September 28th, 2011

(Source: aaronscanvas)

September 2nd, 2011

Black Holes

Cosmic sink-holes or Black Holes is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that marks the point of no return. It is called “black” because it absorbs all the light that hits the horizon, reflecting nothing, just like a perfect black body in thermodynamics. Quantum mechanics predicts that black holes emit radiation like a black body with a finite temperature. This temperature is inversely proportional to the mass of the black hole, making it difficult to observe this radiation for black holes of stellar mass or greater.

(Source: kenobi-wan-obi)

August 21st, 2011

geopolicraticus:

Recently on my other blog, in Beyond the Big Bang, I wrote about some of the recent stories about the “multiverse” that I’ve been seeing, which I assume to be due to the fact that this is on the cover of this month’s Scientific American.

Some years ago I read the remark — now I have no idea whatsoever where I found it — that some time in the early modern period, someone was the first to realize that our sun is a star, like the other stars we see in the night sky, and these stars are all suns in turn (though they aren’t our sun).

The realization that our sun is a star, though now a commonplace, was a discovery of momentous importance, and we don’t know who the discoverer was: someone was the first to have the idea, the first to think the thought, but we don’t know who. This is a discovery the discoverer of which is unknown, an unsung hero of cosmology.

The discovery that our sun is a star, and that the stars are suns in turn, is an application to cosmology of uniformitarianism. The uniformity of nature, like the principle of parsimony and methodological naturalism, belongs among the small number of philosophical principles that are constitutive of the scientific enterprise.

The Copernican Principle is essentially an alternative formulation of uniformitarianism for cosmology: if the universe is uniform, then all perspectives are equal, and there are no privileged observers.

The next stage in the development of the Copernican Principle, which would apply uniformitarianism on an even larger scale — which would indeed apply uniformitarianism to the multiverse — will be to realize that the big bang is, in fact, our big bang.

I think it will take us a long time to get there, as the scope of the multiverse poses problems that observational cosmology cannot yet address, but there will come a time when multiple big bangs are understood to have occurred, and that our big bang is one among many, and the other big bangs are for these other universes as our big bang is to our universe.

Contemporary cosmology is an undertaking of unprecedented scope. It takes time to wrap our minds around concepts this large; our hunter-gatherer minds aren’t really fit for the task, though we can exapt them for it if we push ourselves hard enough. Still, it takes time.

Black holes were once thought to be a theoretical curiosity not likely to be actually instantiated in nature. And then a black hole was discovered at Cygnus, but they were thought to be rare — cosmological oddities. Now it is thought that every major spiral galaxy — of which there are more than we can conceive — has a supermassive black hole at its center.

It will probably be a similarly gradual process in acquainting ourselves with the inconceivable extent of the multiverse and big bangs as plentiful as stars in the night sky or galaxies in the Hubble Ultra Deep Field image.

image

August 18th, 2011
sciencecenter:

Astronomers detect oxygen in space

For the first time, astronomers have found molecular oxygen, which makes up about 20 percent of our air on Earth, in space. Using the large telescope aboard the Herschel Space Observatory, a team of researchers from the European Space Agency and NASA detected the simple molecule in a star-forming region of the Orion Nebula, located about 1,500 light-years from Earth. This takes astronomers one step closer to discovering where all of the oxygen in space is hiding.

sciencecenter:

Astronomers detect oxygen in space

For the first time, astronomers have found molecular oxygen, which makes up about 20 percent of our air on Earth, in space. Using the large telescope aboard the Herschel Space Observatory, a team of researchers from the European Space Agency and NASA detected the simple molecule in a star-forming region of the Orion Nebula, located about 1,500 light-years from Earth. This takes astronomers one step closer to discovering where all of the oxygen in space is hiding.

August 15th, 2011

Splitting Time from Space—New Quantum Theory Topples Einstein’s:
Was Newton right and Einstein wrong? It seems that unzipping the fabric of spacetime and harking back to 19th-century notions of time could lead to a theory of quantum gravity.

