Sep 17, 2021 11:00 PM
(This post was last modified: Sep 18, 2021 02:01 AM by C C.)
As Sean Carroll once ventured, it sounds like Smolin is referring to a growing block universe, or what Carroll labeled as "possibilism". Though Smolin and his associates may have never used the expression. The quantum world applies to the future (indefinite), and the classical world applies to the past (definite), with "now" being the boundary between them or the transition.
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ES = Ethan Siegel
LS= Lee Smolin
https://bigthink.com/surprising-science/...all-wrong/
EXCERPTS: (intro) . . . Lee is a pioneer in the field of quantum gravity and someone whose latest book, Einstein’s Unfinished Revolution, details the search for what lies beyond what’s presently known about the quantum Universe [...]
LS: [...] General Relativity covers very well, to a certain degree of approximation, certain phenomena. Quantum mechanics covers very well, to a certain degree of approximation, certain phenomena. They’re both incomplete. Highly incomplete. [...] we’re living in a conceptual situation much analogous to that faced by Kepler and Galileo, who were contemporaries, they were each halfway between Aristotelian and Newtonian physics. They understood certain things very well, but they were deeply confused about other things. And that’s our situation now.
ES: From the quantum side, I’ve heard many people argue, counter to what you’re arguing, that quantum physics works exactly fine for describing every quantum phenomenon in the Universe, so long as you don’t also fold in quantum gravitational effects. If I can treat spacetime as being a classical or semi-classical background, then I can do everything that my quantum field theory predicts I should do without any errors or uncertainties. Do you disagree with that?
LS: Am I supposed to be impressed by that?
Aristotle worked with orbits and the positions of the planets that were accurate to a part in a thousand over a millennium. That was impressive, but it was bloody wrong. That simple-minded theory that you’re describing… why would somebody take such a little, little, low-ambitious thing? Of course you can make it work if you put in enough caveats and enough approximations, that’s what we’re trained to do.
And there are some beautiful things that come out of it, like Steve Hawking’s prediction of black hole radiation. So that’s fine, but man, that’s 1970s physics; do we want to do 1970s physics forever? I’m being deliberately a bit provocative, but, you know, we’ve got to wake these people up!
ES: So I read, back in 2003, you co-wrote a paper [with Fotini Markopoulou] that showed what I’ll say is an intriguing link between general ideas in quantum gravity and the fundamental non-locality of quantum physics. [...] Does this create any conflict in your mind? Would you say that quantum mechanics is fundamentally non-local?
LS: That quantum mechanics is fundamentally non-local, and therefore, making sense of quantum mechanics requires a strong modification in our understanding of what space is. And that General Relativity requires a strong modification in our ideas of what space is. And therefore, the things should go together. We shouldn’t try to ignore that and do this and then ignore this and do that, we should fix them together, in one move. And that’s what I’ve been trying to do since 19… since I was in college.
That [paper], that was mostly [Markopoulou’s] idea, and that was a very clever demonstration of the principle that space could be is be emergent, so that time could be fundamental. And that’s what she believed and she convinced me, and that’s what I’ve been working on, really, the last 20 years. Is the idea that time and causation are at the bottom, and are fundamental, and that space is a secondary, emergent quantity, like pressure of the air or temperature of the Earth. And so that’s what we’ve been trying to do, and we’ve been having some moderate success along the road.
So that what we experience of the world, evolving in time event-by-event, event-by-event, is real, that’s how the world really is. And out of that fundamental, active notion of time and causation, we make space as a derivative concept, the same way that out of the motion of atoms, you make a gas.
ES: Interesting. So you are very strongly an advocate that this classical notion of cause-and-effect, persists all the way down to the quantum level. I would assume that this means you are not a fan of quantum mechanics interpretations that do not maintain cause-and-effect as a fundamental tenet of all interactions?
LS: Mmm-hmmm, yes.
ES: I know that you have stated, and I don’t know if it’s for ideological or physical reasons, that reality ought to be independent of us, the observer.
LS: Yes, of course.
ES: You say, “yes, of course.” And many people throughout the history of quantum mechanics have not thought, “yes, of course.” Can you explain why reality should be independent of the observer?
