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. abrogard

    What Does Shankar Mean in Prof Shankar's Introduction to Relativity?

    Hope this is a valid question. I can't quite understand this very simple thing. Prof Shankar's introduction to relativity on Youtube starting at about 50 minutes has a quick calculation that comes up with the Lorentz transform. I follow the maths, no problem. But he confuses me a bit when...
  2. T

    Special relativity and particle accelerator

    Homework Statement (a) A spaceship at rest in a certain reference frame S is given a speed increment of 0.50c. Relative to its new frame, it is then given a further 0.50c increment.This process is continued until its speed with respect to its original frame S exceeds 0.999c. How many...
  3. T

    General relativity vs quantum mechanics

    Forgive me if this question is a bit amateurish but i am no physicist. I know in general terms that GR and QM aren't compatible with one another, but my question is...Do they even need to be? can it not be a handoff scenario? why can't GR govern what it is supposed to govern and QM govern what...
  4. Toby_phys

    Special relativity - transformation of angle

    Homework Statement Homework Equations Gamma factor: $$\gamma = \frac{1}{\sqrt{1-\beta^2}} $$ Lorentz contraction $$l'=\frac{l}{\gamma}$$ Trig: $$ cos\theta = \frac{adjacent}{hypotenuse}$$ The Attempt at a Solution I have all the quantities but the algebra doesn't seem to work out...
  5. Dimani4

    I Special relativity: frames of reference

    Hi people, I have a question about the frame of references. Let's have an example: First case: Jill on rocket and Jack stationary on Earth. Jill moves relatives to Jack 0.6c (1.8*10^8m/s). The distance is 18*10^8m. At the zero time Jack and Jill synchronize their clocks. Then Jill starts to...
  6. astrocytosis

    Time Dilation - measured vs observed time interval

    Homework Statement Consider an observer Bob in S standing close beside the x-axis as Alice, who is holding a clock, approaches him at speed VS'S along the axis. As Alice and her clock move from position A to B, Alice’s clock will measure a (proper) time interval ∆t0, but as measured by Bob’s...
  7. A

    B Zeno's arrow paradox and general relativity?

    I don't know much about general relativity, but I'm curious if Zeno somehow foresaw the reallty of the universe many many years before Einstein did(without any rigour ofc, but still the idea holds?). Understanding the Zeno's arrow paradox, stating that an arrow is motionless at a certain moment...
  8. A

    Relativity and Equivalence of Mass and Energy

    Homework Statement An electron is accelerated to a speed that is 99 percent the speed of light, and is moving through a 2-km-long tunnel. The rest mass of the electron is 9.11*10^-31 kg. What is the mass of the electron at this speed? c= speed of light Homework Equations t= (tsubscript(o))/...
  9. ibkev

    Relativity Morin's "Special Relativity: For the Enthusiastic Beginner"

    I just came across this recently released title by David Morin, "Special Relativity: For the Enthusiastic Beginner". If its anything like Morin's past books, it'll be excellent for self studiers. https://www.amazon.com/dp/1542323517/?tag=pfamazon01-20
  10. Anujkumar

    I Spacetime Relativity: Universe Expansion & Our Place in It

    When the universe is expanding then why not we are expanding along with it
  11. MetinErsin

    B Relativity Scenario Help: A Seeing B's Line Shorter or Longer?

    Let's assume there are two observers. Observer B is at rest and observer A is in a spaceship which has transparent walls. A draws line of 1 meter. When A arrives near B, B draws a line of 1 meter. And sees that A's 1 meter is shorter than own 1 meter. before forget i should say that meter is...
  12. I

    I Velocity Addition & Relativity of Simultaneity

    I have some issues understanding the following thought experiment: Suppose you are standing still, and two balls are moving towards you from opposite direction. From your own reference frame, Ball A is ##10^5## m away from you, moving towards you from the left with speed ##0.8c##, and Ball B is...
  13. Paulo Figueiredo

    Time measured by a car-Special relativity

    Homework Statement I wish a help for the following problem: Consider the situation: a car A is moving away from a stationary observer O with velocity c/3. When the point A is at a distance 200.000 Km of the O a light signal is sent from the observer O to the car A. The question is: how long...
  14. S

    I Relativity of simultaneity, time dilation misunderstanding

    Hi everybody, I'm new on this forum so I apologize in advance if I don't respect some formalities (and sorry for my English). It is known that in the perspective of the stationary observer the events in the back and in the front of the moving spaceship are not simultaneous. If I understand well...
  15. M

    A How to Integrate the geodesic equations numerically?

