What is Special relativity: Definition and 1000 Discussions

In physics, the special theory of relativity, or special relativity for short, is a scientific theory regarding the relationship between space and time. In Albert Einstein's original treatment, the theory is based on two postulates:
The laws of physics are invariant (that is, identical) in all inertial frames of reference (that is, frames of reference with no acceleration).
The speed of light in vacuum is the same for all observers, regardless of the motion of the light source or observer.

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  1. K

    Special Relativity Train Scenario

    Assume there is an engineer who built a tunnel, tunnel length is 10m, and we have a train its length is also 10m...so the tunnel can encompasses the entire length of the train. But if we assume that train is a light express train, it always comes through the tunnel at relativistic speed, let's...
  2. D

    Consequences of space-/time-/light-like separations

    I'm trying to prove the following statements relating to space-like, time-like and light-like space-time intervals: 1. There exists a reference frame in which two space-time events are simultaneous if and only if the two events are space-like separated. 2. There exists a reference frame in...
  3. D

    Coincidence of spacetime events & frame independence

    I have been reading these notes: http://isites.harvard.edu/fs/docs/icb.topic455971.files/l10.pdf in which they claim that if two spacetime events are coincident in one frame of reference then they are coincident in all inertial frames of reference, thus spacetime events are absolute i.e. they...
  4. Noctisdark

    Relativity Special Relativity Problem Textbook ,

    Hi PF, I'm trying to learn both special and general relativity, I have read all about them, learned the basic math needed, but that was all without "enough" exercices to completely understand the theory, so I need problem books that are purely or mostly about problems about special relativity...
  5. G

    What is the cause of time dilation in Special Relativity?

    One of the basic foundation of special relativity is that the speed of light is a constant, hence time is relative to the inertial framework reference. Usually GPS is also mentioned as a modern experimental evidence. My questions: if Maxwell's equations describe EM fields, how can we derive a...
  6. D

    What is the definition of Locality (in QFT)

    I am slightly unsure as to whether I have understood the notion of locality correctly. As far as I understand it locality is the statement that if two events occur simultaneously (i.e. at the same time) then no information can be shared between them (they are causally disconnected). Thus a...
  7. D

    Simultaneous events, space-like separation & QFT

    First of all, sorry if this is in the wrong forum, wasn't quite sure which one to post it in given the question. My question is, given two space-time points ##x^{\mu}## and ##y^{\mu}##, if the events that occur at these points are simultaneous, i.e. ##x^{0}=y^{0}##, are the two events...
  8. Raman Choudhary

    Basic doubt of special relativity

    suppose person B was standing with person A at some point O and now person B starts to move with velocity c/2 w.r.t A on a straight track(starting from O) and both the observors(A and B) start to note time on identical clocks attached to their respective frames .Now after 1 second (according to...
  9. J

    2 simple special relativity thought experiments

    Hi. I'm learning about special relativity and want to see whether I understand it correctly. As such, I had 2 thought experiments that I answered, and I want to see whether these answers are correct. If not, could someone please tell me the correct answers? Thanks! Thought Experiment 1: Super...
  10. S

    Could this experiment prove special relativity to be wrong?

    Think about an electric charged object moves linely, it will produce current hence the magnetic field. But if the obserser moves together with the electron charged object, so there is no relative movement between them, that means the electric charged object is static to the observer, hence...
  11. Anaxagoras

    Non causally linked events in special relativity

    My question is about foundations of the special relativity theory. In Minkowski's way of presenting special relativity, with a signature "+ - - -", one associates to every couple of events, a spatio-temporal distance which is null on the light cone, positive if the two events are causally...
  12. L

    Special relativity - four current and dirac's delta

    Homework Statement Hello, in my special relativity course we are making the (electrical charge) current a four-current. I have serious problems understanding the following: http://imageshack.com/a/img540/2046/8IYpxu.png In particular, on line 2, in the last equation, I don't understand why...
  13. gxu

