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New Kepler analysis finds many Earth-like planets; total 3,500 exoplanets

New Kepler analysis finds many Earth-like planets; total 3,500 exoplanets | physics | Scoop.it
Earth-like planets are common around Sun-like stars, too.
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wait but why: Putting Time In Perspective

wait but why: Putting Time In Perspective | physics | Scoop.it
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Why trust climate models? It’s a matter of simple science

Why trust climate models? It’s a matter of simple science | physics | Scoop.it
How climate scientists test, test again, and use their simulation tools.
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Coldest brown dwarfs blur lines between stars and planets

Coldest brown dwarfs blur lines between stars and planets | physics | Scoop.it

Astronomers are constantly on the hunt for ever-colder star-like bodies, and two years ago a new class of objects was discovered by researchers using NASA's WISE space telescope. However, until now no one has known exactly how cool their surfaces really are -- some evidence suggested they could be room temperature.

 

A new study shows that while these brown dwarfs, sometimes called failed stars, are indeed the coldest known free-floating celestial bodies, they are warmer than previously thought with temperatures about 250-350 degrees Fahrenheit.

 

To reach such low surface temperatures after cooling for billions of years means that these objects can only have about 5 to 20 times the mass of Jupiter. Unlike the Sun, these objects' only source of energy is from their gravitational contraction, which depends directly on their mass.

 

"If one of these objects was found orbiting a star, there is a good chance that it would be called a planet," says Trent Dupuy, a Hubble Fellow at the Harvard-Smithsonian Center for Astrophysics. But because they probably formed on their own and not in a proto-planetary disk, astronomers still call these objects brown dwarfs even if they are "planetary mass."

 

Characterizing these cold brown dwarfs is challenging because they emit most of their light at infrared wavelengths, and they are very faint due to their small size and low temperature.

 

To get accurate temperatures, astronomers need to know the distances to these objects. "We wanted to find out if they were colder, fainter, and nearby or if they were warmer, brighter, and more distant," explains Dupuy. Using NASA's Spitzer Space Telescope, the team determined that the brown dwarfs in question are located at distances 20 to 50 light-years away.

 

To determine the distances to these objects the team measured their parallax -- the apparent change in position against background stars over time. As the Spitzer Space Telescope orbits the Sun its perspective changes and nearby objects appear to shift back and forth slightly. The same effect occurs if you hold up a finger in front of your face and close one eye and then the other. The position of your finger seems to shift when viewed against the distant background.

 

But even for these relatively nearby brown dwarfs, the parallax motion is small. "To be able to determine accurate distances, our measurements had to be the same precision as knowing the position of a firefly to within 1 inch from 200 miles away," explains Adam Kraus, professor at the University of Texas at Austin and the other author of the study.


Via Dr. Stefan Gruenwald
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Stars' escape velocity shows how to exit the Milky Way - space - 23 September 2013 - New Scientist

Stars' escape velocity shows how to exit the Milky Way - space - 23 September 2013 - New Scientist | physics | Scoop.it
Speeding stars reveal how fast your spaceship would have to be to escape the Milky Way's gravitational clutches – better start your antimatter
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Fabric of Reality: The origins of space and time - If space and time are not fundamental, what is?

Fabric of Reality: The origins of space and time - If space and time are not fundamental, what is? | physics | Scoop.it
Many researchers believe that physics will not be complete until it can explain not just the behaviour of space and time, but where these entities come from.

 

“Imagine waking up one day and realizing that you actually live inside a computer game,” says Mark Van Raamsdonk, describing what sounds like a pitch for a science-fiction film. But for Van Raamsdonk, a physicist at the University of British Columbia in Vancouver, Canada, this scenario is a way to think about reality. If it is true, he says, “everything around us — the whole three-dimensional physical world — is an illusion born from information encoded elsewhere, on a two-dimensional chip”. That would make our Universe, with its three spatial dimensions, a kind of hologram, projected from a substrate that exists only in lower dimensions.

