Relativity Definition and 998 Threads

Homework Statement I'm using Shankar's Introductory Physics course and I can't get a question out of my head regarding his setup of Relativity. There are two observers, S and S'. Observer S is stationary, while Observer S' is sliding past S (to the right) with velocity u. They agree to set...

What is the force acting on an object according to general theory of relativity? If there is a such a force, can we predict the motion of an object in general relativity just using the modified Newtons laws of mechanics i.e using relativistic mass of an object instead of rest mass ?

Homework Statement Our galaxy is about 10^5 light-years across, and the most energectic particles known have an energy of about 10^19 eV. How long would it take a proton with this energy to traverse the galaxy as measured from (a) the galaxy and (b) the particle? Homework Equations I...

Homework Statement A skydiver is strapped to a rocket and shot into outer space. There is no air resistance so he is able to make his arms into a 45° angle with respect to his body and pretend they are "wings." To a stationary observer on the Moon (we will consider the Moon stationary for our...

Homework Statement The problem states: Racer A and Racer B have the same care length, but from a spectators view Racer A looks (1/2) that of Racer B. Also Racer B is traveling at a speed v = (c/2). I am to find the spedd of Racer A in the spectators frame of reference. Homework Equations...

Homework Statement Assume two masses m1' and m2' are moving in the positive x-direction with velocities v1' and v2' as measured by an observer in S' before a collision. After the collision, the two masses stick together and move with velocity v' in S'. Show that if an observer in S' finds...

I have been wondering what effects a quantum mechanical system would cause in space time. Pick a general state of the system. This would not generaly be in one of the energy eigenstates -rather, it would be on a superposition of energy states. Now, each one of them would cause a different space...

Does General Relativity predicts that in the early universe vacuum energy was converted into matter? How does it relates to the Inflation Theory by Allan Guth? I'm asking this because I remember reading in a book on GR that there are ways of calculating the total amount of energy in the...

Hey so from my understanding of Einsteins theory of relativity the closer you travel to the speed of light the slower time is for you, is that right? if it is right does that give to reason that there could be a critical speed past the speed of light for which time for the object traveling at...

Homework Statement Imagine two inertial frames, S and S'. Inertial frame S' moves with velocity v0 = 5 m = s in the upward (positive y) direction as seen by an observer in frame S. Now imagine that a person at rest in frame S throws a ball with mass m straight up into the air with initial...

Hello, I have read somewhere that the next major step in physics will be unifying general relativity with the quantum theory. Does anyone know about such? I wanted to know a bit more. I have read about such in the book by Stephen Hawking "A Brief History of Time". Thanks, I. P.S. My apologies...

I read the forum rules, I hope I am not breaking them as these principle is generally accepted and I am not contradicting mainstream science. "The principle of relativity, according to which the laws of physical phenomena should be the same, whether for an observer fixed, or for an observer...

Pardon me if this has been asked before, but I'm confused with the implication that SR makes, that there is no objective moment of present. Do the science still believe that the time flows (i don't mean the arrow of time, but the phenomena of flowing/passing, eq. flowing of a river)? I mean, how...

The mainstream interpretation of GRT equations is, that additional double amount of angle of bending of light (Newton vs GRT) is caused by gravity (which is interpreted as curvature of spacetime). But when looking on the equations, it seems that this additional amount of bending is caused by...

Homework Statement A visit to Regulus is on my bucket list. However, it is 77 light years away. Assuming I will live only another 40 years, can I make it to Regulus? How fast would I have to travel (at constant speed) to get there in 40 years? Homework Equations t1 = t0...

If you are observing a particle enter a black hole, you watch its proper time go to zero at the event horizon as it is 'frozen' there from your frame of reference. What happens in your reference frame as the black hole evaporates? While you can't illuminate where the particle is from your frame...

Hello, In my free time, I've been learning about an eclectic range of topics (ie. French History, Kinetic Theory etc.). Most recently I've been focused on Quantum Mechanics, which happens to be most complex topic I've ever looked at. Typically I write up summaries after reading from various...

