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Good afternoon, ladies and gentlemen. Thank you very much for coming to the 17th ANC lecture.

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So I'm privileged to be able to introduce to you Professor Rocky Kolb from the University of Chicago,

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who is the author, Holly Compton, Distinguished Service Professor of Astronomy and Astrophysics.

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So Rocky's contributions to physics are wider and deep,

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and he was one of the first people to realise that you could learn things about the cosmos from understanding particle physics and vice versa.

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So he had a few small number of other people invented a new field, essentially, that does exactly that.

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Rocky grew up in Louisiana, his bachelor's degrees from the University of New Orleans and his Ph.D. is from the University of Texas at Austin.

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He's far from a stranger in Oxford.

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He's participated in a number of things we've done, in particular most recently our Physics of Fine Tuning program.

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He's renowned for the breadth of his knowledge of physics, and he served as the head of astronomy astrophysics in Chicago.

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He played an important part in establishing the key connections with Fermilab and also the

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creation of the Enrico Fermi Institute and the Kavli Institute for Cosmological Physics.

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He's just actually stepped down as the Dean of Physical Sciences.

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He has many accolades amongst them the Dannie Heineman Prize of the American

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Astronomical Society and an honorary degree from the University of Lille in France.

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He also, as well as being a very distinguished physicist, he has a passion for education, science, education and outreach.

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And this has been recognised by a number of teaching awards, notably the USTED,

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Medal of the Association, the American Association of Physics Teachers.

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So without any further adieu, it's my great pleasure to introduce Professor Rocky Cole to give the 17th NC lecture, The Quantum and the Cosmos.

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Thank you very much, Roger. And thanks, everybody, for coming out today on Halloween.

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And I hope the lecture is more of a treat than a trick.

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We'll see. So the title of the lecture is The Quantum in the Cosmos.

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And I would like to illustrate by some examples the connection between the largest things in the universe and the smallest things in the universe.

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So as Roger said in his introduction, I am a cosmologist and cosmology is the study of the origin composition,

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large scale structure and the evolution of the universe.

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I'll talk a little bit about the evolution of the universe.

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And the evolution includes not only the evolution of matter, stars, galaxies, etc., the evolution of the radiation in the universe.

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But in the 20th century, it also involves the evolution of space and time, and how space and time behave is going to play a large role in this story.

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I'm a cosmologist. So of course I think cosmology is very important, but other people think that cosmology is important.

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There is a was an American anthropologist, George P murdoch who spent most of his life at Yale, which I understand is someplace on the East Coast.

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I'm not exactly sure where that is. And one of the things Professor Murdoch did was to survey every culture or

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civilisation known at the time throughout the world and also know throughout history.

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And what he did was to come to a conclusion that cultures throughout the world

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and throughout history shared some things that he called cultural universals.

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And he listed 68, 70 or so cultural, universal universities, cultural universals.

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And one of these cultural universals, courtship rituals, every they weren't always the same,

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but every culture had courtship rituals, marriage, taboos of some type or another.

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Every culture seemed to brew alcoholic beverages.

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I don't think that's done here in Oxford, but it is a cultural, universal body adornment, which are cultural, universal.

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So in addition to cosmology, cosmetology is a cultural universal.

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And in fact, cosmology was also a cultural, universal, universal.

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Every culture had a cosmology, a shared idea, a shared story of the size of the universe,

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the arrangement of the universe, the age of the universe, the origin of the universe.

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Every culture has had one. So 4000 years ago, if we were living in the Nile Valley, we would think about the goddess Newt,

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who every night would swallow the sun and then give birth to the sun the next morning.

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Where does the sun go overnight? Well, it's in a gestation of the goddess Newt.

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There is a cosmology of ancient Hebrew cosmology, which is also the cosmology of the Tea Party in the US.

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And I've got no, no politics. Sorry. And it's a very physical cosmology, the cosmology of Scripture.

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It's a flat earth supported on a primaeval ocean.

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There is an underworld and a firmament with stars.

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In Scripture they talk about the dome of the heavens.

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Then there was an ocean of heaven and a heaven of heavens, and perhaps a heaven of heaven of heavens.

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It was a very physical cosmology, something that could be comprehended and understood at that time.

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In ancient Hindu scripture, they talk about the world elephant, which is on the back of the world turtle.

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And the usual thing you ask, what is the turtle on?

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And the answer is it's turtles all the way down to cosmology.

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I don't know whether it's well, it wasn't universal in Hindu cosmology,

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and but I don't know if people really thought there was a big elephant and turtles,

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but it was written in the Hindu scriptures as part of their cosmology.

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Our cosmology today is the Big Bang cosmology.

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And if I could if I have to say it in one sentence,

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it would be that our universe emerged from a state of high temperature in density 13.8 billion years ago, last Tuesday.

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And since that time has been expanding and cooling, the universe is evolving and dynamic.

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The universe is changing. So the universe visible today was once much smaller and much hotter in the past.

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And in fact, it was once so small and so hot that the quantum nature of matter, the quantum nature was so important in the evolution of the universe.

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So when I say the universe evolves and is changing, you might say, Well, if cosmology is a science,

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what is the evidence that you have for Cosmos, for the fact that the universe evolves?

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How do you really know that the universe evolves?

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Well, cosmologists and astronomers have a great advantage over our friends, the palaeontologists who have to go dusty places and dig up bones.

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Cosmologists can actually see that the universe evolves because cosmologists can use time machines.

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Well, the time machines used by cosmologists are telescopes.

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Telescopes are time machines because as we look out in space, we are looking back in time.

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Light takes a finite amount of time to reach us.

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If you look at the sun, you would see the sun as it existed 8 minutes ago, not as it exists the moment you look at it.

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If you look out into the sky and see a bright object, it's likely an aeroplane.

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But if you look for a star, the light from that star was emitted maybe ten, 20, 100 years ago.

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You're looking at the star as it existed in the past.

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And the farther out in space you look, the further back in time you see looking at objects that are far away, they appear younger.

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That's why the people in the back of the room seem to me well, for some, some of them a little bit younger than the people in the front of the room.

