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

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What would a nuclear explosion look like at relativistic speeds where time dilation and length contraction become significant?

Suppose a rocket carrying a nuclear weapon is moving past our planet at very near the speed of light while a stationary observer watches from here on Earth. As the rocket passes directly overhead, an ...
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Clocks in moving inertial frames [on hold]

A clock $C$ is at rest at the spatial origin of an inertial frame $S$. A second clock $C'$ is at rest at the spatial origin of an inertial frame $S'$ moving with constant speed $u$ relative to $S$. ...
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1answer
37 views

Are the words “coincident” and “simultaneous” considered synonymous? Else, please explain the difference

In discussions, experimental and thought-experimental descriptions (especially concerning the Theory of Relativity) the words "coincident" and "simultaneous" appear, notably for instance in the ...
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3answers
175 views

How can light travel at a speed greater than the speed of light

I was reading John Rennie's answer here, Can light travel faster? I now know that the sentence ''the speed of light is always constant in vacuum'' is just an oversimplification, for example light ...
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2answers
156 views

What exactly is meant by saying that two events had been “simultaneous in an inertial frame”?

In order to address my question based on a concrete example setup let the following two separate events be given: participants $A$ and $J$ encountering each other in passing (additional participants ...
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2answers
281 views

Dimensional aspects of the imaginary unit $i$ in physics [duplicate]

From a real world perspective each dimension in the 3-D Cartesian System can be represented by an axis that is perpendicular to 2 other axes. I read somewhere else that the effect of ${i}$ is to ...
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1answer
312 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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0answers
29 views

What is the speed of gravity? [duplicate]

Hypothetically, let`s say that one day our Sun is suddenly removed from the galaxy. For us, on earth, would take up to 8.3 minutes to notice that the sun was removed, since the distance from the earth ...
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4answers
85 views

What is the proper time interval for simultaneous events?

Let us take a rod of length L and the two ends A and B have two photon guns. A----------------------B Let the end A fire a pulse (event ...
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17 views

Is there any evidence for the increase of mass due to time dilation also causing a strengthening in said mass' gravity? [duplicate]

Logically it make sense that gravity would strengthen with an increase of mass but I want to know if there is evidence for this.
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2answers
182 views

Relativistic mass as seen by different observers

Imagine there are two observers $A$ and $B$ and a particle $P$. $A$ and $B$ are at about the same point, $P$ is some distance away. From $A$'s point of view, $P$ has velocity $V$ and $B$ has ...
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0answers
43 views

What is the force between two points in space due to expansion of space between them?

Is there any way(equations?) to calculate the force between two points due to the expansion of the space between them? (To clearify the question I should add that the reason we donot expand while the ...
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1answer
44 views

Special relativity, electromagnetic fields, charge and Q

Is it true, were Coulomb's constant k to be several orders of magnitude smaller, that there would be no (or increasingly negligible) magnetic fields generated by moving charges? The reason being the ...
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2answers
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In special relativity, is it correct to say the speed of a body B relative to A is the same as measured by every observer?

Here, two objects A and B are moving relative to each other. I use the Einstein velocity addition formula $v = {v_1 + v_2\over 1 + {v_1 v_2\over c^2}}$ to calculate the relative speed between A and ...
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7answers
488 views

Relation between coordinates and frames of reference

I always get a little uneasy that all the theories I can think of (at least since Newton) are constructed in a way such that they would be true in heaven and on earth ... but we can never go ...
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2answers
94 views

How can a photon have energy when its mass is zero? [duplicate]

How can a photon have energy when its mass is zero? According to Einstein's equation $E = mc^2$ energy depends on $mass*c^2$ Light has zero mass so the energy would be zero too but solar cells use ...
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7answers
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Quaternions and 4-vectors

I recently realised that quaternions could be used to write intervals or norms of vectors in special relativity: $(t,ix,jy,kz)^2 = t^2 + (ix)^2 + (jy)^2 + (kz)^2 = t^2 - x^2 - y^2 - z^2$ Is it ...
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0answers
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How can we represent the 3 space coordinates uniquely by one point that can be put on a single axis?

In the Space-Time diagram (in the rest frame) we often take the Space axis as the horizontal axis and the time axis as the axis perpendicular to it as in the given figure. While there are other ...
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69 views

Pauli exclusion principle and relativity

I'm somewhat curious about how the Pauli Exclusion Principle functions when relativistic time becomes a significant factor. Just to clear things up, my (possibly poor) understanding goes like this. ...
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4answers
886 views

Special Relativistic Time Dilation — A computer in a very fast centrifuge

Ok, I've stumbled onto what I think is a bit of a paradox. First off, say you had some computer in a very fast(near light speed) centrifuge. You provide power to this computer via a metal plate on ...
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1answer
59 views

Question about basic formalism of GR and the metric tensor

I really don't know much about GR, but I've come across a few rough sketches of its formalism in my DG books. I'm trying to piece it together to get a very basic intuition of what spacetime is in GR. ...
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2answers
34 views

Space: a vacuous void or an entity?

