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. D

    MATLAB General Relativity Package for Friedman Eqns: MATLAB, Mathematica

    I need to simulate the Friedman equations under different conditions of flat space. Can someone please tell me a good package in MATLAB, Mathematica or stand alone. I am most well versed in MATLAB but have coded in Mathematica before.
  2. C

    Relativity What's the best book to learn general relativity?

    What is the best book to learn general relativity for undergraduate and graduate students ? And why?
  3. G

    I General Relativity & Quantum Theory: Where's the Limit?

    I've always read that these two theories are incompatible, and how General Relativity works for large scales while Quantum Theory represent reality in extra-small cases. So my question is where is the limit where General relativity ceases to exist and Quantum Theory gives a better portrait of...
  4. PhysicallyAmazing

    I Velocity Relativity: Solving a Complex Problem

    A problem I struggle to conceptualise as I have began leanring about relativity and seek your guidance and knowledge on: Consider a stationary observer at point A. Relative to the observer there is a train traveling at -0.6c. A passenger on board the train has a particle gun, and fires it in...
  5. T

    Light Signal Travels Between Earth and a Spaceship

    Hi All, An observer, F, stands on Earth. A spaceship, F', is also on Earth. Their clocks are set at 0. The spaceship then leaves Earth at .5c. After 10 seconds, F sends a light signal to F'. As soon as F' receives the signal, F' sends a light signal back. When does F receive this signal from...
  6. K

    Length contraction and time dilation in relativity

    Homework Statement A graduate student discovers that an elementary particle produced in his experiment travels 0.250 mm through the lab at a speed of 0.950c before it decays (becomes another particle). What is the lifetime of the particle measured in its rest frame (proper lifetime). A) 8.77 x...
  7. C

    Rockets approach: time they meet w.r.t. rocket A?

    This is an IB problem from November 2017. Two rockets are separated by 6E8m (2 sec x c, or two light-seconds), w.r.t. Earth, and are approaching Earth from opposite directions. Rocket A approaches from left at 0.6c. Rocket B approaches form right at 0.4c. According to Earth, when do they...
  8. K

    Special theory of relativity, theoretical problem

    Homework Statement Spaceship A, traveling past us at 0.7c, sends a message capsule to spaceship B, which is in front of A and is traveling in the same direction as A at 0.8c relative to us. The capsule travels at 0.9c relative to us. A clock that measures the proper time between the sending and...
  9. S

    Forward light-cones and special relativity

    Homework Statement How can we tell that quantum effects do not propagate along forward light-cones that represent two separate events? How do light-cones demonstrate this notion of quantum effects? Homework EquationsThe Attempt at a Solution We don't know which events occur first given...
  10. mr1batman

    B Why is the general theory of relativity is so complicated

    why is the general theory of relativity is so complicated i feel that it's very simple no thing hard in it there is a whole website to make people understand it i read the articles and i didn't found any thing complicated knowing the i am 13 so it should be very hard to understand
  11. D

    I Special Relativity: Kinetic Energy Expansion and Contradictions

    When expanding Kinetic energy as T=mc2-m0c2 where m0=rest mass and m=m0/sqrt(1-β2) the first term correction is coming out to be -p4/8m03c2 but taking T=E-m0c2 where E=sqrt(c^2p^2+m02c4) the correction is coming to be 3p^4/8m03c2 is there any contradiction?
  12. T

    I Explaining Relativity within 3 minutes

    Who agrees with the result? I don't think she was sufficiently rigorous on her explanation. (She won $800.000)
  13. M

    I Velocity difference not preserved in special relativity

    Consider single line motion. If an observer sees two objects, and one is seen moving say 50 m/s faster than the other, will all other observers measure the same velocity difference? The answer seems to be 'No' from the velocity addition formula of special relativity? Thus same velocity...
  14. A

    I Testing GR to What Energy Level?

