8.033: Relativity Introduction
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26-2 Spacetime and the Spacetime Interval We Usually Think of Time and Space As Being Quite Different from One Another
Answer to Essential Question 26.1: (a) The obvious answer is that you are at rest. However, the question really only makes sense when we ask what the speed is measured with respect to. Typically, we measure our speed with respect to the Earth’s surface. If you answer this question while traveling on a plane, for instance, you might say that your speed is 500 km/h. Even then, however, you would be justified in saying that your speed is zero, because you are probably at rest with respect to the plane. (b) Your speed with respect to a point on the Earth’s axis depends on your latitude. At the latitude of New York City (40.8° north) , for instance, you travel in a circular path of radius equal to the radius of the Earth (6380 km) multiplied by the cosine of the latitude, which is 4830 km. You travel once around this circle in 24 hours, for a speed of 350 m/s (at a latitude of 40.8° north, at least). (c) The radius of the Earth’s orbit is 150 million km. The Earth travels once around this orbit in a year, corresponding to an orbital speed of 3 ! 104 m/s. This sounds like a high speed, but it is too small to see an appreciable effect from relativity. 26-2 Spacetime and the Spacetime Interval We usually think of time and space as being quite different from one another. In relativity, however, we link time and space by giving them the same units, drawing what are called spacetime diagrams, and plotting trajectories of objects through spacetime. -
Thermodynamics of Spacetime: the Einstein Equation of State
gr-qc/9504004 UMDGR-95-114 Thermodynamics of Spacetime: The Einstein Equation of State Ted Jacobson Department of Physics, University of Maryland College Park, MD 20742-4111, USA [email protected] Abstract The Einstein equation is derived from the proportionality of entropy and horizon area together with the fundamental relation δQ = T dS connecting heat, entropy, and temperature. The key idea is to demand that this relation hold for all the local Rindler causal horizons through each spacetime point, with δQ and T interpreted as the energy flux and Unruh temperature seen by an accelerated observer just inside the horizon. This requires that gravitational lensing by matter energy distorts the causal structure of spacetime in just such a way that the Einstein equation holds. Viewed in this way, the Einstein equation is an equation of state. This perspective suggests that it may be no more appropriate to canonically quantize the Einstein equation than it would be to quantize the wave equation for sound in air. arXiv:gr-qc/9504004v2 6 Jun 1995 The four laws of black hole mechanics, which are analogous to those of thermodynamics, were originally derived from the classical Einstein equation[1]. With the discovery of the quantum Hawking radiation[2], it became clear that the analogy is in fact an identity. How did classical General Relativity know that horizon area would turn out to be a form of entropy, and that surface gravity is a temperature? In this letter I will answer that question by turning the logic around and deriving the Einstein equation from the propor- tionality of entropy and horizon area together with the fundamental relation δQ = T dS connecting heat Q, entropy S, and temperature T . -
Arxiv:1401.0181V1 [Gr-Qc] 31 Dec 2013 † Isadpyia Infiac Fteenwcodntsaediscussed
Painlev´e-Gullstrand-type coordinates for the five-dimensional Myers-Perry black hole Tehani K. Finch† NASA Goddard Space Flight Center Greenbelt MD 20771 ABSTRACT The Painlev´e-Gullstrand coordinates provide a convenient framework for pre- senting the Schwarzschild geometry because of their flat constant-time hyper- surfaces, and the fact that they are free of coordinate singularities outside r=0. Generalizations of Painlev´e-Gullstrand coordinates suitable for the Kerr geome- try have been presented by Doran and Nat´ario. These coordinate systems feature a time coordinate identical to the proper time of zero-angular-momentum ob- servers that are dropped from infinity. Here, the methods of Doran and Nat´ario arXiv:1401.0181v1 [gr-qc] 31 Dec 2013 are extended to the five-dimensional rotating black hole found by Myers and Perry. The result is a new formulation of the Myers-Perry metric. The proper- ties and physical significance of these new coordinates are discussed. † tehani.k.finch (at) nasa.gov 1 Introduction By using the Birkhoff theorem, the Schwarzschild geometry has been shown to be the unique vacuum spherically symmetric solution of the four-dimensional Einstein equations. The Kerr geometry, on the other hand, has been shown only to be the unique stationary, rotating vacuum black hole solution of the four-dimensional Einstein equations. No distri- bution of matter is currently known to produce a Kerr exterior. Thus the Kerr geometry does not necessarily correspond to the spacetime outside a rotating star or planet [1]. This is an indication of the complications encountered upon trying to extend results found for the Schwarzschild spacetime to the Kerr spacetime. -
