Showing posts with label relativity. Show all posts
Showing posts with label relativity. Show all posts

Arthur and the eclipse

by @ulaulaman about #ArthurEddington #AlbertEinstein #GeneralRelativity
On the 17th November 1922, Albert Einstein, accompanied by his wife, arrived in Kobe (see the report of the visit published on the AAPPS Bulletin - pdf). Here he was surrounded by journalists and fans: while the first asked him questions, the latter were on the hunt for an autograph from one of the most famous physicists and scientists of the time. Einstein, as written by Naoki Urasawa on the initial pages of Billy Bat #9, to a specific question on why he won the Nobel Prize for the photoelectric effect and not for the theory of special and general relativity, replied:
Because, that can't be verified.
But the mangaka committed a chronological mistake, probably caused by the Urasawa's need to focus on the innovation represented by the Einstein's theories: the point, in fact, is that just three years earlier, on the 6th November, 1919, during a meeting of the Royal Society and Royal Astronomical Society, Arthur Eddington presented the results of the celestial observations made ​​in mid-spring of that year. The interest and the importance of the discovery was such that the next day, the Times headlined:
Revolution in Science: New Theory of the Universe: Newton's Ideas Overthrown, by Joseph John Thomson:
Our conceptions about the structure of the universe must be changed in a fundamental way
So, when Einstein went to Japan, the evidence of the correctness of his theory had already been around.

Paul Dirac and the relativistic world

posted by @ulaulaman #PaulDirac #DiracDay #DiracEquation #Klein-GordonEquation #relativity #physics
It seems to be one of the fundamental features of nature that fundamental physical laws are described in terms of a mathematical theory of great beauty and power, needing quite a high standard of mathematics for one to understand it.
(Paul Dirac)
For a physicists the beauty of an equation is often in its conciseness and in the amount of physical information that is able to synthesize, and so the wide variety of systems that it can be represented. For example, the Schrodinger equation, in its most synthetic form, is able to describe a disparate number of systems, and only descending the details of each system, physicists are able to describe the system with with more or less complicated solutions. \[i \frac{\partial}{\partial t} \psi = H \psi\] Something like that it's maked by the equations discovered by Klein-Gordon and Dirac, but for the relativistic motion: indeed particles are able to travel even at near the speed of light, and in that case the Schrodinger equation is no longer sufficient to describe their dynamics.
From this we need to describe the world from the point of view of quantum relativistic: the Klein-Gordon equation is born: \[\partial^\mu \partial_\mu \phi + m^2 \phi = 0\] It has two drawbacks: negative energy as a solution and interpretation of the wave function. If, as in quantum mechanics, we associate the wave function with probability, or rather the probability's density, it happens that this can also take on negative values. At this point arrived the Dirac equation: \[\left ( i \gamma^\mu \partial_\mu - m \right ) \psi = 0\] Thanks to the Dirac equation, whose one of the first success was the explanation of half-integer spin of the electron, we now have two fundamental tools: the first for the description of bosons (particles with integer spin), the second for the description of fermions (half-integer spin particles).
Read also: The Relation between Mathematics and Physics, a lecture by Dirac
In the image: Paul Dirac by George Gamow

Poincaré, Einstein and Picasso: children of time

posted by @ulaulaman about #cubism #PabloPicasso #AlbertEinstein #HenriPoincaré #mathematics #art #relativity
A great thanks to Marco Fulvio Barozzi: his post(1) about Miller's book is the main inspiration of my post.

