Relativity Definition and 998 Threads

I am a student of physics at a local Junior College in Mendham NJ and am planning on transferring to a 4 year program at the University of Alabama in a year. Iam having a bit of a difficult time understanding general relativity. Why does a photon bend twice as much under a gravitational field...

Suppose we take a charged particle and a magnet and place them at some particular distance apart .Now let's take 2 frame of reference. [the charged particle and the magnet are in rest with respect to each other through out the whole event]{both of the frames are inertial} frame(a): this frame...

I saw this question on special relativity on the internet: "A spaceship traveling to Alpha Centauri, at 0.95C it takes 4.5 years to get there as measured on Earth.how long does it seems to the spaceship passengers?" the answer was 1.4 years (Lorentz factor of 3.2). this answer makes no sense...

Hello there. In class, our teacher solved one question and asked us what did we wrong specifically in the solution because there were two sets of them. Two spaceships are moving through +x and -x and there is a distance L between them. From one observer which is stationary in the line of L/2...

Hello. I have some questions about general relativity that (I hope) will be permitted in this forum. Not long ago I discovered that there is more than one interpretation of GR. Now, I believe that the issue of interpretation is considered to be philosophy and therefore off topic. If that's...

I'm trying to solve this problem but I get a different answer depending on which observer I solve it for. For the observer in the cloud, the parallel light has traveled 2.294cs, but this is only 0.23cs in front of the ship. 0.23 cs is only 0.086cs in the perspective of the ship due to length...

In Lee Smolins book Time Reborn he discusses simultaneous events and says events that are far from each other we find that there is no absolute ordering that all observers can agree on. For some observers the two events may be simultaneous for other observers one event may be in the past of the...

Hey my fellow physics-students/physicists. I'd like to ask if you guys could suggest me a textbook/s that sufficient for integrated course of "special" and "general relativity". More precisely, That contain about: Introduction about the birth of relativity and principle, and the transformation...

This week I am at "General Relativity as a Challenge for Physics Education" 690. WE-Heraeus-Seminar https://www.we-heraeus-stiftung.de/veranstaltungen/seminare/2019/general-relativity-as-a-challenge-for-physics-education/ (...

How do you know what fields can be coupled with the gravitational field? Is there a general procedure for knowing it or we have to try out and see whether it makes sense or not?

A while back I posted a black hole horizon puzzle. This is another puzzle in the same general spirit. It is based on the scenario described in this old PF thread: https://www.physicsforums.com/threads/a-flaw-of-general-relativity.115418/ Needless to say, as was the case with my previous...

I've always wondered how we came to come up with such an idea. Was he one day sitting around and thinking, then made a random assumption and go "ah hah!". Or did his idea come up through his calculations on the nature of how gravity should cause interaction? Is their a literal fabric of space...

Peeling this out into its own thread for clarity: How is time dilation of extreme reference frames (photons, black holes, intergalactic space-time) taken into account in Big Bang cosmology? Since from the POV of a singularity or a photon, their clocks have effectively stopped and any lower...

Say there is a circular fence that has a diameter of 10 meters, and a rocket ship that is normally 20 meters goes very quickly so that its relativistic length is 1m from the position of an observer standing at rest with relation to the fence. The rocket ship starts to go in a circle inside the...

Something that crossed my mind recently; I know that satellites have to adjust their clock due to their relativistic time variations in relation to us. I was wondering do they adjust their times in accordance to general relativity or special relativity or both? Or is their speed so insignificant...

Does General Relativity allow for transformations which are not isometries of the metric?

Summarized: Which mathematical fields should you focus on if your goal is to gain a better understanding of relativity and related subjects? (My apologies if there are already other threads asking this question, but 'math' and 'relativity' aren't really useful search terms on this forum.) Hi...

I just found this on the internet. It reminded me of a joke I once made: https://www.physicsforums.com/threads/science-jokes-p2.847743/page-8#post-5603278 It's a nice illustration about the "relativity" of light - kudos https://www.linkedin.com/in/james-o-donoghue-astronomer/

Is it possible to solve a problem of overcoming of speed of light with solid objects using faraday cage Theory with equivalent charge?

Homework Statement You make repeated measurements of the electric field ##\vec E## due to a distant charge, and you find it is constant in magnitude and direction. At time ##t=0## your partner moves the charge. The electric field doesn't change for a while, but at time ##t=24## ns you observe a...

In his book, Landau mentioned varying the relativistic lagrangian However, I do not understand how he got from varying the integral of ds to varying only the contravariant components. Would the general procedure not be varying $$\delta S = -mc\delta\int_a^b\frac{dx_idx^i}{\sqrt{ds}}$$ and...

Hello. The book "General Relativity, Astrophysics, and Cosmology", by Raychaudhuri, et al., looks like a good compact exposition of GR, astrophysics and cosmology, which is exactly the kind of book I'm looking for. What do you think of this book? Thank you in advance.

Greetings: I can understand that an object's trajectory curves about a greater mass (e. g., satellite in Earth's orbit). The spacetime is curved via the great mass and the moving object simply follows the curvature. My problem is this: Why does a stationary object at a short distance from...

Is it possible to calculate with precision the orbits of the Earth, Moon and Sun with general relativity instead of Newtonian Physics? How would this work? Would the software have to record past positions of each body and have the Earth be attracted to the old sun's position 8 minutes ago...

