May 23, 2023 06:18 PM
(This post was last modified: May 24, 2023 01:56 PM by C C.)
The laws of physics have not always been symmetric. And it may explain why you exist
https://www.eurekalert.org/news-releases/990204
INTRO: For generations, physicists were sure the laws of physics were perfectly symmetric. Until they weren’t.
Symmetry is a tidy and attractive idea that falls apart in our untidy universe. Indeed, since the 1960s, some kind of broken symmetry has been required to explain why there is more matter than antimatter in the universe – why, that is, that any of this exists at all.
But pinning down the source behind this existential symmetry violation, even finding proof of it, has been impossible.
Yet in a new paper, University of Florida astronomers have found the first evidence of this necessary violation of symmetry at the moment of creation. The UF scientists studied a whopping million trillion three-dimensional galactic quadruplets in the universe and discovered that the universe at one point preferred one set of shapes over their mirror images.
This idea, known as parity symmetry violation, points to an infinitesimal period in our universe’s history when the laws of physics were different than they are today, with enormous consequences for how the universe evolved.
The finding, established with a high level of statistical confidence, has two primary consequences. First, this parity violation could only have imprinted itself on the future galaxies during a period of extreme inflation in the earliest moments of the universe, confirming a central component of the Big Bang theory of the origin of the cosmos... (MORE - details)
Quantum theory’s ‘measurement problem is a poison pill for objective reality
https://www.scientificamerican.com/artic...e-reality/
Solving a notorious quantum quandary could require abandoning some of science’s most cherished assumptions about the physical world
EXCERPTS: . . . Attempts to avoid the measurement problem—for example, by envisaging a reality in which quantum states don’t collapse at all—have led physicists into strange terrain where measurement outcomes can be subjective. “One major aspect of the measurement problem is this idea ... that observed events are not absolute,” says Nicholas Ormrod of the University of Oxford. This, in short, is why our imagined quantum coin toss could conceivably be heads from one perspective and tails from another.
But is such an apparently problematic scenario physically plausible or merely an artifact of our incomplete understanding of the quantum world? Grappling with such questions requires a better understanding of theories in which the measurement problem can arise—which is exactly what Ormrod, along with Vilasini Venkatesh of the Swiss Federal Institute of Technology in Zurich and Jonathan Barrett of Oxford, have now achieved. In a recent preprint, the trio proved a theorem that shows why certain theories—such as quantum mechanics—have a measurement problem in the first place and how one might develop alternative theories to sidestep it, thus preserving the “absoluteness” of any observed event. Such theories would, for instance, banish the possibility of a coin toss coming up heads to one observer and tails to another.
But their work also shows that preserving such absoluteness comes at a cost many physicists would deem prohibitive. “It’s a demonstration that there is no pain-free solution to this problem,” Ormrod says. “If we ever can recover absoluteness, then we’re going to have to give up on some physical principle that we really care about.”
Ormrod, Venkatesh and Barrett’s paper “addresses the question of which classes of theories are incompatible with absoluteness of observed events—and whether absoluteness can be maintained in some theories, together with other desirable properties,” says Eric Cavalcanti of Griffith University in Australia. (Cavalcanti, along with physicist Howard Wiseman and their colleagues, defined the term “absoluteness of observed events” in prior work that laid some of the foundations for Ormrod, Venkatesh and Barrett’s study.)
Holding on to absoluteness of observed events, it turns out, could mean that the quantum world is even weirder than we know it to be.
[...] one model that preserves the absoluteness of the observed event—meaning that it’s either heads or tails for all observers—is the Ghirardi-Rimini-Weber theory (GRW). In GRW, quantum systems can exist in a superposition of states until they reach some as-yet-underdetermined size, at which point the superposition spontaneously and randomly collapses, independent of an observer. Whatever the outcome—heads or tails in our example—it shall hold for all observers. ... By postulating a random collapse, GRW theory destroys the possibility of knowing what led up to the collapsed state—which, by most accounts, means information about the system prior to its transformation becomes irrecoverably lost...
[..] To prove their theorem without getting mired in any particular theory or interpretation, quantum mechanical or otherwise, Ormrod, Venkatesh and Barrett focused on perspectival theories that obey three important properties...
[...] All the pieces are in place to understand the trio’s result. Ormrod, Venkatesh and Barrett’s work comes down to a sophisticated analysis of how such “BIL” theories (those satisfying all three aforementioned properties) handle a deceptively simple thought experiment..
[...] Using this scenario, the team proved that the predictions of any BIL theory for the measurement outcomes of the four observers contradict the absoluteness of observed events. In other words, “all BIL theories have a measurement problem,” Ormrod says.
[...] This leaves physicists at an unpalatable impasse: either accept the nonabsoluteness of observed events or give up one of the assumptions of a BIL theory.