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Every foot you stand away from somebody, you appear a nanosecond younger.

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If you want to look young, don't stand too close to someone.

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The farther out in space you look, the further back in time you can see.

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So we can use telescopes, modern telescopes, to see that the universe evolves.

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We can see what the universe was like a billion years ago with the universe

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was like 5 billion years ago with the universe was like 10 billion years ago.

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And a telescope I will talk about using is a particle accelerator like the Large Hadron Collider that is in Switzerland,

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a huge underground accelerator.

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And in this huge accelerator in Switzerland, protons are smashed together at very high energy,

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recreating the conditions that were present in the primordial soup of the universe.

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So we can see in the laboratory today on Earth what the universe was like in the earliest seconds.

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And what we see when the universe was like in its earliest seconds, it was determined by the laws of quantum mechanics.

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And to understand the largest things in the universe, we have to understand how quantum mechanics works.

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We have to understand the smallest things in the universe and to understand something about the smallest things in the universe.

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We can observe the largest things in the universe and deduce how nature on the smallest scales work.

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So this is something that was nicely expressed.

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By the American naturalist John Muir.

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Apologies to anyone Scottish. I know he was born in Scotland, but I'll say he's an American naturalist.

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He said when one tries to pick out anything by itself,

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we find it bound fast by a thousand invisible cords that cannot be broken to everything else in the universe.

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So at universities, we neatly divide up nature into a physics department, a chemistry department, a biology department.

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But nature is not divisible. Everything is connected.

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And we to understand the largest things in the universe, in the smallest things in the universe are connected.

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And one aspect of that that I find amazing is the idea that humans.

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Or mid-size in the universe. The scale of common everyday experiences.

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As we experience, life is about a metre, you know about this big.

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Now the smallest scales we can sensibly speak of today, we don't understand everything about it,

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but we can sensibly speak of nature on scales of ten to the -26 metres.

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And the larger scales we can speak of today sensibly is nature on scales of ten to the plus 26 metres.

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And the scale of humans is sort of the geometric mean between the largest things and the smallest things we study in the universe now.

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Nature on the smallest scales, in nature, on the largest scales, on the micro scales and the cosmic scale.

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It's much different than the everyday life that we observe.

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So we do not experience in everyday life the nature of quantum mechanics.

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We do not experience in everyday life the relativistic effects of speeds near the velocity of light.

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We do not in everyday experience. See the expansion of the universe.

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So it's remarkable to me that we, our species,

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has developed the ability to ask these questions and try to find answers that really have nothing to do with our survival in turn,

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in an evolutionary way. This is often shown this connection between inner space and outer space by the snake swallowing its tail,

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a image that goes back at least to the ancient Egyptians.

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And here is our people at the scale of one metre or so, a very large ant, you know,

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amoeba DNA atoms on scales of ten to the minus ten metres nuclei on scales of ten to the -50 metres particles

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like the W and G that our experimental physics friends study at accelerators and going on larger scales,

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mountains on scales of a kilometre, the earth ten to the seven metres, the sun ten to the nine metres, the solar system,

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the star clusters, the galaxy, the larger structures we see, we are just right there in the middle, but they are connected.

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So the sun shines because of nuclear reactions.

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And to understand why the sun shines and how stars evolve, we have to understand not physics on scales,

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not only physics on a scale of ten to the nine metres, but here in the micro world on scales of ten to the -50 metres.

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So turning back to cosmology, I said that modern cosmology just studies the evolution of space and time.

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So let me spend just a couple of minutes talking about how our idea of space and time has changed again in our everyday experience.

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We experience space and time in the classical Newtonian picture.

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In Newton's book, The Print Kippah, he wrote about absolute space and absolute time.

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He wrote that absolute space remains always similar and immovable.

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And he wrote that absolute true and mathematical time flows without regard to anything external.

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So in the Newtonian picture of space and time, physics describes the motion of objects through space, how things change with time.

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But space and time are like a fixed pitch.

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You know, you draw the the lines on the field and the game is played out.

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But as the game is played out, you don't change the size of the field.

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The field is fixed. And in most sports, there's a time that's capped that everyone can see.

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There's no injury time in most sports.

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But, you know, this time that's kept and time and space are fixed and the game is played out on a fixed pitch of space and time.

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And this led to another cosmology, Newton's clockwork universe.

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And in the Newtonian picture, once you start, you you imagine the initial conditions,

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you use the absolute space and absolute time in Newtonian law, Newton's laws, and just watch the universe.

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Do its thing. Now this idea of space in time changed at the beginning of the 20th century because of the work of Albert Einstein.

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In 1905, Einstein had the realisation that space and time are not completely independent.

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They're relatives. And you shouldn't think about space and time as independent.

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You should imagine a unified space time.

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Einstein didn't stop there. He went on ten years later to develop a theory of gravity based upon space and time,

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and came to the conclusion that the best description of gravity is curved space.

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So a little bit more than 100 years ago, Einstein had in his hands a new theory of gravity, a new theory of micro physics in some sense.

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And he realised that he could use this new theory of gravity to understand the cosmos.

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And in 1917, Einstein developed his cosmological model, and he started with two basic assumptions.

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The first assumption is that gravity shapes the universe on the larger scale.

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It's the force of gravity that is important in understanding how the universe works.

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And he brought in the new idea that gravity is curved space.

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So in 1917, one of the first applications of its new theory of relativity, his theory of gravity was cosmology.

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And he knew that he could, with his new machinery that he built, try to understand something about the universe.

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So I'll show one equation in this lecture.

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And it's an equation by Einstein and it's not equals M.C. squared.

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You're too sophisticated for that.

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The equation I'll show is the Einstein field equations that describe his theory of gravity, and it's written here on his tablet.

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Now it looks like one equation, but if you take the general relativity course here,

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you'll discover that this is really a shorthand notation for ten equations,

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ten nonlinear partial differential equations, sort of like the Ten Commandments.

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Now, if you take general relativity, maybe in graduate school, you will learn that you don't actually have to obey ten equations.

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You can just obey six. Just like the Ten Commandments, right.

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For, you know, six out of ten is a pretty good day for many people like that.

