Chapter 6

Question 1

How can space and time be related?

Answer 1

They are both physical entities

Question 2

What is meant by ‘t=0’?

Answer 2

It is an arbitrary demarcation in time. Since we have a boundary less world, this boundary in time is arbitrary

It is like the North Pole. The NP is the furthest we can technically go in the direction we call north, but this is nevertheless just a point on a continuous, boundary-less globe

Question 3

What are ‘initial conditions’?

Answer 3

These are the conditions at the earliest time in the universe, the conditions from when it was first created

Question 4

What does t=0 imply?

Answer 4

That there was a specific point of creation and that that point had initial conditions

Question 5

What are the initial conditions of the Big Bang?

Answer 5

• certain amount of energy and matter

- certain physical laws and fundamental constraints

Question 6

Why is the Big Bang testable and falsifiable?

Answer 6

Initial conditions are constrained by the laws of physics

Question 7

What is the anthropic principle?

Answer 7

The fact that our existence carries implications for the nature of the universe

Question 8

What is the weak anthropic principle?

Answer 8

The conditions that we observe in the universe must be compatible with our own existence

Question 9

What is the strong anthropic principle?

Answer 9

The universe was created in order for us to be here. It was created FOR US.

Question 10

What does a contemplation of the weak anthropic principle tell us?

Answer 10

That there could bee other universes, with the correct conditions to sustain life. Perhaps, we are not the only ones

Question 11

What is the Copernican Principle?

Answer 11

The idea that Earth or the Sun occupies no special place in the universe

Question 12

Is there a centre of the universe?

Answer 12

We have no way of knowing. We are yet to explore all of the universe and therefore we can’t make this judgement

Question 13

What is isotropy?

Answer 13

Uniformity in all directions

EG a forest on a level plain with identical trees. There is no way of telling differences in any one direction

EG the surface of an unmarked sphere

Question 14

Is the universe isotropic from what we can tell?

Answer 14

Yes. From the largest scale it seems to be isotropic

Question 15

What is the strongest evidence for our universe being isotropic?

Answer 15

Cosmic background radiation

Question 16

What is cosmic background radiation?

Answer 16

The microwave energy that is present at every point in the sky and has the spectral distribution of a blackbody

Question 17

What is homogeneity?

Answer 17

The property of similarity of all locations. Things are the same in all places but not in all directions

EG a cylinder

Question 18

Is the universe homogenous from what we know?

Answer 18

Looks to be. Distant stars and galaxies seem to act in a similar manner to the nearby ones.

The same elements on earth are found in far away parts of the universe

Question 19

What is the cosmological principle?

Answer 19

The universe is the same in all directions at all points

Question 20

What is the perfect cosmological principle?

Answer 20

The idea that the universe is not only inform in physical principles in all directions, but also that the universe has been like this throughout all time

Question 21

Is the perfect cosmological principle reasonable?

Answer 21

No, it goes far too far

Question 22

What does Newtonian physics depend upon?

Answer 22

An absolute space and time

Question 23

What did Newton think about the relationship between space and time?

Answer 23

They were completely separate

Question 24

What was the problem with Newton’s law of Gravity?

Answer 24

It required a force to act instantaneously across empty space.

• What conducts the force?
• if gravity is uniform, and it can only attract, then what is to prevent the whole universe collapsing in on itself?

Question 25

What did Newtonian mechanics imply?

Answer 25

That everything could be foretold if the initial conditions were known well enough