Cosmologists

"We do not know why we are born into the world, but we can try to find out what sort of a world it is — at least in its physical aspects."

"The whole thing is so much bigger than I am, and I can't understand it, so I just trust myself to it; and forget about it."

"...there must be no favored location in the universe, no center, no boundary; all must see the universe alike. And, in order to ensure this situation, the cosmologist postulates spatial isotropy and spatial homogeneity."

"The history of astronomy is a history of receding horizons."

"Eventually, we reach the utmost limits of our telescopes. There, we measure shadows and search among ghostly errors of measurement for landmarks that are scarcely more substantial."

"Science is the one human activity that is truly progressive."

"Equipped with his five senses, man explores the universe around him and calls the adventure Science."

"But sometimes reality chooses not to conform to our preferences."

"What we can’t do is demand that the universe scratch our explanatory itches. Curiosity is a virtue, and it’s good to look for answers to “Why?” questions whenever we might be able to find them, or when we think that asking such questions might help us to understand things better. But we should be at peace with the possibility that, for some questions, the answer doesn’t go any deeper than “That’s what it is.” We’re not used to that—our intuition assures us that every event can be explained in terms of some reason why. To understand why we have that impression, we need to dig more deeply into how our actual universe has evolved."

"The “reasons” and “causes” why things happen, in other words, aren’t fundamental; they are emergent. We need to dig in to the actual history of the universe to see why these concepts have emerged."

"Metaphysical principles are tempting shortcuts but not reliable guides. There are good reasons why things often seem to happen for reasons—and also reasons why that’s not a bedrock principle."

"The momentary or Laplacian nature of physical evolution doesn’t have much relevance for the choices we face in our everyday lives. For poetic naturalism, the situation is clear. There is one way of talking about the universe that describes it as elementary particles or quantum states, in which Laplace holds sway and what happens next depends only on the state of the system right now."

"What we’re seeing is a manifestation of the layered nature of our descriptions of reality. At the deepest level we currently know about, the basic notions are things like “spacetime,” “quantum fields,” “equations of motion,” and “interactions.” No causes, whether material, formal, efficient, or final. But there are levels on top of that, where the vocabulary changes."

"Poetic naturalism is a philosophy of freedom and responsibility. The raw materials of life are given to us by the natural world, and we must work to understand them and accept the consequences. The move from description to prescription, from saying what happens to passing judgment on what should happen, is a creative one, a fundamentally human act. The world is just the world, unfolding according to the patterns of nature, free of any judgmental attributes. The world exists; beauty and goodness are things that we bring to it."

"Meaning in life can’t be reduced to simplistic mottos. In some number of years I will be dead; some memory of my time here on Earth may linger, but I won’t be around to savor it."

"The broader ontology typically associated with atheism is naturalism—there is only one world, the natural world, exhibiting patterns we call the “laws of nature,” and which is discoverable by the methods of science and empirical investigation. There is no separate realm of the supernatural, spiritual, or divine; nor is there any cosmic teleology or transcendent purpose inherent in the nature of the universe or in human life. “Life” and “consciousness” do not denote essences distinct from matter; they are ways of talking about phenomena that emerge from the interplay of extraordinarily complex systems. Purpose and meaning in life arise through fundamentally human acts of creation, rather than being derived from anything outside ourselves. Naturalism is a philosophy of unity and patterns, describing all of reality as a seamless web."

"... I just want to understand the large-scale story that string gas cosmology is trying to sell us. We have nine dimensions of space — they are all very small — and in three dimensions they start unwinding and getting bigger. Is that the basic idea?"

"People don't like to read papers — they like to read titles."

"But the very fact that matter in the cosmos is still moving, rather than at rest, is the single most surprising thing about the universe."

"When exactly does an observation occur? ... What were the laws of physics doing before there was anyone measuring things? And what do you mean by a measurement, anyway? Does it have to be a consciousness human being? ... Can a rock or a virus or an earthworm do an observation?"

"All of my advice comes from remembering what I did wrong and then telling people not to do it. ... Don't wait to read the most recent research papers. ... Wonder how you could do better. ... Do your own research projects. Take the initiative. ... Ask your own questions — try to answer them. ... At some point you stop being a student and you start being a scientist. ... And it's a completely different skill set ...""

"There probably are more forces than we know about, but they’re only going to be of direct interest to physicists, I’m afraid. No tractor beams."

