Sr Definition and 477 Threads

I am having problems with this presentation of the train thought experiment. I actually think it's incorrect, but I'm not sure. From Ray D'Inverno's book: -- Imagine a train travelling along a straight track with velocity v relative to an observer A on the bank of the track. In the train, B...

This might be a tired topic but please help me to understand. Assume a photon moving in vacuum, ignore potential interstellar medium absorption and re-emission since it is not relevant to discussion of space expansion in this context. Redshifted photons will undergo energy loss between *right...

Anyone know a good place to read about the Lagrangian or Hamiltonian approach to the equations of motion of classical point particles in Minkowski spacetime? It doesn't have to go very deep into it, but it should at least include a discussion of symmetries and conserved quantities.

How is it that the lack of any info transferred between 2 entangled particles means that SR and Entanglement are not in conflict? I guess what I’m really asking is, well, it sounds to me like the lack of info is really just a lack of evidence that anything is transferred instantaneously. So if...

The two postulates of SR are: 1) the laws of physics are the same in every inertial frame 2) light is measured traveling isotropically at c in every inertial frame I intend to derive SR by applying only the second postulate alone, that the speed of light is measured isotropically at c in...

I have a simple question. If we put a clock in a satellite in orbit for some amount of time, and then brought it back to earth, will the clock's reading of time passed be less than a clock on Earth's measured passed time. *(This is strictly ignoring any general relativistic time dilation!) In...

How are inertial frames defined in Special and General Relativity? In Newtonian physics, an inertial frame is usually defined as one in which N2 holds. Clearly this cannot be the same definition as for SR. In GR an inertial frame is one in which SR holds (I think). However, there is now a...

Let a particle mass m charge q be placed in a uniform magnetic field \vec B = B\hat k with an initial velocity v_0\hat i Clearly, it will enter a circular path of radius so and so with angular frequency so and so. But, it will not move in a straight line, not at all. Its momentum will...

three spaceships, two moving at 0.9C and the 3rd stationary relative to the first two. the two moving ships are 1 LY apart but moving in the same direction toward the 3rd ship. as the first of the two moving ships passes the 3rd (stationary) ship, the ship which is now 1 LY from both the other...

the unit of cosmic ray flux is expressed as flux /(m^2.sr.s.GeV), so what does sr stand for? Thanks.

Hi, I'm working through an Excercise in Sean Carrol's spacetime and geometry book. The question asks you to consider an inertial frame S with coordinates x^\mu=(t,x,y,z) and a frame S' with primed coordinates. Which is related to S by a boost v in the y direction. Imagine a wall( or mirror)...

2 textbooks I have give postulate 2 of SR as: "The speed of light in vacuum is constant in all inertial reference frames". But "Classical Dynamics" by Jerry B. Marion has: "The velocity of light in free space is a universal constant independent of any relative motion of the source and...

SR "Reference Frames" in QM ? The SR concept of “Reference Frame” cannot be transferred to the micro-world of QM because, due to the HUP, space and time are blurry in that world. Comments? (Thanks in advance).

Hello all, this is my first post on this forum, though I have been perusing it for a while. I am currently re-reading through Carroll's text on SR and there is a curious comment on p24 that intrigues me. Carroll says that the *only* tensors in SR which are invariant are the Kronecker delta...

This is actually for a graduate course but it's a basic special relativity problem, i.e. undergraduate-level material, so I'm posting it here... Homework Statement Homework Equations U^{\mu} = (1, 0, 0, 0) (in the observer's rest frame) V^{\mu} = (\gamma, \gamma \vec{v}) P^{\mu} =...

A little question which I thought of today. I thought about what happened in a medium with Lorentz transformation. With a refraction index n, the speed of light is altered to c/n. However, as far as I can see now this shouldn't influence the Lorentztransformations, right? It's tempting to put...

Hey guys can someone explain to me what does an inertial frame of refence mean? From what i know its a frame of reference whereby the observer frame of reference is at constant velocity? But i don't really get what it means. I have been reading some articles on SR and it seems that there is...

