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Interview with P. A. M. Dirac By Thomas S. Kuhn and Eugene Paul Wigner At Wigner’s home, Princeton, New Jersey April 1, l962

scienceisbeauty:

Mandatory reading for anyone interested in modern physics, the vision of one of its main precursors, Paul Dirac, interviewed by Thomas Kuhn and Eugene Wigner, nothing less.

About Dirac I always recomend this wonderful book from Graham Farmelo: The Strangest Man: The Hidden Life of Paul Dirac, Mystic of the Atom, and alternatively, this conference by the author:

h/t TRF

26 notes

spherical-harmonics:

Quantum bounce could make black holes explode

If space-time is granular, it could reverse gravitational collapse and turn it into expansion.

One of the leading approaches to merging quantum theory and gravity, pioneered by, among others, theoretical physicist Carlo Rovelli of Aix-Marseille University in France, posits that it is not just gravity but space-time itself that is quantized, woven from tiny, individual loops that cannot be subdivided any further. The loops in this ‘loop quantum gravity’ — a theoretical attempt that has yet to find experimental support — would be so tiny that to any observer space-time looks smooth and continuous. In the new work1, Rovelli and his Aix-Marseille colleague Hal Haggard have calculated that the loop structure would halt the collapse of a black hole.
The collapsing star would reach a stage at which its inside can shrink no further, because the loops cannot be compressed into anything smaller, and in fact they would exert an outward pressure that theorists call a quantum bounce, transforming a black hole into a white hole. Rather than being shrouded by a true, eternal event horizon, the event would be concealed by a temporary ‘apparent horizon’, says Rovelli. (Theoretical physicist Stephen Hawking of the University of Cambridge, UK, has recently suggested that true event horizons would be incompatible with quantum physics.)

spherical-harmonics:

Quantum bounce could make black holes explode

If space-time is granular, it could reverse gravitational collapse and turn it into expansion.

One of the leading approaches to merging quantum theory and gravity, pioneered by, among others, theoretical physicist Carlo Rovelli of Aix-Marseille University in France, posits that it is not just gravity but space-time itself that is quantized, woven from tiny, individual loops that cannot be subdivided any further. The loops in this ‘loop quantum gravity’ — a theoretical attempt that has yet to find experimental support — would be so tiny that to any observer space-time looks smooth and continuous. In the new work1, Rovelli and his Aix-Marseille colleague Hal Haggard have calculated that the loop structure would halt the collapse of a black hole.

The collapsing star would reach a stage at which its inside can shrink no further, because the loops cannot be compressed into anything smaller, and in fact they would exert an outward pressure that theorists call a quantum bounce, transforming a black hole into a white hole. Rather than being shrouded by a true, eternal event horizon, the event would be concealed by a temporary ‘apparent horizon’, says Rovelli. (Theoretical physicist Stephen Hawking of the University of Cambridge, UK, has recently suggested that true event horizons would be incompatible with quantum physics.)

279 notes

scienceisbeauty:

CERN announces LHC restart schedule:
2 June 2014 - Restart of the Proton Synchrotron Booster
18 June 2014 - Restart of the Proton Synchrotron (PS)
Early July - Powering tests at the Super Proton Synchrotron (SPS)
Mid-July - Physics programme to restart at the ISOLDE facility and at the PS
Mid-August - Antimatter Physics programme to restart at the Antiproton Decelerator
Mid-October - Physics programme to restart at the SPS
Early 2015 - Beam back into the Large Hadron Collider (LHC)
Spring 2015 - Physics programme to restart at the LHC experiments

scienceisbeauty:

CERN announces LHC restart schedule:

(via spherical-harmonics)

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astrodidact:

The towers will be built in the city of Wuhan in China, with one slightly taller than the other. With a planned height of almost a kilometre, the tallest of the pair will edge out the Burj Khalifa in Dubai as the tallest building in the world. 

They’ll also be two of the most environmentally friendly buildings ever made. According to Adele Peters at FastCompany, the pair will be built on an island, and the larger tower will be responsible for ‘feeding’ sustainable power to the smaller tower. It will also be responsible for cleaning its surroundings by pulling water up out of the lake, cleaning it, and then putting it back.

“The water goes up through a series of filters,” said Laurie Chetwood, chairman of UK-based Chetwoods architect firm in charge of the project. “We don’t use power to pull the water up, we’re using passive energy. As it goes through the filters and back, we’re also putting air back into the lake to make it healthier.”

"The towers also have pollution-absorbing coatings to help clean the air, vertical gardens that filter more pollution, and a chimney in the middle of the larger tower naturally pulls air across the lake for better ventilation. Wind turbines, lightweight solar cladding, and hydrogen fuel cells running on the buildings’ waste will generate all of the power used by the towers, plus a little extra for the rest of the neighbourhood."

Once approved by the city’s mayor, construction is planned to start at the end of the year, with a completion date of 2017 or 2018.

http://sciencealert.com.au/news/20143006-25779.html

astrodidact:

The towers will be built in the city of Wuhan in China, with one slightly taller than the other. With a planned height of almost a kilometre, the tallest of the pair will edge out the Burj Khalifa in Dubai as the tallest building in the world.

