Politics, Religion, Science, Culture and Humanities > Science, Culture, & Humanities

Physics & Mathematics

<< < (2/19) > >>

Crafty_Dog:
Laws of Nature, Source Unknown
NYTimes
By DENNIS OVERBYE
Published: December 18, 2007


“Gravity,” goes the slogan on posters and bumper stickers. “It isn’t just a good idea. It’s the law.”

And what a law. Unlike, say, traffic or drug laws, you don’t have a choice about obeying gravity or any of the other laws of physics. Jump and you will come back down. Faith or good intentions have nothing to do with it.

Existence didn’t have to be that way, as Einstein reminded us when he said, “The most incomprehensible thing about the universe is that it is comprehensible.” Against all the odds, we can send e-mail to Sri Lanka, thread spacecraft through the rings of Saturn, take a pill to chase the inky tendrils of depression, bake a turkey or a soufflé and bury a jump shot from the corner.

Yes, it’s a lawful universe. But what kind of laws are these, anyway, that might be inscribed on a T-shirt but apparently not on any stone tablet that we have ever been able to find?

Are they merely fancy bookkeeping, a way of organizing facts about the world? Do they govern nature or just describe it? And does it matter that we don’t know and that most scientists don’t seem to know or care where they come from?

Apparently it does matter, judging from the reaction to a recent article by Paul Davies, a cosmologist at Arizona State University and author of popular science books, on the Op-Ed page of The New York Times.

Dr. Davies asserted in the article that science, not unlike religion, rested on faith, not in God but in the idea of an orderly universe. Without that presumption a scientist could not function. His argument provoked an avalanche of blog commentary, articles on Edge.org and letters to The Times, pointing out that the order we perceive in nature has been explored and tested for more than 2,000 years by observation and experimentation. That order is precisely the hypothesis that the scientific enterprise is engaged in testing.

David J. Gross, director of the Kavli Institute for Theoretical Physics in Santa Barbara, Calif., and co-winner of the Nobel Prize in physics, told me in an e-mail message, “I have more confidence in the methods of science, based on the amazing record of science and its ability over the centuries to answer unanswerable questions, than I do in the methods of faith (what are they?).”

Reached by e-mail, Dr. Davies acknowledged that his mailbox was “overflowing with vitriol,” but said he had been misunderstood. What he had wanted to challenge, he said, was not the existence of laws, but the conventional thinking about their source.

There is in fact a kind of chicken-and-egg problem with the universe and its laws. Which “came” first — the laws or the universe?

If the laws of physics are to have any sticking power at all, to be real laws, one could argue, they have to be good anywhere and at any time, including the Big Bang, the putative Creation. Which gives them a kind of transcendent status outside of space and time.

On the other hand, many thinkers — all the way back to Augustine — suspect that space and time, being attributes of this existence, came into being along with the universe — in the Big Bang, in modern vernacular. So why not the laws themselves?

Dr. Davies complains that the traditional view of transcendent laws is just 17th-century monotheism without God. “Then God got killed off and the laws just free-floated in a conceptual vacuum but retained their theological properties,” he said in his e-mail message.

But the idea of rationality in the cosmos has long existed without monotheism. As far back as the fifth century B.C. the Greek mathematician and philosopher Pythagoras and his followers proclaimed that nature was numbers. Plato envisioned a higher realm of ideal forms, of perfect chairs, circles or galaxies, of which the phenomena of the sensible world were just flawed reflections. Plato set a transcendent tone that has been popular, especially with mathematicians and theoretical physicists, ever since.

Steven Weinberg, a Nobel laureate from the University of Texas, Austin, described himself in an e-mail message as “pretty Platonist,” saying he thinks the laws of nature are as real as “the rocks in the field.” The laws seem to persist, he wrote, “whatever the circumstance of how I look at them, and they are things about which it is possible to be wrong, as when I stub my toe on a rock I had not noticed.”

The ultimate Platonist these days is Max Tegmark, a cosmologist at the Massachusetts Institute of Technology. In talks and papers recently he has speculated that mathematics does not describe the universe — it is the universe.

