Chapter 6 Flashcards
How can space and time be related?
They are both physical entities
What is meant by ‘t=0’?
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
What are ‘initial conditions’?
These are the conditions at the earliest time in the universe, the conditions from when it was first created
What does t=0 imply?
That there was a specific point of creation and that that point had initial conditions
What are the initial conditions of the Big Bang?
- certain amount of energy and matter
- certain physical laws and fundamental constraints
Why is the Big Bang testable and falsifiable?
Initial conditions are constrained by the laws of physics
What is the anthropic principle?
The fact that our existence carries implications for the nature of the universe
What is the weak anthropic principle?
The conditions that we observe in the universe must be compatible with our own existence
What is the strong anthropic principle?
The universe was created in order for us to be here. It was created FOR US.
What does a contemplation of the weak anthropic principle tell us?
That there could bee other universes, with the correct conditions to sustain life. Perhaps, we are not the only ones
What is the Copernican Principle?
The idea that Earth or the Sun occupies no special place in the universe
Is there a centre of the universe?
We have no way of knowing. We are yet to explore all of the universe and therefore we can’t make this judgement
What is isotropy?
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
Is the universe isotropic from what we can tell?
Yes. From the largest scale it seems to be isotropic
What is the strongest evidence for our universe being isotropic?
Cosmic background radiation
What is cosmic background radiation?
The microwave energy that is present at every point in the sky and has the spectral distribution of a blackbody
What is homogeneity?
The property of similarity of all locations. Things are the same in all places but not in all directions
EG a cylinder
Is the universe homogenous from what we know?
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
What is the cosmological principle?
The universe is the same in all directions at all points
What is the perfect cosmological principle?
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
Is the perfect cosmological principle reasonable?
No, it goes far too far
What does Newtonian physics depend upon?
An absolute space and time
What did Newton think about the relationship between space and time?
They were completely separate
What was the problem with Newton’s law of Gravity?
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?
What did Newtonian mechanics imply?
That everything could be foretold if the initial conditions were known well enough
