Cosmology Lecture 2

(September 21, 2013) Leonard Susskind solves the expansion equation for universes with zero total energy, and then adds a non-zero total energy term, which leads to an exploration of matter versus radiation dominated universes.

Originally presented in the Stanford Continuing Studies Program.

Stanford University:

Stanford Continuing Studies Program:

Stanford University Channel on YouTube:

[gmokhin]

Review of the 1st lecture ends at 27:00

[vasilikivelija]

2022 I'm so impressed by any video on this channel!

[tomlyle]

Dr. S doesn’t just tell the students what IS, but he tells them WHY it is. At first I had a tough time following him, but by mid-lesson 2 I became aware of his brilliance, and I became captivated, decided to audit this entire Cosmology semester. .

[mediumvibesonly]

Sometimes, I fall asleep watching memes or something else I like and when I wake up I'm half way through one of these videos.

[patriciaheil]

I'm trying hard to follow the math; he's doing a very good job of explaining what each term does which you don't always get. NOW I get why there had to be inflation. That third term in the conservation equation is new to me but he explained it beautifully.

[coastwalker]

Cracking course, could not be more highly recommended. Absolutely brilliant.

[Entropyko]

There are not standard lessons for standard students, but for non-students who wish to learn more about science. As I understand it these classes take place in the evening, so he's tired and hungry :P

[UpstairsPancake]

"Coffee is a good planet" - Leonard Susskind, 2013

[aadityatrivedee]

1:44:49 Isn’t adiabatic expansion the case where temperature of the system cools down due to work done by internal energy due to substantial fast motion due to which dQ = 0 & non-adiabatic expansion is where temperature remains constant? *Lenny said the exact opposite*

[varujanartinyan]

Brilliant lectures. Keep up the good work Dr.

[paulingvar]

There is a question at 1:14 about matter transforming to radiation. It is neglected, but this happens in every star. How can this be not counted for ?

[psegre]

Ok, he’s wrong at 1:25:00, energy is not conserved in an expanding universe. For instance, the cosmic microwave background radiation has been stretched out by a factor of 1000 since its creation, and its energy has dropped by 1000 times also. There are no ‘walls’ to the universe that photons are doing work on. This is the only time in physics that energy is not conserved, because the universe as a whole has a time dependence to it as it expands.

[EladarImm]

This is because cosmological models grow from the Einstein field equations (the fundimentals of general relativity - GR). GR, which uses (in general) curved, Riemannian manifolds (from differential geometry), is why he starts with that. On small scales (locally), it looks flat; globally, things are curved.

A couple things to help:
1. GPS works
2. You can see down the street, and the city looks flat. But the earth is curved; you can't see it, but it is. That's essentially what it boils down to.

[jacobvandijk]

You are right, Sarah. But these videos follow a historic line. Mr Susskind first outlined a model of the universe based on assumptions made by Sir Isaac Newton. You're going to fast :-)

[vlastopetras]

I find very relaxing when he moves those markers on board :)

[ericmelton]

So if space is curved like the earth then you can’t see past the horizon when you’re in the middle of the ocean everything looks the same and all directions it would be is a trophic and homogeneous but that’s not everything that’s out there

[mrpotatohed]

1:37:00 kind of like the node theorem in quantum mechanics

[Onegod-vh]

Which book can I take along with this course?

[pranavlimaye]

If the velocity is negative we know that the universe will decelerate and contract. What will happen to acceleration in this case, will it be negative or positive?

[peteruelimaa]

So one question: If a is the scale factor to get from grid units to meters, then a is different for every pair of particles in the grid right? Because if you just make the grid to fit galaxies, than the a for the Milky Way and Andromeda is different than the Milky Way and our next neighbor over to the other side. Is that correct?