Lecture Three

Question 1

What happened 10^-30 to 10^-10 seconds after the Big Bang?

Answer 1

• Dark matter was created (this holds the structure of the universe together).

Question 2

What happened 10^-2 seconds after the Big Bang?

Answer 2

• 100 billion degrees Kelvin, super high density.

- Photons, neutrions and electrons mixed with smaller numbers of protons and neutrons.

Question 3

What happened ~3 minutes and 46 seconds after the Big Bang?

Answer 3

• 900 million degrees Kelvin.
• Fussion of the nuclei of Helium atoms.
  The seeds of other galaxies and structures are formed and shaped by dark matter.
• After this the universe cools down and gas condenses to form infant nebula and galaxies, inflation stops and expansion slows.

Question 4

What occurred in the inflationary era?

Answer 4

• From the Big Bang to around 300,000 years.
• Initial exponential acceleration, followed by slowing.
• For the past 6 billion years, the universe is accelerating again, but at a slower rate.

Question 5

What occur in the dark universe?

Answer 5

• For the first 380,000 years after the Big Bang, there was no light, as photos couldn’t escape into the universe.
• Microwave radiation “visible” at around 300,000 years.
• Visible light at about 400 million years.

Question 6

What evidence is there for the dark universe?

Answer 6

• Predicted ‘afterglow of creation.’
• This is background microwave radiation from explosion predicted to be visible everywhere you look in space.
• Theory was tested and proved in 1992 by COBE, 2003 by WMAP and in 2013 by the Planck Satellite.

Question 7

What is the Universe made of?

Answer 7

• 70% dark energy.
• 26% dark matter.
• 4% everything else.

Question 8

What are dark energy and dark matter?

Answer 8

• They are little understood, but it is know that they are needed to explain how the universe appears to work.

Dark energy: A theoretical for of energy postulated to act in opposition to gravity and to occupy the entire universe, accounting for most of the energy in it, and causing it to accelerate.

Dark matter: Non-luminous material which is postulated to exist in space and which could take either of the two forms:
1) Weakly interacting particles (could dark matter).
2) High energy random moving particles created soon after the Big Bang (hot dark matter).
Unseen materials that is postulated to be responsible for a large portion of the mass that appears to be missing from the universe.

Question 9

How do we know that dark matter exists?

Answer 9

By looking at dwarf galaxies for dark matter, where the motion of strs can’t be explained by the mass of the stars along, we can try to understand.

Question 10

How can one estimate the age of the universe?

Answer 10

• Ages of stars (life cycles).
• Ages of stars (radiometric dating).
• Hubble constant (initial evidence of accelerating universe.

Question 11

How are the life cycles of stars used to estimate the age of the universe?

Answer 11

• Measure luminosity of stars that burn H and He - main sequence stars.
• Luminosity decreases with temperature and time - measure of age.
• Universe age from life cycles –> 12.1 billion years with 95% confidence.

Question 12

How is radiometric dating used to estimate the age of the universe?

Answer 12

• Some elements are radioactive and can be used for dating archaeological sites, rocks and the universe.
• Estimating the relative proportions of a particular radioactive isotope in a sample.
• Using radiometric dating, mean age of the universe is –> 11.5 to 17.5 billion years.

Question 13

How is the Hubble Constant used to estimate the age of the universe?

Answer 13

• Edwin Hubble noticed that the further away a galaxy cluster was, the faster it moved.
• He proposed the equation:
  V = Hr
  Where V is velocity of cluster in km/s
  H is the Hubble constant in km/second/MPc
  r is the distance to the cluster from Earth in MPc.
• The age of the universe according to this theory is 1/H = 13.82 billion years.

Question 14

What would cause the Big Rip to occur?

Answer 14

If dark energy increases, acceleration increases so quickly that everything will eventually be town apart (including atoms). This is known as the Big Rip.

Question 15

What would cause the Big Crunch to occur?

Answer 15

If dark energy decreases, acceleration decreases and everything collapses back into one spot in space and time. This is known as the Big Crunch.

Question 16

What will happen to the universe if dark energy remains constant?

Answer 16

If dark energy remains constant, it will keep accelerating and expanding forever.