This diagram shows two spiral-shaped vortexes (yellow) of whirling space sticking out of a black hole, plus the vortex lines (red curves) that form the vortexes.
By Alan Boyle, Science Editor, NBC News
No one's ever seen a black hole up close, but physicists can nevertheless visualize how two colliding black holes send ripples through space-time like waves on the ocean. They've even invented a new word — "tendex" — to describe the lines of force that stretch the objects caught in a space-time warp.
A research paper published online this week in Physical Review Letters delves into the effects of black hole collisions in unprecedented detail. "We've found ways to visualize warped space-time like never before," Caltech theoretical physicist Kip Thorne said in a news release.
Thorne and his colleagues at Caltech, Cornell University and the National Institute for Theoretical Physics in South Africa combined theory and computer simulations to describe the beautiful patterns of gravitation force lines emanating from black holes. Such lines are analogous to the invisible field lines created by electromagnetic forces.
In some scenarios, warping space-time creates swirls of force lines that twist around each other in a region of space called a vortex. "Anything that falls into a vortex gets spun around and around," said Cornell physicist Robert Owen, the paper's lead author. An astronaut falling through a gravitational vortex would be wrung out like a wet towel.
Caltech/Cornell SXS Collaboration
In this simulation, two doughnut-shaped vortexes are ejected by a pulsating black hole. Also shown at the center are two red and two blue vortex lines attached to the hole, which will be ejected as a third doughnut-shaped vortex in the next pulsation.
Tendex lines describe the stretching effect of a strong gravitational field. "Tendex lines sticking out of the moon raise the tides on the earth's oceans," said David Nichols, the Caltech graduate student who coined the term. When many such lines are bunched together, as in the surroundings of a black hole, that creates a super-stretching region called a tendex. An astronaut passing through a tidal tendex would be pulled apart like taffy — an effect sometimes known as "spaghettification."
The researchers contend that the vortex and tendex concepts can lead to a clearer understanding of black hole collision modeling. If two black holes smash into each other head-on, that creates doughnut-shaped vortexes and tendexes that emanate from the merged black hole like smoke rings. But if the black holes spiral in toward each other before merging, the field lines swirl outward like sprays of water from a rotating sprinkler.
Whether they're more like smoke rings or sprinkler jets, the force lines create gravitational waves — the kinds of waves that the Laser Interferometer Gravitational-Wave Observatory, or LIGO, has been built to detect. "With these tendexes and vortexes, we may be able to much more easily predict the waveforms of the gravitational waves that LIGO is searching for," said Caltech physicist Yanbei Chen.
The researchers suggest that the vortex-tendex model could explain a theoretical phenomenon that other physicists noticed three years ago: Using computer models, the Rochester Institute of Technology's Manuela Campanelli and her colleagues found that a black hole collision could result in a gravitational kick so powerful that the merged black hole is thrown out of its galaxy. The newly published paper proposes that gravitational waves from spiraling vortexes and tendexes are added together on one side of the black hole, but cancel out each other on the other side. The result would be a burst of waves in one direction, creating the kick.
"Though we've developed these tools for black hole collisions, they can be applied wherever space-time is warped," said Cornell's Geoffrey Lovelace. "For instance, I expect that people will apply vortex and tendex lines to cosmology, to black holes ripping apart, and to the singularities that live inside black holes. They'll become standard tools throughout general relativity."
Columbia physicist Brian Greene inhabits a multiple-perspective landscape modeled after M.C. Escher's artwork in a scene from the NOVA series based on his 1999 best-seller, "The Elegant Universe." Greene says his latest book, "The Hidden Reality," ranges over an even broader cosmic canvas. Click on the image to watch the NOVA program.
By Alan Boyle, Science Editor, NBC News
Is it preposterous to consider the existence of parallel universes? Or is it preposterous not to? Physicist Brian Greene would tend toward the latter view.
Those works presented step-by-step guides to string theory and space-time, respectively, leavened with pop-culture references and analogies drawn from everyday life (that is, if your idea of "everyday life" involves watching ants crawl on a power line). "The Hidden Reality" follows a similar formula, using slices of bread, "South Park" and the Wizard of Oz to explain weird ideas such as brane theory, the inflaton field and the holographic universe.
Greene doesn't explain just one scenario in which unreachable universes co-exist alongside our own. He delves into nine possibilities, drawn from different corners of scientific speculation. Is that too much speculation? Some folks think so.
Scientific American's John Horgan wrote that he used to get fired up over the idea that our universe was just one of many making up a grander "multiverse." But not anymore:
"Now, multiverse theories strike me as not only unscientific but also immoral, for two basic reasons: First, at a time when we desperately need science to help us solve our problems, it's irresponsible for scientists as prominent as Greene to show such a blithe disregard for basic standards of evidence. Second, like religious visions of paradise, multiverses represent an escapist distraction from our world."
"My own moral concerns about the multiverse have more to do with worry that pseudo-science is being heavily promoted to the public, leading to the danger that it will ultimately take over from science, first in the field of fundamental physics, then perhaps spreading to others."
As a string theorist, Greene is used to such criticism. Like parallel universes, the idea that matter's fundamental building blocks are tiny vibrating strings or multidimensional membranes has often been knocked as unprovable, unverifiable, unfalsifiable speculation. Lawrence Krauss, a theoretical physicist at Arizona State University, is fond of saying that string theory's vision of a "theory of everything" is actually a "theory of anything" that turns out being a "theory of nothing."
"That's provocative nonsense," Greene told me last week. Theorists are not just pulling this stuff out of thin air, he said. Rather, they're being led to seemingly wild conclusions while working within what he called "the tight straitjacket of mathematics."
"The Hidden Reality" is Columbia physicist Brian Greene's latest literary excursion to the frontiers of physics. Click on the image to read an excerpt.
In a telephone interview conducted during his book tour, Greene addressed the suggestion that multiverse theory was an empty exercise, and explained why scientists have to take parallel universes seriously. Take a look at this edited transcript of the Q&A, read an excerpt from the book, and then let me know what you think in the comment space below:
Cosmic Log: Some people have said, "Oh, no, not another book about the multiverse ... all these things we can't see, all these claims that we can't prove. Why do we need another book about this subject when there have been so many already? And isn't it all speculation anyway?"
Brian Greene: Well, when we are doing mathematical investigations in physics, we as theorists allow the math to take us where it will go. We have seen, time and again, that math is a very potent guide to revealing the true nature of reality. That's what the past couple of hundred years have established. So all we're doing is following the same kinds of procedures that we always have. And as we follow the procedures, as we push the mathematics forward, the math is clearly suggesting that there may be other universes out there.