Chapter 5 the Relativistic Point Particle
Chapter 5 The Relativistic Point Particle To formulate the dynamics of a system we can write either the equations of motion, or alternatively, an action. In the case of the relativistic point par- ticle, it is rather easy to write the equations of motion. But the action is so physical and geometrical that it is worth pursuing in its own right. More importantly, while it is difficult to guess the equations of motion for the rela- tivistic string, the action is a natural generalization of the relativistic particle action that we will study in this chapter. We conclude with a discussion of the charged relativistic particle. 5.1 Action for a relativistic point particle How can we find the action S that governs the dynamics of a free relativis- tic particle? To get started we first think about units. The action is the Lagrangian integrated over time, so the units of action are just the units of the Lagrangian multiplied by the units of time. The Lagrangian has units of energy, so the units of action are L2 ML2 [S]=M T = . (5.1.1) T 2 T Recall that the action Snr for a free non-relativistic particle is given by the time integral of the kinetic energy: 1 dx S = mv2(t) dt , v2 ≡ v · v, v = . (5.1.2) nr 2 dt 105 106 CHAPTER 5. THE RELATIVISTIC POINT PARTICLE The equation of motion following by Hamilton’s principle is dv =0. (5.1.3) dt The free particle moves with constant velocity and that is the end of the story. -
Lecture Notes 17: Proper Time, Proper Velocity, the Energy-Momentum 4-Vector, Relativistic Kinematics, Elastic/Inelastic
UIUC Physics 436 EM Fields & Sources II Fall Semester, 2015 Lect. Notes 17 Prof. Steven Errede LECTURE NOTES 17 Proper Time and Proper Velocity As you progress along your world line {moving with “ordinary” velocity u in lab frame IRF(S)} on the ct vs. x Minkowski/space-time diagram, your watch runs slow {in your rest frame IRF(S')} in comparison to clocks on the wall in the lab frame IRF(S). The clocks on the wall in the lab frame IRF(S) tick off a time interval dt, whereas in your 2 rest frame IRF( S ) the time interval is: dt dtuu1 dt n.b. this is the exact same time dilation formula that we obtained earlier, with: 2 2 uu11uc 11 and: u uc We use uurelative speed of an object as observed in an inertial reference frame {here, u = speed of you, as observed in the lab IRF(S)}. We will henceforth use vvrelative speed between two inertial systems – e.g. IRF( S ) relative to IRF(S): Because the time interval dt occurs in your rest frame IRF( S ), we give it a special name: ddt = proper time interval (in your rest frame), and: t = proper time (in your rest frame). The name “proper” is due to a mis-translation of the French word “propre”, meaning “own”. Proper time is different than “ordinary” time, t. Proper time is a Lorentz-invariant quantity, whereas “ordinary” time t depends on the choice of IRF - i.e. “ordinary” time is not a Lorentz-invariant quantity. 222222 The Lorentz-invariant interval: dI dx dx dx dx ds c dt dx dy dz Proper time interval: d dI c2222222 ds c dt dx dy dz cdtdt22 = 0 in rest frame IRF(S) 22t Proper time: ddtttt 21 t 21 11 Because d and are Lorentz-invariant quantities: dd and: {i.e. -
A Short and Transparent Derivation of the Lorentz-Einstein Transformations
A brief and transparent derivation of the Lorentz-Einstein transformations via thought experiments Bernhard Rothenstein1), Stefan Popescu 2) and George J. Spix 3) 1) Politehnica University of Timisoara, Physics Department, Timisoara, Romania 2) Siemens AG, Erlangen, Germany 3) BSEE Illinois Institute of Technology, USA Abstract. Starting with a thought experiment proposed by Kard10, which derives the formula that accounts for the relativistic effect of length contraction, we present a “two line” transparent derivation of the Lorentz-Einstein transformations for the space-time coordinates of the same event. Our derivation make uses of Einstein’s clock synchronization procedure. 1. Introduction Authors make a merit of the fact that they derive the basic formulas of special relativity without using the Lorentz-Einstein transformations (LET). Thought experiments play an important part in their derivations. Some of these approaches are devoted to the derivation of a given formula whereas others present a chain of derivations for the formulas of relativistic kinematics in a given succession. Two anthological papers1,2 present a “two line” derivation of the formula that accounts for the time dilation using as relativistic ingredients the invariant and finite light speed in free space c and the invariance of distances measured perpendicular to the direction of relative motion of the inertial reference frame from where the same “light clock” is observed. Many textbooks present a more elaborated derivation of the time dilation formula using a light clock that consists of two parallel mirrors located at a given distance apart from each other and a light signal that bounces between when observing it from two inertial reference frames in relative motion.3,4 The derivation of the time dilation formula is intimately related to the formula that accounts for the length contraction derived also without using the LET. -
