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. C

    I Accelerator Particles: Speed of Light & Mass Increase

    In an accelerator when you're pushing/pulling a charged particle with a field that travels at the speed of light why should we expect to the particle to exceed the speed of light.
  2. Kairos

    I Inverse results in special relativity

    The mass of an object moving at speed v increases such that $$\frac{m'}{m}=\frac{1}{\sqrt{1-\frac{v^{2}}{c^{2}}}}$$ and its apparent frequency decreases such that $$\frac{\nu'}{\nu}=\sqrt{1-\frac{v^{2}}{c^{2}}}$$ so $$\frac{\nu'}{\nu}=\frac{m}{m'}$$ but equating the energies $$ h\nu= mc^{2}$$...
  3. Efeguleroglu

    How to calculate the minimum kinetic energy (special relativity)?

    Sadly, that's what all I could do.
  4. W

    How Does Conservation of Momentum Apply to Particle Decay?

    Attempt at solution: By conservation of momentum: $$P = (M,0,0,0) = p_1 + p_2 = (E_1 + E_2, 0, 0,0)$$ thus $$ M = E_1 + E_2 = 2k^2 + m_1^2 + m_2^2$$ Now $$E_1^2 - E_2^2 = m_1^2 - m_2^2 = (m_1 + m_2)(m_1-m_2)$$ $$ = M(m_1-m_2) = (2k^2+m_1^2+m_2^2)(m_1-m_2)$$ Isolating k: $$ k =...
  5. A

    I Special Relativity: Train in Tunnel Paradox Solved

    Hello, I was wondering if anyone could set up and solve a classic train in a tunnel paradox from special relativity with unique values for multiple observers including time space diagrams. Thanks
  6. vanhees71

    Relativity M. Tsamparlis' book on Special Relativity

    I just stumbled over the following book on SRT Michael Tsamparlis, Special Relativity, Springer (2010) It's a gem! On the beginning-graduate level it explains the special theory of relativity from ground up, starting with a chapter on the math of Minkowski space and then providing a complete...
  7. cianfa72

    I Rotation or acceleration defined without relation to something else

    Starting from this post, we are able to define the concept of (proper) acceleration or rotation without any reference to something else About this definition which is the physical meaning of gyroscopes axes pointing in three mutually orthogonal spacelike directions ? In other words, from a...
  8. P

    Why Does t' Include vx/c² in Lorentz Transformations?

    I understand x' = λ(x - vt) but why does t' = λ(t - vx/c^2)? where does the vx/c^2 come from? and honestly I don't understand what t' is. because from what I understand is that t' is the length of time t as observed from the reference frame S'. which means t' = t*λ?
  9. TheBigDig

    Energy of Two Gamma Rays Produced by Pion Decay

    So I worked out the first part and obtained ##E_1 = 478.8MeV##, ##E_2 = 459.4MeV## and ##p = 0.49 MeV/c## but I can't quite wrap my head around the second part. Normally, I'd use the equation for s but I'm confused since I don't know the angle between the gamma rays.
  10. Abhishek11235

    Understanding the reasoning of this answer

    N.A
  11. Celso

    Required speed for two events to be simultaneous

    I'm doing some exercises about special relativity and one of them asks to find the speed in an arbitrary frame of reference (1) in such a way that it perceives two events at the same time that didn't happen simultaneously in other frame of reference(2). Is it correct to state that if the...
  12. sharinglanguage

    B Special Relativity Calc: Half Speed of Light - Jose

    Hello! I am trying to make some calculations on the Special theory of relativity over a practical example, considering the time dilation, but I may (more than likely..) be doing something wrong (probably with my assumptions). I would appreciate any comment on it. The example is that of a rocket...
  13. W

    Geodesics and Motion in an EM Field

    I've also attached my attempt as a pdf file. My main issue seems to be I only get one A partial term. Any help would be appreciated.
  14. Abhishek11235

    Is This the Proper Frame for Your Needs?

    The attempt is above
  15. Abhishek11235

    Calculating elapsed time in different frames

    The attempt is above
  16. N

    How can the time dilation equation explain faster moving clocks running slower?

    Since for the two events of Samir starting the stopwatch, and the stopwatch reaching 10.0s, Samir and his stopwatch are stationary from his own frame of reference, I said it was the proper time and that delta t0 = 10s. Then the speed of the moving frame of reference was 0.6c. I thought placing...
  17. C

    Mass of Hadrons: Verifying Special Relativity

    Hmm the mass of a hadron is an example of the verification of special relativity.The total mass of the quarks isn't equal to the mass of a hadron at rest frame.But quarks are moving very fast due to strong interaction and they gain mass (mass-energy equivalence)
  18. H

    B Magnetic field and moving charge special relativity

    Hi. In a current carrying conductor because of special relativity amount of protons and electrons differ so we get an electric field or as we call it magnetic field. So if magnetic field is just an electric field how is it that the charge has to move so that magnetic field would exert a force on...
  19. K

