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. 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...
  2. 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...
  3. 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?
  4. 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...
  5. 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...
  6. 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...
  7. 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...
  8. 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...
  9. 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%...
  10. 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...
  11. 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
  12. 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...
  13. 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...
  14. 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?
  15. 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...
  16. 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...
  17. 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?
  18. 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...
  19. 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?
  20. RealKiller69

    Special relativity and Lorentz factor problem

    Homework Statement There are 2 particles(1,2) separated ∆x=L moving with the same velocity u_x in frame of reference S , there's an other reference S' moving at v . I have to calculate ∆x'. GAMMA(LORENTZ'S FACTOR) Homework EquationsThe Attempt at a Solution I have done x1=0 when t=0 So for...
  21. R

    I Relativity of Time for Two Observers

    I have the following dilemma and ask for advice: Observer A is swings on the springs, while the observer B is stationary nearby. (See diagram: http://www.frozman.si/slike/Vzmet.jpg ) According to the theory of relativity to observer A the time flows slower due to its speed (as in the paradox...
  22. Philip Dhingra

    I Feedback Requested: Special Relativity Simplified by Phil

    I took a stab at simplifying Special Relativity, but I want to be 100% sure I'm not butchering physics in the process. Anybody care to weigh in on that? Here is a draft of my Medium article: https://medium.com/@philipkd/special-relativity-explained-with-a-deck-of-cards-f99bfd873bd5 Thanks, - Phil
  23. Mohammad Hunter

    I General Relativity & Gravity: Exploring the Conundrum

    So the other day I saw a YouTube video on how gravity works according to general relativity. From what I understand, objects bend space_time with their mass and create a shape which is close to a cone. Since objects only move forward in time through a straight line, the bent space_time makes...
  24. P

    B Layman's Question about Special Relativity

    I'm just an undergraduate with a layman's interest in Physics. With regards to special relativity, I think I grasp the concept that the laws of physics are the same for all observes in uniform motion relative to one another. So if I am standing still and a spaceship zooms past me at 80% the...
  25. N

    I What time structure supports info moving backward in time?

    This of course is speculative, but IF faster-than-light travel (or wormhole tunneling or some other exotic means) was found to be able to communicate information from the future to the present, what would that indicate about the structure of time? Some might argue that indicates a block-type of...
  26. TeeTex

    Relativity What are some recommended books on relativity?

    Hi guys, i am preparing my self for the second year in physics and i have subject about relativity but i couldn't find any good book about it, that contains : Lorentz transformations, relative motion, stellar abbreviation,sequence of events connected causally, minkowski, co-variance of dynamics...
  27. Cocoleia

    Momentum dealing with decay, special relativity

    Homework Statement A particle A (mother particle) with a mass of mA decays to two particles B and C (daughter particles) with mass values of respectively mB and mC. Calculate momentum of the two daughter particles, pB and pC. (at first the mother particle is at rest) Homework Equations The...
  28. U

    I How does gravitational time dilation work?

    I understand time dilation due to speed, but am confused on why time dilates depending on the distance from a mass. Help?
  29. 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...
  30. Z

    How was Newtonian relativity ruled out in EM propagation?

    What I've read on the Michelson/Morley experiment explains that it made the idea of the luminiferous aether seem less likely, but I don't think I've ever seen an explanation of why everyone didn't just assume that light follows normal Newtonian relativity. What I mean is this: according to...
  31. S

    A General relativity: time dilation and speed of light

    Hello everyone, I'll go straight to the question. The gravitational time dilation is equal to tearth = tspace*sqrt(1 - rs/r), with rs = 2GM/c2. However, the formula for speed of light in gravitational field is equal to v = c(1 - rs/r). My intuition tells me that these two formulas must be the...
  32. K

    I Lie Derivative in Relativity: Examples & Uses

    Can someone point me some examples of how the Lie Derivative can be useful in the General theory of Relativity, and if it has some use in Special Relativity. I'm asking this because I'm studying how it's derived and I don't have any Relativity book in hand so that I can look up its application...
  33. starstruck_

    I Relativity and speed of light basics

    I decided to read up on the chapters we didn’t cover in first year Physics from my textbook, and decided to start with general relativity since it was in the same section of the textbook as the last topic we covered (that topic was physical optics - not lenses- photons and the double slit...
  34. 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...
  35. K

    B Lack of Numerical Examples in Relativity & Quantum Mechanics: Exploring Reasons

    It's rare to encounter concrete, numerical examples of what is being taught about Relativity, Quantum Mechanics.. On the other hand there's plenty of numerical examples in the undergraduate general physics textbooks, for instance problems of mechanics. As for General Relativity I did find only...
  36. 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...
  37. R

    B What is the theory of relativity?

    Is the Theorey of relativity that there is no absolute movement, only movement of one frame relative to another or that there is absolute movement but we cannot measure it ?
  38. 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...
  39. 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...
  40. 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...
  41. 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...
  42. Giulio Prisco

    I Einstein-Bohr "photon box" debate and general relativity

    I see this has been already discussed but the old threads are closed. EPR before EPR: a 1930 Einstein-Bohr thought experiment revisited "In this example, Einstein presents a paradox in QM suggesting that QM is inconsistent, while Bohr attempts to save consistency of QM by combining QM with the...
  43. M

    Space Travel & Relativity: Is it Possible?

    I had a bit of a thought experiment the other day, does relativity mean that technically you couldn’t travel faster than the speed of light to the observer. But if you were traveling from Earth to another planet, could you technically be traveling faster than the speed of light relative to the...
  44. 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...
  45. ohwilleke

    I What false hints of new physics were most notable?

    Sometimes experimental or observational evidence from credible physicists points to new physics and then turns out to be wrong due to statistical flukes, experimental error or a theoretical analysis mistake. What cases of this happening do you find most notable, what showed that the hints were...
  46. K

    I Lie Algebras & Relativity: Usefulness & Purpose

    What's the usefulness of a Lie Algebra? As I see on Wikipedia a Lie Algebra is a vector space with an operation on it called Lie Bracket.. This seems to be the formal definition. In Relativity, we have the Lie Algebra of the Lorentz group, the Lie Algebra of the Poincaré Group, which are those...
  47. binbagsss

    General Relativity - geodesic - affine parameter

    Homework Statement Question attached: Homework Equations see below The Attempt at a Solution [/B] my main question really is 1) what is meant by 'abstract tensors' as I have this for my definition: to part a) ##V^u\nabla_uV^a=0## but you do say that ##V^u=/dot{x^u}## ; x^u is a...
  48. C

    I The deviation of Universe expansion from general relativity

    What is the deviation in the expansion of the universe exactly quantified, when I would assume general relativity and project it backwards? As a statistician I am asking for data, for either the backwards projected general relativity case and either the real expansion case, as it is...
  49. 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.
  50. W

    I Accuracy of Relativity vs Quantum Mechanics Measurement

    Just for a bit of fun, which theory , relativity or quantum mechanics has the most accurate ( i.e to how many decimal places confirmation between theory and experiment) measurement ever made?
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