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mugaliens
2010-Apr-16, 06:40 AM
Questions at the bottom, so please read through before you jump to conclusions and an answer:

While reading through the following three things, I had an interesting thought - just how closely are these three related, anyway?

Unruh effect (http://en.wikipedia.org/wiki/Unruh_effect)

Comoving coordinates (http://en.wikipedia.org/wiki/Comoving_distance#Comoving_coordinates)

Cosmic microwave background radiation (http://en.wikipedia.org/wiki/Cosmic_microwave_background_radiation)

The Unruh effect is where an accelerating observer will observe black-body radiation whereas an inertial observer sees none. Put simply, to an accelerating observer, the vacuum around an inertial observer appears to contain particles in thermal equilibrium i.e. "a warm gas."

Reading this made me think of the edge of the observable universe. Interestingly, under comoving coordinates, it states:


A comoving observer is the only observer that will perceive the universe, including the cosmic microwave background radiation, to be isotropic. Non-comoving observers will see regions of the sky systematically blue-shifted or red-shifted. Thus isotropy, particularly isotropy of the cosmic microwave background radiation, defines a special local frame of reference called the comoving frame.

Then I considered this possibility: What if the CMBR isn't echos of the Big Bang, but rather, simply Unruh effect from the edge of the universe (if not the most distant 5 to 30%) that's moving away fast enough, up to c, that we see it as background radiation?

I also thought of the blue/red shifting, and devised a simple experiment: Accelerate a probe as fast as possible to see if it detects a measurable blue-shifting of the CMBR in the direction of travel, and a measurable red-shifing behind it. If so, the CMBR is indeed echoes of something.

If not, however, if there's no doppler shift, then the CMBR may very well simply be the Unruh effect of the most distance edges of our observable universe receeding from us close to, and up to c.

Questions:

How sensitive are our instruments? Is Hubble sensitive enough to detect a doppler difference in the CMBR from the varying relative velocities it'll achieve every six months given Earth's orbit around the sun? Is there another instrument out there sensitive enough to detect/reject any shift?

sirius0
2010-Apr-16, 11:27 AM
Interesting. Could not the Unruh effect then have created a lot of the radiation and matter during inflation? So there could be an echo and a continuing Unruh? I don't know enough but have trouble seeing how there would be any doppler even if it is an echo. I mean a red shift in black body radiation would simply mean your bluish is my red but we both see a full spectrum. Isn't the microwave peak due to the ammount of space time this radiation has had to propogate through whilst it is expanding? Perhaps you are right and they are right because Unruh and CMBR are the same thing?

sirius0
2010-Apr-16, 11:32 AM
Yes the comoving link says I am wrong with my confusion on the doppler effect but I still wonder. Well thanks! I will have to go and think now.

Andrew D
2010-Apr-16, 02:42 PM
Interesting. Could not the Unruh effect then have created a lot of the radiation and matter during inflation? So there could be an echo and a continuing Unruh? I don't know enough but have trouble seeing how there would be any doppler even if it is an echo. I mean a red shift in black body radiation would simply mean your bluish is my red but we both see a full spectrum. Isn't the microwave peak due to the ammount of space time this radiation has had to propogate through whilst it is expanding? Perhaps you are right and they are right because Unruh and CMBR are the same thing?

The Unruh effect describes how an observer's assigned coordinates affect how he measures radiation in general, or the cosmic microwave background, specifically. Look at it this way: the principles of the Unruh effect say that two observers who are not co-moving (do not observe the other at rest) will not measure objects at the same temperature, and that the temperature at which each observer measures the CMB radiation depends not only on the velocity and location of the object that emitted the radiation, but the velocity at which he observes the radiation.

DrRocket
2010-Apr-16, 03:03 PM
The Unruh effect is where an accelerating observer will observe black-body radiation whereas an inertial observer sees none. Put simply, to an accelerating observer, the vacuum around an inertial observer appears to contain particles in thermal equilibrium i.e. "a warm gas."



