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Scientists Extend Einstein’s Relativity To The Universe’s First Moments
By Davide Castelvecchi

Instants after the big bang, the universe underwent a burst of rapid expansion known as inflation. In this period, according to standard cosmology, tiny ripples of energy seeded galaxies and the other large-scale structures we see today. But no one can explain how the ripples formed in the first place. Three physicists now say the key to this riddle lies in quantum gravity, a still tentative theory in which gravity would display the same fuzzy “uncertainty” typical of subatomic physics.

Standard cosmology, based on Einstein’s general theory of relativity, cannot explain the origin of the ripples, because it breaks down at very small scales. During the infinitesimally brief period before the start of inflation, called the Planck era, the entire known universe was stuffed into a region many orders of magnitude smaller than an atom. If pushed that far back, relativity makes nonsensical predictions such as infinite energy densities.

To extend the reach of Albert Einstein’s theory to such extreme regimes, researchers have developed a theory called loop quantum gravity. Beginning in the 1980s, Abhay Ashtekar, now at Pennsylvania State University, rejiggered Einstein’s equations to make them quantum-friendly. Among the consequences are that space itself, instead of being a smooth backdrop, would consist of discrete units called loops and that its microscopic structure could fluctuate among multiple simultaneous states. In recent years physicists have also found that if loop quantum gravity is correct—a big if because experimental evidence is still lacking—then the big bang would really have been a “big bounce” from an earlier collapsing universe.

Ashtekar’s team now says that by extending loop quantum gravity techniques it has bridged the gap between the big bounce—which is in the Planck regime—and the onset of inflation and that it can explain those all-important ripples without which you and I would not be here. The ripples, the researchers calculate, would be the natural outcome of quantum fluctuations existing at the time of the big bounce.

The team’s predictions, however, differ slightly from those of “vanilla” inflation in a way that could be tested in future surveys of cosmic structure, Ashtekar says.

These results, to appear in Physical Review Letters, provide “a self-consistent extension of inflation all the way to the Planck scale,” Ashtekar says.

The conclusion that quantum gravity might have left an imprint on today’s large-scale cosmic structures is “quite surprising and beautiful,” says Jorge Pullin of Louisiana State University, an expert on loop quantum gravity who was not involved in the research.

Neil Turok, director of the Perimeter Institute for Theoretical Physics in Ontario, says that the team still needs “artificial assumptions,” which it pushes back from the onset of inflation to an earlier time. Loop quantum gravity “has many interesting ideas,” Turok says, “but it is not yet a theory one should take too seriously as making predictions.”

Beyond ‘absolute zero’ temperatures get hotter
Posted January 5, 2013 - 06:30 by Flora Malein

It sounds like a contradiction in terms but scientists have reached temperatures that go beyond absolute zero in a lab, and get hotter as they do so.

Whereas we’re all aware of what happens when temperatures hit negative temperatures on the Fahrenheit and Celsius scales (hint: it gets really cold), the Kelvin scale is an absolute temperature scale in physics where it is not possible to go beyond 0 degrees Kelvin. Therefore, the lowest point that any temperature can reach is 0 K or −460 °F (−273.15 °C); at least that’s what scientists thought until till now.

When they cooled an atomic gas to extreme lows, known as ‘ultracooling’, physicists at the Ludwig-Maximilians University Munich and the Max Planck Institute of Quantum Optics in Germany created a gas that went beyond absolute zero.

They found that the atoms in the ultracooled gas attract each other and give rise to a negative pressure. Instead of standing still when they go beyond 0 K, the gas becomes hotter.

“The gas is not colder than zero kelvin, but hotter,” says physicist Ulrich Schneider, lead author on the paper that is published in the journal Science.

“It is even hotter than at any positive temperature.”

This strange behavior has everything to do with how energy is spread throughout the atoms in a gas known as the ‘Boltzmann distribution’. A gas at any temperature will have different amounts of energy spread amongst its atoms. In a gas that is cooled, the majority of the particles will have low energy states although a few will have higher energy states.

When the Kelvin temperatures become negative in the ultracooled gas, the distributions of energy is the opposite way round so that most of the particles have very high energy states while very few have low ones. In this case, the Boltzmann distribution is said to be ‘inverted’ so that the normal state of affairs is reversed.

“The inverted Boltzmann distribution is the hallmark of negative absolute temperature; and this is what we have achieved,” says Schneider.

Their finding suggests that the previously impossible idea of a combustion engine that is 100 percent efficient may actually be achievable. Their finding offers a tantalizing insight into how ‘dark energy’, the elusive force that cosmologists believe is responsible for the expansion of the universe, might work.

As the Universe should be contracting under the force of gravity, rather than expanding as measurements suggest, the authors believe that dark energy could cause the expansion of the Universe by behaving in the opposite way to what is expected from the force of gravity. In the same way that the gas particles attract each other at negative temperatures rather than being repelled, dark energy may cause the expansion of the Universe by acting as a sort of negative gravity.

A universe without purpose

New revelations in science have shown what a strange and remarkable universe we live in.

