What is Special relativity: Definition and 1000 Discussions

In physics, the special theory of relativity, or special relativity for short, is a scientific theory regarding the relationship between space and time. In Albert Einstein's original treatment, the theory is based on two postulates:
The laws of physics are invariant (that is, identical) in all inertial frames of reference (that is, frames of reference with no acceleration).
The speed of light in vacuum is the same for all observers, regardless of the motion of the light source or observer.

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  1. alexandrinushka

    B Sagnac effect for matter beams

    Hello, I have recently come across this article by Rizzi and Ruggiero, called "The Relativistic Sagnac Effect: Two Derivations": https://arxiv.org/pdf/gr-qc/0305084.pdf In section 3, the authors derive the Sagnac proper time difference for all beams (light beams and matter beams, including...
  2. A

    A Generalize Special Relativity for Flat Spacetime

    I am looking for generalizations of special relativity for flat spacetime. Of course, most well known generlaization of SR is general relativty. There are many other generalizations of SR for curved spacetime. All what I found is for curved spacetime. Are any more or less successfull attempts to...
  3. Halc

    I Cat Chasing Red Dot Faster Than c: Results & Analysis

    This topic assumes special relativity only, so no gravity is involved. I wanted to know how a superluminal thing would appear to an observer, and two of the 'things' I thought of were a moiré pattern and the red dot projected by a laser pointer. The former can be discussed, but this post will...
  4. J

    I What is the Meaning of Lagrangian in Special Relativity?

    According to @vanhees71 and his notes at https://itp.uni-frankfurt.de/~hees/pf-faq/srt.pdf under certain conditions one can choose ##\tau## as the parameter to parametrize the Lagrangian in special relativity. For instance if we have, $$A[x^{\mu}]=\int d\lambda...
  5. R

    Galilean transform and Lorentz transform questions

    I have a quick question about the Galilean transform. If I have Alice running and Bob stationary. The Galilean transform will tell me the position of Alice from Bob's stationary position. Also if I have Alice's position which is moving it will tell me Bob's stationary position. If I want Bob...
  6. F

    I Comparing Clock Rates in Accelerated vs Constant Velocity Frames

    @PeroK sent me here based on a discussion starting at https://www.physicsforums.com/threads/some-ideas-on-interstellar-space-travel.1006562/post-6550265. Summary: Someone claimed that an accelerated observer's clock (observer at 1g from Earth to halfway to Alpha Centauri, then -1g the rest of...
  7. S

    I Time Dilation Paradoxes Near C: Exploring the Twin Paradox of Special Relativity

    I'm struggling to wrap my head around the twin paradox in special relativity especially when dealing with multiple vectors. In my thought experiment say I have a set of twins. Both set out in opposite directions and intend to sling shot around two different black holes(luckily equidistant from...
  8. Diracobama2181

    Special Relativity Muon problem

    i) The muon reaches the ground ii) To a ground observer, the decay time is dilated $$\Delta t_d=\frac{1}{\sqrt{1-\frac{v^2}{c^2}}}\Delta\tau_d>\Delta \tau_d$$ The time for the muon to reach the ground is $$\Delta t_g=\frac{10 km}{0.999c}< \Delta t_d$$ which is why it reaches the ground...
  9. Samama Fahim

    I Deriving Lorentz Transformations: Hyperbolic Functions

    While deriving Lorentz transformation equations, my professor assumes the following: As ##\beta \rightarrow 1,## $$-c^2t^2 + x^2 = k$$ approaches 0. That is, ##-c^2t^2 + x^2 = 0.## But the equation of the hyperbola is preserved in all inertial frames of reference. Why would ##-c^2t^2 + x^2##...
  10. L

    A Special Relativity: A^μ_ν Differences Explained

    Can someone explain me difference between A^{\mu}_{\hspace{0.2cm} \nu} A^{\hspace{0.2cm} \mu}_{\nu} and A^{\mu}_{\nu}?
  11. thedubdude

    B Special Relativity violation via Quantum Mechanics?

