The union of special (SR) and general (GR) relativity. Use this tag if both SR and GR apply.

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Does a body curve spacetime at higher velocities? [duplicate]

Suppose we have two objects where the distance over time decreases. Now, as I understand it, general relativity says that we can observe the Universe from the perspective of both objects an get a ...
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26 views

Using Special Relativity in Uniform Circular Motion [duplicate]

Can one utilize the formulas of Special Relativity in uniform circular motion? The radial component of the object does accelerate, but sometimes we are just interested in its tangential speed. Here ...
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Two-Observer Spacetime Diagram

What is the significant in a two-observer spacetime diagram's primed axes? More specifically, the area enclosed by them. Obviously, if an event occurs within the axes, it is simple to find its ...
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76 views

Books on special and general relativity? [duplicate]

I have idea about all the theories related to space and time and stuff. But I wanna dig deep into it and understand all the theories like special and general relativity to begin with for now. Can ...
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2answers
113 views

Time dilation in outer space vs in a gravitational field? [duplicate]

I have been wondering how could aging process differ for a person moving close to velocity of light or for a person close to a very strong gravitational field compared to a person who is in a slow ...
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25 views

Can a characterization of “inertial motion” be expressed in terms of interval ratios?

Consider a "material point" $A$ having taken part in the two distinct events $\varepsilon_{A J}$, and $\varepsilon_{A Q}$, as well as in additional events "inbetween", such as any event ...
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22 views

Thomas Precession of an orbiting electron

So I am working through a problem on Thomas Precession. The set up is that we're given at lab time zero, the initial spin of an electron in circular orbit is: $$ ...
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2answers
50 views

Time Dilation, Multiple Earth's?

I was reading about time dilation and suddenly a question raised in my mind. (This might be a misconception but please do correct me if I am wrong) I read that if we travel near to the speed of ...
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49 views

Doppler effect for the electrons emitted from ions moving at a particular velocity

If I have ions moving in X axis (along both directions; positive X axis and negative X axis) and if I irradiate laser along the positive X axis, electron will be ejected from the ions (if I am using a ...
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28 views

Are photons travelling in future? Are they lifespan 0 (or close to 0)? [duplicate]

We know that if we are going closer to speed of light, we are travelling in future. Since the photons are travelling at the speed of light, that means that they are travelling into future? Also, if ...
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55 views

Conditions that the coordinate must satisfy in order to become local inertial

Consider the coordinate transformation $$ \tilde x^a=x^a+\frac{1}{2}\Gamma^a_{bc}x^bx^c $$ I have shown that at the origin $O=(0,0,0,0)$, $$ \frac{\partial\tilde g_{ab}}{\partial\tilde x^c}=0 $$ ...
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(Special Relativity) Points that can be seen by an observer

Let the metric be $$ ds^2=(1+gz)^2dt^2-dx^2-dy^2-dz^2 $$ where $g$ is a positive constant. Let an observer be stationary at $x=y=0$ on the surface $z=0$ and look upwards at an angle $\theta$, how ...
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39 views

Relative effects of forces

Excuse me for my ignorance but I really couldn't find a solution. According to Einstein, every happening is possible to describe by both of interacted objects. Is there any other way to describe the ...
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1answer
78 views

Theoretical Physics Notation (Hamilton-Jacobi in the Relativistic Domain)

I am having trouble understanding how to solve some theoretical physics problems I have come across. Specifically how to convert the Hamilton-Jacobi equation: $$(\partial_\mu S+e A_\mu)^2=m^2$$ From ...
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79 views

How to move from Special to General Relativity

I have understood special relativity nicely, and right now I am trying to learn general relativity from D'Inverno's book. I an finding it rather difficult to understand the pre-requisite math (i.e. ...
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34 views

concept of density in gravitational lensing

I may just be being very dense (no pun intended) but i'm reading up on gravitational lensing and it seems to require a notion of density (e.g. see here) I'm working on a question involving light ...
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1answer
59 views

Conservation laws vs Einsteinian space-time

The way I understand conservation laws - which I am asking you to correct - is that if I observe any slice of the universe perpendicular to the time axis and count up all the mass/energy, momentum, ...
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126 views

At near light speeds, are small objects in your path a problem?

A mental exercise: A space ship is accelerating toward me from far away. As it approaches me, I can observe its acceleration. This high speed ship keeps accelerating faster toward the speed of light. ...
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41 views

Isn't Dark Matter just an Indication that Relativity breaks down when describing large masses? [duplicate]

It seems to me that Dark Matter is just an indication that our models of gravity do not scale to the level of galaxies, and thus like Newtonian physics, it is a powerful but incomplete model of the ...
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1answer
822 views

Spacetime and Timelike Intervals

The difference between a “timelike” spacetime interval and a “spacelike” spacetime interval can be understood in the following way: If the spacetime interval between two events is timelike, there ...
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2answers
156 views

Relativity Problem Given Rest Length and Proper Time

A relativistic train with a rest length of 500.0 m takes 780 ns to pass a stationary observer standing on the train platform, as measured by the stationary observer. (a) What is the speed ...
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46 views

What is an example of a situation where Quantum Mechanics and Relativity do not work together? [duplicate]