"Inflation is a simple idea: imagine that the universe begins in a tiny patch of space dominated by the potential energy of some scalar field, a kind of super-dense dark energy. This causes that patch to expand at a terrifically accelerated rate, smoothing out the density and diluting away any unwanted relics. Eventually the scalar field decays into ordinary matter and radiation, reheating the universe into a conventional Big Bang state, after which things proceed as normal."

"The mystery of the arrow of time comes down to this: Why were the conditions in the early universe set up in a particular way, in a configuration of low entropy that enabled all of the interesting and irreversible processes to come?"

"In contrast to the arbitrarily complicated evolution of a (nonintegrable) classical system, all a quantum state ever does is move in circles."

"Even if we don't know the answer, a change of perspective can help us improve the question."

"It can't be stressed enough that the multiverse is utterly hypothetical—but that doesn't mean it isn't real."

"The amazing thing is that every atom in your body came from a star that exploded, and the atoms in your left hand probably came from a different star than your right hand. It really is the most poetic thing I know about physics. You are all stardust. You couldn’t be here if stars hadn’t exploded because the elements—the carbon, nitrogen, oxygen, iron, all the things that matter for evolution—weren’t created at the beginning of time. They were created in the nuclear furnaces of stars, and the only way they could get... into your body is if these stars were kind enough to explode. So, forget Jesus. The stars died so that you could be here today."

"There's a loophole if you weigh galaxies and clusters because you're weighing the total amount of energy around galaxies. What if there's energy where galaxies aren't? What is where galaxies aren't? Nothing."

"[W]e can weigh systems of galaxies. The largest bound objects in the universe are called clusters of galaxies. They're maybe ten million light years across. ...We weigh them using gravity because Einstein told us that mass curves space, and we can... use those large clusters as lenses—if there's a light source behind a cluster the light from it can come around and be lensed... and we've weighed these systems and we've found that there's only 30% of the mass needed to make a flat universe... Theorists like me knew that the universe was flat, because it's the only mathematically beautiful universe... but here these observers kept coming up with only 30% of the stuff needed... But then, what we've discovered... is that the universe actually is flat and the rest of the 70% of the energy of the flat universe comes from the energy of nothing."

"[W]hy presumes purpose... But what if there isn't purpose? Whenever we say why we really mean how."

"[Y]ou... may say, "Well look, we've got no space, no time, no particles, no radiation. That's a pretty good approximation of nothing, but there's still the laws. Who created the laws? And... what we've discovered... in the last ten years or so, and... this is speculative, but it's based on everything we know of in particle physics... It's quite reasonable to suspect that even the laws themselves came into existence when our universe came into existence... There could be many different universes and in each one of them the laws of physics are different. They spontaneously arise when the universe arises."

"[W]hen you apply quantum mechanics to gravity, then even space itself can pop into existence from nothing. Space and time can spontaneously pop into existence... Whole universes can pop into existence and most of them will disappear in a time scale so short you wouldn't know about it. The ones that can survive for a long time have zero total energy..."

"Now some people say, "Well, if there's virtual particles there it's really not nothing," but there are no real particles. You try and measure things there, there's nothing, but those virtual particles can give space energy and in fact we've discovered to our great surprise—it won the Nobel prize two years ago—that empty space has energy, and if you put energy in empty space, then it's really strange because it's not like the normal energy... it's not gravitationally attractive, it's actually repulsive, and we've discovered the expansion of the universe is not slowing down like any sensible universe should do. It's actually speeding up... because it's dominated by the energy of empty space."

"[O]ne of the great things about science is it forces us to refine our idea of what's common sense. It forces us to have our beliefs conform to the evidence of reality rather than the other way around. The universe may not be like we'd like it to be, but it doesn't really care."

"The energy of every galaxy—all the galaxies are moving away from us at, Hubble discovered that in 1929... If you measure their speed and then you work our the attraction the two add up to precisely zero. An amazing discovery that confirms this notion that, not only is the universe flat and mathematically beautiful, but begins to give us an inkling that maybe, maybe, maybe we could come from nothing."

"But what we've discovered is that, in fact... the total energy of the universe could be zero, which is a first clue that maybe it could come from nothing. ...In physics, ...once you include gravity, there's positive energy and negative energy, and our universe appears as if its total energy could be precisely zero, which is the first hint that maybe it could come from nothing. That, and the great discovery... that namely empty space, you take a region of space, get rid of all the particles and all the radiation ...so there's nothing there. That empty space weighs something, and we don't understand why."

