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knudsenlu

Will the Quantum Nature of Gravity Finally Be Measured? - The Atlantic - 0 views

www.theatlantic.com/...555107

quantum gravity research

shared by knudsenlu on 11 Mar 18 - No Cached
  • In 1935, when both quantum mechanics and Albert Einstein’s general theory of relativity were young, a little-known Soviet physicist named Matvei Bronstein, just 28 himself, made the first detailed study of the problem of reconciling the two in a quantum theory of gravity. This “possible theory of the world as a whole,” as Bronstein called it, would supplant Einstein’s classical description of gravity, which casts it as curves in the space-time continuum, and rewrite it in the same quantum language as the rest of physics.
  • His words were prophetic. Eighty-three years later, physicists are still trying to understand how space-time curvature emerges on macroscopic scales from a more fundamental, presumably quantum picture of gravity; it’s arguably the deepest question in physics.
  • The search for the full theory of quantum gravity has been stymied by the fact that gravity’s quantum properties never seem to manifest in actual experience. Physicists never get to see how Einstein’s description of the smooth space-time continuum, or Bronstein’s quantum approximation of it when it’s weakly curved, goes wrong.
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  • Not only that, but the universe appears to be governed by a kind of cosmic censorship: Regions of extreme gravity—where space-time curves so sharply that Einstein’s equations malfunction and the true, quantum nature of gravity and space-time must be revealed—always hide behind the horizons of black holes.
  • Dyson, who helped develop quantum electrodynamics (the theory of interactions between matter and light) and is professor emeritus at the Institute for Advanced Study in Princeton, New Jersey, where he overlapped with Einstein, disagrees with the argument that quantum gravity is needed to describe the unreachable interiors of black holes. And he wonders whether detecting the hypothetical graviton might be impossible, even in principle. In that case, he argues, quantum gravity is metaphysical, rather than physics.
  • The ability to detect the “grin” of quantum gravity would seem to refute Dyson’s argument. It would also kill the gravitational decoherence theory, by showing that gravity and space-time do maintain quantum superpositions.
  • If gravity is a quantum interaction, then the answer is: It depends. Each component of the blue diamond’s superposition will experience a stronger or weaker gravitational attraction to the red diamond, depending on whether the latter is in the branch of its superposition that’s closer or farther away. And the gravity felt by each component of the red diamond’s superposition similarly depends on where the blue diamond is.
Javier E

Lockheed Martin Harnesses Quantum Technology - NYTimes.com - 0 views

www.nytimes.com/...-class-of-speedy-computer.html

quantum technology computer superposition research

shared by Javier E on 22 Mar 13 - No Cached
  • academic researchers and scientists at companies like Microsoft, I.B.M. and Hewlett-Packard have been working to develop quantum computers.
  • Lockheed Martin — which bought an early version of such a computer from the Canadian company D-Wave Systems two years ago — is confident enough in the technology to upgrade it to commercial scale, becoming the first company to use quantum computing as part of its business.
  • if it performs as Lockheed and D-Wave expect, the design could be used to supercharge even the most powerful systems, solving some science and business problems millions of times faster
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  • It could be possible, for example, to tell instantly how the millions of lines of software running a network of satellites would react to a solar burst or a pulse from a nuclear explosion — something that can now take weeks, if ever, to determine.
  • “This is a revolution not unlike the early days of computing,” he said. “It is a transformation in the way computers are thought about.”
  • quantum computing relies on the fact that subatomic particles inhabit a range of states. Different relationships among the particles may coexist, as well. Those probable states can be narrowed to determine an optimal outcome among a near-infinitude of possibilities, which allows certain types of problems to be solved rapidly.
  • Mr. Brownell, who joined D-Wave in 2009, was until 2000 the chief technical officer at Goldman Sachs. “In those days, we had 50,000 servers just doing simulations” to figure out trading strategies, he said. “I’m sure there is a lot more than that now, but we’ll be able to do that with one machine, for far less money.”
  • If Microsoft’s work pans out, he said, the millions of possible combinations of the proteins in a human gene could be worked out “fairly easily.”
  • Quantum computing has been a goal of researchers for more than three decades, but it has proved remarkably difficult to achieve. The idea has been to exploit a property of matter in a quantum state known as superposition, which makes it possible for the basic elements of a quantum computer, known as qubits, to hold a vast array of values simultaneously.
  • There are a variety of ways scientists create the conditions needed to achieve superposition as well as a second quantum state known as entanglement, which are both necessary for quantum computing. Researchers have suspended ions in magnetic fields, trapped photons or manipulated phosphorus atoms in silicon.
  • In the D-Wave system, a quantum computing processor, made from a lattice of tiny superconducting wires, is chilled close to absolute zero. It is then programmed by loading a set of mathematical equations into the lattice. The processor then moves through a near-infinity of possibilities to determine the lowest energy required to form those relationships. That state, seen as the optimal outcome, is the answer.
Javier E

Researchers Report Milestone in Developing Quantum Computer - NYTimes.com - 0 views

www.nytimes.com/...e-google-uc-santa-barbara.html

quantum computer science theory

shared by Javier E on 05 Mar 15 - No Cached
  • In contrast to a bit, which is the basic element of a conventional computer and can represent either a zero or a one, a qubit can exist in a state known as superposition, in which it can represent both a zero and a one simultaneously.If the qubits are then placed in an entangled state — physically separate but acting with many other qubits as if connected — they can represent a vast number of values simultaneously.To date, matrices of qubits that are simultaneously in superposition and entangled have eluded scientists because they are ephemeral, with the encoded information dissipating within microseconds.
  • Researchers have been pursuing the development of computers that exploit quantum mechanical effects since the 1990s, because of their potential to vastly expand the performance of conventional computers
Javier E

Opinion | Even Physicists Don't Understand Quantum Mechanics - The New York Times - 2 views

www.nytimes.com/...quantum-physics.html

quantum physics theory measurement

shared by Javier E on 08 Sep 19 - No Cached
  • “I think I can safely say that nobody really understands quantum mechanics,” observed the physicist and Nobel laureate Richard Feynman.
  • What’s surprising is that physicists seem to be O.K. with not understanding the most important theory they have.
  • Scientists can use quantum mechanics with perfect confidence. But it’s a black box. We can set up a physical situation, and make predictions about what will happen next that are verified to spectacular accuracy. What we don’t do is claim to understand quantum mechanics
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  • There are two problems. One is that quantum mechanics, as it is enshrined in textbooks, seems to require separate rules for how quantum objects behave when we’re not looking at them, and how they behave when they are being observed
  • Why are observations special? What counts as an “observation,” anyway? When exactly does it happen? Does it need to be performed by a person? Is consciousness somehow involved in the basic rules of reality?
  • Together these questions are known as the “measurement problem” of quantum theory.
  • The other problem is that we don’t agree on what it is that quantum theory actually describes, even when we’re not performing measurements.
  • We describe a quantum object such as an electron in terms of a “wave function,” which collects the superposition of all the possible measurement outcomes into a single mathematical object
  • But what is the wave function? Is it a complete and comprehensive representation of the world? Or do we need additional physical quantities to fully capture reality, as Albert Einstein and others suspected? Or does the wave function have no direct connection with reality at all, merely characterizing our personal ignorance about what we will eventually measure in our experiments?
  • For years, the leading journal in physics had an explicit policy that papers on the foundations of quantum mechanics were to be rejected out of hand
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