===========

Page 2 of 3)



Dr. Tegmark maintains that we are part of a mathematical structure, albeit one gorgeously more complicated than a hexagon, a multiplication table or even the multidimensional symmetries that describe modern particle physics. Other mathematical structures, he predicts, exist as their own universes in a sort of cosmic Pythagorean democracy, although not all of them would necessarily prove to be as rich as our own.

“Everything in our world is purely mathematical — including you,” he wrote in New Scientist.

This would explain why math works so well in describing the cosmos. It also suggests an answer to the question that Stephen Hawking, the English cosmologist, asked in his book, “A Brief History of Time”: “What is it that breathes fire into the equations and makes a universe for them to describe?” Mathematics itself is on fire.

Not every physicist pledges allegiance to Plato. Pressed, these scientists will describe the laws more pragmatically as a kind of shorthand for nature’s regularity. Sean Carroll, a cosmologist at the California Institute of Technology, put it this way: “A law of physics is a pattern that nature obeys without exception.”

Plato and the whole idea of an independent reality, moreover, took a shot to the mouth in the 1920s with the advent of quantum mechanics. According to that weird theory, which, among other things, explains why our computers turn on every morning, there is an irreducible randomness at the microscopic heart of reality that leaves an elementary particle, an electron, say, in a sort of fog of being everywhere or anywhere, or being a wave or a particle, until some measurement fixes it in place.

In that case, according to the standard interpretation of the subject, physics is not about the world at all, but about only the outcomes of experiments, of our clumsy interactions with that world. But 75 years later, those are still fighting words. Einstein grumbled about God not playing dice.

Steven Weinstein, a philosopher of science at the University of Waterloo, in Ontario, termed the phrase “law of nature” as “a kind of honorific” bestowed on principles that seem suitably general, useful and deep. How general and deep the laws really are, he said, is partly up to nature and partly up to us, since we are the ones who have to use them.

But perhaps, as Dr. Davies complains, Plato is really dead and there are no timeless laws or truths. A handful of poet-physicists harkening for more contingent nonabsolutist laws not engraved in stone have tried to come up with prescriptions for what John Wheeler, a physicist from Princeton and the University of Texas in Austin, called “law without law.”

As one example, Lee Smolin, a physicist at the Perimeter Institute for Theoretical Physics, has invented a theory in which the laws of nature change with time. It envisions universes nested like Russian dolls inside black holes, which are spawned with slightly different characteristics each time around. But his theory lacks a meta law that would prescribe how and why the laws change from generation to generation.

Holger Bech Nielsen, a Danish physicist at the Niels Bohr Institute in Copenhagen, and one of the early pioneers of string theory, has for a long time pursued a project he calls Random Dynamics, which tries to show how the laws of physics could evolve naturally from a more general notion he calls “world machinery.”

On his Web site, Random Dynamics, he writes, “The ambition of Random Dynamics is to ‘derive’ all the known physical laws as an almost unavoidable consequence of a random fundamental ‘world machinery.’”

Dr. Wheeler has suggested that the laws of nature could emerge “higgledy-piggledy” from primordial chaos, perhaps as a result of quantum uncertainty. It’s a notion known as “it from bit.” Following that logic, some physicists have suggested we should be looking not so much for the ultimate law as for the ultimate program..

Anton Zeilinger, a physicist and quantum trickster at the University of Vienna, and a fan of Dr. Wheeler’s idea, has speculated that reality is ultimately composed of information. He said recently that he suspected the universe was fundamentally unpredictable.

I love this idea of intrinsic randomness much for the same reason that I love the idea of natural selection in biology, because it and only it ensures that every possibility will be tried, every circumstance tested, every niche inhabited, every escape hatch explored. It’s a prescription for novelty, and what more could you ask for if you want to hatch a fecund universe?

============

Page 3 of 3)



But too much fecundity can be a problem. Einstein hoped that the universe was unique: given a few deep principles, there would be only one consistent theory. So far Einstein’s dream has not been fulfilled.Cosmologists and physicists have recently found themselves confronted by the idea of the multiverse, with zillions of universes, each with different laws, occupying a vast realm known in the trade as the landscape.