    When we talk about energy scales, we often hear that we need new theories of gravity and particle physics when we hit the barrier that is the Planck scale. In particle physics we've only probed up to about 13TeV, which is way WAY below that level. It's easy for us to designate the energy to...
  15. N

    B Answer Questions on Relativity & Speed of Light | Beginner Physics

    Can anyone help me with a very basic question please. Is it really not possible for anything to travel faster than the speed of light, as dictated by relativity theory ? I am a complete beginner to Physics and only have very basic mathematics knowledge and I'm trying to understand the basics of...
  16. J

    B Special Relativity & Relativistic Mass

    Hi, If a particle is within 2 m/s of the speed of light (like at CERN) and then more energy is transferred to the particle, where does this energy go? Some sources I have read talk about relativistic mass getting bigger and approaching infinity as a particle approaches 'c'. However, this source...
  17. G

    B How To Consistently Explain Electromagnetism With Relativity

    Superconducting Ring In a superconducting ring does the contraction of space between electrons cause them to move inwards? Like in this animation. Force Between Parallel Wires With Current In the proton frame of two parallel wires with identical current, I've been told they attract and this...
  18. A

    High Energy Recommended books in HEP, QFT, QM, GR

    Hi everyone! I'm trying to make a list of recommended books (introductory and advanced). So far, what I was able to search are the following: Particle Physics: - Griffiths: Introduction to Elementary Particles - Thomson: Modern Particle Physics - Nachtmann: Elementary Particle Physics -...
  19. Santilopez10

    I Help with special relativity mathematics

    I am having a hard time trying to understand this transformation from lorentz:https://imgur.com/a/WYWMO (You should ignore the spanish part and just focus on the math). I can’t understand well why they turn into what you can see in the second picture, when taking really small values of x...
  20. T

    How Does Invariance Apply in Relativity Theory?

    Homework Statement Homework EquationsThe Attempt at a Solution ok so for w' i am getting since the s' is only moving in x direction ## \omega' = \omega \gamma (1 + \beta) ## is this correct then i am having some trouble in dealing with the dot product to derive for ## \bf {ck'} ##
  21. jgarrel

    General relativity- Coordinate/metric transformations

    Homework Statement Consider the metric ds2=(u2-v2)(du2 -dv2). I have to find a coordinate system (t,x), such that ds2=dt2-dx2. The same for the metric: ds2=dv2-v2du2. Homework Equations General coordinate transformation, ds2=gabdxadxb The Attempt at a Solution I started with a general...
  22. F

    I Questions about the general principle of relativity

    One of the founding principles in GR is the principle of general relativity, which loosely states that all coordinate frames (inertial and non-inertial) are equivalent in the sense that the laws of physics are invariant. My question is, does the justification for this come from Einstein's...
  23. G

    I Does Gravity Change Space Density? Exploring Everything and Nothing

    I was watching a movie called Everything and Nothing. It got me thinking. For the sake of argument pretend that you could make the sun pop in and out of existence. If you were to measure the distance between two points on the other side of the solar system with no sun, then if the sun were to...
  24. J

    I Is MWI the Only Solution for Saving the Principle of Relativity?

    Hi guys, I am new to physics forums and am an undergrad who is really interested in the philosophical implications of quantum physics. I know this isn’t a philosophy forum but upon skimming older threads regarding MWI I have come across an interesting number of posts by a few members named...
  25. B

    I Dirac Matrices and the Pythagorean Theorem

    I understand that momentum, rest mass and energy can be put on the sides of a right triangle such that the Pythagorean Theorem suggests E^2=p^2+m^2. I understand that the Dirac equation says E=aypy+axpx+azpz+Bm and that when we square both sides the momentum and mass terms square while the cross...
  26. C

    I Electrical Current Repelling Magnets Due to Relativity

    I recently watched this Varitasium video where he explains the magnetic field due to a current carrying wire. In the video he explains how what we see and describe as the magnetic field produced by a current carrying wire is actually just a electric force caused by the an imbalance of charges...
  27. A