I've learned special relativity in school last semester, and this semester we began learning about Quantum Mechanics, and my teacher told us that there was a Relativistic Schrodinger equation. I was ...
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74 views

Need help with relativistic dynamics

I understand the concept, but I'm having a hard time applying the consequences of conservation (energy/momentum). For example: A proton with kinetic energy 437 MeV hits a proton at rest elastically ...
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Period of Transmission of signals in different frames

A radar transmitter (T) is fixed to a system $S_{2}$ which is moving to the right with speed v relative to system $S_{1}$. A timer in $S_{2}$, having a period $\tau_{0}$ (measured in $S_{2}$) causes ...
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42 views

Why has the ether been disregarded as a valid medium through which light can propagate? [duplicate]

Possible Duplicate: Ether theory acceptance Although the Einstein's theory of relativity seemed to make the concept of an ether obsolete, did it necessarily invalidate it? Are there any ...
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107 views

Can space-like fields not commute and still forbid faster-than-light signalling? [duplicate]

Possible Duplicate: Is microcausality necessary for no-signaling? If we try to measure two non-commuting observables, only the earlier measurement would be valid. The later measurement ...
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3answers
76 views

Simultaneity and quantum indeterminism

How can Relativity talk about simultaneity planes when the events are actually quantum in nature so they are indetermined ? How can you say that if you walk on the street with 1m/s you are ...
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1answer
139 views

Question about time dilation and relativity [duplicate]

Take this scenario for example: I am on a rocket ship that will take a trip into space and back at 90% the speed of light. And my friend "Bob" stays on Earth. As soon as I leave Bob and I both start ...
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1answer
72 views

Possibility of simulating quantum physics and relativity [closed]

I must be clear; this is not a 'specific' question, but rather a hypothetical one. As of now, computer physics simulations are becoming more and more advanced, and I am programming one now. I was ...
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2answers
87 views

Acceleration to lightspeed using gravity

Suppose we have a very advanced spaceship that (aside from colliding with planets or entering a blackhole) is indestructable, and can go very fast, but is incapable of moving at lightspeed on it's ...
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1answer
131 views

Which “space-time coincidences” are described by a “co-ordinate system in which the gravitational field does not appear”?

In Einstein's exposition of the foundations of General Relativity (cmp. http://en.wikisource.org/wiki/The_Foundation_of_the_Generalised_Theory_of_Relativity , end of §3) there appears an emphasis on ...
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2answers
268 views

What's a “noninertial frame”? [duplicate]

In some PSE questions or answers such as here (and comments below) there appears the notion of "accelerating frame" or (more or less equivalently) "noninertial frame". What's the definition of this ...
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Simultaneous observations in relativity

Consider an object which responds to two different signals A and B: it responds to signal A with blue color and signal B with red color. Also, it responds only to the signal that reached first. In ...
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How do photons experience time? [duplicate]

I know that as velocity approaches the speed of light the time dilation shoots to infinity as shown below. 1)So I want to know how time is perceived from the point of view of the photon? 2)Since ...
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369 views

Gravity vs. Velocity Time Dilation [closed]

Can some one give me the unified formula for Gravity Time Dilation and Velocity Time Dilation.
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1answer
90 views

Gravitational Time Dilation Formula? [closed]

What is the equation for calculating the dilation of time at different levels of gravitational force?
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1answer
109 views

attaining the speed of light?? [duplicate]

WHY our time would run slow if we move with the speed close or equal to the speed of light, and is that time dilation restricted to only just '' time' ' or it affects our biological time also (does ...
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132 views

Why is it legitimate to only observe motion, but call it time, such that concepts like “the relativity of simultaneity” are seen as possibly genuine? [duplicate]

My question is asking for evaluation of a new concept or paradigm within the framework of the current mainstream physics understanding of Relativity. Specifically, that concept or paradigm being that, ...
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2answers
115 views

The relativistic mechanics of a battery that is being charged and accelerated at the same time

This might be an interesting question: Let's attach a battery into one end of an electric cable. Then we rotate the battery around, with accelerating speed, using 100 Watts of power, while the ...
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1answer
166 views

frames of reference [duplicate]

Possible Duplicate: Help Me Gain an Intuitive Understanding of Lorentz Contraction Frames k and k' are inertial frames. Frame k' is moving at a velocity of magnitude v relative to frame k ...
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What is the speed of a Photon? [duplicate]

How fast does a Photon travel through space? And is gravity able to influence a Photon's path?
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27 views

Is the Universe a 4D elastic shell that is contracting with time, where particles are traveling waves or standing waves of energy density? [on hold]

In gravitational red shift, “the phenomenon known as the red shift of a photon is really the blue shift of an atom.” This conclusion also applies to Galactic redshift. According to Hubble’s law, when ...
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3answers
292 views

Where in, Einstein’s “On the Electrodynamics of Moving Bodies” (Relativity), is “Time” reasonably shown to exist, or why is it a valid assumption? [closed]

Given the widespread acceptance that “Einstein’s Relativity” reasonably proves the existence of Space-‘Time’, and thus “Time”... Can any member of the Physics StackExchange please show precisely ...
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1answer
471 views

Why are we talking about space curvature as if we know what space is? [closed]

1) Why are we talking about space curvature as if we know what space is? Every question about gravity seems to evoke an answer involving "space curvature" which seems like an undefined placeholder ...