    We know that both momentum and position can not be known precisely simultaneously. The more precisely momentum is known means position is more uncertain. In fact, as I understand quantum mechanics, position probability never extends to 0% anywhere in the universe (except at infinity) for any...
  12. U

    B Special Relativity and the Measurement Problem of QM

    Given what we know about special relativity and its implication for time and the observer, could this in any way be linked to why the isolated processes of QM are exhibiting everything happening at once and then collapsing to classical physics when bigger objects interact - the measurement...
  13. diazdaiz

    B Help Me Determine Validity of Time Dilation Formula

    I recently trying to learn General Relativity by first scraping the surface on ScienceClic's general relativity playlist, and then I stumbled upon a video where it said that we actually move through spacetime on a constant speed of c, and then I remember about time dilation because how speed on...
  14. G

    Special relativity - measure of a rod and simultaneity

    Hi, I´m trying to solve a special relativity problem, and I think I need some help. There are two inertial frames of reference, ##O## and ##O'##, the last one moving with relative velocity ##v## in the ##x## direction. There's a rod with length ##L'## fixed to frame ##O'##, such that front end...
  15. C

    I Special Relativity: Grokking for a Female Neurobiologist in her 60s

    I'm a female neurobiologist in my 60s with a lifelong passion for physics (but my math was not strong enough). I have a special interest in special relativity and a decent grasp of the basics. I can solve Lorenz calculations 'til the cows come home'. I don't need help with homework of any type...
  16. Istiak

    Find second object's velocity in relativity

    > A particle of mass M at rest decays into two particles of masses m1 and m2 traveling in opposite directions at velocity v1 and v2 respectively. Express v2 in terms of v1, m1, m2, and M. Since both objects are from a single object that's why I took relativistic mass of both objects are same. I...
  17. R3ap3r42

    Special relativity and Lorentz Transformation Exercise

    Summary:: Special relativity and Lorentz Transformations - I got this problem from a first-semester course at university. I have been struggling for a few days and decided to get some help. A rocket sets out from x = x' = 0 at t = t' = 0 and moves with speed u in the negative x'-direction, as...
  18. alexandrinushka

    B Why is Lorentz Ether Theory Hard to Rule Out?

    I am reading pretty much everywhere that LET (Lorentz Ether Theory, or call it Neo-Lorentzian Relativity, or whatever theory that involves a preferred undetectable frame with some yet unknown properties that make all the moving objects with respect to this frame length contact and time dilate)...
  19. alexandrinushka

    B Any plausible explanation for dynamical length contraction?

    I am new here, so pardon my ignorance. First of all, I am aware of the impossibility to distinguish experimentally between SR (Special Relativity) and LET (Lorentz Ether Theory). I know there is a PF policy article on LET and the Block Universe. I must admit though that LET is more appealing...
  20. D

    I Time & Gravity in Rotating Faster Than Light?

    If a person was rotating on a verticle axis from head to toe like the Earth or quasar. If nothing can go faster than light, from the person's perspective looking at the stars traveling across the night sky, if you increase the rotation of the earth, stars further than a certain critical distance...
  21. B

    I Judge Original Time & Length Special Relativity

    How to Judge original time and original length of special relativity
  22. R

    I am confused by the concept of space-time in special relativity

    I am confused by the concept of space-time in special relativity, I have 3 spatial dimensions and 1 time dimensions. In Newtonian physics don't I also have 3 spatial dimensions and 1 time dimension? Then why call it space time in special relativity and not in Newtonian physics?
  23. Yink

    An introductory question about special relativity

    The way I was doing is that I list events 1. lightning hits x=0 this is (x_1=0,t_1) 2. lightning hits x=12 (x_2=12,t_2) 3. left lightning reaches "me" (x_3=9,t_3) 4. right lightning reaches "me" (x_4=9,t_4=t_3) t_4=t_3 since "I" see the lightning at the same time Then the...
  24. S

    I Time Dilation at Moving Black Hole Event Horizon

    Hello everyone, I have a hard time to conceptualize the case of a moving black hole. We know from SR that time slows down for moving objects; but time dilation at the event horizon is already equal (tends) to zero. It seems that it can create some sort of conflict for the black hole movement...
  25. alan123hk

    B Solving the twin paradox with special relativity

    I saw a book that uses special relativity to solve the twin paradox, the inference process is roughly as follows. Suppose a spacecraft sets off from the Earth to travel to a distance black hole and then return to the earth. We divide this process into three stages, that is, the process of...
  26. alan123hk

    B Special Relativity & Lorentz Transformation Q: Clock C2 Reading?