A One-Map Two-Clock Approach to Teaching Relativity in Introductory Physics
A one-map two-clock approach to teaching relativity in introductory physics P. Fraundorf Department of Physics & Astronomy University of Missouri-StL, St. Louis MO 63121 (December 22, 1996) observation that relativistic objects behave at high speed This paper presents some ideas which might assist teachers as though their inertial mass increases in the −→p = m−→v incorporating special relativity into an introductory physics expression, led to the definition (used in many early curriculum. One can define the proper-time/velocity pair, as 1 0 well as the coordinate-time/velocity pair, of a traveler using textbooks ) of relativistic mass m ≡ mγ. Such ef- only distances measured with respect to a single “map” frame. forts are worthwhile because they can: (A) potentially When this is done, the relativistic equations for momentum, allow the introduction of relativity concepts at an earlier energy, constant acceleration, and force take on forms strik- stage in the education process by building upon already- ingly similar to their Newtonian counterparts. Thus high- mastered classical relationships, and (B) find what is school and college students not ready for Lorentz transforms fundamentally true in both classical and relativistic ap- may solve relativistic versions of any single-frame Newtonian proaches. The concepts of transverse (m0) and longi- problems they have mastered. We further show that multi- tudinal (m00 ≡ mγ3) masses have similarly been used2 frame calculations (like the velocity-addition rule) acquire to preserve relations of the form Fx = max for forces simplicity and/or utility not found using coordinate velocity perpendicular and parallel, respectively, to the velocity alone. -
The Extended Relativity Theory in Clifford Spaces
THE EXTENDED RELATIVITY THEORY IN CLIFFORD SPACES C. Castroa and M. Pav·si·cb May 21, 2004 aCenter for Theoretical Studies of Physical Systems, Clark Atlanta University, Atlanta bJo·zef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia; Email: [email protected] Abstract A brief review of some of the most important features of the Extended Rela- tivity theory in Cli®ord-spaces (C-spaces) is presented whose " point" coordinates are noncommuting Cli®ord-valued quantities and which incorporate the lines, ar- eas, volumes,.... degrees of freedom associated with the collective particle, string, membrane,... dynamics of p-loops (closed p-branes) living in target D-dimensional spacetime backgrounds. C-space Relativity naturally incorporates the ideas of an invariant length (Planck scale), maximal acceleration, noncommuting coordinates, supersymmetry, holography, higher derivative gravity with torsion and variable di- mensions/signatures that allows to study the dynamics of all (closed) p-branes, for all values of p, on a uni¯ed footing. It resolves the ordering ambiguities in QFT and the problem of time in Cosmology. A discussion of the maximal-acceleration Rela- tivity principle in phase-spaces follows along with the study of the invariance group of symmetry transformations in phase-space that allows to show why Planck areas are invariant under acceleration-boosts transformations and which seems to suggest that a maximal-string tension principle may be operating in Nature. We continue by pointing out how the relativity of signatures of the underlying n-dimensional spacetime results from taking di®erent n-dimensional slices through C-space. The conformal group emerges as a natural subgroup of the Cli®ord group and Relativity in C-spaces involves natural scale changes in the sizes of physical objects without the introduction of forces nor Weyl's gauge ¯eld of dilations. -
Massachusetts Institute of Technology Midterm
Massachusetts Institute of Technology Physics Department Physics 8.20 IAP 2005 Special Relativity January 18, 2005 7:30–9:30 pm Midterm Instructions • This exam contains SIX problems – pace yourself accordingly! • You have two hours for this test. Papers will be picked up at 9:30 pm sharp. • The exam is scored on a basis of 100 points. • Please do ALL your work in the white booklets that have been passed out. There are extra booklets available if you need a second. • Please remember to put your name on the front of your exam booklet. • If you have any questions please feel free to ask the proctor(s). 1 2 Information Lorentz transformation (along the xaxis) and its inverse x� = γ(x − βct) x = γ(x� + βct�) y� = y y = y� z� = z z = z� ct� = γ(ct − βx) ct = γ(ct� + βx�) � where β = v/c, and γ = 1/ 1 − β2. Velocity addition (relative motion along the xaxis): � ux − v ux = 2 1 − uxv/c � uy uy = 2 γ(1 − uxv/c ) � uz uz = 2 γ(1 − uxv/c ) Doppler shift Longitudinal � 1 + β ν = ν 1 − β 0 Quadratic equation: ax2 + bx + c = 0 1 � � � x = −b ± b2 − 4ac 2a Binomial expansion: b(b − 1) (1 + a)b = 1 + ba + a 2 + . 2 3 Problem 1 [30 points] Short Answer (a) [4 points] State the postulates upon which Einstein based Special Relativity. (b) [5 points] Outline a derviation of the Lorentz transformation, describing each step in no more than one sentence and omitting all algebra. (c) [2 points] Define proper length and proper time. -
