## Posts Tagged ‘**Quantum gravity**’

## “Reality leaves a lot to the imagination”*…

Here’s a curious thought experiment. Imagine a cloud of quantum particles that are entangled—in other words, they share the same quantum existence. The behavior of these particles is chaotic. The goal of this experiment is to send a quantum message across this set of particles. So the message has to be sent into one side of the cloud and then extracted from the other.

The first step, then, is to divide the cloud down the middle so that the particles on the left can be controlled separately from those on the right. The next step is to inject the message into the left-hand part of the cloud, where the chaotic behavior of the particles quickly scrambles it.

Can such a message ever be unscrambled?

Today, we get an answer thanks to the work of Adam Brown at Google in California and a number of colleagues, including Leonard Susskind at Stanford University, the “father of string theory.” This team shows exactly how such a message can be made to surprisingly reappear.

“The surprise is what happens next,” they say. After a period in which the message seems thoroughly scrambled, it abruptly unscrambles and recoheres at a point far away from where it was originally inserted. “The signal has unexpectedly refocused, without it being at all obvious what it was that acted as the lens,” they say.

But their really extraordinary claim is that such an experiment throws light on one of the deepest mysteries of the universe: the quantum nature of gravity and spacetime…

Quantum entanglement, and what it might tell us about quantum gravity– the fascinating story in full: “How a tabletop experiment could test the bedrock of reality.”

[The *arXiv* paper on which this article reports, “Quantum Gravity in the Lab: Teleportation by Size and Traversable Wormholes,” is here.]

* John Lennon

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**As we contemplate connection,** we might spare a thought for George Boole; the philosopher and mathematician died on this date in 1864. Boole helped establish modern symbolic logic– he created symbols to stand for logical operations– and an algebra of logic (that is now called “Boolean algebra”). Boole made important contributions to the study of differential equations and other aspects of math; his algebra has found important applications in topology, measure theory, probability, and statistics. But it’s for the foundational contribution that his symbolic logic has made to computer science– from circuit design to programming– that he’s probably best remembered.

**Happy Birthday (1894), James Thurber!!**

## “I think I can safely say that nobody understands quantum mechanics”*…

But we may be getting a little bit closer…

It’s not surprising that quantum physics has a reputation for being weird and counterintuitive. The world we’re living in sure doesn’t feel quantum mechanical. And until the 20th century, everyone assumed that the classical laws of physics devised by Isaac Newton and others — according to which objects have well-defined positions and properties at all times — would work at every scale. But Max Planck, Albert Einstein, Niels Bohr and their contemporaries discovered that down among atoms and subatomic particles, this concreteness dissolves into a soup of possibilities. An atom typically can’t be assigned a definite position, for example — we can merely calculate the probability of finding it in various places. The vexing question then becomes: How do quantum probabilities coalesce into the sharp focus of the classical world?

Physicists sometimes talk about this changeover as the “quantum-classical transition.” But in fact there’s no reason to think that the large and the small have fundamentally different rules, or that there’s a sudden switch between them. Over the past several decades, researchers have achieved a greater understanding of how quantum mechanics inevitably becomes classical mechanics through an interaction between a particle or other microscopic system and its surrounding environment.

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…

How do quantum possibilities give rise to objective, classical reality? More on one possible explanation, quantum Darwinism– and on the three experiments that have have begun to vet the theory: “Quantum Darwinism, an Idea to Explain Objective Reality, Passes First Tests.”

* Richard Feynman

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**As we ruminate on reality,** we might recall that it was on this date in 1975 that Jimmy Hoffa disappeared from the parking lot of the Machus Red Fox restaurant in Bloomfield Hills, Michigan, a suburb of Detroit, at about 2:30 p.m. He was never seen or heard from again.

Hoffa had served as President of the International Brotherhood of Teamsters from 1957. Long suspected of mob ties, he was convicted of jury tampering, attempted bribery and fraud in 1964, and sentenced to 13 years in prison in 1967… from whence he continued in his union office until 1972, when he was pardoned by President Richard Nixon on the condition that he resign Teamsters office. Out of jail, he began to plot an attempt to reverse this condition and return to power. Before he could make much progress, he disappeared. He was declared legally dead in 1982. While there has never been an official explanation of Hoffa’s demise, it is widely believed that he was killed by the Mafia, which was uncomfortable with his efforts to disrupt the power structure of the Teamsters (over which they has reestablished control).