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.

View More On Wikipedia.org
Recent contents Top users
  1. 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...
  2. 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?
  3. D

    I Favorite Visualization of General Relativity?

    I am collecting ways to visualize the curvature of spacetime -- and movement of objects affected by gravity -- as per Einstein's GR. Alternatives to the bowling ball / trampoline image so often used in the popular press. Images that show the similarities / differences between Newton & Einstein...
  4. J

    Relativity Thoughts on General Relativity by Hobson?

    Background: I'm about to graduate with a mathematics degree(in the US), hence I have exposure to multivariable calculus, real analysis, abstract algebra, complex variables etc (no differential geometry however). I have also taken a class on QM(using Griffiths) and I saw some SR during a Modern...
  5. astroman707

    Physics Is gravitational wave research a smart direction to go in?

    Is it a fair prediction to state that in the next several years or so, globally, there will be major investments into gravitational wave research, and many more ‘LIGOs’ being developed? Is it a good idea to venture into that area of physics?
  6. K

    I Displacement vector in general relativity

    Is there a sensible way of defining a displacement vector in a general manifold? That is, the displacement vector being the difference between position vector at two different points... the problem is that these two different points have, in general, different tangent vector spaces. Never the...
  7. N

    I Measuring Star Radii with General Relativity

    Hi, I'm wondering if it is possible to measure radii of stars using general relativity, given its explanation of gravity as curvature of space. Thank you
  8. N

    Best books for special relativity?

    Hello everyone, I'm studying physics as an undergraduate and I'm currently taking the course special relativity. But sadly I'm not too big a fan of the book we are using for the course. So I was wondering what are the best books you know of regarding special relativity for undergraduates.
  9. I

    I Is Mathematics a Paradigm of Truth in General Relativity?

    I have little exposure to mathematics beyond high school algebra and physics, but I have become increasingly interested in physics, particularly its most towering achievements of modern times : Quantum Physics, as well as A. Einstein’s Special and General Relativity, the latter of a...
  10. E

    B What would the universe be like with less mass and energy?

    So I have sort of a conceptual question about the big bang and gravity. Imagine yourself in a universe, in which existed about the number of particles/energy in a 3X3 metre room at any given moment. This universe has the same laws of physics, constants and is identical in every way to our...
  11. R

    I Relativity and Electromagnetism

    Hello, There is a common setup used when describing the intimate relationship between electricity and magnetism. I have a question about the setup. Setup: There is some long current-carrying wire. Outside of that wire, there is some test charge. In the first situation, the test charge is...
  12. A

    I Visual effect in special relativity

    I have an exercise: A distant camera snaps a photograph of a speeding bullet (speed v) with length b in its rest frame. Behind the bullet and parallel to its path is a meter stick, at rest with respect to the camera. The direction to the camera is an angle $\alpha$ from the direction of the...
  13. Jonathan Stanley

    B Special Relativity Self-Contradiction?

    From his original thesis, Einstein said light speed is always constant (c). There is very clear evidence for this. Every ray of light moves in the “stationary coordinate system” with the same velocity c, the velocity being independent of the condition whether this ray of light is emitted by a...
  14. Mr C Odd

    Time dilation in a magnetic field

    Hi all. I was wondering if time is dilated whilst traveling in a stable magnetic field that is generated by the object travelling, and if so, does this vary if you reduce or intensify the magnetic field? Also, what happens if the object is generating two opposing magnetic fields, would...
  15. Amanuel

    How to calculate the energy in gamma photons

    how do I calculate the energy of to photons moving in the opposite direction. starting from the same origin.
  16. E

    B Momentum in special relativity

    Although I thought that I understand special relativity enough, I cannot now clearly answer on the following question: What is the most direct derivation, why momentum in special relativity is ##p=\gamma m v##, where ##v## is velocity of the rocket? Let us assume that Lorentz equations are...
  17. C

    I Mass/Density Increase in Motion: Relativistic or Observable?

