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.

View More On Wikipedia.org
Recent contents Top users
  1. L Drago

    New to Physics forum

    I really like physics especially relativity and classical physics like Newton's laws. I have joined this forum to discuss and learn more about relativity, classical physics and the weird QM
  2. DaTario

    B Very simple exercises in General Relativity

    Hi All Would it be possible to introduce some exercises in general relativity at the high school level? Exercises that would at least help to raise students' awareness of the aspects that will be studied in greater depth at university or in post-doctorate studies? If so, what examples of...
  3. H

    Giveaway General Relativity by Robert M. Wald

    https://www.amazon.com/General-Relativity-Robert-M-Wald/dp/0226870332?tag=pfamazon01-20
  4. approximatelysphere

    Trouble understanding frames in relativity

    I have attached a copy of my work as a pdf file. Please excuse my non-rigorous usage of notation. Thank you so much!
  5. M

    Frequency of Reflected light in special relativity

    In the. solution attached I'm not too sure why in frame K, we apply the doppler effect twice. Also, since the photon is moving away from the source, shouldn't the signs be switched? Thanks
  6. Tribal Blue

    Exploring the Mystical World of Science Brings New Inspiration

    Hello! I am a creator who loves the fascinating world of science. I enjoy exploring science from a unique angle, which often leads to new and creative ideas. While some of these ideas can be speculative and challenging to prove, I make sure they align with scientific principles and logical...
  7. AshanTharuka

    Finding a PhD program which is compatible with GPA 3.485

    I am looking for instructions from you to find out a good university to enroll to a PhD program in Astrophysics and particle physics or a similar study. I have completed my 4 year BSc(Hons) Special in Theoretical Physics with a grade of second class upper division in Sri lanka. My specialized...
  8. A

    Prove v<c for particles with m>0 using two identities

    I can't figure out how to prove this using only those two identities? I mean in general, I could prove it easy when using relativistic equations, and showing that if ## v = c##, the denominator becomes 0, and if ## v>c##, the denominator becomes an imaginary number (a negative square root)...
  9. bob012345

    I Circumnavigating the Universe in Cosmos (1980)

    Sagan describes this on page 207 of his book (1995 reprint hardback edition). In the context of the page he is discussing accelerating at 1g for half the journey and decelerating the other half for trips to Barnard's Star, the center of the Milky Way and the Andromeda galaxy. Then he talks about...
  10. M

    A The meaning of ##(ict, x_1,x_2,x_3)##

    In relativity theory, it's a common habit to use a quadruplet x=(x_0, x_1, x_2, x_3) with x_0=ict (or with c=1, x_0=it ) instead of (t,x_1,x_2,x_3)\in \mathbb R^4, and to use the formal Euclidean metric \|x\|^2=\sum_{i=0}^3x_i^2 instead of the Minkowski pseudo-metric -t^2 + \sum_{i=1}^3x_i^2...
  11. A

    B Is this an Unavoidable Collision between 2 spaceships traveling at 0.6c each?

    Relativity always talks in terms of observer but fail to explain common sense problems like this. The fact that no one can measure anything faster than light does not preclude to objects moving towards each other at a higher velocity than an external observer can measure. Move the observer to...
  12. J

    I Mother of all equations for the Lorentz force

    David J. Griffiths Introduction to Electrodynamics page 460: Lorentz force equation invariance leads to different Lorentz force values in different inertial frames. Is this a problem for conservation of momentum? More specifically conservation of angular momentum?
  13. C

    Struggling with General Relativity Calculations?

    I’ve been self studying some of the concepts related to General Relativity, by trying to model Geodesics and calculate distances on curved surfaces. I found that I seem to understand some of the concepts related to the math, but not others as when I try to make some calculations I find that my...
  14. ric peregrino

    What Are the New Methods and Notations in Differential Geometry?

    Hello, I'm an old fart, that used to self study GR and tensor calculus. I have a BS ECE from UCD, and a MS EE from Stanford. I've since retired from my electrical engineering career which was mostly at the old HP's Stanford Park Division, and I find myself once again pondering these things. I...
  15. U

    Use relativity and the Larmor formula to calculate Lienard's formula

    I am trying to understand the solution to exercise 12.71 in the document linked below which accompanies Griffith's book on electrodynamics. The problem states that we are to use the Larmor formula and relativity to derive the Lienard formula. $$Larmor \ {} formula: P = \frac{\mu_0q^2a^2}{6\pi c}...
  16. S

    I Information transfer between moving bodies - sped up or slowed down?

