What is Relativity: Definition and 997 Discussions

The theory of relativity usually encompasses two interrelated theories by Albert Einstein: special relativity and general relativity, proposed and published in 1905 and 1915, respectively. Special relativity applies to all physical phenomena in the absence of gravity. General relativity explains the law of gravitation and its relation to other forces of nature. It applies to the cosmological and astrophysical realm, including astronomy.The theory transformed theoretical physics and astronomy during the 20th century, superseding a 200-year-old theory of mechanics created primarily by Isaac Newton. It introduced concepts including spacetime as a unified entity of space and time, relativity of simultaneity, kinematic and gravitational time dilation, and length contraction. In the field of physics, relativity improved the science of elementary particles and their fundamental interactions, along with ushering in the nuclear age. With relativity, cosmology and astrophysics predicted extraordinary astronomical phenomena such as neutron stars, black holes, and gravitational waves.

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  1. I

    B Can an Object Exceed the Speed of Light?

    I was curious if the relative speed of an object can exceed the speed of light. Specifically, I am curious about the following thought experiment. I am not a physicists (and if I were asking the following would make me a poor one) and it has been 20 years since college physics. If a vessel is...
  2. Hyotopii

    B Explore Time Perception & Relativity - Get Your Answers Here

    Hello, Dear Readers, as mentioned in the caption and Summary, i'am dearly interested in the perception of time due to relativity. I thought About this for quite some time.What happens to the perception of time to the conciousness, I mean our weight is not the same, and our energy consumption...
  3. Mattv

    B Time Dilation & Relativity: Explained for Beginners

    Good morning I'm a total beginner in physics, but I recently started to read books and watch videos about cool physics stuff, like relativity. I heard that the closer to the speed of light you travel, the "slower" time passes for you. I'm talking about the fact that clocks in GPS satellites...
  4. Souma

    I Using general relativity to violate the uncertainty principle

    Hello everyone, Heisenberg's uncertainty principle tells us that we cannot measure the position and the momentum of a particle to infinite accuracy. My question is, can we use general relativity to overcome this difficulty? From what I know, any mass can curve spacetime even if it was small, and...
  5. B

    B Calculating Relativity of Simultaneity

    The question is in reference to calculating relativity of simultaneity. I am on the step where I take the time in Alice's frame from the front and from the rear clock and minus it to the get the total time. I end up with gamma squared etc (For more details see the picture below) I have...
  6. Matilda111

    B Research Paper: Exploring Decay in c Due to Universe Expansion

    I'm currently writing a research paper about the speed of light. I have researched universe expansion, specifically, the quantised redshift spectral index fluctuations of distant galaxies and other structures over time, however, I need to suggest why universe expansion possibly causes a recorded...
  7. YouAreAwesome

    B Does time dilation work in 1d space?

    Imagine this question in 2 dimensions, time (t) and distance (x), that is (t,x). Alice (A) is at the origin, x=0. Bob (B) begins at x=c. Thus we have A(0,0) and B(0,c). Both Alice and Bob send a light signal towards the other but let's say the signal changes colour every second by the colours of...
  8. A

    Math Courses to Understand General Relativity (by Sean Carroll)

    Hi. What are the math courses should I take in order to understand the mathematics involved in a book such as Sean Carroll in general relativity. Thanks
  9. Nantes

    I Treatment of Relativity in "Las Leyes de la Termodinámica" Movie

    Background: There is a very interesting Catalunyan film on Netflix called "Las Leyes de la Termodinámica" (The Laws of Thermodynamics) which is perhaps the world's first hybrid of a physics documentary and a romance film. The main character is a physics professor who falls in love and attempts...
  10. hagopbul

    Intro Physics Finding Books on Elementary Particle Physics & Special Relativity

    hello all : looking for books to read in this times ,undergraduate level mostly , but i have some problem finding good ones for introductory elementary particle physics other than griffths and for special relativity any recommendations
  11. A

    I Sachs and Wu's General Relativity for Mathematicians

    I am trying to study "religiously" the book by Sachs and Wu, but I am finding the Exercises very much of a challenge. Does anyone know if there exists a source for solutions one can consult when stuck?
  12. P

    Special relativity, a non-inertial perspective

    I have tried calculating it as a Uniform Accelerated Movement problem: , where t is the time for the observer at Earth, O. For calculating t'' (the proper time for the accelerated spaceship observer), it is just using a Lorentz transformation? It seems easy, but as is stated that the frame is...
  13. S

    I What stars were observed @ 1919 solar eclipse to prove relativity?

