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. R

    Intro special relativity problem regarding time dilation

    This example is worked out in the book, and at the beginning, they make the assumption that the muon is traveling at c, and then find the change in time from the Earth reference frame using delta t=100km/c. Then delta t is plugged into the time dilation equation on the left side and we solve for...
  2. Kaguro

    Fractional increase of energy vs momentum with relativity

    My attempt: ##E^2 = p^2c^2 + m_0^2c^4## ##2E dE = 2pc^2 dp ## ##\frac{dE}{E} = \frac{pc^2}{E^2}dp=\frac{p^2c^2}{E^2}## % (dp/p = 1%) ##=\frac{E^2-m_0^2c^4}{E^2}## % ##=1-\frac{m_0^2c^4}{E^2}## % ##=1-\frac{m_0^2c^4}{m^2c^4}## % ##=1-\frac{1}{\gamma ^2}## % ##=\frac{v^2}{c^2} ##% =0.81...
  3. F

    B Energy Conservation in Relativity: Perpetual Motion?

    This is very much, a ... what's wrong with this approach... Consider a large mass with no atmosphere, i.e. the moon. On it, construct a tower of arbitrary height. On the tower build an energy to mass machine, to convert energy to mass via E=mc^2. Once the mass is created, drop it from the...
  4. F

    Magnetic and electric fields in relativity

    I started from: $$\frac{d}{dt}(m\gamma v_x)=qE\ \ \ \rightarrow \ \ \ m\gamma v_x - p_{0x}=qE(t-0)\ \ \ \rightarrow \ \ \ m\gamma v_x=qEt+p_{0x} $$$$\frac{d}{dt}(m\gamma v_y)=0\ \ \ \rightarrow \ \ \ m\gamma v_y -p_{0y}=0\ \ \ \rightarrow \ \ \ m\gamma v_y = p_{0y}$$$$\frac{d}{dt}(m\gamma...
  5. F

    Annihilation: calculation of photon energies

    I set up this problem this way: ##p_a^{\mu}=(E, \sqrt{E^2-m^2}, 0, 0)## ##p_b^{\mu}=(m, 0, 0, 0)## ##p_c^{\mu}=(2E_\gamma, 2E_\gamma, 0, 0)## I have chosen to consider the two photons as a single particle of energy equal to ##2E_\gamma##. At this point I applied conservation of the...
  6. Leo Liu

    Relativity Is it worth to read the chapters on relativity in K&K mechanics book?

    Hello. I have almost finished Kleppner's Newtonian mechanics book except the part discussing special relativity. I plan to read Purcell's EM book after finishing it. I've heard some people saying that Purcell presents some of the EM concepts in a relativistic way, so I am a bit worried that I...
  7. G

    Possible to publish a paper that contradicts Einstein's special relativity?

    Summary:: Is it possible to publish a paper contradicting Einstein's special relativity in any high-ranked Journal? Which Journal is the best, i.e. open minded, for such a paper? I plan to publish a new theory of electromagnetics in a Journal. The findings are purely through strict...
  8. Peter Martin

    B Einstein's train-lightning scenario doesn't demonstrate relativity

    The popular account of Einstein's train-and-lightening thought experiment doesn't demonstrate "the relativity of simultaneity" as it is always claimed. In fact, it does the opposite: By describing the embankment observer as "at rest" relative to the strike locations and the train passenger as...
  9. F

    Minimum energy of a photon to produce ##\pi^+##

    I have a doubt about the first request: I suppose to find the minimum energy of ##\gamma## in the situation where ##p## is stationary, there is no reason to say that the proton is stationary if I were to calculate it in the CM, right?. So I have to consider che LAB-frame to find ##E_\gamma##...
  10. F

    I What tests can falsify general relativity?

