Expanding universe

Question 1

If you look at the spectrum of radiation from 2 stars, how can you tell which star is hotter?

Answer 1

The hotter star has
a smaller peak wavelength
and
a larger area under the curve

Question 2

What does Hubble’s law give evidence for?

Answer 2

the age of the universe
and
the expansion of the universe

Question 3

What does the orbital speed of a galaxy help you work out?

Answer 3

The mass of the galaxy

Question 4

What must exist to explain the fact that the rate at which the universe is expanding is increasing ?

Answer 4

Dark energy

Question 5

What does cosmic microwave background radiation give evidence for?

Answer 5

the big bang theory

Question 6

What law could we use to estimate the age of the universe?

Answer 6

Hubble’s law

Question 7

What’s the name of the effect that causes shifts in wavelength of sound and light?

Answer 7

Doppler effect

Question 8

What is the symbol for redshift on the formula sheet?

Answer 8

z

Question 9

What gives evidence for dark energy?

Answer 9

The fact that the rate of expansion of the universe is increasing (acceleration of the universe)

Question 10

If something making a sound is moving what will happen to it’s wavelength

Answer 10

It will decrease as it is coming towards you and it will increase as it’s going away

Doppler effect (think of the sound a siren makes)

Question 11

What is the evidence for dark matter?

Answer 11

galaxies are rotating faster than their visible mass should cause, so there must be other mass which we can’t see (dark matter)

Question 12

What is redshift?

Answer 12

Objects (eg stars) moving away from us have a longer wavelength (Doppler effect)

most galaxies have redshift - this is evidence for big bang theory

Question 12

What evidence do we have for the big bang theory?

Answer 12

• Cosmic microwave background radiation
• the abundance of lighter elements (hydrogen and helium)
• the darkness of the sky (Olber’s paradox)
• the large number of galaxies showing redshift not blueshift

abundance =large amount of

Question 13

In Doppler equation
when do you use +
and
when do you use -

Answer 13

+ (add) away
- towards

Question 13

What is dark energy?

Answer 13

An unknown form of energy, put forward as a solution to the problem of why the expansion of the Universe is accelerating.

Question 14

If a star is moving away from us what seems to happen to its wavelength?

Answer 14

It will shift to a longer wavelength (red shift)

This is just Doppler effect for light

Question 15

What units does redshift (z) have?

Answer 15

No units!

Question 16

What is the difference between t and t’ in the relativity equation?

Answer 16

t is “real” time - if you were right in front of the thing you are measuring (in the same frame of reference)

t’ is “observed” time - if you are in a different frame of reference (not right in front of the thing that you’re measuring)

t’ is always bigger than or equal to t (time dilates)

Question 17

What is the difference between l and l’ in the relativity equation?

Answer 17

l is “real” length - if you were right in front of the thing you are measuring (in the same frame of reference)

l’ is “observed” length - if you are in a different frame of reference (not right in front of the thing that you’re measuring)

l’ is always smaller than or equal to l (length contracts)

Question 18

What’s the symbol for ‘recessional velocity’

Answer 18

𝜈

Question 19

What’s the symbol for red shift?

Answer 19

z

Question 20

Explain how red shift of galaxies supports the Big Bang theory?

Answer 20

• Redshift is evidence that the galaxies are moving away and the Universe is expanding
• The expanding universe is evidence for the Big bang theory