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. B

    I Rest Energy in special relativity

    I was reading about Rest Energy and came across this line: "In special relativity, however, the energy of a body at rest is determined to be mc2. Thus, each body of rest mass m possesses mc2 of “rest energy,” which potentially is available for conversion to other forms of energy. The...
  2. G

    B Creating a Physics-Based Video Game: A Journey to Learn Relativity

    Hi, I'm trying to make a physics based game to teach my progeny about the universe. My first step will be to show how bodies gravitate around other bodies, and then model a solar system, a galaxy... simple things. I could do it using Newton's laws, but I want to include things like black holes...
  3. M

    B Is General Relativity Incomplete Without Dark Matter and Dark Energy?

    Dark matter and dark energy are fudge factors to solve problems in general relativity such as unexplained mass and drag. Is this correct or am I missing something?
  4. P

    Does the first Maxwell equation work also for moving charges?

    My professor said that the first two maxwell equation's are about static fields Another fast question: Do a single charge that is moVing generate a magnetic field? I saw a demonstration that explains the magnetic field as an electric field using only special relativity, there is a free charge...
  5. Pushoam

    I Is the Principle of Relativity different for different theories?

    The images have been taken from the section : Relativity according to Galileo and Newton, page no.66, special relativity , A.P.French,1968What I understood is: According to the first paragraph, Laws of transformation are needed so that a theory which describes a phenomenon w.r.t. one reference...
  6. Wrichik Basu

    Relativity Book Recommendations in General Relativity

    I have read Special Relativity from Resnick and Halliday's book Fundamentals of Physics. Now I want to read general relativity. I tried reading Einstein's book "Principles of Relativity", but sad to say, many things went tangentially above my head because I couldn't follow many equations, as...
  7. bachir1994

    I Electromagnetism and relativity

    Hello everyone, I read on WIKIPEDIA, that: In 1953 Einstein wrote to the Cleveland Society of Physics on the occasion of the commemoration of Michelson-Morley's experience that "what brought me more and less Directly to the theory of special relativity was the conviction that the electromotive...
  8. A

    B Muon Time Dilation: Earth vs Muon Perspective

    From the reference frame of the earth, the distance between the surface of the Earth and the muon is longer, but the muon survives because time for the muon is slowed down. From the reference frame of the muon, the time experienced by the muon is not slowed down but the muon survives because...
  9. D

    Momentum Energy and relativity question

    Homework Statement A particle of mass m is moving along the positive x direction with momentum p and energy E It collides with a particle of the same mass at rest to form a new particle of mass M. Show that M^2 = 2m/c^2 * (E + mc^2) 2. Homework Equations E^2= p^2c^2 + m^2c^4 The Attempt...
  10. D

    Relativity With velocity of objects moving in different fram

    Homework Statement i)A police spaceship P is chasing another spaceship A. Both ships have velocities βP = βA = 3c/5 as measured along the x-axis in the Solar System reference frame O. The police ship is a distance L = 1 light-second (i.e. the distance traveled by light in one second) behind...
  11. J

    Exploring the Boundless World of EE and Science: A Scientist's Journey

    EE, and life-long science explorer and tinkerer. I look forward to reading the forum, and hopefully contributing at some point. This looks like a great forum! If we weren't limited to 5 tags here, these would have been mine: physics (duh!), relativity, nuclear, antennas, time, radio...
  12. i_hate_math

    I Relativity and Eternalism: Proving the Possibility of 'Seeing the Future

    Eternalism is the view that many moments of time exists and each of these moment are equally privileged/unprivileged. I am trying to back up this view with SR, so I remember watching Brian Greene's documentary "the B-series of time" or something, where he used the spacetime loaf to illustrate...
  13. L

    Other Quantum Information and General Relativity

    Last year I've finished the undergraduate course in Mathematical-Physics and Mathematics and this year I've started on graduate school on Physics in order to obtain a master's degree. What I'm really interested are two main topics: general relativity and quantum field theory. I also like...
  14. Peter Martin

