## What is K in the power spectrum?

Figure 00a Pearson Correlation CDF – It is also expressed in Fourier transform, the power spectrum (k) is the amplitude and sin(kr)/kr is the phase.

**What is a Hubble diagram?**

The Hubble diagram plots velocity against distance. Astronomers measure the velocity of a galaxy from its spectrum by taking the light from a galaxy’s image at the focus of a telescope and passing it through a slit and a prism to create a dispersed rainbow, subtly marked by dark lines.

### What is two point correlation function?

The two-point correlation function, ξ(r), is the measure of the probability that there will be two galaxies within a fixed distance r of each other. The probability of finding a galaxy in volume element dV1 within a distance r of another in volume dV2 is given by. (14) where n is the mean number density of galaxies.

**What is transfer function in cosmology?**

The transfer function is a mathematical tool to explain a physical phenomenon in the period between inflation and Cosmic Microwave Background (CMB) [1]. It allows to explain large galaxy clusters formation.

## What is tensor to scalar ratio?

As with scalar fluctuations, tensor fluctuations are expected to follow a power law and are parameterized by the tensor index (the tensor version of the scalar index). The ratio of the tensor to scalar power spectra is given by. where the 2 arises due to the two polarizations of the tensor modes.

**What is galaxy bias?**

This galaxy “bias” – the relationship between the spatial distribution of galaxies and the underlying dark matter density field – is a result of the varied physics of galaxy formation which can cause the spatial distribution of baryons to differ from that of dark matter.

### What is Cosmic Variance?

For the weblog, see Cosmic Variance (blog). The term cosmic variance is the statistical uncertainty inherent in observations of the universe at extreme distances. It has three different but closely related meanings:

**Why can’t we see all the peaks in the cosmic background spectrum?**

For example, we can only observe one Cosmic Microwave Background, so the measured positions of the peaks in the Cosmic Microwave Background spectrum, integrated over the visible sky, are limited by the fact that only one spectrum is observable from Earth.

## How faint are the fluctuations in the cosmic microwave background?

The cosmic microwave background fluctuations are extremely faint, only one part in 100,000 compared to the 2.73 kelvins average temperature of the radiation field. The cosmic microwave background radiation is a remnant of the Big Bang and the fluctuations are the imprint of density contrast in the early universe.

**What is the energy density of the cosmic background radiation?**

The energy density of the CMB is 0.260 eV/cm 3 (4.17 × 10 −14 J/m 3) which yields about 411 photons/cm 3. The cosmic microwave background was first predicted in 1948 by Ralph Alpher and Robert Herman, in close relation to work performed by Alpher’s PhD advisor George Gamow.