Jul 27, 2018 03:11 PM
History's most successful mathematical prediction
https://cosmosmagazine.com/mathematics/h...prediction
EXCERPT: . . . When electrons move, they emit photons. To describe this process requires quantum mechanics, the physics of the microworld, whose arcane rules permit an electron to emit photons into the great wide world, but also allow it to emit and then quickly reabsorb the same photon. Photons that enjoy only a fleeting existence before being snatched back are called ‘virtual’, to distinguish them from ‘real’ photons that fly off into the yonder.
According to this quantum description, all electrons are enveloped in a cloud of virtual photons. This virtual photon cloud leads to real physical effects, albeit small ones, including slightly altering the electron’s magnetic field.
Calculating by how much is fiendishly difficult. The first attempt was made by Julian Schwinger in 1948 [...] But by the time he died in 1994 experimenters and theorists were in a race to calculate and measure the magnetic field of the electron to ever-greater accuracy. [...] To improve on it meant considering not only virtual photons surrounding the electron but virtual electrons too, forming a seething ferment of particles popping into and out of existence. The calculational effort to factor in these processes is immense. Nevertheless, theory and experiment now agree to about one part per trillion, representing the most successful test of a physical theory in history.
MORE: https://cosmosmagazine.com/mathematics/h...prediction
Swarming Bacteria Create an ‘Impossible’ Superfluid
https://www.quantamagazine.org/swarming-...-20180726/
EXCERPT: . . . Recently, evidence has been mounting that while a free lunch is off the table, a cheap snack might be feasible with a system built around a living fluid. Experimental oddities began to surface in 2015 when a French team confirmed that solutions of E. coli and water could get unnaturally slick. Sandwiching a drop between two small plates, they recorded the force needed to make one plate slide at a certain speed. Liquids usually get harder to stir, or more viscous, when they contain additional suspended particles (think water vs. mud), but the opposite turns out to be true when the particles can swim. When the solution was around half a percent E. coli by volume, keeping the plate moving required no force at all, indicating zero viscosity. Some trials even registered negative viscosity, when the researchers had to apply a bit of force against the plates’ motion to keep them from speeding up. The liquid was doing work, which for any inert fluid would have meant a violation of the Second Law.
The straightforward conclusion was that the organisms were swimming in a way that neutralized the solution’s internal friction to produce something like a superfluid, a liquid with zero resistance. The apparent thermodynamics violation was an illusion because the bacteria were doing the work to offset or overcome the viscosity.
“Each individual bacterium is extremely weak, but there’s strength in numbers,” said Jörn Dunkel, a mathematician at the Massachusetts Institute of Technology who was not involved in the experiment.
But E. coli don’t typically all swim in the same direction, so subsequent research has tried to figure out what might be coordinating their movements. One answer, according to research published in July in the Proceedings of the National Academy of Sciences, is the interactions between individuals....
MORE: https://www.quantamagazine.org/swarming-...-20180726/
https://cosmosmagazine.com/mathematics/h...prediction
EXCERPT: . . . When electrons move, they emit photons. To describe this process requires quantum mechanics, the physics of the microworld, whose arcane rules permit an electron to emit photons into the great wide world, but also allow it to emit and then quickly reabsorb the same photon. Photons that enjoy only a fleeting existence before being snatched back are called ‘virtual’, to distinguish them from ‘real’ photons that fly off into the yonder.
According to this quantum description, all electrons are enveloped in a cloud of virtual photons. This virtual photon cloud leads to real physical effects, albeit small ones, including slightly altering the electron’s magnetic field.
Calculating by how much is fiendishly difficult. The first attempt was made by Julian Schwinger in 1948 [...] But by the time he died in 1994 experimenters and theorists were in a race to calculate and measure the magnetic field of the electron to ever-greater accuracy. [...] To improve on it meant considering not only virtual photons surrounding the electron but virtual electrons too, forming a seething ferment of particles popping into and out of existence. The calculational effort to factor in these processes is immense. Nevertheless, theory and experiment now agree to about one part per trillion, representing the most successful test of a physical theory in history.
MORE: https://cosmosmagazine.com/mathematics/h...prediction
Swarming Bacteria Create an ‘Impossible’ Superfluid
https://www.quantamagazine.org/swarming-...-20180726/
EXCERPT: . . . Recently, evidence has been mounting that while a free lunch is off the table, a cheap snack might be feasible with a system built around a living fluid. Experimental oddities began to surface in 2015 when a French team confirmed that solutions of E. coli and water could get unnaturally slick. Sandwiching a drop between two small plates, they recorded the force needed to make one plate slide at a certain speed. Liquids usually get harder to stir, or more viscous, when they contain additional suspended particles (think water vs. mud), but the opposite turns out to be true when the particles can swim. When the solution was around half a percent E. coli by volume, keeping the plate moving required no force at all, indicating zero viscosity. Some trials even registered negative viscosity, when the researchers had to apply a bit of force against the plates’ motion to keep them from speeding up. The liquid was doing work, which for any inert fluid would have meant a violation of the Second Law.
The straightforward conclusion was that the organisms were swimming in a way that neutralized the solution’s internal friction to produce something like a superfluid, a liquid with zero resistance. The apparent thermodynamics violation was an illusion because the bacteria were doing the work to offset or overcome the viscosity.
“Each individual bacterium is extremely weak, but there’s strength in numbers,” said Jörn Dunkel, a mathematician at the Massachusetts Institute of Technology who was not involved in the experiment.
But E. coli don’t typically all swim in the same direction, so subsequent research has tried to figure out what might be coordinating their movements. One answer, according to research published in July in the Proceedings of the National Academy of Sciences, is the interactions between individuals....
MORE: https://www.quantamagazine.org/swarming-...-20180726/