Jul 27, 2019 07:27 PM
Massless particles can’t be stopped
https://www.symmetrymagazine.org/article...be-stopped
EXCERPT: . . . The mass of an object is measured by its resistance to a force. When you pick something up to test its weight, it is resisting the Earth’s gravity [...] But there’s more to mass than just a resistance to gravity, especially on the scale of the smallest pieces of matter. So physicists’ definition of mass gets a little more complicated.
Most fundamental matter particles, such as electrons, muons and quarks, get their mass from their resistance to a field that permeates the universe called the Higgs field. The more the Higgs field pulls on a particle, the more mass it has. When it comes to composite particles like protons and neutrons, which are made up of quarks, most of their mass comes from the pull of the strong force that holds the quarks together.
Photons and gluons, two force-carrying particles, are fundamental, so they don’t host the internal tug-of-war of a composite particle. They are also unaffected by the Higgs field. Indeed, they seem to be without mass. Massless particles are purely energy. “It’s sufficient for a particle to have energy to have a meaningful sense of existence,” says Flip Tanedo, assistant professor of physics at the University of California, Riverside. These quanta of energy don’t have edges, and they don't have surfaces, says Tien-Tien Yu, an assistant professor of physics at the University of Oregon.
[...] It could be that the photon and the gluon are not the only massless particles in the universe. Scientists could one day (likely in the far future) find the ... graviton. Or it could turn out that the lightest of the three types of neutrinos has zero mass. (MORE - details)
We Have Already Entered The Sixth And Final Era Of Our Universe
https://www.forbes.com/sites/startswitha...f108454e5d
EXCERPT: . . . When we draw the dividing lines based on how the Universe behaves, we find that there are six different eras that will come to pass.
1. Inflationary era: which preceded and set up the hot Big Bang.
2. Primordial Soup era: from the start of the hot Big Bang until the final transformative nuclear & particle interactions occur in the early Universe.
3. Plasma era: from the end of non-scattering nuclear and particle interactions until the Universe cools enough to stably form neutral matter.
4. Dark Ages era: from the formation of neutral matter until the first stars and galaxies reionize the intergalactic medium of the Universe completely.
5. Stellar era: from the end of reionization until the gravity-driven formation and growth of large-scale structure ceases, when the dark energy density dominates over the matter density.
6. Dark Energy era: the final stage of our Universe, where the expansion accelerates and disconnected objects speed irrevocably and irreversibly away from one another.
We already entered this final era billions of years ago. Most of the important events that will define our Universe's history have already occurred. (MORE - details)
Quantum Darwinism, an idea to explain objective reality, passes first tests
https://www.quantamagazine.org/quantum-d...-20190722/
EXCERPT: . . . One of the most remarkable ideas in this theoretical framework is that the definite properties of objects that we associate with classical physics — position and speed, say — are selected from a menu of quantum possibilities in a process loosely analogous to natural selection in evolution: The properties that survive are in some sense the “fittest.” As in natural selection, the survivors are those that make the most copies of themselves. This means that many independent observers can make measurements of a quantum system and agree on the outcome — a hallmark of classical behavior.
This idea, called quantum Darwinism (QD), explains a lot about why we experience the world the way we do rather than in the peculiar way it manifests at the scale of atoms and fundamental particles. Although aspects of the puzzle remain unresolved, QD helps heal the apparent rift between quantum and classical physics.
Only recently, however, has quantum Darwinism been put to the experimental test. Three research groups, working independently in Italy, China and Germany, have looked for the telltale signature of the natural selection process by which information about a quantum system gets repeatedly imprinted on various controlled environments. These tests are rudimentary, and experts say there’s still much more to be done before we can feel sure that QD provides the right picture of how our concrete reality condenses from the multiple options that quantum mechanics offers. Yet so far, the theory checks out
[...] Quantum Darwinism challenges a common myth about quantum mechanics, according to the theoretical physicist Adán Cabello of the University of Seville in Spain: namely, that the transition between the quantum and classical worlds is not understood and that measurement outcomes cannot be described by quantum theory. On the contrary, he said, “quantum theory perfectly describes the emergence of the classical world.”
