Aug 3, 2019 03:05 AM
Scientists seek materials that defy friction at the atomic level
https://www.sciencenews.org/article/scie...vel?tgt=nr
EXCERPT: . . . Scientists can’t fully explain, at the scale of atoms and molecules, why one pair of materials sticks while another moves with ease. The extreme slipperiness of ice, for example, has been a puzzle for more than 160 years. The multitude of water molecules on an icy surface creates a sheen that can send a car spinning or a penguin tobogganing. But getting a handle on the details of how this slippery surface arises from the water molecules is surprisingly tricky.
Despite its everyday nature, “we still don’t really understand a lot of things about friction,” says mechanical engineer Ali Erdemir of Argonne National Laboratory in Lemont, Ill. On its most basic level, friction results from the interactions between atoms in two materials that are butted up against one another. But, Erdemir says, “there is a disconnect” between the large-scale processes of friction that we can see, feel or hear and the smaller, atomic properties of materials that produce those well-known behaviors.
Now, by scrutinizing atoms’ wily ways, scientists are devising new techniques to cut down on friction, going beyond known slippery surfaces like ice, Teflon and the banana peel of countless comedy gags. Some scientists have found ways to bring friction down to near-zero levels, a property known as superlubricity. Others are studying quantum effects that reduce friction.
Atomic acrobatics might help turn friction up and down at will, a useful ability since there are times when friction, a force working against the motion of a sliding or rolling object, is helpful. The frictional force of tires on asphalt, for example, lets a car turn without spinning out. But friction also saps the car’s speed, so that more energy is needed to keep the vehicle moving.
Gaining the ability to wrangle friction could have real-world consequences. It’s estimated that a third of the energy that goes into powering fossil fuel–guzzling cars is lost to friction, converted into other forms of energy like heat and sound. The same hindrance affects just about every other machine imaginable, so that an estimated one-fifth of the world’s annual energy consumption goes to fighting friction. Reducing those losses would mean “huge savings,” Erdemir says. (MORE - detailed elaboration)
The Universal Law That Aims Time’s Arrow
https://www.quantamagazine.org/the-unive...-20190801/
EXCERPT: . . . This gradual spreading of matter and energy, called “thermalization,” aims the arrow of time. But the fact that time’s arrow is irreversible, so that hot coffee cools down but never spontaneously heats up, isn’t written into the underlying laws that govern the motion of the molecules in the coffee. Rather, thermalization is a statistical outcome: The coffee’s heat is far more likely to spread into the air than the cold air molecules are to concentrate energy into the coffee [...] Once coffee, cup and air reach thermal equilibrium, no more energy flows between them, and no further change occurs. Thus thermal equilibrium on a cosmic scale is dubbed the “heat death of the universe.”
But while it’s easy to see where thermalization leads ... it’s less obvious how the process begins. “If you start far from equilibrium, like in the early universe, how does the arrow of time emerge, starting from first principles?” said Jürgen Berges, a theoretical physicist at Heidelberg University in Germany who has studied this problem for more than a decade.
Over the last few years, Berges and a network of colleagues have uncovered a surprising answer. The researchers have discovered simple, so-called “universal” laws governing the initial stages of change in a variety of systems consisting of many particles that are far from thermal equilibrium. Their calculations indicate that these systems — examples include the hottest plasma ever produced on Earth and the coldest gas, and perhaps also the field of energy that theoretically filled the universe in its first split second — begin to evolve in time in a way described by the same handful of universal numbers, no matter what the systems consist of.
The findings suggest that the initial stages of thermalization play out in a way that’s very different from what comes later. In particular, far-from-equilibrium systems exhibit fractal-like behavior, which means they look very much the same at different spatial and temporal scales. [...] All kinds of quantum systems in various extreme starting conditions seem to fall into this fractal-like pattern, exhibiting universal scaling for a period of time before transitioning to standard thermalization.
“I find this work exciting because it pulls out a unifying principle that we can use to understand large classes of far-from-equilibrium systems,” said Nicole Yunger Halpern, a quantum physicist at Harvard University who is not involved in the work. “These studies offer hope that we can describe even these very messy, complicated systems with simple patterns.”
Berges is widely seen as leading the theoretical effort, with a series of seminal papers since 2008 elucidating the physics of universal scaling. co-author took another step this spring in a paper in Physical Review Letters that explored “prescaling,” the ramp-up to universal scaling. A group led by Thomas Gasenzer of Heidelberg also investigated prescaling in a PRL paper in May, offering a deeper look at the onset of the fractal-like behavior.
