Special relativity Definition and 1000 Threads

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. alejandromeira

    Special Relativity Exercise (A.P. French)

    I just solved an exercise in the special relativity book of A.P. French. I would like you to tell me if the answer is correct. Yes I suposse is a very easy exersice. I hope you can help me, because I really like learn relativity and cosmology, but I have not had teachers of this, and I am...
  2. dRic2

    Electromagnetism and special relativity

    Hi I just saw this video . Here it's said that that electromagnetic force is just a consequence of special relativity, but I don't get the explanation. According to the video the electromagnetic force is generated by relative motion of charges, so it is essentially an electric force. It doesn't...
  3. Felipe Prado

    I Fizeau's Exp: TRANSFORMING VELOCITIES to Explain

    In 1851 Fizeau made a famous experiment which corroborated de Fresnel's drag coefficient of the luminiferous ether. In the experiment two light beams traveled through a tube of moving water (at 7cm per second), one moving against the water flow (let's called it beam A), and one for the water...
  4. N

    I Does a blueshift change the energy of a photon?

    The energy of a photon depends on its wavelength, so theoretically when it is blueshifted it should have more energy right? Then what if a spaceship with a solar panel on the front is traveling towards the sun at relativistic speeds. An incoming photon undergoes a blueshift from the observer on...
  5. BookWei

    I Solving Boundary Conditions in 4D Spacetime Volume

    Hi, my classmate asks me an interesting question: For a finite 4D volume in spacetime, its boundary is a 3D close surface. If the 4D volume is a 4D rectangular, the boundary consists of eight 3D surfaces. The boundary condition is specified on these eight 3D surface. Please explain the physical...
  6. G

    Time Dilation for Moving Rectangle with Clocks at its Corner

    Homework Statement A rectangular structure carries clocks at its four corners. The clocks are synchronized in the structure’s rest frame, in which it has length L =4ft and width W = 3ft. In our laboratory frame the rectangle is moving in the positive x direction at speed v = 0.8c. As the clock...
  7. Jan Nebec

    B Is it Possible to Know Which Object is Moving? Special Theory of Relativity

    The Special Theory of Relativity is based on two principles. The first one is, that if you have two objects, then it is not possible to tell which object is moving, and which object is standing still. So someone moving in a spaceship relative to observer, can't say who is actually moving and who...
  8. M

    Special Relativity spaceship problem

    Homework Statement Mavis boards a spaceship and zips Stanley on Earth a constant speed of 0.600c at the instant mavis passes, both start timers. At the instant mavis reads 0.400 s on her timer, what does Stanley read on his? Homework EquationsThe Attempt at a Solution since time from an...
  9. Phantoful

    Speed of a moving object, according to another moving object

    Homework Statement Special Relativity Question. Consider objects 1 and 2 moving in the lab frame; they both start at the origin, and #1 moves with a speed u and #2 moves with a speed v. They both move in straight lines, with an angle θ between their trajectories (again in the lab frame). What...
  10. Andy Bloch

    I Momentum w/o Net Velocity? Exploring the Lorentz Factor

    (I hope this post doesn't cross the border into the forbidden realm of quackery and speculation.) I have what seems like a simple question about Special Relativity but I haven’t seen it discussed anywhere, nor has anyone I've asked. Does the nonlinearity of the Lorentz factor provide a way...
  11. BookWei

    I Examples of invariant quantities

    In SR, we know that ##\vec E \cdot \vec B## and ##E^{2}-B^{2}## are invariant. Although I can prove those two invariant physical quantities mathematically, I do not know how to find at least one example to demonstrate that ##\vec E \cdot \vec B## and ##E^{2}-B^{2}## are invariant. Many thanks!
  12. bananabandana

    I Deriving Covariant Form of $E_{1}E_{2}|\vec{v}|$

    Given a two particle scattering problem with (initial) relative velocity $|\vec{v}|$, apparently the product $E_{1}$E_{2}|\mathb{v}|$ can be expressed in the covariant form: $$ E_{1}E_{2}|\vec{v}| = \sqrt{ (p_{1}\cdot p_{2} - m_{1}^{2}m_{2}^{2}} $$ My textbook gives no further explanation -...
  13. K

    B Quantum entanglement and special relativity

    There are a pair of entangled particles moving in opposite directions. A measurement is done on particle A, the wavefunction collapses randomly, you observe either spin up or spin down, A does an action at a distance on B, particle B instantly collapses to the opposite spin state, a measurement...
  14. Luxucs

    Special Relativity - Relativity of Simultaneity?