"Richard Feynman used to go up to people all the time and he'd say, "You won't believe what happened to me today. You won't believe what happened to me." And people would say "What?" And he'd say, "Absolutely nothing". Because we humans believe that everything that happens to us is special, and significant. And that—and... Carl Sagan wrote beautifully about that in Demon-Haunted World—that is much of the source of religion. OK? Everything that happens is unusual, and I expect that the likelihood that Richard and I ever would've met—if you think about all the variables, the probability that we were in the same place at the same time, ate breakfast at the same... Whatever. It's zero. Every event that happens has small probability... but it happens, and then when it happens; if it's weird, if you dream one million nights and it's nonsense, but one night you dream that your friend is gonna break his leg and the next day he breaks his arm. You think, "ah." ...So the [real] thing that physics tell us about the universe is it's big, rare events happen all the time—including life—and that doesn't mean it's special."

"What's going to happen in the far future? Remember a hundred years ago we thought we lived into static eternal Universe. What will the future bring? The amazing thing is, for civilizations that live in a far future, what will they see? Well, the Universe is accelerating. That means all the distant galaxies are getting carried away from us, and eventually they'll move away from us faster than the speed of light. It's allowed in General relativity. They will disappear. The longer we wait, the less we will see. In a hundred billion years any observers evolving on stars around [us]... and there will be stars just like our Sun in 100 billion years. Any observers and civilizations... evolving around those stars will see nothing except for our Galaxy, which is exactly the picture they had in 1915. All evidence of the Hubble expansion will disappear. Why? Because we won't see other galaxies moving apart from us. So they will have no evidence, in fact, of Big Bang. They won't see the Hubble expansion. They won't even know about dark energy, and I won't go into that. They won't know about the cosmic microwave background - it will disappear too. It will redshift away, and it turns out for fancy reasons: there is a plasma in our Galaxy and when the Universe is 50 times its present age the microwave background won't able to propagate in our Galaxy. All evidence of the Big Bang will have disappeared, and those scientists will discover quantum mechanics, discover relativity, discover evolution, discover all the basic principles of science that we understand today, use the best observations they can do with the best telescopes they will build and they will derive a picture of the Universe which is completely wrong. They will derive a picture of the Universe as being one Galaxy surrounded by empty space that's static and eternal. Falsifiable science will produce the wrong answer. In fact, I want to end with the good news. We live in a very special time, the only time we can observationally verify that we live in a very special time."

"The Universe must be flat. Why? Well, there is two reasons. There's the one I normally say, which is: it's the only mathematically beautiful universe. Which is true, but there's another reason I don't usually... talk about but I'll talk about here. It turns out that in a flat universe the total energy of the universe is precisely zero because gravity can have negative energy. So the negative energy of gravity balances out the positive energy of matter. What's so beautiful about a universe with total energy zero? Well, only such a universe can begin from nothing, and that is remarkable because the laws of physics allow a universe to begin from nothing. You don't need a Deity. You have nothing: zero total energy, and quantum fluctuations can produce a universe. So, if the Universe isn't flat we're worried, because then you've got energy at... the very beginning of Time."

"Science is empirical: knowing the answer is nothing. Testing your knowledge means everything."

"Theorists always know the answer. They're just sometimes right."

"... we're here because of an environmental accident if there is a multiverse and if the laws of physics are different in the different regions ..."

"We only see shadows of reality. We shouldn't expect those shadows to behave sensibly."

"It is a shame when nonsense can substitute for fact with impunity."

"The other thing people don't realise about science which differentiates it from religion is that, the most exciting thing about being a scientist is not knowing and being wrong. Because that means there is a lot left to learn."

"Science simply forces us to revise what is sensible to accommodate the universe, rather than vice versa."

"If you have nothing in quantum mechanics, you will always have something."

"Now, since the time of Newton there had been a debate about whether light was a wave---that is, a traveling disturbance in some background medium---or a particle, which travels regardless of the presence of a background medium. The observation of Maxwell that electromagnetic waves must exist and that their speed was identical to that of light ended the debate: light was an electromagnetic wave."

"There is a maxim about the universe which I always tell my students: That which is not explicitly forbidden is guaranteed to occur."