Just how perfectly remains contentious, however. Some researchers think decoherence and QD provide a complete account of the quantum-classical transition. But although these ideas attempt to explain why superpositions vanish at large scales and why only concrete “classical” properties remain, there’s still the question of why measurements give unique outcomes. When a particular location of a particle is selected, what happens to the other possibilities inherent in its quantum description? Were they ever in any sense real? Researchers are compelled to adopt philosophical interpretations of quantum mechanics precisely because no one can figure out a way to answer that question experimentally.
[...] Quantum Darwinism looks fairly persuasive on paper. But until recently that was as far as it got. In the past year, three teams of researchers have independently put the theory to the experimental test by looking for its key feature: how a quantum system imprints replicas of itself on its environment. The experiments depended on the ability to closely monitor what information about a quantum system gets imparted to its environment. [...] Both teams passed laser photons through optical devices that could combine them into multiply entangled groups. They then interrogated the environment photons to see what information they encoded...
So far, so good for quantum Darwinism. “All these studies see what is expected, at least approximately,” Wojciech Zurek said. Jess Riedel says we could hardly expect otherwise, though: In his view, QD is really just the careful and systematic application of standard quantum mechanics to the interaction of a quantum system with its environment. Although this is virtually impossible to do in practice for most quantum measurements, if you can sufficiently simplify a measurement, the predictions are clear, he said: “QD is most like an internal self-consistency check on quantum theory itself.”
But although these studies seem consistent with QD, they can’t be taken as proof that it is the sole description for the emergence of classicality, or even that it’s wholly correct. For one thing, says Cabello, the three experiments offer only schematic versions of what a real environment consists of. What’s more, the experiments don’t cleanly rule out other ways to view the emergence of classicality... (MORE - full details)
https://www.symmetrymagazine.org/article...be-stopped
EXCERPT: . . . The mass of an object is measured by its resistance to a force. When you pick something up to test its weight, it is resisting the Earth’s gravity [...] But there’s more to mass than just a resistance to gravity, especially on the scale of the smallest pieces of matter. So physicists’ definition of mass gets a little more complicated.
Most fundamental matter particles, such as electrons, muons and quarks, get their mass from their resistance to a field that permeates the universe called the Higgs field. The more the Higgs field pulls on a particle, the more mass it has. When it comes to composite particles like protons and neutrons, which are made up of quarks, most of their mass comes from the pull of the strong force that holds the quarks together.
Photons and gluons, two force-carrying particles, are fundamental, so they don’t host the internal tug-of-war of a composite particle. They are also unaffected by the Higgs field. Indeed, they seem to be without mass. Massless particles are purely energy. “It’s sufficient for a particle to have energy to have a meaningful sense of existence,” says Flip Tanedo, assistant professor of physics at the University of California, Riverside. These quanta of energy don’t have edges, and they don't have surfaces, says Tien-Tien Yu, an assistant professor of physics at the University of Oregon.
[...] It could be that the photon and the gluon are not the only massless particles in the universe. Scientists could one day (likely in the far future) find the ... graviton. Or it could turn out that the lightest of the three types of neutrinos has zero mass. (MORE - details)
We Have Already Entered The Sixth And Final Era Of Our Universe
https://www.forbes.com/sites/startswitha...f108454e5d
EXCERPT: . . . When we draw the dividing lines based on how the Universe behaves, we find that there are six different eras that will come to pass.
1. Inflationary era: which preceded and set up the hot Big Bang.
2. Primordial Soup era: from the start of the hot Big Bang until the final transformative nuclear & particle interactions occur in the early Universe.
3. Plasma era: from the end of non-scattering nuclear and particle interactions until the Universe cools enough to stably form neutral matter.