    I know that general relativity fails in singularities like the center of a black hole or the big bang. GR also fails at fundamental particle levels like electrons, protons and neutrons etc. I.e. GR cannot explain interactions of various fundamental particles?? (Am I correct?) But these does...
  11. T

    B On the four dimensions of special relativity

    Hello. Questions: How can special relativity describe four dimensions when we only see three spatial dimensions and we experience time?Why time is the fourth dimension and not another physical quantity? Is this only a generalisation that was needed to describe more physical phenomena and the...
  12. T

    Time dilatation between straight and curved lines in Minkowsi space

    Summary:: Special relativity - 2 astronauts syncronize their clocks and moves in different paths at different velocities, which clocks is left behind? and why? Hi everyone, i have the following problem and I'm not understanding if my strategy to solve it is correct: Two astronauts synchronize...
  13. E

    I Relativistic Velocity, Perp. Accel., Momentum: Explained

    A stationary observer sees a particle moving north at velocity v very close to the speed of light. Then the observer accelerates eastward to velocity v. What is its new total velocity of the particle toward the north-west relative to the observer? I ask because while the particles total...
  14. D

    I Exploring Matter in General Relativity: Understanding the Lagrangian

    I was going over the Einstein-Hilbert action derivation of the Einstein field equations and came across a term that does not seem to be explicitly defined. That term is the Langragian for the matter fields. What exactly is matter in General relativity in the context of the Lagrangian? Here is...
  15. Qwet

    I Conservation of energy in general relativity

    Hello. I have a question about the law of energy conservation in GR. As time is inhmogeneous, we don't have energy-momentum 4-vector which would be preserved during system's dynamical change. It is only possible to define 4-vector locally. And next, the problem regarding how to sum this vectors...
  16. StenEdeback

    Relativity Good introductory book about general relativity at undergraduate level

    Summary:: I am looking for a good introductory book about general relativity at undergraduate level. I am looking for a good introductory book about general relativity at undergraduate level.
  17. SirMadame

    I Self-Study General Relativity: After Multivariate Calc in HS

    I just finished multivariate calculus (without any linear algebra experience yet) and I am seeking out a path to understanding General Relativity. I am wondering what are the mathematical fields after multivariate calculus that I need to master before beginning to understand GR, and what...
  18. iVenky

    B Mass Reduction in Combustion: Real or Myth?

    I have studied in high school that all chemical reactions obey conservation of mass, as the atoms are merely re-arranged, but when I read through special relativity, I was reading that you can show an infinitesimal change in mass (based on E=mc2) in combustion that's not noticeable that's being...
  19. starkreactor

    I Thought Exp: Gen Relativity & Time Dilation

    I am trying to understand a thought experiment I just posed, which is: if an observer is traveling near the speed of light, and sends out two photons; one in the direction of travel and one in the opposite direction, how does general relativity account for time dilation? The photon "in front"...
  20. phoenix-anna

    B First Experimental Confirmation of GR

    Trying to understand how Einstein predicted the appearance of stars during the solar eclipse around the turn of the 20th century (the first experimental confirmation of General Relativity, I believe). My impression, which is not physically correct, is that the sun attracts the photons as they...
  21. Charlie K Trout

    I Explore Alternative Interpretations of Special Relativity

    A few years ago, a nuclear engineering professor explained to the class that the widely accepted theory between the relationship between space, time, and velocity may be wrong. At the time, I didn't think much about it since he had a lot of out-there beliefs and he seemed to be a bit of a...
  22. G

    Relativity David Morin's special relativity for the enthusiastic beginner

    1.8 Exercises page 49 I can't find the solutions to the questions. Where are they?
  23. G

    Textbook: "Special Relativity For the Enthusiastic Beginner" question....

    Special Relativity: For the Enthusiastic Beginner on page 49 1.8 Exercises I can't find the answers to the questions? I apologize if this is a dumb question.
  24. Martian2020

    B General Relativity and the curvature of space: more space or less than flat?