    I Special Relativity vs Newtonian Gravity: Understanding Their Compatibility

    In his little book for the layman, Seven Brief Lessons on Physics author Carlo Rovelli states: What is it about SR which is incompatible with gravity-as-a-force?
  15. davidge

    I Relativity Matter & Vacuum Energy: Stress-Energy Tensor

    Matter is responsible for the stress-energy tensor. What is included in "matter"? Does vacuum energy contributes somewhat to the stress-energy tensor? Would it be correct to include all forms of energy in the stress-energy tensor, through the mass-energy equivalence?
  16. X

    I Relativity Paradox w/ Charged Spheres

    There is a similar thought experiment I imagined to help me begin to understand the Bell's spaceship paradox: Consider two positively charged spheres, placed side-by-side inside a frame S' with a string stretched to the point where it balances the repulsive electrostatic force between them. For...
  17. C

    Which light turned on first and how much later did the second one turn on?

    Its been a few years since I have done any special relativity so I am a bit rusty, need help with either my working/understanding or if correct, making sense of my answer. This is not CW, just a question from a past exam paper that I am using as preparation. 1. Homework Statement Street light...
  18. binbagsss

    General Relativity - FRW Metric - FRW Equations show that ...

    Homework Statement Homework Equations see above The Attempt at a Solution Using the conservation equation for ##p=0## I find: ##\rho =\frac{ \rho_0}{a^3}##; (I am told this is ##\geq0## , is ##a\geq0## so here I can conclude that ##\rho_0 \geq =0 ## or not?) Plugging this and ##p=0## into...
  19. parshyaa

    I Why does relativity not affect the speed of light?

    Why speed of light is independent of frame of reference,why is it constant everywhere, speed of an object is different from different FOR then why this is not follwed by light, In deep space there is nothing to measure the speed of light relatively, then how it got its speed(299 792 458 m/s)...
  20. O

    B "The search for Relativity Violations"

    I'm reading the 100 years anniversary edition of Sci-am and there is an article called "The Search for Relativity Violations". Some passages perplexed me: "In the case of relativity violations, the equations describing the stick and the applied force are replaced by the equations of the...
  21. I

    I Acceleration towards c without a reference frame and changes

    Hello everyone. Below are two problems I have been thinking about lately. Let’s consider two cases: we have a spaceship surronded by an utter void - nothing outside which the spaceship’s pilot could refer to. The pilot (in his robotic body, allowing him to withstand enormous G-forces) turns on...
  22. Sullivan Stockwell

    B Relativity of Simultaneity: Proving Lightning Strikes A & B Same Time?

    My question is based around the popular thought experiment regarding Einstein's relativity of simultaneity. That is, the one regarding two lightning strikes and two observers. Observer 1 is stationary relative to the ground, and is located equidistant between lightning strikes A and B. Observer...
  23. M

    A Acceleration of a Satellite in General Relativity

    Hi there guys, I'm struggling! I've been looking at the International Earth Rotation Services (IERS) "standards" for motion of a satellite in GR. the expression is far from trivial and I'm battling to determine where to even start with this bad boy. The expression is given by \Delta...
  24. A

    I On the Relativistic Twisting of a rotating cylinder (Max von Laue)

    I'll start with link describing the phenomenon: https://books.google.com/books?id=WTfnBwAAQBAJ&pg=PA43&lpg=PA43&dq=relativity+twist+rotating+cylinder&source=bl&ots=C2SDJNPF2K&sig=ImFDYGm_0qK7JoDU0ulsxLk3sMU&hl=en&sa=X#v=onepage&q=relativity%20twist%20rotating%20cylinder&f=false Quote: "A...
  25. D

    Special Relativity Conceptual Question

    Homework Statement Einstein developed much of his understanding of relativity through the use of gedanken, or thought, experiments. In a gedanken experiment, Einstein would imagine an experiment that could not be performed because of technological limitations, and so he would perform the...
  26. davidge

    I Is the Notation for Coordinate Transformation in Relativity Problematic?