Hi there. I've been reading Brian Greene's book "An Elegant Universe" for the sake of curiosity and one of his examples to demonstrate special relativity really confuses me about the entire concept. To start, this is my current understanding of SR, so please correct me if I am wrong: -The...

Gravity seems to squish space time, velocity seems to also. It seems that through each's affect on distance, a formula containing both could possibly exist. Also, if we stopped and considered GR a law instead of a theory for a moment, then we conclude singularities must not exist. And QM...

Hi everyone, I recently decided that I wanted to the understand the concepts and applications of SR better. I've been reading a lot about it, but it gets confusing at points. For now I'm only concerned with SR and not GR. Here are some examples that I'm sure many of you would find trivial...

My understanding is that SR time dilation and Lorentz contraction are flip sides of the same coin. The two always occur together, never separately. That is implicit in spacetime diagrams. I think this duality requirement is necessary so that light always travels at the speed of c in every...

Imagine you were safely enchambered right at the center of the earth. Here you would "experience" strong gravitational "forces" but since they all point in opposite directions you would float around as if you were in zero-gravity. My question is, whether you would experience time dilation or...

Alice and Bob are each in their own spaceship, and are traveling radially, initially away from each other, and subsequently toward each other, at some highly relativistic relative speed, say 99c. Each ship emits light flashes toward the other. Alice observes the light from Bob's outbound...

I am currently trying to understand SR and am confused on this postulate. Lets say somone is traveling on a some kind of machine that emits photons. When that photon is emited will the person traveling on the machine measure the photon going c or will they measure it going c-v? My next...

In hypothetical empty space, Bob stays home and Alice flies radially away from home at .9c. In the flat Minkowski coordinates, each determines that the other's clock is running slower than their own. Each determines that the radial distance between them is Lorentz-contracted. Now consider...

Homework Statement The planes x= ±a are charged to uniform surface density ±σ respectively. Find the charge and current densities in a frame moving with velocity (0,v,0) - [done] Find also the electromagnetic field in the moving frame by solving the problem in the moving frame...

Let's say you're on a spaceship and you can accelerate to a speed very close to c. As your own time seems to slow down (relative to slow moving observers), your mass also increases. I know that mass increases in the sense that one requires more energy to give the same acceleration, but does...

Imagine a hypothetical large region of empty, non-expanding space whose spacetime is flat. At the start of the scenario, a rocket sits stationary relative to our galaxy at a large proper distance "x", in the common inertial frame. Then at t=0 the rocket quickly accelerates to a constant .99c...

Greetings! This is my first post so go easy. I read through the thread addressing the Sci Am article claiming that entanglement violates relativity. The article actually addresses a symptom of a larger issue that exists between QM and SR. I would like to get feedback on this issue as...

Just seeking a bit of guidance if I may ? If Lambda 1 is the time dilation caused by a gravitational field (ie proper time outside field/proper time inside field for static observers), and Lambda 2 is the usual time dilation under special relativity for a moving body (both lambda's >= 1), how...

Homework Statement The problem in question is 11.10 of "A traveler's guide to spacetime" by Moore. It goes as follows (by the way, the unit of distance that is used in the book is the lightsecond): "A neutral boson of mass m traveling with v=4/5 in the +x direction strikes a snoozon of mass...

I'm new to the study of SR and GR. I have a question that I have not been able to find any discussion about. In the case of two frames of reference where we are comparing events from the point of view between a 'stationary frame' (inertial) to an excelerating frame like the twin paradox is...

When looking at time dilation, I once came across a piece (I don't remember where) that said you could view time dilation as follows. Everything moves through four-dimensional spacetime at a constant velocity c. Something stationary is only moving in the time dimension. Something that has a...

Homework Statement A mirror moves perpendicular to its plane with speed (beta)c. A light ray is incident on the mirror from the \forward" direction (i.e., vm dot vl < 0, where vm is the mirror's 3-velocity and vl is the light ray's 3-velocity) with incident angle µ (measured with respect to...

