Relativity Definition and 998 Threads

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. 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?
  2. 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...
  3. 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?
  4. 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...
  5. 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...
  6. 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...
  7. 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...
  8. 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...
  9. 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...
  10. 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
  11. 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...
  12. 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...
  13. 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.]
  14. 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...
  15. 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...
  16. 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...
  17. 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...
  18. 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...
  19. 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.
  20. Demystifier

    I Is General Relativity More General than Gravity?

    One obvious difference is that gravity is more general, because there are alternative theories of gravity that differ from general relativity. In this sense general relativity can be thought of as a subset of gravity. But I am interested in a different type of difference. I am interested in a...
  21. S

    A Meaning of the word "conserved" in relativity

    I'm reminded of something that I'd be curious to get some thoughts on. There's a semantic issue with the word "conserved" that often flies under the radar: does the term refer to any quantity whose value remains the same before and after some process, or does it specifically refer to an...
  22. Athenian

    [Special Relativity] Lorentz Transformation and Boosts

    [BEGINNGING NOTICE] Before I begin showing my attempted solution, I would just like to quickly mention that this is a "repost" of the same question I had around a week ago. While I would usually use the "reply" function on the same thread, I believe that thread is getting pretty messy (sometimes...
  23. Athenian

    [Special Relativity] - Finding Angle θ as Measured in Frame S

    Below is the attempted solution after researching the contents available on Introduction to Electrodynamics by Griffith. To begin with, I defined the rod as having a length of ##l'## at rest in frame ##S'##. Thus, in frame ##S'##, the height of the rod is ##l' sin(\theta ')## and its horizontal...
  24. Athenian

    [Special Relativity] Scalar Invariant under a Lorentz-transformation

    "My" Attempted Solution To begin, please note that a lot - if not all - of the "solution" is largely based off of @eranreches's solution from the following website: https://physics.stackexchange.com/questions/369352/scalar-invariance-under-lorentz-transformation. With that said, below is my...
  25. D

    B Linking Quantum Physics and Relativity: Theory of Everything?

    I am going to get laughed out of this forum but at least it will put my mind to rest when this happens. I've been thinking about this for a few years now and what better place for an answer than a physics forum? Amongst many other things I have read A Brief History of Time seven or eight times...
  26. M

    Special Relativity question using Lorentz Transformation time dilation

    with distance between planets as 4x10^8m measured by you on the ship My attempt: t' = γ(t - ux/c^2) γ = 5/3 u = 0.8c t = 0.9s x = 4x10^8m answer is: -0.278 Therefore not possible My question is what if we traveled rightwards, from p2 to p1, would the answer change? Should my above information...
  27. Athenian

    [University Special Relativity] Lorentz Transformation and Boosts

    Unfortunately, I am not entirely confident of the above equations being able to do the trick and ultimately solve for the question. However, my guess is that using the equation written above for "boost", I could perhaps use ##v## and insert it into the ##x##-direction part of the matrix...
  28. GravitySK

    Relativity Looking for further Relativity textbooks

    I'm reading chapter 7 of Goldstein Classical Mechanics (the special relativity part) I'm planning to take a deep(very deep!) study on Relativity(Both Special and General Theory) after finishing chapter 7 of Goldstein. Which textbooks will you recommend? If you could give me a suggestion with...
  29. A

    I Architecture & Assumptions of General Relativity Theory

    Every theory, whether it is a physical, a psychological or a sociological theory, is defined in terms of an assumed architecture and in terms of a number of assumptions that apply within that architecture. An example from physics is the previously widely accepted dome theory to explain the...
  30. K

    I Electromagnetic Potentials in Relativity: Retarded Potentials?

    What's the most used type of electromagnetic potential? Is it the retarded potentials?
  31. M

    The sphere in general relativity

    I'm a bit confused about the notation used in the exercise statement, but if I'm not misunderstanding we have $$\begin{align*}(\psi^+_1)^{-1}:\begin{array}{rcl} \{\lambda^1,\lambda^2\in [a,b]\mid (\lambda^1)^2+(\lambda^2)^2<1\}&\longrightarrow& \{\pm x_1>0\}\subset \mathbb{S}^2\\...
  32. RUTA

    Insights Answering Mermin’s Challenge with the Relativity Principle

    Continue reading...
  33. Replusz

    What is the effective Lagrangian in General Relativity?

    Attempt: I don't know what they mean by effective Lagrangian. I am aware there is something called 'the lagrangian' that goes as L=g_ab * dx^a/dk * dx^b/dk, but i don't see how this gives me any of the chrostoffel symbols... cheers
  34. M

    I Connection between General Relativity & Chaos Theory?