    Homework Statement A thin rod of proper length 4a is traveling along the x-axis of a frame S with a speed ##{\frac {\sqrt 3} 2}c## in the positive x-direction. A hollow cylinder CD of proper length 2a is placed with its axis along the x-axis, so that when the ends of the cylinder are open the...
  15. Hamza Abbasi

    How Fast Does Spaceship A Move Relative to Spaceship B?

    Homework Statement Two spaceships pass each other. Spaceship A moves relative to nearby planet at velocity v1 , while spaceship B moves at velocity v2 relative to the planet . How fast does spaceship A moves relative to spaceship B. Homework Equations Velocity Transformation : v* =...
  16. E

    Is Transcending Relativism Possible?

    Greetings Folks, I expect to be interested to post profound news here in a few days. Together with trimmings, it will come in very few lines. So it probably will not take much of your time to decide whether you are interested or not. I hope you do not find such an engagement to be...
  17. F

    How Do You Calculate Proton Beam Energy in a Lab Frame?

    Homework Statement a) [Solved] What is the threshold energy in the center of mass for production of an antiproton in a proton-proton collision? Make sure quantum numbers are conserved. (This one was easy and I manage to solve it) b) In a fixed target experiment calculate the proton beam energy...
  18. T

    Position of the front of an asteroid using special relativity

    Homework Statement I'm stuck on part (d) but I've included the previous subquestions in case they're useful. The length of an asteroid is exactly 300 m = 1 µls (micro light-second) when at rest. Draw a carefully labelled space-time diagram to illustrate the following: (a) Depict the rest...
  19. G

    Ultra-Relativistic Particle Decaying to Identical Particles

    Homework Statement Show that it is impossible for an ultra-relativistic particle with ##pc>>Mc^2## to disintegrate into two identical massive particles of mass m. Homework Equations Conservation of four momentum The Attempt at a Solution The four momentum of the ultra-relativistic particle...
  20. BookWei

    I Spacetime is homogeneous and isotropic

    I read the Special Theory of Relativity in Jackson's textbook, Classical Electrodynamics 3rd edition. Consider the wave front reaches a point ##(x,y,z)## in the frame ##K## at a time t given by the equation, $$c^{2}t^{2}-(x^{2}+y^{2}+z^{2})=0 --- (1)$$ Similarly, in the frame ##K^{'}## the wave...
  21. F

    Relativistic Decay: Calculating Pion Momentum

    Homework Statement A Sigma^+ decays at rest into a neutron and a pion^+ meson, i.e. according to the reaction $$\Sigma \rightarrow n + \pi$$ The n and π masses are assumed known. The kinetic energy of the π + is measured to be 92 MeV. Determine the momentum of the pion. Homework Equations...
  22. mjda

    I What is the difference between covariance and invariance in special relativity?

    Can anyone briefly explain the difference between covariance and invariance in terms of special relativity? My understanding is that an invariant quantity is a value which does not change regardless of frame of reference it is being measured in. Covariance is a value which when measured in...
  23. mjda

    I The relativistic de Broglie equation

    I'm having trouble understanding how the 4-wave vector is derived, and also how it is then used alongside the 4-momentum vector to formulate the relativistic de Broglie equation. The inner product of the 4-momentum vector with itself, is an invariant quantity. If we define the 4-momentum...
  24. stevendaryl

    Insights Rindler Motion in Special Relativity, Part 2: Rindler Coordinates - Comments

    Greg Bernhardt submitted a new PF Insights post Rindler Motion in Special Relativity, Part 2: Rindler Coordinates Continue reading the Original PF Insights Post.
  25. A

    Special relativity - angles between fields

    Homework Statement In an electromagnetic filed, the elctric field ##\vec{E}## forms an angle ##\theta## with the magnetic field ##\vec{B}##, and ##\theta## is invariant for all inertial observers. Finding the value of ##\theta##. Homework Equations Tranformations of fields perpendicular to the...
  26. A

