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

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Null Coordinates

I have a very basic question: what are the advantages of writing a metric in the null coordinates? Which extra insight do they provide? I've looked in Caroll's "Spacetime and Geometry" and Wald's ...
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53 views

Measuring time dilation

After watching a certain recent film, I started wondering whether it would be possible to create a watch (or, more likely due to the sizes of the components, a clock) capable of measuring one's time ...
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Relativistic Induced Magnetic Field in particle's frame

Suppose there is a constant magnetic field: $\vec{\mathbf{B}} = B \hat{z}$. A charged particle orbits that magnetic field perpendicular to the magnetic field, and induces a magnetic field in the ...
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Does Gravity Warp Coulomb's force?

Does gravity effect the "sphericalness" of the Coulomb force? For example, is the field 1 meter above a charge weaker than the field 1 meter below the charge? Could a 0.014% difference in the field ...
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The Higgs field and spacetime intervals

The Higgs field imparts a rest mass to certain fundamental particles, but it also seems to do something more interesting. Particles that don't couple to the Higgs field, i.e. the rest-massless, are ...
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Is there a rigorous, explicitly geometric, general characterization for whether a given clock had been “good”, or not?

In MTW, "Gravitation", there is a brief section (p. 26 and Fig. 1.9) discussing that clocks may be characterized, trial by trial, as having been "good" in the trial under consideration, or having been ...
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60 views

Is the charge of a current carrying wire real or hypothetical?

Realist753 Theory Relativistic Electrodynamics assert that a current carrying wire being neutral in a laboratory frame of reference appears electrostatically charged to an observer in relative ...
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273 views

Mercury's Orbital Precession in Special Relativity

I am researching Mercury's orbital precession. I have considered most perturbations and general relativity. I am still not satisfied. I need your help. I need a solution to Exercise 13, Chapter 6, in ...
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51 views

Is the intuition of “absolute simultaneity” necessarily wrong?

I read about Einstein’s theories of relativity with all the interesting stuff like time dilation, mass increase and whatnot. And also about the relativity or conventionality of simultaneity. The ...
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28 views

What would we see if a camera orbiting close to light speed beamed down images of us on earth?

If a camera was sent up in a satellite, put in orbit at close to light speed, and instructed to beam down images to earth, what would we see if we watched its video feed? (Ignoring the fact that ...
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117 views

Is there any relationship between the $E=mc^2$ equation and the $a_n=\kappa v^2$ formula for the normal component to acceleration?

To clarify, I know very little about physics and don't pretend to have any insight whatsoever into relativity beyond what has entered the popular imagination; my knowledge is more or less at the level ...
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47 views

Does relativistic glider violate principle of equivalence?

The relativistic glider proposed can slow down the fall of an object in gravitational field. Will this violate the principle of equivalence which says that one cannot distinguish between free falling ...
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68 views

Perpetual Mobile and Gravitation

I have fundamental question about what is called the “law of conservation of energy”. We all hear about the tidal power stations which using the tidal power. The source of the tidal power came from ...
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Is there a theory that physically explains the origin equivalence principle / explains gravity via acceleration?

I've been thinking about how gravity could arise from a 4th dimensional spinning cylinder with space-time that has pliability like rubber (which I think is a generally accepted analogy). The ...
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52 views

How is force felt at relativistic speeds?

Hypothetically, should a force feel the same as its measured force at relativistic speeds? Obviously a human body would not survive the force of a rotation at say, 0.6 the speed of light, but it’s ...
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70 views

Is the cross section of a relativistic water hose or string always a perfect circle?

Given is a very long tube, such as a water hose or a tubular string with finite thickness, that has a constant circular cross section of radius $r$ along the length and that is at rest in an inertial ...
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38 views

How do we generalize limitations on the propagation speed of sinusoidal waves to limitations for transmitting any kind of information?

Our calculations on EM waves basically deal with harmonic waves and through such calculations and relations, we derive some relations and limitations for wave like phenomena. Of these relations are ...
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115 views

How to name different approaches to relativistic quantum theory

In the introductory chapter of the QFT book by Mark Srednicki the author notes that [p. 26] So now we have two different approaches to relativistic quantum theory [...] Which [one of those two] we ...
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173 views

How do I extend the Lorentz transformation metric to dimensions>4?

How do I extend the general Lorentz transformation matrix (not just a boost along an axis, but in directions where the dx1/dt, dx2/dt, dx3/dt, components are all not zero. For eg. as on the Wikipedia ...
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What is static mass increase effect predicted by General relativity?

