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. T

    Need help with a special relativity problem

    The example given is as follows : we have 3 space ships(numbered from left to right) placed in space moving at velocity V in the same direction (they are moving to the right) , each one can send a pulse of light to the others and the others can determine time reached. so each of them is an...
  2. I

    Simple (?) special relativity question

    If someone stands up through the sunroof of a car traveling down the freeway at 60 mph and measures the speed of a beam of light they shine from a flashlight in the direction the car's going, they'll record it as c. This is intuitive (no need for relativity). Someone on the roadside, however...
  3. J

    Special relativity effects in general relativity

    SR is a theory based on flat space-time, and all of its effects are there in a flat space-time framework.My question is, how is SR compatible with GR, since GR uses curved space-time? Or to say it better how are time dilation, length contraction and relative simultaneity manifested in curved...
  4. A

    Newtonian gravity and Special Relativity

    Hey guys, in classical mechanics Newton's law of universal gravitationa force says that the force between two bodies is equal to the product of their masses divided by the square root of the distance between them. So far, so good. In SR, lengths depend on the frame that we are in, and so the...
  5. Entanglement

    Mass/Energy in special relativity

    I only understand mass and energy according to Newtonian mechanics, Where mass is the resistance of a body to accelerate, or how much matter there is, and anything has mass is a matter. Energy is the ability to do work and it's not a matter. It was believed that mass and energy are two...
  6. tom.stoer

    Special relativity and gravitation

    It is well-known that Newtonian's law of gravitation \Phi(\vec{r}) = -\frac{Gm}{|\vec{r} - \vec{a}|} for the gravitational potential ##\Phi## generated by a mass ##m## located at ##\vec{a}## is in several ways inconsistent with special relativity. What one could do is to modify the...
  7. A

    Special relativity: fireworks exploding

    A firecracker explodes at the origin of an inertial reference frame. Then, 2.0 microseconds later, a second firecracker explodes 300m away. Astronauts in a passing rocket measure the distance between the explosions to be 200m. According to the astronauts, how much time elapses between the two...
  8. P

    Special Relativity: Relative velocity

    Homework Statement I know that if you have 2 observers, "A", one at rest and the other "B" moving wrt "A" and if the moving observer shoots a projectile, then we can calculate the velocity of the projectile wrt "A" using the standard equation shown below. I was thinking what equation would...
  9. S

    Special theory of relativity: velocity of airplane

    Homework Statement If a clock in an airplane is found to slow down by 5 parts in 1013, (i.e. Δt/Δto = 1 + 5x10-13), at what speed is the airplane travelling? (Hint: You may need to use the binomial expansion for γ.) To be honest, I'm really confused about what this question's telling me...
  10. A

    Special relativity time dilation question

    Out of interest I'm studying a book "A first course in general relativity" which is a great book in my opinion because it explains the subject very well. I'm a beginner though and I have a hard time understanding one particular thing mentioned quite early in the book. I'm attaching a scan of a...
  11. S

    Special Relativity and Biological Clocks.

    Hi. So the whole premise of special relativity seems to me to be hinged on the immutability of the speed of light, the fact that it is the same for every inertial frame of reference, and the fact that information and energy cannot travel faster than this. What really puzzles me is this whole...
  12. P

    Special Relativity: Rocket Signal Reception Time and Frequency Shift

    Homework Statement A rocket of proper length 100m travels at a speed 0.6c relative to a space station, which is on the rocket’s flight path. I have so far had to work out that: According to an observer on the space station, the nose of the rocket is a distance of 200m away from the station...
  13. jlefevre76

    Aerodynamics/Special Relativity Analogy

    I'm sure that most people on these forums are familiar with the similarities between compressible flow in aerodynamics and the relations between relativistic mass and rest mass in general relativity. A common example that's brought up frequently is the Prandtl-Glauert rule. After playing around...
  14. C

    Special relativity - compute relative velocity

    Homework Statement A spaceship travels from Earth to the vicinity of the star that is measured by astronomers on Earth to be six light-years away. The spaceship and its occupants have a total rest mass of 32 000 kg. Assume that the spaceship travels at constant velocity. The time taken as...
  15. P

    Special relativity theory train and mosquito

    Homework Statement Train is moving along the x-axis with speed v relative to platform, inside the train mosquito is flying with 3D speed v0. 1) Write mosquito s 4-speed components with respect to train coordinate system. 2) Using 4-vector component transformation write mosquito's 4-speed...
  16. A

    Finding the Centre of Mass Speed for a High and Low Energy Photon Collision

    Homework Statement High energy photon of energy E collides with a low energy photon of energy 1eV. It forms an electron-positron pair. I have found the threshold energy as E=261GeV. I am asked to find the speed of the centre of mass at this threshold energy. Homework Equations E=γmc2 The...
  17. E

    "Special" and "General" relativity- Who invented those terms?