    Hello there, I've been considering the geodesic equations of motion for a test particle in Schwarzschild geometry for some time now. Similar to what we can do with the Kepler problem I would like to be able to numerically integrate the equations of motion. I'm quite interested to see how...
  16. Spikemarlene

    B Einstein relativity is invalid

    Hi, Need your help to unravel the claims made by a poster in my local forum, if it has any merits. I do not have the expertise to evaluate his claims but am hoping if you can give me a few points on his line of reasoning, if it is faulty or not. I have a general background in undergraduate...
  17. J

    B DeltaT of clocks at endpoints of a rocket post acceleration

    Following scenario: A rocket measuring 10 lightseconds in length accelerates near instantaneously to v=0.4c. Pre-acceleration two clocks placed at the endpoints of the rocket were synced. What will be the time difference between the two clocks post acceleration? I tried to figure it out...
  18. Dimani4

    B Special Relativity: What Time is it?

    This question based on the site located here: http://galileo.phys.virginia.edu/classes/252/srelwhat.html The question is: If the object (spaceship) moving close to the velocity of light and I'm as a static object. The time goes slower in the object moving with constant velocity (inertial frame)...
  19. Andy_K

    Cosmology Review of Hidden In Plain Sight Series

    Has anyone read the 7-book series http://amzn.to/2lwgn66 by Andrew Thomas? Just wondering what you think of his conjectures / speculations at the final sections of each book, i.e. on the link between relativity and quantum mechanics, equation of the universe, etc... I like that he...
  20. P

    B Another question about relativity: the force

    So, i want to derive the relativistic force using the definition F= dp/dt and p= γ mv I consider a frame of reference solidal with the particle. Algebrically i can do it and it works, but why can i do it? Why do i have to differentiate also γ? That would mean that the speed of the frame of...
  21. J

    I Farthest distance a human can travel from Earth in a life

    I've been stuck on this physics problem for several years now. I would be very grateful if someone could explain how to solve this problem. The farthest a human could travel from Earth in one lifetime theoretically is limited only by the acceleration a human can withstand, and the length of...
  22. P

    I Query on basic mechanics of Special Theory of Relativity

    The Special Theory of Relativity is based on the observations of an outside observer on a system traveling at the speed of light. There is no single point of reference to determine speed. So speed is determined relative to another object. This being the case an Apple traveling at the speed of...
  23. N

    Partial Differential Equation in Special Relativity

    Homework Statement (a) Light waves satisfy the wave equation ##u_{tt}-c^2u_{xx}## where ##c## is the speed of light. Consider change of coordinates $$x'=x-Vt$$ $$t'=t$$ where V is a constant. Use the chain rule to show that ##u_x=u_{x'}## and ##u_{tt}=-Vu_{x'}+u_{t'}## Find ##u_{xx},u_{tt},##...
  24. Invutil

    I Shining a light beam back -- relativity

    According to the textbook, "In this case, you (A) and Jackie (B) no longer agree about her speed _relative_ to the speed of the light beam. She'll see the light beam pass by her at the speed of light, c, but you'll see it going only 0.1c faster than she is going." Illustration here, under "The...
  25. F

    I "General Relativity" by Wald -- question

    I desire to read General relativity by Wald. I am a student who is self teaching, and I know tensor calculus by Pavel grinfield's introduction to tensor analysis and calculus of moving objects. The book states things from advanced calculus. Do I have more math to learn before hand?
  26. H

