space physics - red shift and expanding universe

Question 1

what is the doppler effect

Answer 1

if a wave source (light, sound, microwaves) is moving relative to an observer, there will be a change in the observed wavelength and frequency

Question 2

example of doppler effect

Answer 2

p1 - - > - - - > - car siren - > - - p2

for p1, the police car is moving away so the sound waves are more spread out - wavelength increases, frequency decreases

for p2, the police car is moving towards so the sound waves are bunched up - wavelength decreases, frequency increases

Question 3

explain the red shift

Answer 3

arcturas
when a star moves away from us, it is moving away from the light it is emitting in our direction.
this makes the light aves we see expand.
because the light waves are longer, the light shifts towards the red side of the spectrum.

Question 4

explain the blue shift

Answer 4

sirius
when a star moves towards us, it is moving towards the light it is emitting in our direction.
this makes the light waves we see contract.
because the wavelengths are shorter, the light shifts towards the blue side of the spectrum

Question 5

what is the absorption spectra

Answer 5

spectral absorption lines - created by gases absorbing signature frequencies in light travelling to us from galaxies faraway.

• the blue/redshift of these lines tell us how fast the galaxy is moving relative to ours

Question 6

what did edwin hubble discover

Answer 6

1920s - all objects in the universe are moving away from us.
the further away a galaxy is, the faster it is moving away (recessional velocity)

Question 7

explain expansion of universe

Answer 7

• relationship between recessional velocity and distance tells us that the universe is ever expanding
• origin of universe is the big bang, occurring 13.7 billion years ago
• steady state theory: as universe expands, new galaxies form between the old ones, so the density of matter stays constant

Question 8

what is cmb

Answer 8

cosmic microwave background - 1960s
- excess energy released at the big bang was emitted in all directions, filling universe with gamma rays
–> electromagnetic radiation has stretched to occupy the waveband = to microwaves

Question 9

evidence for big bang

Answer 9

• cmb radiation is observable in every direction in the universe
• the relationship between recessional velocity and distance from earth is directionally proportional

Question 10

what is the future of the universe

Answer 10

• recent observations indicate that the rate of universe expansion is increasing
• explanation for acceleration: dark energy makes up a large unseen part of universe