Can somebody explain my error to me? 1. The base of SR is that nothing can move faster than light, c + v == c, c - v = c 2 The next step many authors do is proving non-existance of simultaneity by on observer at the platform versus one in a fast train. Flash from the front, to...

D.J. Griffiths in his "Introduction to Electrodynamics" writes: "Some authers consider Einstein's second postulate redundant - no more than a special case of the first. They maintain that the very existence of ether would violate the principle of relativity, in the sense that it would define...

An inertial observer in reference frame S makes the following determinations about you and me. (By that I mean all values below are with respect to the inertial observer.) You: Position (x, y, z) = ( 0, 0, 0) Velocity (vx, vy, vz) = ( 0, 0, 0) Acceleration (ax, ay, az)...

In your view, what contradictions remain? My guess is some might say none since entanglement can’t be used for FTL communication. Still others might say something (wave collapse and such) goes nondeterministic (FTL or back in time) between entangled particles so there is still a conflict. I’m...

Hi, Could you explain me a few things I still don't get about special relativity ? I've been tought a few years ago that special relativity wasn't good for handling accelerations... well I've been reading books and a few topics here, and I'm now convinced it is not true... for exactly the...

heuristic explanation of why quantum field theory imply antiparticles I'm looking for a heuristic explanation of why quantum mechanics plus special relativity requires antiparticles, Does anybody want to take a crack at it? Or am I asking for the impossible?

Light sources A & B begin at the same location. Then, source A begins moving directly (and soon inertially) away from Observer at 0.8c, while source B begins moving directly (and soon inertially) toward Observer at 0.8c. SR Doppler redshift causes the light received by Observer from A to be...

Homework Statement A cosmonaut spends a few years in an orbit above the Earth. We would like to estimate how his age will differ from his age if he had stayed on Earth. We will consider two separate effects. (a) First calculate the effect due to time dilation from Special Relativity. Let...

I assume that, in SR, both observers moving relative to each other calculate the same relative velocity (v). But I wonder how. If they use clocks and rods, I see two possible methods: (a) combination of the measurements of two frames and (b) only "home-made" measurements. In method (a), Mr A...

I've been trying to understand something for the past few days but can't seem to get my head around it. Could someone please explain to me how an extra internal degree of freedom arises for a particle when special relativity is combined with quantum mechanics?

I was thinking of this thought experiment the other day and it didnt quite seem to make sense to me. I hope some of you can explain it. I have drawn a quick example of the setup: and sorry for my english (c = 1 m/s) Imagine a 1 meter long spaceship with a velocity of 0,5 m/s (c/2). The...

Hello all. I wonder if you could help explain something to me. No matter how much I read I am not sure if my understanding of special relativity is correct. My confusion is with respect to a light clock constructed as one mirror above the other and a photon reflecting between the two mirrors...

Homework Statement A 100kev photon scatters from a free electron initially at res. Find the recoil velocity of the electron if the photon scattering angle is 180 degrees. Homework Equations Conservation of Energy, Conservation of Momentum (It is not allowed to use Compton's effect...

Homework Statement In frame S , particle 1 is at rest and particle 2 is moving to the right with velocity v. Consider frame S ′ , moving relative to S , with speed u. Find the value of u such that the two particles appear in S ′ to be approaching each other with equal but opposite...

Hi, In a previous thread https://www.physicsforums.com/showthread.php?t=240886 we concluded that an observer moving away from a luminous object would see the luminosity as reduced by a factor of 1/(1+z)^n where n is 3 or 4 and z is defined as : z= \frac{\sqrt{1+v/c}}{\sqrt{1-v/c}} -1 The...

I'm going to use this thread to ask questions about acceleration in SR. I'll just ask one or two at at time. First question: How do you calculate what the world line of a rocket with constant proper acceleration looks like in an inertial frame? Assume v=0 at t=0 and v>0 after that.