    Was there a published report of exactly which stars which were supposed to be at position A but were observed at position B, etc.?
  14. Lynch101

    B Bell's theorem, QFT, and the Relativity of Simultaneity

    I've been slowly grinding away with what I can about quantum mechanics and QFT. I'm not sure how far I've gotten but I've come up against a bit of a roadblock concerning how the relativity of simultaneity applies in QFT with specific reference to the outcome of Bell tests. My misunderstanding...
  15. L

    Laws of conservation in special relativity

    Momentum ##\vec{p}## before collision is momentum of proton of the energy ##E=76.4\mbox{GeV}##. Law of conservation of energy is E+mc^2=E_1+E_2+...+E_n mc^2=0.94\mbox{GeV} We could generate only even number of particles after collision because of law of conservation of electric charge. Also...
  16. P

    Quick Check for Relativity HW, rocket passing by space station

  17. H

    Does Galilean relativity imply infinite propagation speed?

    Without assuming a universal speed that is constant in all inertial reference frames, is it a necessary consequence of Galilean symmetry that interactions are instantaneous? If this is the case how can we prove this?
  18. F

    I Electromagnetic field according to relativity

    Hello, I am still trying to fully grasp the general idea of the EM field, which always travels at the speed of light regardless of the reference frame, and is represented by a tensor with 16 components in relativity theory. My understanding is that, depending on the observer's frame of...
  19. PainterGuy

    Stats on Students Understanding Theory of Relativity

    Hi, I'm not sure if it's a good idea to start a thread about the following problem but I didn't want to PM anyone. Some time ago I came across a thread which had stats related to the problems faced by students learning the theory of relativity. It showed like how many undergraduates really...
  20. danielhaish

    B Relativity & Computer Calculations: Speed Up 300x?

    there is many analog dividing machine that base on time counting . so does this machines work faster on height speed system such as Particle Accelerator it may help in decryption of public encryption and other coculation . It looked at relative calculator and in the speed that close to the...
  21. B

    Series of questions about Special Relativity

    https://scholar.harvard.edu/files/david-morin/files/relativity_chap_1.pdf The questions start at page 44 Whenever I refer to y, y = gamma. 1.1 This question is primarily deriving LV/C^2? How does 2LV / c^2-v^2 becomes 2Lv / c^2(1-v^2/c^2)1.4 On the solution page it shows fig 1.61 and fig...
  22. B

    I want to learn special and general relativity

    Summary:: I want to learn special and general relativity I am curious what is the best way to learn special and general relativity. https://www.coursera.org/learn/einstein-relativity/home/info I started this course but it seems relativity easy so far. Only on week 2. Being easy is not bad I...
  23. P

    (Relativity) A flash of light is emitted at x1 and absorbed at x1 + l

    My answers are quite different and here are my attempts a) What is the spatial separation ##\ell'## between the point of emission and absorption? (In the frame going ##v = \beta c##) From what I know is that moving causes lengths to be contracted according to the formula ##\ell_{travel} =...
  24. M

    I Where is Contraction Point in Special Relativity?