    General relativity. Curvature of spacetime: ok. time dilation: ok. What about space? Curvature is intrinsic and given by complex equations. But could we definitely say is there more space between 2 points along curved space through the star than would be through flat space (no star there) or...
  25. F

    I Momentum Conservation in Special Relativity: mwu

  26. robphy

    B Einstein's Universe (1979) - Nigel Calder, Peter Ustinov

    In contributing to the thread https://www.physicsforums.com/threads/i-need-recommendations-to-read-about-physics.996304/ , I see that the video that greatly influenced me to study relativity is now available online on YouTube (made available by the film distributor). In 7th-grade, after...
  27. I

    B Doubt about the relativity of simultaneity

    (I hope my English is understood). Hello, I have a question regarding the relativity of simultaneity. The mean temperature of the cosmic microwave background tells us how big the universe is with respect to the recombination epoch. If I now measure that the mean temperature of the cosmic...
  28. D.S.Beyer

    B Lagrangian Point in General Relativity

    Is there a relationship between the Lagrangian ‘hill diagram’ and the spacetime curvature embedment graphs? The Lagrangian map shows effective potential, which deals with centrifugal force. As centrifugal force is a fictitious force (and gravity is as well), I would assume the underlying...
  29. LCSphysicist

    Special relativity — Observer measuring the velocity of a passing rocket

    I am a little confused with the text above. Actually, all is ok until 2.51, i think i am missing something. What is this? Another way to define gamma? (The doubt is not about the raising indices, neither about "n00 = -1", is just where does the equation came from. That is, the equation is easy...
  30. SamRoss

    I Gravitons Replacing General Relativity: Can it Work?

    Einstein's theory describes gravity as a curvature of spacetime. As such, everything is affected by it. This includes light, which has no mass, as was made clear for the first time during the famous 1919 solar eclipse. In the standard model, the cause of gravity is supposed to be gravitons...
  31. R

    I Special Relativity: Intuition & Quantities Explained

    Hi, I'm taking an introduction course to Special Relativity and encountered a fairly simple problem: Dirac travels to alfa centauri, which is 4.37 lightyears away. He stays there one Earth year and then travels back, and when he comes back he has aged 5 years. At what speed did he travel...
  32. Amrator

    Relativity: Force and a Collision

    I don't know if I did this correctly. ##\int Fdx = \int dE## ##F \Delta x = \Delta E## ##Fx = Mc^2 - (mc^2 + mc^2)## ##M = \frac{Fx + 2mc^2}{c^2}## ##M## is the mass of the resulting particle. ##2mc^2## is the total energy before the collision. The issue is I'm assuming that the resulting...
  33. ThisTimeTomorrow

    I Logic question on relativity- no math

    Checking my understanding. Can it be said that it is the overlap of the reach and effect of each of the 4 forces, from each respective point of origin possible within the universe, that gives us universal general relativity? Like the most intricate gear set ever? Could it then also be said...
  34. J

    Special Relativity - relative motion of two bars

    Hi, I'm stucked in this exercise. I don't know how to proceed. Any hints I appreciate it.Two bars of the same proper length L, moves in the same way on the x axis. In the referential of one of the bars the time interval between the events, when the extremity right of one bar and the extremity...
  35. S

    Compton Effect with the electron initially moving

    Hello! I do not understand how to prove the exercise. I have searched all over but I have found no hints on how to get started. Can anybody help me?
  36. LCSphysicist

    Relativity problem -- A person walking in a train that is traveling at 3c/5

    "(a) How much time does this take in the ground frame? (b) What is the person’s speed with respect to the ground? (c) How much time elapses on the person’s watch?" I solved it, but i am with a doubt yet wrt to the letter b. We can find that the train length in the ground frame is 4L/5, so, why...
  37. F

    I Special Relativity & Non-Instantaneous Force Equations

    In classical mechanics, the gravitational force is described by the equation: F = Gm1m2/r^2 What would this equation - or other similar equations - look like in special relativity? This equation cannot be correct because it implies that the force acts instantaneously.
  38. LCSphysicist

    Confused about relativity and a train

    We can find the difference of time to light reach both clocks, it should be Lv/c², what i am confused is why the rear clock show a higher reading of the front clock. Ok, the light take longer time to travel and reach the rear clock, and here is the thing! What i am interpreting is: When the...
  39. Amaterasu21

    I How Does Relativity of Simultaneity Clash w/Thermodynamics?