LS: Because I’m a realist, and for me the goal of science is precisely the description of nature as it would be in our absence. Now, that doesn’t mean that there isn’t a role for the observer. For example, in the theories I’ve been developing for the last five years — it’s called the theory of views — what is real in that Universe is a view of that Universe, looking back, causally, into the past. And that’s exactly what’s real. John Bell, who was very much a realist, used to say, “we have to say not what the observables are, but what the viewables are.” So I’ve been developing this theory where we have events, and then have information or news that comes to them from the past, and that’s what’s real: those views. And the dynamics of the world doesn’t depend on differential equations in space, or fields, it depends on the views, and the differences between those views. And the basic dynamical principle of the theory is that the Universe evolves to make the views as varied and as different from each other as possible. [...]
ES: Is that something you could describe for us?
LS: Sure. It’s called, “the variety.” It can be applied to many different kinds of systems, so let’s take cities [...]
ES: So when you say, “we want to increase the variety,” do you think that nature extremizes variety?
LS: Yes, and I can write that down as an equation within the framework I discussed, where there are these causal relations, and there’s energy and momentum, but there’s no space. We can construct a dynamical theory that extremizes, over time, the variety of the system. And we derive from that, quantum mechanics, and as a limit of that, classical mechanics.
Why do we get quantum mechanics out? Roughly speaking, there was an original realist interpretation of quantum mechanics called pilot wave theory, that Louis de Broglie invented in 1927, and it was reinvented by David Bohm in about 1952. And in that theory, there’s potential energy and there’s another new function of the wavefunction, and it sits where the potential energy usually sits. And they derive the Schrodinger equation from maximizing the influence of this function. Well, it turns out that this function that David Bohm invented is a certain limit of the quantity we call the variety, by the way with Julian Barbour, back in the ‘80s. And this was one of the great surprises of my working life.
ES: When you take this limit of the quantity you call the variety, and you’re saying, “we’re extremizing over that,” this sounds to me like something that would be pretty analogous to some type of entropy, some type of thermodynamic quantity. So far, everyone I know who’s tried to come up with a concept of “gravity is emergent” or “space is emergent” or some other quantity that we normally look at as fundamental is in fact emergent, takes something that in typical physics thought we view as emergent and makes that fundamental. I would say the typical view of physics is that entropy is an emergent property that you can calculate based on, say, the microscopic quantum state of all the particles aggregated together. Are you basically doing something similar to that, except with this thing you define as “variety” instead of entropy?
LS: Roughly speaking yes, but that’s a long discussion [...]
ES: I’d like to ask about this idea that Heisenberg and a lot of other people had [...]
LS: [...] you know that Heisenberg said that the wavefunction description does not apply to the past. Somehow, the wavefunction was about the future, and the classical description is about the past. And a few people said this. Freeman Dyson said this at length; Schrodinger said something like that, and even deeper and more mysterious.
What we realized they were trying to say is that in the Copenhagen version of quantum mechanics, there is a quantum world and there is a classical world, and a boundary between them: when things become definite. When things that are indefinite in the quantum world become definite. And what they’re trying to say is that is the fundamental thing that happens in nature, when things that are indefinite become definite. And that’s what “now” is. The moment now, the present moment, that all these people say is missing from science and missing from physics, that is the transition from indefinite to definite. And quantum mechanics, the wavefunction, is a description of the future which is indefinite and incomplete. And classical physics is how we describe the past.
Why? Because the past happened, what happened was definite, and it doesn’t change, because it’s the past. So we have this different way of thinking about quantum mechanics, and it seems to be helpful, we’re having a good time. [...]
ES: Are you saying that right now, the “in progress” things, that have not yet been decided, that will be decided with an interaction at some point in the future, are you saying that everything in the past has already been determined, even those things where that measurement that will draw that line has not yet occurred?