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So in this in Einstein's equations, on the right hand side is the Greek letter Kappa, which is a shorthand notation for eight pi times.

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Newton's cosmological constant g and see is the speed of light.

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Now, the only technical thing that I'm going to use about this equation is it has a left hand side and a right hand side.

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And on the left hand side of the equation is the called the Einstein Tensor.

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It involves space, time, curvature of space, outpacing time, interact how they work and it will turn out it involves the expansion of space.

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On the right hand side of the Einstein equations, we put the information about mass energy particles, forces,

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how much, what is the mass of things, how particles interact, how mass and energy is distributed throughout space.

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So it has a left hand side and a right hand side. So Einstein started with his field equations and then made an additional assumption.

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In looking for a cosmological solution to his equations.

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The additional assumption that Einstein made is that the universe is static.

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In 1917, Einstein thought that the universe we see more or less always existed.

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Stars might move around and things like that. Planets orbit the sun.

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But with large scale and large scales. The universe.

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Which static. So he was dismayed to look at his equations and was unable to find a solution to his equations that describe a static universe.

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So he had spent eight years of incredible labour and insight driving this equation.

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He couldn't find a cosmological solution. So he said, Well, there must be something wrong with my equations.

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And he added something on the left hand side of the equation that involves a constant, a new constant in nature described by the Greek letter Lambda.

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And he described it as a cosmological term or a cosmological constant.

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Now. This was in 1917, but in the 101 years of hard work by theorists,

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we have managed to transport this to the right hand side of the equation and make the letter a capital that we proud 101 years of work doing that.

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It was pretty tough and we have a new, new name for it.

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It's dark energy that I will describe in a moment.

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So Einstein's theory, Einstein's cosmos, his cosmological model, which that gravity shapes the universe.

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Gravity is curved space, the universe is static.

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And in order to find this solution, he had to introduce this cosmological constant, this cosmological term, lambda.

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So new cosmology really, really becomes a science, because one of the hallmarks of science is that there is no authority.

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The models and ideas of even the greatest scientist are subject to falsification.

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They can be shown to be wrong.

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And 12 years later, Einstein's conception of a static universe was shown to be wrong by the observations of Edwin Hubble in 1929,

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discovered in fact that the universe is not static, that the universe is expanding.

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No. At this point I like to brag about Edwin Hubble because he was educated at the University of Chicago and.

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But I have to give credit. He also came here as a Rhodes Scholar after getting his undergraduate degree at

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Chicago and was here as a Rhodes Scholar and it was at the Queen's College,

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Oxford. And if you go in to anybody here from the Queen's College.

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Nobody admits it. Okay. If you go to the Wikipedia page, they have some famous scholars from the Queen's College.

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Henry the Fifth. Edmund Halley, another astronomy astronomer, and they include Edwin Hubble.

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Very proud of that. Tim Berners-Lee and this other scholar, I don't know what he's done, but he must be important because he's on the Web page.

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So in 1917, Einstein proposed a cosmological constant, a static universe.

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In 1929, Hubble said, Well, looks like the universe is expanding.

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And at least by 1931, Einstein was convinced enough to abandon his original cosmological model.

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And some evidence of this can be found here at Oxford in the Museum of the History of Science.

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I hope people have gone there. If you go down in the basement and look high up on a wall, you will see a blackboard,

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which is a blackboard used by Einstein for a lecture that he gave on 23rd May 1931.

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He gave two lectures here, so there are two blackboards.

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The other blackboard was erased by the custodian after the lecture.

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But this blackboard is up there. There's not much explanation of all these equations other than saying It's Einstein's blackboard.

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But these I'm sorry about the photograph that I took.

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This is a blackboard that shows that Einstein in 1931, at least 23, May 1931, had become a big bang or.

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In in 1931. He also wrote a paper on the cosmological problem of the general theory of relativity,

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in which he said It can be shown with the help of these equations, the same equations that was in his paper that the static solution is not stable.

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A solution that deviates only slightly from the static solution at a given point in time will differ even more from it.

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With the passage of time on these grounds alone.

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I am no longer inclined to ascribe a physical meaning to my former solution quite apart.

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He misspelled Hubbard's name throughout the paper from Hubble's observations.

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So Einstein knew about Hubble's observations, but as a true theorist, he did not believe any observation until confirmed by theory.

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There is a nice paper talking about this blackbird,

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and in this paper it goes into some detail about the equations here and what Einstein must've assumed.

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He assumed a model of an expanding universe.

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He assumed a spherical model for the universe.

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He assumed that the cosmological constant is zero little lambda.

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A capital lambda does not enter in any of these equations.

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D On this blackboard is Hubble's constant.

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P is the radius of the three sphere, and P zero is the maximum radius in this cosmology that Einstein now adopted.

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The universe is closed. It has a finite volume.

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It expands to a maximum size, to a maximum radius, and then collapses.

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This is also the black. Interesting because there is some curious numbers on it.

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And by curious, I mean wrong. So I have to mark down Einstein's blackboard.

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He I don't think he is going to get a first class degree here.

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He has the wrong. First of all, he doesn't put his units on Hubble's constant density radius.

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Actually he has it on radius in time which yea yea presumably is centimetres to the minus two and apparently and undergraduates will appreciate this.

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He messed up converting megaparsec two kilometres.

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So it gets marked off for that. So this is wrong.

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And he left. He ends up with an incorrect value for the present density based upon this model and the radius.

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And The Age. But Will.

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Will? Well, I'll give him a first class degree.

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Okay. So the quantum in the cosmos, there are many aspects of the connection between the quantum and the cosmos.

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Dark matter, dark energy, cosmic inflation, and the origin of structure.

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Questions like Is there only one universe?

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Can there be a multiverse? What about that?

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Spacetime singularity a time equal to zero.

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Quantum gravity should be a question mark that the origin of the elements.

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There are a lot of connections between the quantum and the cosmos.

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But I'm going to take advantage of the fact that it's Halloween and talk about the fact that the universe is dark and spooky.

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I'm going to talk about dark matter and dark energy.

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So it's the dark side of the universe. Dark matter seems to pull things together.

