Jun 29, 2021 05:15 PM
Can math help you escape a hungry bear?
https://www.quantamagazine.org/can-math-...-20210629/
In this month’s puzzle, math is a question of life or death.
The end of reductionism could be nigh. Or not.
https://nautil.us/blog/the-end-of-reduct...igh-or-not
EXCERPTS (Sabine Hossenfelder): The history of science so far has been a triumph of reductionism. Biology can be reduced to chemistry, chemistry can be reduced to atomic physics, and atoms are made of elementary particles like electrons, quarks, and gluons. [...] But if Chiara Marletto is right, the success of reductionism has run its course. The next better laws of nature might come from macroscopic objects, not microscopic ones. Her secret ingredient? Counterfactuals.
[...] In The Science of Can and Can’t, her first book (excerpted in Nautilus) Marletto uses a broader definition of counterfactual: Counterfactuals are facts about what could or could not be. Contemporary physics, she argues, does not take into account counterfactuals and this “is getting in the way of progress.”
It is certainly true that contemporary physics has shortcomings, quite possibly because the laws that we currently use in physics all work the same way. First, they require us to fully specify the configuration of a system at one moment in time, known as the initial condition. [...] these theories have gotten us far, but, as Marletto points out, they have limits. The most important one may be that no such theory can ever explain its own initial condition ... The current theories also struggle to explain how complexity grows in the universe....
Marletto’s book is the summary of several years of work with British physicist David Deutsch, together with whom she developed constructor theory. My best attempt at explaining constructor theory is that it posits that the laws of nature distinguish between what is possible and what not. And the best way to describe this may be, not with an initial condition and an evolution law, but with macroscopic objects—the constructors—that can perform certain tasks, but not others. What matters about those constructors is not what they are made of, but what they can and can’t do.
Energy, for example, can neither be created nor destroyed—we know that this is empirically correct to high accuracy. That’s a statement about an impossibility. Or take the fact that quantum mechanics does not allow us to perfectly copy the state of a system without destroying the original—another impossibility. Perpetuum mobiles—machines which beat the second law of thermodynamics—are also not possible.
Physicists currently treat such impossibilities as a consequence of the laws of nature. Constructor theory suggests we instead take them as the starting point: Begin with properties that macroscopic objects can have, then deduce what these objects’ microscopic constituents must be able to do. It’s turning reductionism on its head.
The general idea sounds promising to me [...] I was hoping Marletto’s book would shed light on it. Alas ... Not only does she not explain how one would actually work with constructor theory, or what it’s good for, she makes a number of assertions about physics that I found utterly baffling.
To begin with, Marletto argues that current physics doesn’t use counterfactuals. [...] But of course we use counterfactuals in physics. [...see article...] These are all counterfactuals. Marletto doesn’t mention these techniques.
Instead, she chides “reductionists” because they allegedly “dismiss” emergent criteria—such as information, thermodynamics, and consciousness—as “outside of science.” [...] To the very contrary, reductionists usually stress that consciousness can be explained by science, exactly because it emerges from the interaction of the many particles that make up a brain.
[...] I believe part of the problem is that Marletto neither explains what she means by reductionism nor by emergent. I have, above, used emergent to mean a property of a composite system that can be derived from the laws of the system’s constituents, but which doesn’t make sense on the level of constituents. Conductivity, for example, is a property of materials, but it makes no sense for individual electrons. Temperature is another example. Waves in water, cyclones, the capacity to self-reproduce—these are all emergent properties.
Philosophers often more specifically refer to this as “weak emergence.” “Strong emergence” instead is the hypothetical existence of properties in macroscopic systems that cannot be derived from the laws of the constituents. There is no known example in the real world for strong emergence (which is why physicists normally use the word “emergence” as synonym for “weak emergence”). That ontological reductionism (for all we currently know) is correct, means that strong emergence doesn’t exist: Everything can, in principle, be derived from (“reduced to” as a philosopher might say) the laws of elementary particles and the forces between them.
[...] The one example that she discusses where constructor theory can achieve something that the current theories cannot is to provide macroscopic laws that are truly irreversible. The weakly emergent laws which we obtain by the standard method are only, for all practical purposes, irreversible but remain, in principle, reversible. This means that some reversed processes (like unbreaking an egg) are theoretically possible but in practice they are so incredibly unlikely that we never observe them. That’s the standard explanation, anyway.
In constructor theory, such a process could be rendered impossible indeed, rather than just unlikely. But the standard approach is compatible with all observations [...] In the end, I have found Marletto’s book pleasant to read but not terribly illuminating... (MORE - missing details)
https://www.quantamagazine.org/can-math-...-20210629/
In this month’s puzzle, math is a question of life or death.