Observer with a Constant Proper Acceleration Cannot Be Treated Within the Theory of Special Relativity and That Theory of General Relativity Is Absolutely Necessary
Observer with a constant proper acceleration Claude Semay∗ Groupe de Physique Nucl´eaire Th´eorique, Universit´ede Mons-Hainaut, Acad´emie universitaire Wallonie-Bruxelles, Place du Parc 20, BE-7000 Mons, Belgium (Dated: February 2, 2008) Abstract Relying on the equivalence principle, a first approach of the general theory of relativity is pre- sented using the spacetime metric of an observer with a constant proper acceleration. Within this non inertial frame, the equation of motion of a freely moving object is studied and the equation of motion of a second accelerated observer with the same proper acceleration is examined. A com- parison of the metric of the accelerated observer with the metric due to a gravitational field is also performed. PACS numbers: 03.30.+p,04.20.-q arXiv:physics/0601179v1 [physics.ed-ph] 23 Jan 2006 ∗FNRS Research Associate; E-mail: [email protected] Typeset by REVTEX 1 I. INTRODUCTION The study of a motion with a constant proper acceleration is a classical exercise of special relativity that can be found in many textbooks [1, 2, 3]. With its analytical solution, it is possible to show that the limit speed of light is asymptotically reached despite the constant proper acceleration. The very prominent notion of event horizon can be introduced in a simple context and the problem of the twin paradox can also be analysed. In many articles of popularisation, it is sometimes stated that the point of view of an observer with a constant proper acceleration cannot be treated within the theory of special relativity and that theory of general relativity is absolutely necessary. -
Minkowski's Proper Time and the Status of the Clock Hypothesis
Minkowski’s Proper Time and the Status of the Clock Hypothesis1 1 I am grateful to Stephen Lyle, Vesselin Petkov, and Graham Nerlich for their comments on the penultimate draft; any remaining infelicities or confusions are mine alone. Minkowski’s Proper Time and the Clock Hypothesis Discussion of Hermann Minkowski’s mathematical reformulation of Einstein’s Special Theory of Relativity as a four-dimensional theory usually centres on the ontology of spacetime as a whole, on whether his hypothesis of the absolute world is an original contribution showing that spacetime is the fundamental entity, or whether his whole reformulation is a mere mathematical compendium loquendi. I shall not be adding to that debate here. Instead what I wish to contend is that Minkowski’s most profound and original contribution in his classic paper of 100 years ago lies in his introduction or discovery of the notion of proper time.2 This, I argue, is a physical quantity that neither Einstein nor anyone else before him had anticipated, and whose significance and novelty, extending beyond the confines of the special theory, has become appreciated only gradually and incompletely. A sign of this is the persistence of several confusions surrounding the concept, especially in matters relating to acceleration. In this paper I attempt to untangle these confusions and clarify the importance of Minkowski’s profound contribution to the ontology of modern physics. I shall be looking at three such matters in this paper: 1. The conflation of proper time with the time co-ordinate as measured in a system’s own rest frame (proper frame), and the analogy with proper length. -
Lecture 17 Relativity A2020 Prof. Tom Megeath What Are the Major Ideas
4/1/10 Lecture 17 Relativity What are the major ideas of A2020 Prof. Tom Megeath special relativity? Einstein in 1921 (born 1879 - died 1955) Einstein’s Theories of Relativity Key Ideas of Special Relativity • Special Theory of Relativity (1905) • No material object can travel faster than light – Usual notions of space and time must be • If you observe something moving near light speed: revised for speeds approaching light speed (c) – Its time slows down – Its length contracts in direction of motion – E = mc2 – Its mass increases • Whether or not two events are simultaneous depends on • General Theory of Relativity (1915) your perspective – Expands the ideas of special theory to include a surprising new view of gravity 1 4/1/10 Inertial Reference Frames Galilean Relativity Imagine two spaceships passing. The astronaut on each spaceship thinks that he is stationary and that the other spaceship is moving. http://faraday.physics.utoronto.ca/PVB/Harrison/Flash/ Which one is right? Both. ClassMechanics/Relativity/Relativity.html Each one is an inertial reference frame. Any non-rotating reference frame is an inertial reference frame (space shuttle, space station). Each reference Speed limit sign posted on spacestation. frame is equally valid. How fast is that man moving? In contrast, you can tell if a The Solar System is orbiting our Galaxy at reference frame is rotating. 220 km/s. Do you feel this? Absolute Time Absolutes of Relativity 1. The laws of nature are the same for everyone In the Newtonian universe, time is absolute. Thus, for any two people, reference frames, planets, etc, 2.