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It looks like attractive gravity.

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And the probably the best explanation is that dark matter is a new type of particle species that is yet to be discovered.

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Dark energy seems to be quite different. It seems to push things apart.

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It's repulsive gravity and it is related to the weight of space.

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Dark matter and dark energy are important. If we look at the present composition of the universe, dark matter in most of the universe is dark.

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The radiation in the universe today, which is mostly in the microwave background radiation is only a very small .00 5%.

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This also demonstrates why chemistry is not important.

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But chemical ela. I don't know why people study. Why is it taught here?

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I don't know the chemical elements, by which I mean elements other than hydrogen and helium make up only 0.0 to 5% of the mass.

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And energy in the universe is a larger part of mass of the universe and elementary particles known as neutrinos.

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Stars that astronomers seem to like to look at is less than 2% of the mass in energy in the universe.

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Most of the normal stuff that we understand is a hydrogen and helium gas in clusters of galaxies that makes up about 4%.

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So if I've done my arithmetic correctly and you add up everything that we see and understand and only comes to 5%.

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The universe seems to be 95% dark, 25% dark matter and 70% dark energy.

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So let me first talk about dark matter, because as everyone knows.

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Today is International Dark Matter Day.

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So let me talk about dark matter. Astronomers have been studying galaxies for over 100 years.

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And they own they study the dynamics of stars and galaxies.

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And from the movement of the things that we see,

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we deduce that there must be much more mass to a galaxy than we can account for in the form of stars or any other matter that we see.

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Okay. So this is a beautiful image of a galaxy from a taken from a modern telescope.

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But if we. Asked the question, What does the Galaxy really look like?

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If you could see all of the mass in the galaxy, including the dark matter, then the galaxy would look much different.

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This yellow disk would be the galaxy that we do see the visible part of the galaxy,

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but it seems to be surrounded by a halo, a puffy halo of dark matter that we don't see.

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We have to give it a colour in order to see it very dense and red in the centre.

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The density getting smaller as you go out and there should be clumps of dark matter.

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So a galaxy is actually much larger than the galaxy that we can see.

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And there's much more mass in the dark matter. So if this is Halloween, should you be afraid of the dark?

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So if your child asks, Is there a dark matter under my bed who's afraid of monsters?

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Could be dark matter under the bed. The answer is yes, under the bed at any moment.

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Or about a thousand dark matter particles zipping around at about a million kilometres per second.

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They pass through the mattress, through the covers, through you, through the house, through early.

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But you can't see them, feel them or smell them.

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But they won't hurt you. They don't bite. So what is this dark matter?

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What are these missing pieces in our picture of a galaxy?

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Well, this was really great to be a theorist because you can propose a lot of ideas.

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One idea that was proposed that I'm happy to say that I had nothing to do with is the idea that,

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in fact, there's no dark matter, that somehow our understanding of gravity is completely wrong.

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That Einstein and Newton didn't have the last word on gravity.

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And this goes by the name of modified gravity or modified Newtonian dynamics.

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And one of the ideas is that on very large scales, the F force is not equal to mass times acceleration.

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F is not equal to M. Where else have we seen this?

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What other evidence do we have that is not equal to MRA?

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A precision Swiss chronometer.

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Not even a watch. It's a chronometer. The difference is about 4,000 CHF.

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Velocity is equal to mass times acceleration.

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That is non-Newtonian dynamics right there.

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I'm happy to say I had nothing to do with that either.

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But, you know, on the other hand, I won't buy this watch because if they can't get Newton's laws correct, how can I imagine that they can tell time?

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So another idea for dark matter is that it is normal matter, but it's in a form that we just can't see.

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It doesn't emit light. Planets do not in that light.

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There are different types of planets. There are large gas planets, ice planets.

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My personal favourite are the rocky planets that got to like rocky planets.

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And maybe there are rogue rocky planets throughout the galaxy, the big hunks of rock that we just don't see.

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Or it could be that there are stars, mass challenged stars that are light challenged and a bunch of dim stars around the galaxy.

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Or it could be that the galaxy has a lot of black holes which are made of normal matter but do not emit light.

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These generally are referred to as massive compact halo objects or match those.

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Now observations have closed out the possibility just about all of the possibility of these my chose.

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The only thing that seems to remain is that the dark matter could be 30 solar mass black holes that were somehow primordial reproduce.

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And I used to think that was a crazy idea. But the recent gravitational wave experiments have detected 30 solar mass black holes.

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So there's been a resurgence in interest on primordial black holes as being dark matter every ten years,

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as a resurgence of interest in primordial black holes.

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I don't think this is the answer.

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I think that the answer is that the dark matter is an unknown particle species that was produced early in the history of the universe.

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So the idea that there was a bang and when the universe was a temperature or about one millionth of a millionth of a second,

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maybe after the bang, when the temperature was.

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A gazillion degrees. The high energy collisions in the primordial soup produced a new type of particle that is yet to be discovered.

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Now. I said we can use telescopes to look out in space and back in time.

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Can we use a telescope to look out in space and back in time and look at the dark matter being produced?

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I'm afraid we can't because the universe only became transparent 380,000 years after the bang.

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Before that, the universe was so hot and so dense that we can't see through it.

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So we can't look out in space and back in time that the origin of dark matter.

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But at accelerators we can reproduce the conditions that were present at that time and see if we can make dark matter in the laboratory.

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And the best place to do this now is at the CERN Large Hadron Collider, the LHC.

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So what was the primordial soup like, the conditions that are being produced every day at at CERN?

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So what happens if we have a can of primordial soup that we canned when the universe was a nanosecond old and 100,000,000 million degrees?

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Well, the soup is condensed. In one can of soup is 50 times the earth mass in matter,

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50 times the earth mass in anti-matter and a little bit extra matter because the 50 times earth mass in matter

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is going to annihilate with the 50 times earth mass in anti-matter producing the radiation that we see.

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But there was a little bit extra matter that couldn't find a partner with which to annihilate.

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The soup was condensed. The soup was hot. In one serving of primordial soup.

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It's 10,000,000 million years of the total energy output of the sun.