    Is the increase in mass/density of an object in motion purely relativistic? What I mean is if you were in a spaceship approaching the speed of light would you be able to measure a change in your mass/density or would the change only be observable to someone at rest. I'm aware of the Lorentz...
  18. M

    Physics How is it to work in numerical relativity?

    the problems/challenges that you have to face daily are mostly related to code issues with the physics itself? Is there room to improve our knowledge of fundamental physics while working on it? Do you enjoy doing it? why? I'm asking this because I'm considering working on numerical relativity...
  19. P

    Relative velocity in special relativity

    Homework Statement Imagine we are observing two aeroplaes from the ground and let their velocities be ##\mathbf{u}## and ##\mathbf{v}## respectively. Assume that the first plane has radar equipment permitting a measurement of the speed of the other plane relative to itself. The velocity so...
  20. R

    When Will We Arrive? Calculating Time Differences in Special Relativity

    Homework Statement : You are the first astronaut aboard a ship to travel to Alpha Centauri. Coincidentally, a scientist working on an outer space station post is one of your former classmate. Your ship, with your former classmate onboard, leaves the space station traveling at constant velocity...
  21. MeAndMyLucidLife

    Relative speed of two photons

    Homework Statement What is the speed of a photon with respect to another photon if: the two photons are going in the same direction. they are going in opposite direction? 2. The attempt at a solution I think the answer to the first question should be zero and to the second one be 2xC; C⇒speed...
  22. D

    Other What books to get before studying Quantum Mechanics and General Relativity?

    Hi. I want to learn - amateurishly - Quantum Mechanics, and General Relativity, but my experience with Physics is very small. I want to ask, what should I learn - what books should I read - before I start to learn those theories? Sorry for my english.
  23. Sandeep T S

    A General Relativity Book Recommendations

    Any one please refer some text for general theory of relativity, Also share some link of PDF about GTR
  24. V

    B Special relativity - frame of reference

    This must be a basic question. :) Bob and Alice have the same age. So in special relativity Bob leaves Alice and travels at very high speed and when it returns is younger than Alice. Bob's time is dilated and his space is contracted from Alice frame of reference. But now, if I take Bob's frame...
  25. N

    I Relativity of Simultaneity: Observers Perceiving 3 Events

    In looking at this light cone diagram, I'm focusing on the part in purple. I'm interested to know if mathematics reveals the exact potential difference in time perceived by observers of three events as they shift between their different planes of simultaneity. This makes more sense using this...
  26. Cryo

    A Electromagnetism for Media in Arbitrary Motion

    Hello To develop one interesting idea I need to be able to do calculations on (1) scattering of light from bodies in arbitrary motion, possibly at relativistic speeds; (2) Propagation of light in electromagnetic media that are in arbitrary motion (possibly relativistic). For example, I would...
  27. P

    A Is a volume element in relativity represented by a vector?

    Can we say that a volume element can be represented by a vector, or is there some hidden complication that makes this inadvisable? For some background, the stress-energy tensor has been described as the density of energy and momentum, in for instance MTW. So if one says that the represention...
  28. P

    I GPS relativity error - really?

    There are many popscience articles about relativity and how relativity is essential for GPS and in many is mentioned something like this: If GPS wasnt corrected for time dilation predicted by GRT, there would be an error of 12 kilometers in GPS positioning per day. But when I checked how GPS...
  29. FallenApple

    What is the Relativity of Wrong?

    I read the essay. It's a very interesting account of scientific progress. What type of scientific paradigm is this? It seems to have a very close feel to Bayesian Epistemology and/or Inference Quote from Wiki https://chem.tufts.edu/answersinscience/relativityofwrong.htm
  30. S

    B Using SR & Curved Coordinates for Time Calculation

    Someone told me that I don't need the whole mechanics of GR to be able to calculate the proper time in an accelerated frame of reference. I can just use SR but with curved coordinates and then integrate for time. But he didn't give me a reference where I could find the formula to do this. How do...
  31. M

    B Help with constant acceleration under special relativity

    Hi, I am trying to wrap my brain around special relativity equations but I'm struggling with the math. I am a computer programmer comfortable with the algebra and but never studied calculus or physics. Say I am already traveling at velocity "v" where "v" is approaching the speed of light. I...
  32. J

    B Is wave-particle duality a result of the relativity theory?

    Have thought about this for sometime but couldn't get deeper. I have speculated that wave-particle duality is a direct result of the relativity theory. Especially it could arise from the factor of length contraction (dimensionality reduction). So far, the particle reality is based on various...
  33. J

    I Difference between an electromagnetic field and a photon?

    So I'm kind of confused. The way I understand it, an electromagnetic field is just a regular electric field viewed from a relativistic point of view, meaning that since we see the charges moving relative to us, we feel like the particles and the fields created by them come closer together (I...
  34. J

    I Traveling at Light Speed: Is a Photon Stationary?