    Relativistic motion and time dilation has been of interest to me for a long time, and whilst I am asking this for realism in writing a piece of fiction, I am curious as to how this interaction would work. Let's say there's a large dyson ring built around earth, which is spun up such that the...
  17. G

    A Relativity: Test charge moving perpendicular to a current carrying wire exhibits a force

    Given a test charge moving along a current carrying wire, I'm familiar with the relativity explanation of the magnetic field at the rest frame of the wire and the electric field In the moving particle frame (where the wire is electrically charged). My question is how relativity kicks in in the...
  18. M

    Spaceship, Earth and proton problem in special relativity

    For this problem, My solution to part (a) is ##u'_x = 0.3c##, however, I'm confused by (b) and (c). By definition in (b) and (c), the proper velocity of the proton is the speed of the proton in the proton-frame (frame where proton is at rest). So would the answer for (b) and (c) not both be...
  19. sirapwm

    I Lab energy available in threshold (endothermic) reactions

    I was surprised this morning when I got off on a tangent regarding the amount of energy available in the laboratory frame just at threshold. It reveals an interesting relativistic effect. Consider a reaction (I'm thinking in terms of nuclei and/or particles) ##1 + 2 \to 3 + 4 + \cdots## with...
  20. M

    Stationary observer meaning in relativity problem

    For this problem, I don't understand what it means by the notation of a "stationary" observer. I thought there was no such thing as absolute rest. Does someone please know whether it means stationary with respect to the object? Thanks!
  21. R

    I A problem in the equations for Einstein's Special Theory of Relativity

    How did you find PF?: Google search I encountered a problem in the equations for Einstein's Special Theory of Relativity back when I was in high school in 1964. With the invention of the internet, I tried to discuss this with scientists in sci.physics.relativity, but most of the responses...
  22. billtodd

    Relativity Introduction to Special Relativity by Wolfgang Rindler

    I used in another username to ask questions from this book, its second edition. I made a google search and didn't find any instructor's SM for the second edition, but it seems numerade website has complete solutions for questions from its first edition. Did he add more problems to the second...
  23. H

    I Deriving the relativistic rocket equation with exhaust efficiency

    Hi, I'm looking at this relativistic rocket equation on Wikipedia. Something doesn't make sense here, and I can't find a derivation for this equation in the linked source, so I'm trying to derive it myself with limited success...
  24. A

    Looking for people with similar interests

    Hello, I have been interested in physics and math since I was a student. Now I am just retired and have time to dedicate myself to deepening the study of these subjects. Above all, I would like to know better the theoretical foundations of quantum physics and relativity. I have been a teacher...
  25. M

    I Is the electromagnetic 4-vector indeed a 4-vector?

    About the electromagnetic 4-vector ##A^\mu=(\Phi/c,\mathbf{A})##. If it is indeed a four-vector, then its squared length ##A_\mu A^\mu=\Phi^2/c^2-\mathbf{A}^2## should be a Lorentz invariant. What is the physical significance of ##\Phi^2/c^2-\mathbf{A}^2##? Thanks for any help.
  26. K

    How Does Relativity Influence Our Understanding of the World?

    Hi, I'm a new member, interested in physics and relativity and new ways to think about our world. Cheers Chris
  27. misterously

    I Can someone falsify this analogy contradicting time dilation?

    A spaceship travels at the speed of light from the sun to the earth and back, infinite acceleration and deceleration. Sunlight takes about 8 minutes to reach earth. On the trip to earth, the sun seems to be frozen. On the trip back, sun activity appears to resume and is seen at 2x speed. The...
  28. D

    B How are 'fringe shifts' in the Michelson-Morley experiment calculated?

    Ok for the interferometer let the arm lengths be ##L##, speed of light relative to the aether be ##c## and the speed of the setup relative to the aether be ##v##. By calculation you can show that the distance between the two 'heads' of the beams of light is ##\frac{v^2L}{c^2}##, and using the...
  29. P

    A Correspondence between areal radius differences and proper distances

    Other ways of wording this finding about the extended SC (Schwarzschild) spacetime: - in the local frame of a free faller, radial distance is given r coordinate difference - in either Fermi-normal coordinates, or Riemann-Normal coordinates built from a free faller at an event, coordinate...
  30. C

    B Help understanding the Relativity of Simultaneity

    Hello everyone, So I think maybe what confused me with the symmetry of time dilation was not understanding relativity of simultaneity. After looking into it if you have two clocks P and Q that synchronize when they meet and if ##\gamma## is 2 then from P's reference frame P equaling 10 and Q...
  31. Elimelech70

    I Is it only experience that's relative?

    Reading Einstein Relativity. The trains experiences lightening strikes differently to the embankment. So the two events are experienced differently from the two reference points because they have different distances to the events. Light from the events taking different times to reach each...
  32. C

    B Question about the relative motion of an eye relative to light source

    Hello everyone, I've been thinking about 2nd postulate of relativity, it seems that and the Michaelson-Morley experiment seems to imply that there is no ether, but I was thinking about a special situation that doesn't seem to go against that postulate. I think my question is basic so hopefully...
  33. P

    B Understanding the Twin Paradox: Simplifying with a Clear Experiment

    I have seen many attempts to rationalise the 'Twins Paradox', but none of the seem satisfactory. They usually use acceleration or asymmetric differences in inertial frame, or other aspects of special relativity that tend to obfuscate the problem/explanation. So proposing an experiment that...
  34. patdolan

    I What about the Big Ben Paradox?