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Now the sun is not going to live 10,000,000,000 million years, but there's a lot of energy in the soup.

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And if you look on the label for the ingredients in every spoonful of primordial soup or all of the elementary particles that we know about,

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and perhaps there's dark matter. So every day our experimental friends are looking for dark matter in the primordial soup.

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So far, they haven't found it. We're also looking towards the heavens for evidence of dark matter.

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If their dark matter is an elementary particle.

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If you look in the centre of the galaxy where there's a lot of dark matter, it should be annihilating,

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producing some astronomical signal that could be detected by various experiments.

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Balloon experiments. Telescopes. Satellites, uh.

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A bunch of experiments in space at the South Pole, Namibia and other places that are inhospitable to life like Arizona.

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So we're looking for dark matter there. We're also searching underground for dark matter.

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If dark matter's passing through us, perhaps on occasion a wimp,

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a dark matter particle that's going at a million kilometres per hour will go through the earth, go underground,

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and in a very sensitive detector will bomb a single nuclei, single nucleus in the detector,

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and produce ionisation heat, light vibrations or bubble nucleation.

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And if you have an ultra pure, ultra cold, ultra radio, pure, ultra expensive, solid liquid,

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a gas detector deep underground, shielded from cosmic rays, you might be able to find evidence of wimps that way.

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So dark matter is sort of spooky.

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It's around us, but we don't see it. Uh, but wait.

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There's more to the dark side than just dark matter.

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There is the acceleration of the universe that we attribute to dark energy.

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In 1929, Hubbard discovered Hubbard's law.

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That is an expansion velocity today of the universe.

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Now, as we look farther out in space, we can look further back in time and we can measure the expansion velocity at earlier times.

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Difference in velocity is acceleration.

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And so we can measure if the universe accelerates or decelerates as it expands.

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Every reasonable person expected as the universe expands the expansion velocity to decrease because gravity is attractive.

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But there was an enormous surprise in 1998 when two observational teams of astronomers, led by these three people,

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discovered that, in fact, the universe is accelerating, that the velocity in the past was smaller than the velocity today.

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And for this, they were awarded the Nobel Prize.

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The simplest explanation to to account for these observations is that, in fact, there is a cosmological constant.

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So was Einstein right? After all, in 1917, he proposed a cosmological constant.

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In 1929, Hubble discovered the expansion of the universe.

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And and Einstein said, Well, maybe there's not a cosmological, cosmological constant.

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And in 1934, he said that the introduction of this term, this cosmological term, was my biggest blunder.

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He didn't realise that 64 years later astronomers would find evidence for it.

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Lesson. You never admit you're wrong.

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Einstein could have been famous. He could have predicted dark energy.

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But instead he said, No, I must be wrong. So, no, he's completely forgotten now.

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The explanation of the cosmological constant is not without trouble.

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I think of it as the unbearable lightness of nothing.

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A cosmological constant would mean that there is a mass of ten to the -30 grams in every cubic centimetre of space.

376
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So small, but not zero. So I think that rather than call it a cosmological constant,

377
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it would be better to call it a cosmology illogical constant, because its value does not make sense.

378
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So how do we understand? How can we envision that empty space by itself?

379
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Completely empty space can have a mass. So to do this, we have to understand.

380
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We have to think about nothing. When I lecture at Chicago, I ask the students to think about nothing.

381
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Some of them are really good. They've been doing it all their life.

382
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But. Okay. But I'll tell you. Six Secrets of nothingness.

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Some aspects of nothing that you may not have appreciated before.

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This is the Zen aspect of this lecture.

385
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Six Secrets of Nothingness. We have to get in the right mood.

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Secret number one nothing is uncertain.

387
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Well, this the uncertainty principle of quantum mechanics again connecting quantum in the cosmos.

388
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Werner Heisenberg talked about the uncertainty principle and that is important for us because

389
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all quantum fields I think of is harmonic oscillators and because of the uncertainty principle,

390
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harmonic oscillators do not have zero energy.

391
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They have a minimum energy of one half h bar where each is plunks constant.

392
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Each bar is h divided by one half a by two pi.

393
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Nothing is uncertain. Secret.

394
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Number two, nothing is something.

395
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Zen like think nothing is something because of the uncertainty principle.

396
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Nature on very small scales, on some microscopic scales have fluctuating fields in the vacuum.

397
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So if you would look at empty space with some microscopic eyes, eyes that can discern things about the size of electrons and protons,

398
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you would not see a question vacuum because of the uncertainty principle.

399
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Particles in Antiparticles will be coming out of the vacuum.

400
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Nothing is something. Secret.

401
00:49:46,210 --> 00:49:55,510
Number three, nothing has energy. So the quantum fields for harmonic oscillators with zero point energy.

402
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Then you can calculate. And so the first year of graduate studies, first year quantum field theory the energy density.

403
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That should be contributed by the uncertainty principle, the uncertainty of quantum fields.

404
00:50:13,900 --> 00:50:24,510
Now, I don't know if people are getting ready to take quantum field theory, but I'll tell you the answer to every question.

405
00:50:24,520 --> 00:50:29,890
Every problem in quantum field theory, the answer is infinity.

406
00:50:30,700 --> 00:50:35,110
Everything you calculate in quantum field theory is infinite.

407
00:50:35,800 --> 00:50:42,490
So you calculate the energy density of the vacuum, and you have to put a cut-off to prevent it from infinity.

408
00:50:42,940 --> 00:50:49,390
Because the naive calculation would give an infinity to the fourth power for the energy density of the vacuum.

409
00:50:49,450 --> 00:50:52,930
That's a bad prediction. It can't be infinite, can it?

410
00:50:53,650 --> 00:51:00,910
So you put in a cut-off and you say, Well, maybe gravity provides some cut-off you put in the mass known as the plus mass.

411
00:51:01,570 --> 00:51:06,600
This is a pretty good calculation. You've gone from infinity to ten to the plus 90.

412
00:51:07,840 --> 00:51:13,060
But it's 120 orders of magnitude too large about the worst.

413
00:51:14,740 --> 00:51:18,610
Agreement between theory and prediction than you can imagine.

