Lisa Randall

But we know that it's roughly spherical, whereas ordinary matter can radiate and clumps into a disk. And that's why we see the Milky Way disk. So on large scales, in some sense, yes, all the matter is similar in some sense. In fact, dark matter is in some sense more important because it can collapse more readily than ordinary matter because ordinary matter

has radiative forces, which makes it hard to collapse on small scales. So actually it's dark matter that sort of drives galaxy formation. And then ordinary matter kind of comes along with it. And there's also just more of it. And because there's more of it, it can start collapsing sooner.

has radiative forces, which makes it hard to collapse on small scales. So actually it's dark matter that sort of drives galaxy formation. And then ordinary matter kind of comes along with it. And there's also just more of it. And because there's more of it, it can start collapsing sooner.

has radiative forces, which makes it hard to collapse on small scales. So actually it's dark matter that sort of drives galaxy formation. And then ordinary matter kind of comes along with it. And there's also just more of it. And because there's more of it, it can start collapsing sooner.

That is to say the energy density in dark matter dominates over radiation earlier than you would if you just had ordinary matter.

That is to say the energy density in dark matter dominates over radiation earlier than you would if you just had ordinary matter.

That is to say the energy density in dark matter dominates over radiation earlier than you would if you just had ordinary matter.

Exactly. I mean, in my book, I make kind of sort of jokes about, you know, it's like when we think about a building, we think about the architect, we think about, you know, the high level, but we forget about all the workers that did all the grunt work. And in fact, dark matter was really important in the formation of our universe. And we forget that sometimes.

Exactly. I mean, in my book, I make kind of sort of jokes about, you know, it's like when we think about a building, we think about the architect, we think about, you know, the high level, but we forget about all the workers that did all the grunt work. And in fact, dark matter was really important in the formation of our universe. And we forget that sometimes.

Exactly. I mean, in my book, I make kind of sort of jokes about, you know, it's like when we think about a building, we think about the architect, we think about, you know, the high level, but we forget about all the workers that did all the grunt work. And in fact, dark matter was really important in the formation of our universe. And we forget that sometimes.

Exactly. No, but it is a metaphor, but it also captures something because the fact is we don't directly see it. So we forget it's there or we don't understand it's there or we think it's not. The fact that we don't see it makes it no less legitimate. It just means that we have challenges in order to find out exactly what it is.

Exactly. No, but it is a metaphor, but it also captures something because the fact is we don't directly see it. So we forget it's there or we don't understand it's there or we think it's not. The fact that we don't see it makes it no less legitimate. It just means that we have challenges in order to find out exactly what it is.

Exactly. No, but it is a metaphor, but it also captures something because the fact is we don't directly see it. So we forget it's there or we don't understand it's there or we think it's not. The fact that we don't see it makes it no less legitimate. It just means that we have challenges in order to find out exactly what it is.

It is and it isn't because I think what it's teaching us is that we're human. The universe is what it is. And we're trying to interact with that universe and discover what it is. We've discovered amazing things. In fact, I would say it's more surprising that the matter that we know about constitutes as big a fraction of the universe as it does. I mean, we're limited, we're human.

It is and it isn't because I think what it's teaching us is that we're human. The universe is what it is. And we're trying to interact with that universe and discover what it is. We've discovered amazing things. In fact, I would say it's more surprising that the matter that we know about constitutes as big a fraction of the universe as it does. I mean, we're limited, we're human.

It is and it isn't because I think what it's teaching us is that we're human. The universe is what it is. And we're trying to interact with that universe and discover what it is. We've discovered amazing things. In fact, I would say it's more surprising that the matter that we know about constitutes as big a fraction of the universe as it does. I mean, we're limited, we're human.

And the fact that we see 5% of the energy density of the universe, about one sixth of the energy density of matter, that's kind of remarkable. I mean, why should that be? Anything could be out there, yet the universe that we see is a significant fraction.

And the fact that we see 5% of the energy density of the universe, about one sixth of the energy density of matter, that's kind of remarkable. I mean, why should that be? Anything could be out there, yet the universe that we see is a significant fraction.

And the fact that we see 5% of the energy density of the universe, about one sixth of the energy density of matter, that's kind of remarkable. I mean, why should that be? Anything could be out there, yet the universe that we see is a significant fraction.

That's absolutely true. And it's certainly writing books. I realized also how many of our words are based on how we see the world. And that's true. And that's actually one of the fantastic things about physics is that it teaches you how to go beyond your immediate intuition to develop intuitions that apply at different distances, different scales, different ways of thinking about things.