In several special relativity textbooks, I have read that special relativity only deals with observations made in inertial frames, and that it makes no predictions about observations made in non-inertial frames, and that only general relativity deals with non-inertial frames through the...

After making a couple of comments on this StackExchange question, and pointing yet again to this article, a thought occurred to me. I have been working on an Automatic Differentiation based ODE solver and equation analyzer, mentioned in this thread. Why not use it to solve equation (7) in the...

Hey everyone! So, I just finished my 2nd year intro to SR course, we spent most of the term on Taylor expansions for relativistic corrections vs concepts. I’ve watched a crash course video and a documentary on SR and I do somewhat understand the thought experiment involved with respect to...

I was reading a document from the time of Einstein where the metric is referred to as "the fundamental tensor". That made me wonder if it's possible to derive all concepts of tensor field, scalar product, connectivity etc. starting from the requirement that the metric is invariant under change...

Are there a lot of theoretical research jobs in general relativity or would that be too hard to find?

Maybe I'm just being stupid, missing something simple ? How do you get from the top two equations to the second equation? Many thanks

Hi, It is usually claimed that a person in an accelerating elevator with an acceleration equals to the gravity of the earth; this person cannot make any experiment that makes him know whether he is in the elevator or on the surface of earth. However, if this person project two light beams...

Given that one or both inertial frames must have been subject to acceleration at some point; resulting in an imbalance of application between the two inertial frames, why does the consequential effect of general relativity not feature in calculations. Surely, as such, neither observer's...

Hi, Do we obtain the same escape velocity equation: Ve = sqrt(2GM/r) using both Newtonian and Relativistic approach?

I am collecting ways to visualize the curvature of spacetime -- and movement of objects affected by gravity -- as per Einstein's GR. Alternatives to the bowling ball / trampoline image so often used in the popular press. Images that show the similarities / differences between Newton & Einstein...

Background: I'm about to graduate with a mathematics degree(in the US), hence I have exposure to multivariable calculus, real analysis, abstract algebra, complex variables etc (no differential geometry however). I have also taken a class on QM(using Griffiths) and I saw some SR during a Modern...

Is it a fair prediction to state that in the next several years or so, globally, there will be major investments into gravitational wave research, and many more ‘LIGOs’ being developed? Is it a good idea to venture into that area of physics?

Is there a sensible way of defining a displacement vector in a general manifold? That is, the displacement vector being the difference between position vector at two different points... the problem is that these two different points have, in general, different tangent vector spaces. Never the...

Hi, I'm wondering if it is possible to measure radii of stars using general relativity, given its explanation of gravity as curvature of space. Thank you

Hello everyone, I'm studying physics as an undergraduate and I'm currently taking the course special relativity. But sadly I'm not too big a fan of the book we are using for the course. So I was wondering what are the best books you know of regarding special relativity for undergraduates.

I have little exposure to mathematics beyond high school algebra and physics, but I have become increasingly interested in physics, particularly its most towering achievements of modern times : Quantum Physics, as well as A. Einstein’s Special and General Relativity, the latter of a...

So I have sort of a conceptual question about the big bang and gravity. Imagine yourself in a universe, in which existed about the number of particles/energy in a 3X3 metre room at any given moment. This universe has the same laws of physics, constants and is identical in every way to our...

Hello, There is a common setup used when describing the intimate relationship between electricity and magnetism. I have a question about the setup. Setup: There is some long current-carrying wire. Outside of that wire, there is some test charge. In the first situation, the test charge is...

I have an exercise: A distant camera snaps a photograph of a speeding bullet (speed v) with length b in its rest frame. Behind the bullet and parallel to its path is a meter stick, at rest with respect to the camera. The direction to the camera is an angle $\alpha$ from the direction of the...

From his original thesis, Einstein said light speed is always constant (c). There is very clear evidence for this. Every ray of light moves in the “stationary coordinate system” with the same velocity c, the velocity being independent of the condition whether this ray of light is emitted by a...

Hi all. I was wondering if time is dilated whilst traveling in a stable magnetic field that is generated by the object travelling, and if so, does this vary if you reduce or intensify the magnetic field? Also, what happens if the object is generating two opposing magnetic fields, would...

how do I calculate the energy of to photons moving in the opposite direction. starting from the same origin.

Although I thought that I understand special relativity enough, I cannot now clearly answer on the following question: What is the most direct derivation, why momentum in special relativity is ##p=\gamma m v##, where ##v## is velocity of the rocket? Let us assume that Lorentz equations are...

Is the increase in mass/density of an object in motion purely relativistic? What I mean is if you were in a spaceship approaching the speed of light would you be able to measure a change in your mass/density or would the change only be observable to someone at rest. I'm aware of the Lorentz...

the problems/challenges that you have to face daily are mostly related to code issues with the physics itself? Is there room to improve our knowledge of fundamental physics while working on it? Do you enjoy doing it? why? I'm asking this because I'm considering working on numerical relativity...

Homework Statement Imagine we are observing two aeroplaes from the ground and let their velocities be ##\mathbf{u}## and ##\mathbf{v}## respectively. Assume that the first plane has radar equipment permitting a measurement of the speed of the other plane relative to itself. The velocity so...