414
00:51:19,090 --> 00:51:23,050
So you and you wave your hands and say the magic word, supersymmetry.

415
00:51:23,410 --> 00:51:27,129
It's ten to the well. That sign is wrong. Plus 30.

416
00:51:27,130 --> 00:51:34,090
You want ten to the -30. This is ten to the plus 30. The numbers that you calculate from this are just enormous.

417
00:51:35,170 --> 00:51:43,420
There's another form of energy, and that's the energy contributed by the Higgs boson.

418
00:51:44,020 --> 00:51:47,730
Now, the Higgs boson was studied in Europe. We look for it in the US.

419
00:51:47,740 --> 00:51:52,990
We didn't discover the Higgs boson, but at Fermilab we have the Higgs By-sa.

420
00:51:56,230 --> 00:52:03,940
So nothing has Higgs energy. The quantum vacuum is full of Higgs particle, says the Higgs potential.

421
00:52:04,180 --> 00:52:11,079
And it's this Higgs potential that gives mass to electrons, quarks and other particles at every point in space.

422
00:52:11,080 --> 00:52:16,840
There's the Higgs potential energy of 246 billion electron volts.

423
00:52:18,370 --> 00:52:26,850
Nothing has energy. Secret number four of nothingness.

424
00:52:27,390 --> 00:52:36,920
Nothing is hidden. My friends who are string theorists tell well, actually I don't have any friends who are string theorists,

425
00:52:39,350 --> 00:52:47,240
but if I did, they would tell me that at every point in space we see there are other dimensions of space.

426
00:52:48,820 --> 00:52:51,040
There are six of us, excuse me,

427
00:52:51,100 --> 00:53:01,360
six or six other dimensions of space that are wired up really tight and we can't see them because a really small these the spaces wound up.

428
00:53:02,380 --> 00:53:08,620
There must be energy involved in keeping these extra dimensions of space hidden.

429
00:53:09,880 --> 00:53:15,580
Nothing is hidden. Secret number five Nothing is mysterious.

430
00:53:17,460 --> 00:53:23,820
So the cosmological constant doesn't seem to be related to anything that we can see in physics.

431
00:53:23,850 --> 00:53:27,930
The observed dark energy is ten to the -30 grams per cubic centimetre.

432
00:53:28,590 --> 00:53:33,840
I talked about the uncertainty, energy. There's symmetry, breaking, extra dimensions.

433
00:53:34,500 --> 00:53:42,330
Everything that you can put your hands on to try to relate it to is many, many, many orders of magnitude too large.

434
00:53:42,360 --> 00:53:49,230
Nothing is mysterious. Finally, nothing matters.

435
00:53:50,340 --> 00:53:56,480
Very deep statement. If dark matter.

436
00:53:56,490 --> 00:54:02,370
If dark matter dominates, there are two possible final states for the universe.

437
00:54:02,670 --> 00:54:08,880
The universe could meet, could reach an eventual a maximum size and eventually collapse,

438
00:54:09,540 --> 00:54:14,610
or the universe could expand forever, always decelerating and slowing.

439
00:54:15,480 --> 00:54:26,640
But if dark energy is dominate dominant, then the universe will expand forever, ever at an ever fasting ever faster velocity.

440
00:54:27,030 --> 00:54:33,570
The universe will accelerate, and the galaxies that we see around us today will.

441
00:54:34,580 --> 00:54:42,420
In the far distant future, expand so far away, be travelling so fast that we won't be able to see them.

442
00:54:42,440 --> 00:54:47,450
We will be alone in the universe. Now is the time to do astronomy.

443
00:54:47,480 --> 00:54:52,380
Don't wait. Nothing matters.

444
00:54:54,050 --> 00:55:00,620
So one, what I talked about is that the universe today is 95% mystery.

445
00:55:02,450 --> 00:55:08,120
Now. I also talked about modern cosmology, starting with the work of Einstein.

446
00:55:08,510 --> 00:55:12,920
According to Time magazine, the person of the 20th century.

447
00:55:13,910 --> 00:55:22,840
What would Einstein think that if 100 years after he started us on using general relativity to understand cosmology,

448
00:55:22,840 --> 00:55:25,990
that 95% of the universe would be a mystery.

449
00:55:27,460 --> 00:55:36,990
Well, I think he might be happy. Einstein said the most beautiful thing we can experience is the mysterious, the source of all true art in science.

450
00:55:37,000 --> 00:55:42,430
He thought that those to whom this emotion is a stranger are as good as dead.

451
00:55:42,430 --> 00:55:47,290
Their eyes are closed. Cosmologists today are no.

452
00:55:48,710 --> 00:55:53,580
Stranger to mystery, 95% of the universe is a mystery.

453
00:55:54,980 --> 00:56:02,810
So this is our cosmic mystery today. Connecting the inner space of a quantum in the outer space of the cosmos.

454
00:56:04,390 --> 00:56:09,310
It's a mystery today, but this mystery will be solved.

455
00:56:10,070 --> 00:56:17,270
Somewhere out in the world today is someone who will be the next Einstein.

456
00:56:18,620 --> 00:56:30,800
Out in the world today is someone who will be the person of the 21st century, who will connect the quantum in the cosmos and solve our cosmic mystery.

457
00:56:31,280 --> 00:56:36,320
And I have no doubt that they will develop cosmic mysteries of their own.

458
00:56:38,590 --> 00:57:04,770
Thank you very much. Thank you so much, Rocky, for that insightful lecture delivered with considerable panache.

459
00:57:04,980 --> 00:57:10,080
It's wonderful. I'm sure there will be many questions. Here first.

460
00:57:14,540 --> 00:57:19,249
Great talk. Thank you. About five years ago, I attended approximately five years ago,

461
00:57:19,250 --> 00:57:27,200
I attended a talk by you where you said that if we had not directly detected wimps within about five years, that they would be ruled out.

462
00:57:27,560 --> 00:57:34,200
Any comments? I haven't changed my mind right now.

463
00:57:34,220 --> 00:57:37,430
I'm saying if we haven't detected wimps in five years.

