# Tag Info

Accepted

### Why can we observe the Cosmic Microwave Background no matter the direction we look?

Until the Universe was 380,000 years old, it was filled with a gas of protons an electrons. There was also radiation, in thermal equilibrium with the matter, and because it was so hot, the protons and ...
• 31.9k

### Why does the Fourier transform of this CMB image have a hole in it?

Having now looked at the paper by Aiola et al. (2020), it emerges that for that map, they filtered the data to exclude low frequency multipoles with $|l|<150$, corresponding to about 1 degree. This ...
• 114k
Accepted

• 14.7k
Accepted

### Formation of Cosmic Microwave Background

We observe the temperature of the CMB as a ~2.7 K blackbody, but that's the redshifted version we observe. The CMB is also know as the "surface of last scattering" at the point of recombination when ...
• 1,453
Accepted

### Do the E and B modes of the CMB polarization have anything to do with electric and magnetic fields?

In this context, the $\kappa$ you are referring to is called the dimensionless matter density field. It is gravitational lensing jargon, and is usually just referred to as the 'convergence' field. ...
• 5,955

### Temperature of the intracluster medium (ICM)

The answer to your first question is "Yes, the temperature referred to is the 'normal' temperature, reflecting the average kinetic energy of the gas particles". The answer to your second question is ...
• 31.9k
Accepted

### What is the physics of the "spinning dust" contribution to Cosmic Microwave Background measurements?

"Spinning dust" is a mechanism proposed to explain a particular feature in the foreground emission of CMB; a bump around $\nu\sim20\,\mathrm{GHz}$. Dust grains acquire charge through photoelectric ...
• 31.9k
Accepted

### What would the CMB look like somewhere else in the universe?

The CMB is nearly featureless, but the operative word is nearly. The tiny temperature fluctuations that we've measured should look about the same anywhere within tens to hundreds of millions of light ...
• 7,380
Accepted

### Does the CMB pattern evolve in a human lifetime?

In principle yes, in practice no. As seen in the temperature power spectrum below, the Planck satellite detects power (i.e. "a signal") even on the smallest probed scales, which is a few arcminutes. ...
• 31.9k

### What Is The Maximum Distance Our Finest Instruments Could See When They're Perfected?

The furthest we can "see" is the cosmic microwave background at a redshift of about 1100. The proper distance of the CMB-emitting gas that we see today is about 46 billion light years. If you are ...
• 114k
Accepted

### Why is the Cosmic Microwave Background at the same distance no matter the direction we look?

The CMB is visible at a distance of 13.8 billion light years in all directions from Earth, leading scientists to determine that this is the true age of the Universe. This is wrong in a few ways. ...
• 2,065
Accepted

### Why does the first measurements of the thermal Sunyaev-Zel’dovich effect from ALMA show a temperature decrease and not an increase at the cluster?

Calling it a "temperature decrease" is kind of misleading. (Possibly this is a side effect of the tendency to use "brightness temperature" in radio astronomy to mean measured ...
• 14.7k

### Does the Cosmic microwave background (CMB) have an amplitude? Does it vary, like the 'temperature' (wavel./freq.) and the polarization?

The cosmic microwave background (CMB) does of course vary with direction, in terms of its amplitude, temperature and polarisation. It is these variations which lead to its diagnostic power in ...
• 114k