    Relativity: Solving Pion Homework Problem

    Homework Statement After being produced in a collision between elementary particles, a positive pion (π+) must travel down a 1.00 km -long tube to reach an experimental area. A π+ particle has an average lifetime (measured in its rest frame) of 2.60×10−8s; the π+ we are considering has this...
  27. smodak

    Quantum Relativity, Elementary Particles and Black Holes

    Relativity, Elementary Particles and Black Holes by Thorne & 't Hooft Any idea what this book is and why it is unavailable? Is it a popular science book? I did not know that Thorne and 't Hooft co-authored a book.
  28. N

    I Do nonlocal QM interpretations violate relativity?

    Do interpretations of QM that are non local (Bohmian, collapse, transactional) violate relativity since they allow for faster than light travel?
  29. T

    Does the Laser Blast the Goths?

    Homework Statement The rockets of the Goths and the Huns are each 1000 m long in their respective rest frame. The rockets pass each other, virtually touching, at relative speed of 0.8 c. The Huns have a laser cannon at the rear of their rocket that shoots a deadly laser beam at right angles to...
  30. A

    What should the speed of a pion be

    Homework Statement The speed of a particle in Earth's frame is 0.4 c. A second particle goes away from the first one with speed 0.6 c. What is the speed of the second particle in Earth's frame? Homework Equations u=(u'+v)/(1+u'v/c^2) The Attempt at a Solution I think v=0.4 c and u'=-0.6, but...
  31. A

    Relativity: Spaceship travel times and distances

    Homework Statement A star is 95.0 year lights away from Earth. How much time does it take to a cosmic ship, which moves with speed 0.96 c, to reach the star, if it is measured from a watcher from a) Earth a)ship c)What si the distance of trip, based on the viewer from the ship? Homework...
  32. sander69

    Test of Special Relativity Confirmed - ScienceMag.org

    On the following link it is mentioned that this experiment tests special relativity. Can someone please explain how it does that? http://www.sciencemag.org/news/2016/12/deep-probe-antimatter-puts-einstein-s-special-relativity-test
  33. Ian Baughman

    I What does this symbol represent?

    In my nuclear engineering class we are looking at relativity right now. For one of our homework problems we have to derive an equation for a particle moving at relativistic speed showing the kinetic energy in terms of the particles momentum. In the answer they have a term mc and I have no idea...
  34. W

    What is the Energy Released in a Nuclear Reaction?

    Homework Statement Homework EquationsThe Attempt at a Solution I'm not sure how to go about working on this. What I have tried is this line of reasoning: 1x4He needs 2x3He. 2x3He needs 2x(2H + p) Energy released is therefore 12.98 + 2(5.51) _+ 2(0.41) = 24.82 MeV. However, it does seem...
  35. bananabandana

    Can index swapping be applied to relativistic Lagrangian equations?

    Homework Statement Show that $$ \mathcal{L} = -\frac{1}{4}F^{\mu \nu}F_{\mu \nu} = - \frac{1}{2}\partial^{\mu}A^{\nu}(\partial_{\mu}A_{\nu}-\partial_{\nu}A_{\mu}) $$ Where $$ F^{\mu \nu} = \partial^{\mu}A^{\nu} - \partial^{\nu}A^{\mu} $$ Homework EquationsThe Attempt at a Solution $$...
  36. Andy_K

    What are the Best Books for Learning Special and General Relativity?

    Dear All, I am trying to find some good books that provide a comprehensive one-stop education for special and general relativity, with concise coverage of key fundamentals of the maths involved. It is intended for self study, and I do not have strong fundamentals on advanced physics / maths...
  37. T

    I Change of special relativity formulas?

    We know that while deriving the special theory of relativity formulas like Lorentz Transformation, Length contraction, Time dilation etc, we assume that there is an observer at each point of the space in a certain frame and all these observers contain synchronized clocks and scales. But what if...
  38. D

    What makes physics so fascinating and relevant in our daily lives?