That does not mean that there are. It does mean, however, that there's a compelling enough reason to take these ideas seriously, develop them further, and try to make contact with observation and experiment. I fully agree that none of these hypothetical ideas can be put within the canon of established physics until there is some kind of observational confirmation. But you can't get to that point unless you understand the theories extraordinarily well. And that's what a lot of cutting-edge physics is now doing.
Q: In your book you talk about several types of parallel universes. What do you mean by the term? Often people have the conception of traveling back in time, or living in a quantum world where you're having a drink at a bar and yet not having a drink. In the TV series "Fringe," there are parallel universes in conflict with each other. People have a lot of conceptions about what a parallel universe means, but what does it mean to a scientist?
A: We have for a long time had a conception of what a "universe" is. Look out at the cosmos, and it's the totality of the stars and the galaxies that are out there, everything that we in principle can see. But we have learned, through a variety of approaches in physics, that that notion of "everything" is possibly a small part of a far larger cosmos, a far grander reality.
I like to make this concrete with a simple example that I think helps ground the physics about this. We all know about the big bang, which is basically how our universe got started. The universe was very small in the distant past, it underwent a rapid expansion, and in the course of that expansion, the universe cooled down and allowed matter to coalesce into stars and galaxies.
Now, many people don't fully appreciate that this story of the big bang leaves out something very important: It leaves out the "bang." It leaves out the physical process that started the outward swelling of space in the first place. As we have developed mathematical tools to fill in that gap, to really understand what happened at the beginning, the math has indicated that the big bang may not have been a unique event. There may have been, and may continue to be, many big bangs — each of which gives rise to its own expanding universe, our universe being but one among many. In that sense, we are part of a multiverse.
Q: One of the more provocative ideas that you put forward in your book is the suggestion that there could be other versions of Brian Greene or Alan Boyle that are just slightly off, existing in some other quadrant of the multiverse. Have you gotten some raised eyebrows over that?
A: Well, it's a staggeringly strange idea, but again, we need to emphasize that it doesn't emerge from some scientist sitting in a dark room and letting his imagination run wild. This idea comes from the notion that the expanse of space goes on forever — that it's infinitely large. That's an idea that people have contemplated for a long time. In fact, I would say that the majority of physicists and astronomers, when they speak about space, they do envision it going on forever. Then it takes but a simple little mathematical exercise to establish that, in any finite region of space, matter can only arrange itself in finitely many configurations.
The analogy I like to use is a deck of cards. When you shuffle the deck, the cards come out in different orders, but there are only finitely many different orders of the cards. If you shuffle that deck infinitely many times, the orders necessarily will repeat. Similarly, in an infinite spatial universe, the arrangements of particles have to repeat, too. If they repeat, then indeed, things that we are familiar within the world around us — you, me, Earth, the sun, everything else — would repeat as well.
When one explains this idea to someone who hasn't heard it before, it is shocking at first — you're absolutely right. But when one takes in the mathematical argument and mulls it over, it becomes clear this is what would happen.
Q: That's just one of the nine options suggested for the existence of parallel universes. Do you have a favorite scenario?
A: It depends on how you measure the "favorites." The measure I'm most fond of is, "Which of these stands the greatest chance of receiving some experimental support in the not-too-distant future?" By that measure, I like to focus on the "brane multiverse" theory. That's this idea that string theory doesn't just contain strings. It also contains membranes — two-dimensional objects — and three-branes, which are three-dimensional objects, and so forth.
The brane multiverse imagines that all we have thought to be the universe actually takes place on one of these three-branes, with other three-branes potentially out there. The analogy I like to use is a loaf of bread, where our universe is one slice, but there are other slices out there populating this grander cosmos. And this idea of a brane multiverse can be tested at the Large Hadron Collider.
When you have powerful proton collisions, the math suggests that some of the debris from those collisions can be ejected off our brane, and we would notice that by virtue of having less energy after the collision than before — because the debris would take some of the energy away with it. People are looking for these kinds of missing-energy signatures. If the results prove positive — which, I absolutely need to underscore, I consider a long shot — then it would be evidence that we are living on one of these branes. If we are living on a brane, then there's really no reason to anticipate that our brane would be the only one. There would be other branes out there, other universes.
Q: What energy level would be required to see that sort of evidence?
A: It all depends on the size of the extra dimensions within which all these branes would be embedded. If the extra dimensions are very small, it takes increasingly large amounts of energy to get debris from the collisions to leave our brane and go into this tiny extradimensional space.
That's the unknown: If the dimensions are big enough, then the energies required would be within reach of the Large Hadron Collider. If the extra dimensions are small, then the Large Hadron Collider would not be able to cause this process to happen. So the best we can do is get some evidence that confirms the brane multiverse idea. It's pretty hard to get evidence that would flatly rule it out.
There's one point I want to get out about the book: It's not a "multiverse manifesto." It's not trying to say, "Look at this wonderful idea, and it's true." No. I'm saying, "Look at this curious idea that many leading scientists are thinking about" — including me, I do work on this stuff right now. Let's ask ourselves, "What's this all about? What's the mathematical motivation for thinking about it?" And I ask the question "Is this science?" How can we verify these ideas? What other insights do we need to acquire going forward, in order to make the multiverse idea something that fits squarely within confirmable or falsifiable science?
This idea is controversial for good reason. It is at the cutting edge — not only the cutting edge of science, but also the edge of the kinds of ideas that we want to embrace in science. That's what makes it exciting.
Q: You make the point that it's very difficult to have any sort of direct contact with other universes. The differences are just so great. The only way to conceptualize other universes, I suppose, is through mathematics and the bits of evidence that can be gleaned from particle collisions or the cosmic microwave background radiation. Is there any possible avenue to get substantive information about the bigger picture, or are we pretty much stuck in our own little corner of the multiverse?
A: I think we're certainly stuck physically. But I would not underestimate the power of mathematics to provide the kinds of insights you are referring to. We are definitely at a rudimentary state in our understanding of these multiverse proposals. But if we can refine that understanding, we could produce detailed "universe demographics." We could gain a very detailed understanding of the percentage of universes that would have this or that quality.
In fact, we might get lucky with a well-developed multiverse theory. We might find that universes differ in substantial ways, but we might also find that there are certain common features that all universes share — like a certain class of particle, for instance. Then, to adjudicate that multiverse proposal, all we would need to really do is look for those particles here in our universe. We're part of this multiverse, after all. If we fail to find those particles, we could rule out that proposed theory. It's falsifiable, even though we can't actually see the other universes. If we do find those particles, that would bolster our confidence that the theory is correct, as would be the case for other fields of experimental science.