In this case there is meta law — one law or equation, perhaps printable on a T-shirt — to rule them all. This prospective lord of the laws would be string theory, the alleged theory of everything, which apparently has 10500 solutions. Call it Einstein’s nightmare.

But it is soon for any Einsteinian to throw in his or her hand. Since cosmologists don’t know how the universe came into being, or even have a convincing theory, they have no way of addressing the conundrum of where the laws of nature come from or whether those laws are unique and inevitable or flaky as a leaf in the wind.

These kinds of speculation are fun, but they are not science, yet. “Philosophy of science is about as useful to scientists as ornithology is to birds,” goes the saying attributed to Richard Feynman, the late Caltech Nobelist, and repeated by Dr. Weinberg.

Maybe both alternatives — Plato’s eternal stone tablet and Dr. Wheeler’s higgledy-piggledy process — will somehow turn out to be true. The dichotomy between forever and emergent might turn out to be as false eventually as the dichotomy between waves and particles as a description of light. Who knows?

The law of no law, of course, is still a law.

When I was young and still had all my brain cells I was a bridge fan, and one hand I once read about in the newspaper bridge column has stuck with me as a good metaphor for the plight of the scientist, or of the citizen cosmologist. The winning bidder had overbid his hand. When the dummy cards were laid, he realized that his only chance of making his contract was if his opponents’ cards were distributed just so.

He could have played defensively, to minimize his losses. Instead he played as if the cards were where they had to be. And he won.

We don’t know, and might never know, if science has overbid its hand. When in doubt, confronted with the complexities of the world, scientists have no choice but to play their cards as if they can win, as if the universe is indeed comprehensible. That is what they have been doing for more than 2,000 years, and they are still winning.

Crafty_Dog:
Plane vs. Conveyer Belt: Hell Yeah the Plane Takes Off
by Higgins - January 31, 2008 - 4:20 PM

Last night the Discovery show Mythbusters settled a longstanding debate: whether an airplane on a conveyer belt (running at the same speed, but in the opposite direction as the plane) can take off. The short answer, as liveblogged by Jason Kottke:

HELL YEAH THE PLANE TAKES OFF

It’s a curious problem. As a thought experiment, it seems (at least to me) like the plane shouldn’t take off, since it’s not gaining takeoff velocity relative to the ground. But according to, you know, SCIENCE, the plane doesn’t need to reach takeoff velocity relative to the ground — it just needs lift an appropriate amount of lift. It’s the velocity of the air relative to the wings that counts, which is generated by the action of the engines.

 

Despite explanations of this sort of physicists, the issue wasn’t really settled until last night’s Mythbusters episode — they replicated the experiment on a small scale, then with a real airplane (albeit an ultralight), using a huge tarp dragged by a truck as the “conveyer belt.” Even the plane’s pilot thought the plane wouldn’t take off. When Jason Kottke first blogged about the issue last February, his comment thread was hot with controversy. So Kottke tuned in to Mythbusters last night and liveblogged the event, with results visible above. His exuberance over the plane’s liftoff has resulted in a “HELL YEAH THE PLANE TAKES OFF” tee-shirt available starting at $18. Wow.

 

Watch the Mythbusters clip in question below…. (Note: if this clip is pulled down, I’ll try to dig up another.)

 

See <http://www.mentalfloss.com/blogs/archives/11750> for the Mythbusters clip...

Crafty_Dog:
Electron Filmed for First Time - Yahoo! News

http://news.yahoo.com/s/livescience/20080225/sc_livescience/electronfilmedforfirsttime

Crafty_Dog:
Asking a Judge to Save the World, and Maybe a Whole Lot More



More fighting in Iraq. Somalia in chaos. People in this country can’t afford their mortgages and in some places now they can’t even afford rice.


None of this nor the rest of the grimness on the front page today will matter a bit, though, if two men pursuing a lawsuit in federal court in Hawaii turn out to be right. They think a giant particle accelerator that will begin smashing protons together outside Geneva this summer might produce a black hole or something else that will spell the end of the Earth — and maybe the universe.

Scientists say that is very unlikely — though they have done some checking just to make sure.

