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.

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  1. N

    B General Questions about Special Relativity

    There are a few fundamental questions I wanted to ask about related to special relativity: 1) Firstly, is there an intuitive explanation for length contraction and why lengths are relative? For example, the fact motion is relative is intuitive. E.g. someone sitting inside a train moving 60...
  2. MelissaBlaze

    Question about relativity and distance

    If someone left the Earth on a spacecraft traveling .99% the speed of light for a distance of one light year, and time slowed on the spacecraft relative to the earth, approximately how much time would the person on the spacecraft experience when arriving at the destination? (I'm leaving out...
  3. J

    Relativity Differential Forms and the Geometry of General Relativity

    Hello, I would like to know if anybody here has used the book "Differential Forms and the Geometry of General Relativity" by Tevian Dray and how they found it. Thanks!
  4. scientepid

    I How can you visualize the Higgs field, or can you?

    Just when I thought I had finally wrapped my brain around relativity, Quantum theory took off. Then the Higgs Boson was discovered. How does the Higgs field under-pin relativity, namely space-time? How is the Higgs field distributed? Does it have curvature like space time, or is omnipresent...
  5. V

    Relativity of motion and astronomy

    Greetings, One of the basic postulates of relativity is that the laws of physics hold equally well in all frames of references. This got me wondering about the geocentric model of solar system which necessarily gives rise to motions of peculiar kinds. For example, the epicycles, which are...
  6. TheAnt

    B Study Special Relativity: 6th Formers, Books & Websites

    Hello, I have often heard special relativity was not too difficult to study. I was wondering as a 6th former what knowledge is needed to do so and if it was even possible at my level. If yes does anyone suggest any good books or websites? I am searching for a more in depth mathematical...
  7. A

    B Einstein's relativity of simultaneity & quantum paradox.

    Einstein's relativity of simultaneity & quantum measurement paradox. Suppose a rocket traveling close to the velocity of light which emits a single photon from its midpoint at point A, illustrated below. The rocket is equipped with a single detector drawn in green at the front of the rocket...
  8. Deepak K Kapur

    Nobel Prize in Physics for Relativity?

    Why didn't Einstein get Nobel Prize for ' Relativity' Has anyone else been awarded Nobel Prize for 'Relativity'?
  9. tomasbede

    I Could I travel to andromeda in my lifetime?

    Hi, this is my first post on here. Let's say I departure from Earth in a spaceship and reach a speed very close to c, as I go faster time would run slower and I would feel as if I was going faster and faster with no speed limit, even though I'm not going faster than c. Because my time is...
  10. Daleri Mc Rileda

    B How is the Age of the Universe Determined?

    How can the age of the universe be determined when there is no absolute measure of time or distance in the universe. Every other place in the universe has another rate of the passing of time. Since time expands with the expansion of space, trying to use expanded time to measure time is circular...
  11. C

    A problem regarding Galilean relativity

    Homework Statement Two bodies are moving on the same line. When they move away from each other the distance between them changes for 16m in a time interval of 3 s (Δd1 = 16 m ; Δt1 = 3 s). When they move towards each other the distance between them changes for 3 m in a time interval of 3 s (Δd2...
  12. t_r_theta_phi

    I Metric for Infinite Rod in Gen. Relativity

    What is the metric for the spacetime around an infinitely thin, infinitely long, uniform rod? Could it be written in the form ds2 = A(r)dt2 + B(r)dr2 + C(r)dh2 + r2dθ2 where h is the coordinate along the rod and r is the radial coordinate, or would it be something more complicated?
  13. Daleri Mc Rileda

    B How Far Is It To The Center Of The Milky Way/Tootsie Pop?

