The special theory of relativity describes the motion and dynamics of objects moving at significant fractions of the speed of light.

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Dilemma in race between muon and light

I have a dilemma concerning my understanding of Special Relativity. Maybe I am understanding or calculating something wrong and would hear so. The problem is based on muons created in the upper ...
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3answers
161 views

Is the Speed of Light an universal spacetime constant, the velocity of electromagnetic waves, or of photons?

This question has been touched tangentially by What's a better phrase than "speed of light" for the universal spacetime speed constant? and Could light travel more slowly than the ...
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235 views

Why do we say that light travels at a speed? [duplicate]

According to Einstein's theory of relativity, the more speed something has the slower that time passes for it; and presumably when traveling at the speed of light, time stops entirely. So this means ...
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7answers
241 views

Relativity of Simultaniety

In the first figure, A and B are two equidistant points from the observer O in S. In the second figure (reference frame S') the corresponding points are A'and B' such that A'O'=O'B', where O' is the ...
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48 views

Repulsion and attraction of electric currents

Now, I understand that when a an electron travels, it creates a magnetic field. If you put two wires with current traveling in the same direction they repel, and current traveling in opposite ...
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104 views

Why does Coulomb's law not hold for fast moving charges?

We all remember calculating the electric force of interaction between a stationary nucleus and a revolving electron using Coulomb's law. The electron in this case is moving. Here's what I think about ...
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1answer
39 views

Light cone and order of events?

If one event lies outside the light cone of another, can the events to some observers appear in a different order in one reference frame compared to the other, and is this the only time when this is ...
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1answer
79 views

Does speed in space really matter?

This is about validating the science from a science fiction novel. My understanding is that speed is all relative. So while I am in a car on the freeway my speed relative to another passenger is ...
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3answers
81 views

Problem on speed of light

As I was reading special relativity, my book says the speed of light is $c$ with respect to any other thing. Does that mean the speed of an individual photon is $c$ even with respect to another ...
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2answers
106 views

Can matter be created from energy? [duplicate]

The small, hot, dense early universe the size of an atom was made up entirely of energy, it wasn't until after the expansion began and the universe cooled down some of that energy began converting ...
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2answers
196 views

Why time is considered a dimension?

Why time is considered to be a dimension? And the other 7 (except the 3 dimensions of space, and the dimension of time) dimensions that string theory suggests, why can't they be realized?
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1answer
136 views

Why doesn't light travel instantly? [duplicate]

I've read that the faster you travel in space, the slower you travel in time. And when you reach the speed of light (which we won't be able to) time will stand still. So when light travels at the ...
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2answers
426 views

Special relativity and electromagnets

This Veritasium video explains how electromagnets can be explained by special relativity, and how the magnetic field surrounding a current-carrying wire can also be viewed as an electric field, if ...
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How can the 'choice' of a photon said to be delayed?

My question arises from two ideas that seem to be contradictory. Idea One: Wheeler's Delayed Choice experiment is an interesting variation of the double slit experiment. Idea Two: In the "reference ...
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35 views

Since “coordinate time” has a very specific meaning, how to call more general parametrizations?

Recently I've learned that "coordinate time" assigned to a particular time-like spacetime path is not only required (1) to be monotonous and continuous and even differentiable wrt. the "proper time" ...
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2answers
127 views

How can we measure time?

If we cannot define a proper time (or synchronize clocks in different positions) in an inertial frame (independent with the theory of relativity), there seems to be no direct way to confirm the 2 ...
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3answers
639 views

Would a craft travelling increasingly close to the speed of light appear to be decelerating?

I've been pondering the implications of time dilation. Is it right to assume that if a craft was travelling at a speed very close to the speed of light (>= 0.9999c for example), that to an external ...
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4answers
221 views

Traveling between two planets at rest to one another [duplicate]

If I travel at relativistic speed from planet A to planet B which are at rest relative to one another, I will be younger than people on A or B when I arrive. However how does this mesh with the fact ...
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1answer
54 views

Do the Maxwell equations yield the proper time of electromagnetic waves?