The world’s physicists have spent 14 years and $8 billion building the Large Hadron Collider, in which the colliding protons will recreate energies and conditions last seen a trillionth of a second after the Big Bang. Researchers will sift the debris from these primordial recreations for clues to the nature of mass and new forces and symmetries of nature.

But Walter L. Wagner and Luis Sancho contend that scientists at the European Center for Nuclear Research, or CERN, have played down the chances that the collider could produce, among other horrors, a tiny black hole, which, they say, could eat the Earth. Or it could spit out something called a “strangelet” that would convert our planet to a shrunken dense dead lump of something called “strange matter.” Their suit also says CERN has failed to provide an environmental impact statement as required under the National Environmental Policy Act.

Although it sounds bizarre, the case touches on a serious issue that has bothered scholars and scientists in recent years — namely how to estimate the risk of new groundbreaking experiments and who gets to decide whether or not to go ahead.

The lawsuit, filed March 21 in Federal District Court, in Honolulu, seeks a temporary restraining order prohibiting CERN from proceeding with the accelerator until it has produced a safety report and an environmental assessment. It names the federal Department of Energy, the Fermi National Accelerator Laboratory, the National Science Foundation and CERN as defendants.

According to a spokesman for the Justice Department, which is representing the Department of Energy, a scheduling meeting has been set for June 16.

Why should CERN, an organization of European nations based in Switzerland, even show up in a Hawaiian courtroom?

In an interview, Mr. Wagner said, “I don’t know if they’re going to show up.” CERN would have to voluntarily submit to the court’s jurisdiction, he said, adding that he and Mr. Sancho could have sued in France or Switzerland, but to save expenses they had added CERN to the docket here. He claimed that a restraining order on Fermilab and the Energy Department, which helps to supply and maintain the accelerator’s massive superconducting magnets, would shut down the project anyway.

James Gillies, head of communications at CERN, said the laboratory as of yet had no comment on the suit. “It’s hard to see how a district court in Hawaii has jurisdiction over an intergovernmental organization in Europe,” Mr. Gillies said.

“There is nothing new to suggest that the L.H.C. is unsafe,” he said, adding that its safety had been confirmed by two reports, with a third on the way, and would be the subject of a discussion during an open house at the lab on April 6.

“Scientifically, we’re not hiding away,” he said.

But Mr. Wagner is not mollified. “They’ve got a lot of propaganda saying it’s safe,” he said in an interview, “but basically it’s propaganda.”

In an e-mail message, Mr. Wagner called the CERN safety review “fundamentally flawed” and said it had been initiated too late. The review process violates the European Commission’s standards for adhering to the “Precautionary Principle,” he wrote, “and has not been done by ‘arms length’ scientists.”

Physicists in and out of CERN say a variety of studies, including an official CERN report in 2003, have concluded there is no problem. But just to be sure, last year the anonymous Safety Assessment Group was set up to do the review again.

“The possibility that a black hole eats up the Earth is too serious a threat to leave it as a matter of argument among crackpots,” said Michelangelo Mangano, a CERN theorist who said he was part of the group. The others prefer to remain anonymous, Mr. Mangano said, for various reasons. Their report was due in January.

This is not the first time around for Mr. Wagner. He filed similar suits in 1999 and 2000 to prevent the Brookhaven National Laboratory from operating the Relativistic Heavy Ion Collider. That suit was dismissed in 2001. The collider, which smashes together gold ions in the hopes of creating what is called a “quark-gluon plasma,” has been operating without incident since 2000.

=========



Mr. Wagner, who lives on the Big Island of Hawaii, studied physics and did cosmic ray research at the University of California, Berkeley, and received a doctorate in law from what is now known as the University of Northern California in Sacramento. He subsequently worked as a radiation safety officer for the Veterans Administration.


Mr. Sancho, who describes himself as an author and researcher on time theory, lives in Spain, probably in Barcelona, Mr. Wagner said.

Doomsday fears have a long, if not distinguished, pedigree in the history of physics. At Los Alamos before the first nuclear bomb was tested, Emil Konopinski was given the job of calculating whether or not the explosion would set the atmosphere on fire.