    With length contraction being ever increased while approaching the mass of a black hole singularity, how does one measure the distance to the virtual infinite contracting frames of reference of time and space /distance of the singularity? Related question : How can one measure the size of a...
  14. Basicsofphysics

    A A Unified Theory of Relativity and Particle Physics

    Is there a peer reviewed paper that proposes a way to connect the relativity of time dilation, length contraction and the relative effects of gravitation per acceleration with respect to mass with the standard model of particle physics? An established theory which also takes into account both...
  15. Meddusa

    I Action in Relativity: Non-Relativistic vs Relativistic Particles

    Hi, I found that action in relativity is written in two ways: 1) S = ∫ ds 2) S= -mc ∫ ds is (1) for non-relativistic particles and (2) for the relativistic particle ? why there is a minus sign in front of it? I read that writing (2) is up to a guess (-mc term), is it very interesting...
  16. J

    Relativity On Sean Carroll's General Relativity textbook

    I have heard/read that Carroll's Spacetime and Geometry: An Introduction to General Relativity is one of the best books on General Relativity but its price is insanely high! Does anybody know any place which sells it at a lower price than, say, Amazon? If not, what are other books that cover...
  17. P

    Special Relativity- Photon/Mirror Collision

    Homework Statement A photon of frequency ν is reflected without change of frequency from a mirror, with an angle of incidence θ. Calculate the momentum transferred to the mirror. Homework Equations E= hν Conservation of four-momentum The Attempt at a Solution If the mirror is in the x-y...
  18. U

    A simple Proper Time Calculation

    Homework Statement Suppose a spaceship starts from rest from a space station floating in deep space and accelerates at a rate of |a| relative to the space station for 1.0 Ms. It then decelerates for the same amount of time at the same constant rate |a| to arrive at rest at another space station...
  19. mertcan

    A Stress energy tensor general relativity

    Hi, I would like say that in this link ( ) and starting from 56.28 Suskind tries to find the energy tensor equation using \phi, afterwards he finds a equation similar to wave equation in terms of \phi. My question is: For what does \phi stand ? I could not capture the meaning of \phi. Could...
  20. Tony Weston

    A Exploring Bell's Theorem with Relativity (No Superluminal Comm.)

    Hi... New to this forum. Be kind! I did not study physics at university, and consider myself an armchair physicist. I am a computer programmer by trade. I first came across Bells inequalities a few years ago, while working with a fello programmer who did have a PHD in physics. Its pretty...
  21. B

    Programs Transferring Math PhD Programs?

    Math grad student here. I'm currently finishing up my first year in a PhD program, and I based on my experiences so far I can definitely say graduate school is something I want to continue. I spent my first year taking courses in preparation for prelims rather than doing research, but I did well...
  22. D

    I Special relativity and magnetism

    I've read in various places that magnetism can be explained in terms of the effects of special relativity. However, all of the explanations of this only mentioned the case of current flowing in a wire. Can special relativity explain the magnetism of free flowing electrons and other moving...
  23. A

    I Galilean Relativity: Can Experiments Tell Motion Relative to Other Frames?

    In Galilean Relativity, laws of mechanics are invariant across frames. In all the frames they are the same. So, in Dynamics and Relativity by W.D.McComb, it is written that this implies you cannot perform any experiment in an inertial frame that can tell whether an inertial frame is moving or...
  24. A

    A Metric with Harmonic Coefficient and General Relativity

    Goodmorning everyone, is there any implies to use in general relativity a metric whose coefficients are harmonic functions? For example in (1+1)-dimensions, is there any implies for using a metric ds2=E(du2+dv2) with E a harmonic function? In (1+1)-dimensions is well-know that the Einstein...
  25. A

    I Understanding General Relativity: A Guide

    I am reading general and special relativity from a book and I am stuck with these lines please can someone provide its detailed explanation "Einstein demanded that the special principle of relativity should be valid also for Maxwell’s electromagnetic theory. This was obtained by replacing the...
  26. G

    I Parametrizing a path through spacetime

    It is customary, when discussing a particle's motion through spacetime, to talk about its path x^{\mu}(\lambda) , where x^{\mu} are the the spacetime coordinates of the particle in some frame, and \lambda is some parameter. I have a doubt regarding this parameter. Everywhere I've looked...
  27. E

    I Meaning of the equivalence principle in General relativity

    It is known that equivalence principle is good for understaning of general relativity (GR). This means comparison of the elevator and falling in homogenic gravitational field. But, I here somewhere something like "in the higher lever of GR, let us forget on principle of equivalence". How it is...
  28. Sachin_Vaidya

    Exploring Why Time Perception Changes: Is Relativity at Play?