Does the amount by which an object changes the spacetime curvature depend on relativistic mass or the rest mass? Through this question I just want to answer whether momentum equals [relativistic mass * velocity] or is it [rest mass * gamma * velocity]. Both the formulas might be the same but I...

Imagine yourself to be bat. You can't see anything. You don't have eyes. All you can do is echolocate, using ultrasound. Now imagine something is moving away from you faster than the speed of sound. Can you locate it ? Can you perceive its existence ? If the answer is yes, how ? If no , then...

Let there be 2 astronauts A and B in uniform relative motion and they are moving towards each other. Let A be moving in a spaceship of length L and there are 2 clocks ca1 and ca2 attached to the front and back of the spaceship respectively and let clock of B be cb. The moment when the front of...

I understand that the concept of a atom resembling a solar system is disregarded as being untrue because this is based on the Bohr model which doesn't represent how an electron would actually appear in its probability cloud. However, would it be possible that if there were an observer on the...

I am trying to understand something. Let me pitch a scenario: You have two asteroids in a vacuum. Each is large enough to be round by gravity. They are separated by roughly the distance from the Earth to the moon. Relative to each other, they are moving at 0 in all directions (aka, they are...

Am i right in thinking that relativistic simultaneity explanations tend not to mention the fact that one of the ‘simultaneous’ events may well be red shifted and the other blue shifted and by analysing wavelengths you could presumably work out whether the event was in reality simultanous or not.

Homework Statement It is not ordinary problem, it is connected to it. I don't understand a figure and how is described. The problem is here http://www.pmaweb.caltech.edu/Courses/ph136/yr2011/1102.2.K.pdf How did equation 2.4 from figure 2.3 arise? Why disappear ##\Delta t^2## from the right...

It seems that with the 2016 LIGO and VIRGO confirmation of the gravitational chirp that we have also experimental confirmation that the speed is indeed the speed of light. True? https://en.wikipedia.org/wiki/First_observation_of_gravitational_waves#Direct_observation

I am trying to get this idea of Time dilation understood. If there exists only two objects in a Universe and one object is stationary and the other object is moving at 99 % the speed of light. Their clocks were both synchronized when both objects were stationary relative to each other. Then the...

Homework Statement I have noticed that in some calculations they use $$ \vec{\nabla}\cdot\vec{u}=\frac{1}{V}\frac{dV}{d\tau}$$. I would like to derive it. Homework Equations ##\vec{u}=(\frac{dt}{d\tau},\frac{dx}{d\tau},\frac{dy}{d\tau},\frac{dz}{d\tau})## ##\vec{A}\cdot\vec{B}=A^{\mu}B_{\mu}##...

Problem statement: A rocket propels itself rectilinearly by giving portions of its mass a constant (backward) velocity ## u ## relative to its instantaneous rest frame. It continues to do so until it attains a velocity ## v ## relative to its initial rest frame. Prove that the ratio of the...

Consider two bodies A &B are moving apart with a velocity V due to the expansion of space. According to an observer in A the body B is moving away and an observer in B feels the body A is moving apart. Can some one answer in which body the time dilates and why?. ( I am specifying once again that...

In Carrolls notes on General Relativity, it is said that the general formula for finding the spin number of a particle is $$\frac{360°}{\theta}$$ where ##\theta## is the angle of rotation, after which the state of the field describing the particle returns to its original state polarization. He...

I think he's pretty much nailed the relativity, QM and BTSM forums: https://xkcd.com/1861/ or https://m.xkcd.com/1861/ for mobile users.

Suppose there is a charged particle far enough of any mass so that there is no gravitational interaction between the particle and any other body. The trajectory of the particle in space-time would appear to us like this (we are at the origin of our coordinate system). Consider that at...

I am trying to understand why the special relativity is not suitable for describing the gravity. Consider a counterexample assuming it is the suitable and the space-time containing a gravitational mass is flat. Then one could describe the acceleration of a test particle from his inertial frame...

(I don't know if this is the right place to post it, but I think the "textbooks" section is'nt. So I'm going to put it here.) I have been self studying S&G relativity for almost eight months, mostly from Weinberg's book on S&G relativity, but also from papers I occasionally find on web and from...