    Hello everybody! I am excited to be part of this forum. It's the first time for me. I am 41, from France and with my sons (9, 7 and 6) we love physics. I have studied economics and discovered my interest for physics only a few years ago. I try to learn things by myself with videos from You tube...
  39. A

    I The space-time interval definition in special relativity

    Hello, please note that the following is only about special relativity, not general. Of course, if there are any things to point out that fall in general relativity, feel free to do so, but I don't know GR, so I won't understand arguments based in GR. I also am not great with a geometry-based...
  40. smodak

    Particle The Standard Model in a Nutshell - Goldberg

    Just found this new book on amazon. Looks interesting. I purchased. https://www.amazon.com/dp/0691167591/?tag=pfamazon01-20 The TOC, Preface, and intro could be found here http://press.princeton.edu/titles/11050.html I wish they included a sample chapter as well (the book in not cheap), but I...
  41. C

    Special Relativity: Time Dilation Prob

    It has been 2.5years since I last did any special relativity so am rather rusty on it, I have a simple time dilation problem and its making my head hurt which way around it should be. Any help much appreciated! 1. Homework Statement Bob leaves Sarah on Earth and travels in a spaceship at 0.8c...
  42. R

    Pi meson decay (relativistic momentum)

    Homework Statement A charged π meson (rest mass = 273me) decays into a neutrino (zero rest mass) and a μ meson (rest mass = 207me). Find the kinetic energies of the neutrino and the mu meson. Homework Equations E = moγc2 K = mo(γ-1)c2 v = pc2/E p = moγv The Attempt at a Solution In the rest...
  43. nomadreid

    I Bauer's Paradox in General Theory of Relativity?

    Has anyone heard of "Bauer's Paradox" in Einstein's working out his equations for General Relativity? The description I came across was extremely fuzzy (something about an expression for a certain tensor adding up to be zero when it shouldn't, or vice-versa), so I am looking for a better...
  44. R

    I Theory of Relativity: Light, Mass & Gravitational Lensing

    If light is pure energy, then how can gravitational lensing work? And if light has some mass, how can it change directions instantly when it is traveling through a prism? My high school science teacher had no answer 45 years ago.
  45. B

    I Special relativity and sameness

    It seems if the clocks show the same time, the rod is at rest in our frame. If clocks are out of sync, rod is in motion. The closer velocity is to that of light, the more clocks out of sync, Another question - are all these rods the SAME rod? For example you ask me - what is velocity of the rod...
  46. N

    Special Relativity (time/length)

    Homework Statement Spacecraft moving at 0.6c, length 180m with someone sitting at the back. He throws a cage with a mouse towards the front also at a speed of 0.6c. A stationary observer watches. Homework Equations What is length of spacecraft from observers POV? Length according to guy...
  47. R

    Courses Should I take General Relativity?

    I am thinking about taking GR as an elective,but I have no plans on going into cosmology or any related field.I wanted to know if when applying for graduate school,whether it is a positive for them to see you have taken a "high level" course,such as GR. I know that the best thing is to have...
  48. J

    I Absolute Energy in General Relativity?

    Let us assume that a spacetime has a global time-displacement symmetry described by a timelike Killing vector field ##\xi^\mu=(1,0,0,0)##. Further assume that we have a particle with four-momentum ##P^\mu=m\ V^\mu##. It is well-known that a stationary observer with four-velocity ##U^\mu##...
  49. L

    I Electromagnetic Force in Special Relativity

    Hi! I came out with a problem last night I wasn't able to solve: Let's assume we have a condensator with a uniform electric field E confined in its inside, lying on the z axes. Let's also assume we have a piece of a ferromagnetic object aligned with the condensator at time t = 0, on the y-axes...
  50. G

    B How Do You Derive the Full Energy Momentum Relation Using Lorentz Factor?

    Hi community, There is a step on the wiki page about a derivation. I don't seem to get the same thing when I try and solve for (u/c)^2 and then plug into Lorentz factor to get the new Lorentz factor so you can get the full energy momentum relation My gamma term looks more like 1/...
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