By Lawrence M. Krauss April 1, 2012

The illusion of purpose and design is perhaps the most pervasive illusion about nature that science has to confront on a daily basis. Everywhere we look, it appears that the world was designed so that we could flourish.

The position of the Earth around the sun, the presence of organic materials and water and a warm climate — all make life on our planet possible. Yet, with perhaps 100 billion solar systems in our galaxy alone, with ubiquitous water, carbon and hydrogen, it isn’t surprising that these conditions would arise somewhere. And as to the diversity of life on Earth — as Darwin described more than 150 years ago and experiments ever since have validated — natural selection in evolving life forms can establish both diversity and order without any governing plan.

As a cosmologist, a scientist who studies the origin and evolution of the universe, I am painfully aware that our illusions nonetheless reflect a deep human need to assume that the existence of the Earth, of life and of the universe and the laws that govern it require something more profound. For many, to live in a universe that may have no purpose, and no creator, is unthinkable.

But science has taught us to think the unthinkable. Because when nature is the guide — rather than a priori prejudices, hopes, fears or desires — we are forced out of our comfort zone. One by one, pillars of classical logic have fallen by the wayside as science progressed in the 20th century, from Einstein’s realization that measurements of space and time were not absolute but observer-dependent, to quantum mechanics, which not only put fundamental limits on what we can empirically know but also demonstrated that elementary particles and the atoms they form are doing a million seemingly impossible things at once.

And so it is that the 21st century has brought new revolutions and new revelations on a cosmic scale. Our picture of the universe has probably changed more in the lifetime of an octogenarian today than in all of human history. Eighty-seven years ago, as far as we knew, the universe consisted of a single galaxy, our Milky Way, surrounded by an eternal, static, empty void. Now we know that there are more than 100 billion galaxies in the observable universe, which began with the Big Bang 13.7 billion years ago. In its earliest moments, everything we now see as our universe — and much more — was contained in a volume smaller than the size of a single atom.

And so we continue to be surprised. We are like the early mapmakers redrawing the picture of the globe even as new continents were discovered. And just as those mapmakers confronted the realization that the Earth was not flat, we must confront facts that change what have seemed to be basic and fundamental concepts. Even our idea of nothingness has been altered.

We now know that most of the energy in the observable universe can be found not within galaxies but outside them, in otherwise empty space, which, for reasons we still cannot fathom, “weighs” something. But the use of the word “weight” is perhaps misleading because the energy of empty space is gravitationally repulsive. It pushes distant galaxies away from us at an ever-faster rate. Eventually they will recede faster than light and will be unobservable.

This has changed our vision of the future, which is now far bleaker. The longer we wait, the less of the universe we will be able to see. In hundreds of billions of years astronomers on some distant planet circling a distant star (Earth and our sun will be long gone) will observe the cosmos and find it much like our flawed vision at the turn of the last century: a single galaxy immersed in a seemingly endless dark, empty, static universe.

Out of this radically new image of the universe at large scale have also come new ideas about physics at a small scale. The Large Hadron Collider has given tantalizing hints that the origin of mass, and therefore of all that we can see, is a kind of cosmic accident. Experiments in the collider bolster evidence of the existence of the “Higgs field,” which apparently just happened to form throughout space in our universe; it is only because all elementary particles interact with this field that they have the mass we observe today.

Most surprising of all, combining the ideas of general relativity and quantum mechanics, we can understand how it is possible that the entire universe, matter, radiation and even space itself could arise spontaneously out of nothing, without explicit divine intervention. Quantum mechanics’ Heisenberg uncertainty principle expands what can possibly occur undetected in otherwise empty space. If gravity too is governed by quantum mechanics, then even whole new universes can spontaneously appear and disappear, which means our own universe may not be unique but instead part of a “multiverse.”

As particle physics revolutionizes the concepts of “something” (elementary particles and the forces that bind them) and “nothing” (the dynamics of empty space or even the absence of space), the famous question, “Why is there something rather than nothing?” is also revolutionized. Even the very laws of physics we depend on may be a cosmic accident, with different laws in different universes, which further alters how we might connect something with nothing. Asking why we live in a universe of something rather than nothing may be no more meaningful than asking why some flowers are red and others blue.

Perhaps most remarkable of all, not only is it now plausible, in a scientific sense, that our universe came from nothing, if we ask what properties a universe created from nothing would have, it appears that these properties resemble precisely the universe we live in.

Does all of this prove that our universe and the laws that govern it arose spontaneously without divine guidance or purpose? No, but it means it is possible.

And that possibility need not imply that our own lives are devoid of meaning. Instead of divine purpose, the meaning in our lives can arise from what we make of ourselves, from our relationships and our institutions, from the achievements of the human mind.

Imagining living in a universe without purpose may prepare us to better face reality head on. I cannot see that this is such a bad thing. Living in a strange and remarkable universe that is the way it is, independent of our desires and hopes, is far more satisfying for me than living in a fairy-tale universe invented to justify our existence.

Lawrence M. Krauss is director of the Origins Project at Arizona State University. His newest book is “A Universe From Nothing.”

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