    In a change of coordinate system we have ##dx^\mu = (\partial x^\mu / \partial \xi^{\kappa})d \xi^{\kappa}##, where the term in round brackets is the Jacobian. That notation implies a sum over all values that ##\kappa## can take. This don't tell us that it's an alternating sum for the case of...
  27. Grisha

    I Confusion with relativity of simultaneity

    I know variations of these have probably been asked numerous times before, but I'm having trouble with this specific scenario. Imagine the classic Train Paradox, except instead of lighting strikes we have an observer at the centre of the train shooting laser pulses towards the rear (Event E1)...
  28. peroAlex

    Special Relativity: Length Contraction Problem

    Hello! I have a small problem with a task professor gave us. I tried many options (you will see below) but I cannot seem to get the right solution. Any advice or guideline how to solve this would be really helpful. In advance I thank you for helping me. Homework Statement Our professor of...
  29. P

    Special Relativity - Is damage absolute?

    1. The problem statement, all variables, and given/known data A car of proper length 12m is being driven at 0.9c through a garage of proper length 6m. The garage has a front and back door. The garage owner, Joe, says that the car will fit inside the garage with no damage to it, albeit for a tiny...
  30. terryds

    What is the speed of the rocket relative to the Earth?

    Homework Statement Plane A flies with speed 0.6c chasing plane B which speed is 0.4c . Both speed is measured by observer on Earth. Then, plane B fires a small rocket which rest mass is 10 kg towards plane A. Rocket speed is 0.2c relative to plane B where c equals the speed of light in vacuum...
  31. Kara386

    Special relativity where am I going wrong?

    Homework Statement A spaceship moves away from Earth at 0.9c and fires a probe in the same direction as its motion at 0.7c. What is the probe's velocity relative to Earth? Homework EquationsThe Attempt at a Solution The Lorentz velocity transformation is ##v_x' = \frac{v_x -...
  32. davidge

    I Math of Relativity: Topology Needed?

    How much of topology one needs to know to have a great knowledge of the math of Special and General Relativity? I'm asking this because I'm interested in really look at the theory of Relativity with the eyes of a mathematician. I suppose that just knowing what a manifold is or even what a...
  33. S

    A Minimal coupling in general relativity

    Consider the Einstein-Maxwell action (setting units ##G_{N}=1##), $$S = \frac{1}{16\pi}\int d^{4}x\sqrt{-g}\ (R-F^{\mu\nu}F_{\mu\nu})$$ where $$F_{\mu\nu} = \nabla_{\mu}A_{\nu}-\nabla_{\nu}A_{\mu} = \partial_{\mu}A_{\nu}-\partial_{\nu}A_{\mu}.$$ This describes gravity coupled to...
  34. Sophrosyne

    I Big Bang timing: according to what frame of reference?

    My apologies if there are some related discussions on this topic in another thread here, but I could not find one specifically addressing this question. Big bang theory, as it currently stands, talks of some extraordinarily precise time measurements; you see numbers like that 10^-37 sec...
  35. gelfand

    Gravitational forces, speeds and masses

    Homework Statement A comet moves around a stat in ##xy## plane along elliptical orbit, described by $$ 0.16 x^2 + y^2 = 4 $$ where ##x, y## are in ##AU## 1) Sketch the comet in the ##x,y## coordinate system denoting all orbit parameters 2) Find the semi major and minor axes of the orbit...
  36. J

    A General relativity. What does momentum conservation mean?

    In general relativity, does momentum conservation mean conservation of 4-momentum or 3-momentum
  37. J

    A General Relativity: Components of ds^2

    Hello there, suppose we take ##M## to denote the spacetime manifold. Suppose also that ## ds^2 = g_{\mu \nu} dx^\mu dx^\nu##. I have some confusions with regards to the metric and the line elements. My main confusion is at which points in the manifold are ## ds^2## defined? Is it correct that...
  38. J

    A General relativity -- Proof of energy measured by observer

    I want to prove that ##E = -g_{\mu \nu}u^\mu p^\nu## is the energy measured by an observer with velocity ##u^\mu## of an object with momentum ##p^\mu##. My reasoning is that in special relativity we know that ##\gamma m = E##. We can transform to coordinates where ##u'^\mu = (1,\vec{0})##. Since...
  39. davidge

    B Is it that hard to do Relativity in accelerating frames?