    If you were to travel alongside a train, as fast the train, to you the train would seem stationary. I read that if you were to travel along a photon of light, as fast as the speed of light, that photon would not seem stationary. Is this true? If so, why?
  35. 4

    I Measuring Time with Mirrors: Exploring Special Relativity

    Special relativity is replete with examples of turning mirrors into clocks. Place two mirrors across from one another, bounce light between them, and measure the time. But as I thought about this, when a photon hits the mirror, it is absorbed by an electron which moves to a higher energy...
  36. M

    B Exploring the Effects of a Tower at the Earth's Equator

    The Earth rotates around its own axis within 24 hours. Theoretically, if at the equator perform a tower with a height - H, ignoring its effect on the slowdown of the Earth's rotation (we assume that the material of low density), objects and other complications, at a certain height, the linear...
  37. Entr0pic

    Courses Should ALL physicists take a course in general relativity?

    I will be proceeding onto my masters degree in theoretical physics in about two months time. My goal is to learn as much as I can about quantum and statistical physics, as this is the field in which I would like to do my PhD. In my second semester, I have the chance to either study the...
  38. F

    Consolidating maxwells equation with relativity

    Hello I know that maxwells equations are consistent with relativity. The following thought experiment seems to imply otherwise so I am wondering where my mistake lies. Lets say we have some very large conductor loop(with a radius of many lightyears). At the center of the loop is some magnet...
  39. N

    I Exploring the Paradox of Relative Truth in Special Relativity

    As I understand it with an orthodox interpretation of Special Relativity, if in flat space there was a velocity difference between two inertial frames of reference, then observers in either could calculate the clocks in the other to be going slower. And it could be said that both views are...
  40. Sebastiaan

    I Effect of Relativity on Laser Sail Acceleration

    Question, does general or special relativity have any effect on the acceleration of laser sail from an external observer? Let's say a laser-sail is first accelerated to 0.2c. Ignoring diffraction, Due to redshift, the incoming laser beam would get stretched by 20%, reducing the power by 20%...
  41. F

    I Reconciling two observers in two frames

    I am not a physicist—not even close—just a guy who, for some crazy reason, decided to try to understand some of the basics of relativity. I’d like to understand them well enough to be able to explain them (correctly) to another lay person. I’m trying to see how much I could explain without...
  42. T

    I Can Relativity Be Confirmed Again with a Star and a Black Hole?

    A star and a black hole again confirm Relativity. https://www.space.com/41291-relativity-revealed-milky-way-core.html
  43. platosuniverse

    B How can any physical body truly be at rest?

    Can we truly have a rest frame or should it be a close to rest frame? Even if I'm stationary and sitting on my porch and the observer in the car passing is moving, I'm still not at 0 velocity. The Earth is moving at 67,000 mph and the galaxy is moving at 250,000 mph. I'm never in a single...
  44. F

    I Can an object be both a black hole and not a black hole?

    According to Special Relativity, objects moving fast have more mass than objects at rest. So what if there is an object having a mass density near that required to create a black hole. Now if it were moving fast enough as well, it would gain enough mass density to become black hole. But to the...
  45. Osvaldo

    I Circle tangential velocity approaching c

    When a merry go rounds tangential velocity approach c, and horses look closer than when at rest, what is reduced, angular velocity or radius?
  46. H

    B Maxwell's EM Theory vs Principle of Relativity

    What was the problem between Maxwell's EM theory and the principle of relativity? Why went the theory against the principle? I understand that the EM theory says that Light was a wave and ether is it's medium. On the other hand the principle of relativity says that there is no state of...
  47. K

    I Understand Relativity w/o Math: A Different Framework

    Is there any way of obtaining the exact same theory of Special/General Relativity but using a completely different framework? That is, without manifolds, without vectors, etc...
  48. platosuniverse

    B Do photons interact with spacetime?

    The way I understand this is that Relativity says space-time is like a field that's affected by the way mass moves through it. Photons are massless so is this why the speed of light is the same in all reference frames?
  49. frostysh

    What representation of time did Poincare use in his work in 1905?

    Recently have a discussion with a Scientist (myself is not a Scientist, but trying to become :P), about priority of Einstein and Poincarè for Special Relativity Theory invention in Science. Those, what actually contribution of Einstain, what actually contribution of Poincarè and what...
  50. Subrahmanyan

    Relativity Books for learning the maths used in learning Relativity

    Can anyone suggest a book from where I can learn the math used in relativity like Tensors,Minkowski spacetime metric ,etc ? A suggestion of pdfs would also be appreciated?
Back
Top