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Full Version: Defying friction at atomic level + Simple, universal laws found that aim time's arrow
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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)
Do we really know that the direction of time has a thermodynamic explanation? I kind of doubt it.

The thing is that pretty much all of the equations of mathematical physics are time-reversal-invariant. They can run equally well in both temporal directions. (If we film a billiard ball hitting another billiard ball, the mathematics of the physical equations is equally valid if we ran the video backwards.) Just about the only aspect of mathematical physics that isn't time-reversal-invariant is entropy. So theorists and philosophers of physics have historically looked to entropy for the key to the direction of time.

I'm skeptical and suspect that the direction of time is more fundamental than that. I'm more inclined to think that entropy is a reflection of the underlying assymmetry of time, not its explanation.
Entropy is a thermodynamic quantity, so you may be splitting hairs there. But I do agree with the sentiment that the arrow of time is more fundamental...just more fundamental than even entropy. Entropy is just one of the many side effects of the directionality of time.
(Aug 3, 2019 04:33 PM)Yazata Wrote: [ -> ]Do we really know that the direction of time has a thermodynamic explanation? I kind of doubt it.

The thing is that pretty much all of the equations of mathematical physics are time-reversal-invariant. They can run equally well in both temporal directions. (If we film a billiard ball hitting another billiard ball, the mathematics of the physical equations is equally valid if we ran the video backwards.) Just about the only aspect of mathematical physics that isn't time-reversal-invariant is entropy. So theorists and philosophers of physics have historically looked to entropy for the key to the direction of time.

I'm skeptical and suspect that the direction of time is more fundamental than that. I'm more inclined to think that entropy is a reflection of the underlying assymmetry of time, not its explanation.


There might be something circular, redundant or tautological about it. Referring to the same thing in a different way -- abstracting a feature from it (entropy) and proclaiming that as an explanation for the overall situation. Kind of like saying that the reason a river is flowing south is because the water goes that way.

Huw Price (from "Time's Arrow & Archimede's Point"): Chapter 2 deals with thermodynamics. Few ideas in modern physics have had as much impact on popular imagination and culture as the second law of thermodynamics. As everyone knows, this is a time-asymmetric principle. It says that entropy increases over time. In the late nineteenth century, as thermodynamics came to be addressed in terms of the symmetric frame work of statistical mechanics, the puzzle just described came slowly into view: where does the asymmetry of the second law come from?

I shall explain how, as this problem came into view, it produced the first examples of a kind of fallacy which has often characterized attempts to explain temporal asymmetry in physics. This fallacy involves a kind of special pleading, or double standard. It takes an argument which could be used equally well in either temporal direction and applies it selectively, in one direction but not the other. Not surprisingly, this biased procedure leads to asymmetric conclusions. Without a justification for the bias, however, these conclusions tell us nothing about the origins of the real asymmetry we find in the world. Fallacies of this kind crop up time and time again. One of the main themes of this book is that we need the right starting point in order to avoid them.

[...] The real puzzle is to explain the low-entropy past. The standard debate has tended to concentrate on the wrong end of the entropy gradient. Writers have asked about the assumptions required to show that entropy increases toward (what we call) the future, for example, rather than the conditions required to ensure that it decreases toward (what we call) the past. At the root of this mistake lies a failure to characterize the issue in sufficiently atemporal terms. Despite Boltzmann's progress toward a view of this kind in the 1870s and 1890s, it has not been properly appreciated that we have no right to assume that it is an objective matter that entropy increases rather than decreases, for example. What is objective is that there is an entropy gradient over time, not that the universe "moves" on this gradient in one direction rather than the other.



Physicists define time to be the thing that clocks read. But clocks are not globally in sync due to relativistic effects, and it would be ridiculous to proclaim that the "huge" seconds of everyday clocks are the objective rate that changes happen, since atomic clocks (or subatomic events) measure time in vastly smaller durations. Even a Planck time unit would be controversial as a so-called objective rate of the speed of time: ". . .there is no reason to believe that exactly one unit of Planck time has any special physical significance."


Huw Price: ". . . if it made sense to say that time flows then it would make sense to ask how fast it flows, which doesn't seem to be a sensible question. Some people reply that time flows at one second per second, but even if we could live with the lack of other possibilities, this answer misses the more basic aspect of the objection. A rate of seconds per second is not a rate at all in physical terms. It is a dimensionless quantity, rather than a rate of any sort. (We might just as well say that the ratio of the circumference of a circle to its diameter flows at 71 seconds per second!) "


If there's no non-relativism affected and non-subjective interval measurement for change or "time passing" (how odd to project a "flowing" property upon temporal coordinates to begin with!)... Then a direction for this non-physical essence that's claimed to be "moving" seems similarly superfluous (it going unidentified apart from supplying yet another meaning or significance to the word "time"). As Price stated above, the entropy gradient is there, but the idea that a special ghost-like slice of the universe "moves" along it seems more like an add-on from conscious experience. Just as the phenomenal qualities of green or the flavor of fat molecules or the pain of a sharp thorn are not "out there" with the objective versions of the applicable objects. There's probably more anthropocentrism going on than issues swirling around the "temporal asymmetry" focus below.


Huw Price: Galileo is telling us that tastes, odors, colors, and the like are not part of the objective furniture of the world; normally, in thinking otherwise, we mistakea by-product of our viewpoint for an intrinsic feature of reality. In Galileo and later seventeenth-century writers, the move to identify and quarantine these secondary qualities is driven in part by the demands of physics; by the picture supplied by physics of what is objective in the world.

This is not a fixed constraint, however. It changes as physics changes, and some of these changes themselves involve the recognition that some ingredient of the previously excepted physical world view is anthropocentric. These examples suggest that anthropocentrism infects science by at least two different routes. In some cases the significant factor is that we happen to live in an exceptional part of the universe. We thus take as normal what is really a regional specialty: geocentric gravitational force, or friction, for example.

In other cases the source is not so much in our location as in our constitution. We unwittingly project onto the world some of the idiosyncrasies of our own makeup, seeing the world in the colors of the in-built glass through which we view it. But the distinction between these sources is not always a sharp one, because our constitution is adapted to the peculiarities of our region.

It is natural to wonder whether modern physics is free of such distortions .Physicists would be happy to acknowledge that physics might uncover new locational cases. Large as it is, the known universe might turn out to be an unusual bit of something bigger. The possibility of continuing constitutional distortions is rather harder to swallow, however. After all, it challenges the image physics holds of itself as an objective enterprise, an enterprise concerned with not with how things seem but with how they actually are. It is always painful for an academic enterprise to have to acknowledge that it might not have been living up to its own professed standards!

In the course of the book, however, I want to argue that in its treatment of time asymmetry, contemporary physics has failed to take account of distortions of just this constitutional sort—distortions which originate in the kind of entities we humans are, in one of our most fundamental aspects. If we see the historical process of detection and elimination of anthropocentrism as one of the adoption of progressively more detached standpoints for science, my claim is that physics has yet to achieve the standpoint required for an understanding of temporal asymmetry. In this case the required standpoint is an atemporal one, a point outside time, a point free of the distortions which stem from the fact that we are creatures in time—truly, then, a view from nowhen.