The end of reductionism could be nigh. Or not.
https://nautil.us/blog/the-end-of-reduct...igh-or-not
EXCERPTS (Sabine Hossenfelder): The history of science so far has been a triumph of reductionism. Biology can be reduced to chemistry, chemistry can be reduced to atomic physics, and atoms are made of elementary particles like electrons, quarks, and gluons. [...] But if Chiara Marletto is right, the success of reductionism has run its course. The next better laws of nature might come from macroscopic objects, not microscopic ones. Her secret ingredient? Counterfactuals.
[...] In The Science of Can and Can’t, her first book (excerpted in Nautilus) Marletto uses a broader definition of counterfactual: Counterfactuals are facts about what could or could not be. Contemporary physics, she argues, does not take into account counterfactuals and this “is getting in the way of progress.”
It is certainly true that contemporary physics has shortcomings, quite possibly because the laws that we currently use in physics all work the same way. First, they require us to fully specify the configuration of a system at one moment in time, known as the initial condition. [...] these theories have gotten us far, but, as Marletto points out, they have limits. The most important one may be that no such theory can ever explain its own initial condition ... The current theories also struggle to explain how complexity grows in the universe....
Marletto’s book is the summary of several years of work with British physicist David Deutsch, together with whom she developed constructor theory. My best attempt at explaining constructor theory is that it posits that the laws of nature distinguish between what is possible and what not. And the best way to describe this may be, not with an initial condition and an evolution law, but with macroscopic objects—the constructors—that can perform certain tasks, but not others. What matters about those constructors is not what they are made of, but what they can and can’t do.
Energy, for example, can neither be created nor destroyed—we know that this is empirically correct to high accuracy. That’s a statement about an impossibility. Or take the fact that quantum mechanics does not allow us to perfectly copy the state of a system without destroying the original—another impossibility. Perpetuum mobiles—machines which beat the second law of thermodynamics—are also not possible.
Physicists currently treat such impossibilities as a consequence of the laws of nature. Constructor theory suggests we instead take them as the starting point: Begin with properties that macroscopic objects can have, then deduce what these objects’ microscopic constituents must be able to do. It’s turning reductionism on its head.
The general idea sounds promising to me [...] I was hoping Marletto’s book would shed light on it. Alas ... Not only does she not explain how one would actually work with constructor theory, or what it’s good for, she makes a number of assertions about physics that I found utterly baffling.
To begin with, Marletto argues that current physics doesn’t use counterfactuals. [...] But of course we use counterfactuals in physics. [...see article...] These are all counterfactuals. Marletto doesn’t mention these techniques.
Instead, she chides “reductionists” because they allegedly “dismiss” emergent criteria—such as information, thermodynamics, and consciousness—as “outside of science.” [...] To the very contrary, reductionists usually stress that consciousness can be explained by science, exactly because it emerges from the interaction of the many particles that make up a brain.
[...] I believe part of the problem is that Marletto neither explains what she means by reductionism nor by emergent. I have, above, used emergent to mean a property of a composite system that can be derived from the laws of the system’s constituents, but which doesn’t make sense on the level of constituents. Conductivity, for example, is a property of materials, but it makes no sense for individual electrons. Temperature is another example. Waves in water, cyclones, the capacity to self-reproduce—these are all emergent properties.
Philosophers often more specifically refer to this as “weak emergence.” “Strong emergence” instead is the hypothetical existence of properties in macroscopic systems that cannot be derived from the laws of the constituents. There is no known example in the real world for strong emergence (which is why physicists normally use the word “emergence” as synonym for “weak emergence”). That ontological reductionism (for all we currently know) is correct, means that strong emergence doesn’t exist: Everything can, in principle, be derived from (“reduced to” as a philosopher might say) the laws of elementary particles and the forces between them.
[...] The one example that she discusses where constructor theory can achieve something that the current theories cannot is to provide macroscopic laws that are truly irreversible. The weakly emergent laws which we obtain by the standard method are only, for all practical purposes, irreversible but remain, in principle, reversible. This means that some reversed processes (like unbreaking an egg) are theoretically possible but in practice they are so incredibly unlikely that we never observe them. That’s the standard explanation, anyway.
In constructor theory, such a process could be rendered impossible indeed, rather than just unlikely. But the standard approach is compatible with all observations [...] In the end, I have found Marletto’s book pleasant to read but not terribly illuminating... (MORE - missing details)