    No-faster-than-light in the special relativity

    I saw the following question in the Physics-SE, and thought it is interesting. "In the special relativity it is well established that, in the vacuum no one can ever travel faster than light, due to the relativistic velocity addition formula. However, it is legitimated to ask whether the...
  14. B

    Flow of Magnetic Charge: A Source in Ampere's Law? - Bob Eisenberg

    If magnetic charge exists, it can flow. Would the flow of magnetic charge produce a current that would be a source for the curl of B, in Ampere's law? Ever yours Bob Eisenberg Chairman emeritus Dept of Molecular Biophysics Rush University Medical Center
  15. J

    Charge Dropping on Rindler Horizon: Coulomb Force Effects?

    Let's say I keep on dropping electrons on one spot of a Rindler horizon. Does the charge of the spot increase without a limit? When the charge of the spot is very large, does the spot exert a Coulomb force on the electron I'm about to drop, causing the electron to start moving away from the...
  16. U

    Fraction of particles getting through?

    Homework Statement An unstable ion of mass ##M##, energy ##E## emits a massless particle of energy ##E_\nu## at angle ##\theta##. In the rest frame of the ion, find ##E_\nu^*## and ##cos \theta^*##. Ions are now accelerated to ##\gamma=100## and a detector with radius ##r=20m## is placed...
  17. N

    Question Regarding the Twin Paradox

    Homework Statement In the twin paradox suppose the twins are named Dick and Jane. And they both are 20 years old.Dick takes off on a voyage at a speed of 0.8c to a star 20 light years away.Lets say that both the twins send each other signals once a year while Dick is away.How many signals does...
  18. Caneholder123

    Relativistic motion of the bullet

    1. A distant camera is taking an image of a bullet of proper length l_0 and velocity v. The bullet is moving on a straight line which is parallel to the ruler (a bit behind the bullet, when it is watched from the camera). An angle between the velocity vector and the line that connects the camera...
  19. MidgetDwarf

    Intro Physics Questions regarding special relativity.

    I recently found and interest in physics after reading KK Introductory Mechanics. I was thinking of learning EnM from Purcell. From my reading of these forums. Purcell introduces Max. Equations using special relativity. I do not know anything about SR (you can I am a virgin at physics). I...
  20. U

    Relativistic Doppler Effect - Arbitrary Velocity

    Homework Statement Find the observed frequency ##\nu## in terms of proper frequency ##\nu_0##, speed ##v## and radial velocity component ##v_r## for a source moving at velocity ##\vec v## with respect to the observer. Now consider an observer in frame S where the source is seen moving at...
  21. B

    How Does Special Relativity Affect Pion Decay Measurements?

    Homework Statement A beam of pion mesons travels down a tube at the CERN accelerator moving at v/c=0.95 with respect to the laboratory. (i) Compute the γ factor for these pions. (ii) The pion lifetime is 2.6 × 10−8 s, what is the lifetime measured at the laboratory? (iii) The pions travel 50...
  22. E

    Special Relativity problem regarding relat. energy/ momentum

    An object having mass of 90 kg and traveling at a speed of 0.850c collides with a stationary object having mass 1400 kg. The two objects stick together. (8pts) a) Find the speed of the composite object.b) Find the mass of the composite object Hello, I would appreciate any insight into...
  23. arpon

    Is Net Charge Conserved in Special Relativity with Current Flowing in a Wire?

    Consider an infinite wire that has no electric current initially. Then current starts to flow in the wire, i.e. the free electron drifts at speed ##v## (and the positive charges are fixed) Applying special relativity, it appears that the distance between the electrons shrinks, i.e, density of...
  24. U

    Charge's Frame: Electric Field of Moving Charge

    We all know that in the lab frame observing a charge moving along x-axis, we see an electric field ##E = \frac{Q}{4\pi \epsilon_0 x^2\gamma^2}##, picking up an extra factor of ##\gamma^2## at the bottom. Assuming no external fields are present, what would the charge see in its own rest frame...
  25. U

    How Does a Relativistic Photon Rocket Calculate Acceleration and Speed?