According to wikipedia, static mass increase is predicted by Einstein's General Relativity. In the book 'The Meaning of Relativity' by Einstein, inertia will increase when the object is near a ...
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93 views

What are the equations of motion that model near light speed orbits of a massive body about incredibly massive bodies?

In Kip Thorne's recently published book, The Science of Interstellar, he describes, by means of an illustration, the complex nature of a spacecraft orbiting a massive black hole with velocities ~ ...
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46 views

Can photons travel through space independent of time?

I read an article about advanced photons and they stated that photons traveled back in time to hit an electron. Can photons really travel back in time and if so, how?
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92 views

Will relativistic glider cause lower gravitational force in Newtonian gravitation?

In the articles The relativistic glider and The relativistic glider revisited, the relativistic glider is proposed where a quasi-rigid body can slow down its fall under gravity without any reaction ...
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52 views

What is the physical meaning of the norm of the electromagnetic four-potential?

In SI units this would be $\frac{1}{c^2}\phi^2 - A_x^2 - A_y^2 - A_z^2$. Is this just not a physically meaningful quantity at all because it's not gauge invariant?
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39 views

Are signals exchanged between a rotating frame and a central frame assymetric?

This question pertains to EM signals exchanged between an inertial central clock and an orbiting clock i.e. non-inertial frame. (I edited out the variables connected with gravity and separation ...
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176 views

Relativistic beaming - which power of the Doppler factor

The context is that I'm building a simulation of a starfield, as seen from a relativistic spaceship. (EDIT: the simulation can now be found here.) One reference that I'm using is this paper by John ...
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102 views

What is Einstein regarding as the problem of physical relativity in his lecture of 1923?

The following is the extract from Albert Einstein's lecture to the Nordic Assembly of Naturalists (July 11, 1923). If we consider that part of the theory of relativity which may nowadays in a ...
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46 views

Accelerated charge in relativistic frame

An accelerated charge radiates energy as electromagnetic waves. Imagine a point charge at rest in an inertial frame We are standing on a frame accelerating with respect to the charge. Now with respect ...
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27 views

Does radar distance depend on the future of the observer in special relativity?

Radar time and distance which are defined as $\tau^\star = \frac{\tau^+ + \tau^-}{2}$ and $r^\star = \frac{c(\tau^+ - \tau^-)}{2}$, can be used in the context of general relativity to attribute time ...
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18 views

Weizsäcker–Williams approximation

I'm having some trouble understanding the Weizsäcker-Williams approximation What I think it is is the following: I have a charged particle at high speed, close to the speed of light, at this speed ...
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27 views

How can I calculate time dilation as viewed from an accelerated frame?

Imagine I am speeding past you at near the speed of light, at a constant velocity. It is very simple for me to calculate what I will see looking at you. According to the Lorentz transformations from ...
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36 views

Laws of physics for a point in cyclical 2D motion

A follow up question to the question in What does the statement "the laws of physics are invariant" mean? and Formal definition of an observer? Which laws of physics are they talking about ...
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24 views

Will the center of mass of the whole system change when object swims on curved surface?

In the example given here, the object can move on the frictionless surface of the sphere by changing its shape periodically. So will the center of mass of the whole system change after the object ...
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26 views

Relative time difference and the gravitational potential of the geoid

I'm having trouble with something from a problem set on relativity and time. We are given the equation for time elapsed on a clock on the Earth's surface relative to time at the geocenter ...
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41 views

Possible Lack of Invariance in Two Inertial Reference Frame Scenarios

Two objects are connected together via a ideal spring which is compressed initially. Then the spring is released, the two balls are no longer connected and go their separate ways. Assume no other ...
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28 views

What would an relativistically expanding sphere look like for an external observer?

Consider a reflecting sphere, whose radius is increasing at constant rate V close to light speed. What would the collision look like for a remote observer stationary relative to the centre of the ...
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27 views

Gibbons Hawking metric and space $X$

I am studying the Gibbons-Hawking metric. The metric is : $$g = U^{-1}(d\tau + \omega\cdot dx )^2 + Udx\cdot dx$$ with $$U= \sum_{n=1}^s \frac{1}{|x-x_n|}.$$ and would like to understand the space $X$ ...
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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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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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21 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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38 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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54 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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35 views

(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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When High-Speed Traveler is On Differently-Shaped Surface Compared to Observer, What Does Observer See When He/She Goes Around Corner?

As stated in my other question, the length of a traveler going at relativistic speeds compared to an observer only gets contracted in a single direction, i.e. the direction of motion. Well, what ...
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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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77 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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31 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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116 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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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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22 views

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 ...