Venkatesh thinks that there’s something compelling about giving up absoluteness of observed events. After all, she says, physics successfully transitioned from a rigid Newtonian framework to a more nuanced and fluid Einsteinian description of reality. “We had to adjust some notions of what we thought was absolute. There was absolute space and time for Newton,” Venkatesh says. But in Albert Einstein’s conception of the universe, space and time are one, and this single spacetime isn’t something absolute but can warp in ways that don’t fit with Newtonian ways of thinking.
On the other hand, a perspectival theory that depends on observers creates its own problems...
[...] So if one were to insist on absoluteness of observed events, then something has to give. It’s not going to be Bell nonlocality or preservation of information: the former is on solid empirical footing, and the latter is considered an important aspect of any theory of reality. The focus shifts to local dynamics—in particular, to dynamical separability.
Dynamical separability is “kind of an assumption of reductionism,” Ormrod says. “You can explain the big stuff in terms of these little pieces.”
Preserving the absoluteness of observed events could imply that such reductionism doesn’t hold: just like a Bell nonlocal state cannot be reduced to some constituent states, it may be that the dynamics of a system are similarly holistic, adding another kind of nonlocality to the universe...
[...] “Perhaps the lesson of Bell is that the states of distant particles are inextricably linked, and the lesson of the new ... theorems is that their dynamics are, too,” Ormrod, Venkatesh and Barrett wrote in their paper.
“I like the idea of rejecting dynamical separability a lot, because if it works, then ... we get to have our cake and eat it, [too],” Ormrod says. “We get to continue to believe what we take to be the most fundamental things about the world: the fact that relativity theory is true, and information is preserved, and this kind of thing. But we also get to believe in absoluteness of observed events.”
Jeffrey Bub, a philosopher of physics and a professor emeritus at the University of Maryland, College Park, is willing to swallow some bitter pills if that means living in an objective universe. “I would want to hold on to the absoluteness of observed events,” he says. “It seems, to me, absurd to give this up just because of the measurement problem in quantum mechanics.” To that end, Bub thinks a universe in which dynamics are not separable is not such a bad idea. “I guess I would agree, tentatively, with the authors that [dynamical] nonseparability is the least unpalatable option,” he says.
The problem is that no one yet knows how to construct a theory that rejects dynamical separability—assuming it’s even possible to construct—while holding on to the other properties such as preservation of information and Bell nonlocality... (MORE - missing details)
https://www.eurekalert.org/news-releases/990204
INTRO: For generations, physicists were sure the laws of physics were perfectly symmetric. Until they weren’t.
Symmetry is a tidy and attractive idea that falls apart in our untidy universe. Indeed, since the 1960s, some kind of broken symmetry has been required to explain why there is more matter than antimatter in the universe – why, that is, that any of this exists at all.
But pinning down the source behind this existential symmetry violation, even finding proof of it, has been impossible.
Yet in a new paper, University of Florida astronomers have found the first evidence of this necessary violation of symmetry at the moment of creation. The UF scientists studied a whopping million trillion three-dimensional galactic quadruplets in the universe and discovered that the universe at one point preferred one set of shapes over their mirror images.
This idea, known as parity symmetry violation, points to an infinitesimal period in our universe’s history when the laws of physics were different than they are today, with enormous consequences for how the universe evolved.
The finding, established with a high level of statistical confidence, has two primary consequences. First, this parity violation could only have imprinted itself on the future galaxies during a period of extreme inflation in the earliest moments of the universe, confirming a central component of the Big Bang theory of the origin of the cosmos... (MORE - details)
Quantum theory’s ‘measurement problem is a poison pill for objective reality
https://www.scientificamerican.com/artic...e-reality/
Solving a notorious quantum quandary could require abandoning some of science’s most cherished assumptions about the physical world
EXCERPTS: . . . Attempts to avoid the measurement problem—for example, by envisaging a reality in which quantum states don’t collapse at all—have led physicists into strange terrain where measurement outcomes can be subjective. “One major aspect of the measurement problem is this idea ... that observed events are not absolute,” says Nicholas Ormrod of the University of Oxford. This, in short, is why our imagined quantum coin toss could conceivably be heads from one perspective and tails from another.
But is such an apparently problematic scenario physically plausible or merely an artifact of our incomplete understanding of the quantum world? Grappling with such questions requires a better understanding of theories in which the measurement problem can arise—which is exactly what Ormrod, along with Vilasini Venkatesh of the Swiss Federal Institute of Technology in Zurich and Jonathan Barrett of Oxford, have now achieved. In a recent preprint, the trio proved a theorem that shows why certain theories—such as quantum mechanics—have a measurement problem in the first place and how one might develop alternative theories to sidestep it, thus preserving the “absoluteness” of any observed event. Such theories would, for instance, banish the possibility of a coin toss coming up heads to one observer and tails to another.