    Hi all, I can't seem to find any historic account of when those two theories got their (quite strange) names. Can someone point me to a source? One of the reasons I am interested in this is the persistent idea in popularizing texts, especially from the 1970's, that Special Relativity could...
  18. Logic Cloud

    Phase space in special relativity

    In classical mechanics we can get a nice overview of the dynamics of a system by looking at its position-momentum phase space. Is there a useful analogue of this concept in special relativity? Can the dynamics of a relativistic system be represented by its phase space in the same way as is done...
  19. H

    Special Relativity and pion

    How fast must a pion be moving, on average, to travel 9.0 m before it decays? The average lifetime, at rest, is 2.60 ✕ 10-8 s. (Answer in terms of c) I'm not exactly sure what equations I have to use but I believe it relates to time dilation. I originally didn't realize it was a time...
  20. M

    Understanding Special Relativity on a Geometric and Intuitive Level

    So here's the deal guys: I have a bachelor's in physics and have gotten an A in an undergraduate special relativity course but I do not feel that I fully understand the subject. I can do the problems in special relativity which require the various formulas involved in the subject and I even...
  21. AGNuke

    Velocity of Separation in Special Relativity

    An observer sees two spaceships flying apart with speed .99c. What is the speed of one spaceship as viewed by the other? I considered two spaceships A and B. A is moving with velocity vA in the left direction and B is moving with velocity vB in the right direction. Hence, ##v_{sep} = v_A +...
  22. L

    Why does special relativity exclude gravity?

    Hello, I was unable to find a similar thread, so I would like to ask about this myself. I have several textbooks on SR and GR at my disposal but none of them gave me the answer to my question. I remeber from undergraduate course that SR brakes down if we want to include gravitation. I feel...
  23. B

    Special relativity and magnetism

    Hi! I am trying to understand how magnetic fields actually are electric fields viewed in a different frame of reference. I understand the basics of it, however I am confused by how the magnetic field is rotational around a wire when current moves through it and why the force isn't "outwards" at...
  24. I

    Explain how light moves in relative motion due to special relativity?

    I've been told on many occasions that light will always be measured at the same speed regardless of measuring equipment speed as long as there is no acceleration and you are moving the same speed relative to that object you are measuring from if that is incorrect please ignore what i say...
  25. C

    Special Relativity, light down a rocket

    Homework Statement A rocket of length ##L_o## flies with constant velocity ##v## (in frame S' relative to a frame S in the x direction). At time t=t'=0, the capsule on the top of the rocket passes the point ##P_o## in S. At this moment, a light signal is sent from the top of the rocket to the...
  26. B

    Calculating Distances in Special Relativity - Bob's Question

    Hi there, I think I understand how, using Lorentz transformations, I can find relative speeds of objects within different frames of reference. However, I'm struggling to transfer that understanding to distance. I'm sure that the distance as measured by observers within two different...
  27. R

    Relativistic Collision: Calculating Mass, Energy & Momentum

    Homework Statement Two relativistic particles "L" and "R", each of rest mass ##m_0##, are moving at speed ##v## towards each other (in the frame of an observer). They collide squarely and are stationary afterwards. (a) From the perspective of one particle, what is the oncoming speed of the...
  28. R

    Showing that Energy-momentum relation is invariant

    Homework Statement [/B] A particle of mass m is moving in the +x-direction with speed u and has momentum p and energy E in the frame S. (a) If S' is moving at speed v, find the momentum p' and energy E' in the S' frame. (b) Note that E' \neq E and p' \neq p, but show that...
  29. M

    Three Reference Frame Relativity Problem - Velocity Addition or Proper Lengths

    Homework Statement Anna and Bob have identical meter sticks. Anna an observer on Earth, sees Bob traveling in a spaceship at 0.5c away from her. Bob leaves his spaceship in an escape pod, moving away from Earth and the spaceship at 0.1c with respect to the spaceship. How long is Bob's meter...
  30. M

    Archived Special relativity: train between two cities

    Homework Statement A high-speed train is traveling from Capital City to Shelbyville. According to an observer at rest on the ground, the clocks at the railroad stations in Capital City and Shelbyville both strike noon at the same time. According to a passenger on the train, when the Capital...
  31. binbagsss

    Special Relativity quick problem

    The question is : Let s be the speed of light through water. If water is flowing at speed v in a given frame, find the speed of light in that frame, were the light propagates in the same direction as the water? My question: I am having a sign issue. I can not see how the following is flawed...
  32. Y

    Is temperature an invariant in Special Relativity?

    In another current thread on the possible invariance of pressure, I mentioned: What is the current consensus on how temperature transforms in relativity? Here is another simple thought experiment. Consider two very long rectangular objects A and B, that are moving relative to each other...
  33. V

    Is pressure an invariant in Special Relativity?