 

This 'holographic principle' is strange even by the usual standards of theoretical physics. But Van Raamsdonk is one of a small band of researchers who think that the usual ideas are not yet strange enough. If nothing else, they say, neither of the two great pillars of modern physics — general relativity, which describes gravity as a curvature of space and time, and quantum mechanics, which governs the atomic realm — gives any account for the existence of space and time. Neither does string theory, which describes elementary threads of energy. Van Raamsdonk and his colleagues are convinced that physics will not be complete until it can explain how space and time emerge from something more fundamental — a project that will require concepts at least as audacious as holography.

 

But, where is the evidence that there actually is anything more fundamental than space and time? A provocative hint comes from a series of startling discoveries made in the early 1970s, when it became clear that quantum mechanics and gravity were intimately intertwined with thermodynamics, the science of heat. In 1974, most famously, Stephen Hawking of the University of Cambridge, UK, showed that quantum effects in the space around a black hole will cause it to spew out radiation as if it was hot. Other physicists quickly determined that this phenomenon was quite general. Even in completely empty space, they found, an astronaut undergoing acceleration would perceive that he or she was surrounded by a heat bath. The effect would be too small to be perceptible for any acceleration achievable by rockets, but it seemed to be fundamental. If quantum theory and general relativity are correct — and both have been abundantly corroborated by experiment — then the existence of Hawking radiation seemed inescapable.

 

A second key discovery was closely related. In standard thermodynamics, an object can radiate heat only by decreasing its entropy, a measure of the number of quantum states inside it. And so it is with black holes: even before Hawking's 1974 paper, Jacob Bekenstein, now at the Hebrew University of Jerusalem, had shown that black holes possess entropy. But there was a difference. In most objects, the entropy is proportional to the number of atoms the object contains, and thus to its volume. But a black hole's entropy turned out to be proportional to the surface area of its event horizon — the boundary out of which not even light can escape. It was as if that surface somehow encoded information about what was inside, just as a two-dimensional hologram encodes a three-dimensional image.

 

In 1995 then, Ted Jacobson, a physicist at the University of Maryland in College Park, combined these two findings, and postulated that every point in space lies on a tiny 'black-hole horizon' that also obeys the entropy–area relationship. From that, he found, the mathematics yielded Einstein's equations of general relativity — but using only thermodynamic concepts, not the idea of bending space-time. Ted's result suggested that gravity is statistical, a macroscopic approximation to the unseen constituents of space and time.

 

In 2010, this idea was taken a step further by Erik Verlinde, a string theorist at the University of Amsterdam, who showed that the statistical thermodynamics of the space-time constituents — whatever they turned out to be — could automatically generate Newton's law of gravitational attraction. In separate work, Thanu Padmanabhan, a cosmologist at the Inter-University Centre for Astronomy and Astrophysics in Pune, India, showed that Einstein's equations can be rewritten in a form that makes them identical to the laws of thermodynamics — as can many alternative theories of gravity. Padmanabhan is currently extending the thermodynamic approach in an effort to explain the origin and magnitude of dark energy: a mysterious cosmic force that is accelerating the Universe's expansion.


Via Dr. Stefan Gruenwald
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Alain Coetmeur's comment, August 31, 2013 5:56 AM
Yes, there is more and more hint that physics is ruled by information theory. 2d TD law is information law. Note that 1st TD law, is implied by 2nd TD law (give me a machine violating TD2, I build a TD1 violating machine). TD2 is heisenberg inequality. Quantum physics is based on the fact that the only reality is what you measure, ie information. Bose-einsteain inequality cliam that if something is same it is counted as one. Relativity claim that information flows below lightspeed, and that any observer is equivalent to another... finally you have informations... where does the lightspeed limit came ? is it an axiom or a consequence of symmetries... funny.
RUBEN RODRIGUEZ AMADOR's curator insight, October 17, 2013 9:58 AM

¿Qué Teoría del Espacio-Tiempo es convalida por la Física actual?