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. T

    B On the four dimensions of special relativity

    Hello. Questions: How can special relativity describe four dimensions when we only see three spatial dimensions and we experience time?Why time is the fourth dimension and not another physical quantity? Is this only a generalisation that was needed to describe more physical phenomena and the...
  2. J

    I What is the four-momentum of a photon?

    I'm trying to understand the Energy-Momentum relativistic relationships for a light particles. It is commonly said that the Energy of a photon depends on the observer by the relationship ## E = - \mathbf{p} \cdot \mathbf{u}## where p is the 4-momentum of the source emitting light particles and u...
  3. T

    Time dilatation between straight and curved lines in Minkowsi space

    Summary:: Special relativity - 2 astronauts syncronize their clocks and moves in different paths at different velocities, which clocks is left behind? and why? Hi everyone, i have the following problem and I'm not understanding if my strategy to solve it is correct: Two astronauts synchronize...
  4. J

    I Movement of a guitar string at relativistic speeds

    Hey! I'm and undergrad in the third year of my applied physics program. I'm taking a course in Special Relativity, and due to Corona the exam has been replaced by a pretty free project where we delve deeply into a topic related to the course. I'm interested in music, so my professor suggested I...
  5. Charlie K Trout

    I Explore Alternative Interpretations of Special Relativity

    A few years ago, a nuclear engineering professor explained to the class that the widely accepted theory between the relationship between space, time, and velocity may be wrong. At the time, I didn't think much about it since he had a lot of out-there beliefs and he seemed to be a bit of a...
  6. G

    Relativity David Morin's special relativity for the enthusiastic beginner

    1.8 Exercises page 49 I can't find the solutions to the questions. Where are they?
  7. F

    I Momentum Conservation in Special Relativity: mwu

  8. LCSphysicist

    Special relativity — Observer measuring the velocity of a passing rocket

    I am a little confused with the text above. Actually, all is ok until 2.51, i think i am missing something. What is this? Another way to define gamma? (The doubt is not about the raising indices, neither about "n00 = -1", is just where does the equation came from. That is, the equation is easy...
  9. steve1763

    A Determining Geometry of Line Element: A General Method?

    Is there a general method to determine what geometry some line element is describing? I realize that you can tell whether a space is flat or not (by diagonalising the matrix, rescaling etc), but given some arbitrary line element, how does one determine the shape of the space? Thanks
  10. J

    Can Heat Transfer Through Conduction Occur at Relativistic Speeds?

    Are there any known instances of heat transfer via conduction or convection happening at relativistic speeds? Is this even possible or is there a non-relativistic limit to how fast heat can transfer in these ways, like how sound can only move so fast?
  11. R

    I Special Relativity: Intuition & Quantities Explained

    Hi, I'm taking an introduction course to Special Relativity and encountered a fairly simple problem: Dirac travels to alfa centauri, which is 4.37 lightyears away. He stays there one Earth year and then travels back, and when he comes back he has aged 5 years. At what speed did he travel...
  12. Adams2020

    I The center of mass & relativistic collisions

    In special relativity (especially relativistic collisions), is the center of mass frame as useful as Newtonian mechanics?
  13. J

    Special Relativity - relative motion of two bars

    Hi, I'm stucked in this exercise. I don't know how to proceed. Any hints I appreciate it.Two bars of the same proper length L, moves in the same way on the x axis. In the referential of one of the bars the time interval between the events, when the extremity right of one bar and the extremity...
  14. F

    I Special Relativity & Non-Instantaneous Force Equations

    In classical mechanics, the gravitational force is described by the equation: F = Gm1m2/r^2 What would this equation - or other similar equations - look like in special relativity? This equation cannot be correct because it implies that the force acts instantaneously.
  15. Amaterasu21

    I How Does Relativity of Simultaneity Clash w/Thermodynamics?

    In special relativity, observers can disagree on the order of events - if Alice thinks events A, B and C are simultaneous, Bob can think A happened before B which happened before C, and Carlos thinks C happened before B which happened before A - provided A, B and C are not causally connected, of...
  16. F

    I Acceleration in Special Relativity

    Can special relativity handle acceleration? I believe the answer is yes, but I don’t recall dealing with any acceleration problems when I took SR. I remember using the time dilation, length contraction and Lorentz transformation equations. These equations all assume constant motion iirc.
  17. cianfa72

    I Does Lorentz invariance imply Einstein's synchronization convention?

    Hi, I've read a number of posts here on PF about Einstein's clock synchronization convention. In the context of SR we know the transformation law between inertial frame's coordinates is actually the Lorentz one. The invariant speed for Lorentz transformation is c (actually it coincides with...
  18. cianfa72

    I Check for geodesically-followed path in a coordinate-free way

    Hi, My question can result a bit odd. Consider flat spacetime. We know that inertial motions are defined by 'zero proper acceleration'. Suppose there exist just one free body in the context of SR flat spacetime (an accelerometer attached to it reads zero). We know that 'zero proper...
  19. thequantumcat

    I Special Relativity and Velocity

    I can't seem to wrap my head around it: if an object is moving at speed v in frame S, and its observed to move at speed v' in S', what is the relationship?
  20. Pyter

    I What happens when twins synchronize clocks and one teleports?

    Hello all. Recently this twin paradox variant occurred to me, and I can't wrap my head around it: Alice and Bob are in the same (roughly inertial, for our purposes) reference frame, separated by a sideral distance. Let's say Alice is on Earth and Bob on Pluto. They synchronize their clocks at...
  21. F

    I Why Does Special Relativity Not Contradict General Philosophy?

