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. Demystifier

    I Is General Relativity More General than Gravity?

    One obvious difference is that gravity is more general, because there are alternative theories of gravity that differ from general relativity. In this sense general relativity can be thought of as a subset of gravity. But I am interested in a different type of difference. I am interested in a...
  2. S

    A Meaning of the word "conserved" in relativity

    I'm reminded of something that I'd be curious to get some thoughts on. There's a semantic issue with the word "conserved" that often flies under the radar: does the term refer to any quantity whose value remains the same before and after some process, or does it specifically refer to an...
  3. Athenian

    [Special Relativity] Lorentz Transformation and Boosts

    [BEGINNGING NOTICE] Before I begin showing my attempted solution, I would just like to quickly mention that this is a "repost" of the same question I had around a week ago. While I would usually use the "reply" function on the same thread, I believe that thread is getting pretty messy (sometimes...
  4. Athenian

    [Special Relativity] - Finding Angle θ as Measured in Frame S

    Below is the attempted solution after researching the contents available on Introduction to Electrodynamics by Griffith. To begin with, I defined the rod as having a length of ##l'## at rest in frame ##S'##. Thus, in frame ##S'##, the height of the rod is ##l' sin(\theta ')## and its horizontal...
  5. Athenian

    [Special Relativity] Scalar Invariant under a Lorentz-transformation

    "My" Attempted Solution To begin, please note that a lot - if not all - of the "solution" is largely based off of @eranreches's solution from the following website: https://physics.stackexchange.com/questions/369352/scalar-invariance-under-lorentz-transformation. With that said, below is my...
  6. D

    B Linking Quantum Physics and Relativity: Theory of Everything?

    I am going to get laughed out of this forum but at least it will put my mind to rest when this happens. I've been thinking about this for a few years now and what better place for an answer than a physics forum? Amongst many other things I have read A Brief History of Time seven or eight times...
  7. M

    Special Relativity question using Lorentz Transformation time dilation

    with distance between planets as 4x10^8m measured by you on the ship My attempt: t' = γ(t - ux/c^2) γ = 5/3 u = 0.8c t = 0.9s x = 4x10^8m answer is: -0.278 Therefore not possible My question is what if we traveled rightwards, from p2 to p1, would the answer change? Should my above information...
  8. Athenian

    [University Special Relativity] Lorentz Transformation and Boosts

    Unfortunately, I am not entirely confident of the above equations being able to do the trick and ultimately solve for the question. However, my guess is that using the equation written above for "boost", I could perhaps use ##v## and insert it into the ##x##-direction part of the matrix...
  9. GravitySK

    Relativity Looking for further Relativity textbooks

    I'm reading chapter 7 of Goldstein Classical Mechanics (the special relativity part) I'm planning to take a deep(very deep!) study on Relativity(Both Special and General Theory) after finishing chapter 7 of Goldstein. Which textbooks will you recommend? If you could give me a suggestion with...
  10. A

    I Architecture & Assumptions of General Relativity Theory

    Every theory, whether it is a physical, a psychological or a sociological theory, is defined in terms of an assumed architecture and in terms of a number of assumptions that apply within that architecture. An example from physics is the previously widely accepted dome theory to explain the...
  11. K

    I Electromagnetic Potentials in Relativity: Retarded Potentials?

    What's the most used type of electromagnetic potential? Is it the retarded potentials?
  12. M

    The sphere in general relativity

    I'm a bit confused about the notation used in the exercise statement, but if I'm not misunderstanding we have $$\begin{align*}(\psi^+_1)^{-1}:\begin{array}{rcl} \{\lambda^1,\lambda^2\in [a,b]\mid (\lambda^1)^2+(\lambda^2)^2<1\}&\longrightarrow& \{\pm x_1>0\}\subset \mathbb{S}^2\\...
  13. RUTA

    Insights Answering Mermin’s Challenge with the Relativity Principle

    Continue reading...
  14. Replusz

    General Relativity easy question

    Attempt: I don't know what they mean by effective Lagrangian. I am aware there is something called 'the lagrangian' that goes as L=g_ab * dx^a/dk * dx^b/dk, but i don't see how this gives me any of the chrostoffel symbols... cheers
  15. M

    I Connection between General Relativity & Chaos Theory?