The Large Hadron Collider is designed to fire up protons to energies of seven trillion electron volts before banging them together. Nothing, indeed, will happen in the CERN collider that does not happen 100,000 times a day from cosmic rays in the atmosphere, said Nima Arkani-Hamed, a particle theorist at the Institute for Advanced Study in Princeton.

What is different, physicists admit, is that the fragments from cosmic rays will go shooting harmlessly through the Earth at nearly the speed of light, but anything created when the beams meet head-on in the collider will be born at rest relative to the laboratory and so will stick around and thus could create havoc.

The new worries are about black holes, which, according to some variants of string theory, could appear at the collider. That possibility, though a long shot, has been widely ballyhooed in many papers and popular articles in the last few years, but would they be dangerous?

According to a paper by the cosmologist Stephen Hawking in 1974, they would rapidly evaporate in a poof of radiation and elementary particles, and thus pose no threat. No one, though, has seen a black hole evaporate.

As a result, Mr. Wagner and Mr. Sancho contend in their complaint, black holes could really be stable, and a micro black hole created by the collider could grow, eventually swallowing the Earth.

But William Unruh, of the University of British Columbia, whose paper exploring the limits of Dr. Hawking’s radiation process was referenced on Mr. Wagner’s Web site, said they had missed his point. “Maybe physics really is so weird as to not have black holes evaporate,” he said. “But it would really, really have to be weird.”

Lisa Randall, a Harvard physicist whose work helped fuel the speculation about black holes at the collider, pointed out in a paper last year that black holes would probably not be produced at the collider after all, although other effects of so-called quantum gravity might appear.

As part of the safety assessment report, Dr. Mangano and Steve Giddings of the University of California, Santa Barbara, have been working intensely for the last few months on a paper exploring all the possibilities of these fearsome black holes. They think there are no problems but are reluctant to talk about their findings until they have been peer reviewed, Dr. Mangano said.

Dr. Arkani-Hamed said concerning worries about the death of the Earth or universe, “Neither has any merit.” He pointed out that because of the dice-throwing nature of quantum physics, there was some probability of almost anything happening. There is some minuscule probability, he said, “the Large Hadron Collider might make dragons that might eat us up.”

Body-by-Guinness:
How to map the multiverse

04 May 2009 by Anil Ananthaswamy

BRIAN GREENE spent a good part of the last decade extolling the virtues of string theory. He dreamed that one day it would provide physicists with a theory of everything that would describe our universe - ours and ours alone. His bestselling book The Elegant Universe eloquently captured the quest for this ultimate theory.

"But the fly in the ointment was that string theory allowed for, in principle, many universes," says Greene, who is a theoretical physicist at Columbia University in New York. In other words, string theory seems equally capable of describing universes very different from ours. Greene hoped that something in the theory would eventually rule out most of the possibilities and single out one of these universes as the real one: ours.

So far, it hasn't - though not for any lack of trying. As a result, string theorists are beginning to accept that their ambitions for the theory may have been misguided. Perhaps our universe is not the only one after all. Maybe string theory has been right all along.

Greene, certainly, has had a change of heart. "You walk along a number of pathways in physics far enough and you bang into the possibility that we are one universe of many," he says. "So what do you do? You smack yourself in the head and say, 'Ah, maybe the universe is trying to tell me something.' I have personally undergone a sort of transformation, where I am very warm to this possibility of there being many universes, and that we are in the one where we can survive."

We keep banging into the possibility that we are one universe of many. Maybe that's telling us something
Greene's transformation is emblematic of a profound change among the majority of physicists. Until recently, many were reluctant to accept this idea of the "multiverse", or were even belligerent towards it. However, recent progress in both cosmology and string theory is bringing about a major shift in thinking. Gone is the grudging acceptance or outright loathing of the multiverse. Instead, physicists are starting to look at ways of working with it, and maybe even trying to prove its existence.

If such ventures succeed, our universe will go the way of Earth - from seeming to be the centre of everything to being exposed as just a backwater in a far vaster cosmos. And just as we are unable to deduce certain aspects of Earth from first principles - such as its radius or distance from the sun - we will have to accept that some things about our universe are a random accident, inexplicable except in the context of the multiverse.

