Nov 1, 2024 12:17 AM
(This post was last modified: Nov 1, 2024 10:07 PM by C C.)
Can classical worlds emerge from parallel quantum universes?
https://physics.aps.org/articles/v17/155
EXCERPT: . . . A different approach is to explain the emergence of a classical world as an inherent consequence of the Schrödinger equation itself. In the many-worlds interpretation, for example, this equation is understood as describing a set of parallel worlds that continually branch out into new worlds as a result of quantum events.
Schrödinger’s cat is always either dead or alive in each world, according to whether the atom has decayed or not decayed in that world. The promise of this approach is to unify quantum evolution and our perceived reality: Everything is quantum on the smallest and largest scales, with no need for modified dynamics or wave-function collapses.
However, many physicists are not convinced that this promise has been fulfilled: How does the constant branching of worlds lead to the persistent reality of cats, moons, and people rather than to a thoroughly chaotic randomness?
Strasberg and his collaborators tackle this question in a novel way. Much previous work connects the answer to the idea of environment-induced decoherence, whereby stable objects arise from interactions of the many components of a quantum system with their external environment. These interactions effectively hide quantum interference effects deep within many far-flung environmental degrees of freedom, making them impossible to observe in practice.
However, this approach suffers from a problematic fine-tuning, meaning that it only works well for specific types of interactions and initial wave functions. What’s more, it has typically only been investigated for extremely simplified models.
In contrast, Strasberg and colleagues show that, for a wide range of possible evolutions of a wave function with many energy levels, a self-consistent set of stable features emerges at observable coarse-grained scales. Further, their model doesn’t require fine-tuning: These features are robust to the choice of initial conditions and to the details of the interactions between energy levels at small scales.
To achieve their result, the researchers take advantage of the tremendous power of modern computers to simulate quantum evolution up to an impressive 50,000 energy levels. Such a number is still modest compared to what would be needed to simulate everyday classical phenomena but is still significant compared to previous simulations on much simpler systems.
The team considers a broad range of coupling strengths and initial wave functions (randomly selected within particular classes of evolutions described by Hamiltonians with the same broad form). Their results show that, irrespective of these choices, approximately the same large-scale structure of stable branchings emerges. This conclusion, obtained without appealing to an external environment or to fine-tuning, supports the idea that our classical reality is able to pull itself up by its bootstraps from a purely quantum substrate... (MORE - missing details)
UCLA chemists just broke a 100-year-old rule and say it’s time to rewrite the textbooks
https://www.eurekalert.org/news-releases/1062561
INTRO: UCLA chemists have found a big problem with a fundamental rule of organic chemistry that has been around for 100 years — it’s just not true. And they say: It’s time to rewrite the textbooks.
Organic molecules, those made primarily of carbon, are characterized by having specific shapes and arrangements of atoms. Molecules known as olefins have double bonds, or alkenes, between two carbon atoms. The atoms, and those attached to them, ordinarily lie in the same 3D plane. Molecules that deviate from this geometry are uncommon.
The rule in question, known as Bredt’s rule in textbooks, was reported in 1924. It states that molecules cannot have a carbon-carbon double bond at the ring junction of a bridged bicyclic molecule, also known as the “bridgehead” position. The double bond on these structures would have distorted, twisted geometrical shapes that deviate from the rigid geometry of alkenes taught in textbooks. Olefins are useful in pharmaceutical research, but Bredt’s rule has constrained the kind of synthetic molecules scientists can imagine making with them and prevented possible applications of their use in drug discovery.
A new paper published by UCLA scientists in the journal Science has invalidated that idea. They show how to make several kinds of molecules that violate Bredt’s rule, called anti-Bredt olefins, or ABOs, allowing chemists to find practical ways to make and use them in reactions... (MORE - details, no ads)
https://physics.aps.org/articles/v17/155
EXCERPT: . . . A different approach is to explain the emergence of a classical world as an inherent consequence of the Schrödinger equation itself. In the many-worlds interpretation, for example, this equation is understood as describing a set of parallel worlds that continually branch out into new worlds as a result of quantum events.
Schrödinger’s cat is always either dead or alive in each world, according to whether the atom has decayed or not decayed in that world. The promise of this approach is to unify quantum evolution and our perceived reality: Everything is quantum on the smallest and largest scales, with no need for modified dynamics or wave-function collapses.
However, many physicists are not convinced that this promise has been fulfilled: How does the constant branching of worlds lead to the persistent reality of cats, moons, and people rather than to a thoroughly chaotic randomness?
Strasberg and his collaborators tackle this question in a novel way. Much previous work connects the answer to the idea of environment-induced decoherence, whereby stable objects arise from interactions of the many components of a quantum system with their external environment. These interactions effectively hide quantum interference effects deep within many far-flung environmental degrees of freedom, making them impossible to observe in practice.
However, this approach suffers from a problematic fine-tuning, meaning that it only works well for specific types of interactions and initial wave functions. What’s more, it has typically only been investigated for extremely simplified models.
In contrast, Strasberg and colleagues show that, for a wide range of possible evolutions of a wave function with many energy levels, a self-consistent set of stable features emerges at observable coarse-grained scales. Further, their model doesn’t require fine-tuning: These features are robust to the choice of initial conditions and to the details of the interactions between energy levels at small scales.
To achieve their result, the researchers take advantage of the tremendous power of modern computers to simulate quantum evolution up to an impressive 50,000 energy levels. Such a number is still modest compared to what would be needed to simulate everyday classical phenomena but is still significant compared to previous simulations on much simpler systems.
The team considers a broad range of coupling strengths and initial wave functions (randomly selected within particular classes of evolutions described by Hamiltonians with the same broad form). Their results show that, irrespective of these choices, approximately the same large-scale structure of stable branchings emerges. This conclusion, obtained without appealing to an external environment or to fine-tuning, supports the idea that our classical reality is able to pull itself up by its bootstraps from a purely quantum substrate... (MORE - missing details)
UCLA chemists just broke a 100-year-old rule and say it’s time to rewrite the textbooks
https://www.eurekalert.org/news-releases/1062561
INTRO: UCLA chemists have found a big problem with a fundamental rule of organic chemistry that has been around for 100 years — it’s just not true. And they say: It’s time to rewrite the textbooks.
Organic molecules, those made primarily of carbon, are characterized by having specific shapes and arrangements of atoms. Molecules known as olefins have double bonds, or alkenes, between two carbon atoms. The atoms, and those attached to them, ordinarily lie in the same 3D plane. Molecules that deviate from this geometry are uncommon.
The rule in question, known as Bredt’s rule in textbooks, was reported in 1924. It states that molecules cannot have a carbon-carbon double bond at the ring junction of a bridged bicyclic molecule, also known as the “bridgehead” position. The double bond on these structures would have distorted, twisted geometrical shapes that deviate from the rigid geometry of alkenes taught in textbooks. Olefins are useful in pharmaceutical research, but Bredt’s rule has constrained the kind of synthetic molecules scientists can imagine making with them and prevented possible applications of their use in drug discovery.
A new paper published by UCLA scientists in the journal Science has invalidated that idea. They show how to make several kinds of molecules that violate Bredt’s rule, called anti-Bredt olefins, or ABOs, allowing chemists to find practical ways to make and use them in reactions... (MORE - details, no ads)
