The Universe may eventually stabilize?

[Mind Bender]

It's funny how astrophysicists and cosmologists always debate back and forth about the ultimate fate of the Universe. Either they think the Universe will collapse upon itself...or it will expand until nothing is left.

I'm willing to bet these scientists never considered a third outcome: The Universe will actually stabilize and stop expanding altogether, but it will not start contracting either. I know there's a term that describes a condition like this but I can't think of it just now. But yes, I think the Universe will eventually stabilize and stop expanding and contracting.

 

[dacruick]

You should support that claim should you not? Your thread risks being locked.

 

[Calimero]

Well, you are sort of right. The term you are looking for is - static universe. You may want to take a look at this paper: The Return of a Static Universe and the End of Cosmology

 

[Tanelorn]

Calimero thanks for the paper, it was interesting.

Presumably the amplitude or intensity of the CMBR also drops as the CMBR is redshifted.
I have wondered how many dB it can drop before it becomes undetectable due to other sources of RF or noise?

 

[bapowell]

Well, you are sort of right. The term you are looking for is - static universe. You may want to take a look at this paper: The Return of a Static Universe and the End of Cosmology

Be careful with this -- it's not a static universe in the sense of the OP. The model under discussion in this paper is LCDM; the authors are pointing out that in the far future observers on Earth will, for all intents and purposes, observe what appears to be a static universe (no detectable CMB, no Hubble recession, etc). Of course, LCDM is not static; it is an accelerating spacetime with an event horizon. Future observers will be duped into concluding that the universe is static simply because there are no observations to suggest otherwise. And so, this is not an example of a universe with a static fate, but rather one that continues expanding indefinitely.

Also, remember that a static universe is unstable according to GR. It is therefore an unlikely model for the late-time universe.

 

[Calimero]

Be careful with this -- it's not a static universe in the sense of the OP. The model under discussion in this paper is LCDM; the authors are pointing out that in the far future observers on Earth will, for all intents and purposes, observe what appears to be a static universe (no detectable CMB, no Hubble recession, etc). Of course, LCDM is not static; it is an accelerating spacetime with an event horizon. Future observers will be duped into concluding that the universe is static simply because there are no observations to suggest otherwise. And so, this is not an example of a universe with a static fate, but rather one that continues expanding indefinitely.

Also, remember that a static universe is unstable according to GR. It is therefore an unlikely model for the late-time universe.

Not necessarily so. Models are human construct. Universe simply does what it does. We just observe parts of it that are available to us and build mathematical models about them. One day there will be no evidence of expansion, thus making it effectively static universe. That paper is about that, about disappearance of FLRW cosmology. I don't say it is right, but it is about that. I think that there will be some clues left, like radiation from cosmological event horizon, enough to make future astronomers wonder, if they can detect it.
You wrote one very interesting sentence. Future observers will be duped into concluding that the universe is static simply because there are no observations to suggest otherwise. How wrong and shallow are our conclusions then?

Edit: Of course you are right that OP was intended in different manner.

 

[bapowell]

You wrote one very interesting sentence. Future observers will be duped into concluding that the universe is static simply because there are no observations to suggest otherwise. How wrong and shallow are our conclusions then?

Just one interesting sentence??

Indeed, one can argue that our reality is completely derived from our observations and that there might then be no difference between LCDM and a static universe if no discriminating evidence presents itself. That said, we *do* have evidence today that supports LCDM; if in the future that evidence is no longer available, we can understand this (in fact, predict it) using the models we develop *today*. The physical reality of a future LCDM universe is still that of an LCDM universe, whether or not our unfortunate progeny know it or not!

 

[Calimero]

Just one interesting sentence??

No disrespect intended. I value your posts very much, they are always on target. I think that you know what I meant :)

Calimero thanks for the paper, it was interesting.

Presumably the amplitude or intensity of the CMBR also drops as the CMBR is redshifted.
I have wondered how many dB it can drop before it becomes undetectable due to other sources of RF or noise?

Cmb temperature is inversely proportional to the scale factor. Look at the page four of the paper I linked to. Vanishing CMB. It is very well explained.

 

[Tanelorn]

Calimero I read it, but I wasnt sure what was being said.

"While a uniform radio background at this frequency would in principle be observable, the intensity of the CMB will also be redshifted by about 12 orders of magnitude."


If he means attenuated instead of redshifted then 12 orders of magnitude is 120dB.
Unfortunately, I have no idea what the current signal level is so I cannot figure out what the signal to noise (or interferers) is then, or now for that matter.


Also what is the relationship between redshift frequency and redshift intensity?


I guess we can always build bigger dish antennas until we can extract enough signal to overcome the receiver thermal noise floor and interfering sources, what ever they may be at the various red shift frequencies.


This is one of the most interesting parts of Cosmology for me, I am a Radio Engineer.

 

[Tanelorn]

Looking at the way information will be lost to us in the distant future suggests that we ourselves could have already reached a point where other critically important information for a higher level understanding of Cosmology may have also already been lost to us. Perhaps another civilisation which is 8 Billion years old already would have such information, which is an excellent reason for making contact despite Hawking's fears for doing so.

 

[bapowell]

Excellent point Tanelorn.

 

[Calimero]

Calimero I read it, but I wasnt sure what was being said.

"While a uniform radio background at this frequency would in principle be observable, the intensity of the CMB will also be redshifted by about 12 orders of magnitude."


If he means attenuated instead of redshifted then 12 orders of magnitude is 120dB.
Unfortunately, I have no idea what the current signal level is so I cannot figure out what the signal to noise (or interferers) is then, or now for that matter.


Also what is the relationship between redshift frequency and redshift intensity?

He means that intensity will drop about 12 orders of magnitude. I guess that you can say attenuated.

Intensity (basically irradiance - total energy radiated per unit surface area - but astrophysicists call it intensity) of the black body is directly proportional to the fourth power of temperature. Temperature is inversely proportional to the scale factor, so if he talks about epoch when scale factor will be 1000 times of what it is now, intensity of cmb radiation will be 1/1000^4, or 12 orders of magnitude less of what it is now.