Physics

everything is stooopid

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Every 250m years the sun, with its entourage of planets, completes a circuit of the Milky Way. Its journey around its home galaxy, though, is no stately peregrination. Rather, its orbit oscillates up and down through the galactic disc. It passes through that disc, the place where most of the galaxy’s matter is concentrated, once every 30m years or so.

This fact has long interested Michael Rampino of New York University. He speculates that it could explain the mass extinctions, such as that of the dinosaurs and many other species 66m years ago, which life on Earth undergoes from time to time. Palaeontologists recognise five such humongous events, during each of which up to 90% of species have disappeared. But the fossil record is also littered with smaller but still significant blips in the continuity of life.

Many hypotheses have been put forward to explain these extinctions (and the events may, of course, not all have the same explanation). The two that have most support are collisions between Earth and an asteroid or comet, and extended periods of massive volcanic activity. Dr Rampino observed some time ago that cometary collisions might be triggered by gravitational disruptions of the Oort cloud, a repository of comets in the outermost part of the solar system. That would send a rain of them into the part of space occupied by Earth. This has come to be known as the Shiva hypothesis, after the Hindu god of destruction. […]

In his latest paper, Dr Rampino speculates that the real culprit may be not stars, but dark matter—and that this might explain the volcanism as well.

{ The Economist | Continue reading }

‘Anaxagoras agrees with Leucippus and Democritus that the elements are infinite.’ –Aristotle

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New theories suggest the big bang was not the beginning, and that we may live in the past of a parallel universe.

[…]

Time’s arrow may in a sense move in two directions, although any observer can only see and experience one.

{ Scientific American | Continue reading }

photo { Tania Shcheglova and Roman Noven }

The time is out of joint

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O’Brian oversees America’s master clock. It’s one of the most accurate clocks on the planet: an atomic clock that uses oscillations in the element cesium to count out 0.0000000000000001 second at a time. If the clock had been started 300 million years ago, before the age of dinosaurs began, it would still be keeping time — down to the second. […]

At the nearby University of Colorado Boulder is a clock even more precise than the one O’Brian watches over. […] This new clock can keep perfect time for 5 billion years.”It’s about the whole, entire age of the earth,” says Jun Ye, the scientist here at JILA who built this clock. […]

But this new clock has run into a big problem: This thing we call time doesn’t tick at the same rate everywhere in the universe. Or even on our planet.

Right now, on the top of Mount Everest, time is passing just a little bit faster than it is in Death Valley. That’s because speed at which time passes depends on the strength of gravity. Einstein himself discovered this dependence as part of his theory of relativity, and it is a very real effect.

The relative nature of time isn’t just something seen in the extreme. If you take a clock off the floor, and hang it on the wall, Ye says, “the time will speed up by about one part in 1016.” […] Time itself is flowing more quickly on the wall than on the floor. These differences didn’t really matter until now. But this new clock is so sensitive, little changes in height throw it way off. Lift it just a couple of centimeters, Ye says, “and you will start to see that difference.” […]

The world’s current time is coordinated between atomic clocks all over the planet. But that can’t happen with the new one.

{ NPR | Continue reading }

photo { Petra Collins }

‘The freaks of chance are not determinable by calculation.’ —Thucydides

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An interesting idea is that the universe could be spontaneously created from nothing, but no rigorous proof has been given. In this paper, we present such a proof based on the analytic solutions of the Wheeler-DeWitt equation.

{ arXiv | Continue reading | more }

Three quarks for Muster Mark

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In a little over a century, we’ve discovered that what we once thought was the fundamental, smallest unit of matter — the atom — is actually made up of even smaller particles: nuclei and electrons. The nuclei themselves are made of protons and neutrons, and those protons and neutrons are made of still smaller particles: quarks and gluons.