    B Resolving the Relativity of Simultaneity: A Geometric Approach

    Hi, I read through einsteins popular book on relativity translated into english around 1922 and subsequently read the original 1905 paper on the electrodynamics of moving bodies. So we have a fixed observer seeing flashes happening at the same time and we have a moving observer seeing one...
  28. T

    I Singularities in General Relativity

    There are two kind of singularities which are familiar in General Relativity. One of them is the singularity of Black Holes and the other is at the beggining of the universe. I'm confortable with the former singularity --it seems to make sense. But as with the latter, I'm not so confortable...
  29. Megaton

    B Can General Relativity and Quantum Field Theory Be Reconciled?

    Please don't kill me here...I am really just a curious creature...QFT and GR are mutually incapabatable ergo they cannot both be correct...so best is that one is used for low energy large scale predictions (as per theory) and small scale high energies ( as part theory) ...(BTW I know what the...
  30. A

    A Relativity implies antimatter?

    https://arxiv.org/pdf/hep-ph/0609174.pdf page 8. 2.1.2 Special Relativity Requires Antiparticles This article describes a scenario in which atom A releases an electron which is absorbed by atom B. A=> A+ and B => B- However in a different inertial frame (F) it is possible due to Heisenberg's...
  31. P

    B Time Dilation: Moving Rocket 0.5c vs Accelerating Rocket 0.5c

    A non-moving observer is looking at two different rockets in space. One rocket is moving at a steady velocity of 0.5c, and the other rocket is currently moving in 0.5c but has steadily accelerated from 0.3c and will continue accelerating until it gets to 0.7c. Assuming that there is no...
  32. S

    B Volumes and Hyper Volumes Related Special Relativity

    How can volumes and hypervolumes be related to Einstein's theory of special relativity and to quantum mechanics? Also, can volumes and hypervolumes of objects be used for modeling how different scenarios can change over time? Oh yeah, and hi my name is Sasha Jaffarove!
  33. A

    B According to General Relativity, would the Earth be 'flat'?

    I thought about the geometry of Earth by definition and thought of the implications of 'curved space-time'. I understand a trajectory of a satellite and other objects to be straight geodesics through warped space-time. Would the Earth then therefore be able to described as a straight surface in...
  34. P

    The electric field in an expanding, statically-charged tube

    Imagine that I have a straight, statically-charged, cylinder-shaped tube with arbitrary (ideally infinite) extent. The charge is distributed evenly over the tube such that the field inside the tube is zero. For convenience, let's line up the tube centered along the x-axis such that the...
  35. T

    Acceleration in special relativity

    Homework Statement Homework EquationsThe Attempt at a Solution it is known that ##a_0 ##is the proper acceleration ## a= \frac{a_0}{\gamma^3} ## hence integrating it gets ## v = \frac{a_0t}{\sqrt{1 + (\frac{a_0 t}{c})^2}} ## but this is in terms of t how to make it in terms of t'
  36. J

    B Postulates of General Relativity

    Hi guys, A real easy one. Are the following postulates completely true about general relativity as they are pretty amazing to me. 1) Black holes are a solution to his field equations for GR (or are predicted by the theory) 2) His field equations also suggested the universe was expanding 3)...
  37. P

    Dust in special relativity - conservation of particle number

    Homework Statement My textbook states: Since the number of particles of dust is conserved we also have the conservation equation $$\nabla_\mu (\rho u^\mu)=0$$ Where ##\rho=nm=N/(\mathrm{d}x \cdot \mathrm{d}y \cdot \mathrm{d}z) m## is the mass per infinitesimal volume and ## (u^\mu) ## is...
  38. P

    Emitting one or two opposite charges along the x-axis

    Let's consider that I have an emitter that can emit both negative and positive electric charges. Here let's consider only scenarios with two particles (one negative and one positive) that start initially at the tip of some electrode, where one or both the charges will separate from at the same...
  39. M