One of the first to argue for a multiverse was Russian physicist Andrei Linde, now at Stanford University in California. In the 1980s, Linde extended and improved upon an idea called inflation, which suggests that the universe underwent a period of exponential expansion in the first fractions of a second after the big bang. Inflation successfully explains why the universe looks pretty much the same in all directions, and why space-time is "flat", despite Einstein showing that it can just as easily be curved.

Linde realised that inflation could be ongoing or "eternal", in the sense that once space-time starts inflating, it can stop in some parts (such as ours) yet take off with renewed vigour elsewhere. This process continues ad infinitum, giving rise to a patchwork of regions of space, each with different properties. When and how inflation ceases in a particular patch dictates the exact nature and types of fundamental particles there and the laws of physics that govern their behaviour. Over time, eternal inflation gives rise to just about every possible type of universe predicted by string theory. Our universe, argues Linde, is a part of this multiverse.

It wasn't until 1998, however, that the multiverse gained any traction, when astronomers studying distant supernovae announced that the expansion of the universe is accelerating. They put this down to the vacuum of space having a small energy density, which exerts a repulsive force to counteract gravity as the universe ages. This became known as dark energy, or the cosmological constant.

Its discovery was a huge blow. Up till then, physicists had hoped that some ultimate theory would deduce the values of fundamental constants of nature from first principles, including the cosmological constant, and explain why the laws of physics are as they are, just right for the formation of stars and galaxies and possibly the emergence of life. This seems not to be the case. Nothing in string theory, or indeed any other theory in physics, can predict the observed value of the cosmological constant.

However, if our universe is part of a multiverse then we can ascribe the value of the cosmological constant to an accident. The same goes for other aspects of our universe, such as the mass of the electron. The idea is simply that each universe's laws of physics and fundamental constants are randomly determined, and we just happen to live in one where these are suited for life. "If not for the multiverse, you would have these unsolved problems at every corner," says Linde.

The other compelling argument for a multiverse comes from string theory. This maintains that all fundamental particles of matter and forces of nature arise from the vibration of tiny strings in 10 dimensions. For us not to notice the extra six dimensions of space, they must be curled up, or compacted, so small as to be undetectable. For decades, mathematicians toiled over what different forms this compaction could take, and they found myriad ways of scrunching up space-time - a staggering 10500 or more.

Each form gives rise to a different vacuum of space-time, and hence a different universe - with its own vacuum energy, fundamental particles and laws of physics. The hope, nurtured by Greene and others, was that there was some kind of uniqueness principle that would pick out the particular form of space-time that produces our universe.

That hope has since receded dramatically. In 2004, Michael Douglas of the State University of New York in Stony Brook, and Leonard Susskind of Stanford University surveyed the developments in string theory to date and concluded that all these theoretical varieties of space-time should be taken seriously as physical realities - that is, they point to a multiverse. Susskind coined the term "the landscape of string theory" to describe the 10500 or more different universes. Nothing in string theory suggests that any one of these universes is preferred over others. Rather, it appears all are equally likely.

Together, dark energy and string theory are making physicists see the multiverse anew. "Just about everybody is convinced that the idea of uniqueness has gone down the drain," says Susskind. So what are we to do? Throw up our hands and admit that we will never be able to explain why our universe is the way it is?

Exploring the landscape

Not a bit of it. Susskind argues that we can still ask meaningful questions within the context of the multiverse, just not the ones we'd ask if ours were the only universe. Questions such as: can we identify the exact point in the landscape that corresponds to our universe, or at least the parts of the landscape that most closely resemble our universe? Is it possible to tell which of our universe's properties can be derived from first principles and which ones are random?

We can still ask meaningful questions about the universe, just not the ones we'd ask if it were unique
Also, can we find parts of the landscape with the right conditions for eternal inflation to take place? After all, the landscape and eternal inflation are independent concepts. Confirming that they are compatible would lend more credence to the multiverse idea.

These are not trivial questions to answer, but string theorists are rising to the challenge by feverishly exploring the landscape. Investigating a collection of 10500 universes is not a matter of enumerating the properties of each of them, however. "We just can't make a list of 10500 things," says Nobel laureate Steven Weinberg of the University of Texas at Austin. "That's more than the number of atoms in the observable universe."