Unruh's original paper

http://www2.lns.mit.edu/fisherp/Unruh.pdf

Andrew D
2010-Apr-16, 11:49 PM
The Unruh effect is where an accelerating observer will observe black-body radiation whereas an inertial observer sees none. Put simply, to an accelerating observer, the vacuum around an inertial observer appears to contain particles in thermal equilibrium i.e. "a warm gas."

can you clarify "particles"? I thought the inertial observer just saw black body radiation.

Ken G
2010-Apr-17, 07:35 AM
Then I considered this possibility: What if the CMBR isn't echos of the Big Bang, but rather, simply Unruh effect from the edge of the universe (if not the most distant 5 to 30%) that's moving away fast enough, up to c, that we see it as background radiation?I've seen a serious paper, somewhere (I can't recall, unfortunately, but likely on this forum), that made that exact argument. I don't know its validity, but it is not a crazy notion. The CMBR is in thermal equilibrium, and that tends to "hide its tracks": all thermal equilibria are created equal (that's their beauty, and the infuriating thing about them). Maybe it is not possible to distinguish these origins of the CMBR, and maybe there isn't even any fundamental difference between the two pictures. I don't know, but the idea is apparently worth consideration.



I also thought of the blue/red shifting, and devised a simple experiment: Accelerate a probe as fast as possible to see if it detects a measurable blue-shifting of the CMBR in the direction of travel, and a measurable red-shifing behind it. If so, the CMBR is indeed echoes of something.I don't actually think that could distinguish the two origins of the CMBR. The Unruh effect is going to be due to what is happening to the scale factor of the universe, and if that is indeed a legitimate way to look at the CMBR, it's going to work fine for all particular motions of any observer relative to the comoving frame in which the Unruh effect is being derived. You could no more distinguish a cosmological redshift from "tired light" by moving your observing apparatus, it's "too late" by then-- the signal has already been established, moving the observer is only going to change it in the usual way in either case.

tommac
2010-Dec-20, 06:35 PM
Sorry to raise a long dead thread back from its grave .... but I was just about to post almost the exact same question but before I did so I did a quick search and came accross this thread that worded my confusion much better than I could have.

Could all of the CMBR be modelled to be purely unruh?

If the universe is expanding and accelerating couldnt the CMBR just be unruh?

forrest noble
2010-Dec-20, 08:03 PM
How sensitive are our instruments? Is Hubble sensitive enough to detect a doppler difference in the CMBR from the varying relative velocities it'll achieve every six months given Earth's orbit around the sun? Is there another instrument out there sensitive enough to detect/reject any shift?

Sorry you're not back for real, Mugs.

Even though you cannot respond to this posting you possibly might be able to view it.

Since it is well accepted that there is no real motion of matter concerning the observed redshift of galaxies it seemingly could be unrelated to any possible Unruh effect that concerns motion relative the the CMBR.

So accordingly the Unruh effect is the prediction that an accelerating observer will observe black-body type radiation where an inertial observed will observe none. Even though the universe according to the dark energy model, would be expanding at an accelerating rate, just like uniform expansion there would be no real motion of galaxies involved and therefore no Unruh effect.

Ken G
2010-Dec-20, 08:28 PM
Could all of the CMBR be modelled to be purely unruh?I don't understand Unruh radiation well enough to say, but probably the CMBR itself could not be Unruh (it comes from the era of recombination, the "surface of last scattering" if you will, and there's not much you can do with that and still have any hope of a working model), so the issue is more could the original light energy found in the Big Bang, responsible for the subsequent temperature evolution, be Unruh radiation. The key idea with Unruh radiation is (apparently) that if you change from an inertial reference frame where the vacuum looks empty of light to a rapidly accelerating frame, the vacuum becomes filled with a thermal radiation field. This is a lot like the Hawking radiation that a noninertial observer perched just outside the event horizon would see. But in the Big Bang, all the observers are inertial (they are acted on only by gravity), so it's not clear exactly how Unruh radiation comes into play there. But maybe the inflationary era, or some such thing, "changed the vacuum" such that we are only inertial with respect to the "new" vacuum, and might be noninertial with respect to the "old" vacuum, enough to see Unruh radiation emanating from the old vacuum. I'm not suggesting this is a correct picture, only that I couldn't rule it out.

tommac
2010-Dec-20, 09:10 PM
Even though there is no "real motion" arent we in fact accelerating away from any point in the universe?