Those particles — quarks, gluons, and electrons — are just some of the particles that cannot be broken up into smaller constituents to the best of our knowledge. All told, when we count up the fundamental particles that we know of, the ones that cannot be broken apart into anything smaller or lighter, we count a number of different types:

— six quarks (and their antiquark counterparts), each coming in three different color possibilities and two different spins,

— three charged leptons, the electron, muon and tau (and their anti-lepton counterparts), each allowed two different spin states,

— three neutral leptons, the neutrinos, along with the three anti-neutrinos, where the neutrinos all have a left-handed spin and the antis have a right-handed spin,

— the gluons, which all have two different spin states and which come in eight color varieties,

— the photon, which has two different allowable spins,

— the W-and-Z bosons, which come in three types (the W+, W-, and Z) and have three allowable spin states apiece (-1, 0, and +1), and

— the Higgs boson, which exists in only one state.

That’s the Standard Model of elementary particles. […] However, we know there must be more to the Universe, as this doesn’t account for dark matter, for one. Furthermore, there are theoretical limitations and inconsistencies to the physics we presently know and so we suspect there’s more physics beyond the Standard Model to explain it.

{ Ethan Siegel | Continue reading }

‘Psychologists have hitherto failed to realize that imagination is a necessary ingredient of perception itself.’ –Kant

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For centuries, scientists studied light to comprehend the visible world. […] But in the late 19th century all that changed […] the whole focus of physics—then still emerging as a distinct scientific discipline—shifted from the visible to the invisible. […] Today its theories and concepts are concerned largely with invisible entities: not only unseen force fields and insensible rays but particles too small to see even with the most advanced microscopes. […] Theories at the speculative forefront of physics flesh out this unseen universe with parallel worlds and with mysterious entities named for their very invisibility: dark matter and dark energy. […]

…the concept of “brane” (short for membrane) worlds. This arises from the most state-of-the-art variants of string theory, which attempt to explain all the known particles and forces in terms of ultra-tiny entities called strings, which can be envisioned as particles extended into little strands that vibrate. Most versions of the theory call for variables in the equations that seem to have the role of extra dimensions in space, so that string theory posits not four dimensions (of time and space) but 11. As physicist and writer Jim Baggott points out, “there is no experimental or observational basis for these assumptions”—the “extra dimensions” are just formal aspects of the equations. However, the latest versions of the theory suggest that these extra dimensions can be extremely large, constituting extra-dimensional branes that are potential repositories for alternative universes separated from our own like the stacked leaves of a book. Inevitably, there is an urge to imagine that these places too might be populated with sentient beings, although that’s optional. The point is that these brane worlds are nothing more than mathematical entities in speculative equations, incarnated, as it were, as invisible parallel universes. […]

Scientists, of course, are not just making things up, while leaning on the convenience of supposed invisibility. They are using dark matter and dark energy, and (if one is charitable) quantum many-worlds and branes, and other imperceptible and hypothetical realms, to perform an essential task: to plug gaps in their knowledge with notions they can grasp.

{ Nautilus | Continue reading }

related { How it works: An ultra-precise thermometer made from light }

Intrance on back. Most open on the lay-days.

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In a paper published in the journal Science, physicists reported that they were able to reliably teleport information between two quantum bits separated by three meters, or about 10 feet.

Quantum teleportation is not the “Star Trek”-style movement of people or things; rather, it involves transferring so-called quantum information — in this case what is known as the spin state of an electron — from one place to another without moving the physical matter to which the information is attached.

{ NY Times | Continue reading }

‘Nothing exists except atoms and empty space, everything else is opinion.’ –Democritus

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The atomists held that there are two fundamentally different kinds of realities composing the natural world, atoms and void. Atoms, from the Greek adjective atomos or atomon, ‘indivisible,’ are infinite in number and various in size and shape, and perfectly solid, with no internal gaps. They move about in an infinite void, repelling one another when they collide or combining into clusters by means of tiny hooks and barbs on their surfaces, which become entangled. Other than changing place, they are unchangeable, ungenerated and indestructible. All changes in the visible objects of the world of appearance are brought about by relocations of these atoms: in Aristotelian terms, the atomists reduce all change to change of place. Macroscopic objects in the world that we experience are really clusters of these atoms; changes in the objects we see—qualitative changes or growth, say—are caused by rearrangements or additions to the atoms composing them. While the atoms are eternal, the objects compounded out of them are not.

In supposing that void exists, the atomists deliberately embraced an apparent contradiction, claiming that ‘what is not’ exists.

