Stephen Hawking, one of the most brilliant theoretical physicists in history, wrote the modern classic A Brief History of Time to help nonscientists understand the questions being asked by scientists today: Where did the universe come from? How and why did it begin? Will it come to an end, and if so, how? Hawking attempts to reveal these questions (and where we’re looking for answers) using a minimum of technical jargon. Among the topics gracefully covered are gravity, black holes, the Big Bang, the nature of time, and physicists’ search for a grand unifying theory. This is deep science; these concepts are so vast (or so tiny) as to cause vertigo while reading, and one can’t help but marvel at Hawking’s ability to synthesize this difficult subject for people not used to thinking about things like alternate dimensions. The journey is certainly worth taking, for, as Hawking says, the reward of understanding the universe may be a glimpse of “the mind of God.” –Therese Littleton …… [More…. Science Leads to God [ ……….]
He was just so famous, an icon, and I found it hard to imagine that his contributions to physics were really proportional to his fame. There’s just something about a guy who speaks in a computer voice that automatically makes him sound like a genius. Like someone who knows things no mortal human could ever know. The late physicist’s radical ideas are still changing the way we look at the cosmos.
Not that I was immune to his celebrity. I was fortunate to have met Hawking on a few occasions, at physics conferences I was attending as a journalist. Once, during a lecture, I found myself sitting directly behind him. I tried my best to pay attention to the speaker, but I was mesmerized by the words flashing across the computer screen mounted to the arm of Hawking’s wheelchair. Paralyzed by a motor neuron disease, Hawking had one last functioning muscle in his cheek, and by twitching it he could control the cursor on his monitor. The cursor constantly scrolled though a catalog of his most commonly used words, and with a properly timed twitch he could select one from the list, slowly and arduously building up sentences for that oracular voice to deliver. In his otherworldly presence, I couldn’t help thinking those sentences contained the answers to the universe.
Universe Science and Quran
Later I learned about Hawking’s work. I learned that in the 1970s he had performed a remarkable calculation, in an attempt to disprove the work of another physicist who had annoyed him. The result ended up proving three things. First, that revenge is an excellent fuel for genius. Second, that I was a moron, because if anything, Hawking is underrated. His physics was brilliant and the only thing that was disproportionate was the fact that everyone has heard of Stephen Hawking but few people know what he really did that was so great. Something about black holes? The universe? Time? The profound meaning of his work is all too often overlooked. The meaning, that is, of the third thing he proved: that particles are not ultimately real.Physicists define something as “real”—truly, ultimately, fundamentally real—if it remains invariant across reference frames. If that sounds abstract, it’s not—in fact, it’s how normal people define reality, too. Say you suddenly see a purple elephant in the corner of the room. You might wonder whether the elephant is really there or if you’re having some kind of breakdown. Instinctively, you know there are two ways to find out. The first is to get up, walk over to the elephant and tread a careful circle around it, viewing it from every angle, eyeing it suspiciously. If at some angle it disappears, you’ll know it was more likely a mirage than a mammal. The other strategy is to turn to the guy next to you and ask, “Do you see an elephant?” If he says no (or stares at you blankly), you’ll probably want to call a neurologist. Because you know, intuitively, that something is only real if it persists in every point of view. Just because something’s not ultimately real doesn’t mean it’s a hallucination. Take a rainbow. Is it real? Not really. It’s not a hallucination, but it’s also not a physical object hanging in the sky. You can’t go touch it because it’s a product of your reference frame, a lucky confluence of circumstance, your standing in the right place at the right time with the sun streaming in from behind you and the light being refracted by the moisture in the air. Ask the guy next to you, “Do you see that rainbow?” and he’ll probably say yes, but run the test of walking around it, and you’ll see it disappear. Its existence is dependent on your reference frame. It’s a product of physics, but it’s not invariant. If you want to find the fundamental ingredients of ultimate reality, you have to find the invariants.Particles always seemed like good candidates. After all, they comprise all the stuff in the universe. They give things heft and solidity and object-hood. They’re the reason there are things at all.But Hawking’s calculation suggested otherwise.To appreciate what Hawking did, there’s one more thing you need to know. According to quantum mechanics, empty space isn’t really empty. The so-called uncertainty principle tells us that there’s a trade-off between time and energy—the more defined the one, the vaguer the other. That means that on very short timescales—fractions of fractions of fractions of seconds—large amounts of energy can (and do) bubble up out of empty space. To ensure it’s all paid back in full, the energy manifests as pairs of particles and antiparticles, which, in the blink of an eye, will collide and annihilate, the existence of one canceling out the existence of the other, returning the energy back to the emptiness from whence it came. This cycle of creation and destruction is happening all the time, right now, all around us, particles emerging in pairs and