Sorry you're not back for real, Mugs.

Even though you cannot respond to this posting you possibly might be able to view it.

Since it is well accepted that there is no real motion of matter concerning the observed redshift of galaxies it seemingly could be unrelated to any possible Unruh effect that concerns motion relative the the CMBR.

So accordingly the Unruh effect is the prediction that an accelerating observer will observe black-body type radiation where an inertial observed will observe none. Even though the universe according to the dark energy model, would be expanding at an accelerating rate, just like uniform expansion there would be no real motion of galaxies involved and therefore no Unruh effect.

tommac
2010-Dec-20, 09:11 PM
Why would it need to from then ( era of recombination )? Why cant it be unruh from some point in the not so distant past?


I don't understand Unruh radiation well enough to say, but probably the CMBR itself could not be Unruh (it comes from the era of recombination, the "surface of last scattering" if you will, and there's not much you can do with that and still have any hope of a working model), so the issue is more could the original light energy found in the Big Bang, responsible for the subsequent temperature evolution, be Unruh radiation. The key idea with Unruh radiation is (apparently) that if you change from an inertial reference frame where the vacuum looks empty of light to a rapidly accelerating frame, the vacuum becomes filled with a thermal radiation field. This is a lot like the Hawking radiation that a noninertial observer perched just outside the event horizon would see. But in the Big Bang, all the observers are inertial (they are acted on only by gravity), so it's not clear exactly how Unruh radiation comes into play there. But maybe the inflationary era, or some such thing, "changed the vacuum" such that we are only inertial with respect to the "new" vacuum, and might be noninertial with respect to the "old" vacuum, enough to see Unruh radiation emanating from the old vacuum. I'm not suggesting this is a correct picture, only that I couldn't rule it out.

forrest noble
2010-Dec-20, 10:26 PM
Even though there is no "real motion" arent we in fact accelerating away from any point in the universe?

No tommac. According to the standard model and even every other "competing" model that I can think of, there is no real galactic motion at all involved with the proposed accelerated expansion of the universe. The standard model explains it as the accelerated expansion of space, again no real motion of separation. Accordingly we could have motion relative to the CMB but seemingly no accelerated motion resulting in the Unruh effect if it exists.

tommac
2010-Dec-21, 03:02 PM
I understand there is no real motion ... but there is a change in distance. If I were to measure the distance to any point in the universe it would get further away and accelerate away from us. So maybe not real motion but things are moving further away ... Wouldnt there be a correlation to the redshifting of light?



No tommac. According to the standard model and even every other "competing" model that I can think of, there is no real galactic motion at all involved with the proposed accelerated expansion of the universe. The standard model explains it as the accelerated expansion of space, again no real motion of separation. Accordingly we could have motion relative to the CMB but seemingly no accelerated motion resulting in the Unruh effect if it exists.

Ken G
2010-Dec-21, 03:08 PM
Why would it need to from then ( era of recombination )? Why cant it be unruh from some point in the not so distant past?
The CMB itself is just a thermal radiation field, and there are lots and lots of ways of making that, but there are many other constraints that also need to be fit by the model. There's a whole history of the universe, with lots of interlocking effects, and the Big Bang model makes them all fit together like a jigsaw puzzle. No piece by itself is decisive-- it is how they all fit together that supports the model. Also, bear in mind that the acceleration of the universe is time dependent-- a long time ago it passed from deceleration to acceleration. So one would need a whole model for the time behavior of the Unruh radiation, whereas the 2.7 K CMB fits perfectly with the history models. Finally, Unruh radiation applies to locally noninertial acceleration in one direction, but the acceleration of the universe is locally inertial and isotropic. So I think anyone wanting to make that case has a lot of work to do first.

forrest noble
2010-Dec-21, 07:42 PM
tommac,


I understand there is no real motion ... but there is a change in distance. If I were to measure the distance to any point in the universe it would get further away and accelerate away from us. So maybe not real motion but things are moving further away ... Wouldnt there be a correlation to the redshifting of light?