    In special relativity, observers can disagree on the order of events - if Alice thinks events A, B and C are simultaneous, Bob can think A happened before B which happened before C, and Carlos thinks C happened before B which happened before A - provided A, B and C are not causally connected, of...
  40. F

    I Acceleration in Special Relativity

    Can special relativity handle acceleration? I believe the answer is yes, but I don’t recall dealing with any acceleration problems when I took SR. I remember using the time dilation, length contraction and Lorentz transformation equations. These equations all assume constant motion iirc.
  41. F

    Calculate a specific boost and rotation

    Let's begin with the first point. a.I) Apply a generic boost in the y-z plane (take advantage of the arbitrariness in deciding the alignment of the y and z axes). \begin{equation*} B_{yz} = \begin{pmatrix} \gamma & 0 & -\gamma v_y & -\gamma v_z \\ 0 & 1 & 0 & 0 \\ -\gamma v_y & 0 &...
  42. S

    Can Flying Ships Defy Inertia and Make Instant 90-Degree Turns?

    I haven't gone to movie theaters in 6 months. So I have to be content with online movies, and reading sci fi models, and maybe writing a short story or two. If a flying ship could travel thousands of miles per second, it can't suddenly turn 90 degrees because of inertia, the occupants would be...
  43. T

    A Alternative theories to General Relativity

    Hey there.Have you read about the alternative theories proposed by other scientists to General Relativity?So far General Relativity still stays the most accurate.But if we could generalise it?Perhaps try with some new maths like complex differentiable manifolds or Lie groups or another...
  44. AHSAN MUJTABA

    General Relativity: How many Christoffel symbols?

    Actually I know there would be some permutations used here. I know how to calculate the symbols but estimating is quite a new thing to me
  45. Boltzman Oscillation

    I Particle Perspective: How Relativity Affects Us

    Some background, I am an undergraduate electrical engineering student with a knack for physics. I plan to attend graduate school for physics but for the meanwhile I've only taken an undergraduate course in QM mechanics, which used griffith's book, and a modern physics course, which covered some...
  46. thequantumcat

    I Special Relativity and Velocity

    I can't seem to wrap my head around it: if an object is moving at speed v in frame S, and its observed to move at speed v' in S', what is the relationship?
  47. F

    I Why Does Special Relativity Not Contradict General Philosophy?

    I hear that philosophy refuse to "relativity concepts"(e.g relativity moral).Relativity theory says about the relativity of spacetime.I do not understand why special relativity does not contradict with general philosophy?(I know the theory Idea Form of Plato)
  48. Data Base Erased

    I Beginner question about tensor index manipulation

    For instance, using the vector ##A^\alpha e_\alpha##: ##g_{\mu \nu} e^\mu \otimes e^\nu (A^\alpha e_\alpha) = g_{\mu \nu} (e^\mu, A^\alpha e_\alpha) e^\nu ## ##g_{\mu \nu} e^\mu \otimes e^\nu (A^\alpha e_\alpha) = A^\alpha g_{\mu \nu} \delta_\alpha^\mu e^\nu = A^\mu g_{\mu \nu} e^\nu = A_\nu...
  49. fingerprintregion

    Relativity: Relativistic Kinematics and Dynamics

    I’ve read Beiser’s Modern Physics Chapter 1 and I am able to grasp the general theories but not so much when applying it to problems. I major in Chemistry and would really appreciate any head start/help/suggestions. For number 1 I thought of using L = L0 sqrt 1-v^2/c^2 but can’t seem to find the...
  50. S

    Courses Statistical Physics vs QFT vs General relativity

    Good day, I'm starting my master in physics, and it's time for me to choose my courses. I will take one or two of the following three courses, which are: Statistical Physics, QFT and General relativity. Now, I'm finding it very hard to decide as on the one hand, I'm interested in QFT and...
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