My point is, I'm laying out the way in which various multiverse proposals could rise to the level of being testable, of being falsifiable. The mere fact that you can find ways to do that shows quite clearly that the subject can't simply be written off.
Q: You've had quite the range of experiences during your book tour — including an appearance on "The Colbert Report." [During his chat, Greene told host Stephen Colbert that he could be described as "a bag of particles governed by the laws of physics," leading Colbert to quip, "That is a great pickup line."] In a parallel universe, is there anything you'd want to change about the past few weeks?
A: Oh, goodness. ... If I could get a couple more hours of sleep in the day, that would be welcome. But that's about it.
This map illustrates the numerous star-forming clouds, called cold cores, that Planck observed throughout our Milky Way galaxy. Planck, a European Space Agency mission with significant NASA participation, detected around 10,000 of these cores, thousands of which had never been seen before.
By Alan Boyle, Science Editor, NBC News
It'll be another couple of years before the European Space Agency's Planck probe delivers its baby picture of the universe, but in the meantime, the long-wavelength surveyor has pinpointed thousands of hot spots (and cold spots) worth watching.
The hot spots are huge galaxy clusters — including one cluster that holds the equivalent of a quadrillion stars, making it one of the most massive structures ever seen in the universe. The cold spots are clouds of chilly gas and dust within our own galaxy that are on the verge of forming their first stars.
Identifying these spots isn't the main reason for the billion-dollar Planck mission, which was launched in May 2009 along with the Herschel Space Telescope. Planck's main goal is to chart the cosmic background radiation in unprecedented detail, in wavelengths ranging from the infrared to the radio spectrum. The mission is expected to produce a map of the cosmic "afterglow" from just 380,000 years after the big bang, at a resolution that's three times bettern than the map produced by NASA's Wilkinson Microwave Anisotropy Probe in 2003.
Such maps provide scientists with their best guide to the infant universe's inflationary expansion. But before scientists can chart the cosmic background radiation, they have to retouch Planck's picture to remove all the "foreground" radiation — that is, all the stars, galaxies and pockets of gas and dust that lent their glow to the all-sky survey. These radiation sources are like "bugs on the windshield," Charles Lawrence of NASA's Jet Propulsion Laboratory, the U.S. project scientist for the Planck mission, told journalists today at the American Astronomical Society's winter meeting in Seattle.
In Planck's case, even the bugs are valuable. The cold spots and the hot spots were the headliners for today's release of the mission's first scientific results. "So today, we're all entomologists," Lawrence joked.
An ESA video, prepared in advance of the Herschel-Planck launch, explains what the probes are designed to do.
Planck's data catalog includes about 10,000 so-called "cold cores," thousands of which are newly discovered. The dark, dense, dusty clouds are expected to fall in on themselves due to gravitational forces, and squeeze stars into existence. "These are the equivalent of a mother's womb before anything has happened," George Helou, a member of the Planck team, said at the Seattle briefing.
Temperatures in the cores approach absolute zero — to be precise, between 7 and 17 Kelvin, or as low as minus-447 degrees Fahrenheit. To measure such temperatures, the Planck detectors had to be chilled to 0.1 Kelvin, or a fraction of a degree above absolute zero.
Helou said astronomers will be studying all those cold cores to come up with a model explaining how the frigid wombs give birth to hot, young stars.
On the other side of the spectrum, the Planck team has identified 189 galaxy clusters so far, including 20 that have never been seen before. Those previously undetected clusters are being confirmed by cross-checking X-ray observations from ESA's XMM-Newton orbiting observatory.
The newly detected galaxy supercluster PLCK G214.6+37.0 was identified in imagery from the Planck probe (left), and its existence was confirmed by checking X-ray imagery from the XMM-Newton observatory (right).
Studying the clusters could yield new insights into the evolution of galaxies, as well as the effects of dark matter and dark energy. The data from Planck confirm the view that galaxies form along a network of dense regions that spread across empty space like the threads of a spider web.
"They sit in the knots of the cosmic web," said Elena Pierpaoli, a Planck team member from the University of Southern California.
Planck's first findings are the focus of a major scientific conference in Paris this week, based on 25 scientific papers that have been submitted to the journal Astronomy & Astrophysics. As impressive as all that sounds, it's just "the tip of the scientific iceberg," David Southworth, ESA's director fo science and robotic exploration, said in a statement released today.
"This catalog contains the raw material for many more discoveries," Southworth said. "Even then, we haven't got to the real treasure yet, the cosmic microwave background itself."
That big reveal is scheduled for the next data release ... in January 2013.
Stars, galaxies, and other visible stuff in the universe only make up a tiny fraction of what's out there. The rest consists of the more mysterious dark matter and dark energy.
Scientists infer the presence of dark matter by the way it distorts the light of distant galaxies that pass through it on the way to observers. A circular galaxy, for example, may appear elliptical ... or even as curved as a fingernail clipping. The technique, called gravitational lensing, allowed scientists to infer the presence of dark matter in the giant galaxy cluster Abell 1689, as mapped in the image above.
But dark matter doesn't distort all galaxies equally. Unlike the obvious distortions in the Hubble image, the effect is often "so small that you can't really see it by the eye," challenge organizer Thomas Kitching from the University of Edinburgh told me. "So we need to do it statistically."
Astronomers want to measure this lensing effect in 52 million galaxies. An additional layer of complexity arises from the blurring of images due to other distortions from the atmosphere and the telescopes themselves.
"The challenge is to undo the blurring effect of the atmosphere and the telescopes, and get back to measuring the very slight distortion. And if algorithms and software can be developed to measure that, it then means we can directly use those algorithms to map out the dark matter," Kitching said.
The scientists ultimately hope to map out dark matter in the universe as a function of time. That would let them see how the structure of dark matter has changed as the expansion of the universe has accelerated due to an effect of another dark force -– dark energy. Astronomical observations suggest that ordinary matter accounts for just 4 percent of the universe's content, and that dark matter takes in another 25 percent or so.
"We can actually say something about dark energy, which accounts for the other 70 percent of the universe and is causing the accelerated expansion," Kitching told me.
The challenge is open to anyone, though organizers are particularly keen for citizen scientists with experience in image manipulation and software development to step up to the plate -- for instance, the kind of people behind Galaxy Zoo, another online science project.