    Homework Statement (a) Show ##a = \frac{a_0}{\gamma^3}##. (b) Find proper acceleration of rocket (c) Find speed as a function of time. (d) Find acceleration of second rocket. Homework EquationsThe Attempt at a Solution Part(a) 4-vector acceleration is given by ##\gamma^2 \left[...
  26. H

    Problem Perceiving Simultaneity (Special Relativity)

    Hi, This is not a question aimed at answering a homework problem, but since it is part of a course on Special Relativity, I believe I'm supposed to put my question here. The course itself, however, is a Dutch High School syllabus on SR, so I won't be able to link to source material. The...
  27. Strilanc

    Flat Donut Universes & Special Relativity

    Suppose there was a universe that was small, and flat, but globally it was connected like a torus. Basically, pac-man's universe (except special relativity is in effect). The space ##(\mathbb{R} \pmod{1})^3##. Does this assumed universe have a distinguished inertial frame where the...
  28. A

    What is the Velocity of a Starship Traveling at 5c in Star Wars?

    Hi! First of all, sorry for my english, I'll try to do my best translating the exercise. I've been working on it this evening but I'm having some troubles: Problem: On the Star Wars film, there's a starship traveling at a velocity of 5c. This is nonsense, but we can assume this if we suppose...
  29. D

    Transverse Doppler Effect for a Moving Star

    Homework Statement A star travels in a direction transverse to the line of observation from Earth, with a speed 0.5c. It also emits light with wavelength ##\lambda_0## in the rest frame of the star. Calculate the wavelength of the light as observed on Earth, and also the angle at which the...
  30. Clueless

    How are space-like intervals important?

    Time-like and light like separations between events make sense, because a particle or a light flash can travel between them. However, how can you have a space-like interval when even light cannot travel such an interval (because its velocity is not greater than c). Obviously the first event...
  31. J

    Special relativity and really fast trains

    Homework Statement Two passenger trains A and B, each 240 m long, pass a 60 m long railroad platform in Winnepeg. The trains are moving in opposite directions at equal speeds of 0.665c with respect to the ground. Train A is traveling west and all tracks are perfectly straight. A) From the...
  32. A

    Relativistic Kinetic Energy as a solution to a DE

    Has anyone ever seen KE derived this way? The only non-classical assumption is that mass = Energy/c^2 (I know, that's a big one) and that it accumulates as mass as the object is accelerated. (sorry for the plain text formatting, I need to learn how to do it right, I may reply with my first try)...
  33. J

    Addition of Velocities Special Relativity Problem

    [Mentor's note: this post does not use the homework template because it was originally posted in a non-homework forum.] ----------------------------- A ship (attached to reference frame S') is passing us (standing in reference frame S) with velocity v= 0.933c. A proton is fired at speed...
  34. blue_leaf77

    Relativity Introductory book on special relativity

    I'm looking for an introduction level books on special relativity. My goal is to get familiar with Dirac equation as I'm into atomic physics in this semester. My background on the subject is that I have taken a course in the past which was designed to be kind of introductory to modern physics in...
  35. binbagsss

    Understanding Proper Time in General Relativity & Special Relativity

    I'm reading An Intro to GR, Hughston and Tod, it says that in GR the idea is that the geometry of st varies from point to point, represented by allowing the metric to vary over space-time. It uses a (+,-,-,-) signature and so ##proper time=ds^{2}##. It then makes the comment that proper time...
  36. shmijda

    Two MC Special Relativity Questions

    Homework Statement 1. You observe two events to occur simultaneously. A friend is moving with respect to you. The friend will see : The event the friend is moving towards occurs first, in their perspective The order of the events is random and cannot be predicted The events occur...
  37. L

    Inequalities. Special relativity.