    Consider a distant observer traveling at .867 c ( 𝛾=2 ) relative to the solar system along the line that is collinear with the sun's axis of rotation. As the clockwork solar system spins beneath him, the distant observer peers through his powerful telescope at Big Ben in London. After taking...
  35. P

    I Clock Synchronisation -- Do clock speeds go out of synch?

    When reading about the one way speed of light, I think it's fair to say that most potential methods to obtain this fail because it is said to be impossible to have two non co-located clocks in synch. My question is really about terminology. Normally, two things can be said to be in synch if...
  36. Sciencemaster

    Misc. DIY Experiment of Special Relativistic Effects?

    I'd like to perform an experiment that will build intuition for Special Relativity in the real world. While I do believe that it occurs in the real world, I'd like to be able to prove it for myself, and I feel that such an experiment would help others on this forum as well. Is there an...
  37. Physicsperson123

    I Terrell rotation is confusing!

    Imagine in the distance you see a glowing spherical object hovering in the air. Suppose light from point B on the surface of the sphere facing away from you can arrive at the camera simultaneously with light from A: Since the object is moving at relativistic speeds, by the time light begins to...
  38. Hak

    I Doubts about the relativistic description of electrical interactions

    I would like help with an issue that I have not yet fully mastered. Consider a particle resting on a plane, it is subjected to a gravitational force, which can be interpreted as the result of a deformation of space-time. It remains at rest due to the upward binding reaction provided by the...
  39. Jpolisa

    B What Is Relativity Theory in Simple Terms?

    Yes... Can someone please explain the relativity theory to me in as much simple terms as possible. It's really way in over my head. Thanks.
  40. Hak

    I What causes the magnetic force in a uniform magnetic field?

    As is well known, when electric current flows in a straight wire, a charge in motion in the vicinity of the wire, parallel to it, is affected by a force called the magnetic force, which is attributable to the relativistic contraction effects that the wire undergoes in the frame of reference of...
  41. Hak

    I Existential problem on Electromagnetism and the combination of Relativity and Quantum Mechanics

    In Feynman's famous Physics book, in a discussion of the generality of Maxwell's equations in the static case, in which he addresses the problem of whether they are an approximation of a deeper mechanism that follows other equations or not, he says: I was wondering first of all if this was a...
  42. L

    I I think the special theory of relativity self-contradicts

    Consider two rulers that have the same rest length. Denote it by L0. Now let the two rulers be in relative motion. First consider things from the rest frame of the unprimed ruler illustrated below. A'_____B' ............A_______________B. State 1 ............A'_____B'...
  43. C

    I Is Simultaneity Absolute or Relative in the Theory of Relativity?

    When two remote events are observed/measured to be simultaneous in one inertial frame, the same events will not be simultaneous when observed from a second frame in uniform motion relative to the first. Why is this distinction in the kinematics of light not considered an operational distinction...
  44. substitute materials

    I Asymmetry in Length contraction?

    Instead of a twin paradox, let’s just consider an inbound starship approaching Earth at relativistic speed. The traveler is on a flyby mission, he will never change speed or direction. We will disagree with the traveler on how much time will have elapsed when he passes Earth. The discrepancy can...
  45. D

    I What was the four-momentum meant to include?

    Hello, was the four-momentum of relativity, Pν, supposed to include all mass and energy contributions from every field i.e. electromagnetic, strong, gravitational... Or is it just the momentum of what was known in Einstein's time?
  46. Slimy0233

    B What is m in Kinetic Energy? Relativistic mass or Rest mass?

    note: m = relativistic mass ##m_o## = rest mass v = velocity of the objectQuestion 1: If a particle is moving at relativistic speeds what would it's kinetic energy be? I think it's ##K.E. = \frac{1}{2} m_o v^2## and my friend thinks it's ##K.E. = \frac{1}{2} \frac{m_o...
  47. NoobieDoobie

    Calculation of Thomas Precession in Rindler's relativity book

    I am trying to work through rindler's relativity book. However, I got stuck at what I think should be a simple approximation. I calculated the angles ##\theta## and ##\theta''## using the formula for velocity transformation. If I simply expand ##\gamma(v)## and ##\gamma(v')## using taylor...
  48. S

    Speed of Message Relative to a Space Station: Relativistic Addition

    u is the speed of the message relative to the station v is the speed of the spaceship relative to the station u’ is the speed of the message relative to the spaceship u=(-0.5c+0.7c)/(1+((-0.5c)(0.7c))/c^2 ) =0.2c/0.65=0.308c This just seems way too high, and I'm not sure if I'm doing it...
  49. K

    I How does an observer moving at relativistic speeds perceive a pulsar?

    Let us suppose our velocity towards a distant neutron star roughly equated to a dilation factor of 10. On board our vessel we are equipped with a NIST-F2 atomic clock . Since the clock travels with us, it also experiences the same dilation; thus, in our frame, the clock keeps time the same as...
  50. jaketodd

    B Photons on a perpendicular bisector path from a black hole's core

    Not directly from the core, but a trajectory that goes to the event horizon, and gets corrected to a perfect, perpendicular bisector path by the gravity of the core, when it reaches the event horizon. Would they escape the event horizon, since they have to always move at c? On this trajectory...
Back
Top