Posts Tagged ‘Chiara Marletto’
“Nothing in life is certain except death, taxes and the second law of thermodynamics”*…
The second law of thermodynamics– asserting that the entropy of a system increases with time– is among the most sacred in all of science, but it has always rested on 19th century arguments about probability. As Philip Ball reports, new thinking traces its true source to the flows of quantum information…
In all of physical law, there’s arguably no principle more sacrosanct than the second law of thermodynamics — the notion that entropy, a measure of disorder, will always stay the same or increase. “If someone points out to you that your pet theory of the universe is in disagreement with Maxwell’s equations — then so much the worse for Maxwell’s equations,” wrote the British astrophysicist Arthur Eddington in his 1928 book The Nature of the Physical World. “If it is found to be contradicted by observation — well, these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation.” No violation of this law has ever been observed, nor is any expected.
But something about the second law troubles physicists. Some are not convinced that we understand it properly or that its foundations are firm. Although it’s called a law, it’s usually regarded as merely probabilistic: It stipulates that the outcome of any process will be the most probable one (which effectively means the outcome is inevitable given the numbers involved).
Yet physicists don’t just want descriptions of what will probably happen. “We like laws of physics to be exact,” said the physicist Chiara Marletto of the University of Oxford. Can the second law be tightened up into more than just a statement of likelihoods?
A number of independent groups appear to have done just that. They may have woven the second law out of the fundamental principles of quantum mechanics — which, some suspect, have directionality and irreversibility built into them at the deepest level. According to this view, the second law comes about not because of classical probabilities but because of quantum effects such as entanglement. It arises from the ways in which quantum systems share information, and from cornerstone quantum principles that decree what is allowed to happen and what is not. In this telling, an increase in entropy is not just the most likely outcome of change. It is a logical consequence of the most fundamental resource that we know of — the quantum resource of information…
Is that most sacrosanct natural laws, second law of thermodynamics, a quantum phenomenon? “Physicists Rewrite the Fundamental Law That Leads to Disorder,” from @philipcball in @QuantaMagazine.
* “Nothing in life is certain except death, taxes and the second law of thermodynamics. All three are processes in which useful or accessible forms of some quantity, such as energy or money, are transformed into useless, inaccessible forms of the same quantity. That is not to say that these three processes don’t have fringe benefits: taxes pay for roads and schools; the second law of thermodynamics drives cars, computers and metabolism; and death, at the very least, opens up tenured faculty positions.” — Seth Lloyd
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As we get down with disorder, we might spare a thought for Francois-Marie Arouet, better known as Voltaire; he died on this date in 1778. The Father of the Age of Reason, he produced works in almost every literary form: plays, poems, novels, essays, and historical and scientific works– more than 2,000 books and pamphlets (and more than 20,000 letters). He popularized Isaac Newton’s work in France by arranging a translation of Principia Mathematica to which he added his own commentary.
A social reformer, Voltaire used satire to criticize the intolerance, religious dogma, and oligopolistic privilege of his day, perhaps nowhere more sardonically than in Candide.
“This potential possibility need only play a role as a counterfactual, according to quantum theory, for it to have an actual effect!”*…
Contemplate counterfactuals: things that have not happened — but could happen — a neglected area of scientific theory…
If you could soar high in the sky, as red kites often do in search of prey, and look down at the domain of all things known and yet to be known, you would see something very curious: a vast class of things that science has so far almost entirely neglected. These things are central to our understanding of physical reality, both at the everyday level and at the level of the most fundamental phenomena in physics — yet they have traditionally been regarded as impossible to incorporate into fundamental scientific explanations. They are facts not about what is — the ‘actual’ — but about what could or could not be. In order to distinguish them from the actual, they are called counterfactuals.
Suppose that some future space mission visited a remote planet in another solar system, and that they left a stainless-steel box there, containing among other things the critical edition of, say, William Blake’s poems. That the poetry book is subsequently sitting somewhere on that planet is a factual property of it. That the words in it could be read is a counterfactual property, which is true regardless of whether those words will ever be read by anyone. The box may be never found; and yet that those words could be read would still be true — and laden with significance. It would signify, for instance, that a civilization visited the planet, and much about its degree of sophistication.