    I am very new to such ideas but was wondering if there is any connection to what I am asking. Taking two events, let's say at opposite ends of the globe. Would even A, only have a potential on event B, if light could travel between these event in the given time frame of these event occurring...
  16. RodolfoM

    Relativity - Time between events

    Firstly, I calculated the relative speed between the two rockets, finding v=1.6c/1.64. Then, I applied the length contraction: the length of the moving rocket will be 0.6L due to this phenomena, so the total distance traveled by one rocket, with respect to the the other, will be 1.6L. Therefore...
  17. matternat968

    B Relative Nature of Speed: Einstein and Orbits

    At the risk of sounding stupid, this question has always perplexed me. Einstein theorized that mass can not travel faster than the speed of light. I don't really understand it, I assume it has something to do with mass just being energy. Anyway imagine two objects in orbit of something with...
  18. Demystifier

    A Implications of quantum foundations on interpretations of relativity

    Physicists often discuss interpretations of quantum mechanics (QM), but they rarely discuss interpretations of relativity. Which is strange, because the interpretations of quantum non-locality are closely related to interpretations of relativity. The field of interpretations of relativity is...
  19. Demystifier

    I Special relativity vs Lorentz invariance

    The Lorentz covariance of Maxwell equations was known before Einstein formulated special relativity. So what exactly special relativity brought new with respect to mere Lorentz covariance? Is special relativity just an interpretation of Lorentz invariance, in a sense in which Copenhagen...
  20. M

    Acceleration in special relativity

    I'm struggling in the details of this exercise. Let ##S'## be the reference frame where the acceleration of the spaceship is constant, in which case we have ##u'(t')= a' t'## (since we assume no acceleration at the beginning). The rest frame of the rocket ##S## is connected to ##S'## via a...
  21. Cerenkov

    B The Strong Energy Condition in General Relativity

    Hello. I've recently been reading this paper... https://arxiv.org/pdf/gr-qc/0001099.pdf ...in the hope that I can begin to understand some the role of the energy conditions in General Relativity. But I'm not making much progress and so I've turned to this paper...
  22. Replusz

    Why is this true? General relativity

    "their scalar product is..." why?
  23. M

    I Special Relativity: 2-D Collisions for Alice & Bob

    Alice and Bob are initially in the same inertial frame. There are 2 point test masses m1 and m2. Initially m1 is at the origin and m2 is on the positive x-axis. At time zero, m1 is instantaneously accelerated to velocity Vx in the positive x-direction. After some time, m1 collides with m2...
  24. M

    I Accel. in Spec. Relativity in 2-Dims: Point Test Mass

    Let m be a point test mass. Initially m has velocity Vy in the poisitive y-direction, and zero velocity in the x-direction. At time zero, m is accelerated in the positive x-direction. In the limit as the time goes to infinity, the velecity in the positive x-direction goes to the speed of...
  25. D

    Homework question on relativity

  26. Meruem

    B Quantum Gravity and Special Relativity

    is there a equation that links quantum gravity and special relativity?
  27. N

    Prerequisites for General Relativity (Advice needed)

    Summary: At this point, I am thorough with single variable, multivariable calculus, differential equations, linear algebra and basic concepts of point-set topology and tensor analysis. To learn General Relativity along-with its mathematical rigor, what are the topics I should first be thorough...
  28. Pencilvester

    I Pullback of Vector Field in Relativity: Restrictions?

    Since coordinate transformations should be one-to-one and therefore invertible, wouldn’t there be no restriction on pushforwarding or pullbacking whatever fields we feel like (within the context of coordinate transformations)?
  29. adosar

    I Position of Particle in Special Relativity (A vs B)

    Recently I have come into Special Relativity and specifically Lorentz transformation. Let's assume two frames A and B moving relative with speed ##v##. The position of a particle moving with respect to B is given by ##x′=f(t′)=3t′##. What is the function of position ##x=f(t)## of the particle...
  30. N

    I Special relativity question driving me crazy....

    Hey guys. Noob here. Question; S frame = x,y,z,t S' frame = x',y',z',t' S' is moving with a speed v relative to S and t=t'=0 when origins coincide v= 0.6c find the coordinates of x = 4 & t = 0 in S' When I use lorentz transformation, I get a negative t' and x' = 5. This doesn't make sense to...
  31. P

    I Dark energy questioning Relativity?

    Forgive my naive understanding of these topics. I have a layman's interest in science and follow all the popular science I can, but I'm certainly not a physicist and even my degree in mathematics is now all but forgotten in the past. But I have two questions (the other I'll post in another...
  32. A

    I Mechanical system with de Broglie-like features

    Hello, I am curious if I have this correct and if it has a name. A thin walled cylinder is spinning on its axis along its length in a closed system. It begins to draw itself in converting its invariant mass to kinetic energy. In polar coordinates ##E=\gamma_\theta m c^2, L=\gamma_\theta m...
  33. x-vision

    B Reference frame symmetry in Special Relativity

    Hello, I have a couple of questions related to reference frames in Special Relativity. Let's consider a rocket that is inertially moving towards a star with a relative velocity 0.9c. I'd like to look at this example from both the rocket's and the star's perspectives. In the reference frame of...
  34. V

    B Special Theory of Relativity: Ques on Thought Experiment

    I have a doubt ,the thought experiment performed by einstein he thought that the clock was behind him and he is moving away from clock with speed of light what if he is approaching a clock with speed of light won't time run at very high speed
  35. K

    I Is Relativity a Complete Theory? Investigating Math Formulation

    Is it complete in the sense that there's nothing further to investigate in terms of its mathematical formulation? I mean, in the sense that we don't need to introduce new mathematical tools or review existing ones for the theory.
  36. S

    I Is Time Travel Possible with Entangled Particles?