    HI : Consider a cylinder of length L and volume V that contains one mole of an ideal gas. The familiar ideal gas law states that: PV = RT Now, if the cylinder were to move with velocity v parallel to the length direction, special relativity requires the...
  34. C

    Special Relativity, Train, Ball

    Homework Statement A train with proper length L moves at speed 5c/13 with respect to the ground. A ball is thrown from the back of the train to the front. The speed of the ball with respect to the train is c/3. As viewed by someone on the ground, how much time does the ball spend in the air...
  35. George Jones

    New Book: Special Relativity in General Frames by Gourgoulhon

    https://www.amazon.com/dp/3642372759/?tag=pfamazon01-20 http://www.springer.com/physics/theoretical,+mathematical+%26+computational+physics/book/978-3-642-37275-9 I have just ordered (actually, my wife did, but she has yet to realize this :biggrin:) this new, comprehensive, advanced book on...
  36. F

    Finding CM frame velocity in special relativity

    Homework Statement An electron of energy 10 GeV strikes a proton at rest. What is the velocity of the electron-proton CM system? What energy is available to produce new particles? Homework Equations Conservation of momentum and energy, E2=p2c2+m2c4 The Attempt at a Solution...
  37. N

    Simple special relativity mistake - find i can't

    First: thanks for reading Second: I'm not interested in other "experiments" that prove contraction of lengths (i know them and i know it works) Third: Please find where is the problem in my simple thought Let be a "rest frame" S with an object to measure its length and do it with a ray of...
  38. I

    Special Relativity - Finding Velocity

    A spaceship is measured to be 50m long in it's own rest frame takes ##1.50 \times 10^{-6} s## to pass overhead, as measured by an observer on earth. What is its speed relative to earth? My attempt at the solution involves the use of the equation for length contraction, ##l = l_{0}\sqrt{1 -...
  39. V

    Special relativity and photons

    Hello everyone! There is a postulate of special relativity that says that the speed of light in vacuum is the same for all observers. This seems to imply (to me) that all the results of special relativity must only be used when dealing with observers who conform to the condition set by the...
  40. R

    Special Relativity, AP French 6.10: Atom Emits Photon

    Homework Statement I'll copy down the exact phrasing, so there's no question that this is what we're being asked: "An atom in an excited state of energy Qo (as measured in its rest frame) above the ground state moves towards a scintillation counter with speed v. The atom decays to its...
  41. M

    Special Relativity: Doppler Effect?

    Homework Statement Homework Equations Shown below The Attempt at a Solution I know I probably did something wrong...but what?
  42. M

    Special Relativity: Conservation of Energy + Momentum?

    Homework Statement Homework Equations Energy of a moving particle = γmc^2 Momentum of a moving particle = γmv The Attempt at a Solution I feel like there is something wrong here...I know I'm supposed to find the VERTICAL component of velocity, but can the total velocity...
  43. Z

    Special Relativity - Conservation of Energy/Momentum

    Homework Statement An atom of rest mass M in an excited state of energy Q0 (measured in its rest frame) above the ground state moves towards a counter with speed v. The atom decays to its ground state by emitting a photon of energy Q (as recorded by the counter), coming completely to rest as...
  44. S

    QUESTION: Relativistic Doppler Effect & Special Relativity

    Hey all, I was just wondering something which I couldn't get my head around tonight. If special relativity states that the speed of light is constant for all observers, regardless of the reference frame of any observer, then how is it possible for light to Doppler shift? Wouldn't the...
  45. M

    Special Relativity: Photoproduction of Mesons?

    Homework Statement 12-16 K + mesons can be photoproduced by the reaction γ + p → K+ + Λ where the initial proton is at rest in the lab. From the conservation laws, discover if it is possible for either the K+ or the Λ to be at rest in the lab, and for what photon energy (in terms of...
  46. R

    What is the simplest way to explain general and/or special relativity?

    Recently (or a few weeks ago), I've started to take interest in the idea of relativity but after watching many videos and reading a couple of websites, I still don't think that I really understand it. I'm probably not suppose to understand it (or at least not yet) considering that I'm still...
  47. B

    Special relativity and quantum mech

    An atom can exist in two states , ground state of M and excited state of mass M+Δ , it goes to excited state by absorption of an photon, what is the photon frequency in the in the lab frame of reference ( where the atom is initially at rest )? A simple energy equation gives the answer: E=(...
  48. T

    What is the proof/validity of Born rigidity in Special relativity?

    Relativity theory always find some ridiculous explanations like "born rigidity or relativity of simultaneity" when in face paradoxes What is the experimental validity of such predictions?
  49. binbagsss

    Special Relativity. Lorentz Boosts.

    The question is given a straight rod parallel to the x-axis moving in the y direction at speed u, to find the angle between the rod and x'axis in R'. (the chosen method to solve being to write equations for the endpoints and transform them to R') I am looking at my book's solution and don't...
  50. S

    What are the energies of the photons in a meson decay?

    Homework Statement A meson with rest mass 135 MeV has kinetic energy 1 GeV. It decays into two photons. 1 photon moves in the direction of motion, 1 is in the opposite. What are the energies of the photons? Homework Equations E=m_0c^2 E=hf λ'(\pi) = λ(\frac{(1+\beta)}{(1-\beta)})^{0.5} λ'(0)...
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