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. V

    I Momentary Co-Moving Reference Frame in SR

    In SR, for the momentary co-moving reference frame, U (the velocity four vector) takes the form (1,0,0,0). I'm wondering whether the basis vectors associated with this velocity are zero or if the coefficients in front of the basis vectors are zero. In classical mechanics we would say that the...
  2. I

    B Fundamentals of Lightspeed: Questions & Answers

    Hey there, I'm aware this is a bit of a stupid question, and I think that I understand the principle fundamentally, however, my intuition is still having a little trouble catching up, and I'm trying to figure out if it is because of an important detail that I have missed/misinterpreted. I think...
  3. entropy1

    I Which clock was slower in special relativity?

    I don't know much about the math of SR, but this is what's bothering me: if a moving clock B ticks slower than the stationary one I have (A), then from the viewpoint of B, my clock (A) is ticking slower. So if we turn around and meet each other in the middle, which clock was slower than which...
  4. S

    B Light Clock & Length Contraction in GR

    Hi, can i use a light clock made out of mirrors a distance appart to measure whether there is length contraction in different regions of spacetime? If the clock speeds up then the distance between the mirrors decreased. If the clock slows down the distance between mirrors increased.
  5. Haorong Wu

    Relativity How are David Tong's Lectures on General Relativity?

    Hi. I have tried David Tong's note on QFT. I think it works well for me and lead me into QFT. Now I am confident to read Peskin's book. Now I am trying to learning GR. I planned to try David Tong's lectures on GR first and then read Sean Carroll's book. But I am not sure this plan now. I got...
  6. M

    Length of a Wave Train in Special Relativity

    I am confused about how to find the length of a wave train emitted within a time interval T and that is moving with speed c relative to a moving frame that is itself moving with velocity v. Apparently the answer is that the wave train's length is cT - vT, but I tried to plug in variables into...
  7. M

    Special Relativity Math Thing (Fresnel's Drag Coefficient)

    I am wondering if there is a typo in my textbook. Please see the attachment. The textbook says "...keeping only the lowest term in x = v/c." I am wondering if it should be "x = v/(nc)," as I circled in blue on the left side. It is a binomial expansion of the denominator. Shouldn't x be v/(nc)...
  8. F

    I Understanding the Stress-Energy Tensor in Special Relativity

    Hello, I try to understand how to get the last relation below ##(3)## ( from stress energy tensor in special relativity - Wikipedia ). I understand how to get equation ##(1)## but I don't grasp how to make appear the gradient operator in the dot product and the divergence operator in the...
  9. V

    Which course should I take? (General/Special Relativity or Astrophysics)

    I'm about to be a senior in the physics program. I can choose General/Special Relativity or Astrophysics. The astrophysics course is not as intensive - the GR/SR course requires mechanics and is more math-savvy. I've been doing some modeling with Lagrangian mechanics for star systems etc. and...
  10. D

    B Special Relativity for Beginners: Clock Comparison

    Hi, I have no education in physics beyond the intro undergrad level. How do the clocks compare in the following scenarios? In the beginning, two clocks are placed next to each other and synchronized. Then they are moved in opposite directions, traveling an equal distance from the beginning with...
  11. BruceAW

    I Apparent Violations of Principle of Relativity?

    I have for a long time been pondering the concept of 'Absolute velocity'. Or, 'Proper motion'. The velocity of an object, with respect to the center of mass of the universe, and the cosmic microwave background radiation. Ways, it seems to make more sense, than merely relative velocities, with no...
  12. J

    I Does General Relativity explain inertia?

    As far as I understand it general relativity does not explain the origin of the inertial mass ##m_i## in Newton's law of motion ##\vec{F}=m_i\ d\vec{v}/dt## but rather it simply applies the concept to curved spacetime. For example if we have a particle with inertial mass ##m_i## and charge...
  13. R

    B General Relativity, Twins & Schopenhauer: Analyzing Timing Diff.

    Consider a mass ##M## that generates a curvature of the space-time and an observer ##O##, fixed and positioned at such a great distance from ##M## that the time ##t## of its clock is not affected by ##M##. Suppose that the observer ##O##, in his polar coordinates reference system centred at...
  14. jk22

    A Nonlocality Theorems & Relativity Principles

    Do nonlocality theorems imply that the local inertial frame principle of general relativity is wrong (since it is local) ?
  15. greg_rack

    B Space is Relative: A 17 Yr Old's Exploration

    Hello everybody, my question may sound stupid, especially speaking of such a mind-blowing and important theory... but here I am! I'm 17 and I'm reading a fabulous book by Stephen Hawking, "A Brief History of Time", and it introduced me to relativity theories... I literally started looking the...
  16. D

    B Why the stay-at-home twin is not considered to be accelerating?