    Why time perception changes continuously...? Could relativity be playing some role?
  29. nomadreid

    I Reconciling Simultaneity & Relativity: Navigating the Spacetime Maze

    Oops, forgot to finish the title, but don't see how I can edit it. Sorry. How does one reconcile the idea that, according to relativity, one cannot talk of simultaneity, yet one can talk of a slice of spacetime to be space where all the points are at the same time? That is my main question...
  30. PabloAMC

    A Problems between Quantum Mechanics and General Relativity

    I have read several times that general relativity has some problems with quantum mechanics and they are not compatible. However, special relativity can be introduced in quantum mechanics mainly by Dirac equations (so I am pretty sure that the problem of passing from a frame where the parameter...
  31. S

    Relativity What Are Good Beginner Books on General Relativity with Mathematics?

    HI, can anyone suggest a good book on general relativity with fairly good mathematics for beginner for self study?
  32. Clever Penguin

    B Deriving Special Relativity Formulae Steps

    I was bored, so I decided to derive the special relativity formulae. I drew the following diagram of a light clock: In order to find t, I did sinθ=d/ct Which gives tsinθ=d/c Which gives t=d/csinθ If v = 0, vt = 0, and θ = 90 sin90 = 1 t = d/csinθ = d/c We call this t0If v is greater than 0, vt...
  33. wolram

    B On the relativity of red shift

    arXiv:1605.08634 (cross-list from physics.pop-ph) [pdf] On The Relativity of Redshifts: Does Space Really "Expand"? Geraint F. Lewis Comments: 6 pages, 5 figures, appeared in Australian Physics Journal-ref: Australian Physics (2016), 53(3), 95-100 Subjects: Popular Physics (physics.pop-ph)...
  34. DaTario

    I Quantum Mechanics & Relativity: Vacuum Connection?

    Hi All, Once in the past I have heard that the vacuum in quantum mechanics, having its energy given by ## \sum_n \frac{1}{2}\hbar \omega_n ## was also obtained by methods of Einstein's relativity, through the claim that the vacuum should be a field which is invariant under a boost...
  35. P

    I Special relativity of two clocks

    Why is it that for two clocks that are synchronised in one frame, S, but not in another, S', is there an offset in the time by a factor of ##\frac{Lv}{c}##, as measured in S'. Where L is the proper length of the body, as measured in S. I'm confused as to why there is not a factor of ##\gamma##...
  36. i_hate_math

    Calc Time for Electron to Travel 100m in Lab Frame

    Homework Statement This is an extract of a very long question. The electron is moving relative to the lab at 0.98c. In the reference frame of the electrons, calculate the time required for an electron to travel the length of a beam pipe which has a proper length of 100 m measured in the...
  37. Gerald Kaiser

    Are temperature and pressure related by relativity?

    Since the temperature of a gas is related to its average molecular energy and the pressure to the average molecular momentum, it would seem that a Lorentz transformation would somehow relate the two. Does anyone know of related work?
  38. zdroide

    I Is there a real need for a theory of everything (ToE)?

    I been studying quantum field theory and standard model lately. I not see how a unified theory could fit between quantum field and special or general relativity. One being for big objects and the other for microscopic one. In fact, standard model not seem to be all proven. Many particles are not...
  39. Kara386

    Special relativity muon example

    Homework Statement Here's a standard example of special relativity in action: The mean lifetime of the muon as measured in a laboratory is about 2µs (rounded to 1 s.f.). Thus, the typical distance traveled by a muon should be about ##3\times 10^8ms^{-1}\times 2\times 10^6s = 600m##. The...
  40. Chris Frisella

    EM Phenomenon: Magnetism from a Cathode Ray?

