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. 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...
  2. 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...
  3. 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
  4. 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.
  5. 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...
  6. 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...
  7. 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...
  8. 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...
  9. 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.
  10. 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...
  11. 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?
  12. P

    Why is My Relativity Light Clock Calculation Incorrect?

    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...
  13. 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.
  14. 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?
  15. 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...
  16. 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...
  17. 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...
  18. 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 $$ h\nu= mc^{2}$$...
  19. Efeguleroglu

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

    Sadly, that's what all I could do.
  20. Buckethead

    B Relativity: Twin Paradox - Is Age Determinable?

    (I swore to myself I would never ask a relativity question again...oh well) I don't know why I can't find anything about this in a search so I guess I'll just have to ask. Is a twin that takes off to Mars to stay, younger than a stay at home twin or is it ambiguous? I would think that this...
  21. SJay16

    B How well should Astronomers know General Relativity?

    I know that it would vary depending on the type of research a specific astronomer would be doing ( Astrophysics/Cosmology research versus an Astronomer researching exoplanets ) ; but in your opinion, “how much” or “how well” should an Astronomer with a graduate degree in Astronomy know General...
  22. A

    I Special Relativity: Train in Tunnel Paradox Solved

    Hello, I was wondering if anyone could set up and solve a classic train in a tunnel paradox from special relativity with unique values for multiple observers including time space diagrams. Thanks
  23. vanhees71

    Relativity M. Tsamparlis' book on Special Relativity

    I just stumbled over the following book on SRT Michael Tsamparlis, Special Relativity, Springer (2010) It's a gem! On the beginning-graduate level it explains the special theory of relativity from ground up, starting with a chapter on the math of Minkowski space and then providing a complete...
  24. nearc

    B Prereqs for Posting in Special & General Relativity

    i am far from an expert in Special and General Relativity, however, my attempts to learn from this forum are hampered by the large volume of posts involving common misconceptions and lack of understanding of the material. while the members of the forums patiently [usually] help our novice and...
  25. Bill_K

    Insights Understanding Precession in Special and General Relativity

    Continue reading...
  26. DaTario

    A Thermal State in Relativity Theory: Can It Happen?

    Hi All, Considering a set of many many small hard balls which start colliding inside a box. The velocities of these balls being mostly greater than c/2. Is it possible, in this case, to speak of convergence to a thermal state in the same sense of ordinary thermodynamics (i.e., using...
  27. B

    I Problems with Einstein's 1920 "Relativity"

    Hi, I have been reading and watching a lot of physics lately but I have come across this problem. I have the basics of special relativity down, and it all seems clear to me. This is not in question to me. For example, I am reading a book on string theory by Brain Greene, and in it he covers...
  28. G

    A Significance of "Change of Signature" in Classical Relativity

    I'm a bit confused about the idea of "Change of Signature in Classical Relativity". As I see it, a metric is just a scalar function that I make up. For example, in the x,y plane I can define the functions x^2+y^2 and x^2-y^2 simultaneously. What, then, is the significance of "changing" the...
  29. J

    B Bohr's Views on Relativity: What Did He Think?

    We hear a lot of Einstein on quantum physics. Did Bohr ever say what he thought of relativity?
  30. C

    Relativity - energies of particles in circular motion

    Summary: What is energy of proton, deuteron and alpha particle in circular motion of the same radius. Hello, I have a problem. Here is the content of an exercise: In some experiment, proton with energy of 1MeV is in circular motion in isotropic magnetic field. What energies would have...
  31. Noah332

    B Is Time Relative? Understanding Special Relativity

    Im just asking this general question.
  32. sharinglanguage

    B Special Relativity Calc: Half Speed of Light - Jose

    Hello! I am trying to make some calculations on the Special theory of relativity over a practical example, considering the time dilation, but I may (more than likely..) be doing something wrong (probably with my assumptions). I would appreciate any comment on it. The example is that of a rocket...
  33. B

    I Issue With Derivation of Gravitational Time Dilation

    Why do we use the equation ##\frac {1}{2}mv^2 = \frac {GmM}{r}## to derive potential velocity, and then put that in the Lorentz factor in order to derive gravitational time dilation? Shouldn't we be using the relativistic definition of kinetic energy -> ##mc^2(\gamma - 1)## to derive the...
  34. haael

    A What does the image of the black hole say about general relativity?

    We all heard about the "photo of black hole". My question is: did this image show any hints of physics beyond general relativity? I read once (not sure where) that the apparent size of black hole shadow is very sensitive to corrections to general relativity. Add some minor correction and the...
  35. N

    How can the time dilation equation explain faster moving clocks running slower?