Kitching also would love to hear from people who have an idea but are not sure how to express it mathematically or with software. "If we think it is a good idea, then we are happy to work with them and turn their idea into a method that we can test," Kitching added.
Participants who download the GREAT10 data analysis package for the "Galaxy Challenge" will have nine months to run the simulations and process imaging data. The winning teams will receive an iPod or iPad, as well as an all-expenses-paid trip to NASA's Jet Propulsion Laboratory in Pasadena, Calif., for one of the team members. JPL is where organizers will meet for a workshop on the GREAT10 project in September 2011. (Check out the project FAQ for details.)
In addition to the prizes, the winners will also get the feeling "that they helped us understand the dark matter and dark energy," Kitching added.
An artist's impression shows the young galaxy UDFy-38135539 gathering up the hydrogen and helium gas surrounding it and forming many young stars. Astronomers have determined that UDFy-38135539 is the most distant known galaxy.
By Alan Boyle, Science Editor, NBC News
Astronomers have confirmed that an incredibly faint galaxy in the constellation Fornax is the most distant known object in the universe, shining more than 13 billion light-years away and reflecting an era when stars were just beginning to emerge from a cosmic fog.
The galaxy, known as UDFy-38135539, is one of several super-distant objects picked out from the Hubble Ultra Deep Field, the most sensitive snapshot ever taken of deep space. In time, astronomers may well spot objects that are even farther away, but this particular galaxy was the first of its type to go through the arduous process of having its measurements checked.
In fact, the astronomers behind the observations say they couldn't have seen UDFy-38135539 unless there were other, fainter galaxies nearby to help clear out the space around it. "Without this additional help, the light from the galaxy, no matter how brilliant, would have been trapped in the surrounding hydrogen fog, and we would not have been able to detect it," Durham University's Mark Swinbank said in a news release from the European Southern Observatory.
The ESO researchers, led by Matt Lehnert of the Observatoire de Paris, published their findings in this week's issue of the journal Nature. Those findings shed unprecedented light (so to speak) on a mysterious period in the development of the universe, about 600 million years after its big-bang origin, when the radiation of the first stars began clearing out the neutral hydrogen that filled the infant universe. That process, known as reionization, transformed the cosmos from an opaque haze to the mostly empty space we know today.
"Measuring the redshift of the most distant galaxy so far is very exciting in itself, but the astrophysical implications of this detection are even more important," Nicole Nesvadba of France's Institute d'Astrophysique Spatiale said. "This is the first time we know for sure that we are looking at one of the galaxies that cleared out the fog which had filled the very early universe."
Further observations are likely to flesh out the scientific story of how the universe emerged from its dark ages.
G. Illingworth / UCO-Lick and UCSC / NASA / ESA / HUDF09
The Hubble Ultra Deep Field shows several candidates for breaking observational distance records, but confirming those distances is difficult. The inset picture highlights the galaxy UDFy-38135539, which is the farthest observed object to have its distance confirmed.
How the measurement was done The story of UDFy-38135539 begins with last year's release of the latest Hubble Ultra Deep Field imagery, captured using the Hubble Space Telescope's brand-new Wide Field Camera 3. Astronomers checked the spectral signatures of thousands of faint objects in the picture, looking for the telltale signs of extreme redshift -- that is, a shift in the spectrum that is linked to how far away an object is in our expanding universe.
The ESO astronomers found several galaxies that had their light shifted so far to the red side of the spectrum that they knew those galaxies had to be incredibly distant. Numerically speaking, their redshift had to be greater than 8. But how much greater?
To figure out the precise redshift number, the astronomers booked 16 hours of time on the ESO's Very Large Telescope in Chile, which is equipped with an ultra-sensitive infrared spectroscopic instrument called SINFONI. After weeks of data analysis, the team ran the numbers and came up with a redshift of 8.55. That meant the galaxy was farther away than the most distant previously known galaxy (redshift 6.96) as well as the most distant previously known object (a gamma-ray burst at redshift 8.2).
That redshift means the light left the galaxy when the 600-million-year-old universe was in its era of reionization. But based on the models for the development of galaxies, UDFy-38135539 would not have had enough power at that time to clear out enough empty space for the light to shine through as it did. That's why scientists suspect that other, undetected galaxies were helping to clear out the bubble of space.
In a Nature commentary, Michele Trenti, an astronomer at the University of Colorado's Center for Astrophysics and Space Astronomy, hailed the results as "a fundamental leap forward in observational cosmology." He noted that there was "robust statistical confidence" that the team's interpretation was correct, with only a 0.1 percent chance that the interpretation of the galaxy's spectrum was incorrect.
Trenti said the study "opens up exciting proects for spectroscopy of high-redshift objects" -- not only using the data currently at hand, but also drawing upon future studies to be conducted by Hubble and its successor, the James Webb Space Telescope, as well as the European Extremely Large Telescope.
Q&A with the research team's leader The leader of the research team, Matt Lehnert of the Observatoire de Paris, answered a couple of my follow-up questions in an e-mail exchange:
Cosmic Log: Could you explain why this observation is so difficult? Of course the faintness of the galaxy is one of the big issues, but I understand that the high redshift is another big issue.
Matt Lehnert: You are correct, it is not only the faintness. It becomes increasingly difficult because the night sky becomes brighter (which causes more background noise), contains a plethora of emission lines caused mainly by OH molecules in the upper atmosphere of the earth, and light is increasingly absorbed due to many molecules and other complex interactions. We cannot overcome all of these problems. Light lost is light lost. Having a very efficient spectrograph helps.
SINFONI is certainly that. Perhaps the best currently available. You also have to have good data reduction software. It's not very romantic, but removing those night sky lines is tricky -- they are strong, much, much stronger than the signal, and they vary with time. Because they are bright, they add lots of noise, but much of that "additional" noise is due to improper removal. My colleague, Nicole Nesvadba, has literally developed an excellent set of tools for extracting the most out of these data.
Q: Could you please also talk about the significance of the conclusions you reached on the galaxy's place in the epoch of reionization. I understand that the luminosity from the galaxy alone wouldn't have been enough to allow the redshifted photons to escape, and that the assumption is that there were surrounding smaller galaxies that aided in "carving" out a suitable bubble of ionized hydrogen gas. Does this fit with the existing models for galaxy formation during that epoch, or does it rule out any models that theorists have come up with? What do scientists hope to gain by learning more about the reionization epoch?
A: Well ... I always believe that models should be tested with results! Astronomy is still an empirical science and so much of what we model is based on observational results.
