Chapter 20: Cosmology

Question 1

What is the Doppler Effect?

Answer 1

The change in wavelength and frequency of a wave as a source moves away from or towards the observer

Question 2

What is Stellar parallax?

Answer 2

The apparent shift in position of an object against a backdrop of distant objects due to the orbit of the Earth
Used to calculate distances of up to 100pc

Question 3

Parsec

Answer 3

The distance from which 1 AU (distance between the Earth and Sun) subtends an angle of 1 arcsecond (1/3600th of a degree)

Question 4

Cosmological Principle

Answer 4

Universe is isotropic and homogeneous and the laws of physics are universal

Question 5

Isotropic

Answer 5

universe is the same in all direction to every observer, no centre of edge

Question 6

Homogenous

Answer 6

Matter is uniformly distributed - for a large volume of the Universe the density is the same

Question 7

Red shift

Answer 7

Shift in wavelength and frequency of waves from a retreating source towards/ beyond the red end of the electromagnetic spectrum
Evidence of the Big Bang

Question 8

Hubble’s Law

Answer 8

The velocity of receding objects is directly proportional to their distance from Earth

Question 9

What are quasars?

Answer 9

Nucleus of an active galaxy; a supermassive black hole surrounded by a disc of matter. As matter falls in into the black hole, jets of radiation are emitted from the poles of the quasar.

Question 10

What suggests quasars are extremely distant objects?

Answer 10

Large optical red shift shows quasars are the most distant observable objects. From the inverse square law for intensity we know they are extremely powerful, with the same energy output as several galaxies. Initially found to be powerful radio sources but it was found to emit all EM radiation

Question 11

What is the Big Bang theory?

Answer 11

13.8 Billion years ago, the universe exploded from an extremely hot and dense point and is still expanding now

Question 12

What is the evidence for the Big Bang theory?

Answer 12

CMBR is the heat signature left behind from the Big Bang.
EM radiation is released in the explosion shifted from extremely high energy waves into the microwave region as the Universe expanded, stretching out the waves.
CMBR has a black body distribution with a peak that corresponds to a temperature of 2..7K
There was nuclear fusion of hydrogen into helium which explains the large abundance of helium in today’s universe.

Question 13

What is dark energy?

Answer 13

• When astronomers calculated the distance to some Type 1A supernova, they discovered them to be dimmer than expected. This suggested the expansion of the universe is accelerating, which is attributed to dark energy.
• Dark energy is thought to be energy that has an overall repulsive effect throughout the Universe.

Question 14

light year

Answer 14

Distance travelled by light in a vacuum in a time of one year

Question 15

What happened microseconds after the Big Bang?

Answer 15

first fundamental particles gain mass

Question 16

What happens milliseconds after the Big Bang?

Answer 16

Most of the mass is created using pair production. First hadrons come from quarks

Question 17

What happens seconds after the Big Bang?

Answer 17

Production of mass is halted

Question 18

What happens 100s after the Big Bang?

Answer 18

Protons and neutrons fuse to form deuterium, helium, lithium and beryllium but nothing heavier.
Rapid expansion continues.
25% of matter is helium nuclei

Question 19

What happens 380 thousand years after the Big Bang?

Answer 19

Now cool enough for first atoms to form

Question 20

What happens 30 million years after the Big Bang?

Answer 20

First stars form, fusion creates heavier elements

Question 21

What happens 200 million years after the Big Bang?

Answer 21

The first star forms, fusion creates heavier elements

Question 22

What happens 9 billion years after the Big Bang?

Answer 22

Solar system forms by a nebula from a supernova. This is followed by the formation of our Sun

Question 23

What happens 11 billion years after the Big Bang?

Answer 23

Primitive life begins on Earth

Question 24

What happens 13.7 billion years after the Big Bang?

Answer 24

first modern humans evolve