What is Relativity: Definition and 997 Discussions

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. 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...
  2. 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...
  3. 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...
  4. 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},##...
  5. 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...
  6. 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?
  7. 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...
  8. 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.
  9. 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?
  10. T

    Special relativity application

    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...
  11. 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...
  12. 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...
  13. 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
  14. 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...
  15. 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...
  16. 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 $$...
  17. 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...
  18. 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...
  19. 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...
  20. 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...
  21. 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...
  22. 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...
  23. 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...
  24. 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...
  25. 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.
  26. 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...
  27. 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...
  28. 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...
  29. 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##...
  30. 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...
  31. 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/...
  32. W

    Relativity: Time dilation and distance calculations

    Homework Statement Could someone help point out certain conceptual errors in my interpretation of the mirror clocks time dilation thought experiment? Say S' is the frame of reference traveling at speed V w.r.t to frame S, which means that events happen at the same coordinate in S'. We know...
  33. B

    B Why Special Relativity have overcome Ether Theory?

    My question is very simple. As far as I know, once upon a time there was the Lorentz Ether Theory. This theory admitted existence of so-called Ether as a certain preferred frame, which was undetectable because of physical contraction of moving material bodies in direction of their motion. In...
  34. L

    Other Graduate Research topic involving QFT and General Relativity

    Last year I finished the undergraduate course in Mathematical Physics. This year, more precisely in March, I'm going to start the graduate course to acquire a master's degree in Physics. Now, for this course I must choose a research topic and find an advisor. This is being a little bit...
  35. B

    Thoughts on Newton's Bucket and the relativity of rotation

    Isaac Newton imagined a bucket of water suspended on a fine (ideally torsionless) rope, set spinning. Friction eventually causes the water to rotate along with the bucket. The surface develops a dip in the middle and rises at the edges owing to the water's inertia. (You see this effect every...
  36. W

    Relativity of Simultaneity and lightening

    Homework Statement You are standing at x = 9.0 km and your assistant is standing at x = 3.0 km. Lightning bolt 1 strikes at x = 0 and lighting Bolt #2 strikes at x = 12.0 km. You see the flash from Bolt #2 at t = 10 μs and the flash from Bolt #1 at t = 50 μs. According to your assistant, were...
  37. R

    Special Relativity: Rotated Michelson Interferometer

    Homework Statement The aether-wind theory of the Michelson-Morley experiment was discussed in class for the special case where the arms of the interferometer (each of equal length L) are parallel and perpendicular to the wind. In this problem we consider the general case for an angular setting...
  38. O

    Special relativity simultaneity

    Homework Statement [/B] Homework Equations The rear clock ahead example gives vL/c^2: The Attempt at a Solution I think the solution is the same, because even if there is a time dilation due to u (downward velocity) both clocks would slow down at the same rate and so the time difference...
  39. Conservation

    I Relativity of Simultaneity and frames

    Hello everyone, sorry if this is a noob question; I'm just starting out with special relativity. I was wondering whether relativity of simultaneity is a direct consequence of our ability to "know" being dependent on sight (light reaching a point). If, for example, we could only judge an event...
  40. binbagsss

    General Relativity asymmetry identity

    Homework Statement I have ##R^{u}_{o b u } F^{o}_a - R^{u}_{oau}F^{o}_{b}## and I want to show that this equal to ##2R_{o[aF^{o}_b]}## where ## [ ] ## denotes antisymmetrization , and ##F_{uv} ## is a anitymstric tensor Homework Equations Since ##F_{uv} ##is antisymetric the...
  41. Crowxe

    I Relativity's "time dilation" or clock accuracy alteration

    i've seen the double slit experiment and the delayed choice . my mind rejected the conclusion, but the experiment setting and configuration of delayed choice is rational and holds water so i accepted the experiment outcome even if it means the world isn't real. i had to give that intro that...
  42. W

    I Explaining Different Types of Time in Relativity

    What different types of time are there is relativity. I have heard phrases like "proper time" "co-oridnate time" and "conformal time". but what would be great to get a layman friendly definition. Thanks.
  43. P

    General Relativity and the Circumference of a Circle

    Homework Statement Calculate the circumference of the circle θ = θ0 (a constant) in the spatial geometry \begin{eqnarray*} dS^2 = a^2(d\theta^2 + sin^2\theta cos^2\theta d\phi^2) \end{eqnarray*} Hence, (by finding R(z)) sketch the cross section of the surface embedded in three dimensions via...
  44. phosgene

    Time taken for two relativistic particles to meet

    Homework Statement A particle P undergoes the hyperbolic motion x_{P}(t) = \frac{c}{a}(c^2 + a^2 t^2)^\frac{1}{2} along the x-axis of frame S, where c is the speed of light and a is a constant. A second particle, Q, undergoes the motion x_{Q}(t) = \frac{1}{2}ct + \frac{c^2}{a} and so...
  45. S

    On the relativity of time and speed

    Speed can only be measured relative to some other object, like the speed of a tennis ball during a match at Wimbledon can only be measured relative to the ground, or a cloud, or the planet Mars. On the other hand, time is relative. An object traveling at speeds approaching the speed of light in...
  46. J

    Relativity Books about Special Relativity for preparation for QFT

    Hello, I want to learn QFT but I feel that my understanding of Special Relativity is not good enough. Could you please recommend to me any good relativity books to fill my gaps? My gaps are mostly conceptual. Thanks in advance!
  47. J

    Quantum Theoretical Physics course textbooks

    Hello, I will be attending an undergraduate course called "Theoretical Physics" and I want to borrow some books from the library that cover the material of this course. I would appreciate any suggestions. The syllabus of the course is the following(I will be translating so I am sorry If...
  48. rharrex

    B Boundary between Quantum and Relativity

    At what point does quantum physics cease and general relativity take over. Where is the boundary? Is it a quantum of mass?
  49. O

    I Relativity of simultaneity -- an example in D.Morin's book

    Ok, so here's an example from David Morin's book that I seriously don't understand: Two clocks are positioned at the ends of a train of length L (as measured in its own frame). They are synchronized in the train frame. The train travels past you at speed v. It turns out that if you observe the...
  50. E

    I Collision in special relativity

    Let us assume that we have inelastic collision of masses ##m_1=1## and ##m_2=k## This means ##m_2=k m_1##. (##k>>1##) ##v_1=v##, ##v_2=0##, Velocity after collision is ##v'##. Units are such that ##c=1##. Let us assume that ##v_1## is close to one. At inelastic collision we respect conservation...
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