# Fate of relict radiation patterns

Relict radiation has spatial fluctuations: hot and cool spots. Of rather modest amplitude, but yet detectable.

Have these patterns undergone any change?

Galaxies are supposed to form a few hundred million years after big bang.

If you watched a given hot spot of relict radiation, would it eventually be seen to evolve into a galaxy cluster, and cold spots into voids, or vice versa?

And how long would it take in order to watch an object visible as a relict radiation pattern as of now to evolve into a young galaxy?

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mfb
Mentor
Without accelerated expansion, you could do this. The cosmic microwave background is redshifted by a factor of ~1100 - everything we observe there is slowed down by that factor. The factor changes with time, so you cannot just multiply it with the time it took for stars to form, but it should give a rough estimate how long we would have to wait.

This is not the world we live in, however. Expansion is accelerating. Assuming this will continue, you can never observe how the currently visible patterns evolve into stars or galaxies. Those objects are too far away, their light will never reach us.
Neglecting observational issues (there is no light emitted in this period), you would see that light from this matter gets more and more redshifted, and correspondingly the passage of time appears slower and slower to us.

Neglecting observational issues (there is no light emitted in this period),
After relic radiation, atomic hydrogen would have emitted mainly 21 cm radiation, right? Which, at the relic radiation end, has been redshifted to 230 m, and smaller wavelengths at later times?

mfb
Mentor
Right. The detection of this radiation is one of the goals of LOFAR.

If we look at an object of a specified age:
Would we see that object for a finite time, or infinite time, here?

Would our observations from now on span a finite time at the said object, or infinite time there?

mfb
Mentor
For objects gravitationally bound to us, you can observe them as long as you like (both with their and our clock).
For other objects, you can keep watching them as long as you like, but the intensity will drop so much that it becomes impractical after a while (up to the point where you get "the last photon"). The total evolution of those objects that will be visible to us is finite, similar to the matter that emitted the CMB we see today.

George Jones
Staff Emeritus
Gold Member
Relict radiation has spatial fluctuations: hot and cool spots. Of rather modest amplitude, but yet detectable.

Have these patterns undergone any change?

Galaxies are supposed to form a few hundred million years after big bang.

If you watched a given hot spot of relict radiation, would it eventually be seen to evolve into a galaxy cluster, and cold spots into voids, or vice versa?

And how long would it take in order to watch an object visible as a relict radiation pattern as of now to evolve into a young galaxy?
The answers to these questions are fairly subtle. For example, if we watch in real time the redshifts of a high redshift object, we see its redshift decrease.

I hope to do some fairly realistic calculations, and, sometime in the next few days, I hope post some graphs.

Relic radiation was said to have been emitted over a period of about 115 000 years.

Since it was emitted at redshift 1100, it would seem that over a period of about 120 million years, all relic radiation patterns now visible ought to recombine and be extinguished - revealing completely new relic radiation patterns beyond, at (slightly) bigger redshifts.

Is that correct?

mfb
Mentor
The same correlations we see in space are present in time as well, that makes the analysis more complicated - but the main point is right, the fluctuations will change in time.

Chronos
Gold Member
Another issue is the integrated Sachs-Wolfe effect. Subtracting that from the cmb is a problem.

The temperature of relic radiation decreases with time.
The temperature of relic radiation at its origin patterns is unchanged - it is determined by the temperature where hydrogen recombined long ago.

Say that in a hundred million years or so, the redshift of relic radiation seen on Earth increases from 1100 to 1110.
It will be completely new patterns - but originating at the same temperature, further behind the patterns we see now.
The relic radiation patters we see now will in a hundred million years be seen in galaxies a hundred million years behind us - and these will also be at redshift 1110 there.

So, we see the new and further relic radiation patterns at redshift 1110. But what will have happened to the old relic radiation patterns we saw now at redshift 1100?
They will have cooled and become transparent. Well, we can continue observing them in other manners, like the 21 cm line. They will be in the foreground of the relic radiation, and they will have redshift now smaller than the 1110 of background relic radiation.

Will their redshift be still 1100? Something bigger than 1100 but smaller than 1110, like 1105? Or something smaller than 1100, like 1090?

George Jones
Staff Emeritus
Gold Member
Will their redshift be still 1100? Something bigger than 1100 but smaller than 1110, like 1105? Or something smaller than 1100, like 1090?
The observed redshift will decrease until it reaches a minimum, and then it will increase. I haven't yet calculated by how much and how long the redshift will decrease.

The observed redshift will decrease until it reaches a minimum, and then it will increase.
At any one time, are the redshifts of specific objects all decreasing, or some decreasing and some increasing?

George Jones
Staff Emeritus
Gold Member
At any one time, are the redshifts of specific objects all decreasing, or some decreasing and some increasing?
Some are decreasing, and some are increasing. Right now, the higher redshift objects have redshifts that are decreasing, and lower redshift objects have redshifts that are increasing.

As Aimless said, observation time have been too short to see redshift change. We are close to being able to do this, but, for economic and other reasons, such a project won't start for several decades. Once started, the project would take a couple of decades to start to get good results. See

http://arxiv.org/abs/0802.1532

Also, redshifts don't necessarily increase with time. Figure 1 from this paper plots redshift versus time. The three red curves are for objects in our universe. As we watch (over many years) a distant, high redshift object, A, we will see the object's redshift decrease, reach a minimum, and then increase. If we watch a much closer, lower redshift object, B, we see the object's redshift only increase.

Roughly, when light left A, the universe was in a decelerating matter-dominated phase, and when light left B, the universe was in the accelerating dark energy-dominated phase.
I wanted to do the analysis myself in different way, but it doesn't look like this is going to happen before I go on holiday on Monday.

Some are decreasing, and some are increasing. Right now, the higher redshift objects have redshifts that are decreasing, and lower redshift objects have redshifts that are increasing.
What is the redshift that is staying constant, right now?