disappearing, but it all happens so quickly that we call them “virtual particles”—not because they’re fundamentally different from ordinary particles, but because they don’t stick around long enough to count. Hawking realized that something different—something profound—happens when virtual particle pairs arise in the presence of an event horizon. An event horizon marks an edge beyond which light can’t reach an observer, rendering the far side of the horizon fatefully dark. A black hole, for instance, is surrounded by an event horizon, the edge beyond which light can’t escape gravity’s clutches to reach an external observer.When a pair of virtual particles bubble up out of empty space near a horizon, something extraordinary happens. The horizon can separate the pairs, so that while one particle travels out into the universe, its partner falls behind the horizon into the black hole. Now they can’t annihilate, so instead of disappearing, they just stick around. The virtual particles are no longer virtual. They’re real—as real as any other particle. You could collect a bunch of them and build a chair.But there would be something really weird about that chair. It would owe its very existence to the horizon—but the horizon is not like a brick wall sitting in space, blocking the light. A horizon is like a rainbow. It’s a feature of certain reference frames, namely the reference frame of the observer who is lucky enough not to fall into the black hole. Most textbooks call him Bob, but I like to call him Safe. There’s another kind of an observer who is not so lucky. An observer in inertial free fall cannot escape the black hole’s gravity; he falls straight through the horizon into dark. I like to call him Screwed. From Safe’s point of view, particles that can no longer be annihilated are streaming out from the horizon, as if the black hole is radiating. But for Screwed, the horizon doesn’t exist. He falls straight through it. And without a horizon to separate them, the virtual particles and antiparticles, from Screwed’s point of view, continue to annihilate as usual, so that where Safe sees a stream of particles, Screwed sees nothing but empty space.That difference in what these two observers see means everything. It means that the particles are not invariant. Hawking’s discovery was as radical as it was monumental: Particles aren’t ultimately real. He showed that the very meaning of a particle, its existence, depends on your reference frame, not only in the vicinity of a black hole but everywhere, because every one of us is surrounded by a horizon.We live in a universe that’s expanding at an accelerated rate, faraway galaxies being pushed out of our field of vision at speeds proportional to their distance. Their light tries to reach us, but space-time just keeps growing, preventing the light from covering any ground. Far from here, the space-time grows faster than the light, trapping it there, a light beam on a treadmill; it will never reach us, no matter how long we wait. The boundary separating the light that will reach us from the light that won’t is an event horizon, precisely of the kind you’d find around a black hole. Because each of us occupies a unique point in space, we each have our own unique horizon. Technically speaking, every one of us is Screwed. Not to be morbid, but all the light in the universe will eventually be swept away by the expansion of space-time, and we’ll be left here in the dark, our Milky Way a lonely beacon in a swelling, spreading nothing. Of course, if we were out there, in one of those distant galaxies falling off the edge of the universe, everything would seem just fine. From their perspective, we’d be the ones exiting the observable universe at light speed, and they’d be left alone in the void. The point is, every one of us lives in a region of space-time delineated by a cosmic horizon, and that horizon defines what we mean by a particle, and whether or not one exists, not only out there at the horizon’s edge, but here right in front of us, too.When Hawking set out to do his calculation, his disease had already made it impossible for him to write out long equations by hand, and he was forced to do it all in his head. That inspired him to think about things in a totally new way—to think not in numbers but in shapes. In geometry. He saw, in his mind’s eye, how event horizons affect the entire space-time they bind—he saw how they determine the symmetries of the whole space-time, which in turn determine what we mean by a vacuum and what we mean by a particle. He saw this grand, global picture, which changed everything, and he attributed it, in part, to his illness, which he once said was the best thing that ever happened to him.It’s no exaggeration to say that Hawking’s discovery has driven, and continues to drive, theoretical physics forward for the last four decades. It’s because the three great pillars of physics—general relativity, quantum mechanics and thermodynamics—all collide in his brilliant calculation, pointing the way toward some deeper unified theory. And it’s because it’s rife with paradoxes, and there’s nothing better for physics than a paradox forcing you to question your most basic assumptions about the world. Finally, it’s because Hawking’s discovery that the very building blocks of that world, of everything we see around us, of us, are not ultimately real has forced us to ask, well, what is? The truth is, no one knows. The search for reality continues, but it was Hawking who blazed the trail. He—and his physics—deserve to be better known.
A Brief History of Time – By Stephen Hawkings
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- How did the universe begin—and what made its start possible?
- Does time always flow forward? Is the universe unending—or are there boundaries?
- Are there other dimensions in space?
- What will happen when it all ends?
