100:00:21,840 --> 00:00:28,410yeah 200:00:51,840 --> 00:00:54,840yeah 300:01:18,750 --> 00:01:25,140yeah 400:01:25,920 --> 00:01:31,80ladies and gentlemen it's my privilegeto introduce the messenger lecture as 500:01:31,80 --> 00:01:37,470Richard be fine men of the CalifoiaInstitute of Technology professor fine 600:01:37,470 --> 00:01:41,429man is a distinguished theoreticalphysicist and he's done much to bring 700:01:41,430 --> 00:01:45,630order out of the confusion whichادامه مطلب

“It is odd, but on the infrequent occasions when I have been called upon in a formal place to play the bongo drums, the introducer never seems to find it necessary to mention that I also do theoretical physics. I believe that is probably because we respect the arts more than the sciences. The artists of the Renaissance said that man’s main conce should be for man, and yet there are other things of interest in the world. Even the artists appreciate sunsets, and the ocean waves, and the march of the stars across the heavens. There is then some reason to talk of other things sometimes. As we look into these things we get an aesthetic pleasure from them directly on observation. There is also a ” “rhythm and a patte between the phenomena of nature which is not apparent to the eye, but only to the eye of analysis; and it is these rhythms and pattes which we call Physical Laws. What I want to discuss in this series of lectures is the general characteristic of these Physical Laws; that is another level, if you will, of higher generality over the laws themselves. Really what I am considering is nature as seen as a result of detailed analysis, but mainly I wish to speak about only the most overall general qualities of nature.Now such a topic has a tendency to become too philosophical because it becomes so general, and a person talks in such generalities, that everybody can understand him. It is then considered to be some deep philosophy. I would like to be rather more special, anادامه مطلب

100:00:21,840 --> 00:00:28,410yeah 200:00:51,840 --> 00:00:54,840yeah 300:01:18,750 --> 00:01:25,140yeah 400:01:25,920 --> 00:01:31,80ladies and gentlemen it's my privilegeto introduce the messenger lecture as 500:01:31,80 --> 00:01:37,470Richard be fine men of the CalifoiaInstitute of Technology professor fine 600:01:37,470 --> 00:01:41,429man is a distinguished theoreticalphysicist and he's done much to bring 700:01:41,430 --> 00:01:45,630order out of the confusion which ismarked much of the spectacular 800:01:45,630 --> 00:01:50,640development in physics during thepost-war period among his honors and 900:01:50,640 --> 00:01:55,470awards i will mention only the AlbertEinstein award in 1954 1000:01:56,39 --> 00:02:00,270this is an award which is made everythird year in which includes a gold 1100:02:00,270 --> 00:02:03,270medal and a substantial sum of money 1200:02:03,929 --> 00:02:09,360professor Fineman did his undergraduatework at MIT and his graduate work at 1300:02:09,360 --> 00:02:10,590Princeton 1400:02:10,590 --> 00:02:15,780he worked on the Manhattan Project atPrinceton and later at Los Alamos he was 1500:02:15,780 --> 00:02:20,310appointed an assistant professor here atCoell in 1944 1600:02:20,310 --> 00:02:23,459although he did not assume residenceuntil the end of the war 1700:02:24,540 --> 00:02:28,709I thought it might be interesting to seewhat was said about him when he was 1800:02:28,709 --> 00:02:30,32ادامه مطلب

Extra-dimensions are a common topic in popular descriptions of theoretical physics with whichundergraduate student most often have no contact in physics courses. This paper shows how studentscould be introduced to this topic by presenting an approach to two basic consequences of thepresence of compact extra-dimensions based on undergraduate-level physics. The insensibility oflow-energy physics to compact extra dimensions is illustrated in the context of non-relativisticquantum mechanics and the prediction of Kaluza-Klein excitations of particles is discussed in theframework of relativistic wavادامه مطلب

Aims. Daily observation conditions are needed when observing the Sun at high angular resolution. MISOLFA is a daytime seeingmonitor developed for this purpose that allows the estimation of the spatial and temporal parameters of atmospheric turbulence. Thisinformation is necessary, for instance, for astrometric measurements of the solar radius performed at Cale Observatory (France)with SODISM II, the ground-based version of the SODISM instrument of the PICARD mission.Methods. We present a new way to estimate the spatial parameters of atmospheric turbulence for daily observations. This method ادامه مطلب

The double-slit experiment is used as thearchetypal interference experiment to dramat-ically demonstrate the quantum weirdness ofwave-particle duality. It is a long-held assump-tion that whether which-way detectors are placedat one slit or both will yield the same results, ren-dering the second detector redundant. Here weshow that the presence of the second detector canhave measurable effects on the interference pat-te, violating this assumption. We show thatthis effect forms the basis for a new measure ofBo rule violation which is correct to all orders.It opens new experimental opportunities for theaccurate testing of the Bo rule.Particle nature is demonstrated in double-slit experi-ments by placing which-way detectors at the slits. Thereason that a second which-way detector is believed to beredundant, is that a detection at one slit means that theparticle is assumed to not have gone through the otherslit. Now on the other hand, in the Feynman path inte-gral formulation of quantادامه مطلب