464
00:57:39,460 --> 00:57:50,690
I've been saying that for 30 years. Before I take the next question, I remember that I'm supposed to tell you that these proceedings are being filmed,

465
00:57:50,990 --> 00:57:55,460
and if you do not wish to be filmed, you should hold this up and then you will be removed from the film.

466
00:57:56,420 --> 00:58:03,080
So if you. Yeah. So next question at the back and then here.

467
00:58:08,950 --> 00:58:13,920
Sort of to follow up on that question experimentally. Where do you think the next hint is going to come from?

468
00:58:13,930 --> 00:58:20,770
Will it be a particle collider cosmic ray experiment? And okay, so I guess everyone heard the question.

469
00:58:23,070 --> 00:58:28,080
Let me answer a slightly different question, which is a good trick when you're a professor, right.

470
00:58:29,460 --> 00:58:33,390
Rather than ask. Then trying to answer when the next Higgs will come from.

471
00:58:33,900 --> 00:58:39,209
When will particle our friends to particle physicists discover a new phenomenon?

472
00:58:39,210 --> 00:58:42,360
A new particle, even if it's not dark matter?

473
00:58:42,720 --> 00:58:47,730
Will it come from building a larger version of CERN?

474
00:58:47,850 --> 00:58:51,660
And there are other ideas building linear accelerators or this and that.

475
00:58:52,140 --> 00:58:59,370
And we don't know where it will come from. We never know what's just beyond the horizon where we can see.

476
00:59:00,030 --> 00:59:06,419
And I think a clearest example of that is Galileo's Galileo,

477
00:59:06,420 --> 00:59:13,680
who first really used a telescope to do astronomy, and he turned a telescope to the heavens.

478
00:59:13,680 --> 00:59:20,790
He didn't invent the telescope. He appropriated that. He never denied inventing the telescope, but he didn't invent the telescope.

479
00:59:21,270 --> 00:59:31,649
And within just a year of using the telescope, he made a remarkable discoveries that, you know, the craters on the moon,

480
00:59:31,650 --> 00:59:38,490
they could resolve the Milky Way, the moons of Jupiter and, you know, just incredible discoveries.

481
00:59:39,910 --> 00:59:49,840
Of course, you used a new instrument. But it only increased his vision, his power of his unaided eye, originally by about a factor of three.

482
00:59:50,930 --> 00:59:57,380
So you never know just what a small increase in our instruments will reveal.

483
00:59:57,410 --> 01:00:06,709
There could be a new world waiting to be discovered, and that's that possibility that keep experimentalists added,

484
01:00:06,710 --> 01:00:10,580
trying to build larger and larger things and look harder and harder.

485
01:00:11,360 --> 01:00:18,430
Those experimentalists work hard. I mean, they can work for years to disprove a theory.

486
01:00:18,440 --> 01:00:22,510
It took me 10 minutes to come up with. That's not fair.

487
01:00:22,520 --> 01:00:25,820
But. Uh, Paul? Yeah.

488
01:00:27,370 --> 01:00:32,510
You got a microphone? So let's use this one.

489
01:00:39,670 --> 01:00:44,299
Yeah. Yeah. Rocky, I wanted to ask if, hypothetically,

490
01:00:44,300 --> 01:00:55,700
Einstein had been able to live to the age of 117 so that he would be alive in 1998 and assume he possessed the same intellect that he did in 1915.

491
01:00:56,860 --> 01:01:04,570
What do you think he might have thought of this discovery of dark energy, what we call what he would have thought of dark energy?

492
01:01:04,850 --> 01:01:10,030
I don't know. So would Einstein eventually have accepted quantum mechanics?

493
01:01:11,050 --> 01:01:15,340
I don't know whether Einstein would have eventually accepted quantum mechanics.

494
01:01:15,370 --> 01:01:17,889
You know, he he had these brilliant insights.

495
01:01:17,890 --> 01:01:26,520
But essentially, you know, he was educated in the 19th century, essentially, and he never did accept quantum mechanics.

496
01:01:26,530 --> 01:01:28,900
And I would hope that if he had lived long enough,

497
01:01:29,530 --> 01:01:36,290
he would have eventually accepted quantum mechanics and maybe he would have become a string theorists.

498
01:01:39,160 --> 01:01:44,350
I don't know what he would have done. He. So Ray in the power.

499
01:01:46,900 --> 01:01:52,240
Right here. It's like well let's say Carlos and you them off and then get them and then.

500
01:01:56,530 --> 01:01:59,710
So like, what do you have on the board?

501
01:01:59,920 --> 01:02:07,780
What is that represented? What is that? Yes. So 15 years ago or so, I was on a NASA committee.

502
01:02:08,950 --> 01:02:11,349
Space Science Advisory Committee was the name of it.

503
01:02:11,350 --> 01:02:17,440
And we came up with a new program called Beyond Einstein that we wanted to launch telescopes to do this and that.

504
01:02:17,950 --> 01:02:26,230
So Nassau and it was conducting Einstein and modern observations and particle physics and cosmology.

505
01:02:27,010 --> 01:02:32,919
And NASA came up with this image. I don't know what it means, but I think it's a pretty cool image.

506
01:02:32,920 --> 01:02:36,040
But I have it's moderate, it's it's art.

507
01:02:36,050 --> 01:02:43,710
So I have an interpretation. So that's sort of the quantum mechanics on the left, sort of fuzzy things that we don't get.

508
01:02:43,720 --> 01:02:52,050
At least that's my view of it. And somehow. There's a bridge that connects that to the cosmos.

509
01:02:55,020 --> 01:03:00,810
And if you just think of it as a I think it's a pretty picture, right?

510
01:03:00,840 --> 01:03:11,400
Yeah. Yeah. So you mentioned that as the expansion of the universe accelerates in response to dark energy, the galaxies would pull farther apart.

511
01:03:11,820 --> 01:03:17,129
I was wondering, will the galaxies themselves, the individual galaxies, also become more tenuous?

512
01:03:17,130 --> 01:03:21,690
Or is there enough dark matter in the galaxies to hold individual galaxies together

513
01:03:21,690 --> 01:03:25,590
where they can continue forming stars even when the universe becomes a lonely place?

