chapter 20

Question 1

Astronomical unit

Answer 1

1 AU is equal the average distance from the sun to the earth, 150 million km
1.5 x 10^11m

Question 2

Light year

Answer 2

Distance that light travels in one year, 9.46 x 10^15m

Question 3

1 parsec

Answer 3

the distance at which a radius of 1 AU subtends an angle of one arc seconds
equal to 3.1 x 10^16m

Question 4

Cosmological Principle

Answer 4

For a large volume, the universe is isotropic and homogenous and so the laws of physics are universal

isotropic - the universe looks the same in every direction to every observer with no centre or edge

homegenous - matter is uniformly distributed
throughout the universe on a large scale and there is uniform density

Question 5

Estimating the age of the universe:

Answer 5

from a centre point any point must move a distant d over a constant velocity v

Question 6

How does hubble’s law prove big bang theory

Answer 6

It proves that every point in the universe is moving away from each(the space itself)
this is why the further you go the higher the recessional speed from earth
shows the universe is expanding from an initial point

Question 6

what is Hubbles constant

Answer 6

67.8 Kms^-1Mpc^-1
Km and Mpc are both distance so it can also be 67.8s^-1

Question 7

estimating the age of the universe

Answer 7

if all points in the universe started at one point, then the distance of a galaxy from earth and the speed it is moving away are related,
d/v = t
t = 1 / H₀

Question 8

Evolution of the universe up untik matter formation has ceased

Answer 8

Space-Time is created, the universe is an infinitely dense and hot singulairty

10^-35s, the universe expands rapidly in a process call inflation. There is no matter, only high energy EM waves and gamma photons

10^-6s The first fundamental particles(quarks, leptons) are formed through some mechanism involving the higgs boson

10^-1s The fundamental particles combine to form hadrons, in a process called pair production, where high energy photon turn into particle anti particle pairs

1s No more matter is formed at this point

Question 9

Evolution of the universe after matter formation

Answer 9

100s Hadrons combine to form deuterium and helium nuclei
Small amount of hydrogen and beryllium are also formed
25% of matter is helium nuclei

380,000 years after: Atoms form once temperature is cool enough for nuclei to capture electrons
at this stage what is now CMBR is formed as high energy em waves

Question 10

Features of CMBR

Answer 10

uniform in all directions everywhere
temperature corresponds to 2.7K as modelled by the big bang
gamma radiation produced in ifrst second of the big bang red shifted due to the expansion of the universe and is now of the order microwave