The critical density of a universe is around 5×10 kg/m³. Estimate the Hubble constant for this universe.

Explain briefly the main physical processes that occurred in the era of recombination. If the recombination era took place at a redshift (1 + z) = 1100, calculate the temperature of the Universe at the era of recombination considering that the Cosmic Microwave Background (CMB) is a perfect black body and today has a temperature T = 2.725 K. State the peak wavelength at which the Universe emitted its radiation during the era of recombination, expressing your answer in nm.

In the reading, you were told that there were roughly 10,000 galaxies in the image of the Hubble Ultra Deep Field alone. The image is roughly 10 square arcminutes and there are roughly 1.5*10^8 square arcminutes composing the entire sky. With that in mind and assuming that the Hubble Ultra Deep Field represents an average part of the sky, roughly how many galaxies may exist in the observable universe? (Please include commas for every factor of 1,000; for example 2,343,567,890)

What is Hubble constant?

Please answer within 90 minutes.

Calculate the Hubble constant for a universe that is 20 billion years old.

There are two parts to this question. I need to know the years for both. I have tried 14,000,000,000, 17,908,900,000, 17.29 x 10^9, and 17.9089 x 10^9 for the hubble time and all those are wrong. I have tried 17,908,900,000, 17.29 x 10^9, and 17.9089 x 10^9 for the second question and those are wrong too.

What is hubble law

Please answer within 90 minutes.

Calculate the critical density of a universe with H0 of 55 km/s/Mpc.