    Relativity: Initial velocity and e/m of Thomson's experiment

    Homework Statement In an experiment similar to Thomson’s, we use deflecting plates 5 cm in length with an electric field of 1.0×10^4 V/m. Without the magnetic field, we find an angular deflection of 30°, and with a magnetic field of 8×10^-4 T we find no deflection. What is the initial velocity...
  40. Moayd Shagaf

    Relativity Learning Einstein's General Relativity

    So, I'm going to learn general relativity but I'm confused in which book I start with Bernard Schutz book seems excellent but I'm more interested in d'Inverno book, And Misner/Throne Book Seems complete but its giant and good for reference, So I think I will go with d'Inverno , but first I need...
  41. L

    Relativistic Doppler Shift for Transverse Movement

    Homework Statement A sodium light source moves in a horizontal circle at a constant speed of 0.100c while emitting light at the proper wavelength of λ0=589 nm. Wavelength l is measured for that light by a detector fixed at the center of the circle. What is the wavelength shift λ-λ0? Homework...
  42. M

    B Could this FTL idea with a fast moving large mass be possibl

    Could this FTL idea with a fast moving large mass be possible? I have recently come up with a possible way to achieve faster-than-light (FTL) travel by using a high speed singularity or large mass. Background As everyone knows, according to relativity, under normal conditions, it is impossible...
  43. D

    Simple Special Relativity Problem of Length Contraction

    Hello, I'm self-studying Ta-Pei Cheng's Relativity, Gravitation and Cosmology. Problem 2.8 is the following: Two spaceships traveling in opposite directions pass one another at a relative speed of ##1.25 \times 10^8## m/s. The clock on one spaceship records a time duration of ##9.1 \times...
  44. jedishrfu

    B Solving Mysterious Relativity Paradox: New Derivation of E=mc^2

    Interesting new derivation of ##E=mc^2## from an experiment of moving atoms emitting photons. http://flip.it/AfcjP9 http://flip.it/AfcjP9
  45. T

    A Unstable 5D Theories: The Search for Stable Black Holes in Higher Dimensions

    I tried a cursory search for this but couldn't find it. I was talking with my advisor about 5D theories such as those of Paul Wesson and Randall-Sundrum, and he said that I shouldn't spend too much time studying those theories because they are unstable, or require so many corrections to...
  46. T

    Basic Question about Relativity Reference Frame Shifts

    Homework Statement I'm using Shankar's Introductory Physics course and I can't get a question out of my head regarding his setup of Relativity. There are two observers, S and S'. Observer S is stationary, while Observer S' is sliding past S (to the right) with velocity u. They agree to set...
  47. K

    I Force on an Object according to the General theory of relativity

    What is the force acting on an object according to general theory of relativity? If there is a such a force, can we predict the motion of an object in general relativity just using the modified Newtons laws of mechanics i.e using relativistic mass of an object instead of rest mass ?
  48. senatorarmstrong

    Calculating the Travel Time of High-Energy Particles Across Our Galaxy

    Homework Statement Our galaxy is about 10^5 light-years across, and the most energectic particles known have an energy of about 10^19 eV. How long would it take a proton with this energy to traverse the galaxy as measured from (a) the galaxy and (b) the particle? Homework Equations I...
  49. jlmccart03

    Finding Angle Theta in Relativistic Skydiving Scenario

    Homework Statement A skydiver is strapped to a rocket and shot into outer space. There is no air resistance so he is able to make his arms into a 45° angle with respect to his body and pretend they are "wings." To a stationary observer on the Moon (we will consider the Moon stationary for our...
  50. jlmccart03

    Calculating Relative Velocity and Length Contraction in Special Relativity

    Homework Statement The problem states: Racer A and Racer B have the same care length, but from a spectators view Racer A looks (1/2) that of Racer B. Also Racer B is traveling at a speed v = (c/2). I am to find the spedd of Racer A in the spectators frame of reference. Homework Equations...
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