20 - Cosmology

Question 1

what happens to wave relative to position of wave

Answer 1

source moving to receiver - shorter𝝀 (squashed)
source moving away - longer𝝀 (stretched)

Question 2

changing of wavelength effect names for sound and light

Answer 2

sound - doppler effect
light - red/blue shift

Question 3

red shift and blue shift

Answer 3

red - 𝝀 stretched, f low (away from earth) shifted to red end of spectrum
blue - 𝝀 shortens, f high (towards earth) shifted to blue end of spectrum

Question 4

first piece of evidence for big bang and universe expansion

Answer 4

red shift - most galaxies are moving away and ones further away moving faster showing greater red shift

Question 5

binary start systems and red shift

Answer 5

they come in many forms but specific type:

one side gets red shifted and the other gets blue shifted

Question 6

amount of red shifted calculation

Answer 6

z=change in 𝝀 / original 𝝀 = v/c

faster, the bigger the change in wavelength

Question 7

Hubbles law

Answer 7

speed of galaxy moving away is directly proportional to its distance

v=Hod where Ho is hubbles constant
t=d/s =1/Ho = age of universe
assuming expansion of universe rate is constant and also Cosmological principles

Question 8

how can we tell galaxies are red shifting

Answer 8

by looking at absorption lines from light. Pattern is similar to our sun but is stretched. the amount of red shift can be calculated using z=change in 𝝀 / original 𝝀 = v/c

Question 9

what is the big bang theory

Answer 9

universe began with colossal explosion roughly 13.7b years ago from singularity and has been expanding ever since. evidence - red shift, CMBR …

Question 10

what is cmbr

Answer 10

cosmic microwave background radiation

radiation remaining from big bang that fills the whole universe, reminiscent of atom formation. formed as gamma rays during big bang but now in micro wave part of spectrum (temp 2.7K) due to cooling of universe and red shift

piece of evidence for big bang and at this time the universe became transparent and light could travel through (before was plasma)

Question 11

intensity of cmbr

Answer 11

uniform in all directions but small ripples in intensity correspond to forming of first stars and galaxies

Question 12

third piece of evidence for big bang

Answer 12

primordial helium and hydrogen - so much helium and hydrogen during the evolution of universe as hadrons were forming nuclei

Question 13

universe evolution timeline

Answer 13

13.7b years ago - big bang - time and space created as a singularity - infinitely dense and hot

10-35s - no matter only energy - temp roughly 10^28K INFLATION STAGE

10-6s - quarks and leptons are made - energy > mass

10-3s - quarks combine to form hadrons

1s - matter is all made , temp roughly 10^9K

100s - hadrons combine to form nuclei (H and He)
PRIMORDIAL HYDROGEN AND HELOUM EVIDENCE 3

380,000 years - nuclei and electrons combine to form atoms, CMBR is made (atoms formed late her as it is cool enough for electrons to stay in energy levels)

30my - stars formed

200my - our galaxy is formed

4.5by - our solar system is made

400,000 years ago - first humans , temp roughly 2.7K

Question 14

what is the doppler effect

Answer 14

the apparent shift in wavelength of a wave caused by relative motion between source and observer

Question 15

how may weather doppler effect distinguish between different types of precipitation

Answer 15

different forms of precipitation may reflect different amounts of energy. hail may reflect more for example so difference in the reflected microwaves affects the intensity received by receiver

Question 16

doppler effect to figure out speed of a tennis ball serve

Answer 16

source sends out microwaves that are reflected off the ball. ball acts as a source and speed measured by measuring the doppler shift of the wave

Question 17

how is doppler effect used to determine relative velocity of distant galaxy?

Answer 17

absorption spectrum of specific element is determined laboratory. same spectrum is observed from light of distant galaxy and compared. any difference in absorption lines and wavelength is caused by relative motion of the galaxy and earth. if… blue shift and if… red shift (each absorption line changes by same percentage)

Question 18

state the cosmological principle

Answer 18

universe is isotropic and homogeneous

Question 19

why is our understanding of the universe unreliable for the early moments?

Answer 19

no experimental or physical evidence, energies unreproducible (high temp)

Question 20

nature and origin of dark matter

Answer 20

hydrogen and helium gas formed after big bang, left from supernova

Question 21

how does density of neutron star compare to that of materials commonly found on earth

Answer 21

neutron star much more dense than earth materials, density same as atomic nucleus

Question 22

explain how temperature of universe changed after first millisecond

Answer 22

temp decreases as energy is turned into mass and work is done against attractive force

Question 23

explain how universe became transparent

Answer 23

protons and electrons separate initially. charge prevents passage of EM waves. proton bind to electron as atoms formed, mean EM waves are no longer absorbed

Question 24

explain the existence of primordial hydrogen and helium

Answer 24

too high to originate solely on stellar fusion

Question 25

sim and diff of composition of sun and early stars

Answer 25

both hydrogen and helium in core fusing
sun has greater proportion of helium as hydrogen fuses to helium in sun
sun also contains traces of heavier elements up to iron

Question 26

explain how hubble showed that universe was expanding by studying light from stars and galaxies

Answer 26

redshift data - velocity calculated by red shift z=v/c
distance data
v is proportional to d
for galaxies receding from earth - universe began from single point

Question 27

why is the ultimate fate of universe not known

Answer 27

critical density not known
density of universe uncertain