    I am not a physicist. I need your kind help in removing my following doubt about twin paradox. What I have been able to understand about twin paradox is this- 1. Special relativity deals with non-accelerating (inertial) motion. 2. The traveling twin (A) moves at a high speed in relation to the...
  17. Bob Walance

    B General Relativity & External Forces: 2 Cases Examined

    It seems that there are two distinct gravitational cases to consider: a) Object with no external contact with any type of stuff (e.g., a person in free-fall in a vacuum) b) Object WITH external contact (e.g., a person standing on the ground) I've enjoyed reading and listening to various...
  18. A

    I Solve Constant Acceleration Problem in Special Relativity

    Basically I just want to work out a constant acceleration problem in relativity, of the same kind of introductory physics. Vo= 0.9999c Vf = 0 D= 50 Au Accel, Earth frame? Accel, Ship frame? Time of transit, Earth frame? Time of transit, ship frame? Motion is 1-D. All origins line up at the...
  19. H

    I Mass Unit in General Relativity

    James Clerk Maxwell deduced that the unit of mass has the dimensions of (L^3)(T^-2). But he assumed Newton's Law. What would it be under general relativity?
  20. I

    B Can an Object Exceed the Speed of Light?

    I was curious if the relative speed of an object can exceed the speed of light. Specifically, I am curious about the following thought experiment. I am not a physicists (and if I were asking the following would make me a poor one) and it has been 20 years since college physics. If a vessel is...
  21. Hyotopii

    B Explore Time Perception & Relativity - Get Your Answers Here

    Hello, Dear Readers, as mentioned in the caption and Summary, i'am dearly interested in the perception of time due to relativity. I thought About this for quite some time.What happens to the perception of time to the conciousness, I mean our weight is not the same, and our energy consumption...
  22. Mattv

    B Time Dilation & Relativity: Explained for Beginners

    Good morning I'm a total beginner in physics, but I recently started to read books and watch videos about cool physics stuff, like relativity. I heard that the closer to the speed of light you travel, the "slower" time passes for you. I'm talking about the fact that clocks in GPS satellites...
  23. Souma

    I Using general relativity to violate the uncertainty principle

    Hello everyone, Heisenberg's uncertainty principle tells us that we cannot measure the position and the momentum of a particle to infinite accuracy. My question is, can we use general relativity to overcome this difficulty? From what I know, any mass can curve spacetime even if it was small, and...
  24. B

    B Calculating Relativity of Simultaneity

    The question is in reference to calculating relativity of simultaneity. I am on the step where I take the time in Alice's frame from the front and from the rear clock and minus it to the get the total time. I end up with gamma squared etc (For more details see the picture below) I have...
  25. Matilda111

    B Research Paper: Exploring Decay in c Due to Universe Expansion

    I'm currently writing a research paper about the speed of light. I have researched universe expansion, specifically, the quantised redshift spectral index fluctuations of distant galaxies and other structures over time, however, I need to suggest why universe expansion possibly causes a recorded...
  26. YouAreAwesome

    B Does time dilation work in 1d space?

    Imagine this question in 2 dimensions, time (t) and distance (x), that is (t,x). Alice (A) is at the origin, x=0. Bob (B) begins at x=c. Thus we have A(0,0) and B(0,c). Both Alice and Bob send a light signal towards the other but let's say the signal changes colour every second by the colours of...
  27. A

    Math Courses to Understand General Relativity (by Sean Carroll)

    Hi. What are the math courses should I take in order to understand the mathematics involved in a book such as Sean Carroll in general relativity. Thanks
  28. Nantes

    I Treatment of Relativity in "Las Leyes de la Termodinámica" Movie

    Background: There is a very interesting Catalunyan film on Netflix called "Las Leyes de la Termodinámica" (The Laws of Thermodynamics) which is perhaps the world's first hybrid of a physics documentary and a romance film. The main character is a physics professor who falls in love and attempts...
  29. hagopbul

    Intro Physics Finding Books on Elementary Particle Physics & Special Relativity

    hello all : looking for books to read in this times ,undergraduate level mostly , but i have some problem finding good ones for introductory elementary particle physics other than griffths and for special relativity any recommendations
  30. A

    I Sachs and Wu's General Relativity for Mathematicians

    I am trying to study "religiously" the book by Sachs and Wu, but I am finding the Exercises very much of a challenge. Does anyone know if there exists a source for solutions one can consult when stuck?
  31. P

    Special relativity, a non-inertial perspective

    I have tried calculating it as a Uniform Accelerated Movement problem: , where t is the time for the observer at Earth, O. For calculating t'' (the proper time for the accelerated spaceship observer), it is just using a Lorentz transformation? It seems easy, but as is stated that the frame is...
  32. S

    I What stars were observed @ 1919 solar eclipse to prove relativity?