According to the standard model galactic redshifts are caused by the expansion of space. The Unruh effect, if it exists, is related to real accelerated motion. Real motion, as you understand, is different from relative motion -- which is simply a matter of perspective. The redshift could be considered relative motion. Real motion or acceleration might be determined by the effects of a gravitational field upon something that is moving or accelerating within it.

tommac
2010-Dec-21, 10:14 PM
Which piece would rule out unruh in favor of CMBR?


The CMB itself is just a thermal radiation field, and there are lots and lots of ways of making that, but there are many other constraints that also need to be fit by the model. There's a whole history of the universe, with lots of interlocking effects, and the Big Bang model makes them all fit together like a jigsaw puzzle. No piece by itself is decisive-- it is how they all fit together that supports the model. Also, bear in mind that the acceleration of the universe is time dependent-- a long time ago it passed from deceleration to acceleration. So one would need a whole model for the time behavior of the Unruh radiation, whereas the 2.7 K CMB fits perfectly with the history models. Finally, Unruh radiation applies to locally noninertial acceleration in one direction, but the acceleration of the universe is locally inertial and isotropic. So I think anyone wanting to make that case has a lot of work to do first.

tommac
2010-Dec-21, 10:15 PM
Why would it not also be created due to expansion of space and is limmited to only REAL motion?


tommac,



According to the standard model galactic redshifts are caused by the expansion of space. The Unruh effect, if it exists, is related to real accelerated motion. Real motion, as you understand, is different from relative motion -- which is simply a matter of perspective. The redshift could be considered relative motion. Real motion or acceleration might be determined by the effects of a gravitational field upon something that is moving or accelerating within it.

Ken G
2010-Dec-21, 10:54 PM
Which piece would rule out unruh in favor of CMBR?Galaxy formation. H/He ratio. Deuterium content. Cosmological redshift of quasars. Cosmological redshift of supernovae, and concomitant time dilation of their duration. The Hubble law. What piece of extragalactic astronomy does not favor the CMBR interpretation? There's a whole history there, a story that works. It's not that an Unruh interpretation is expressly ruled out by any of those, it's that the CMBR interpretation fits in with the larger jigsaw puzzle, and the recent-time Unruh interpretation does not. Now, I don't rule out that there might be some coordinate system that causes us to reinterpret the CMB as Unruh radiation in those coordinates, that's a sticky business in GR. But such coordinates would have a lot of other things different as well, if they exist at all-- they would most likely generate a much more artificial language for talking about the Big Bang than the comoving frame coordinates that are based on expressing the cosmological principle in the most natural and convenient way.

tommac
2010-Dec-22, 03:20 AM
Can you go into the reasons these are directly related to the CMBR?

For example ... why would the cosmological redshift of quasars disprove that the radiation we detect here on earth if from tthe CMBR rather than from unruh?

Also how would one determine the "concomitant" redshift of the CMBR?


Galaxy formation. H/He ratio. Deuterium content. Cosmological redshift of quasars. Cosmological redshift of supernovae, and concomitant time dilation of their duration. The Hubble law. What piece of extragalactic astronomy does not favor the CMBR interpretation? There's a whole history there, a story that works. It's not that an Unruh interpretation is expressly ruled out by any of those, it's that the CMBR interpretation fits in with the larger jigsaw puzzle, and the recent-time Unruh interpretation does not. Now, I don't rule out that there might be some coordinate system that causes us to reinterpret the CMB as Unruh radiation in those coordinates, that's a sticky business in GR. But such coordinates would have a lot of other things different as well, if they exist at all-- they would most likely generate a much more artificial language for talking about the Big Bang than the comoving frame coordinates that are based on expressing the cosmological principle in the most natural and convenient way.

WayneFrancis
2010-Dec-22, 05:09 AM
Can you go into the reasons these are directly related to the CMBR?