    I have recently studied about relativity being the reason for magnetism. The example given was about a magnetic field generated from current down a long wire. When two such wires with current in the same direction were parallel to each other there was an attractive force between them because...
  41. V

    (Special relativity) Two masses connected by spring

    Homework Statement Hi all--humanist here. Now that the semester is over, I am taking the opportunity to (attempt to) self-study introductory SR. This is problem 12 in chapter 1 of Special Relativity by AP French. (1-12) A body of mass m1+Δm is connected to a body of mass m2-Δm by a spring of...
  42. philipp

    I Time dilation in special vs. general relativity

    Hi all, I was trying to understand the time dilation in special and general relativity and after much time of "overthinking" I am pretty much stuck now. My problem is, that what seems to me to be the same premises apparently imply opposite things. In special relativity, for two inertial...
  43. D

    A Interpretation of the EM tensor as a rotation matrix

    In special relativity, the electromagnetic field is represented by the tensor $$F^{\mu\nu} = \begin{pmatrix}0 & -E_{x} & -E_{y} & -E_{z}\\ E_{x} & 0 & -B_{z} & B_{y}\\ E_{y} & B_{z} & 0 & -B_{x}\\ E_{z} & -B_{y} & B_{x} & 0 \end{pmatrix}$$ which is an anti-symmetric matrix. Recalling the...
  44. i_hate_math

    When Will the Proton Meet the Rear of the Ship?

    Homework Statement The figure shows a ship (attached to reference frame S') passing us (standing in reference frame S) with velocity http://edugen.wileyplus.com/edugen/shared/assignment/test/session.quest2564447entrance1_N1002E.mml?size=14&ver=1463885870814 =...
  45. F

    I Does Relativity and Quantum Mechanics NEED to be reconcile?

    One of the greatest quest in physics is to reconcile Relativity with QM. But is this reconciliation really necessary? They both work quite well in their respective fields so why not just leave it at that? The only issue I can see is the problem of the singularity but can't that be solved by...
  46. i_hate_math

    Special Relativity of Train Problem

    Homework Statement A relativistic train of proper length 237 m approaches a tunnel of the same proper length, at a relative speed of 0.951c. A paint bomb in the engine room is set to explode (and cover everyone with blue paint) when the front of the train passes the far end of the tunnel (event...
  47. X

    Mathematica Best Mathematica Tensor/General Relativity Package?

    Hello can anyone recommend me a good mathematics package for solving the Einstein Field equations. You know one that can easily compute covariant derivatives and calculate the Reinman curvature tensor and can also minimize the Einstien Hilbert Action?
  48. J

    I Velocity of Timelike Curve in Special Relativity

    In special relativity we can view spacetime as ##\mathbb{R}^4## with its standard smooth structure, and a metric ##\eta_{ab} = \sum\limits_{\mu, \nu = 0}^3 \eta_{\mu, \nu} (dx^\mu)_a (dx^\nu)_b## where ##\nu_{\mu \nu} = \mathrm{diag}(-1, 1, 1, )##. Given a curve ##\gamma: I \rightarrow...
  49. Supantho Raxit

    Field of Moving Masses: EM Purcell

    A moving charge that starts or stops generates a spherical wave-front of EM wave, can the same analogy be drawn for a moving mass? Reference: Electricity & Magnetism by EM Purcell
  50. S

    Relativity - velocity of object travelling perpendicular to the observer

    Homework Statement Two light beams collide head on. Calculate their relative velocity. (c) A particle moves north at speed 0.85c relative to an observer standing on the Earth. What is the velocity of this particle as observed by a fast ship traveling east on the Earth at speed 0.9c? Give the...
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