I apologize in advance for possible errors in my premises as I have no precise knowledge of Maxwell equations. Proposals for the correction or even abandon of my question are welcome. As Maxwell ...
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1answer
98 views

Is speed of light invariant in different inertial frame?

Don't get angry at me. I believe in special relativity just as any scientist would. But reading this article http://arxiv.org/abs/0708.2687 I realize that actually I haven't done any experiments on ...
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1answer
122 views

Can special relativity be extended such that the frame of a photon makes sense?

Suppose I want to know what the universe looks like from the perspective of a frame of reference moving at $c$ relative to my current frame. As discussed at length in various other questions on this ...
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3answers
281 views

Link between Special relativity and Newtons gravitational law

If I make the two statements: General relativity is an extension of special relativity that accounts for gravity. Newton's law of gravitation is a special case of general relativity for when the ...
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1answer
65 views

Interpretation of space time Minkowski diagram [closed]

How to interpret the following space-time diagram in the image. I know how to interpret euclidean distance from Euclidean space diagram omit the line "whereas for Euclidean space".
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0answers
53 views

special relativity from minkowsky space-time [closed]

is there any use for learning special relativity from einstein's postulates once you understand the minkowskian structure of space-time . why isn't it straight away taught using minkowski geometry
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1answer
72 views

Tensors in special relativity [duplicate]

I'm trying to understand tensors, but I've come across the following question: Let $T^{\mu\nu}$ by a $(2,0)$ tensor. Give the definitions of $T_\mu^{\,\nu}$, $T_{\mu\nu}$, and ...
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1answer
78 views

Black holes and Time Dilation at the horizon

What is the difference between proper time and the observer time? Whilst thinking about Black holes, when we see the Schwarzschild metric $$c^2\tau ^2 = \left ( 1 - \frac{r_{s}}{r} \right )c^2t^2 - ...
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2answers
917 views

What is imaginary time? [duplicate]

I am not professional physicist; but I am curious about Stephen Hawking's "imaginary time". It would be better to elaborate exactly what it is. I am not confused because of the word "imaginary" but I ...
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1answer
70 views

Lorentz transformations, why $t$ and not $t'$?

In the derivation of the Lorentz tranformation you get the fromuls: $$x=k(x'-ut')$$ $$x'=k(x+ut)$$ where $k$ is a constant that is yet to be determied ($k= \frac{1}{\sqrt{1-\frac{u^2}{c^2}}}$) ...
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2answers
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Moving towards a clock at .866C [duplicate]

If you set up a clock that sends out a light pulse every second, and move towards it at a speed of .866c, will the clock appear to run faster?
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4answers
77 views

How can time dilation be symmetrical? [duplicate]

I recently posted a version of the twin paradox with a twist but here I'd like to propose a new thought experiment all together. Take two clocks, A & B, and place A 1 AU away from B. Once the ...
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116 views

Twin Paradox Without Acceleration

So I've been doing a lot of reading about the twin paradox and have encountered several different explanations that strive to resolve it. First off let me start by saying general relativity is not an ...
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2answers
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Is space-time a Kantian concept - just a concept of the working mind? [closed]

Is space time a Kantian concept – that is, just a concept of the mind at work? That is that there is no ‘out there’ – it’s in the ‘mind’? Relativity might work but it certainly requires a stretch of ...
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3answers
78 views

Arguments for finite speed of physical processes

When beginning a study of the special theory of relativity, one discovers that the theory of special relativity has as an axiom that the laws of physics are invariant with respect to transformations ...
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3answers
205 views

Conservation of 4-momentum in special relativity

I understand that the inner product of two 4-vectors is conserved under the Lorentz transformations, so that the absolute value of the four momentum is the same in any reference frame. This is what I ...
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2answers
219 views

Is time subjective?

