The Expanding Universe

Question 1

what is the doppler effect?

Answer 1

the apparent change in frequency of a wave when the source and observer are moving relative to each other

Question 2

doppler effect: when to add or subtract

Answer 2

add when moving away

subtract when moving towards

Question 3

doppler effect equation

Answer 3

fo=fs(v/(v+/-vs)

Question 4

what is redshift?

Answer 4

the ratio of recessional velocity of a galaxy to the speed of light

Question 5

what to remember about redshift

Answer 5

no units

will always be <1

Question 6

difference between redshift and blueshift

Answer 6

redshift - travelling away

blueshift - travelling towards

Question 7

two scenarios for the future of the universe

Answer 7

1. closed universe - slow its expansion then contract

2. open universe - will expand forever

Question 8

what is Hubble’s law?

Answer 8

v=Hod

further away galaxies travelling faster

Question 9

what is Hubble’s constant?

Answer 9

2.3x10^-18 s^-1

Question 10

how to prove age of the universe

Answer 10

using hubble’s constant and d=vt

Question 11

chocolate muffin analogy

Answer 11

galaxies moving away from each other

not individual galaxies expanding

Question 12

dark matter

Answer 12

a considerable amount of matter in galaxies that we cannot see

accounts for the observation of unusually high orbital speeds of stars in the outer arms of galaxies

thought to make up around 22% of all matter in the Universe

Question 13

dark energy

Answer 13

force which acts against gravitational force of attraction, pushing matter apart

accounts for observation that expansion of Universe is accelerating

It is thought to make up around 74% of all matter in the Universe

Question 14

what does the temperature of an object determine?

Answer 14

the frequency of light that it emits

Question 15

very hot stars are what colour

Answer 15

blue

Question 16

is the peak wavelength small or large for hot stars?

Answer 16

small

Question 17

stars emit light over a…

Answer 17

range of wavelengths

Question 18

4 pieces of evidence for Big Bang theory

Answer 18

1. Abundance of hydrogen and helium
2. Cosmic Microwave Background Radiation
3. Olber’s Paradox
4. Expansion of the Universe

Question 19

abundance of hydrogen and helium

Answer 19

H and He are the simplest to form and should be most abundant as atoms only formed when the Universe was cold enough

Other elements formed inside stars

Question 20

Cosmic Microwave Background Radiation

Answer 20

should be residual background electromagnetic radiation from Big Bang

every direction in sky, small amount of microwave radiation - 2.7K

Question 21

Olber’s paradox

Answer 21

why isn’t the sky always bright/ star in every line of sight?

1. we can only see 13.8 billion lightyears into the Universe
2. Galaxies travelling away will redshift. Cannot see infrared