The underlying physics is very complicated. For example, we really do not have a robust picture of how individual stars form. As you might imagine, since galaxies are made up of stars, and are to some extent defined by these stars, it is difficult to understand how galaxies form without this essential understanding of how stars form. Having said all of that, our current models do in fact predict that reionization was mostly due to numerous faint objects and that the first places to be reionized were the ones that had higher densities of objects. Was it a surprise for me? Yes. Was it a surprise for all astronomers? No way!
What we hope to learn is, what types of galaxies were really responsible and in fact, were only galaxies responsible? There are other ideas, mini-quasars -- small black holes that accrete matter and contribute, to decaying particles, to several other [ideas that have been] at least proposed if not all that plausible.
We would like to know how reionization proceeded. Was it in fits and starts? Did it start in regions of the highest densities and then proceed to the lowest? How long did it take? How did this gas cool to form the first galaxies, and how did galaxy formation change because the universe was reionized?
These first galaxies literally changed the state of the universe. It was most neutral -- composed mainly of hydrogen and helium atoms -- to mostly ionized between galaxies -- composed mostly of protons, electrons, and helium nuclei (although helium re-ionization came later at lower redshifts).
It is a great challenge to understand how did these humble galaxies, humble because they are small, low-mass galaxies, change the state of the universe? It's an exciting puzzle and a challenge to our understanding of physics.
Correction for 11 p.m. ET: I originally wrote that the galaxy was seen as it was 600,000 years after the big bang, but the figure is actually 600 million years. Sorry for putting the decimal point in the wrong place, and thanks to those who pointed out the error.
Agence France-Presse provides the latest take on the suggestion that time itself has a 50-50 chance of ending within the next 3.7 billion years. The claim is contained in a paper submitted to the arXiv.org website by Berkeley's Raphael Bousso and colleagues, and discussed last month in Technology Review's arXiv Blog. In the long run, we're all dead, and in much less than 3.7 billion years. Nevertheless, it's sobering to think that Earth might actually still be around when the end comes. The caveat is that many physicists say Bousso's suggestion arises only because of a mismatch in statistical and theoretical assumptions. For more on the planet's demi-doom, check out the perspectives from New Scientist and Australia's ABC News.
This is a two-dimensional visualization of a Calabi-Yau space. Some scientists speculate that every point in space-time consists of a six-dimensional Calabi-Yau space crumpled into a structure we can never directly perceive.
British physicist Stephen Hawking may claim that extra dimensions provide the key to understanding the "grand design" of the universe, but it's Chinese-American mathematician Shing-Tung Yau who actually figured out how those extra dimensions work.
In his new book, "The Shape of Inner Space," Yau and his co-author, Steve Nadis, touch upon the work that led to the discovery of theoretical "Calabi-Yau spaces" — and the cosmic implications of multidimensional geometry.
The typical representation of a Calabi-Yau space looks like twisted web of a crumpled-up piece of paper. There's something elegant about its look — in fact, Calabi-Yau paperweights were voted the most popular gewgaw for holiday giving in last year's Cosmic Log Geek Gift Guide contest. But these shapes aren't just abstract art: String theorists believe that every single point in our universe is actually a compactified Calabi-Yau space in six dimensions.
Why would they think that? It's because the best theory they've been able to come up with for the universe's grand design requires 10 dimensions to make all the mathematics come out right. Because we can only perceive three dimensions of space and one dimension of time, they suggest that the other six dimensions curled up into near-nothingness when our universe took shape.
Yau was the one who worked out the mathematics for the curled-up spaces. At first, he was trying to disprove a conjecture about complex geometry that was proposed by another mathematician named Eugenio Calabi. But then Yau came around to the view that Calabi was actually right, and in 1976 he published the proof that laid the groundwork for the concept of Calabi-Yau spaces. String theorists eventually seized upon the concept in their explanations for the universe's 10-dimensional structure. Later, the theorists threw in an extra dimension to make it 11, because that helped make sense out of five different subtheories. It's that 11-dimensional view of the universe, known as M-theory, that Hawking is touting as the groundwork for the grand design.
"The Shape of Inner Space" delves deeply into the math behind M-theory. It also traces Yau's life story, which started with his birth in China in 1949 and and Hong Kong and eventually brought him to Harvard. There are plenty of career highlights along the way: In 1982 Yau won the math world's most prestigious prize, the Fields Medal, for proving the Calabi conjecture. In 2006 he played a role in the tale of Russian mathematician Grigory Perelman's refusal to accept the Fields Medal for proving the famous Poincare conjecture. And Yau is also known for his high-profile criticism of the Chinese educational system and scientific establishment.
You can read all about that and more (including Yau's early yen for kung-fu novels) in an extended interview on Discover magazine's website. During my telephone chat with Yau this week, we focused more on the cosmic perspective. Here's an edited transcript of the Q&A:
Cosmic Log: Recently there's been a lot of talk about multiple dimensions. Stephen Hawking also recently wrote a book, I hear ... and he talked about how M-theory was really the secret to the "grand design." But in your book, you point out that the grand design really has a lot to do with geometry. So a lot of people wonder what's going on with multiple dimensions that we can't directly perceive. What difference does it make for our understanding of the universe?
Shing-Tung Yau: We physicists always try to bridge two important discoveries in physics together. One is general relativity, and the other is quantum mechanics. There were many efforts to discover such a unification field, [but none was successful] until string theory came along. So far that's the only consistent theory. In order to make quantum mechanics consistent with general relativity, there is no other choice but to make space-time be 10-dimensional. On the other hand, we do have to try to understand the space-time that we perceive. So we make six dimensions very, very tiny.
We still see the four-dimensional space-time that we experience in general physics, special relativity and all that. This six-dimensional space is what we call "internal space." There are a lot of models for this, but the most effective and useful model is Calabi-Yau space, where We can do all the calculations. And in fact, if we can choose the right Calabi-Yau space, we should be able to calculate the properties of the particles in the universe. But the trouble is, right now, we have many candidates for these calculations. One day, if we have the fundamental physics that can lead us to know how to calculate such geometry, and if we pick the right geometry, we will be able to calculate the masses of all the particles in the universe.
In any case, a great number of important discoveries have been made, in terms of philosophical principles as well as mathematics. So as a mathematician I'm very excited about this.
Q: Some people say that our universe could be just one among 10 to the 500th power possibilities. I guess that has led some people to say that the study of the structure of our universe can do nothing more than catalog one of those possibilities, and that there's no particular reason why the laws of physics work one way rather than another way. The only answer would be, "Well, this is just the way it is." Just as one cave is more habitable than another because of the way it's laid out, it just so happens that the geometry of our universe makes it more suitable for life, and there's no use trying to figure out why that is.
