Can we detect the Cosmic Microwave Background getting redder?

[repoman]

So, the CMB has been redshifted by the about z=1,091 times currently. I assumed it is getting redder all the time. But how long of a time baseline would be needed to be able to have the precision to see a change in redshift? Like going from z=1,091 to 1,091.0001. This would be calculated from the peak frequencies of CMB.

Now, if you did have a change in redshift and a time span for that, what would that be able to tell you about the expansion rate of the universe?

Currently one of the best ways is to use type 1a supernovae as standard candles. IIRC, the absolute magnitudes of these events are near constant, so by combining the apparent magnitude and getting a redshift through a spectrograph you can get a chart of "redshift vs distance". This shows an accelerating universe.

 

[skepticalbip]

So, the CMB has been redshifted by the about z=1,091 times currently. I assumed it is getting redder all the time. But how long of a time baseline would be needed to be able to have the precision to see a change in redshift? Like going from z=1,091 to 1,091.0001. This would be calculated from the peak frequencies of CMB.

Now, if you did have a change in redshift and a time span for that, what would that be able to tell you about the expansion rate of the universe?

Currently one of the best ways is to use type 1a supernovae as standard candles. IIRC, the absolute magnitudes of these events are near constant, so by combining the apparent magnitude and getting a redshift through a spectrograph you can get a chart of "redshift vs distance". This shows an accelerating universe.

Yes, since 1929 the type 1a supernova has been considered to be very precise standard candle. However, since the early 2000s some questions have arisen as to how precise that "standard candle" actually is. These questions could cast some doubt on the universe's expansion rate - not so much on that the universe is expanding but on our certainty of the rate of that expansion.

http://www.universetoday.com/90670/astronomy-without-a-telescope-inconstant-supernovae/

As standard candles, Type 1a supernovae (or SNe1a) are key to determining the distance of their host galaxies. But one key consideration in determining their absolute luminosity is the reddening caused by the dust in the host galaxy. A higher than expected UV flux in some SNe1a could lead to an underestimate of this normal reddening effect, which dims the visible light of the star irrespective of its distance. Such an atypical SNe1a would then be picked up in ground-based SNe1a sky surveys as misleadingly dim – and their host galaxies would be determined as being further away from us than they really are.

The researchers call this another possible systematic error within the current SNe1a-based calculations of the nature of the universe – those other possible systematic errors including the metallicity of the supernovae themselves, as well as the size, density and chemistry of their host galaxy.

 

[repoman]

I had read that before, but didn't want to clutter up my post. Fun details.

 

[Bomb#20]

So, the CMB has been redshifted by the about z=1,091 times currently. I assumed it is getting redder all the time. But how long of a time baseline would be needed to be able to have the precision to see a change in redshift? Like going from z=1,091 to 1,091.0001. This would be calculated from the peak frequencies of CMB.

I looked up the error bars on that 1091 figure; what I found said the redshift was 1091 +- 1. I.e., we can't measure redshift precisely enough to tell 1091.0000 from 1091.0001. Assuming the CMB is getting redder all the time roughly linearly, that would mean the time baseline you'd need is about ten million years. Bummer...

 

[Elixir]

So, the CMB has been redshifted by the about z=1,091 times currently. I assumed it is getting redder all the time. But how long of a time baseline would be needed to be able to have the precision to see a change in redshift? Like going from z=1,091 to 1,091.0001. This would be calculated from the peak frequencies of CMB.

I looked up the error bars on that 1091 figure; what I found said the redshift was 1091 +- 1. I.e., we can't measure redshift precisely enough to tell 1091.0000 from 1091.0001. Assuming the CMB is getting redder all the time roughly linearly, that would mean the time baseline you'd need is about ten million years. Bummer...

Patience is a virtue.

 

[lpetrich]

The timescale for the CMB's redshift to change is roughly the Hubble time, around 14 billion years. So to see a 1% change, you'll have to wait around 140 million years.