514
01:03:26,070 --> 01:03:37,230
The definite answer is that it depends. So we don't know if the energy of space, the dark energy increases with time or not.

515
01:03:37,530 --> 01:03:41,340
If it's a cosmological constant, it will not increase with time.

516
01:03:41,760 --> 01:03:46,800
But it's possible that it's not a constant, that it's going to slowly increase with time.

517
01:03:47,400 --> 01:03:57,980
And that would lead to something that we call the big rip that would tear space apart, even on scales of Ray and, you know.

518
01:03:57,990 --> 01:04:03,000
Yeah, spooky. But but don't worry, it would be billions of years in the future.

519
01:04:03,210 --> 01:04:07,550
If it's a cosmological constant, the Earth would still be here.

520
01:04:07,560 --> 01:04:10,720
Well, we'll still be bound. The galaxy will still exist.

521
01:04:11,040 --> 01:04:14,310
Our local group of galaxies will still be bound.

522
01:04:14,760 --> 01:04:18,120
But the other galaxies will expand away from us.

523
01:04:21,750 --> 01:04:26,100
You showed us a calculation based on elementary quantum field theory,

524
01:04:26,100 --> 01:04:31,680
which showed that the prediction for the accelerating universe was wrong by 220 orders of magnitude.

525
01:04:32,130 --> 01:04:35,700
Would you care to speculate why quantum theory goes so badly wrong?

526
01:04:36,710 --> 01:04:44,740
Because we don't understand nothing. So I no one knows the answer to that.

527
01:04:45,960 --> 01:04:54,460
Maybe there are other terms that cancel it, but it would have to be other terms that cancel it to 120 significant figures.

528
01:04:54,480 --> 01:04:58,430
It's hard to imagine that. I scratch my head about this.

529
01:04:58,440 --> 01:05:04,710
You know, this is something I thought about every night and it kept me up at night.

530
01:05:05,250 --> 01:05:15,540
So I became a dean so I could get some sleep. If you were forced to kind of give one of your wildest speculations, what would that be?

531
01:05:19,270 --> 01:05:28,240
Um, somehow. Well, there are various ideas that maybe the graviton is sort of fat and doesn't see nature on very small scales.

532
01:05:30,520 --> 01:05:40,300
Then there, when we talk about some of the crazy ideas that people have, but even it's a crazy thing that maybe we need a crazy idea to solve it.

533
01:05:43,710 --> 01:05:49,830
Any more questions? This one right at the back there in the middle of the row.

534
01:05:50,700 --> 01:06:01,370
Hardest place to get. One of your earlier slides, you talked about neutrinos,

535
01:06:02,360 --> 01:06:08,269
and I was lucky enough to go to Fermilab last year and go into the ethics of the Tevatron and also

536
01:06:08,270 --> 01:06:12,620
know that the versioning of the collider there is now being used as a neutrino factory or whatever.

537
01:06:12,860 --> 01:06:19,489
So what is neutrinos in what? Where does it fit in? Because there's a lot of money being put into neutrinos at the moment.

538
01:06:19,490 --> 01:06:25,520
And does this fit into your picture and why? Well, I think it's an important part of of nature.

539
01:06:25,520 --> 01:06:31,969
Neutrinos are and in cosmology, it's proof that a weekly interacting,

540
01:06:31,970 --> 01:06:39,080
massive particle that was produced in the early universe has a mass and contributes to the mass density.

541
01:06:39,710 --> 01:06:48,860
So one of the motivations of wimps is that could there be a really heavier version of the neutrinos we know that was sort of produced in the same way.

542
01:06:49,310 --> 01:06:54,320
That could be the dark matter. So that's the cosmological answer.

543
01:06:54,650 --> 01:07:01,760
And it also has an effect on detailed calculations of what we see in the microwave background radiation.

544
01:07:02,360 --> 01:07:08,720
But neutrinos are so important in understanding the generation of nuclear energy and stars how stars work,

545
01:07:09,560 --> 01:07:13,220
supernova lose their energy by producing neutrinos.

546
01:07:13,790 --> 01:07:21,890
We just can't ignore the neutrino. It's an important part of our understanding of nature and even the little neutrino.

547
01:07:23,230 --> 01:07:27,220
Enters into very large things like stars in supernovae.

548
01:07:29,890 --> 01:07:34,150
Yeah. One last question. Anybody on the side?

549
01:07:34,150 --> 01:07:37,780
We have another question from this. BLOCK it. Yeah, well, with slackers.

550
01:07:40,810 --> 01:07:43,530
Well, okay, we've got one question here. At least got to.

551
01:07:47,670 --> 01:07:55,860
So to the young cosmologists in the room who are starting to to study these problems, what's your best advice for a career in this field?

552
01:07:57,490 --> 01:08:05,470
Oh, my best my best advice about what you should do and stay in the future.

553
01:08:06,310 --> 01:08:14,080
Was the advice that was given, according to David Mamet, who's a he's from Chicago, a playwright.

554
01:08:14,080 --> 01:08:18,010
He wrote many plays and television scripts and things like that.

555
01:08:18,940 --> 01:08:21,130
He said that when you're a young playwright,

556
01:08:21,520 --> 01:08:28,720
someone will come up to you and give you advice and you must absolutely ignore everything that person tells you.

557
01:08:29,650 --> 01:08:38,440
So my advice to you is to ignore whatever you're told and do whatever makes your heart beat faster.

558
01:08:39,220 --> 01:08:43,780
You have to love what you do. If you do science, if you do physics.

559
01:08:43,780 --> 01:08:47,380
Because to me, it's not so easy. Maybe to others it's easy.

560
01:08:47,980 --> 01:08:51,300
And it's trying to plan ahead.

561
01:08:51,310 --> 01:08:56,080
My career. This will be a good thing for me to get a job. I don't think you can do that.

562
01:08:56,470 --> 01:09:03,720
I think just do what makes your heart beat faster. Well, that is a terrific note on which to end this lecture, so please join me.

563
01:09:03,730 --> 01:09:04,570
Thank you for offer.