Yesterday, on the Guardian, Arthur I. Miller, the author of the book Einstein, Picasso: Space, Time and the Beauty that Causes Havoc, wrote a briefly article in which he resumed his thesis about the connections between Poincaré and Einstein, between Poincaré and Picasso and, for translation, between Einstein and Picasso.
Henri Poincaré was one of the most important mathematician of the early XX century: his most important contributions, that have a great impact also in physics, are in group theory and representation theory. His work was indeed important for the birth of the ray representations (the theory was developed in particular by Valentine Bargmann starting from Weyl and Wigner's works) and basic for special relativity and in particular for general relativity. Poincaré was the first to propose the symmetrical form of the Lorentz transformations, and his work was important for the creation of the Poincaré group, the symmetry group of the general relativity. In particular about the relativity, Poincaré written on his book Science and Hypothesis (1902)
Our Euclidean geometry is itself a sort of linguistic convention; we may state the facts of mechanics in relation to a non-Euclidean space, but this would be a less convenient reference, although legitimate like our ordinary space.(1)
He also defined the principle of relative motion like
the physical impossibility of observing absolute motion.(1)
Two years later he named it Principle of Relativity.
At the other hand, Einstein did not cite Poincaré's works in his paper published in 1905 by Annalen der Physik and only in a conference in 1921 Einstein confirmed his debt to the french mathematician, but only about general relativity and non-euclidean geometry. And this is the only documented connection between Einstein and Poincaré: we must suppose that the two scientists worked indipendetly and also after his first paper Einstein used Poincaré's discoveries in order to develop the mathematical formalism of the general relativity.
Some years later the first Einstein's paper, the cubism was born in France:
A circle of poets and critics, and followers of the philosopher Bergson, stood up for cubism in the visual arts. This group became known as the Cubists. The poet and publicist G. Apollinaire became the undisputed leader of this movement.(2)
It seems that relativity played a relevant role in the phylosophy of the artistic movement
Like the scientists, the artists has come to recognize thatclassic conceptions of space and volume are limited and one-sided. (...) The presentation of objects from several point of view introduces a principle which is intimately bound up with modern life - simultaenity. It is a temporal coincidence that Einstein should havebegan his famous work (...) with a careful definition of simultaneity.(5)
In this quotation by Sigfried Giedion, the connection was simply casual, only a temporal coincidence, but a lot of art historians think that the connection is not so casual. One of this is Paul M. Laporte, who published two paper about cubism and relativity, and submitted them to Albert Einstein. The great physicist reply with a long letter, in which he concludes:
This new artistic "language" has nothing in common with the Theory of Relativity.(5)
And probably it is so. Indeed in 1903 the Introduction to Metaphysics by Henri Bergson was published. In the book Bergson argued that
human consciousness experiences space and time as ever-changing and heterogeneous. With the passage of time, an observer accumulates in his memory a store of perceptual information about a given object in the external visible world, and this accumulated experience becomes the basis for the observer’s conceptual knowledge of that object. By contrast, the intellect or reasoning faculty always represents time and space as homogenous. Bergson argued that intellectual perception led to a fundamentally false representation of the nature of things, that in nature nothing is ever absolutely still. Instead the universe is in a constant state of change or flux. An observer views an object and its surrounding environment as a continuum, fusing into one another. The task of metaphysics, according to Bergson, is to find ways to capture this flux, especially as it is expressed in consciousness. To represent this flux of reality, Picasso began to make references to the fourth dimension by "sticking together" several three-dimensional spaces in a row.(4)

David Merritt and June Barrow-Green at Milano

The next Monday (28/05/2012) will be a great day for science in Italy. Indeed the astrophysicist David Merritt and the mathematician June Barrow-Green will be at Milano for two distinct talks.
Merritt will be at the Osservatorio Astronomico di Brera for the following talk:

Relativistic Dynamics at the Centers of Galaxies (h 14:00)
Encounters between stars and stellar remnants at the centers of galaxies drive many important processes, including generation of gravitational waves via extreme-mass-ratio inspirals (EMRIs). The fact that these encounters take place near a supermassive black hole (SMBH) turns out to be important for two reasons: (1) The orbital motion is quasi-Keplerian, so that correlations are maintained for much longer than in purely random encounters. (2) Relativity affects the motion, through mechanisms like precession of the periapse and frame-dragging. The interplay between these processes is just now beginning to be understood, based on N-body simulations that contain a post-Newtonian representation of relativistic dynamics. A key result is that relativity can be important even for orbits that extend outward to a substantial fraction of the SMBH influence radius, by destroying the long-term correlations that would otherwise drive the evolution. I will discuss this work and its implications for the EMRI problem, for experimental tests of theories of gravity, and for the long-term evolution of SMBHs and galactic nuclei.(1)
And June Barrow-Green will be at Mathematics Department "Federigo Enriques" with the talk Poincaré and the three body problem.(2) (h 16:30)
The problem was stated by Poincaré in 1890 with the following quotation:
I consider three masses, the first very large, the second small but finite, the third infinitely small; I assume that the first two each describe a circle around their common centre of gravity and that the third moves in the plane of these circles. An example would be the case of a small planet perturbed by Jupiter, if the eccentricity of Jupiter and the inclination of the orbits are disregarded.(3)

(1) From inSPIRE I found the following paper, Towards relativistic orbit fitting of Galactic center stars and pulsars (arXiv), that seems about the subject of the thalk.
(2) From the introduction of Oscar II's prize competition and the error in Poincaré's memoir on the three body problem by June Barrow-Green:
In the autumn of 1890 Henri Poincaré's memoir on the three body problem was published in the journal Acta Mathematica as the winning entry in the international prize competition sponsored by Oscar II, King of Sweden and Norway, to mark his 60th birthday on January 21, 1889. Today, Poincaré's published memoir is renowned for containing the first mathematical description of chaotic behavior in a dynamical system. Correspondence preserved at the Institut Mittag-Leffler reveals that the competition was beleaguered by difficulties throughout. In particular, it has emerged that only weeks before the prize-winning memoir was due to be published, Poincaré discovered an error in his work which forced him to make very substantial changes. Indeed it was only as a result of correcting the error that he discovered the existence of what today are known as homoclinic points. This paper is an account of the troubled history of the competition together with an explanation of the error in Poincaré's memoir.
(3) Quotation extracted from Poincaré and the Three Body Problem

Video abstract: Diffusion in curved spacetimes

In the following video, that I uploaded on youtube, Matteo Smerlak speaks about his recently published paper, Diffusion in curved spacetimes (arXiv):