4. Dark Ages era: from the formation of neutral matter until the first stars and galaxies reionize the intergalactic medium of the Universe completely.
5. Stellar era: from the end of reionization until the gravity-driven formation and growth of large-scale structure ceases, when the dark energy density dominates over the matter density.
6. Dark Energy era: the final stage of our Universe, where the expansion accelerates and disconnected objects speed irrevocably and irreversibly away from one another.
We already entered this final era billions of years ago. Most of the important events that will define our Universe's history have already occurred. (MORE - details)
Quantum Darwinism, an idea to explain objective reality, passes first tests
https://www.quantamagazine.org/quantum-d...-20190722/
EXCERPT: . . . One of the most remarkable ideas in this theoretical framework is that the definite properties of objects that we associate with classical physics — position and speed, say — are selected from a menu of quantum possibilities in a process loosely analogous to natural selection in evolution: The properties that survive are in some sense the “fittest.” As in natural selection, the survivors are those that make the most copies of themselves. This means that many independent observers can make measurements of a quantum system and agree on the outcome — a hallmark of classical behavior.
This idea, called quantum Darwinism (QD), explains a lot about why we experience the world the way we do rather than in the peculiar way it manifests at the scale of atoms and fundamental particles. Although aspects of the puzzle remain unresolved, QD helps heal the apparent rift between quantum and classical physics.
Only recently, however, has quantum Darwinism been put to the experimental test. Three research groups, working independently in Italy, China and Germany, have looked for the telltale signature of the natural selection process by which information about a quantum system gets repeatedly imprinted on various controlled environments. These tests are rudimentary, and experts say there’s still much more to be done before we can feel sure that QD provides the right picture of how our concrete reality condenses from the multiple options that quantum mechanics offers. Yet so far, the theory checks out
[...] Quantum Darwinism challenges a common myth about quantum mechanics, according to the theoretical physicist Adán Cabello of the University of Seville in Spain: namely, that the transition between the quantum and classical worlds is not understood and that measurement outcomes cannot be described by quantum theory. On the contrary, he said, “quantum theory perfectly describes the emergence of the classical world.”
Just how perfectly remains contentious, however. Some researchers think decoherence and QD provide a complete account of the quantum-classical transition. But although these ideas attempt to explain why superpositions vanish at large scales and why only concrete “classical” properties remain, there’s still the question of why measurements give unique outcomes. When a particular location of a particle is selected, what happens to the other possibilities inherent in its quantum description? Were they ever in any sense real? Researchers are compelled to adopt philosophical interpretations of quantum mechanics precisely because no one can figure out a way to answer that question experimentally.
[...] Quantum Darwinism looks fairly persuasive on paper. But until recently that was as far as it got. In the past year, three teams of researchers have independently put the theory to the experimental test by looking for its key feature: how a quantum system imprints replicas of itself on its environment. The experiments depended on the ability to closely monitor what information about a quantum system gets imparted to its environment. [...] Both teams passed laser photons through optical devices that could combine them into multiply entangled groups. They then interrogated the environment photons to see what information they encoded...
So far, so good for quantum Darwinism. “All these studies see what is expected, at least approximately,” Wojciech Zurek said. Jess Riedel says we could hardly expect otherwise, though: In his view, QD is really just the careful and systematic application of standard quantum mechanics to the interaction of a quantum system with its environment. Although this is virtually impossible to do in practice for most quantum measurements, if you can sufficiently simplify a measurement, the predictions are clear, he said: “QD is most like an internal self-consistency check on quantum theory itself.”
But although these studies seem consistent with QD, they can’t be taken as proof that it is the sole description for the emergence of classicality, or even that it’s wholly correct. For one thing, says Cabello, the three experiments offer only schematic versions of what a real environment consists of. What’s more, the experiments don’t cleanly rule out other ways to view the emergence of classicality... (MORE - full details)