But their work also shows that preserving such absoluteness comes at a cost many physicists would deem prohibitive. “It’s a demonstration that there is no pain-free solution to this problem,” Ormrod says. “If we ever can recover absoluteness, then we’re going to have to give up on some physical principle that we really care about.”
Ormrod, Venkatesh and Barrett’s paper “addresses the question of which classes of theories are incompatible with absoluteness of observed events—and whether absoluteness can be maintained in some theories, together with other desirable properties,” says Eric Cavalcanti of Griffith University in Australia. (Cavalcanti, along with physicist Howard Wiseman and their colleagues, defined the term “absoluteness of observed events” in prior work that laid some of the foundations for Ormrod, Venkatesh and Barrett’s study.)
Holding on to absoluteness of observed events, it turns out, could mean that the quantum world is even weirder than we know it to be.
[...] one model that preserves the absoluteness of the observed event—meaning that it’s either heads or tails for all observers—is the Ghirardi-Rimini-Weber theory (GRW). In GRW, quantum systems can exist in a superposition of states until they reach some as-yet-underdetermined size, at which point the superposition spontaneously and randomly collapses, independent of an observer. Whatever the outcome—heads or tails in our example—it shall hold for all observers. ... By postulating a random collapse, GRW theory destroys the possibility of knowing what led up to the collapsed state—which, by most accounts, means information about the system prior to its transformation becomes irrecoverably lost...
[..] To prove their theorem without getting mired in any particular theory or interpretation, quantum mechanical or otherwise, Ormrod, Venkatesh and Barrett focused on perspectival theories that obey three important properties...
[...] All the pieces are in place to understand the trio’s result. Ormrod, Venkatesh and Barrett’s work comes down to a sophisticated analysis of how such “BIL” theories (those satisfying all three aforementioned properties) handle a deceptively simple thought experiment..
[...] Using this scenario, the team proved that the predictions of any BIL theory for the measurement outcomes of the four observers contradict the absoluteness of observed events. In other words, “all BIL theories have a measurement problem,” Ormrod says.
[...] This leaves physicists at an unpalatable impasse: either accept the nonabsoluteness of observed events or give up one of the assumptions of a BIL theory.
Venkatesh thinks that there’s something compelling about giving up absoluteness of observed events. After all, she says, physics successfully transitioned from a rigid Newtonian framework to a more nuanced and fluid Einsteinian description of reality. “We had to adjust some notions of what we thought was absolute. There was absolute space and time for Newton,” Venkatesh says. But in Albert Einstein’s conception of the universe, space and time are one, and this single spacetime isn’t something absolute but can warp in ways that don’t fit with Newtonian ways of thinking.
On the other hand, a perspectival theory that depends on observers creates its own problems...
[...] So if one were to insist on absoluteness of observed events, then something has to give. It’s not going to be Bell nonlocality or preservation of information: the former is on solid empirical footing, and the latter is considered an important aspect of any theory of reality. The focus shifts to local dynamics—in particular, to dynamical separability.
Dynamical separability is “kind of an assumption of reductionism,” Ormrod says. “You can explain the big stuff in terms of these little pieces.”
Preserving the absoluteness of observed events could imply that such reductionism doesn’t hold: just like a Bell nonlocal state cannot be reduced to some constituent states, it may be that the dynamics of a system are similarly holistic, adding another kind of nonlocality to the universe...
[...] “Perhaps the lesson of Bell is that the states of distant particles are inextricably linked, and the lesson of the new ... theorems is that their dynamics are, too,” Ormrod, Venkatesh and Barrett wrote in their paper.
“I like the idea of rejecting dynamical separability a lot, because if it works, then ... we get to have our cake and eat it, [too],” Ormrod says. “We get to continue to believe what we take to be the most fundamental things about the world: the fact that relativity theory is true, and information is preserved, and this kind of thing. But we also get to believe in absoluteness of observed events.”
Jeffrey Bub, a philosopher of physics and a professor emeritus at the University of Maryland, College Park, is willing to swallow some bitter pills if that means living in an objective universe. “I would want to hold on to the absoluteness of observed events,” he says. “It seems, to me, absurd to give this up just because of the measurement problem in quantum mechanics.” To that end, Bub thinks a universe in which dynamics are not separable is not such a bad idea. “I guess I would agree, tentatively, with the authors that [dynamical] nonseparability is the least unpalatable option,” he says.
The problem is that no one yet knows how to construct a theory that rejects dynamical separability—assuming it’s even possible to construct—while holding on to the other properties such as preservation of information and Bell nonlocality... (MORE - missing details)