    Electromagnetic Tensor: Calculating $\det{F^{\mu}}_\nu$

    Homework Statement Given an electromagnetic tensor ##F^{\mu\nu}##, showing that: $$\det{F^{\mu}}_\nu=-(\vec{B}\cdot\vec{E})^2$$ Homework Equations The Attempt at a Solution I had only the (stupid) idea of writing explictly the matrix associated with the electromagnetic tensor and calculating...
  27. James Chase Geary

    Special Relativity problem: Lorentz transformation and Reference Frames

    Homework Statement S and S' are in standard configuration with v=αc (0<α<1). If a rod at rest in S' makes an angle of 45o with Ox in S and 30o with O'x in S', then find α. Homework Equations We are in the world of Lorentz transformations so we have t'=(t-vx/c2)/(1-v2/c2)1/2...
  28. A

    Special relativity - Gauge invariance

    Homework Statement In an inertial reference frame ##S## is given the four-potential: $$A^\mu=(e^{-kz}, e^{-ky},0,0)$$ with ##k## a real constant. ##A^\mu## fullfills the Lorentz gauge? And the Coulomb gauge? Which is the four-potential ##A'^\mu## in a reference frame ##S'## which is moving...
  29. K

    B Distance Expansion When Moving Away from an Object?

    In a physics video on YouTube it's told that moving away from an object causes eextension of the length. (Link: from 6:00, but video is Norwegian) Imagine: From planet B to planet C, the distance is 20 light years. And from planet A to planet B the distance is 20 light years. We are on...
  30. A

    Special relativity - Transformation of angles

    Homework Statement Let's have a three-particle decay of equal mass ##m##; in the CM frame the three particles have equal energy ##E## and they form angles of ##\frac{2\pi}{3}## between each other. Which is the angle between two of the three particles in the rest frame of the other one. (The...
  31. K

    B How can the speed of light be constant for all observers?

    A rocket is in constant velocity. The velocity of the rocket is 150Mm/s (or 0.5 of the speed light, or 150 million meters per second) relative to us (we as observer). We observe two lights, one moving in parallell with the rocket, another is moving in the opposite direction. Below I have made...
  32. A

    Special relativity - kinematics

    Homework Statement A photon hits a proton at rest in the laboratory frame and there is the process: $$\gamma + p \rightarrow n+\pi^+$$ The mass of the pion is ##m_\pi## and assuming that the masses of the proton and the neutron are the same (##m##): Finding the threshold energy of the foton...
  33. stevendaryl

    Insights Rindler Motion in Special Relativity: Hyperbolic Trajectories - Comments

    Greg Bernhardt submitted a new PF Insights post Rindler Motion in Special Relativity: Hyperbolic Trajectories Continue reading the Original PF Insights Post.
  34. F

    Synchronized clocks in two moving reference frames

    Homework Statement My professor gave us a werid question which is as follows In the laboratory frame, two clocks are synchronized and measure two light sources at the same time situated at 3 years in time axis and 3 light years and 2 light years in x-axis >At what velocity is the frame ##S'##...
  35. ZapperZ

    "Classical Physics Is Wrong" Fallacy - Comments

    Greg Bernhardt submitted a new PF Insights post "Classical Physics Is Wrong" Fallacy Continue reading the Original PF Insights Post.
  36. V

    A Understanding E-Field Transformation in Feynman II_26

    I have been learning SR from various sources. Most of the time from Feyman's Lectures but that's not the only place. In II_26 he gives the transformation for the E-field of a moving charge in the x direction under a standard Lorentz configuration. In Eqn 26.11 he derives a formula for the Ex...
  37. Adgorn

    Solution of basic special relativity problem

    Homework Statement This is more of a solution check than an actual problem, but I didn't see any other fitting thread to post this on. I'm starting to learn special relativity and have received 2 starting questions on the subjects, I solved them to the best of my abilities but have no actual...
  38. A

    Change in time due to accelerated light-clock

    Homework Statement A light-clock (a photon traveling between two mirrors) has proper length l and moves longitudinally through an inertial frame with proper acceleration ##\alpha## (ignore any variation of a along the rod). By looking at the time it takes the photon to make one to-and-fro...
  39. F

