that like this? and isn't this what we had over here? so how much do we weigh at the surface there? four times as much, you would weigh four times as much when you get closer. on the earth, you went half as close and you got-- you weighed a half as much burrowing inside. that's because the ground is pulling the other way, but over here now it increases because you're getting closer and there's no other mass pulling you off, so it increases. if you understand that, you can answer this question. let's suppose this star collapsed and you rolled on it and you're right here and it collapsed as to 1/10 the size, so it's d/10 of the radius, 10 times closer. how much more you're going to weigh? check your neighbor. what's it going to be, gang?

it turns out 100 times as much. you would weigh 100 times as much at the surface of that star and it would become harder and harder to throw things into orbit, harder and harder. later on, we're going to learn that the surface of the earth to throw something away from the grav-- to escape, to escape the locality of the earth and to keep--to outrun gravity, you would have to throw something at 11.2 kilometers per second. that's called escape speed and we're gonna learn that on the sun for something to be ejected off the sun, so it doesn't get suck back in again. so we can outrun the ever present sun gravity, you have to go at 620 kilometers per second. that's the escape speed for the sun. what do you suppose happens to the escape speed as it gets closer and more and more compact from the surface, get harder and harder, you have this a little faster and faster, or slower and slower, what do you suppose? common sense, well now, what's physics anyway, gang? common sense, isn't it? okay. and it turns out it would be--

you'll have to throw it faster and faster and let me just give you a little fact. if our sun collapsed to a size less than 3 kilometers in radius and all the matter of the sun gets scrunched up to less than 3 kilometers, do you know how fast you would have to throw something from the surface of the sun to escape? 300,000 kilometers per second, that's the speed of light because from that particular configuration, escape speed would be the speed of light and if it shrunk down any more than that, forget it. you can't move anything at the speed-- in fact, light itself couldn't get out. you know, right now, you look at the sun as nice and bright, yeah? if i cut that small, ooh, i can't see it anymore because the light itself would be sucked right back into it, the enormous gravitational field at its surface. and so we'd say, it's just part of the black sky. we'd say, it's a black hole in space and that's what a black hole is.

it's a star that collapses and the gravitational pressure collapses and becomes-- and whereby it collapses to a point where the escape speed is the speed of light or more, black holes. it turns out, gang the astronomer types tell us that the sun will never become a black hole. it's simply not big enough and the gravitational pressure wouldn't do that. so black holes are made of larger stars, but nonetheless i've got an intriguing question for you. if our sun did turn into a black hole, what effect would there be on the orbital motion of planet earth? do you suppose you could grasp physics enough to not remember it, but to understand it? let's try, let's try.

over here, we went from a weight one to a weight four, to a weight 100, ain't that right? let's suppose over here when this star collapsed down to half size. let's suppose we climbed the ladder... and at the top of the ladder, we put a bathroom scale and we weighed ourselves with a more highly packed dense star. what would you weigh up there when you're just as far from the center compared to here? what your neighbors say? how many say, same, same? hey, that's right. you know why? because your mass is the same, the mass--is the same and the distance is the same you had over here. so you wouldn't weigh more or less. every part of your equation would be the same, these equations guide our thinking, gang. they tell us how to think,

over here, let's suppose you had a ladder, get a longer ladder now. so you're just as far out from the center of this than you were to begin with? what would you write here compared to over here? the same, it's one more step, gang. let's suppose this thing collapses to a black hole and somehow-- a thought experiment, you can put a ladder here and you stand right there and you're like, "oh my gosh, you black hole, i've read about those dudes." how's your weight going to be? how many say, "this time not the same." show hands. how many say, "no, i think the same." show hands. yeah, all right my people. what's going to change? not the gravity force, maybe the sunlight, you might get cold, okay?