In Minkowski spacetime time is subjective [or more precisely: time is different for every particle/ reference frame]. It is the coordinate time of an observer whose reference frame travels up the ...
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1answer
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what if the time is zero in one reference frame

Consider measuring the length of an object in another frame of reference. Of course this should happen at the same instance in the frame of reference the measurement takes place in. but using Lorentz ...
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116 views

A question on an exercise from Gravitation by Misner, Thorne and Wheeler

My question is on problem 4.1 of Gravitation. In a generic case of electric field and magnetic field(i.e not $E=0$ or $B=0$ or $E$ and $B$ perpendicular), define the direction $\hat{n}$ unit vector , ...
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2answers
101 views

Energy definition in special relativity

I'm going through the early homework assignments for my special relativity course and I've got myself a little confused about energy. I've got a basic understanding of what the 4-momentum is, having ...
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0answers
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Existence and uniqueness of solutions to $\nabla^a T_{ab}$ in general (or special) relativity

The equation in the title of this question can be a relativistic analogue of the Navier-Stokes equation (in the sense that, in the low-velocity limit, it reduces to Euler's equation when $T_{ab}$ is ...
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1answer
211 views

Relationship between the continuity equation and the wave equation

What exactly is the relationship between the continuity equation and the wave equation? Suppose $J^\mu$ is a contravariant vector that satisfies the continuity equation $\partial_\mu J^\mu=0$. Let ...
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2answers
57 views

Equilibrium: Inertia & Applied Force

Thank you for taking the time to read this. I am lay and will understand if the question is closed. My understanding is that in a vacuum, a constant force of $n$ applied to an object of mass $m$, ...
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4answers
616 views

Time dilation derivation of special relativity

In almost all of the derivations using the postulates of special relativity (SR), we use experiments involving light signals. For example, we make a clock using a light signal or measure lengths using ...
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3answers
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Is proper time an intrinsic value of Minkowski space?

What is proper time? Is it a part of Minkowski space (that is a mere spacetime interval)? Or is it an intrinsic characteristic of massive particles (a sort of "aging")? Example: In the following ...
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1answer
28 views

Application of special relativity on sound waves

What is the difference between an electromagnetic wave and other waves that amounts to the EM wave following the Special Relativity. I have been reading about the Special Relativity for some time, and ...
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1answer
65 views

Deriving Lorentz transformation - Serway

in Serway, the derivation of Lorentz transformation started from these two equations $$x′=\gamma(x−ut),$$ $$x=\gamma(x′+ut′).$$ The book derived the first equation and then deduced the second. Is ...
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How can Lorentz contraction be “directly” measured?

If one is watching a relativistic object of e.g. spherical shape, which emits enough light to be detectable, it will, despite being Lorentz contracted, appear of its natural shape, although rotated. ...
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22 views

Explain polarization in RF in which the conductor is stationary

Consider a metal rod parallel to $x$-axis moving with velocity $\vec v =(0,v,0)$ perpendicular to magnetic field $\vec B=(0,0,B)$. Lorentz force will give rise to the electric field $\vec E = - ...
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1answer
75 views

Driving car with (almost) the speed of the light and switch the headlights on [duplicate]

I'm curious what will happen if we 'drive' a car with (almost) the speed of light, and all of sudden we switch the car headlights on? Will the car headlights ray have double speed (speed of ...
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2answers
99 views

“Vectors” (i.e. 1-tensors) their definition and motivation for relativity

I'm reading Einstein Gravity in a Nutshell (by Zee) and here he defines a vector as an object which is invariant under coordinate representation; concretely, if in one coordinate representation, $V$, ...
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1answer
66 views

How much time passed for the passenger traveling with at speed-of-light spaceship? [duplicate]

Let's suppose we have a spaceship with the exact speed of light. If a traveller takes this spaceship to go to proxima centauri (approximately 4 years light away from Earth) and come back, we (as ...