Chapter 11 Flashcards
Why was the newtonian view of the universe problematic?
His idea that all of the stars were bound to each other by gravity meant that the world would collapse on itself.
How could Newton’s theory work?
The stars were bound by equal gravitation on all sides. This was a far too delicate of a balance
What is escape velocity?
The velocity required for something to leave the atmosphere of a planet/star/black hole etc
What happens if the universe has negative net energy?
It cannot escape its own gravity and will collapse back on itself
What happens if the universe has positive net energy?
It can escape its own gravity and will continue to expand forever
What happens if the universe has zero net energy?
It will expand but eventually slow and stop
What shape of the universe does Newtonian gravity apply to?
Closed/spherical
What is ‘k’ in the Robertson-Walker metric?
the curvature constant
What are the 3 values of ‘k’?
1
-1
0
What does the Friedmann Equation solve for?
The rate of expansion of the universe
What makes up cosmic background radiation?
Leftover photons from the Big Bang
What are standard models?
the simplest of universe models that obeys the conservation of mass/energy, suntan some specified total mass-energy density, and have a cosmological constant of 0
What do we know about the rate of expansion for standard models?
It is getting decelerating. All universes that follow the standard model of gravity will decelerate
What does R equal when t=0?
0
What will a flat model of the universe do?
expand forever, but eventually slow
What will a hyperbolic model of the universe do?
expand forever
What will a closed model of a universe do?
collapse on itself eventually
what happens when k=1?
the universe is closed so it will collapse
what happens when k=0?
the universe is flat so it will expand forever, but slow down
what happens when k=-1?
the universe is hyperbolic so it will expand forever
What is it called when a closed universe eventually collapses?
the big crunch
What is the symbol for the current Hubble Constant?
Ho (H naught)
What is the Hubble Constant?
The rate of expansion of the universe
What is critical density?
The density where, if it is larger, it will collapse and if it is lower it will continue to expand forever.
If the density of the universe is exactly the critical density, however, then the universe will not be expanding
What is the density of the universe?
6 protons per metre cubed
How do you calculate the age of the universe?
1/Ho
What is the age off the universe called?
Hubble time
What is the shape of the universe when omega=1?
flat
What is the shape of the universe when omega>1?
closed
What is the shape of the universe when omega<1?
hyperbolic
What is the relation between Hubble time and the age of the universe?
Hubble Time is an overestimate of the age of the universe
If the expansion of the universe is slowing, then the Hubble constant will be smaller than it was previously. This means that the universe will have a greater age than it should have
What is the age of a closed universe?
less than 2/3 of the Hubble time
What is the age of a flat universe?
2/3 of the Hubble time
What is the age of a hyperbolic universe?
greater than 2/3 of the Hubble time