    Was there a published report of exactly which stars which were supposed to be at position A but were observed at position B, etc.?
  33. Lynch101

    B Bell's theorem, QFT, and the Relativity of Simultaneity

    I've been slowly grinding away with what I can about quantum mechanics and QFT. I'm not sure how far I've gotten but I've come up against a bit of a roadblock concerning how the relativity of simultaneity applies in QFT with specific reference to the outcome of Bell tests. My misunderstanding...
  34. L

    Laws of conservation in special relativity

    Momentum ##\vec{p}## before collision is momentum of proton of the energy ##E=76.4\mbox{GeV}##. Law of conservation of energy is E+mc^2=E_1+E_2+...+E_n mc^2=0.94\mbox{GeV} We could generate only even number of particles after collision because of law of conservation of electric charge. Also...
  35. P

    Quick Check for Relativity HW, rocket passing by space station

  36. H

    Does Galilean relativity imply infinite propagation speed?

    Without assuming a universal speed that is constant in all inertial reference frames, is it a necessary consequence of Galilean symmetry that interactions are instantaneous? If this is the case how can we prove this?
  37. F

    I Electromagnetic field according to relativity

    Hello, I am still trying to fully grasp the general idea of the EM field, which always travels at the speed of light regardless of the reference frame, and is represented by a tensor with 16 components in relativity theory. My understanding is that, depending on the observer's frame of...
  38. PainterGuy

    Stats on Students Understanding Theory of Relativity

    Hi, I'm not sure if it's a good idea to start a thread about the following problem but I didn't want to PM anyone. Some time ago I came across a thread which had stats related to the problems faced by students learning the theory of relativity. It showed like how many undergraduates really...
  39. danielhaish

    B Relativity & Computer Calculations: Speed Up 300x?

    there is many analog dividing machine that base on time counting . so does this machines work faster on height speed system such as Particle Accelerator it may help in decryption of public encryption and other coculation . It looked at relative calculator and in the speed that close to the...
  40. B

    Series of questions about Special Relativity

    https://scholar.harvard.edu/files/david-morin/files/relativity_chap_1.pdf The questions start at page 44 Whenever I refer to y, y = gamma. 1.1 This question is primarily deriving LV/C^2? How does 2LV / c^2-v^2 becomes 2Lv / c^2(1-v^2/c^2)1.4 On the solution page it shows fig 1.61 and fig...
  41. B

    I want to learn special and general relativity

    Summary:: I want to learn special and general relativity I am curious what is the best way to learn special and general relativity. https://www.coursera.org/learn/einstein-relativity/home/info I started this course but it seems relativity easy so far. Only on week 2. Being easy is not bad I...
  42. P

    (Relativity) A flash of light is emitted at x1 and absorbed at x1 + l

    My answers are quite different and here are my attempts a) What is the spatial separation ##\ell'## between the point of emission and absorption? (In the frame going ##v = \beta c##) From what I know is that moving causes lengths to be contracted according to the formula ##\ell_{travel} =...
  43. M

    I Where is Contraction Point in Special Relativity?

    Generally speaking, when a simple contraction occurs there is a contraction point. Length contraction in special relativity appears to be a simple contraction, and hence there should be a contraction point. Where is this contraction point located?
  44. M

    I Special Relativity & No Special Inertial Frame of Reference

    As per special theory of relativity, no inertial reference frame is special! If a spaceship is moving at 100 m/s, no one can conduct an experiment to determine whether it is moving at 100 m/s or the rest of the universe is moving to the opposite direction at -100 m/s, if I understand the...
  45. HaoBoJiang

    It's pleased to meet everybody

    I am a physics graduate student, also a physics enthusiast.I prefer Mathematical Physics, and often do some related research.Like everyone of you, I also have a strong interest in physics, and I hope to generate more new ideas and broaden my knowledge through exchanges with you.
  46. Lincon Ribeiro

    I Lorentz Arguments for Ether: Critical Analysis of 1895 Paper

    I bought the book "The principle of Relativity" by Einstein et al. and was really surprised by the (low) level of explanation by Lorentz regarding the compression of rods on the experiment carried out by Michelson & Morley. I reproduce part of it below: Well, he gave absolutely no arguments to...
  47. K

    I Special Relativity: Constant Speeds or More Complex GRT?

    I'm reading the online version of a book that says Rindler observer comes right into my mind when I read this. So I think the book is wrong. What do you all think? On a second guess, perhaps the author takes the view that SR is only for constant speeds in the same sense that one could say that...
  48. LeeHilliard

    B Time & Special Relativity: Is Time Object-Specific?

    If time slows as an object increases velocity wouldn't that indicate that time is object specific? And if the speed of light is a constant and does not change regardless of the velocity of an object wouldn't that indicate that time used to measure the speed of light changes? The video I have...
  49. T

    A shot in the dark -- Need help understanding Special Relativity

    first off hi all. Just joined, i was looking for someone to help me understand time dilation and spatial contraction in relativity. its not homework just something i was watching, very good btw, but left me with some contradictory information as i see it. if anyone with any level of expertise at...
  50. KipIngram

    I Struggling with a special relativity "paradox"

    Ok, I hope someone can help me see how to sort this out. Alice has a full-frame (no rolling shutter) video camera that records exactly 30 frames per second. It's mounted to a telescope looking far out into space. Bob is out there in space with a digital clock that reads out to the millisecond...
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