Some researchers are now exploring far-from-equilibrium dynamics in the lab, as others dig into the origins of the universal numbers. Experts say universal scaling is also helping to address deep conceptual questions about how quantum systems are able to thermalize at all. There’s “chaotic progress on various fronts,” said Zoran Hadzibabic of the University of Cambridge. He and his team are studying universal scaling in a hot gas of potassium-39 atoms by suddenly dialing up the atoms’ interaction strength, then letting them evolve. (MORE - detailed elaboration)
https://www.sciencenews.org/article/scie...vel?tgt=nr
EXCERPT: . . . Scientists can’t fully explain, at the scale of atoms and molecules, why one pair of materials sticks while another moves with ease. The extreme slipperiness of ice, for example, has been a puzzle for more than 160 years. The multitude of water molecules on an icy surface creates a sheen that can send a car spinning or a penguin tobogganing. But getting a handle on the details of how this slippery surface arises from the water molecules is surprisingly tricky.
Despite its everyday nature, “we still don’t really understand a lot of things about friction,” says mechanical engineer Ali Erdemir of Argonne National Laboratory in Lemont, Ill. On its most basic level, friction results from the interactions between atoms in two materials that are butted up against one another. But, Erdemir says, “there is a disconnect” between the large-scale processes of friction that we can see, feel or hear and the smaller, atomic properties of materials that produce those well-known behaviors.
Now, by scrutinizing atoms’ wily ways, scientists are devising new techniques to cut down on friction, going beyond known slippery surfaces like ice, Teflon and the banana peel of countless comedy gags. Some scientists have found ways to bring friction down to near-zero levels, a property known as superlubricity. Others are studying quantum effects that reduce friction.
Atomic acrobatics might help turn friction up and down at will, a useful ability since there are times when friction, a force working against the motion of a sliding or rolling object, is helpful. The frictional force of tires on asphalt, for example, lets a car turn without spinning out. But friction also saps the car’s speed, so that more energy is needed to keep the vehicle moving.
Gaining the ability to wrangle friction could have real-world consequences. It’s estimated that a third of the energy that goes into powering fossil fuel–guzzling cars is lost to friction, converted into other forms of energy like heat and sound. The same hindrance affects just about every other machine imaginable, so that an estimated one-fifth of the world’s annual energy consumption goes to fighting friction. Reducing those losses would mean “huge savings,” Erdemir says. (MORE - detailed elaboration)
The Universal Law That Aims Time’s Arrow
https://www.quantamagazine.org/the-unive...-20190801/
EXCERPT: . . . This gradual spreading of matter and energy, called “thermalization,” aims the arrow of time. But the fact that time’s arrow is irreversible, so that hot coffee cools down but never spontaneously heats up, isn’t written into the underlying laws that govern the motion of the molecules in the coffee. Rather, thermalization is a statistical outcome: The coffee’s heat is far more likely to spread into the air than the cold air molecules are to concentrate energy into the coffee [...] Once coffee, cup and air reach thermal equilibrium, no more energy flows between them, and no further change occurs. Thus thermal equilibrium on a cosmic scale is dubbed the “heat death of the universe.”
But while it’s easy to see where thermalization leads ... it’s less obvious how the process begins. “If you start far from equilibrium, like in the early universe, how does the arrow of time emerge, starting from first principles?” said Jürgen Berges, a theoretical physicist at Heidelberg University in Germany who has studied this problem for more than a decade.
Over the last few years, Berges and a network of colleagues have uncovered a surprising answer. The researchers have discovered simple, so-called “universal” laws governing the initial stages of change in a variety of systems consisting of many particles that are far from thermal equilibrium. Their calculations indicate that these systems — examples include the hottest plasma ever produced on Earth and the coldest gas, and perhaps also the field of energy that theoretically filled the universe in its first split second — begin to evolve in time in a way described by the same handful of universal numbers, no matter what the systems consist of.
The findings suggest that the initial stages of thermalization play out in a way that’s very different from what comes later. In particular, far-from-equilibrium systems exhibit fractal-like behavior, which means they look very much the same at different spatial and temporal scales. [...] All kinds of quantum systems in various extreme starting conditions seem to fall into this fractal-like pattern, exhibiting universal scaling for a period of time before transitioning to standard thermalization.
“I find this work exciting because it pulls out a unifying principle that we can use to understand large classes of far-from-equilibrium systems,” said Nicole Yunger Halpern, a quantum physicist at Harvard University who is not involved in the work. “These studies offer hope that we can describe even these very messy, complicated systems with simple patterns.”
Berges is widely seen as leading the theoretical effort, with a series of seminal papers since 2008 elucidating the physics of universal scaling. co-author took another step this spring in a paper in Physical Review Letters that explored “prescaling,” the ramp-up to universal scaling. A group led by Thomas Gasenzer of Heidelberg also investigated prescaling in a PRL paper in May, offering a deeper look at the onset of the fractal-like behavior.
Some researchers are now exploring far-from-equilibrium dynamics in the lab, as others dig into the origins of the universal numbers. Experts say universal scaling is also helping to address deep conceptual questions about how quantum systems are able to thermalize at all. There’s “chaotic progress on various fronts,” said Zoran Hadzibabic of the University of Cambridge. He and his team are studying universal scaling in a hot gas of potassium-39 atoms by suddenly dialing up the atoms’ interaction strength, then letting them evolve. (MORE - detailed elaboration)