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Category: particle physics – Page 566

Harnessing Zero-Point Energy

From the fictional universe of Stargate Atlantis and Marvel Comic’s Realm of Kings to NASA’s Eagleworks Propulsion laboratory, zero-point energy, also known as vacuum energy, is touted as a potentially limitless and ubiquitous source of energy, if one can only find the means to harness it. [1] Zero-point energy can be formulated in a few different ways, but in its most basic form, it is the minimal yet non-zero energy of a quantum mechanical system. In quantum field theory, zero-point energy can be considered by computing the expected energy of the zero photon mode. [2] In a system with no physical boundaries, the expected energy of the zero photon mode diverges! Yet, if this energy uniformly permeates all of space-time, it is not directly observable.

Conceptual Framework

For pedagogical reasons, we will consider the popular formulation of zero-point energy. The most interesting and relevant framework for zero-point energy can be understood from the quantum field theory for photons and electrons: quantum electrodynamics. Glossing over an exceptional amount of mathematical and conceptual background, the energy of a state in quantum field theory is computed as an expectation of a Hamiltonian„ which describes the energy of the state in terms of operators acting on wavefunctions. The final computation usually requires an integral over the allowed momenta of particles in the state.

A method to simulate strongly correlated phases of quantum gauge theories

Quantum gauge theories are mathematical constructs that are typically used by physicists to describe subatomic particles, their associated wave fields and the interactions between them. The dynamics outlined by these theories are difficult to compute, yet effectively emulating them in the lab could lead to valuable new insight and discoveries.

In a recent study, a team of researchers at ETH Zurich’s Institute for Quantum Electronics successfully implemented a fundamental ingredient for the simulation of quantum gauge theories in a laboratory experiment. Their hope is that by simulating in a highly controlled environment, they will gather interesting observations and broaden their understanding of many-body systems (i.e., systems with many particles that interact with each other).

“Usually, our work is inspired by phenomena in solid state physics such as strongly correlated phases of electrons in complex materials,” Tilman Esslinger, one of the researchers who carried out the study, told Phys.org. “In our current work, however, we wanted to extend the scope of our experimental platform (i.e., in optical lattices) in order to investigate a new set of phenomena occurring in high-energy and condensed matter physics. The objective was to demonstrate that it is possible to engineer gauge fields in our setup that are dynamical quantum degrees of freedom due to their coupling to a matter field.”

A new alphabet to write and read quantum messages with very fast particles

Quantum information relies on the possibility of writing messages in a quantum particle and reading them out in a reliable way. If, however, the particle is relativistic, meaning that it moves with velocities close to the speed of light, it is impossible for standard techniques to decode the message unambiguously, and the communication therefore fails.

Thanks to the introduction of a new method, researchers at the University of Vienna and the Austrian Academy of Sciences have developed reliable decoding of quantum messages transmitted at extremely . The results, published in the journal Physical Review Letters, opens up new possibilities of technological applications in and quantum communication.

Imagine the following situation: Anna and Bill want to exchange a message by using a property of a , say the spin of an electron, which is an intrinsic form of particle’s rotation. Bill needs Anna’s message as quickly as possible, so Anna has to send the electron at maximum speed, very close to the speed of light. Given that Anna has the electron in her laboratory localized, the Heisenberg uncertainty principle forbids the velocity of the electron to be defined with arbitrary precision. When the electron travels at extremely high , the interplay between special relativity and quantum physics causes the spin and the velocity of the electron to become entangled. Due to this correlation, which is stronger than what is classically possible, Bill is not able to read out the spin with the standard method. Can Anna and Bill improve their communication strategy?

Into the eleventh dimension

Circa 1997

By Michio Kaku

IS THERE a Final Theory in physics? Will we one day have a complete theory that will explain everything from subatomic particles, atoms and supernovae to the big bang? Einstein spent the last 30 years of his life in a fruitless quest for the fabled unified field theory. His approach has since been written off as futile.

In the 1980s, attention switched to superstring theory as the leading candidate for a final theory. This revolution began when physicists realised that the subatomic particles found in nature, such as electrons and quarks, may not be particles at all, but tiny vibrating strings.

M Theory As A Matrix Model: A Conjecture

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.

Stephen Hawking had pinned his hopes on ‘M-theory’ to fully explain the universe—here’s what it is

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.

String Theory and Supersymmetry

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.

Introduction to Supersymmetry

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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