Special relativity Definition and 1000 Threads

So I've often heard that when GR is applied to the entire observable universe to calculate its curvature, we get a value of zero, meaning that the entire universe is flat. I've got 2 problems with this. The first is that I thought GR was a local theory i.e. it only applies locally. Trying to...

I have a question about the concept of length contraction. The black line from (0, 0) to (1, 0) represents a meter stick in my stationary frame, call it frame A. The blue axes represent my coordinate system with coordinates x and t. The green axes represent the coordinate system of a moving...

Susskind's book "Special Relativity and Classical Field Theory" derived the Lorentz transformations $$x'=(x-vt)\frac{1}{\sqrt{1-v^2}}$$ $$t'=(t-vx)\frac{1}{\sqrt{1-v^2}}$$ $$x=(x'+vt')\frac{1}{\sqrt{1-v^2}}$$ $$t=(t+vx')\frac{1}{\sqrt{1-v^2}}$$ While redoing the calculations, I reached a...

I am following the book "Special Relativity and Classical Field Theory: The Theoretical Minimum" by Susskind. I want to go through a sequence of ideas to try to understand simultaneity. We have a rest frame A and a moving frame B along the x-axis. Let the coordinates be ##x## and ##t## in...

Hey, What is meant by Coulomb gauge not being Lorenz invariant? The Coulomb gauge is just a constraint on \mathbf{A} and \phi and thus it is independent of inertial frame. I posted the question in the wrong section. This question is in the context of QFT. The notes says: A disadvantage of...

Does it violate the postulate of special relativity in any sense?

In the mental experiment of special relativity (which has been experimentally proven anyway), in which it is shown that for the traveler on the spaceship, time passes more slowly because the clock (the tick-tock of light beams) goes slower... What is the correlation between the traveler's...

For quite a while I thought that time dilation was the effect of bodies moving close to the speed of light dilates the passage of time. I also have read about red shift, which seems to be the same thing, though I’m sure they are totally different. I learned in special relativity (the time...

[Moderator's note: Thread moved to relativity forum as it is not a specific homework problem but a general question about SR.] Homework Statement: While studying relativity, a question arose for me about time intervals measured by stationary and moving observers. In particular, one of the...

Let's assume Dark Flow is real. If so can't we measure it based on 2 atomic clocks. Dark Flow occurs presumely in a southerly direction. One atomic clock must start at the time the earth's rotation begins to bring the first atomic clock in a slightly southerly direction, (due to the earth's 23.4...

Hi all, Recently I've tried to wrap my head around a common explanation of magnetic fields that you see online, especially among science educators like veritasium or minute physics. The setup is as follows: there is a wire, composed of the same number of negative charges (electrons) and...

So I would get ##u=\frac{vc}{\sqrt{4c^2-3v^2}}=0.996c##. But the right answer is ##0.956c##. Where is my mistake?

I considered example of time dilation with light clock. I have a question about measuring time in reference frame with clock. If we know that clock move from A to B in the reference frame with clock then what time of motion is measured in this reference frame? (In non-moving reference frame...

If we have an observer that is accelerating in one direction (perhaps a rocket ship accelerating towards the sun), would its reference frame be identical to an observer at the same point that is not accelerating, but has the same instantaneous velocity? In other words, is an accelerating...

Here is a screenshot from Einstein's 1905 ELECTRODYNAMICS OF MOVING BODIES:My understanding is that here Einstein says that the rod, the 2 observers and the 2 clocks are in the moving system, one observer & clock at each end of the rod. From their point of view they are not moving. They can very...

Full disclosure: I have asked this question on stackexchange too, but I think I didn't frame my question properly there, which probably led to misunderstandings and complicated answers. Plus some comments there led me to refine the question a bit so I hope it's in a good state now. I am new to...