I'll be entering my sophomore year as a physics major and all the classes seem really cool and standard; however, there is one class I'm curious about. It's called "Relativity and Quanta" and it's description is as follows; "Special relativity: Lorentz transformation, dynamics, and conservation...

Dear All, Just wanted to share this excellent free Special Relativity online course I came across by Brian Greene, which I believe is one of the best around. Not sure if it's been shared before here. Special Relativity — World Science U, by Brian Greene...

Homework Statement A cone has half angle θ0 and lateral surface area S0 in the frame in which the cone is at rest. If someone moves at relative speed β=v/c along the cones symmetry axis, what surface area will they see for the cone? Homework Equations I believe the lateral surface area of a...

I found this spacetime diagram at https://en.wikipedia.org/wiki/Proper_acceleration with an accelerating traveler, resulting in "curved" hyperplanes of simultaneity. Notice how the simultaneity planes are angled "normally" (The faster the steeper the slope and no slope when stationary) but...

Homework Statement A.P. French q.no. 4.3 Homework Equations t = L\c, (1) L0 = ϒ L The Attempt at a Solution The observer's frame is that frame w.r.t. which the meter stick is moving with speed 0.8c. The observer sees the mid-point at (x,y) at a time to(measured from the clock situated at...

Homework Statement Homework EquationsThe Attempt at a Solution [/B] Let ##k^u## denote the KVF. We have that along a geodesic ##K=k^uV_u## is constant , where ##V^u ## is the tangent vector to some affinely parameterised geodesic. ##k^u=\delta^u_i## , ##V^u=(\dot{t},\vec{\dot{x}})## so...

Homework Statement To show that ##K=V^uK_u## is conserved along an affinely parameterised geodesic with ##V^u## the tangent vector to some affinely parameterised geodesic and ##K_u## a killing vector field satisfying ##\nabla_a K_b+\nabla_b K_a=0## Homework Equations see above The Attempt at...

Is there any way to travel back in time in reality according to GR? Let me know!

Homework Statement question attached Homework EquationsThe Attempt at a Solution Attempt : Check if ##V^{\alpha}\nabla_{\alpha}V^u=0## Since Minkowski space, connection tensors/christoffel symbols are zero so this reduces to: ##V^{\alpha}\partial_{\alpha}V^u=0## where...

Is it really hard to find a solution of a GR equation maybe two planet system ? Or It could be a different system.I just wonder 1-How much its difficult ( Like can a person calculate those solutions) 2- Whats the boundries (Like we can solve 2 planet system but not 5 etc ? ) 3- Can...

I think special relativity would disallow our universe from having the structure similar to an ant on a sphere. What I mean is that it can't be possible to travel in a constant direction and to come back to your original location. Suppose there is an observer S on a planet and an observer S'...

Do we know if experiments with plasma fusion could test relativity and its speed limit because of the maximal speed ? Like $$3/2kT=1/2mc^2$$ hence for example with hydrogen the maximal temperature should be around $$10^{12}K $$. I read that they achieved 8*10^7 in wendelstein. Or should it be...

This may seem like a stupid question, but i can't get my head around this so please bear with me. I just looked at the derivation of Dirac equation and my question is: do the solutions for a free particle obey special relativity? because if yes why? I mean I thought using E2=(mc2)2+(pc)2 would...

Hi, i got little confused after this conversation in https://www.physicsforums.com/threads/some-questions-about-light-and-relativity.918094/page-2 There was also this conversation: So i want to clear the confusion. As was pointed out to me, in STR mass is defined as m2=E2 - p2, which...

So there will be a few hypothetical in the original story here, but in the end ill wrap it up with what I believe are facts. My question, how does Einstien’s theory of relativity interact with consciousness? Let’s say I have a twin, he becomes a farmer and I become an astronaut. I go to space...

I'm trying to study on light velocity and relativity. And I have a few questions I hope someone can make clear to me. Please try to not use math but just explain in layman's terms if possible. I know the light is measured at the same speed regardless of the observer. Why? More to my...