    1. An elementary particle like a photon or electron can be measured in 2 possible states - spin up or down in electron, vertical or horizontal in photons. We'll call those states state 1 or 2, and the measuring device state A or B. If for example, we measure a photon with a polarizer in State...
  37. E

    I Relativity of Simultaneity: What Einstein's Contribution Was

    Something that I consider very silly, yet I try to solve relates to the relativity of simultaneity. According to SR , two evevnts taking place in different positions along the line of relative motion of two inertial observers are not simultaneous in both frames. Now, I wanted to see how this...
  38. K

    I Succeed in Learning Relativity: Transport, Frames, Tensors

    How much essential is it to learn concepts such as - different types of transport of vectors, like Fermi Walker and Parallel transport; - different frames (basis vectors); - tensor densities and integrations To put it another way, do they play a important role in the theory? If one for some...
  39. P

    I On the Relativity of Lengths and Times

    I'm struggling to understand Section 2 of Einstein's 1905 paper, "The Electrodynamics of Moving Bodies." This is my source for the paper: http://hermes.ffn.ub.es/luisnavarro/nuevo_maletin/Einstein_1905_relativity.pdf In section 1 Einstein states that by definition light travels at the same...
  40. cordless03

    B Finding Flaws in General Relativity: A Question of Knowledge

    This thread is supposed to be about finding flaws in General Relativity, but the way these people talk they sound like they have no real knowledge of GR. I was just curious if any of you guys could explain further.
  41. SpookyAction_

    I Exploring Special Relativity and Time

    So I was reading a book on special relativity and it was explaining how, if we were to go very near the speed of light, time (relative to us traveling) would slow and space itself would condense. It used the example that if we were to try and travel to a galaxy 1 million light years away, Yet we...
  42. K

    I Usefulness of Diagrams for Relativity: 1-5

    On a scale of 1 to 5, how useful do you think are diagrams for understanding / studying special relavity? What about general relativity?
  43. P

    Relativity light clock problem

    1. I'm fine with this one, I simply calculated L = L0/γ = 5/1.2 5= 4m. 2. This is the one I'm having problems with. My approach was to say that both observers would measure the light beam to have velocity of ‘c’. Therefore, if 4m is the distance between the mirrors as observed in the frame of...
  44. M

    A Developments to unify quantum theory with General Relativity?

    Have there been any recent developments in the attempt to unify the standard model of quantum theory with General Relativity? It appears the no progress has been made recently in string theory or loop quantum gravity.
  45. DuckAmuck

    I Universe Expansion: Does Speed of Motion Matter?

    So the universe is expanding, and galaxies are getting farther apart from one another on average. Does this motion count the same as ordinary motion, in that if a galaxy is being expanded away from us at 0.5c, that clocks in that galaxy would appear to tick slower at 0.866 the rate of clocks here?
  46. TheQuestionGuy14

    B Is Time Really Flowing in Relativity?

    In relativity, time is a dimension like space, a co-ordinate system. Depending on your motion, your co-ordinates shift and this leads to time dilation, simultaneity and length contraction. So, does time flow at all in relativity? Does time 'move forward'? If not, what would be different if time...
  47. S

    I Confused by nonlocal models and relativity

    Hello everyone! Recently I saw this paper: https://arxiv.org/pdf/1304.4801.pdf ("Any nonlocal model assuming “local parts” conflicts with relativity " by Antoine Suarez). He mentions standard experimental configuration with beam-splitters and detectors. Then he distinguishes possible models...
  48. Bob R

    B Confirm General Relativity: Eddington's Starlight Experiment

    If Earth's motion about the sun is described by General Relativity why was Eddington's experiment with the bending of starlight needed to confirm the theory? In other words, don't we see enough common phenomena in our every day experiences to confirm GR without verifying subtle phenomena such as...
  49. Kairos

    I Inverse results in special relativity

    The mass of an object moving at speed v increases such that $$\frac{m'}{m}=\frac{1}{\sqrt{1-\frac{v^{2}}{c^{2}}}}$$ and its apparent frequency decreases such that $$\frac{\nu'}{\nu}=\sqrt{1-\frac{v^{2}}{c^{2}}}$$ so $$\frac{\nu'}{\nu}=\frac{m}{m'}$$ but equating the energies $$ h\nu= mc^{2}$$...
  50. Efeguleroglu

    How to calculate the minimum kinetic energy (special relativity)?

    Sadly, that's what all I could do.
Back
Top