A: That's one point of view. I do not necessarily take that point of view. The fact that we can already see that there is a finite number of possibilities is very exciting. There could have been an infinite number of possibilities for space-time. But right now we know of only a finite number, and that should be considered a good starting point.
Other people have called this the "cosmic landscape." Maybe that's what they think, but that's not what I believe. There must be some more fundamental principle in order to choose the right geometry to tell what the universe is supposed to be.
Q: What do you think are the most promising experimental avenues for determining the geometry of the universe?
A: If supersymmetry can be found, that would be very exciting for string theory. The whole theory is based on this supersymmetry. It may be possible to find supersymmetric partners in the Large Hadron Collider. If supersymmetry exists, most people would start to think that string theory has a strong foundation.
First, the experimental data have to come out. Then it will be time to look for more concrete statements about the geometry, and hopefully based on that, we can try to make more concrete statements about the geometry of the universe. Right now we don't have the experimental data, so we cannot say much. On the other hand, we can do a lot of theoretical calculations, using computers, and the calculations come out to be very beautiful. They have led to many important discoveries in math itself.
Some of the discoveries in mathematics are extraordinary. The calculations have solved problems that we didn't know how to solve for 100 years.
Q: Do you have particular solutions in mind?
A: Mathematicians have been looking at polynomial equations. You want to know how many solutions are there. We didn't know how to do this for a long, long time. In some important cases, string theory has inspired us to find the right formula. The formula is extremely complicated. If we didn't know much about string theory, I believe that even now, we still would not be able to find such a formula. But based on the inspiration and the intuition from string theory, we found the formula, and we also proved it. We proved it independently of whether string theory itself is right or wrong.
Q: So string theory already has yielded important scientific advances, even if it hasn't unraveled the deepest mysteries yet.
A: That's right. Many, many important problems in mathematics and geometry were solved, and that's why many mathematicians are actually looking to string theory, because it provides intuitions that we did not have before.
Q: The mathematics of string theory is beautiful, but there's also a beauty to these depictions of Calabi-Yau spaces. How do you feel about those representations? Are they simplications of what you've done, or do you see them as tributes to what you've done?
A: Those pictures are grossly simplified versions of what we know. We cannot really draw a Calabi-Yau space, because it is a six-dimensional space. We use computers to make some slice of these Calabi-Yau spaces. What we see is far away from being the original picture of what we think in our heads, but it's useful, I think, even to look at the slice. In our original philosophical description for the space, we can do a huge amount of things — in algebra and number theory, many problems can go back to this space.
I constructed this space eight years before string theory became an important subject. I just thought that it was exotic and beautiful. I couldn't imagine that any other space could be more beautiful. We went on to many discoveries in math. And then, to my great surprise, the string theorists came along, and all these great people in string theory came to ask me how this space was constructed. I was really excited by the possibility that such spaces could be used to understand nature.
Q: In the past, you've talked a lot about China's status in science, math and technology, so I can't let you go without asking at least one question about global competitiveness and the worries that people have about American innovation.
A: There is absolutely no question that America will be the leader for a very long time. I think it would take a long time for any Chinese universities to be as good as our top universities. It may take 50 years, it may take a century. So America's science and technology is really far ahead of China's. I don't think Americans should worry about it. But on the other hand, of course, there are a lot of good Chinese scientists coming up, and they are very competitive. I wish that they would be as original as our American colleagues.
So it's very interesting to have a good group of Chinese scientists competing with us. They will make us better. I always feel it is important to have challenges — to have people competing with us. Otherwise we'll think that we are just great and will not evolve toward a better scientific world. So I don't think there'll be any negative effect from this competition. It will be positive — for both sides.
Update for 7 p.m. ET Oct. 3: Toward the latter part of the book, Yau and Nadis take the concept of a 10-dimensional (or 11-dimensional) universe into some speculative frontiers. For example, what would happen if those rolled-up dimensions were to "un-scrunch" themselves? That phenomenon, known as decompactification, would be a very bad thing for the universe as we know it. It's the kind of stuff that science-fiction nightmares are made of.
On the smallest scale, you might look for supersymmetric particles in the Large Hadron Collider, as Yau said in the Q&A, or you could look for special types of particles leaking back and forth through extra dimensions. Kaluza-Klein particles would have unusual masses or spins due to their sojourn through the multidimensional realm.
This is a two-dimensional artistic visualization of a six-dimensional Calabi-Yau shape — an intricately folded knot of space. Such visualizations play a role in conceptualizing M-theory, which physicists Stephen Hawking and Leonard Mlodinow say is "the unified theory Einstein was hoping to find."
More than a decade ago, British physicist Stephen Hawking said there was a 50-50 chance that a unified "theory of everything" would be discovered in 20 years' time. Now Hawking thinks the theory has been found.
In "The Grand Design," he and co-author Leonard Mlodinow explain why a concept called M-theory offers the only path they can see to understanding the universe's grand design. Hawking got a lot of click traffic earlier this week for his observation that God wasn't needed to explain the origin of the universe. But his claim that "M-theory is the unified theory Einstein was hoping to find" could be, if anything, more scientifically controversial.
"Stephen often overstates the case, and that's fine," said Lawrence Krauss, a theoretical physicist at Arizona State University who's coming out with his own book about the ultimate questions of physics next year. "That's by virtue of the fact that it's hard for him to go into detail because of his medical condition. Because of that, he makes brief, blunt statements. It's almost like the Bible. Whenever he says anything, people jump on it."
M-theory is a key jumping-off point for "The Grand Design." The string theorists who came up with the term have never agreed on exactly what the "M" stands for, although the words "membrane," "matrix," "mystery" and "magic" have all been floated as possibilities. My favorite explanation is that M-theory is the "mother of all theories."
Pulling strings String theory suggests that the fundamental constituents of reality are not pointlike particles (such as the concepts we have for protons, neutrons and electrons) but are more like tiny strings vibrating at different "frequencies." Such ideas can be used to make linkages between gravity and the other fundamental forces in physics, but only if you build 10 dimensions into the picture.
Theorists found that five different strains of string theory explained how the universe worked, from five seemingly irreconcilable perspectives. But if you added one more dimension to the picture, effectively turning the dimensional dial up to 11, everything made sense. The five perspectives could be seen merely as different ways of expressing the same super-theory. That's what's known as M-theory.