{ The Stanford Encyclopedia of Philosophy | Continue reading }

Scientists discover how to turn light into matter after 80-year quest.

{ The Stanford Encyclopedia of Philosophy | Continue reading }

Even if you knew the entire past history of the universe, this would not contain the information about what the particles will do in the experiment

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Quantum physics is famously weird, counterintuitive and hard to understand; there’s just no getting around this. So it is very reassuring that many of the greatest physicists and mathematicians have also struggled with the subject. The legendary quantum physicist Richard Feynman famously said that if someone tells you that they understand quantum mechanics, then you can be sure that they are lying. And Conway too says that he didn’t understand the quantum physics lectures he took during his undergraduate degree at Cambridge.

The key to this confusion is that quantum physics is fundamentally different to any of the previous theories explaining how the physical world works. In the great rush of discoveries of new quantum theory in the 1920s, the most surprising was that quantum physics would never be able to exactly predict what was going to happen. In all previous physical theories, such as Newton’s classical mechanics or Einstein’s theories of special and general relativity, if you knew the current state of the physical system accurately enough, you could predict what would happen next. “Newtonian gravitation has this property,” says Conway. “If I take a ball and I throw it vertically upwards, and I know its mass and I know its velocity (suppose I’m a very good judge of speed!) then from Newton’s theories I know exactly how high it will go. And if it doesn’t do exactly as I expect then that’s because of some slight inaccuracy in my measurements.”

Instead quantum physics only offers probabilistic predictions: it can tell you that your quantum particle will behave in one way with a particular probability, but it could also behave in another way with another particular probability. “Suppose there’s this little particle and you’re going to put it in a magnetic field and it’s going to come out at A or come out at B,” says Conway, imagining an experiment, such as the Stern Gerlach experiment, where a magnetic field diverts an electron’s path. “Even if you knew exactly where the particles were and what the magnetic fields were and so on, you could only predict the probabilities. A particle could go along path A or path B, with perhaps 2/3 probability it will arrive at A and 1/3 at B. And if you don’t believe me then you could repeat the experiment 1000 times and you’ll find that 669 times, say, it will be at A and 331 times it will be at B.”

{ The Free Will Theorem, Part I | Continue reading | Part II | Part III }

‘In practical life we are compelled to follow what is most probable ; in speculative thought we are compelled to follow truth.’ —Spinoza

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When a coin falls in water, its trajectory is one of four types determined by its dimensionless moment of inertia I∗ and Reynolds number Re: (A) steady; (B) fluttering; (C) chaotic; or (D) tumbling. The dynamics induced by the interaction of the water with the surface of the coin, however, makes the exact landing site difficult to predict a priori.

Here, we describe a carefully designed experiment in which a coin is dropped repeatedly in water to determine the probability density functions (pdf) associated with the landing positions for each of the four trajectory types, all of which are radially symmetric about the centre drop-line.

{ arXiv | PDF }

If you’re five minutes late, just keep walking to Canada

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What if the universe had no beginning, and time stretched back infinitely without a big bang to start things off? That’s one possible consequence of an idea called “rainbow gravity,” so-named because it posits that gravity’s effects on spacetime are felt differently by different wavelengths of light, aka different colors in the rainbow. […]

“It’s a model that I do not believe has anything to do with reality,” says Sabine Hossenfelder of the Nordic Institute for Theoretical Physics.

{ Scientific American | Continue reading }

The trouble is, Gemini, you keep discovering the same thing: nobody and nothing is perfect.

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According to the Standard Model of particle physics, the universe should be empty. Matter and antimatter, which are identical except for their opposite electric charges, seem to be produced in equal parts during particle interactions and decays. However, matter and antimatter instantly annihilate each other upon contact, and so equal amounts of each would have meant a wholesale annihilation of both shortly after the Big Bang. The existence of galaxies, planets and people illustrates that somehow, a small surplus of matter survived this canceling process. If that hadn’t happened, “the universe would be void,” Schönert said.

The explanation for the survival of some matter may lie in subatomic particles called neutrinos. These particles might have a special property that would give rise to neutrino-less double beta decay.

{ Quanta | Continue reading }