    4 momentum mass non-conservation, special relativity

    Homework Statement A particle with mass M and speed v along the positive x-axis hits a stationary mass m. Two particles, each with mass µ, emerge from the collision, at angles with respect to the x-axis. (a) Write the equation for conservation of the 4-momenta, for arbitrary angles θ_1, θ_2 of...
  20. PeterDonis

    Insights Fermi-Walker Transport in Kerr Spacetime - Comments

    Greg Bernhardt submitted a new blog post Fermi-Walker Transport in Kerr Spacetime Continue reading the Original Blog Post.
  21. M

    Origins of magnetic fields from permanent static magnets versus current

    The videos from Veritasium explaining permanent static magnets and electromagnets were quite good I thought… But they have me a little confused with regard to the origins of magnetic fields generated by an electric current as opposed to a permanent static magnet from say iron. 1. An...
  22. Hawkingo

    I Can this event vary relatively?

    Suppose we take a charged particle and a magnet and place them at some particular distance apart .Now let's take 2 frame of reference. [the charged particle and the magnet are in rest with respect to each other through out the whole event]{both of the frames are inertial} frame(a): this frame...
  23. PeterDonis

    Insights Fermi-Walker Transport in Schwarzschild Spacetime - Comments

    Greg Bernhardt submitted a new blog post Fermi-Walker Transport in Schwarzschild Spacetime Continue reading the Original Blog Post.
  24. X

    B Special Relativity: Time Measurements on Two Systems - Mike's Question

    I saw this question on special relativity on the internet: "A spaceship traveling to Alpha Centauri, at 0.95C it takes 4.5 years to get there as measured on Earth.how long does it seems to the spaceship passengers?" the answer was 1.4 years (Lorentz factor of 3.2). this answer makes no sense...
  25. PeterDonis

    Insights How to Study Fermi-Walker Transport in Minkowski Spacetime

    Greg Bernhardt submitted a new blog post How to Study Fermi-Walker Transport in Minkowski Spacetime Continue reading the Original Blog Post.
  26. universal2013

    I Solving Special Relativity Problem w/ Two Spaceships

    Hello there. In class, our teacher solved one question and asked us what did we wrong specifically in the solution because there were two sets of them. Two spaceships are moving through +x and -x and there is a distance L between them. From one observer which is stationary in the line of L/2...
  27. pixel

    I Implication of length contraction

    I had posted a similar question on another forum but didn't get much of a discussion. I'm interested to know what people here think. So consider a spaceship midway between stars A and B and initially at rest in the reference frame of the stars. The ship then accelerates away from A to some...
  28. N

    Relativity Paradox: Solving for Different Observers in the Cloud and Ship

    I'm trying to solve this problem but I get a different answer depending on which observer I solve it for. For the observer in the cloud, the parallel light has traveled 2.294cs, but this is only 0.23cs in front of the ship. 0.23 cs is only 0.086cs in the perspective of the ship due to length...
  29. Q

    Maximum Horizontal Force of Relativistic Point Charge

    Homework Statement A charge q1 is at rest at the origin, and a charge q2 moves with speed βc in the x-direction, along the line z = b. For what angle θ shown in the figure will the horizontal component of the force on q1 be maximum? What is θ in the β ≈ 1 and β ≈ 0 limits? (see image) Homework...
  30. S

    I Relativistic mass and gravitational potential

    Hello everyone, Any object has a gravitational potential energy as a function of the distance from the Earth (R). Does this energy depend only on the rest mass of the object; or one must take into account it's relativistic mass? In other words, if we imagine two identical bullets on the top...
  31. wafelosek

    A Killing vectors corresponding to the Lorentz transformations

    Hi everyone! I have a problem with one thing. Let's consider the Lorentz group and the vicinity of the unit matrix. For each ##\hat{L}## from such vicinity one can prove that there exists only one matrix ##\hat{\epsilon}## such that ##\hat{L}=exp[\hat{\epsilon}]##. If we take ##\epsilon^{μν}##...
  32. D

    Studying John Baez's list of books math prerequisites?

    my current skills in math are differential eq and linear algebra... and I am about to start reading Feynman lectures of physics and planning to read all John Baez's recommended books.. after reading Feynman's, what would be the next best thing to do? learn more math? or jump already to core...
  33. universal2013

    I Exploring Maxwell Equations & Hyperbolic Functions

    I am trying to understand why maxwell equations are correct in any reference frames? While i started to understand of his laws of physics a bit i could not imagine why he uses hyperbolic functions such as coshw instead of spherical ones in position and time relation between moving frames...
  34. H

    I Any direct evidence of gravitational mass increase?