Hawking and Mlodinow may make it sound as if M-theory has to be the theory of everything, but Krauss says it's too early to declare "M-Mission Accomplished." One big issue is that M-theory makes more than one prediction about the nature of the universe. In fact, the number of predictions it makes is somewhere around 10 to the 500th power. That's a 1 followed by 500 zeroes.
"On the surface, that sounds like a bad thing," Krauss said. He has observed that this kind of string theory isn't so much a theory of everything as it is a theory of anything (or a theory of nothing). But most scientists have come around to the view that the multiplicity of M-theory's predictions is actually a virtue. Seen from this perspective, it may be that anything is possible when it comes to creating universes. We just happen to be in a universe where all the lottery numbers have added up to win what astrobiologist Paul Davies calls the "cosmic jackpot."
"Interestingly enough, what people are hanging onto is the lack of ability to make predictions," Krauss said. "It turns a wart into a beauty mark."
What Krauss finds exciting is that there could be ways to verify that something can come from nothing -- which is the point behind Hawking's claim that God isn't necessary to explain the universe's creation.
Physicists have noted that the positive energy contained in particles and the negative energy represented by gravitational attraction appear to balance out precisely. "Empirically, we can actually have evidence that the universe came from nothing. One of the key things is that the total energy of the universe is zero, which is only possible if the universe came from nothing. It could have been otherwise. It could have been not zero," Krauss said.
The concept of a zero-energy universe and getting something from nothing may sound crazy, but this article from Mercury magazine and this video of one of Krauss' lectures, both titled "A Universe From Nothing," show that the ideas has been percolating among scientists for years. Such ideas are central to "The Grand Design," as well as to the book that Krauss is currently in the midst of writing.
"This is very premature, because we still don't know what M-theory is," Krauss told me. "The interesting question for me, ultimately, more than this metaphysics, is whether we'll be able to empirically answer these questions. Science has gotten to the point where there's the hope that we'll be able to turn some of this metaphysics into physics."
Physicists Leonard Mlodinow and Stephen Hawking work together in Hawking's office in Cambridge, England.
Mlodinow agrees with Krauss that M-theory still has miles to go, but he says it may be as close as science can get to the fabled theory of everything. The Caltech physicist has collaborated with Hawking for years -- not only on "The Grand Design," but also on "A Briefer History of Time," a streamlined version of Hawking's classic work. Mlodinow has also done science writing as a solo act, as the author of "Feynman's Rainbow" and "The Drunkard's Walk."
During a telephone interview, Mlodinow told me that "The Grand Design" was truly a joint effort, in which he and Hawking traded, debated and restated each other's prose. "Everything was pretty much passed back and forth, so actually it would be hard to identify which one of us wrote what," he said. "In fact, at times where I've tried, I've gone back to my computer to see -- and sometimes I'm wrong."
Thus, Mlodinow is as good a source as Hawking for insights into the meaning of "The Grand Design." Here's an edited transcript of our Q&A:
Cosmic Log: In the past, Stephen has talked about the quest for a theory of everything. The book makes it sound as if it's not so much one theory of everything, but a series of theories for different model-based views of reality. Do you get a sense that it's going to be possible to come up with one unified theory of physics?
Leonard Mlodinow: Well, the book is about why the laws of nature are what they are, and where the universe came from. We do say in the book that we believe the unified theory is M-theory. So we not only believe that it's possible, but we believe that it's here.
Q: But M-theory is an array of different perspectives on reality, and one of the things about that approach is that one model works for one scale, or one sphere of physics, and perhaps another theory -- I don't know whether you'd call it a subtheory, or another perspective -- works for a different one.
A: M-theory is the most general quantum theory that would include gravity, using the constraints that we feel need to be employed -- for example, that it's finite and would make reasonable predictions. Whether it's a single theory or a network of theories is not yet known. I think Stephen feels that there's a good chance it's a network of theories, which is what we see today. Where they overlap, they agree. In other areas where they don't overlap, they make their own predictions. Stephen believes that's OK, and we shouldn't be disappointed if the final theory is a network of theories. According to model-dependent realism, all that is OK. It's just the way reality is. You can't ask which of the theories in that network is more "real."
Q: Do you have a slightly different point of view? Because it sounds as if you're presenting Stephen's view as distinct from your own.
A: No, I agree with Stephen. We debated this idea of model-dependent realism over quite a period of time. I'm saying that just because I'm assuming you were interested in Stephen's opinion more than mine. But I'm happy to jump in as well.
Q: In the latter part of the book, there's some discussion about how God does or does not play a role in the big questions about the universe....
A: Well, people have always wondered about the big questions: Where did the universe come from? Why is nature the way it is? At first we had mythology to answer that question. I suppose people just made up stories, and they became the myths. Or they evolved. Later we had the religions that we have today, and philosophy grew up. People used applied reason, intuition and some small amount of observation as well -- and came up with their own concepts on the answers to these questions.
"The Grand Design" delves into subjects ranging from M-theory to God's role.
A few hundred years ago we developed this thing called the scientific method, where we come up with theories phrased in mathematics, and we require that they not only describe what we're looking to describe but also make further predictions that can be tested. Then we do experiments, and if we find that the predictions are not right, if they're not verified, then we alter or discard the theory.
In the book, we argue that this is a better method. It's led to the modern society that we have today -- to vaccinations, computers, electricity, television, telephones, everything else. When you understand nature to that extent, you can apply it. Since you really understand what's going on, you can create all this technology, which you don't create based on mythology, philosophy and religious explanations.
As far as God goes, we describe our theory of where the universe came from, and why the laws of nature are as they are. And we show that with this theory, there's no need for a God to create the universe or to create the laws of physics as they are. All of this can come purely from physics, from science, from nature.
Q: There's always a question about "what happened before the big bang," or about the nature of time. Stephen dealt with that in "A Brief History of Time," and you helped with that vision through your work on "A Briefer History of Time." How does this book advance the ball?
A: One of Stephen's big ideas in this book is called "top-down cosmology." It's the idea that we should trace the history of the universe from the present time backwards -- and that the universe has many histories because it's a quantum system. In "normal" physics, we work in a laboratory and we do experiments. We set up the experiment in an initial state, then we let it go for a while, then we do measurements on its final state -- and we check predictions. The theory tells us how the initial state should develop, and then we make predictions about the final state.
We can't do that with the universe as a whole. We don't set up the initial state. We don't have a laboratory where we can control what's going on. We can't repeat the experiment and take the data. Also, the universe -- since we believe in quantum theory now -- is a quantum system.