    Generally speaking, when a simple contraction occurs there is a contraction point. Length contraction in special relativity appears to be a simple contraction, and hence there should be a contraction point. Where is this contraction point located?
  25. M

    I Special Relativity & No Special Inertial Frame of Reference

    As per special theory of relativity, no inertial reference frame is special! If a spaceship is moving at 100 m/s, no one can conduct an experiment to determine whether it is moving at 100 m/s or the rest of the universe is moving to the opposite direction at -100 m/s, if I understand the...
  26. HaoBoJiang

    It's pleased to meet everybody

    I am a physics graduate student, also a physics enthusiast.I prefer Mathematical Physics, and often do some related research.Like everyone of you, I also have a strong interest in physics, and I hope to generate more new ideas and broaden my knowledge through exchanges with you.
  27. Lincon Ribeiro

    I Lorentz Arguments for Ether: Critical Analysis of 1895 Paper

    I bought the book "The principle of Relativity" by Einstein et al. and was really surprised by the (low) level of explanation by Lorentz regarding the compression of rods on the experiment carried out by Michelson & Morley. I reproduce part of it below: Well, he gave absolutely no arguments to...
  28. K

    I Special Relativity: Constant Speeds or More Complex GRT?

    I'm reading the online version of a book that says Rindler observer comes right into my mind when I read this. So I think the book is wrong. What do you all think? On a second guess, perhaps the author takes the view that SR is only for constant speeds in the same sense that one could say that...
  29. LeeHilliard

    B Time & Special Relativity: Is Time Object-Specific?

    If time slows as an object increases velocity wouldn't that indicate that time is object specific? And if the speed of light is a constant and does not change regardless of the velocity of an object wouldn't that indicate that time used to measure the speed of light changes? The video I have...
  30. T

    A shot in the dark -- Need help understanding Special Relativity

    first off hi all. Just joined, i was looking for someone to help me understand time dilation and spatial contraction in relativity. its not homework just something i was watching, very good btw, but left me with some contradictory information as i see it. if anyone with any level of expertise at...
  31. KipIngram

    I Struggling with a special relativity "paradox"

    Ok, I hope someone can help me see how to sort this out. Alice has a full-frame (no rolling shutter) video camera that records exactly 30 frames per second. It's mounted to a telescope looking far out into space. Bob is out there in space with a digital clock that reads out to the millisecond...
  32. D

    I Is the four current in Relativity an invariant quantity?

    Is the four current in relativity an invariant quantity? I know the divergence is zero for the four gradient, i.e. the continuity equation. But is the four current a vector in the sense that it has invariant properties?
  33. L

    B Calculating Triangle Area in Relativity Theory

    Area of triangle from picture https://en.wikipedia.org/wiki/Special_right_triangle#/media/File:45-45-triangle.svg is ##A_0=\frac{1}{2}##. If that triangle staying still in system S' and S' moving across one of the sides of length ##1## in respect to system ##S## area of the triangle in the...
  34. BadgerBadger92

    I Special Relativity vs Lorentz Transformation: Difference Explained

    What is the difference between special relativity and the Lorentz transformation? Aren't they basically the same thing? Also, I was wondering what about matter makes spacetime curve?
  35. Saptarshi Sarkar

    I Why does Special Theory of Relativity leave out Potential Energy?

    While studying Special Theory of Relativity I came across the formula for the energy of a particle. The total energy of a relativistic particle in STR contains the Rest Mass energy and the Kinetic energy. But, in Classical and Quantum Mechanics, we consider the total energy of the particle to be...
  36. virgil1612

    I Time Dilation Effects of Travel to Star 10ly Away

    If an astronaut travels to a 10 ly distant star with a speed very close to light speed, then he will measure a distance to his star much smaller than 10 ly (length contraction) so his time for reaching the star will be smaller than 10 years, let's say 1 year. Then, without delay, he returns back...
  37. LukasMont

    I Special Relativity Controversy: Solving the Paradox

    Hey guys, My question is a bit confusing: When we observe a train moving close to the speed of light, passing by the platform, according to the frame of reference in the platform, the clocks in the train are ticking slower than the clocks in the platform itself. According to the frame of...
  38. Athenian