    Speed and direction of b and anti-b quark

    Homework Statement A Higgs particle of mass M is moving in the z-direction with speed $\Beta_H$c compared to the lab system. It decays to a b-quark ans anti-b quark, each of mass m. What is the speed and direction of the b-quark compared to the lab-system, if the Higgs system, (a) it is emitted...
  40. P

    I Relativistic Energy Dispersion Relation: Explained

    I'm in the process of learning special relativity (SR), and I'm a bit confused as to why the relativistic energy dispersion relation ##E^{2}=m^{2}c^{4}+p^{2}c^{2}## gives the energy for a free particle? I get that it is the sum of (relativistic) kinetic energy plus the rest mass term (a...
  41. A

    Inertial frame where rods have same length

    Homework Statement I was re-reading my old Relativity book (by Rindler) and taking a look at some of the problems. He asks: Using a Minkowski diagram to establish the following result: Given two rods of rest lengths ##l_1## and ##l_2 (l_2 < l_1)##, moving along a common line with relativity...
  42. VIctor Medvil

    A SR/GRs Views on QM/QFT | Physics Forums

    This ties into this thread https://www.physicsforums.com/threads/i-want-to-know-the-exact-problems-of-merging-gr-and-qm.939509/ , I would like to know SR/GR's opinion of QM/QFT. I need both sides of the story.
  43. VIctor Medvil

    A I want to know the exact problems of Merging GR and QM

    This thread is I want a set of experts in the subject to show me the exact math of why Einstein's field Equations along with Special Relativity and Schrodinger's Equation along with deeper QM like QFT cannot be fused with GR. I want to see the exact anomalies in the equations myself from the...
  44. A

    Special relativity - Maximum mass

    Homework Statement Finding the maximum mass ##M_x## which can be made from a collision of identical particles with mass ##m##, in the laboratory frame, in which one particle is at rest and the other one has energy ##E##. The reaction is the following: ##a+b \rightarrow a+b+x##.The Attempt at a...
  45. G

    Relativistic Harmonic Oscillator Lagrangian and Four Force

    Homework Statement Consider an inertial laboratory frame S with coordinates (##\lambda##; ##x##). The Lagrangian for the relativistic harmonic oscillator in that frame is given by ##L =-mc\sqrt{\dot x^{\mu} \dot x_{\mu}} -\frac {1}{2} k(\Delta x)^2 \frac{\dot x^{0}}{c}## where ##x^0...
  46. A

    Special relativity - constant acceleration

    Homework Statement A rocket is flying away from the Earth with a costant acceleration ##a## in a frame in which the rocket is at rest. Finding the equation of motion (the relation between the distance from the Earth and the terrestrial time). Showing that there is a maximum time ##T## after the...
  47. Destroxia

    Special Relativity - Length Contraction

    1. Homework Statement Why does the non-relative simultaneous frame have an additional term of ##v \Delta t## along with the contracted length ## L ## for ## \Delta x ##? 2. Homework Equations ## L + v \Delta t = \Delta x ## ---- (1) ## \Delta x = \gamma \Delta x' = \gamma L_{\star} ## ----...
  48. A

    Special relativity - inverse Compton scattering

    Homework Statement In the inverse Compton scattering there is a particle, with energy ##E## in the laboratory frame and mass at rest ##m##, which collide head on with a photon with energy ##E_\gamma##. Finding the maximum energy the photon can have after being scattered. The Attempt at a...
  49. A

    Special relativity - scattering angle

    Homework Statement Finding the maximum scattering angle of a particle whose mass in ##m_1## which hits with relativistic velocity ##v## a particle at rest with mass ##m_2<m_1##. The Attempt at a Solution I've written the 4-momenta (p before the collision, k after the collision and the z-axis...
  50. A

    Special relativity - transformation of electromagnetic fields

    Homework Statement In a reference frame ##S## there is a particle with mass ##m## and charge ##q## which is moving with velocity ##\vec{u}## in an electric field ##\vec{E}## and in a magnetic field ##\vec{B}##. Knowing the relativisitc laws of motion for a particle in an EM field, find the...
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