    Is there any evidence that objects moving increasingly closer to light speed gain gravitational mass, in the sense of attracting surrounding (and not co-moving) masses more strongly, rather than solely possessing the increased inertial mass implied by the greater force necessary to...
  35. J

    I Extended Twin Paradox: Explaining Time Lapse and Symmetry Principle

    Suppose an observer (O) sees a traveler (T1) pass by at time t=0, moving a speed 3c/5. Five years later (according to O), T1 returns. If we assume that T1 traveled at 3c/5 for half the journey and instantaneously reversed direction, returning at the same speed, we can calculate that T1 aged only...
  36. A

    I Calculate mass from time dilation

    Based on the exponential growth of time dilation 0.0 - 1.0 if given the radius of an object how do you calculate the mass of the object? Time dilation is a function of gravity. Which can be thought of as escape velocity from a gravitational field. So if you have to achieve .866 c to escape...
  37. Alex Petrosyan

    Relativistic Dynamics in Hamiltonian Formulation

    hi all! I’m trying to generalise the Caldeira-Leggett Hamiltonian (heat bath + particle) to the case of high velocities. Naturally, the multi-oscillator Hamiltonian needs to change and I have a gnawing suspicion that the multi-particle Hamiltonian is just the sum of single-particle hamiltonians...
  38. T

    How do proper time and time dilation differ?

    Homework Statement I am currently stuck on a problem as shown below. My confusion really come from the fact that I can never seem to understand the difference between proper time and time dilation. As in some books they seem to mean the same thing and never give a clear indication Homework...
  39. L

    I Does Special Relativity Deal with Non-Inertial Frames?

    In several special relativity textbooks, I have read that special relativity only deals with observations made in inertial frames, and that it makes no predictions about observations made in non-inertial frames, and that only general relativity deals with non-inertial frames through the...
  40. S

    B Can gravitational time dilation explain the galaxy rotation curve?

    Hello everyone, By considering the effects of the gravitational time dilation the speed of the inner stars must be higher for the local observer than for the external one. So why the gravitational time dilation can not potentially explain the galaxy rotation curve? I already read that the...
  41. F

    I Computer Performance Evaluation (CPE)

    I would like to know if there are any Physics Instructors or Professors who may believe that Queuing Theory as well as Relativity Theory may be relevant to CPE where communications platforms are moving at relativistic velocities with respect to (wrt) each other?
  42. starstruck_

    B Understanding Special Relativity: 2nd Year SR Course Explained

    Hey everyone! So, I just finished my 2nd year intro to SR course, we spent most of the term on Taylor expansions for relativistic corrections vs concepts. I’ve watched a crash course video and a documentary on SR and I do somewhat understand the thought experiment involved with respect to...
  43. L

    B I got confused about SR after trying to reply to another

    So let us say that there are 3 separate alien species that somehow speak and write the same language. Let us say that 2 of these have always lived and died in their spaceships/asteriod ... going at speeds close to that of light. Alien species 3. A3 leaves behind a message saying that at time t0...
  44. F

    Lagrangian for relativistic angular momentum

    Hi everyone, I have a question that can't solve. Does exist a lagrangian for the relativistic angular momentum (AM)? I can't even understand the question because it has no sense for me... I mean, the lagrangian is a scalar function of the system(particle,field,...), it isn't a function FOR the...
  45. L

    I Do we have to accept the physical existence of time?

    So, I am confused about the following.I learned in high school and in my first year of university that there is something called time dilation that observers observe that time is slower for objects that are moving faster. As in if there were two initially synchronized clocks that you could...
  46. L

    Relativistic Dynamics Problem - Reference Frames

    Homework Statement Two images are attached. The first image details the problem. The second image has an x',y' coordinate system depiction of the problem. Homework Equations The total energy of a particle is defined as E = mc^2, with m = γ*m_0. The Attempt at a Solution If the x', y'...
  47. zehkari

    Relativistic momentum of two photons from a decay

    Homework Statement Homework Equations (1) E2 = p2c2 + m02c4 (2) E = γm0c2 (3) E = Eγ1 - Eγ2 (4) p = E / c (5) E = hf (6) λ = c / f The Attempt at a Solution a) Using eqn (1), rearranged p = (E - m0c2) / c , I obtained 2.9 MeV c-1. Not sure if I have the right answer here as I...
  48. M

    B Special Relativity & Acceleration: Unequal Inertial Frames

    Given that one or both inertial frames must have been subject to acceleration at some point; resulting in an imbalance of application between the two inertial frames, why does the consequential effect of general relativity not feature in calculations. Surely, as such, neither observer's...
  49. S

    I Escape Velocity: Newtonian vs Relativistic

    Hi, Do we obtain the same escape velocity equation: Ve = sqrt(2GM/r) using both Newtonian and Relativistic approach?
  50. J

    B Basic Lorentz transformation derivation

    The Lorentz transformations are mathematically simple. I had always imagined they could be easily derived. I however just found out from another PF thread that this is not so. Their originators Lorentz and Poincaré simply stated them without derivation. And the "proofs" I have seen to date have...
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