I was reading Einstein's Simple Derivation of the Lorentz Transformation which is Appendix I in his book Relativity: the Special & the General Theory. (Online copies can be found at Bartleby's and the Gutenberg Project websites.) I came across an interesting but confusing result by using the...

The ship left Earth at a speed of 0.5c . When the distance between the ship and Earth was 0.25 light year, a terrorist was caught on Earth who said that he had planted a bomb at the time of departure and activated it for 10 months. At that moment, a warning signal was sent from Earth. The...

I'd like to understand how to obtain equation (2) below. **My question is how to obtain (2)?** **Here is my attempt to answer this question (which runs into an obstacle)** Suppose we have a telescope on earth with air inside the tube (instead of water) and around the telescope. Consider...

Recollections of a late Spring semester's lesson describing the derivation of Lorentz's Transformation often solicit many unanswered questions. The textbook used has been secured; however, it is unknown. Whether, that secondary school instructor provided the premises used for the derivation from...

A large disk rotates at uniform angular speed ##\Omega## in an inertial frame ##S##. Two observers, ##O_1## and ##O_2##, ride on the disk at radial distances ##r_1## and ##r_2##, respectively, from the center (not necessarily on the same radial line). They carry clocks, ##C_1## and ##C_2##...

This is a response to a recent insight article regarding the twin paradox. The idea is to model the most basic scenario in a way, that the paradox disappears. This basic scenario and its kinematic effects are then modeled using only a straightedge and a compass. The best way to read this post...

i have just started on relativity, so be simple. you are going to travel 1 lightyear at half the speed of light. therefore, it would take 2 years to travel 1 lightyear. on Earth, you would see me going half the speed of light, so it should take two years as well? i calculated gamma as being...

I am looking at some of the threads on the twin paradox, and getting even more confused. I have been trying to run through the details of what each twin is seeing, and was wondering if I could get some help. I am just trying to imagine how each twin is “seeing” the other twin at each step as the...

The following is more of an interesting example and observation than a question that I am presenting for public comment. It's somewhat related to a recently thread, which was closed for moderation, but I think it's different enough not to fall under the ban of reposting threads that have been...

Hey, I have this problem from the Special Relativity by AP. French . Exercise 3.3, Chapter 3. The figure shows a double-star system with two stars, A and B, in circular orbits of the same period T about their center of mass. The earth is in the plane definied by these orbits at a distance R of...

Hi guys! Is there a simple explanation to describe why light owns the faster speed at the universe ?

This was part of a test we did a while back, so I forgot how exactly I solved it, but I think I basically solved the question by putting the values into equations and hoping for the best, since I didn't have a good understanding back then. Since then, I have learnt that it's a good idea to break...

From this morning's Economist briefing: The Laser Interferometer Gravitational-Wave Observatory—the world’s most sensitive device for spotting gravitational waves—starts up again on Wednesday after a three-year hiatus for upgrades. LIGO is designed to detect subtle ripples in space and time...

Let's consider three observers A, B and C. The experiment starts at t = 0. A is 'absolutely' stationary. B immediately (please imagine it) starts moving at speed v1 with respect to A. C immediately starts moving at speed v2 with respect to A in the same direction as B. Let's say A measures a...

If an object is going close to the speed of light, will outside frames of references perceive the moving object as going slow or fast?

Exercise: Solution: The result is correct, but I'm unsure about equation from 29 to 30 where right-hand side became just the covariant dual field tensor. I assumed that I could interchange the covariant dual- and normal covariant field tensor, but don't think it's possible since matrices...

This was a practice question, so it had the answer with it, which is 31 minutes. However, I'm confused as to why Lisa experiences T0. It isn't exactly an event happening in Lisa's rocket, but rather her just moving through space. From her perspective, it should look like Earth is moving at the...

Hi guys, I have heard a lot of claims about ChatGPT and how it is going to put a lot of people out of work. I have a friend who is a teacher of humanities and he is fearful of losing his job in the long term. People seem to be in awe at the thing and think it understand what is saying. So I...