The motion of material bodies formed the subject of some of the earliest researchpursued by the pioneers of physics. From their efforts there has evolved a vastfield known as analytical mechanics or dynamics, or simply, mechanics. In thepresent century the term "classical mechanics" has come into wide use to denotethis branch of physics in contradistinction to the newer physical theories, espe-especially quantum mechanics. We shall follow this usage, interpreting the name toinclude the type of mechanics arising out of the special theory of relativity. It isthe purpose of this book to develop the structure of classical mechanics and tooutline some of its applications of present-day interest in pure physics. Basic toany presentation of mechanics are a number of fundamental physical concepts,such as space, time, simultaneity, mass, and force. For the most part, however,these concepts will not be analyzed critically here; rather, they will be assumed asundefined terms whose meanings are faادامه مطلب

The coerstone of mode cosmology is the belief that the place that we occupy in theUniverse is in no way special. This is known as the cosmological principle, and it is anidea which is both powerful and simple. It is intriguing, then, that for the bulk of the historyof civilization it was believed that we occupy a very special location, usually the centre, inthe scheme of things.The ancient Greeks, in a model further developed by the Alexandrian Ptolemy, believedthat the Earth must lie at the centre of the cosmos. It would be circled by the Moon, the Sunand the planets, and then the ‘fixed’ stars would be yet further away. A complex combina-tion of circular motions, Ptolemy’s Epicycles, was devised in order to explain the motionsof the planets, especially the phenomenon of retrograde motion where planets appear totemporarily reverse their direction of motion. It was not until the early 1500s that Coper-nicus stated forcefully the view, initiated nearly two thousand years beforادامه مطلب

For most of history, astronomers have had to rely on light in the visible part of the spec-trum in order to study the Universe. One of the great astronomical achievements of the20th century was the exploitation of the full electromagnetic spectrum for astronomicalmeasurements. We now have instruments capable of making observations of radio waves,microwaves, infrared light, visible light, ultraviolet light, X-rays and gamma rays, whichall correspond to light waves of different (in this case increasing) frequency. We are evenentering an epoch where we can go beyond the electromagnetic spectrum and receive in-formation of other types. A remarkable feature of observations of a nearby supeova in1987 was that it was also seen through detection of neutrinos, an extraordinarily weaklyinteracting type of particle normally associated with radioactive decay. Very high energycosmic rays, consisting of highly-relativistic elementary particles, are now routinely de-tected, though as yet there is nادامه مطلب

It is perfectly possible to discuss cosmology without having already leaed general rel-ativity. In fact, the most crucial equation, the Friedma equation which describes theexpansion of the Universe, tus out to be the same when derived from Newton’s theoryof gravity as it is when derived from the equations of general relativity. The Newtonianderivation is, however, some way from being completely rigorous, and general relativity isrequired to fully patch it up, a detail that need not conce us at this stage. Readers withsome familiarity with general relativity may wish to study the relativistic derivation givenin Advanced Topic 1.In Newtonian gravity all matter attracts, with the force exerted by an object of mass Mon one of mass m given by the famous relationshipF =GM m,r 2(3.1)where r is the distance between the objects and G is Newton’s gravitational constant. Thatis, gravity obeys an inverse square law. Because a force on an object induces an accelerationwhich is also propادامه مطلب

We now consider the real meaning of the constant k which appears in the Friedmaequationa ̇a2=8πGkρ − 2 .3a(4.1)While the Newtonian derivation in the last chapter introduced this as a measure of theenergy per particle, the true interpretation, apparent in the context of general relativity, isthat it measures the curvature of space. General relativity tells us that gravity is due to thecurvature of four-dimensional space–time, and a full analysis can be found in any generalrelativity textbook. Here I will be purely descriptive, and focus on the interpretation ofk as measuring the curvature of the three spatial dimensions. Further details of generalrelativistic cosmology can be found in Advanced Topic 1.We have demanded that our model universes be both homogeneous and isotropic. Thesimplest type of geometry which can have this property is what is called a flat geometry,in which the normal rules of Euclidean geometry apply. However, it tus out that theassumption of isotropy is nادامه مطلب

In Chapter 3 we derived the equations satisfied by an expanding isotropic gas. They are theFriedman equation 1a ̇a2=8πGkρ − 2 ,3a(5.1)which goves the time evolution of the scale factor a(t), and the fluid equationρ ̇ + 3a ̇pρ + 2ac= 0 ,(5.2)which gives us the evolution of the mass density ρ(t). I stress that, despite their Newtonianderivation, these are the real equations used by cosmologists, more traditionally derivedvia the equations of general relativity as described in Advanced Topic 1.This chapter finds and discusses some simple solutions to these equations, which willbe used extensively during the book. However, while they have wide applicability duringthe early stages of the Universe, it will tu out that these are not sufficient to describe thepresent state of the Universe, for which an extra ingredient, the cosmological constant, willbe needed. It is introduced in Chapter 7.Before finding solutions to these equations, we can study two of their implications.5.1Hubادامه مطلب

The Big Bang model does not give a unique description of our present Universe, but ratherleaves quantities such as the present expansion rate, or the present composition of the Uni-verse, to be fixed by observation.It is a standard practice to specify cosmological models via a few parameters, which onethen tries to determine observationally to decide which version of the model best describesour Universe. In this chapter and the next I’ll discuss the most commonly-considered pa-rameters, including ones we have already seen and new ones.6.1The expansion rate H 0The Hubble constant H 0 tells us the present expansion rate of the Universe, making it avital cosmological parameter as measurements of other properties of the Universe oftendepend on it. It also ought to be the easiest to measure, since all galaxies are supposed toobey v = H 0 r. So all we have to do is measure the velocities and distances of as manygalaxies as we can and get an answer. However, each measurement has its problemادامه مطلب