They’ll also be two of the most environmentally friendly buildings ever made. According to Adele Peters at FastCompany, the pair will be built on an island, and the larger tower will be responsible for ‘feeding’ sustainable power to the smaller tower. It will also be responsible for cleaning its surroundings by pulling water up out of the lake, cleaning it, and then putting it back.

“The water goes up through a series of filters,” said Laurie Chetwood, chairman of UK-based Chetwoods architect firm in charge of the project. “We don’t use power to pull the water up, we’re using passive energy. As it goes through the filters and back, we’re also putting air back into the lake to make it healthier.”

"The towers also have pollution-absorbing coatings to help clean the air, vertical gardens that filter more pollution, and a chimney in the middle of the larger tower naturally pulls air across the lake for better ventilation. Wind turbines, lightweight solar cladding, and hydrogen fuel cells running on the buildings’ waste will generate all of the power used by the towers, plus a little extra for the rest of the neighbourhood."

Once approved by the city’s mayor, construction is planned to start at the end of the year, with a completion date of 2017 or 2018.

http://sciencealert.com.au/news/20143006-25779.html

91 notes

vendittelli:

Don’t just read it; fight it! Ask your own questions, look for your own examples, discover your own proofs. Is the hypothesis necessary? Is the converse true? What happens in the classical special case? What about the degenerate cases? Where does the proof use the hypothesis?—- Paul R. Halmos [x]

vendittelli:

Don’t just read it; fight it! Ask your own questions,
look for your own examples, discover your own proofs.
Is the hypothesis necessary? Is the converse true?
What happens in the classical special case? What
about the degenerate cases? Where does the proof
use the hypothesis?

—- Paul R. Halmos [x]

105 notes

thenewenlightenmentage:

'Cosmic own goal' another clue in hunt for dark matter
The hunt for dark matter has taken another step forward thanks to new supercomputer simulations showing the evolution of our “local Universe” from the Big Bang to the present day.
Physicists at Durham University, UK, who are leading the research, say their simulations could improve understanding of dark matter, a mysterious substance believed to make up 85 per cent of the mass of the Universe.
Continue Reading

thenewenlightenmentage:

'Cosmic own goal' another clue in hunt for dark matter

The hunt for dark matter has taken another step forward thanks to new supercomputer simulations showing the evolution of our “local Universe” from the Big Bang to the present day.

Physicists at Durham University, UK, who are leading the research, say their simulations could improve understanding of , a mysterious substance believed to make up 85 per cent of the mass of the Universe.

Continue Reading

(via astrodidact)

840 notes

fouriestseries:

Gabriel’s Horn and the Painter’s Paradox 
Gabriel’s Horn is a three-dimensional horn shape with the counterintuitive property of having a finite volume but an infinite surface area.
This fact results in the Painter’s Paradox — A painter could fill the horn with a finite quantity of paint, “and yet that paint would not be sufficient to coat [the horn’s] inner surface” [1].
If the horn’s bell had, for example, a 6-inch radius, we’d only need about a half gallon of paint to fill the horn all the way up. Even though this half gallon is enough to entirely fill the horn, it’s not enough to even coat a fraction of the inner wall!
The mathematical explanation is a bit confusing if you haven’t taken a first course in calculus, but if you’re interested, you can check it out here.
Mathematica code:
x[u_, v_] := u
y[u_, v_] := Cos[v]/u
z[u_, v_] := Sin[v]/u
Manipulate[ParametricPlot3D[{{x[u, v], y[u, v], z[u, v]}}, 
    {u, 1, umax}, {v, 0, 2*Pi}, 
    PlotRange -> {{0, 20}, {-1, 1}, {-1, 1}}, 
    Mesh -> {Floor[umax], 20}, Axes -> False, Boxed -> False], 
    {{umax, 20}, 1.1, 20}]
Additional source not linked above.

fouriestseries:

Gabriel’s Horn and the Painter’s Paradox 

Gabriel’s Horn is a three-dimensional horn shape with the counterintuitive property of having a finite volume but an infinite surface area.

This fact results in the Painter’s Paradox — A painter could fill the horn with a finite quantity of paint, “and yet that paint would not be sufficient to coat [the horn’s] inner surface” [1].

If the horn’s bell had, for example, a 6-inch radius, we’d only need about a half gallon of paint to fill the horn all the way up. Even though this half gallon is enough to entirely fill the horn, it’s not enough to even coat a fraction of the inner wall!

The mathematical explanation is a bit confusing if you haven’t taken a first course in calculus, but if you’re interested, you can check it out here.

Mathematica code:

x[u_, v_] := u
y[u_, v_] := Cos[v]/u
z[u_, v_] := Sin[v]/u
Manipulate[ParametricPlot3D[{{x[u, v], y[u, v], z[u, v]}}, 
    {u, 1, umax}, {v, 0, 2*Pi}, 
    PlotRange -> {{0, 20}, {-1, 1}, {-1, 1}}, 
    Mesh -> {Floor[umax], 20}, Axes -> False, Boxed -> False], 
    {{umax, 20}, 1.1, 20}]

Additional source not linked above.