    I believe this does not belong to the homework category. I hope I won't be mistaken. I am reading a book to self-study special relativity, the following is an example mentioned in the book. When clock C' and clock C1 meet at times t'=t1=0, both clocks read zero. The Observer in reference frame...
  27. Andreas S-H

    B Calculating Energy Loss of Muon Moving Through a Medium

    Hello everyone. I have just complete an experiment calculating the speed of a muon. I got it to 2.6E8 m/s, however I know that they are created at close to speed of light to be able to get down to Earth's surface in their short lifespan. This speed could not have been its initial speed, as it...
  28. FMJalink

    I Proof of Special Relativity w/ Michelson–Morley Experiment

    Dear readers, Maybe someone can enlighten me on the understanding of the proof given by the Michelson–Morley experiment on the special relativity. Just as introduction to detail the setting: There are 2 coordinate systems A and B. A stands still and B moves with the velocity v along one of...
  29. BadgerBadger92

    I Time Dilation vs. Doppler Effect: Similarities & Differences

    Does time dilation in Special Relativity relate to the Doppler effect? If you move near the speed of light you experience time differently and the sound is stretched. Are these similar phenomenon?
  30. L

    Relativity Special relativity in Lagrangian and Hamiltonian language

    Some introduction books on Lagrangian and Hamiltonian mechanics use classical mechanics as the theoretical framework, and when it come to special relativity it goes back to the basics and force language again. I would like to ask for some recommendations on good books that introduces Lagrangian...
  31. L

    I Understanding Special Relativity and Coordinates

    I'd like to get some help on checking my understanding of special relativity, specifically I'm trying to clarify the idea of coordinates. Any comment is really appreciated! The spacetime is an affine space ##M^4##, which is associated with a 4 dimensional real vector space ##\mathbb{R}^4##...
  32. R

    Why is time = ct and not t in special relativty?

    Why is time = ct and not t in special relativity? I just started reading the book I was recommended. Maybe I missed it but as stated in the title why is time = ct and not t in special relativity? I understand they want distance/space = time. Just how do they go about doing that mathematically...
  33. Andreas S-H

    B Proving Special Relativity w/ Standard Equipment

    Hello everyone, I am preparing to write an exam project in college about special relativity, however i am missing the critical experiment to prove that it is true. I thought about using the life time of muons, but i don't have a scintillator to detect them, so unless a standard geiger counter...
  34. LCSphysicist

    Special relativity and simultaneity: Spacecraft and Target

    I made an exercise whose question is like that: A spacecraft moves with speed v at the axis x. There are two target at the axis x, in which the distance between them is L at the ground frame. Suppose that the spacecraft shoot the target simultaneously when it passes by the target. A|so...
  35. Trysse

    I Exploring Physicists' Opinion on 'Moving Through Time

    I recently had a discussion with my brother, about what it means to "move through time". His opinion is, that physicists cannot take this literally. His opinion is, that time is just an expression for change that takes place at different rates for different observers depending on their speed...
  36. R

    Minkowski diagram, where to put an event

    I drew the Minkowski diagram, but I'm not sure if this is correct. From what I drew the angle between x and ct ##\approx 0## then the event is "inside" the light ray and will eventually reach A.
  37. BadgerBadger92

    B Special Relativity and Light -- How does speed of an object affect time?