In normal cosmology, people start with the initial state as if it were a laboratory -- which it's not -- and they use classical ideas, meaning that there's one history of the universe which they trace forward. Stephen believes that we should start from our observations now, because that's all we can do, and trace it backwards, taking into account the fact that the universe has many histories and not just one.
Q: Right, there's a discussion in the book about how the past is as much affected by quantum mechanics as the future is. So there's uncertainty about the past -- which is counterintuitive. That must be a hard sell with normal people who say, well, I remember specifically what I had for dinner yesterday. We know for sure what happened in the past because of things ranging from human memory to the fossil record to the process of baryogenesis at the beginnings of the universe. So how can you say that there's a factor of uncertainty about past events?
A: Well, if you happened to have experienced all possible aspects of the universe for all of time, there would not be uncertainty. Quantum theory doesn't say that if you ate an egg, you might not have eaten the egg. Let's get that straight. What quantum theory says is that in between the times when we observe and measure, and interact in that way, these properties that we talk about have no meaning.
For instance, in classical theory, if you push a billiard ball down the table, and if no one is interacting with it or measuring it, it still has one path with a well-defined position at every time. Those properties exist. In quantum theory, if you push it and then no one interacts with it, you cannot in general say that it has a particular position and velocity at any time. In classical theory, we say that it has those properties, and when we measure it, we're just reading off those properties. In quantum theory, it's not correct to say that a measurement is merely reading off those properties. Rather, it doesn't have those properties when we don't measure it.
Now, if you had an egg yesterday, you interacted with the egg, and there's an egg there. When we look at the universe today, with top-down cosmology, we don't allow for the possibility that the moon is made of green cheese -- because we already know that the moon isn't made of green cheese. We put in all the data of all our observations, and that prunes down the number of different histories that have to be taken into account. But where observations haven't been made, we don't.
So the vagueness of the past is the vagueness of things unmeasured in the past.
Q: Does that imply then that there will be no way to answer that classic question, "What happened before the big bang"? Because the uncertainty goes to an indeterminately high level?
A: No, it's not that. As you go backward in time, quantum theory, combined with general relativity, tells you that if you go back early enough in the universe, time ceases to have the meaning that we assign to it today. It ceases to act as we know it. So it's not a well-posed question to say, "What happened at the beginning of time?" -- because time doesn't go back to the beginning.
According to general relativity, time and space exist under certain conditions. Quantum theory tells you that there are always fluctuations in empty space, and if you make the universe small enough, the fluctuations are great enough that the matter is squashed down enough that this affects the character of space and time itself. Time doesn't exist at that point. So the question doesn't make any sense.
Q: I know we're coming to end of our time -- speaking of that -- but do you hold out hope that humans will at some point understand the totality of the grand design? Or is the grand design something that our brains aren't just big enough to hold? Or is it something that is unknowable, because that's just the nature of the universe?
A: No, we believe that humans can understand it. That's the great triumph and the great miracle of the universe.
Physicist Stephen Hawking delivers a lecture in South Africa in 2008. In a new book, he says science doesn't need God to explain the origin of the universe.
British physicist Stephen Hawking's latest book is already making waves with his observation that science can explain the universe's origin without invoking God.
"Because there is a law such as gravity, the universe can and will create itself from nothing," Hawking and his co-author, Caltech physicist Leonard Mlodinow, write in "The Grand Design," which is due to be issued next week. "Spontaneous creation is the reason there is something rather than nothing, why the universe exists, why we exist. It is not necessary to invoke God to light the blue touch paper and set the universe going."
That's the quote that lit the fuse in The Guardian as well in The Times of London, which published an excerpt from the book in its Thursday editions. But by itself, the quote doesn't have much "there" there. If Hawking is saying merely that something can arise from nothing willy-nilly, that's not much of an explanation for the origin of the universe.
What he's actually saying in the book is that when we study the universe's origins, we have to work our way back from the present, rather than assuming there's an arbitrary point 13.7 billion years ago when Someone pressed the button on a cosmic stopwatch. And when you look at it that way, the universe looks more and more like a quantum phenomenon, in which a multitude of histories diverge. This is what Hawking calls top-down cosmology.
Space and time fizzle out, so it can't be said that there is a time before the big bang — just as you can't say that there is something north of the North Pole. (I'm talking "north," not "up.")
Gravity is part of the picture because it helps keep the cosmic balance sheet in line. Here's the part of the paragraph just before the quote cited above: "Because gravity shapes space and time, it allows space-time to be locally stable but globally unstable. On the scale of the entire universe, the positive energy of the matter can be balanced by the negative gravitational energy, and so there is no restriction on the creation of whole universes."
"The Grand Design" puts together ideas that Hawking has been trying out for a long time. Five years ago, for example, he noted that eliminating the question of what happened before the big bang meant "the beginning of the universe would be covered by science." And four years ago, he joked that he had presented a paper suggesting how the universe began during the same conference at which Pope John Paul II asked scientists to set the question aside.
Does Hawking's view mean that modern physics "leaves no place for God in the creation of the universe," as the Times suggests, or that "God did not create the universe," as The Guardian claims? Not unless you need a "God of the Gaps" to step into science's place. A more sophisticated view would hold that physics (and evolutionary biology, to cite another example) are the not-always-mysterious ways in which God routinely works. In fact, Soren Kierkegaard would say that God's workings have to be transparent — and I tend to side with Soren.
Some will argue that such a concept of divinity is so weak it should be sliced away with Occam's Razor. Others will quote chapter and verse to support their claim that religion trumps science. And still others will argue that science and religion should be non-overlapping magisteria. But hey, that's what the comment box below is for. Feel free to weigh in with your comments, and stay tuned for my Q&A with Leonard Mlodinow later in the week.
Update for 1:50 p.m. ET Sept. 2: The waves continue to roll across the Internet. Here's a transcript of a Times of London chat about Hawking's comments, featuring evolutionary biologist (and atheist) Richard Dawkins talking about God. "Darwin kicked him out of biology, but physics remained more uncertain," Dawkins says. "Hawking is now administering the coup de grace."
Reaction is also coming in from godly types such as Chief Rabbi Lord Sacks, Britain's top Jewish leader, as well as the Rev. Dr. David Wilkinson, an astrophysicist who is principal of St. John's College, Durham. "There is more to wisdom than science. It cannot tell us why we are here or how we should live," Sacks is quoted as saying. Wilkinson, meanwhile, says that Hawking "raises a number of questions which for many opens the door to the possibility of an existence of a creator," such as cosmic purpose, the source of the laws of physics and the intelligibility of the universe.
Dawkins says those questions either don't matter to him or are unanswerable.