American theoretical physicist (1933-2021)
Steven Weinberg (born 3 May 1933 – 23 July 2021) was an American physicist. He was awarded the 1979 Nobel Prize in Physics (with colleagues Abdus Salam and Sheldon Glashow) for combining electromagnetism and the weak force into the electroweak force.
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It seems to me that we are in the position of a company of players who have by chance found their way into a great theater. Outside, the city streets are dark and lifeless, but in the theater the lights are on, the air is warm, and the walls are wonderfully decorated. However, no scripts are found, so the players begin to improvise—a little psychological drama, a little poetry, whatever comes to mind. Some even set themselves to explain the stage machinery. The players do not forget that they are just amusing themselves, and that they will have to return to the darkness outside the theater, but while on the stage they do their best to give a good performance. I suppose that this is a rather melancholy view of human life, but melancholy is one of the distinctive creations of our species, and not without its own consolations.
's kindness to me and my wife went beyond his help with this research. He had my wife and me to dinner at his house and at that dinner I went to the bathroom and I learned something about Källén that I don't think anyone knows. And that is that he had hand towels embroidered with the . And I mentioned this to Mrs. Källén and she said they were a present from Pauli.
In 1709 Hauksbee observed that when air inside a glass vessel was evacuated... [to] 1/60 normal air pressure and the vessel was attached to... frictional electricity, a strange light would be seen... Flashes... similar... had... been noticed in the partial vacuum above... mercury in barometers. ...[T]oday we know ...[w]hen an electric current flows through a gas, the electrons knock into the gas atoms and give up some... energy... reemitted as as light. Today's fluorescent lights and neon signs are based on the same principle... but even at 1/60 atmospheric pressure the air interfered too much with the flow of electrons to allow their nature to be discovered. Real progress became possible only when the gas... could be removed...
In fact, there is something puzzling about the Higgs mass we now do observe. It is generally known as the “hierarchy problem.” Since it is the Higgs mass that sets the scale for the masses of all other known elementary particles, one might guess that it should be similar to another mass that plays a fundamental role in physics, the so-called Planck mass, which is the fundamental unit of mass in the theory of gravitation. (It is the mass of hypothetical particles whose gravitational attraction for one another would be as strong as the electric force between two electrons separated by the same distance.) But the Planck mass is about a hundred thousand trillion times larger than the Higgs mass. So, although the Higgs particle is so heavy that a giant particle collider was needed to create it, we still have to ask, why is the Higgs mass so small?
[T]he distance at present is<math>d_{\mathrm{max}}(t_0) = \frac{1}{H_0} \int_{0}^{1} \frac{dx}{x^2 \sqrt{\Omega_\Lambda+\Omega_K x^{-2}+\Omega_M x^{-3}}}</math>...[T]here may have been a time before the radiation-dominated era in which there was nothing in the universe but , in which case the particle horizon distance would... be infinite. But as far as telescopic observations... [<math>d_{max}(t_0)</math>] gives the proper distance beyond which we cannot now see.
In 1999 I finished my three volume book on the quantum theory of fields (..."QTF"), and... set... the task of learning... the theory underlying the great progress in cosmology in the previous two decades. ...Review articles ...gave good summaries of the data, but ...often quoted formulas without ...derivation, and sometimes ...without reference to the original derivation. Occasionally the formulas were wrong, and extremely difficult for me to rederive. ...[O]riginal ...articles sometimes had gaps in their arguments, or relied on hidden assumptions, or used unexplained notation. Often massive computer programs had taken the place of analytic studies. In many cases... it was easiest to work out the relevant theory myself.
This book is the result. Its aim... self-contained explanations of the ideas and formulas... used and tested in modern cosmological observations.
Consider the geometry of a three-dimensional homogeneous and isotropic space. ...[G]eometry is encoded in a metric <math>g_{ij}(\mathbf{x})</math> (with i and j running over the three coordinate directions), or equivalently a line element <math>ds^2 \equiv g_{ij} dx^i dx^j</math>, with summation over repeated indices... <math>ds</math> is the proper distance between <math>\mathbf{x}</math> and <math>\mathbf{x}+\mathbf{dx}</math>, meaning... the distance measured by a surveyor who uses a... Cartesian [coordinate system] in a small neighborhood of... point <math>\mathbf{x}</math>.) One... homogeneous isotropic three-dimensional space with positive definite lengths is flat space, with line element<math>ds^2=d\mathbf{x}^2</math>...The coordinate transformations that leave this invariant are... ordinary three-dimensional rotations and translations. ...Another ...possibility is a four-dimensional with some radius <math>a</math>, with line element<math>ds^2=d \mathbf{x}^2+dz^2,\;\;z^2 + \mathbf{x}^2 = a^2</math>,...Here the transformations that leave the line element invariant are four-dimensional rotations; the direction of <math>\mathbf{x}</math> can be changed to any other direction by a four-dimensional rotation that does not change <math>z</math>. ...[T]he only other possibility (up to a coordinate transformation) is a hyperspherical surface in four-dimensional , with line element<math>ds^2 = d\mathbf{x}^2 - dz^2,\;\;z^2 - \mathbf{x}^2 = a^2</math>,...where <math>a^2</math> is (so far) an arbitrary positive constant. The coordinate transformations that leave this invariant are four-dimensional pseudo-rotations, just like s, but with <math>z</math> instead of time.