Lecture 35

Question 1

What are bright spots in the CMB?

Answer 1

Seeds of galaxy clusters and large-scale structure

Question 2

What are the origins of density/temperature fluctuations in the universe?

Answer 2

• occurred in the Planck Era
• quantum fluctuations expand with the universe
• uncertainty principle- cannot tell exact position (or energy) on the Planck scale

Question 3

What are peaks and valleys in the CMB?

Answer 3

• quantum fluctuations before inflation lead to slight differences in matter distribution
• matter was pulled into the valleys and denser regions attract particles from less dense regions by gravity

Question 4

What can we think of CMB temperature anisotropies as?

Answer 4

The seeds of structure

Question 5

What is the density contrast?

Answer 5

• denser regions have more gravity than less dense regions
• matter is pulled into dense regions from less dense regions

Question 6

How is the cosmic web formed?

Answer 6

• gravity makes dense regions get denser and empty regions get emptier
• the cosmic web is formed with galaxies at the centre of collapsing halos

Question 7

What is the largest redshift that we can make observations to?

Answer 7

Around z~10 but it is very difficult

Question 8

What occurred during the Dark Ages (~400,000yr to ~50Myr)?

Answer 8

• the universe was made of neutral hydrogen
• cooling
• density was too small to form galaxies and stars

Question 9

What occurred during the Epoch of reionisation?

Answer 9

• around 50 Myrs after the big bang
• first light appears
• hydrogen reionisation begins

Question 10

What occurred at around z~50-10?

Answer 10

• regular matter collapses into the centre of dark matter halos (cold enough to reach high density)
• first stars formed
• cores of protogalaxies may host large black holes (quasars)
• first starlight is redshifted to mid-IR

Question 11

When approximately did the first galaxies form?

Answer 11

z~ 15-8

Question 12

What occurred during the ionised universe?

Answer 12

• t~600 Myr
• enough stars and galaxies to keep hydrogen ionised
• universe becomes transparent to UV

Question 13

What occurred during the era of galaxies?

Answer 13

-z= 8-1
- large galaxies (Milky Way) formed
- star formation was at its maximum
- many galaxy collisions

Question 14

What occurred during the modern universe?

Answer 14

• z<1
• fewer stars form
• most galaxies in a stable form
• the solar system forms (z=0.6)

Question 15

What does the future of expansion depend on?

Answer 15

How dark energy behaves

Question 16

What are the three theories for the future of the universe?

Answer 16

1. big rip
2. constant dark energy
3. big crunch

Question 17

What would occur in a heat death?

Answer 17

• constant dark energy accelerates the universe
• Hubble constant grows
• everything redshifted into oblivion
• everything stops- the big chill

Question 18

What will happen to the Milky Way?

Answer 18

In ~2-4 Gyr it will collide with Andromeda and become an elliptical galaxy

Question 19

What will happen to the Sun ~5 Gyr?

Answer 19

It will become a red giant, planetary nebula then white dwarf

Question 20

What will happen at ~100 Gyr?

Answer 20

Expansion accelerated so fast that all galaxies are beyond our horizon and only red dwarves remain

Question 21

What will occur at ~10^12 years

Answer 21

All stars will have reached the end of their lives. Proton decay may occur

Question 22

What will happen at ~10^37 years?

Answer 22

Only black holes will remain- they will be evaporating

Question 23

What will occur at ~10^100 years?

Answer 23

Black holes are gone. Only electrons,
neutrinos, proton decay products,
and photons exist. The temperature will be 0K.