Physicists have struggled to marry quantum mechanics with gravity for decades. In contrast, the other forces of nature have obediently fallen into line. For instance, the electromagnetic force can be described quantum-mechanically by the motion of photons. Try and work out the gravitational force between two objects in terms of a quantum graviton, however, and you quickly run into trouble—the answer to every calculation is infinity. But now Petr HoYava, a physicist at the University of California, Berkeley, thinks he understands the problem. It’s all, he says, a matter of time.
More specifically, the problem is the way that time is tied up with space in Einstein’s theory of gravity: general relativity. Einstein famously overturned the Newtonian notion that time is absolute—steadily ticking away in the background. Instead he argued that time is another dimension, woven together with space to form a malleable fabric that is distorted by matter. The snag is that in quantum mechanics, time retains its Newtonian aloofness, providing the stage against which matter dances but never being affected by its presence. These two conceptions of time don’t gel.
The solution, HoYava says, is to snip threads that bind time to space at very high energies, such as those found in the early universe where quantum gravity rules. “I’m going back to Newton’s idea that time and space are not equivalent,” HoYava says. At low energies, general relativity emerges from this underlying framework, and the fabric of spacetime restitches, he explains.
HoYava likens this emergence to the way some exotic substances change phase. For instance, at low temperatures liquid helium’s properties change dramatically, becoming a “superfluid” that can overcome friction. In fact, he has co-opted the mathematics of exotic phase transitions to build his theory of gravity. So far it seems to be working: the infinities that plague other theories of quantum gravity have been tamed, and the theory spits out a well-behaved graviton. It also seems to match with computer simulations of quantum gravity.
HoYava’s theory has been generating excitement since he proposed it in January, and physicists met to discuss it at a meeting in November at the Perimeter Institute for Theoretical Physics in Waterloo, Ontario. In particular, physicists have been checking if the model correctly describes the universe we see today. General relativity scored a knockout blow when Einstein predicted the motion of Mercury with greater accuracy than Newton’s theory of gravity could.
Can HoYYava gravity claim the same success? The first tentative answers coming in say “yes.” Francisco Lobo, now at the University of Lisbon, and his colleagues have found a good match with the movement of planets.
Others have made even bolder claims for HoYava gravity, especially when it comes to explaining cosmic conundrums such as the singularity of the big bang, where the laws of physics break down. If HoYava gravity is true, argues cosmologist Robert Brandenberger of McGill University in a paper published in the August Physical Review D, then the universe didn’t bang—it bounced. “A universe filled with matter will contract down to a small—but finite—size and then bounce out again, giving us the expanding cosmos we see today,” he says. Brandenberger’s calculations show that ripples produced by the bounce match those already detected by satellites measuring the cosmic microwave background, and he is now looking for signatures that could distinguish the bounce from the big bang scenario.

Read More on HoYava’s New Theory of Gravity, Reshaping Space and Time

Splitting Time from Space—New Quantum Theory Topples Einstein’s:

Was Newton right and Einstein wrong? It seems that unzipping the fabric of spacetime and harking back to 19th-century notions of time could lead to a theory of quantum gravity.

Physicists have struggled to marry quantum mechanics with gravity for decades. In contrast, the other forces of nature have obediently fallen into line. For instance, the electromagnetic force can be described quantum-mechanically by the motion of photons. Try and work out the gravitational force between two objects in terms of a quantum graviton, however, and you quickly run into trouble—the answer to every calculation is infinity. But now Petr HoYava, a physicist at the University of California, Berkeley, thinks he understands the problem. It’s all, he says, a matter of time.

More specifically, the problem is the way that time is tied up with space in Einstein’s theory of gravity: general relativity. Einstein famously overturned the Newtonian notion that time is absolute—steadily ticking away in the background. Instead he argued that time is another dimension, woven together with space to form a malleable fabric that is distorted by matter. The snag is that in quantum mechanics, time retains its Newtonian aloofness, providing the stage against which matter dances but never being affected by its presence. These two conceptions of time don’t gel.

The solution, HoYava says, is to snip threads that bind time to space at very high energies, such as those found in the early universe where quantum gravity rules. “I’m going back to Newton’s idea that time and space are not equivalent,” HoYava says. At low energies, general relativity emerges from this underlying framework, and the fabric of spacetime restitches, he explains.

HoYava likens this emergence to the way some exotic substances change phase. For instance, at low temperatures liquid helium’s properties change dramatically, becoming a “superfluid” that can overcome friction. In fact, he has co-opted the mathematics of exotic phase transitions to build his theory of gravity. So far it seems to be working: the infinities that plague other theories of quantum gravity have been tamed, and the theory spits out a well-behaved graviton. It also seems to match with computer simulations of quantum gravity.

HoYava’s theory has been generating excitement since he proposed it in January, and physicists met to discuss it at a meeting in November at the Perimeter Institute for Theoretical Physics in Waterloo, Ontario. In particular, physicists have been checking if the model correctly describes the universe we see today. General relativity scored a knockout blow when Einstein predicted the motion of Mercury with greater accuracy than Newton’s theory of gravity could.

Can HoYYava gravity claim the same success? The first tentative answers coming in say “yes.” Francisco Lobo, now at the University of Lisbon, and his colleagues have found a good match with the movement of planets.

Others have made even bolder claims for HoYava gravity, especially when it comes to explaining cosmic conundrums such as the singularity of the big bang, where the laws of physics break down. If HoYava gravity is true, argues cosmologist Robert Brandenberger of McGill University in a paper published in the August Physical Review D, then the universe didn’t bang—it bounced. “A universe filled with matter will contract down to a small—but finite—size and then bounce out again, giving us the expanding cosmos we see today,” he says. Brandenberger’s calculations show that ripples produced by the bounce match those already detected by satellites measuring the cosmic microwave background, and he is now looking for signatures that could distinguish the bounce from the big bang scenario.

Read More on HoYava’s New Theory of Gravity, Reshaping Space and Time

(via kenobi-wan-obi)

(Source: sfphysics)