    I hear that philosophy refuse to "relativity concepts"(e.g relativity moral).Relativity theory says about the relativity of spacetime.I do not understand why special relativity does not contradict with general philosophy?(I know the theory Idea Form of Plato)
  22. 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...
  23. Data Base Erased

    Why Does a Moving Rod Appear Inclined in Different Reference Frames?

    Ateempt of solution: There are two key coordinates in this scenario, the leftmost tip of the rod, which in ##S'## is ##C_{0} = (t', 0, ut',0)## and the opposite tip ##C_{1} = (t', L,ut',0)## An angle ##\phi## could be found through a relationship such as ##tan(\phi) = \frac{ \Delta x}{ \Delta...
  24. 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...
  25. 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)...
  26. 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...
  27. docnet

    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...
  28. L

    I Proving Antisymmetry of Electromagnetic Field Tensor with 4-Force

    I've already made a post about this topic here, but I realized that I didn't understand the explanation on that post. in Chapter 7 of Rindler's book on relativity, in section about electromagnetic field tensor, he states that _and introducing a factor 1/c for later convenience, we can ‘guess’...
  29. George Plousos

    I A version of the twin paradox without accelerations

    Bob is standing on Earth and Alice is on a distant planet at a constant distance from Earth. Their watches are already synchronized in the following sense: Suppose Alice's planet is a light-year away from Earth. Bob emits a light signal to Alice at time t = 0 according to Bob's watch. When Alice...
  30. Stephen Bulking

    Length contraction and Time dilation for LIGHT?

    Radio wave travels at the speed of light 3x10^8 (m/s) Converting the distance to meter: 1.3 x 3.1x 10^16 = 4.03x10^16m The time it takes in our Earth frame of reference is: 4.03x10^16m/3x10^8 (m/s) = 4.26 years The answer is B But wouldn't the time in light's frame of reference be 0 and it's...
  31. 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...
  32. R

    I Derive Lorentz Transformation by Visualizing Space-Time Coordinates

    This approach is seeming intuitive to me as I can visualize what's going on at each step and there's not much complex math. But I'm not sure if I'm on the right track or if I'm making some mistakes. Here it is: ##A## has set up a space-time co-ordinate system with some arbitrary event along his...
  33. Sabertooth

    Transforming Y-axis table values into a separate formula?

    Hey everyone, I have generated a nice little velocity vs time graph that I would love if somebody could help me put to use. I have marked data points on the x-axis for the Y-value for every second on the function. Just to be clear: X-axis = time in seconds & Y-axis = velocity in meters/second...
  34. 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...
  35. 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
  36. ersa17

    I Why does time dilation only affect one of the twins?

    I am more confused by the theory of relativity as I start thinking about it. I have a question and it might sound silly but please, correct me if I am wrong. Suppose, A and B are twins where A is at the Earth, and B is moving on a spacecraft at a speed near to the speed of light. In this...
  37. A

    A Solving Jackson's 3rd Ed. Equations Involving A, L and g

    In Jackson, (3rd edition p. 545), there are equations they are given as, $$A = e^L $$ $$det A = det(e^L) = e^{Tr L}$$ $$g\widetilde{A}g = A^{-1} $$ $$ A = e^L , g\widetilde{A}g = e^{{g\widetilde{L}g}} , A^{-1} = e^{-L}$$ $$ g\widetilde{L}g = -L $$ I have several doubts. 1) $$det(e^L) =...
  38. AhmadKhaqan

    A Constant Scalings of 4-Vectors" - Zweibach, 2nd Ed.

    If anybody has studied the book: A First course in String Theory - Barton Zweibach - 2nd edition This statement is present in 6th chapter of book on pg 110
  39. AhmadKhaqan

    An Undergraduate working on a project in String Theory

    Well I became interested in String theory before my high school. Now I am in ginal year of my BS in Physics. I am working on a project in string theory.
  40. 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...
  41. S

    Lorentz transformation for an approaching observer

    I think this should be t'= Lorentz factor* (1+v/c)t, but that doesn't make sense to me.
  42. 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...
  43. Antarres

    A Proving Free-Fall in Rindler Spacetime is Finite

    Okay, so, while discussing Rindler space with my professor, I was asked to prove that for a free-falling observer, proper time for passing through the Rindler horizon is finite. That is at least how the question is phrased. So, the professor obviously assumes that it is clear and trivial to me...
  44. 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...
  45. S

    Infinitesimal coordinate transformation of the metric

    I kinda know how to do this problem, it is just that I hit a sign problem. If I take the partial derivative of the coordinate transformation with respect to ##x'^\mu##, I get writing it first in the inverse form, ##x^\alpha = x'^\alpha - \epsilon^\alpha## ##\frac{\partial x^\alpha}{\partial...
  46. cianfa72

    I Speed of Light in Vacuum in Non-Inertial Frame

    Hi, I read various threads in PF about the concept of invariant speed and the speed of light in vacuum that in our universe happens to be the same as the 'invariant speed'. My doubt is about the speed of the light in vacuum as measured from a non-inertial frame (basically in the context of SR...
  47. LawH

    B Energy, Mass, Speed of Light: Can We Reach It?

    Hello everyone! Let's say that you were to attempt to go as fast as possible on a spaceship with the mass of an average car in an absolute perfect vacuum. What I am wondering is, that if you were to reach a certain speed, and stop applying energy to this imagined spaceship, would the spaceship...
  48. Bob Enyart

    I Do We Need ESC in Earth's Atmosphere?

    Einstein's synchrony convention (ESC) defines the one-way speed of light as equal to the roundtrip speed IN A VACUUM, at least, the discussions and papers I read on it (even Einstein's 1905 paper) always seem to set the context as in space (a near vacuum) or in a (theoretical) vacuum. I'm...
  49. 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?
  50. 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...
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