    I am very new to such ideas but was wondering if there is any connection to what I am asking. Taking two events, let's say at opposite ends of the globe. Would even A, only have a potential on event B, if light could travel between these event in the given time frame of these event occurring...
  35. RodolfoM

    How Do Relativity and Time Dilation Affect the Time Between Events?

    Firstly, I calculated the relative speed between the two rockets, finding v=1.6c/1.64. Then, I applied the length contraction: the length of the moving rocket will be 0.6L due to this phenomena, so the total distance traveled by one rocket, with respect to the the other, will be 1.6L. Therefore...
  36. matternat968

    B Relative Nature of Speed: Einstein and Orbits

    At the risk of sounding stupid, this question has always perplexed me. Einstein theorized that mass can not travel faster than the speed of light. I don't really understand it, I assume it has something to do with mass just being energy. Anyway imagine two objects in orbit of something with...
  37. Demystifier

    A Implications of quantum foundations on interpretations of relativity

    Physicists often discuss interpretations of quantum mechanics (QM), but they rarely discuss interpretations of relativity. Which is strange, because the interpretations of quantum non-locality are closely related to interpretations of relativity. The field of interpretations of relativity is...
  38. Demystifier

    I Special relativity vs Lorentz invariance

    The Lorentz covariance of Maxwell equations was known before Einstein formulated special relativity. So what exactly special relativity brought new with respect to mere Lorentz covariance? Is special relativity just an interpretation of Lorentz invariance, in a sense in which Copenhagen...
  39. M

    How Does Acceleration Transform in Special Relativity?

    I'm struggling in the details of this exercise. Let ##S'## be the reference frame where the acceleration of the spaceship is constant, in which case we have ##u'(t')= a' t'## (since we assume no acceleration at the beginning). The rest frame of the rocket ##S## is connected to ##S'## via a...
  40. Cerenkov

    B The Strong Energy Condition in General Relativity

    Hello. I've recently been reading this paper... https://arxiv.org/pdf/gr-qc/0001099.pdf ...in the hope that I can begin to understand some the role of the energy conditions in General Relativity. But I'm not making much progress and so I've turned to this paper...
  41. Replusz

    Why is this true? General relativity

    "their scalar product is..." why?
  42. M

    I Special Relativity: 2-D Collisions for Alice & Bob

    Alice and Bob are initially in the same inertial frame. There are 2 point test masses m1 and m2. Initially m1 is at the origin and m2 is on the positive x-axis. At time zero, m1 is instantaneously accelerated to velocity Vx in the positive x-direction. After some time, m1 collides with m2...
  43. M

    I Accel. in Spec. Relativity in 2-Dims: Point Test Mass

    Let m be a point test mass. Initially m has velocity Vy in the poisitive y-direction, and zero velocity in the x-direction. At time zero, m is accelerated in the positive x-direction. In the limit as the time goes to infinity, the velecity in the positive x-direction goes to the speed of...
  44. D

    What Is Relativity in Physics?

  45. Meruem

    B Quantum Gravity and Special Relativity

    is there a equation that links quantum gravity and special relativity?
  46. N

    Prerequisites for General Relativity (Advice needed)

    Summary: At this point, I am thorough with single variable, multivariable calculus, differential equations, linear algebra and basic concepts of point-set topology and tensor analysis. To learn General Relativity along-with its mathematical rigor, what are the topics I should first be thorough...
  47. Pencilvester

    I Pullback of Vector Field in Relativity: Restrictions?

    Since coordinate transformations should be one-to-one and therefore invertible, wouldn’t there be no restriction on pushforwarding or pullbacking whatever fields we feel like (within the context of coordinate transformations)?
  48. adosar

    I Position of Particle in Special Relativity (A vs B)

    Recently I have come into Special Relativity and specifically Lorentz transformation. Let's assume two frames A and B moving relative with speed ##v##. The position of a particle moving with respect to B is given by ##x′=f(t′)=3t′##. What is the function of position ##x=f(t)## of the particle...
  49. N

    I Special relativity question driving me crazy....

    Hey guys. Noob here. Question; S frame = x,y,z,t S' frame = x',y',z',t' S' is moving with a speed v relative to S and t=t'=0 when origins coincide v= 0.6c find the coordinates of x = 4 & t = 0 in S' When I use lorentz transformation, I get a negative t' and x' = 5. This doesn't make sense to...
  50. P

    I Dark energy questioning Relativity?

    Forgive my naive understanding of these topics. I have a layman's interest in science and follow all the popular science I can, but I'm certainly not a physicist and even my degree in mathematics is now all but forgotten in the past. But I have two questions (the other I'll post in another...
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