on expansion. I'll let you know his view.

I am out for a few days to start-up a one man pot-hole patcher.

Ari Jokimaki
2004-Jul-12, 02:12 PM
Ari, Accoustic or electric? I bought my first about 8 years ago - Les Paul (Gibson). You think this will help us with string theory? :)

I bought another book, Extravagant Universe. It has a whole chapter on expansion. I'll let you know his view.

I am out for a few days to start-up a one man pot-hole patcher.

Electric, for about 25 years now.

In a few days I'll be out too for a week in a rented lakeside cottage, maybe I get some redshift for my skin there. So I quess we continue after that, have fun!

George
2004-Jul-15, 09:06 PM
Ari, Accoustic or electric? I bought my first about 8 years ago - Les Paul (Gibson). You think this will help us with string theory? :) ....

Electric, for about 25 years now.

In a few days I'll be out too for a week in a rented lakeside cottage, maybe I get some redshift for my skin there. So I quess we continue after that, have fun!
Hope you have some fun. My reading of Kirshner, so far, reveals that redshift is due to expansion. (not very helpful) :-? Cool book, otherwise.

Joe87
2004-Jul-16, 02:55 AM
The expansion doesn't cause redshifting? So, what do we need expansion for? I mean, shouldn't that redshift mechanism work for static universe also?

As a non-astronomer who took a few physics courses years ago, I have to wonder if there are other observed phenomena that corroborate expansion other than redshift? Anything besides the redshift that can only be explained by expansion?

Ari Jokimaki
2004-Jul-16, 05:14 AM
As a non-astronomer who took a few physics courses years ago, I have to wonder if there are other observed phenomena that corroborate expansion other than redshift? Anything besides the redshift that can only be explained by expansion?

Supernova time dilation is one piece of evidence that points towards expansion, but recently Jerry Jensen has been casting some doubts (http://lanl.arxiv.org/ftp/astro-ph/papers/0404/0404207.pdf) on that. You can see more of his thoughts in the "Against the mainstream" forum.


My reading of Kirshner, so far, reveals that redshift is due to expansion.

Well, that's not the most detailed explanation I have seen. :) (I'll leave today, so this is my last post for a week.)

George
2004-Jul-16, 02:44 PM
As a non-astronomer who took a few physics courses years ago, I have to wonder if there are other observed phenomena that corroborate expansion other than redshift? Anything besides the redshift that can only be explained by expansion?
There would be no "bang" in Big Bang Theory without expansion. Those who favor a Steady State universe are arguing against expansion.

As a result, all the Big Bang evidence supports expansion, directly or indirectly. CMB, especially, is evidence for expansion. This was a prediction of Big Bang and was sought by a couple of teams prior to the Wilson/Penzias discovery of it. This is not proof, however, as some better explanation may come along that can be verified.

George
2004-Jul-16, 02:59 PM
My reading of Kirshner, so far, reveals that redshift is due to expansion.

Well, that's not the most detailed explanation I have seen. :) (I'll leave today, so this is my last post for a week.)
You can guess my disapointment. However, I haven't finished the book and I am now getting a detailed story on the history and use of supernovas in expansion studies. Quite interesting. Hopefully, I'll have some cool stuff for you by the time you're back.