The first line of attack has been to develop mathematical models of the landscape. These describe the landscape as a terrain of hills and valleys, where each valley represents a place with its own parameters (such as the mass of the electron) and fields (such as gravity).

How does a universe develop according to this scenario, and what can it tell us about ours? Imagine the universe as it starts off as a speck of space-time. This baby universe is filled with fields, whose properties change due to quantum fluctuations. If the conditions are ripe for inflation, the speck will grow and this will alter its nature. Depending on the changing environment inside the emerging universe, the inflationary process could grind to a halt, continue apace or even spawn other specks of space-time.

According to the landscape picture, the baby universe starts off in one valley. Quantum fluctuations can then cause the entire universe to "tunnel" through an adjoining hill, eventually ending up in another valley with different properties. This process continues, with the universe tunnelling from valley to valley, until it reaches a place stable enough for inflation to run its full course.

Given this scenario, one of the most important tasks is reconciling eternal inflation with the landscape. "The whole picture can be boiled down to one issue: is there eternal inflation in the landscape?" says Henry Tye of Cornell University in Ithaca, New York. In Linde's model of eternal inflation, the speck of space-time starts off with high energy density. The energy density slowly falls as space-time inflates. The quest is to find configurations of space-time among the 10500 that match Linde's requirements for eternal inflation.

Until recently, this had seemed impossible. Then, last year, Eva Silverstein and Alexander Westphal of Stanford University identified two places within the landscape for Linde's version of eternal inflation to take place (Physical Review D, vol 78, p 106003).

It's a promising start, but Tye argues that eternal inflation within string theory is not a done deal. Physicists could just as well start with string theory models of the universe with entirely different initial conditions that would lead to inflation, though not eternal inflation.

Experiments are the key to answering such concerns, by testing the predictions of the various alternative theories. For instance, the energy density in the model proposed by Silverstein is high enough to create strong gravitational waves, ripples in space-time generated by the rapid expansion of the universe. Such waves could have polarised the photons of the cosmic microwave background, the radiation left over from the big bang, and such an imprint would still be detectable today. The European Space Agency's Planck satellite, due to launch soon, will look for any polarisation.

If Planck sees it, then it will lend support to Silverstein's models and eternal inflation. But even if experiments like Planck do lend support for eternal inflation, theorists will need independent confirmation for the ideas of string theory. Unfortunately no specific predictions of string theory are yet within experimental reach, but there is one key general property that could be confirmed soon. String theory requires that the universe has a property known as supersymmetry, which posits that every particle known to physicists has a heavier and as yet unseen superpartner. Physicists will be looking for some of these superpartners at the Large Hadron Collider, the new particle accelerator at CERN, near Geneva, Switzerland.

The scenario of a universe tunnelling through the landscape also makes a unique prediction. If our universe emerged after tunnelling in this way, then the theory predicts that space-time today will be ever so slightly curved. That's because in this scenario, inflation does not last long enough to make the universe totally flat.

Today's measurements show the universe to be flat, but the uncertainty in those measurements still leaves room for space-time to be slightly curved - either like a saddle (negatively curved) or like a sphere (positively curved). "If we originated from a tunnelling event from an ancestor vacuum, the bet would be that the universe is negatively curved," says Susskind. "If it turns out to be positively curved, we'd be very confused. That would be a setback for these ideas, no question about it."

Until any such setback the smart money will remain with the multiverse and string theory. "It has the best chance of anything we know to be right," Weinberg says of string theory. "There's an old joke about a gambler playing a game of poker," he adds. "His friend says, 'Don't you know this game is crooked, and you are bound to lose?' The gambler says, 'Yes, but what can I do, it's the only game in town.' We don't know if we are bound to lose, but even if we suspect we may, it is the only game in town."

Anil Ananthaswamy is a consulting editor for New Scientist

http://www.newscientist.com/article/mg20227061.200-how-to-map-the-multiverse.html?full=true&print=true

Navigation

[0] Message Index

[#] Next page

[*] Previous page