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Category: particle physics – Page 525

We suggest and motivate a precise equivalence between uncompactified eleven dimensional M-theory and the N = infinity limit of the supersymmetric matrix quantum mechanics describing D0-branes. The evidence for the conjecture consists of several correspondences between the two theories. As a consequence of supersymmetry the simple matrix model is rich enough to describe the properties of the entire Fock space of massless well separated particles of the supergravity theory. In one particular kinematic situation the leading large distance interaction of these particles is exactly described by supergravity.

The model appears to be a nonperturbative realization of the holographic principle. The membrane states required by M-theory are contained as excitations of the matrix model.

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Rumour has it that Albert Einstein spent his last few hours on Earth scribbling something on a piece of paper in a last attempt to formulate a theory of everything. Some 60 years later, another legendary figure in theoretical physics, Stephen Hawking, may have passed away with similar thoughts. We know Hawking thought something called “M-theory” is our best bet for a complete theory of the universe. But what is it?

Since the formulation of Einstein’s theory of in 1915, every theoretical physicist has been dreaming of reconciling our understanding of the infinitely small world of atoms and particles with that of the infinitely large scale of the cosmos. While the latter is effectively described by Einstein’s equations, the former is predicted with extraordinary accuracy by the so-called Standard Model of fundamental interactions.

Our current understanding is that the interaction between physical objects is described by four fundamental forces. Two of them – gravity and electromagnetism – are relevant for us on a macroscopic level, we deal with them in our everyday life. The other two, dubbed strong and weak interactions, act on a very small scale and become relevant only when dealing with subatomic processes.

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By Andrew Zimmerman Jones, Daniel Robbins

According to string theory, all particles in the universe can be divided into two types: bosons and fermions. String theory predicts that a type of connection, called supersymmetry, exists between these two particle types.

Under supersymmetry, a fermion must exist for every boson and a boson for every fermion. Unfortunately, experiments have not yet detected these extra particles.

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20th century physics has seen two major paradigm shifts in the way we understand Mother Nature. One is quantum mechanics, and the other is relativity. The marriage between the two, called quantum field theory, conceived an enfant terrible, namely anti-matter. As a result, the number of elementary particles doubled. We believe that 21st century physics is aimed at yet another level of marriage, this time between quantum mechanics and general relativity, Einstein’s theory of gravity. The couple has not been getting along very well, resulting in mathematical inconsistencies, meaningless infinities, and negative probabilities. The key to success may be in supersymmetry, which doubles the number of particles once more.

Why was anti-matter needed? One reason was to solve a crisis in the 19th century physics of classical electromagnetism. An electron is, to the best of our knowledge, a point particle. Namely, it has no size, yet an electric charge. A charged particle inevitably produces an electric potential around it, and it also feels the potential created by itself. This leads to an infinite “self-energy” of the electron. In other words, it takes substantial energy to “pack” all the charge of an electron into small size.

On the other hand, Einstein’s famous equation says that mass of a particle determines the energy of the particle at rest. For an electron, its rest energy is known to be 0.511 MeV. For this given amount of energy, it cannot afford to “pack” itself into a size smaller than the size of a nucleus. Classical theory of electromagnetism is not a consistent theory below this distance. However, it is known that the electron is at least ten thousand times smaller than that.

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Incorporating individual metal atoms into a surface in the right way allows their chemical behavior to be adapted. This makes new, better catalysts possible.

They make our cars more environmentally friendly and they are indispensable for the : catalysts make certain chemical reactions possible—such as the conversion of CO into CO2 in car exhaust gases—that would otherwise happen very slowly or not at all. Surface physicists at the TU Wien have now achieved an important breakthrough; can be placed on a metal oxide surface so that they show exactly the desired . Promising results with iridium atoms have just been published in the renowned journal Angewandte Chemie.

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Could physics help people with epilepsy? That’s the question tackled by Louis Nemzer, a physicist at Nova Southeastern University, in the September 2019 issue of Physics World magazine, which is out now in print and digital formats.

He thinks that machine learning and real-time monitoring of the brain could give people with epilepsy live information about how much at risk they are of an imminent seizure – and is even developing a smartphone app to help them in daily life.

Elsewhere in the issue, Peter Martin and Tom Scott from the University of Bristol describe how they’ve used drones to map radiation levels at the Chernobyl plant, which you can also read on this website from 2 September, while Kate Brown from the Massachusetts Institute of Technology examines the health impact of Chernobyl fall-out.

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There’s a crisis brewing in the cosmos. Measurements over the past few years of the distances and velocities of faraway galaxies don’t agree with the increasingly controversial “standard model” of the cosmos that has prevailed for the past two decades. Astronomers think that a 9 percent discrepancy in the value of a long-sought number called the Hubble Constant, which describes how fast the universe is expanding, might be revealing something new and astounding about the universe.

The cosmos has been expanding for 13.8 billion years and its present rate of expansion, known as the Hubble constant, gives the time elapsed since the Big Bang. However, the two best methods used to measure the Hubble constant do not agree, suggesting our understanding of the structure and history of the universe – called the ‘standard cosmological model’ – may be wrong.

There was, writes Dennis Overbye in New York Times Science, a disturbance in the Force: “Long, long ago, when the universe was only about 100,000 years old — a buzzing, expanding mass of particles and radiation — a strange new energy field switched on. That energy suffused space with a kind of cosmic antigravity, delivering a not-so-gentle boost to the expansion of the universe.

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