I am a chemist and, until recently, a senior Research Manager with a major chemical company. Please excuse the potentially naive ramblings of an idiot in what follows, but I do not have the ...
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4answers
123 views

In $1$-dimensional space, how would the gravity generated by an electron affect a photon moving away from the electron if the photon can’t slow down?

Suppose we had a universe obeying the same physical laws as our own. But it had only one spatial dimension (represented by the $x$ axis) and it was totally empty. There are just two point-like ...
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1answer
56 views
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1answer
139 views

Has anyone yet been able to prove relativity wrong? [closed]

I was in a physics group, then a student (or a professor, I don't know) posted this- Mohammad Shafiq Khan > Physics > The space-time concept including the formula $E=mc^2$ are proved baseless in ...
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1answer
52 views

Boyles law & relativity

In relativity when an object approaches the speed of light, $c$,its volume decreases due to length contraction. As a thought experiment, consider a rectangular metal box travelling at a relativistic ...
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1answer
66 views

Special relativity and Lorentz transformation

I recently learned about special relativity and different reference frames. The conversion from two inertial reference frames is given by Lorentz transformations: $$x' = ...
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20 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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1answer
86 views

Why invariance is important?

The concept of invariance seems to have a great importance. Indeed, the fact that the laws of Electrodynamics are not invariant in every inertial reference frame led to the theory of Special ...
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3answers
102 views

Is it possible to express various nonlinear motions as straight lines in transformed spacetime?

I am trying to understand simple examples of space-time curvature. Assume for the moment that $c$ is infinite (classical curvature due to Newton's laws). Also, I will only consider 1+1-dimensional ...
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2answers
77 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
118 views

Could there be a time dilation of 2,000,000x between Earth and other parts of the universe?

Don't ask me why, but you may be able to guess why I would ask such a question. The question is, what kind of conditions would have to be present in a universe in order for billions of years pass in ...
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4answers
176 views

Expected result of vertical Michelson-Morley Experiment [duplicate]

What would the result of a vertical variation of the Michelson-Morley experiment be? I.e., if one were to compare light traveling along a horizontal arm with light traveling along a vertical arm ...
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4answers
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What is the mass of a sphere?

A solid sphere of mass M is rotating along an axis. We can consider it as a collection of large number of point masses, every point mass is moving with respect to center of mass with velocity which ...
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Relativity: stationary vs moving

In the book The Elegant Universe, Greene describes a situation in which there are two space travelers, George and Gracie, moving in relationship towards each other at a constant velocity with no other ...
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1answer
54 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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0answers
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Do photons exert gravity? [duplicate]

I read about GR today and came across the Bonnor beam. As I understand it, two parallel light beams (in a flat space) will in fact creep – slowly – towards each other. As Wikipedia puts it: On the ...
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2answers
858 views

Mechanism by which electric and magnetic fields interrelate

I read that force due to electric field on some particle in one reference frame can exhibit itself as force due to magnetic field in some other reference frame and that electric and magnetic fields ...
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1answer
49 views

Relativistic addition of velocities in the y-direction? [closed]

I've been having some difficulty with the problem described below, please have a look: Two particles with identical masses (m) undergo a collision. Before the collision they move with velocities ...
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5answers
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Light's oscillation in time

Electromagnetic waves have electric (and magnetic) fields that oscillate spatially and with time. But light, moving at the universal speed limit, is a "space-like" object according to relativity since ...
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2answers
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Careers in physics that are related to quantum mechanics or relativity? [closed]

Personally I learned Physics in high-school and found it very interesting, I read up a lot about physics in my free time. Personally I am also a programmer which I think is also good when it comes to ...
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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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1answer
42 views

Time and speed - Theory of relativity - 'felt time'

Assuming time is relative according to the objects current speed, means that a clock within a space shuttle which has 30% of light speed is 'ticking' slower than a clock staying on planet earth just ...
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1answer
118 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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2answers
51 views

Michelson & Morley

I KNOW this is a common question in it's topic, but not in this form.. I'm reading a book which explains the significance of certain aspects of experiments.. This section is called "null ...
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1answer
29 views

Orbital variations [closed]

My question relates to relativity and the warping of spacetime. If the geodesics approaching the star are coplanar with the ecliptic how can polar planetary orbits form?
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3answers
3k views

How to calculate time dilation in approaching speed of light

If a spaceship travels close to the speed of light (say, at 0.9c), how do I calculate the time as the spaceship pilot experience it? I thought the formula was $$t = \frac{t_0}{\sqrt{1-v^2/c^2}}$$ ...
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1answer
56 views

Long rod in an expanding universe

Suppose you have a metal rod, of vast length, floating in space. From it's center-of-mass reference frame it is assumed to be at rest with respect to the CMB. The rod will have some degree of ...
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1answer
81 views

Laws of physics in curved space-time

The speed of light is not constant everywhere in a gravitational field. Suppose there is a region of space-time which is curved due to gravity such that the speed of light or any electromagnetic ...
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4answers
368 views

Effect of gravity upon light and bagels

According to this question and this web site, photons undergo twice the deflection from gravitational fields as do physical objects. However, the weak equivalence principle states that locally, ...