I started by expanding ##dx## and ##dt## using chain rule: $$dt = \frac{dt}{dX}dX+\frac{dt}{dT}dT$$ $$dx = \frac{dx}{dX}dX+\frac{dx}{dT}dT$$ and then expressing ##ds^2## as such: $$ds^2 =...

Hi, i am not a physicist but i have the intuition that time dilation is just slow in the movement of particle's and causality instead of slow in time itself and that this does not affect photons. I understand that there is no way to distinguish between a slow in time and a slow in movement and...

In sect. 2.3.2 "Ideal Clock", p. 33, of É. Gourgoulhon's text book on "Special Relativity in General Frames" $$ \tau_C [ \, \text{tick}_{j}, \text{tick}_{(j + N)} \, ] = K_C \, N. $$ (equation (2.11); notation adapted.) The only other reference to this "constant K" is on the following page...

This is probably a stupid question but, ## \frac{d\partial_p}{d\partial_c}=\delta^p_c ## For the notation of a 4D integral it is ##d^4x=dx^{\nu}##, so if I consider a total derivative: ##\int\limits^{x_f}_{x_i} \partial_{\mu} (\phi) d^4 x = \phi \mid^{x_f}_{x_i} ## why is there no...

In the context of the Theory of Relativity are there any spacetimes or metrics with a complete absence of symmetries? I mean, consider a type of space or metric where no symmetries would hold (at least not exactly, but approximately). A space or metric where the Poincaré invariance (including...

Einstein's two postulates of special relativity reads, according to Wikipedia: The postulates are most often formulated similarly to this. But in my opnion, the second postulate shouldn't be formulated as above, because then one misses the point. This is particular true for the second...

The constancy of the speed of light is a fundamental principle in modern physics, and it is supported by a wide range of current experimental evidence. There is no evidence to suggest that the speed of light was different in the past, and the idea that it could have been different is at odds...

I refer to the video of this page, where there is a description of Galilean relativity that is meant to be an introduction to SR, making the comprehension of the latter easier as a smooth evolution from the former. All the series is in my opinion excellent, but I think that this aspect is...

Hi every one.How can i prove the below equation? And then that it's Lorentz invariant quantitude ? Thanks for your help

Hello all you clever people, I was wondering if you guys could answer a question for me regarding special relativity and the none existence of time. At least in the sense that the block universe people believe. So I'm writing as if the block universe is the correct interpretation What does...

I have previously studied special relativity, but only at an introductory level. So I decided to explore the subject more in detail later by thinking and working things out on my own, in addition to doing research online. In particular, I seem to have noticed some intriguing patterns between...

I once read (though I don’t remember where) that in the same way that you talk about a dimensionless ratio between Y and X in ordinary space, you can conceive of c as a dimensionless ratio between T and X in spacetime. Do you know where I can find a reliable treatment of that idea? As...

If conservation of charge gets violated in future experiments, what would be the implications on relativity? I have some faint idea that this will cause photons to have non-zero rest mass, but does this affect special relativity at all? Also, does special relativity make conservation of charge...

I have been reading Wikipedia’s derivations of the Lorentz Transformations. Many of them start with the equation of a spherical wavefront and this reasoning: - We are asked to imagine two events: light is emitted at 1 and absorbed somewhere else at 2. For a given reference frame, the distance...

I have a rocket and it is moving straight from a point P with a velocity ##v##. When I say that ##x'=0## is at the place we sit in the rocket, then when the event happened outside his rocket at the point P, can I say that the coordinate of the event is for him negative, so ##x'=-vt'##, although...

Hello. This is my first post on this site. anyone here familiar with "Doubly Special Relativity"? an ARXIV paper was linked in the OP. Some follow up links or other advice would be appreciated. Kowalski-Glikman, J., "Introduction to Doubly Special Relativity", (2004). arXiv:hep-th/0405273...