    I am an amateur in physics and I have a question. How does speed of an object affect time?
  38. R

    Relativity I want to learn special relativity. More details below

    I want to learn special relativity.I have read a tiny bit of 2nd edition of Spacetime Physics: Introduction to Special Relativity and am liking it. Is it a good book? I also want problems to solve. I tried Special Relativity: For the Enthusiastic Beginner but found it to difficult. Does anyone...
  39. LCSphysicist

    Special relativity, a train and a light pulse

    i am having some hard time thinking about this problem: It is basically this: Imagine a bulb and a receptor distant L from each other (at the same axis x) inside a room, the roof of the room is at a height d from the bulb and receptor. Now you are at a train moving horizontally, parallel to...
  40. HakemHa

    Two observers viewed from different sources

    I builded the translated lorentz transform, at t=0 t'=-22.5 and x'(x=0)=67.5 after that I just didn't the question
  41. Harry Case

    I Understanding Jacobian Matrix Transformation in Special Relativity

    While learning about Special Relativity I learned that we use the Transformation matrix to alter the space .This matrix differs for Contravariant and Covariant vectors.Why does it happen?,Why one kind of matrix (Jacobian) for basis vectors and other kind(Inverse Jacobian) for gradient...
  42. A

    I Time Dilation on 3D Torus: Clock Speed & Why It Matters

    Assume that space is a three-dimensional torus ( a 3D donut) . If there is a clock traveling at a CONSTANT speed in a direction parallel to the torus (inside out of the hole) and one clock that is still. Which clock ticks faster and why? I know that the clock rotating will tick slower, but I...
  43. N

    I Hafele-Keating Exp: Balancing SR Effects in Plane Ref Frame

    I have seen the "Hafele-Keating with the plane as reference frame?" thread (https://www.physicsforums.com/threads/hafele-keating-with-the-plane-as-reference-frame.767913/ ), but the replies do not seem to explain (to me anyway) what when taking a plane as a reference frame, balances the slowing...
  44. LCSphysicist

    Special relativity and acceleration

    A particle is moving along the x-axis. It is uniformly accelerated in the sense that the acceleration measured in its instantaneous rest frame is always g, a constant. Find x and t as functions of the proper time τ assuming the particle passes through x0 at time t = 0 with zero velocity.I n...
  45. fee_de

    B Understanding Spacetime Diagrams from "Reality is not What it Seems

    I'm reading a book called "Reality is not what it seems: the journey to quantum gravity" by Carlo Rovelli and I'm struggling to understand this diagram that is part of the chapter about special relativity. https://i.stack.imgur.com/JgBDJ.jpg Before this image Rovelli writes: "It's not...
  46. U

    Some help in understanding energy conservation

    While I am working through proving the homework statement, I encountered a problem. The problem is as follows: From the energy equation above, one can see that the minimum value of ##p## is ##m_T##. However, how does one explain why when ##p=m_T##, ##\sqrt{m^2_B+m^2_T}>m_A##?
  47. L

    I Relativistic Force & Velocity Relation to Acceleration

    According to this link here https://en.wikipedia.org/wiki/Relativistic_mechanics#Force , we can inverse the relation of force in terms of velocity and acceleration: $$ \mathbf{F} = \frac{m\gamma^3}{c^2}(\mathbf{v} \cdot \mathbf{a})\mathbf{v} + m\gamma\mathbf{a} $$ to get: $$ \mathbf{a} =...
  48. V

    B Time Dilation: Traveling to a Distant Star in 4.5yr

    If there is a spaceship traveling at 0.999c, the time to reach a star 100 lyr away would be approx 100 yr (assuming no accel and decel). But on the spaceship, It would be 100 yr * sqrt(1-0.999^2) = 4.5yr. Why do we take 100 yr as the time seen on Earth and not the time on the spaceship?
  49. P

    Question on special relativity from "Basic Relativity"

    Summary:: Require confirmation regarding answers to a question posed by the book "Basic Relativity" by Richard A. Mould. Here is a problem which I encountered while going through Basic Relativity by Richard A. Mould- I'd like to receive a confirmation regarding the answers I've come up with to...
  50. P

    I Violation of Special Relativity Principle?

    From the michelson-morley experiment, if a clock were to measure the time period of light hitting the mirror and returning back, it would be 2L/c, where L is the distance between the laser nd the mirror. For a moving observer, the time period would have a factor of *gamma*, the boost factor...
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