To further grasp the importance of counterfactual properties, and their difference from actual properties, imagine a computer programmed to produce on its display a string of zeroes. That is a factual property of the computer, to do with its actual state — with what is. The fact that it could be reprogrammed to output other strings is a counterfactual property of the computer. The computer may never be so programmed; but the fact that it could is an essential fact about it, without which it would not qualify as a computer.
The counterfactuals that matter to science and physics, and that have so far been neglected, are facts about what could or could not be made to happen to physical systems; about what is possible or impossible. They are fundamental because they express essential features of the laws of physics — the rules that govern every system in the universe. For instance, a counterfactual property imposed by the laws of physics is that it is impossible to build a perpetual motion machine. A perpetual motion machine is not simply an object that moves forever once set into motion: it must also generate some useful sort of motion. If this device could exist, it would produce energy out of no energy. It could be harnessed to make your car run forever without using fuel of any sort. Any sequence of transformations turning something without energy into some thing with energy, without depleting any energy supply, is impossible in our universe: it could not be made to happen, because of a fundamental law that physicists call the principle of conservation of energy.
Another significant counterfactual property of physical systems, central to thermodynamics, is that a steam engine is possible. A steam engine is a device that transforms energy of one sort into energy of a different sort, and it can perform useful tasks, such as moving a piston, without ever violating that principle of conservation of energy. Actual steam engines (those that have been built so far) are factual properties of our universe. The possibility of building a steam engine, which existed long before the first one was actually built, is a counterfactual.
So the fundamental types of counterfactuals that occur in physics are of two kinds: one is the impossibility of performing a transformation (e.g., building a perpetual motion machine); the other is the possibility of performing a transformation (e.g., building a steam engine). Both are cardinal properties of the laws of physics; and, among other things, they have crucial implications for our endeavours: no matter how hard we try, or how ingeniously we think, we cannot bring about transformations that the laws of physics declare to be impossible — for example, creating a perpetual motion machine. However, by thinking hard enough, we can come up with more and better ways of performing a possible transformation — for instance, that of constructing a steam engine — which can then improve over time.
In the prevailing scientific worldview, counterfactual properties of physical systems are unfairly regarded as second-class citizens, or even excluded altogether. Why? It is because of a deep misconception, which, paradoxically, originated within my own field, theoretical physics. The misconception is that once you have specified everything that exists in the physical world and what happens to it — all the actual stuff — then you have explained everything that can be explained. Does that sound indisputable? It may well. For it is easy to get drawn into this way of thinking without ever realising that one has swallowed a number of substantive assumptions that are unwarranted. For you can’t explain what a computer is solely by specifying the computation it is actually performing at a given time; you need to explain what the possible computations it could perform are, if it were programmed in possible ways. More generally, you can’t explain the presence of a lifeboat aboard a pirate ship only in terms of an actual shipwreck. Everyone knows that the lifeboat is there because of a shipwreck that could happen (a counterfactual explanation). And that would still be the reason even if the ship never did sink!
Despite regarding counterfactuals as not fundamental, science has been making rapid, relentless progress, for example, by developing new powerful theories of fundamental physics, such as quantum theory and Einstein’s general relativity; and novel explanations in biology — with genetics and molecular biology — and in neuroscience. But in certain areas, it is no longer the case. The assumption that all fundamental explanations in science must be expressed only in terms of what happens, with little or no reference to counterfactuals, is now getting in the way of progress. For counterfactuals are essential to a number of things that are currently explained only vaguely in science, or not explained at all. Counterfactuals are central to an exact, unified theory of heat, work, and information (both classical and quantum); to explain matters such as the appearance of design in living things; and to a scientific explanation of knowledge…
An excerpt from Chiara Marletto‘s The Science of Can and Can’t: A Physicist’s Journey Through the Land of Counterfactuals, via the invaluable @delanceyplace.
[Image above: source]
* Roger Penrose, Shadows of the Mind: A Search for the Missing Science of Consciousness
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As we ponder the plausible, we might send superlatively speculative birthday greetings to an accomplished counterfactualist, H.G. Wells; he was born on this date in 1866. A prolific writer of novels, history, political and social commentary, textbooks, and rules for war games, Wells is best remembered (with Jules Verne and Hugo Gernsback) as “the father of science fiction” for his “scientific romances”– The War of the Worlds, The Time Machine, The Invisible Man, The Island of Doctor Moreau, et al.
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