LS: So that event has not yet occurred, so that’s rather compatible. The notion of the “now” that gives rise to is not a thin instant, where it has to happen here; it’s what the philosophers call a thick now. So there can be events that turn something definite, that are late, or that are early, so our “now” can zigzag quite a bit. At least, that’s the way we try to understand those cases. They’re not in the original two papers, but we’re going through all these thought experiments in detail and show how to think about what’s going on... (MORE - missing details)
- - - - - -
ES = Ethan Siegel
LS= Lee Smolin
https://bigthink.com/surprising-science/...all-wrong/
EXCERPTS: (intro) . . . Lee is a pioneer in the field of quantum gravity and someone whose latest book, Einstein’s Unfinished Revolution, details the search for what lies beyond what’s presently known about the quantum Universe [...]
LS: [...] General Relativity covers very well, to a certain degree of approximation, certain phenomena. Quantum mechanics covers very well, to a certain degree of approximation, certain phenomena. They’re both incomplete. Highly incomplete. [...] we’re living in a conceptual situation much analogous to that faced by Kepler and Galileo, who were contemporaries, they were each halfway between Aristotelian and Newtonian physics. They understood certain things very well, but they were deeply confused about other things. And that’s our situation now.
ES: From the quantum side, I’ve heard many people argue, counter to what you’re arguing, that quantum physics works exactly fine for describing every quantum phenomenon in the Universe, so long as you don’t also fold in quantum gravitational effects. If I can treat spacetime as being a classical or semi-classical background, then I can do everything that my quantum field theory predicts I should do without any errors or uncertainties. Do you disagree with that?
LS: Am I supposed to be impressed by that?
Aristotle worked with orbits and the positions of the planets that were accurate to a part in a thousand over a millennium. That was impressive, but it was bloody wrong. That simple-minded theory that you’re describing… why would somebody take such a little, little, low-ambitious thing? Of course you can make it work if you put in enough caveats and enough approximations, that’s what we’re trained to do.
And there are some beautiful things that come out of it, like Steve Hawking’s prediction of black hole radiation. So that’s fine, but man, that’s 1970s physics; do we want to do 1970s physics forever? I’m being deliberately a bit provocative, but, you know, we’ve got to wake these people up!
ES: So I read, back in 2003, you co-wrote a paper [with Fotini Markopoulou] that showed what I’ll say is an intriguing link between general ideas in quantum gravity and the fundamental non-locality of quantum physics. [...] Does this create any conflict in your mind? Would you say that quantum mechanics is fundamentally non-local?
LS: That quantum mechanics is fundamentally non-local, and therefore, making sense of quantum mechanics requires a strong modification in our understanding of what space is. And that General Relativity requires a strong modification in our ideas of what space is. And therefore, the things should go together. We shouldn’t try to ignore that and do this and then ignore this and do that, we should fix them together, in one move. And that’s what I’ve been trying to do since 19… since I was in college.
That [paper], that was mostly [Markopoulou’s] idea, and that was a very clever demonstration of the principle that space could be is be emergent, so that time could be fundamental. And that’s what she believed and she convinced me, and that’s what I’ve been working on, really, the last 20 years. Is the idea that time and causation are at the bottom, and are fundamental, and that space is a secondary, emergent quantity, like pressure of the air or temperature of the Earth. And so that’s what we’ve been trying to do, and we’ve been having some moderate success along the road.
So that what we experience of the world, evolving in time event-by-event, event-by-event, is real, that’s how the world really is. And out of that fundamental, active notion of time and causation, we make space as a derivative concept, the same way that out of the motion of atoms, you make a gas.
ES: Interesting. So you are very strongly an advocate that this classical notion of cause-and-effect, persists all the way down to the quantum level. I would assume that this means you are not a fan of quantum mechanics interpretations that do not maintain cause-and-effect as a fundamental tenet of all interactions?
LS: Mmm-hmmm, yes.
ES: I know that you have stated, and I don’t know if it’s for ideological or physical reasons, that reality ought to be independent of us, the observer.
LS: Yes, of course.
ES: You say, “yes, of course.” And many people throughout the history of quantum mechanics have not thought, “yes, of course.” Can you explain why reality should be independent of the observer?
