1
vote
2answers
26 views

Length contraction and simultaneous length measurements

I am just working through an argument from Halliday Resnick to derive the Lorentz contraction (see quote below). Some paragraphs before this, the authors note that: If the rod is moving, ...
2
votes
0answers
44 views

Moon's orbit period as seen from a spaceship traveling at 0.8c

I am studying special relativity and I am trying to figure out the following small problem which occurred to me: An observer, the pilot of a spaceship flying to or from earth at v = 0.8c, is ...
2
votes
2answers
81 views

If two events both have a spacetime interval of zero, can they both be said to be happening “now”?

Can the concept of c be validly expressed as "the rate at which an event propagates through space"? There was a television program last year featuring Prof Brian Cox. The presenter asked him "Is it ...
1
vote
0answers
46 views

Verification of the Poincare Algebra

The generators of the Poincare group $P(1;3)$ are supposed to obey the following commutation relation to be verified: $$\left[ M^{\mu\nu}, P^{\rho} \right] = i \left(g^{\nu\rho} P^{\mu} - g^{\mu\rho} ...
-4
votes
1answer
68 views

Massless particles and the speed of light - New? Theories of existence [on hold]

"The best understanding we have is that it [light] is a disturbance in the electromagnetic fields of charged bodies." http://einstein.stanford.edu/content/relativity/q212.html This is a link to the ...
0
votes
1answer
100 views

How does it seem to be that space/time always equals c?

Given the way objects move, they seem to be going all the same "velocity" so to speak, that velocity being the speed of light. Except, velocity is displacement/time, so if something goes faster, the ...
3
votes
0answers
39 views

Derivation of force law in special relativity

I've seen force defined in special relativity as the rate of change of 4-momentum $$ {\bf{F}} = \frac{d {\bf{p}}}{dt} $$ Can anyone comment on the following derivation of that relation? Take one ...
2
votes
4answers
86 views

How much could one slow down aging using existing spacecraft?

Imagine that I board a spacecraft and head away from the Earth at top speed until I've aged twenty years, then I turn around and come back. How much younger will I be than the unexciting folk who hung ...
2
votes
0answers
65 views

Notation for Translation Group Generators

The generators of the translation group $T(4)$ are given below: $P_0 \equiv -i \begin{pmatrix} 0 & 0 & 0 & 0 & 1 \\ 0 & 0 & 0 & 0 & 0 \\ 0 ...
0
votes
5answers
335 views

Why Light and Observers have different laws of physics [on hold]

Special relativity states: The speed of light in a vacuum is always $c$, regardless of the velocity of the observer. The laws of physics are the same for all observers in uniform motion. These two ...
1
vote
0answers
19 views

Twice the speed of light [duplicate]

If you were able to ride along a photon and a second photon passed you in the opposite direction, would what you observe be twice the speed of light? And would that change what you would see of the ...
4
votes
2answers
142 views

Metric tensor in special and general relativity

I'm having trouble understanding the metric tensor in general relativity. What I've understood so far has come from my course lecture notes used in conjunction with "The Road to Reality" by Roger ...
3
votes
2answers
100 views

Frame dragging — is there a “non-tiny” example?

Now. As I understand it, in fact, the earth (10^25 kg) creates a very small, very tiny, frame dragging effect. Indeed, we have measured this using satellite experiments. So, the Earth (10^25 kg) ...
1
vote
0answers
32 views

Special relativity allows arbitrarily low travel times between two locations [duplicate]

I wish I had a good way of illustrating this, but anyway, doesn't the following travel strategy allow you to get anywhere in arbitrarily little time? You're at rest at the origin of space-time, and ...
0
votes
1answer
54 views

Two related questions about double-slit experiments moving at a relativistic speed

I was wondering as how would appear the interference pattern of a double-slit experiment moving at a relativistic speed v, 1) in the case of light and, 2) in the case wave matter (i.e. electrons for ...
-5
votes
2answers
93 views

Do the laws of physics that apply to all observers also apply to a non-observer? [on hold]

The Timelessness of a photon https://www.youtube.com/watch?v=5ELA3ReWQJY An observer's laws of physics are time based. "When you're traveling at the speed of light, time does not exist" - Neil ...
2
votes
0answers
57 views

Gravitational atraction of fast object [duplicate]

Let's imagine a asteroid that travels with 0.99999999999999999c. (I know it's impossible). Anyway... Relativistic mass of such object would be almost equal to earth's stationary mass. Now let's ...
2
votes
1answer
88 views

Twins Paradox Paradox

I've recently has special-relativity explained to be in a rather elegant way. All objects travel at the speed of light in space time. Thus, when you travel faster through the three dimensions of ...
1
vote
1answer
53 views

Relatvity of Promise [closed]

Suppose there are two observers moving at a speed c/2 w.r.t. each other. Now they won't agree on simultaneity of space separated events. Now they decide to host a race between two racers, with common ...
-1
votes
1answer
90 views

Does physics recognize the particle of light separately from the wave of light? [closed]

To frame this question, we need to assume that time freezes when traveling at the speed of light. This is theoretically congruent with Einstein's theory of relativity and the theory of time dilation, ...
33
votes
4answers
4k views

Does time move slower at the equator?

While answering the question GPS Satellite - Special Relativity it occurred to me that time would run more slowly at the equator than at the North Pole, because the surface of the Earth is moving at ...
-1
votes
3answers
110 views

Twin Paradox speed of light

Twin Paradox Can anyone clarify and or correct the following for me? A space ship is flying at speed v equal to 0.8 times the speed of light. Within the ship are three stations, a transmitter at ...
1
vote
1answer
110 views

GPS Satellite - Special Relativity

I'm going through an old relativity assignment, and I've been asked to calculate the time dilation for a satellite which orbits the earth in 12 hours at 26000km from the surface, and travels at a ...
0
votes
1answer
25 views

Action of the Poincare Group on a Scalar Function

Let $F(x^\mu)$ is a scalar function; i.e. $F(x^\mu): \mathbb{R}^{1,3} \rightarrow \mathbb{R}$. How the Poincare Group $P(1,3)$ will act on it; i.e., by which formula I can calculate it for a specific ...
1
vote
3answers
138 views

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 ...
1
vote
3answers
101 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 ...
-1
votes
3answers
207 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 ...
2
votes
7answers
218 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 ...
1
vote
1answer
29 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 ...
1
vote
0answers
72 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 ...
0
votes
0answers
48 views

A method providing FTL communication? [closed]

I would like to see a rebuttal of my proposition of how to provide FTL communication by what I call "The Hedgehog Method". I have seen question #78460 but would not bother about entanglements nor ...
1
vote
1answer
32 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 ...
0
votes
1answer
68 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 ...
0
votes
3answers
75 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 ...
1
vote
2answers
78 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 ...
3
votes
2answers
169 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?
-1
votes
0answers
54 views

Does anything at speed of light won't be able to see anything? [duplicate]

They say that if a object travels at the speed of light will be able to pause time only for that object, but if it travels at the speed of light, will the object will not see the light and see total ...
0
votes
1answer
113 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 ...
7
votes
2answers
384 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 ...
1
vote
0answers
36 views

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 ...
2
votes
0answers
32 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" ...
3
votes
2answers
121 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 ...
2
votes
3answers
617 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 ...
3
votes
4answers
209 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 ...
1
vote
1answer
47 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 ...
2
votes
1answer
87 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 ...
1
vote
1answer
102 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 ...
3
votes
3answers
264 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 ...
1
vote
1answer
41 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".
2
votes
0answers
44 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