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. 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)...
  2. 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...
  3. 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...
  4. 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...
  5. 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...
  6. 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...
  7. 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...
  8. 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...
  9. 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)...
  10. 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...
  11. 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...
  12. 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...
  13. 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 -...
  14. 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...
  15. 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...
  16. 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...
  17. 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...
  18. J

    A General relativity. What does momentum conservation mean?

    In general relativity, does momentum conservation mean conservation of 4-momentum or 3-momentum
  19. 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...
  20. 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...
  21. 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...
  22. 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)
  23. 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...
  24. 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...
  25. 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...
  26. 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.
  27. 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...
  28. 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...
  29. 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...
  30. 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...
  31. 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...
  32. 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.
  33. abrogard

    What Does Shankar Mean in Prof Shankar's Introduction to Relativity?

    Hope this is a valid question. I can't quite understand this very simple thing. Prof Shankar's introduction to relativity on Youtube starting at about 50 minutes has a quick calculation that comes up with the Lorentz transform. I follow the maths, no problem. But he confuses me a bit when...
  34. T

    Special relativity and particle accelerator

    Homework Statement (a) A spaceship at rest in a certain reference frame S is given a speed increment of 0.50c. Relative to its new frame, it is then given a further 0.50c increment.This process is continued until its speed with respect to its original frame S exceeds 0.999c. How many...
  35. T

    General relativity vs quantum mechanics

    Forgive me if this question is a bit amateurish but i am no physicist. I know in general terms that GR and QM aren't compatible with one another, but my question is...Do they even need to be? can it not be a handoff scenario? why can't GR govern what it is supposed to govern and QM govern what...
  36. Toby_phys

    Special relativity - transformation of angle

    Homework Statement Homework Equations Gamma factor: $$\gamma = \frac{1}{\sqrt{1-\beta^2}} $$ Lorentz contraction $$l'=\frac{l}{\gamma}$$ Trig: $$ cos\theta = \frac{adjacent}{hypotenuse}$$ The Attempt at a Solution I have all the quantities but the algebra doesn't seem to work out...
  37. Dimani4

    I Special relativity: frames of reference

    Hi people, I have a question about the frame of references. Let's have an example: First case: Jill on rocket and Jack stationary on Earth. Jill moves relatives to Jack 0.6c (1.8*10^8m/s). The distance is 18*10^8m. At the zero time Jack and Jill synchronize their clocks. Then Jill starts to...
  38. astrocytosis

    Time Dilation - measured vs observed time interval

    Homework Statement Consider an observer Bob in S standing close beside the x-axis as Alice, who is holding a clock, approaches him at speed VS'S along the axis. As Alice and her clock move from position A to B, Alice’s clock will measure a (proper) time interval ∆t0, but as measured by Bob’s...
  39. A

    B Zeno's arrow paradox and general relativity?

    I don't know much about general relativity, but I'm curious if Zeno somehow foresaw the reallty of the universe many many years before Einstein did(without any rigour ofc, but still the idea holds?). Understanding the Zeno's arrow paradox, stating that an arrow is motionless at a certain moment...
  40. A

    Relativity and Equivalence of Mass and Energy

    Homework Statement An electron is accelerated to a speed that is 99 percent the speed of light, and is moving through a 2-km-long tunnel. The rest mass of the electron is 9.11*10^-31 kg. What is the mass of the electron at this speed? c= speed of light Homework Equations t= (tsubscript(o))/...
  41. ibkev

    Relativity Morin's "Special Relativity: For the Enthusiastic Beginner"

    I just came across this recently released title by David Morin, "Special Relativity: For the Enthusiastic Beginner". If its anything like Morin's past books, it'll be excellent for self studiers. https://www.amazon.com/dp/1542323517/?tag=pfamazon01-20
  42. Anujkumar

    I Spacetime Relativity: Universe Expansion & Our Place in It

    When the universe is expanding then why not we are expanding along with it
  43. MetinErsin

    B Relativity Scenario Help: A Seeing B's Line Shorter or Longer?

    Let's assume there are two observers. Observer B is at rest and observer A is in a spaceship which has transparent walls. A draws line of 1 meter. When A arrives near B, B draws a line of 1 meter. And sees that A's 1 meter is shorter than own 1 meter. before forget i should say that meter is...
  44. I

    I Velocity Addition & Relativity of Simultaneity

    I have some issues understanding the following thought experiment: Suppose you are standing still, and two balls are moving towards you from opposite direction. From your own reference frame, Ball A is ##10^5## m away from you, moving towards you from the left with speed ##0.8c##, and Ball B is...
  45. Paulo Figueiredo

    Time measured by a car-Special relativity

    Homework Statement I wish a help for the following problem: Consider the situation: a car A is moving away from a stationary observer O with velocity c/3. When the point A is at a distance 200.000 Km of the O a light signal is sent from the observer O to the car A. The question is: how long...
  46. S

    I Relativity of simultaneity, time dilation misunderstanding

    Hi everybody, I'm new on this forum so I apologize in advance if I don't respect some formalities (and sorry for my English). It is known that in the perspective of the stationary observer the events in the back and in the front of the moving spaceship are not simultaneous. If I understand well...
  47. M

    A How to Integrate the geodesic equations numerically?

    Hello there, I've been considering the geodesic equations of motion for a test particle in Schwarzschild geometry for some time now. Similar to what we can do with the Kepler problem I would like to be able to numerically integrate the equations of motion. I'm quite interested to see how...
  48. Spikemarlene

    B Einstein relativity is invalid

    Hi, Need your help to unravel the claims made by a poster in my local forum, if it has any merits. I do not have the expertise to evaluate his claims but am hoping if you can give me a few points on his line of reasoning, if it is faulty or not. I have a general background in undergraduate...
  49. J

    B DeltaT of clocks at endpoints of a rocket post acceleration

    Following scenario: A rocket measuring 10 lightseconds in length accelerates near instantaneously to v=0.4c. Pre-acceleration two clocks placed at the endpoints of the rocket were synced. What will be the time difference between the two clocks post acceleration? I tried to figure it out...
  50. Dimani4

    B Special Relativity: What Time is it?

    This question based on the site located here: http://galileo.phys.virginia.edu/classes/252/srelwhat.html The question is: If the object (spaceship) moving close to the velocity of light and I'm as a static object. The time goes slower in the object moving with constant velocity (inertial frame)...
Back
Top