LS: Because I’m a realist, and for me the goal of science is precisely the description of nature as it would be in our absence. Now, that doesn’t mean that there isn’t a role for the observer. For example, in the theories I’ve been developing for the last five years — it’s called the theory of views — what is real in that Universe is a view of that Universe, looking back, causally, into the past. And that’s exactly what’s real. John Bell, who was very much a realist, used to say, “we have to say not what the observables are, but what the viewables are.” So I’ve been developing this theory where we have events, and then have information or news that comes to them from the past, and that’s what’s real: those views. And the dynamics of the world doesn’t depend on differential equations in space, or fields, it depends on the views, and the differences between those views. And the basic dynamical principle of the theory is that the Universe evolves to make the views as varied and as different from each other as possible. [...]
ES: Is that something you could describe for us?
LS: Sure. It’s called, “the variety.” It can be applied to many different kinds of systems, so let’s take cities [...]
ES: So when you say, “we want to increase the variety,” do you think that nature extremizes variety?
LS: Yes, and I can write that down as an equation within the framework I discussed, where there are these causal relations, and there’s energy and momentum, but there’s no space. We can construct a dynamical theory that extremizes, over time, the variety of the system. And we derive from that, quantum mechanics, and as a limit of that, classical mechanics.
Why do we get quantum mechanics out? Roughly speaking, there was an original realist interpretation of quantum mechanics called pilot wave theory, that Louis de Broglie invented in 1927, and it was reinvented by David Bohm in about 1952. And in that theory, there’s potential energy and there’s another new function of the wavefunction, and it sits where the potential energy usually sits. And they derive the Schrodinger equation from maximizing the influence of this function. Well, it turns out that this function that David Bohm invented is a certain limit of the quantity we call the variety, by the way with Julian Barbour, back in the ‘80s. And this was one of the great surprises of my working life.
ES: When you take this limit of the quantity you call the variety, and you’re saying, “we’re extremizing over that,” this sounds to me like something that would be pretty analogous to some type of entropy, some type of thermodynamic quantity. So far, everyone I know who’s tried to come up with a concept of “gravity is emergent” or “space is emergent” or some other quantity that we normally look at as fundamental is in fact emergent, takes something that in typical physics thought we view as emergent and makes that fundamental. I would say the typical view of physics is that entropy is an emergent property that you can calculate based on, say, the microscopic quantum state of all the particles aggregated together. Are you basically doing something similar to that, except with this thing you define as “variety” instead of entropy?
LS: Roughly speaking yes, but that’s a long discussion [...]
ES: I’d like to ask about this idea that Heisenberg and a lot of other people had [...]
LS: [...] you know that Heisenberg said that the wavefunction description does not apply to the past. Somehow, the wavefunction was about the future, and the classical description is about the past. And a few people said this. Freeman Dyson said this at length; Schrodinger said something like that, and even deeper and more mysterious.
What we realized they were trying to say is that in the Copenhagen version of quantum mechanics, there is a quantum world and there is a classical world, and a boundary between them: when things become definite. When things that are indefinite in the quantum world become definite. And what they’re trying to say is that is the fundamental thing that happens in nature, when things that are indefinite become definite. And that’s what “now” is. The moment now, the present moment, that all these people say is missing from science and missing from physics, that is the transition from indefinite to definite. And quantum mechanics, the wavefunction, is a description of the future which is indefinite and incomplete. And classical physics is how we describe the past.
Why? Because the past happened, what happened was definite, and it doesn’t change, because it’s the past. So we have this different way of thinking about quantum mechanics, and it seems to be helpful, we’re having a good time. [...]
ES: Are you saying that right now, the “in progress” things, that have not yet been decided, that will be decided with an interaction at some point in the future, are you saying that everything in the past has already been determined, even those things where that measurement that will draw that line has not yet occurred?
LS: So that event has not yet occurred, so that’s rather compatible. The notion of the “now” that gives rise to is not a thin instant, where it has to happen here; it’s what the philosophers call a thick now. So there can be events that turn something definite, that are late, or that are early, so our “now” can zigzag quite a bit. At least, that’s the way we try to understand those cases. They’re not in the original two papers, but we’re going through all these thought experiments in detail and show how to think about what’s going on... (MORE - missing details)