    [Special Relativity] Test Particle Inside the Sun's Gravitational Field

    Below is an attempted solution based off of another user's work on StackExchange: Source: [https://physics.stackexchange.com/questions/525169/special-relativity-test-particle-inside-the-suns-gravitational-field/525212#525212] To begin with, I will be using the following equation mentioned in...
  39. Povel

    A Kinnersley’s “photon rocket” and gravitational radiation

    In this paper by Carlip, a comparison is made between electromagnetic and gravitational aberration. For the latter case, he takes as a study subject the Kinnersley’s “photon rocket”, an exact solution which is known to have the strange property of not producing any gravitational waves, even...
  40. P

    Particle decaying into two daughter particles - special relativity

    Right, so I thought I'd done this correctly but clearly not because my velocity is greater than the speed of light, where have I gone wrong? P = (M, 0, 0, 0) p1 = (E1, p1x, p1y, p1z) p2 = (E2, p2x, p2y, p2z) P = p1 + p2 p2 = P - p1 square each side to get (p2)2 = P2 - 2Pp1 + p12 therefore (m2)2...
  41. P

    A moving pi-meson decaying into 2 photons - finding their energy

    I've tried using gammamc^{2} = E1 + E2 but how do i find gamma?? If i try to use the kinetic energy then I just get gammamv^2 = 1gev but i don't know v? very confused
  42. B

    Special relativity problems — More details below

    [Note from mentor: this was originally posted in a non-homework forum, so it lacks the homework template.] Summary:: Special relativity problems. More details below The formula for speed for special relativity is V = (u-v) / (1-u*v) / (c^2) Here the book...
  43. R

    Collisions in special relativity

    Happy new year, I got very far in this question. I attempted to use conservation of energy first. Ei=(Pfc)^2+mec^2 Where pf is the initial momentum of the photons Ef=(γmec^2)+(pf'c)^2 Then used conservation of momentum Pf=γmvcos(Θ) Pf'=-γmvsin(Θ). After that I added Pf and Pf'. and used...
  44. R

    Finding u and v for a Moving Rocket: Applying the Lorentz Transformation

    we are asked to find u and v. I thought by listing the known I can proceed to solve the question, but got no idea where I should start solving the question from. [Moderator's note: Moved from a technical forum and thus no template.]
  45. K

    I How it's known that the variational principle works for relativity

    This question is actually about relativity and quantum field theories. I have the impression that we just use the variational principle, and given the right lagrangian, they lead to equations that we know, are correct. That seems to me a good reason for "believing" that the variationa principle...
  46. N

    B Development of Special Relativity

    I'm interested in the history of thought that led to the discovery of special relativity. Of all the equations in special relativity, e.g. the equation for the invariant interval, the equation for gamma, the Lorentz transformation equations, the equation for velocity addition, etc., which one...
  47. L

    I Momentum and energy calculation in special relativity

    ## \ \ \ \ \ ##In ##K##，System ##M## is composed of a spring ## N ## and four particles ## P, Q, A and B ##. The ends of spring ## N ## are fixedly connected with particles ## P and Q ## respectively. Particle ## A ## is adjacent to particle ## P ##, and particle ## B ## is adjacent to particle...
  48. bos3yed651

    I Exploring Special Relativity: A Pickle in Lorentz Theory

    This is my first thread. I hope I do it right. I just started reading the book Special Relativity by W.Rindler. And as I was reading it, I stumbled upon a pickle. So in Lorentz theory, it says, supposedly we could measure the original to-and-fro time T2 directly with a clock, and suppose we...
  49. G

    I General Relativity & Curvature Explained: How Objects Fall

    I always was confused on how objects fall on Earth due to curvature of space. All I see everywhere is a flat stretched piece of fabric and balls going round and round the central massive ball. But that does not explain anything, how objects actually fall. Finally I saw this video where it...
  50. K

    I Bohmian mechanics and special relativity

    [Moderator's note: Thread spun off from previous thread due to topic change.] Thanks! I am working on understanding why non-local effects violate the special theory of relativity. I am not there yet, but maybe when I finally get there I will leave the BM train.
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