    Since for the two events of Samir starting the stopwatch, and the stopwatch reaching 10.0s, Samir and his stopwatch are stationary from his own frame of reference, I said it was the proper time and that delta t0 = 10s. Then the speed of the moving frame of reference was 0.6c. I thought placing...
  36. C

    Mass of Hadrons: Verifying Special Relativity

    Hmm the mass of a hadron is an example of the verification of special relativity.The total mass of the quarks isn't equal to the mass of a hadron at rest frame.But quarks are moving very fast due to strong interaction and they gain mass (mass-energy equivalence)
  37. H

    B Magnetic field and moving charge special relativity

    Hi. In a current carrying conductor because of special relativity amount of protons and electrons differ so we get an electric field or as we call it magnetic field. So if magnetic field is just an electric field how is it that the charge has to move so that magnetic field would exert a force on...
  38. K

    4 momentum mass non-conservation, special relativity

    Homework Statement A particle with mass M and speed v along the positive x-axis hits a stationary mass m. Two particles, each with mass µ, emerge from the collision, at angles with respect to the x-axis. (a) Write the equation for conservation of the 4-momenta, for arbitrary angles θ_1, θ_2 of...
  39. M

    I General Relativity and light deflection

    I am a student of physics at a local Junior College in Mendham NJ and am planning on transferring to a 4 year program at the University of Alabama in a year. Iam having a bit of a difficult time understanding general relativity. Why does a photon bend twice as much under a gravitational field...
  40. Hawkingo

    I Can this event vary relatively?

    Suppose we take a charged particle and a magnet and place them at some particular distance apart .Now let's take 2 frame of reference. [the charged particle and the magnet are in rest with respect to each other through out the whole event]{both of the frames are inertial} frame(a): this frame...
  41. X

    B Special Relativity: Time Measurements on Two Systems - Mike's Question

    I saw this question on special relativity on the internet: "A spaceship traveling to Alpha Centauri, at 0.95C it takes 4.5 years to get there as measured on Earth.how long does it seems to the spaceship passengers?" the answer was 1.4 years (Lorentz factor of 3.2). this answer makes no sense...
  42. universal2013

    I Solving Special Relativity Problem w/ Two Spaceships

    Hello there. In class, our teacher solved one question and asked us what did we wrong specifically in the solution because there were two sets of them. Two spaceships are moving through +x and -x and there is a distance L between them. From one observer which is stationary in the line of L/2...
  43. Cerenkov

    B General Relativity: Finding Info on Interpretation

    Hello. I have some questions about general relativity that (I hope) will be permitted in this forum. Not long ago I discovered that there is more than one interpretation of GR. Now, I believe that the issue of interpretation is considered to be philosophy and therefore off topic. If that's...
  44. N

    Relativity Paradox: Solving for Different Observers in the Cloud and Ship

    I'm trying to solve this problem but I get a different answer depending on which observer I solve it for. For the observer in the cloud, the parallel light has traveled 2.294cs, but this is only 0.23cs in front of the ship. 0.23 cs is only 0.086cs in the perspective of the ship due to length...
  45. T

    I Confusion about Simultaneous Events in Relativity

    In Lee Smolins book Time Reborn he discusses simultaneous events and says events that are far from each other we find that there is no absolute ordering that all observers can agree on. For some observers the two events may be simultaneous for other observers one event may be in the past of the...
  46. MatthewNITX

    Relativity Suggestions for a Physics Textbook on Special & General Relativity

    Hey my fellow physics-students/physicists. I'd like to ask if you guys could suggest me a textbook/s that sufficient for integrated course of "special" and "general relativity". More precisely, That contain about: Introduction about the birth of relativity and principle, and the transformation...
  47. robphy

    B General Relativity as a Challenge for Physics Education

    This week I am at "General Relativity as a Challenge for Physics Education" 690. WE-Heraeus-Seminar https://www.we-heraeus-stiftung.de/veranstaltungen/seminare/2019/general-relativity-as-a-challenge-for-physics-education/ (...
  48. K

    I Allowed fields in General Relativity

    How do you know what fields can be coupled with the gravitational field? Is there a general procedure for knowing it or we have to try out and see whether it makes sense or not?
  49. PeterDonis

    I General Relativity rocket puzzle

    A while back I posted a black hole horizon puzzle. This is another puzzle in the same general spirit. It is based on the scenario described in this old PF thread: https://www.physicsforums.com/threads/a-flaw-of-general-relativity.115418/ Needless to say, as was the case with my previous...
  50. Zack K

    B How did Einstein come up with the thought of a space fabric?

    I've always wondered how we came to come up with such an idea. Was he one day sitting around and thinking, then made a random assumption and go "ah hah!". Or did his idea come up through his calculations on the nature of how gravity should cause interaction? Is their a literal fabric of space...
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