Chapter 19 - Evolution Of The Universe

Question 1

What is the Planck time?

Answer 1

First 10^-43s after Big Bang = shortest interval into which time can be divided

Question 2

Why can’t we know about before the Big Bang?

Answer 2

The condensing of all matter to one point destroyed ‘fossil’ evidence

Question 3

Stages 1-5 (only 3) with time from Big Bang and temp (K) and what?

Answer 3

1) time - 0s
temp - infinite
what? Infinitely small, infinitely dense, all 4 fundamental forces unified

2/3) time - 10^-6s
temp - 10^14K
what? Quark and lepton soup

4/5) time - 10^-3s
temp - 10^12K
what? Quarks combine to form hadrons such as protons and neutrons

Question 4

Stages 6-8 with time from Big Bang and temp (K) and what?

Answer 4

6) time - 10^2s
temp - 10^7K
what? ‘Primordial’ helium nuclei form by fusion

7) time - 3x10^5years
temp - 10^4K
what? Electrons combine with neutrons to make atoms. Universe becomes transparent tf ER moves freely.

8) time - 10^6years - present
temp - 10^3 - 2.7K
what? matter clumps to form gas clouds, stars, dust, galaxies etc. Universe saturated with ER approximately 2.7K

Question 5

Where did the mass of the universe come from and equation?

Answer 5

In the first second it came from pair production

γ + γ -> e- + e+

Gamma + gamma -> electron + positron

Question 6

Look at temp/time graph in notes?

Answer 6

Now

Question 7

3 pieces of evidence for standard model?

Answer 7

Redshift showing expanding universe

Old light showing chemicals (explain)

Detectors detecting cosmic background radiation in space (explain)

Question 8

Explain first piece (old light) of evidence?

Answer 8

Scientists looking at distant galaxies are seeing light from start of universe. Using spectrometers they can only see 4 chemicals (H, He, Li, Be). Standard model predicts that only these 4 could be formed in the first years of the universe tf implies it is correct

Question 9

Explain second piece (cosmic background radiation) of evidence?

Answer 9

Detectors can detect cosmic background radiation in space (roughly 2.7K) in all directions that is uniform. This confirms isotropic nature of universe and tf backs up cosmological principal

Question 10

What is the standard model of the universe?

Answer 10

The Big Bang

Question 11

Define cosmic microwave background radiation and what is it?

Answer 11

ER radiation in the microwave region of the spectrum that corresponds to a temperature of the universe of 2.7.

It is cooled remnants of radiation which started travelling the universe after the big bang

Question 12

Why is the temperature in the universe falling?

Answer 12

As the universe expands, space expands, stretching ER waves to longer wavelengths therefore reducing temperature

Question 13

Define open universe?

Answer 13

A model of the universe in which gravitational force cannot halt the expansion of matter therefore the universe will expand forever.

Question 14

Define closed universe?

Answer 14

A model of the universe in which gravitational force is strong enough to halt its expansion, and reverse the process towards a big crunch.

Question 15

Define flat universe?

Answer 15

A universe that expands forever, but whose rate of expansion tends to 0 after infinite time.

Question 16

Explain the causes of the low-density universe and a high-density universe?

Answer 16

Low-density - gravity too weak, tf OPEN UNIVERSE

High-density - gravity strong enough, tf CLOSED UNIVERSE

Question 17

Define critical density (p0) and give its equation?

Answer 17

The density of the universe that will give rise to a flat universe given by the equation:

p0 = (3H0^2)/8πG

= 9.5 x10^-27 kgm^-3

Question 18

Why do scientists think that the universe may be flat?

Answer 18

Calculations suggest density is close to p0. Due to it being so close cosmologists believe it may be exactly p0 tf flat universe.

Question 19

Two problems with calculating universe density?

Answer 19

• lots of matter is unobservable

- difficult to estimate no. of stars and galaxies etc.

Question 20

Define dark matter?

Answer 20

Matter that emits little ER, making it difficult to detect.

Question 21

How do we know that dark matter exists?

Answer 21

We know it exists due to its pull on distant galaxies due to gravity

Question 22

Define dark energy?

Answer 22

A form of energy in the distributed throughout the universe and which may be causing the expansion of the universe to accelerate.