## Posts Tagged ‘**Steven Weinberg**’

## Steven Weinberg in conversation with Andrew Strominger

**Steven Weinberg** is a professor of physics and astronomy at the University of Texas at Austin. His research on elementary particle physics and cosmology has been honored with the Nobel Prize in Physics, the National Medal of Science, the Benjamin Franklin Medal of the American Philosophical Society, the Dannie Heinemann Prize for Mathematical Physics, and numerous other awards. He has written over 300 scientific articles, and six treatises on general relativity, quantum field theory, cosmology, and quantum mechanics. Among his books for general readers are Dreams of a Final Theory and The First Three Minutes, and two collections of published essays, Facing Up: Science and its Cultural Adversaries, and Lake Views: This World and the Universe.

**Andrew Strominger** is the Gwill E. York Professor of Physics at Harvard University and a founding member of the Black Hole Initiative. He is a renowned theoretical physicist who has made pathbreaking contributions to classical and quantum gravity, quantum field theory and string theory. In recognition of his accomplishments, Strominger has been awarded the prestigious 2017 Breakthrough Prize in Fundamental Physics, the 2016 Dannie Heineman Prize from the American Physical Society, and numerous other honors.

## Quantum Mechanics Without State Vectors

**Steven Weinberg**

It is proposed to give up the description of physical states in terms of ensembles of state vectors with various probabilities, relying instead solely on the density matrix as the description of reality. With this definition of a physical state, even in entangled states nothing that is done in one isolated system can instantaneously effect the physical state of a distant isolated system.

This change in the description of physical states opens up a large variety of new ways that the density matrix may transform under various symmetries, different from the unitary transformations of ordinary quantum mechanics.

Such new transformation properties have been explored before, but so far only for the symmetry of time translations into the future, treated as a semi-group. Here new transformation properties are studied for general symmetry transformations forming groups, rather than semi-groups.

Arguments are given that such symmetries should act on the density matrix as in ordinary quantum mechanics, but loopholes are found for all of these arguments.

Read more at http://arxiv.org/pdf/1405.3483v1.pdf

## Physics: What We Do and Don’t Know

## Steven Weinberg

In the past fifty years two large branches of physical science have each made a historic transition. I recall both cosmology and elementary particle physics in the early 1960s as cacophonies of competing conjectures. By now in each case we have a widely accepted theory, known as a “standard model.”

Cosmology and elementary particle physics span a range from the largest to the smallest distances about which we have any reliable knowledge. The cosmologist looks out to a cosmic horizon, the farthest distance light could have traveled since the universe became transparent to light over ten billion years ago, while the elementary particle physicist explores distances much smaller than an atomic nucleus. Yet our standard models really work—they allow us to make numerical predictions of high precision, which turn out to agree with observation.

Up to a point the stories of cosmology and particle physics can be told separately. In the end, though, they will come together…..

Read more at http://www.nybooks.com/articles/archives/2013/nov/07/physics-what-we-do-and-dont-know/?pagination=false

## Steven Weinberg on Symmetry Principles in Physics

Steven Weinberg explains how physical laws can be deduced from symmetry principles, such as how, due to Einstein’s Theory of General Relativity, the difference in symmetry between a rotating and non-rotating frame of reference generates a gravitational field that we recognize as the centrifugal force.

This verified Mach’s Principle of an interaction of mass which is not self generating and that, in Einstein’s view, the metric tensor of spacetime has inertia which influences inertia of massive objects.

These simple thoughts show that General Relativity does not only govern how masses influence spacetime but describes how spacetime influences masses.

Steven Weinberg is an American theoretical physicist, most famous for formulating the Electroweak Interaction with Abdus Salam and Sheldon Glashow in the Standard Model of Particle Physics, earning the 3 of them the 1979 Nobel Prize in Physics.

The 3 volumes of his textbook, “The Quantum Theory of Fields” are standard material for anyone studying theoretical particle physics, and his “Cosmology” textbook is probably the best book available for anyone seriously studying astrophysics in senior undergraduate and graduate years.

He also wrote the transcript of Richard Feynman’s famous talk “Elementary Particles and the Laws of Physics” for The 1986 Dirac Memorial Lecture.

He is also the author of “The First 3 minutes”, a popular science book discussing how the first 3 minutes in the history of the universe were, due to the fine tunings of the electroweak interaction, responsible for shaping our universe today and making it even remotely habitable.

## Goldstone Bosons as Fractional Cosmic Neutrinos

**Steven Weinberg**

It is suggested that Goldstone bosons may be masquerading as fractional cosmic neutrinos, contributing about 0.39 to what is reported as the effective number of neutrino types in the era before recombination. The broken symmetry associated with these Goldstone bosons is further speculated to be the conservation of the particles of dark matter.

Read more at http://arxiv.org/pdf/1305.1971v1.pdf

## Steven Weinberg: Collapse of the State Vector

Modifications of quantum mechanics are considered, in which the state vector of any system, large or small, undergoes a stochastic evolution. The general class of theories is described, in which the probability distribution of the state vector collapses to a sum of delta functions, one for each possible final state, with coefficients given by the Born rule….

Read more: http://arxiv.org/PS_cache/arxiv/pdf/1109/1109.6462v1.pdf

## Dreams of a Final Theory by Steven Weinberg – review

Here is an elegant, leisurely and profound contemplation of science by a man who doesn’t know what he is talking about. That last barb is true only in one very limited sense. In every other respect, Steven Weinberg is the perfect guide: he is a Nobel laureate; he woke the publishing world up more than 30 years ago with a stunning introduction to modern cosmology called The First Three Minutes; he was a driving force behind what was going to be the world’s most extravagant experiment; and he explains himself with a fabulous command of language….. Read the rest of this entry »