but this doesn't change. this doesn't change. the weight doesn't change. the only thing that changes is this mass gets crunched up, but there's nothing in the equation that talks about that and, you know, what's after the equation? a period. so whenever i ask anything about gravity, the only thing is to consider what are the masses involved? how far away are they and that's it. and if you want a numerical value, then you have to put in the g which will make this have the same unit as this side, but that's it, that's it. see what i mean? the equations guide you're thinking. so it turns out if the sun turns into black hole, everything would be okay. you know why the sun's round? you know why the earth's round? you know why the planets are round? because if there are great, big cubes the corners could be pulled in by gravity, gravity pulls everything in until it gets round.

the whole universe, it turns out the idea of gravity underlies our thinking about the universe. you guys hear about the big bang theory? the idea that about 14 to 20 billion years ago the whole universe was in one point and exploded out, all flying out. let's look at that in terms of the gravity bit here. let's suppose, here's the big bang and all these pieces are flying. now let's suppose that we knock the whole universe into four halves just to make the thinking easy. if we can understand the simple examples then maybe we can deal with complexities. here's part of the universe here, here's part of the universe here, part of the universe here and all are flying apart. there's nothing else that exist just this and there they go. any force of attraction between these phases? how many say, yeah? it turns out this would be attracted to here, this would be attracted to here, be attracted to here and all these will act as if what?

it'll all act right back down there and this would act back down there. therefore, these things would be going against a gravitational force. if that's true and the universe exploded, does that mean as time goes by the universe will speed up or the universe would slow down? and it turns out the universe should slow down if this model is correct, and you know what? when the astronomer types look out in the heavens, they find out that the universe is slowing down. you know, how they know that? because when you look at the things that are furthest ago, i mean, furthest away and the thing that's furthest away is longest to go. you guys hit to the idea that it takes 8 minutes for the sunlight to get from the sun, right? when you look at the sun, you're looking at 8 minutes ago, you know that? and the next near star alpha centauri, looking at it four years ago. so if you're looking at something way, way back there, you're looking at it way, way back in time too and they find out the things that are farthest away, longest to go, we're going faster than things now. and that means, the universe is slowing down

and furthermore we find everything is getting further, further away from us, it's like a balloon expanding, expanding and everything is getting further away, slowing down, slowing down. maybe what happens is it goes like this... and maybe it just keeps going forever and ever and ever, but maybe it might go... to a whole universe? it's calculated to be about 100 billion years. it's called the oscillating theory of the universe, every 100 billion years another cycle. now take your diaries, take all the things that you like, take all your scrapbooks, okay? put 'em in a nice lead, lead casket, gang and when it comes and goes like this, how much is going to be left? nothing, it turns out, i don't think we can leave a record. all--everything would be--all the atoms, everything would be smashed right back down to elementary parts and fly right out the other side and the whole should bang go again.

the whole dance, the whole story, and maybe be a little different next time, maybe not. and how do we know? we don't. and if there is, how many times this happen? we don't. we think about these ideas. those are big ideas, gang. what is going on with the whole cosmos, and there are people that from day to day work on those kind of things and that's how they bring their lunch every day to work on. those are the astrophysicists and the astronomers, really wild stuff. but when you start to think about these things that are far away like that and big, it kind of humbles you. because let's make a graph about what this whole thing is. here we are right here. here is the big bang, i'm going to just draw a graph right on this space here. here's the big bang, this is 50 billion years later and a hundred, okay? when is the time that human beings learned how to control fire in this whole cycle? it's about here.

when that graph is about here, the human beings learned how to make fire. where are human beings now? about here, okay? here's where we used to be when we were in the caves and now we're like this and we got this to go off in this one cycle. i got a question for you. what will it be like? what will we be like when we get to here? what will be important to us? how will we relate to each other and how will our perception in the scheme of things be like when we get to here. i've got a little mental exercise for you. take a piece of paper and write down an operational definition of god, okay?

god means many things to many people. write an operational definition. by operational means god is a being, a spirit, a consciousness who can do this, like who can read minds, okay, who can be in all places at one time, who can... make your list, honey, that being is what i called god, okay? write that up. take your list. put it in a drawer. wait. i speculate the day will come when humanoids could look over that list and say, yes, we can do all of these things. we all can now. if that's true then what is going on? think about that.

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