For example ... why would the cosmological redshift of quasars disprove that the radiation we detect here on earth if from tthe CMBR rather than from unruh?

Also how would one determine the "concomitant" redshift of the CMBR?

Arrrrg I wish tommac didn't have me on ignore.

Honestly he doesn't read papers he tries to put up in defence of his ideas and he doesn't even read the answers given to him


Galaxy formation. H/He ratio. Deuterium content. Cosmological redshift of quasars. Cosmological redshift of supernovae, and concomitant time dilation of their duration. The Hubble law. What piece of extragalactic astronomy does not favor the CMBR interpretation? There's a whole history there, a story that works. It's not that an Unruh interpretation is expressly ruled out by any of those, it's that the CMBR interpretation fits in with the larger jigsaw puzzle, and the recent-time Unruh interpretation does not. Now, I don't rule out that there might be some coordinate system that causes us to reinterpret the CMB as Unruh radiation in those coordinates, that's a sticky business in GR. But such coordinates would have a lot of other things different as well, if they exist at all-- they would most likely generate a much more artificial language for talking about the Big Bang than the comoving frame coordinates that are based on expressing the cosmological principle in the most natural and convenient way.

It DOESN'T disprove the the unruh effect. It is just the CMBR is a better fit because it explains a ton of stuff we observe while the Unruh effect might be able to explain 1 small detail but then you have to figure out a different explanations for a ton of other observations.

Someone point out to tommac that he should learn to read the posts that respond to him and he then quotes asking a question to which the quote he includes already answers that question.

Ken G
2010-Dec-22, 06:52 AM
Can you go into the reasons these are directly related to the CMBR?

For example ... why would the cosmological redshift of quasars disprove that the radiation we detect here on earth if from tthe CMBR rather than from unruh? WayneFrancis answered that well with "It is just the CMBR is a better fit because it explains a ton of stuff we observe while the Unruh effect might be able to explain 1 small detail but then you have to figure out a different explanations for a ton of other observations." That is also what I meant above when I said " It's not that an Unruh interpretation is expressly ruled out by any of those, it's that the CMBR interpretation fits in with the larger jigsaw puzzle."


Also how would one determine the "concomitant" redshift of the CMBR?Via a complete model, like the Big Bang model, which is precisely what is lacking in speculations about interpreting the CMB as a recent (cosmologically speaking) manifestation of Unruh radiation. The goals of cosmology are not to match up each observed tidbit with some isolated explanatory device, but rather to tell a unified story of the history of the entire observable universe, that fits reasonably well with every single one of the observed tidbits.

tommac
2010-Dec-22, 02:31 PM
So to summerize ... looking at the radiation that we call CMBR alone ... we could interpret it as any of a number of things ...

However because we would expect CMBR due to the theory as a whole and then in fact find data the could be interepreted as CMBR we assume it is CMBR.

without coming up with a better theory that would rule out CMBR and incorporate unruh you wouldnt rule out CMBR.

Is that roughly what you are saying?


WayneFrancis answered that well with "It is just the CMBR is a better fit because it explains a ton of stuff we observe while the Unruh effect might be able to explain 1 small detail but then you have to figure out a different explanations for a ton of other observations." That is also what I meant above when I said " It's not that an Unruh interpretation is expressly ruled out by any of those, it's that the CMBR interpretation fits in with the larger jigsaw puzzle."
Via a complete model, like the Big Bang model, which is precisely what is lacking in speculations about interpreting the CMB as a recent (cosmologically speaking) manifestation of Unruh radiation. The goals of cosmology are not to match up each observed tidbit with some isolated explanatory device, but rather to tell a unified story of the history of the entire observable universe, that fits reasonably well with every single one of the observed tidbits.

Ken G
2010-Dec-22, 02:48 PM
So to summerize ... looking at the radiation that we call CMBR alone ... we could interpret it as any of a number of things ...

However because we would expect CMBR due to the theory as a whole and then in fact find data the could be interepreted as CMBR we assume it is CMBR.
That's it exactly.