    According to the Lorentz transformations, in the absence of gravity, the relations between coordinates of a primed system to those of a unprimed system are $$x'^{\ \alpha} = \Lambda^{\alpha}{}_{\beta}x^{\beta}$$ For the Lorentz invariance to be satisfied we must have...
  40. davidge

    I Why Open Manifolds are Relevant in Relativity

    Why manifolds in General (and Special) Relativity have to be open? Would this be because an open manifold have a continuous interval? (i.e. an interval with no interruptions)
  41. L

    Special Relativity -- two ships moving in one dimension

    Homework Statement You approach an enemy ship at a speed of 0.5c measured by you, and the ship fires a missile toward your ship at a speed of 0.7c relative to the enemy ship. What speed of the missile do you measure, and how much time do you have measured by you and the enemy ship before the...
  42. I

    Speed of an object relative to another

    Homework Statement In a colliding beam apparatus, two beams of protons are aimed at each other. The first proton moves with a speed of 0.82c to the right; the second moves with a speed of 0.86c to the left. Both speeds are measured relative to the laboratory frame of reference. What is the...
  43. I

    Calculating Speed of Protons in a Linear Accelerator: 530 MeV Kinetic Energy

    Homework Statement In a proton linear accelerator, protons are accelerated to have a kinetic energy of 530 MeV. What is the speed of these protons? (The rest mass of a proton is 1.67 × 10-27 kg.) Homework Equations E0=m0c^2 E=E0/√1-(v^2)/(c^2) E = KE + E0 The Attempt at a Solution Recognize...
  44. robphy

    Insights Relativity using the Bondi k-Calculus - Comments

    robphy submitted a new PF Insights post Relativity using the Bondi k-Calculus Continue reading the Original PF Insights Post.
  45. P

    I Relativity, magnetic attraction, and comoving electrons....

    How can relativity explain the magnetic attraction of two electrons (or two electron beams) comoving in a vacuum at some certain constant velocity? It is well known (https://acceleratorinstitute.web.cern.ch/acceleratorinstitute/ACINST89/Schindl_Space_Charge.pdf) that two parallel electrons or...
  46. Cathr

    B Special Relativity Q: Choosing Light as Ref

    Special relativity states that the speed of light is constant for all the references, as long as they are not accelerating. For example, the speed of light would be c for a train moving linearly with a constant speed and would also be c for an observer who's not moving at all (I took the Earth...
  47. R

    Getting a real understanding of general relativity

    Hello, I am new to this forum, but have read a lot of posts and it seems really cool. I am 38 and have a B.S. in mathematics (from many years ago). I work in insurance, so I am pretty far removed from acedemia now. I have kept up my math studies as a hobby. After studying a lot of theoretical...
  48. S

    Calculating Relative Velocity of Spaceships Using GRE Relativity Equations

    Homework Statement Two spaceships pass each other. Space-ship A moves relative to a nearby planet at velocity ##v_1##, while spaceship B moves at velocity ##v_2## relative to the planet. How fast does spaceship A move relative to spaceship B? Homework EquationsThe Attempt at a Solution I just...
  49. binbagsss

    General Relativity, identity isotropic, Ricci tensor

    Homework Statement Attached Homework EquationsThe Attempt at a Solution So the question says 'some point'. So just a single point of space-time to be isotropic is enough for this identity hold? I don't quite understand by what is meant by 'these vectors give preferred directions'. Can...
  50. robphy

    Insights Relativity Variables: Velocity, Doppler-Bondi k, and Rapidity - Comments

    robphy submitted a new PF Insights post Relativity Variables: Velocity, Doppler-Bondi k, and Rapidity Continue reading the Original PF Insights Post.
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