Stephen Hawking, one of the most brilliant theoretical physicists in history, wrote the modern classic A Brief History of Time to help nonscientists understand the questions being asked by scientists today: Where did the universe come from? How and why did it begin? Will it come to an end, and if so, how? Hawking attempts to reveal these questions (and where we’re looking for answers) using a minimum of technical jargon. Among the topics gracefully covered are gravity, black holes, the Big Bang, the nature of time, and physicists’ search for a grand unifying theory. This is deep science; these concepts are so vast (or so tiny) as to cause vertigo while reading, and one can’t help but marvel at Hawking’s ability to synthesize this difficult subject for people not used to thinking about things like alternate dimensions. The journey is certainly worth taking, for, as Hawking says, the reward of understanding the universe may be a glimpse of “the mind of God.” –Therese Littleton
“Master of the Universe… One scientist’s courageous voyage to the frontiers of the Cosmos” Newsweek “This book marries a child’s wonder to a genius’s intellect. We journey into Hawking’s universe, while marvelling at his mind” The Sunday Times “He can explain the complexities of cosmological physics with an engaging combination of clarity and wit… His is a brain of extraordinary power” Observer “To follow such a fine mind as it exposes such great problems is an exciting experience” The Sunday Times “One of the most brilliant scientific minds since Einstein” Daily Express
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About the Author
Stephen Hawking held the post of Lucasian Professor of Mathematics and Theoretical Physics at Cambridge, the chair held by Isaac Newton in 1663, for thirty years. Professor Hawking is now Director of Research for the Centre for Theoretical Cosmology at the University of Cambridge. He has over a dozen honorary degrees, and was awarded the Companion of Honour in 1989. He is a fellow of the Royal Society and a Member of the US National Academy of Science. His books include the bestselling Black Holes and Baby Universes and Other Essays, The Universe in a Nutshell, and A Briefer History of Time. His most recent book, The Grand Design, was a Sunday Times bestseller. Stephen Hawking is regarded as one of the most brilliant theoretical physicists since Einstein. He lives in Cambridge.
OUR PICTURE OF THE UNIVERSE
Most people would find the picture of our universe as an infinite tower of tortoises rather ridiculous, but why do we think we know better? What do we know about the universe, and how do we know it? Where did the universe come from, and where is it going? Did the universe have a beginning, and if so, what happened before then? What is the nature of time? Will it ever come to an end? Can we go back in time? Recent breakthroughs in physics, made possible in part by fantastic new technologies, suggest answers to some of these longstanding questions. Someday these answers may seem as obvious to us as the earth orbiting the sun–or perhaps as ridiculous as a tower of tortoises. Only time (whatever that may be) will tell.
Ptolemy’s model provided a reasonably accurate system for predicting the positions of heavenly bodies in the sky. But in order to predict these positions correctly, Ptolemy had to make an assumption that the moon followed a path that sometimes brought it twice as close to the earth as at other times. And that meant that the moon ought sometimes to appear twice as big as at other times! Ptolemy recognized this flaw, but nevertheless his model was generally, although not universally, accepted. It was adopted by the Christian church as the picture of the universe that was in accordance with Scripture, for it had the great advantage that it left lots of room outside the sphere of fixed stars for heaven and hell.
A simpler model, however, was proposed in 1514 by a Polish priest, Nicholas Copernicus. (At first, perhaps for fear of being branded a heretic by his church, Copernicus circulated his model anonymously.) His idea was that the sun was stationary at the center and that the earth and the planets moved in circular orbits around the sun. Nearly a century passed before this idea was taken seriously. Then two astronomers–the German, Johannes Kepler, and the Italian, Galileo Galilei–started publicly to support the Copernican theory, despite the fact that the orbits it predicted did not quite match the ones observed. The death blow to the Aristotelian/Ptolemaic theory came in 1609. In that year, Galileo started observing the night sky with a telescope, which had just been invented. When he looked at the planet Jupiter, Galileo found that it was accompanied by several small satellites or moons that orbited around it. This implied that everything did not have to orbit directly around the earth, as Aristotle and Ptolemy had thought. (It was, of course, still possible to believe that the earth was stationary at the center of the universe and that the moons of Jupiter moved on extremely complicated paths around the earth, giving the appearance that they orbited Jupiter. However, Copernicus’s theory was much simpler.) At the same time, Johannes Kepler had modified Copernicus’s theory, suggesting that the planets moved not in circles but in ellipses (an ellipse is an elongated circle). The predictions now finally matched the observations.
The Copernican model got rid of Ptolemy’s celestial spheres, and with them, the idea that the universe had a natural boundary. Since “fixed stars” did not appear to change their positions apart from a rotation across the sky caused by the earth spinning on its axis, it became natural to suppose that the fixed stars were objects like our sun but very much farther away.
Newton realized that, according to his theory of gravity, the stars should attract each other, so it seemed they could not remain essentially motionless. Would they not all fall together at some point? In a letter in 1691 to Richard Bentley, another leading thinker of his day, Newton argued that his would indeed happen if there were only a finite number of stars distributed over a finite region of space. But he reasoned that if, on the other hand, there were an infinite number of stars, distributed more or less uniformly over infinite space, this would not happen, because there would not be any central point for them to fall to.
This argument is an instance of the pitfalls that you can encounter in talking about infinity. In an infinite universe, every point can be regarded as the center, because every point has an infinite number of stars on each side of it. The correct approach, it was realized only much later, is to consider the finite situation, in which the stars all fall in on each other, and then to ask how things change if one adds more stars roughly uniformly distributed outside this region. According to Newton’s law, the extra stars would make no difference at all to the original ones on average, so the stars would fall in just as fast. We can add as many stars as we like, but they will still always collapse in on themselves. We now know it is impossible to have an infinite static model of the universe in which gravity is always attractive.