    Lorentz transformation. Time separation between two events in system S and system S' is given by Lorentz transformations \Delta t'=\frac{\Delta t-\frac{u \Delta x}{c^2}}{\sqrt{1-\frac{u^2}{c^2}}} If event 2 is caused by event 1 in system S then ##\Delta t=t_2-t_1##. But it is possible to choose...
  38. fezster

    Connection between Lorentz covariance and special relativity

    s2 = t2 - x2 - y2 - z2 This equation is covariant (Lorentz covariance). The interval "s" is invariant (Lorentz invariance). Can you derive everything in special relativity from these facts? Or am I mistaken about that?
  39. B

    Question about Special Relativity and matching results

    Assume a light was emitted from the origins of two frames in relative motion. Assume the light acquired some position (x,y,z,t) in an F frame. Then map that point using the lorentz transformations to (x',y',z',t') in a F' frame. Can anyone prove under all conditions that the the light...
  40. H

    Composition of 2 transformations of E

    Suppose frame ##S^\prime## moves in the positive ##x## direction at ##v## with respect to frame ##S##, and frame ##S^"## moves in the positive ##y## direction at ##v^\prime## with respect to frame ##S^\prime##. Then, ##E^\prime_x=E_x## ##E^\prime_y=\gamma(E_y - vB_z)## ##E^\prime_z=\gamma(E_z...
  41. T

    Combine Special Relativity & Maxwell Equation Easily

    How to combine special relativity and maxwell equation as simple as possible without going into qed? Sorry for such a absurd request as I am not smart at all.
  42. H

    Proof of Transformation Equation for Electric Field Ex

    I want to prove that the transformation equation for electric field holds, namely Ex = Ex', where Ex is the x component of E field in S frame and Ex' is that in S' frame, for the special case in which the charged particle has a vertical velocity Uy' in the S' frame (Ux' = Uz' = 0). It is already...
  43. S

    Speed of Light in Special Relativity: Explained & Questioned

    While trying to understand special relativity, i came across the following explanation several times: Imagine a train moving at c/4 from left to right. If a person A, inside the train standing near the back of the train, flashes a light, the light is supposed to travel in the direction of the...
  44. D

    Teaching relativity to the general public

    In the light of this policy https://www.physicsforums.com/threads/what-is-the-pfs-policy-on-lorentz-ether-theory-and-block-universe.772224/ , is it now considered acceptable to teach relativity by starting out with Lorentz Ether Theory (LET) and its Newtonian time which appears to be...
  45. F

    Special Relativity and lightning

    Homework Statement This is a relativity problem: [/B] A tree and a pole are 3000 m apart. Each is hit by a bolt of lightning. Mark, who is standing at rest midway between the two, sees the two lightning bolts at the same instant of time. Nancy is flying her rocket at v = 0.5c in the direction...
  46. V

    Understanding length contraction in SR

    I seem to be missing something fundamental about length contraction in SR. I would be grateful if someone can point out the error in the following logic. Suppose I have a method to measure lengths of objects in the following manner: I place a mirror at the right end of the object, send a light...
  47. Maxranger

    String Theory's inconsistency with Relativity

    Are the general principles of string theory “the properties of fundamental particles are due to their unique vibrational pattern of strings in 10 or 11 or 26 dimensions” incompatible with both general and special relativity? due to an observer would be able to detect changes in properties of...
  48. thrush

    Time Dilation: SR Basics & Confusion

    Hi everybody, I'm learning Special Relativity, and probably ok with four vectors, the metric equation, the Lorentz Transform, and the Doppler shift, etc., but enough about me. I'm still a little confused about time dilation. In several hypothetical examples of SR that I have seen, two...
  49. Grimble

    Time dilation: speed relative to what?

    I have been asked about time dilation which I thought I understood, but maybe you can help me provide an answer? If a spaceship is traveling at 0.866c then time will slow by a factor of 2 due to the speed the spaceship has. Why? If it is alone in space, light years away from any other body...
  50. seb7

    Measuring possible one-way anistropy of light speed

    wiki says "Experiments that attempted to directly probe the one-way speed of light independent of synchronization have been proposed, but none has succeeded in doing so" Here's a proposed experiment which I could not find any evidence of this being performed before.. Central light source...
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