Lecture Two

Question 0

The shortest time we consider is the first time me in the history of the universe when we believe that physics as we understand it today was applicable

Answer 0

10^-43 seconds

Question 1

How can we measure mass of the sun?

Answer 1

By measuring the velocity of an object orbiting the Sun, and its distance, form the sun

Question 2

Describe e beginning of the universe

Answer 2

Very hot. Particles formed from energy but quickly returned. Then elementary particles, then quarks combines to make protons and antiprotons. Fusion produced He from protons. Plasma of free electrons and H and He nuclei filled the universe. Then the era of atoms, which lasted until stars and galaxies began to form.

Question 3

What is the relative abundance of dark matter?

Answer 3

5x more than baryonic matter

Question 4

How is the universe growing?

Answer 4

Expanding since beginning, an expansion which is now accelerating due to dark energy. Accelerating model.

Question 5

How goes a stars life cycle?

Answer 5

Stars form in the densest regions from clouds of dust, gas and molecules, live their lives, and recycle new elements into the inter-­stellar medium

Question 6

13.7 by in a single year…

Answer 6

Human civilisation - couple of seconds

Human lifetime - tiny fraction of a second

Question 7

Different motions?

Answer 7

1 rotation of earth varies 
2 orbiting the sun 107,000km/hr
3 sun moves with respect to local stars 70,000km/hr
4 galaxy rotation 800,000km/hr 
5 Milky Way moves in local group