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

learn more… | top users | synonyms (5)

3
votes
4answers
269 views

Up or Down? A Question about Relativity

The standard text discussion of the equivalence principle and the bending of light rays goes like this. We, as observers watch a glass elevator ascending. A light beam is fired from left to right. The ...
2
votes
0answers
44 views

Where other frame observer will put new stick [on hold]

my question is with relativity, if we draw two circle of same radii and fill the perimeter with stick (very small so it cover whole perimeter) now if we rotate a stick with veey high speed ...
1
vote
2answers
69 views

Why does time stop its flow? [duplicate]

According to the "list verse" time gets to a pause when someone or something travels at the speed of light. But a question still lies in my mind, if time always travels forward and does not stop at ...
1
vote
3answers
722 views

Why does weak equivalence principle say gravity is equivalent to acceleration?

I am told that the weak equivalent principle, that $m_i=m_g$ (inertial and gravitational masses are equivalent) is equivalent to the statement that in a small system you can't tell whether you are in ...
0
votes
3answers
287 views

why do x Schwarzschild radii equal time dilation effects of speed of light going y times faster than an object^2?

let me walk you through the math. First you start with the gravitational time dilation formula where: $$ T_1=T\sqrt{1-\frac{2GM}{rc^2}} $$ and rather than entering $r$ for the radius we replace $r$ ...
0
votes
2answers
40 views

Conversion of energy to matter? [on hold]

Now, this answer has sort of been asked before. But I haven't really found the answer that I'm looking for. Exactly what is the mechanism by which energy can be converted into matter? By ...
0
votes
1answer
198 views

Physical interpretation of distances

Suppose we have a universe with only two distinguishable particles, neglecting gravitation. These particles start off next to each-other, ostensibly "touching" each-other and at rest. If it takes ...
1
vote
2answers
51 views

When does travelling at a fraction of the speed of light appear to the traveler as if they're going the speed of light? [on hold]

If a spaceship is travelling to Proxima Centari, there is a fraction of the speed of light that would make the spaceship appear to reach Proxima Centauri in four years' time. What fraction of the ...
0
votes
0answers
20 views

Decay of lepton into meson and neutrino using four-momentum

I'm learning about how to use four-momentums and am working through a problem involving the decay of a charged lepton into a charged meson and neutrino. The equation would be: $L^+ \to M^+ + \nu$ ...
2
votes
0answers
22 views

Which date the twin paradox was formulated first time? [migrated]

Any research about real measurements with faster moving than me systems - like GPS for example - leads to a mix of different sideway phenomenons like different gravitational potential on earth and in ...
-1
votes
0answers
58 views

Einsteins Cold Fusion and Black Holes [on hold]

How does a magnetic field heat and Cool objects? Would an Atom rapidly cooled with a magnetic field release photons? Can solid magnets be used in the same manner? Einsteins cold fusion formula is ...
0
votes
0answers
30 views

If humanity was to send a probe to Proxima Centauri, how long would the travel last?

[Feb 3 2016] (I am including the date I asked this as a reference, since technology evolves with time, this question's answer will change in time...) If humanity was to send a probe to the nearest ...
2
votes
1answer
50 views

How do I know which observer is running the time faster or slower

Ok, I'm not a physicist, so I don't know if my question is silly (probably yes), but there is something in special relativity that I can't understand and I would really like it to be clarified. If ...
4
votes
3answers
254 views

How is it possible for the wavelength of light to change in a medium?

So my physics class has just finished a long unit on optics while at the same time I've been trying to teach myself relativity. I admit my understanding is probably rudimentary, but I figured all the ...
0
votes
1answer
53 views

What makes things move in a universe with blocktime? [on hold]

In a universe with blocktime the past, present and future all exist at the same time. But what makes it appear that for example my body is going from one movement ...
0
votes
2answers
142 views

Why acceleration cannot vanish everywhere?

In attempt to introduce gr concepts When there are gravitational accelerations present, as for example in the gravitational field of the earth, the space cannot be the flat Minkowski space. Indeed, ...
1
vote
0answers
32 views

Small particle rotating around neutron star

First let me say I have read the article at "users.ictp.it › lns003 › Ruoff › Ruoff.ps.gz" about a small particles orbiting a neutron star and causing excitation of different modes of gravitational ...
-3
votes
0answers
29 views

Time Travel Plausible? [on hold]

The question of possibly achieving time travel has been exhaustively deliberated over and over again but in the modern era of new discovery and technological advancment, can we reexamine/rethink its ...
0
votes
1answer
50 views

Special Relativity problem - proper time interval

The supernova 1987A explosion in the Large Magellanic Cloud 170 000 light years from Earth produced a burst of anti-neutrinos ν ̄e which were observed in terrestrial detectors. If the anti-neutrinos ...
1
vote
1answer
90 views

Scattering Amplitude Not Invariant under Little Group?

I am trying to make sense of scattering amplitude recently. In some literature people say that if some number of massless particles collide together, one can theoretically express the scattering ...
1
vote
0answers
36 views

Is any photon really moving? [duplicate]

I read that when something moves at the speed of light, length contracts at the direction of motion. Now consider a photon traveling in the z axis. Since it is travelling at the speed of light, the z ...
3
votes
2answers
125 views

Confusion with Weinberg's QFT book, volume 1, chapter 3: time translation and Heisenberg picture

Sorry if this is a naive question, but I am new to QFT. In the treatment of scattering in section 3.1 of The quantum theory of fields, vol.1, Weinberg first presented the general transformation rule ...
3
votes
4answers
438 views

What truly is mass, and is there a direct way to measure it?

We know a mass of an object of one kilogram as an object that weighs W = mg = 9.8 N and we reference it to that, (when it should as a fundamental parameter describe weight not the opposite). But if we ...
1
vote
1answer
54 views

Minkowski's dot product

I am trying to deduce the Minkowski's dot product for two dimentional space: $$g=x^1y^1-c^2t_xt_y$$ If $f$ denote the Lorentz's transformation for two dimentional case: $$\begin{array}{rcll} ...
3
votes
2answers
73 views

Help understanding why can't we measure absolute velocity?

(This is probably a clone of some other question, but I haven't been able to find a satisfactory answer, so I hope this is okay.) So, I know that in special relativity, there's no such thing as a ...
0
votes
1answer
34 views

Time and velocity

Suppose two cars are traveling at a velocity of $c/2$ ($c$=speed of light) in two straight lines parallel to each other but in opposite direction in vacuum. Then what will a person sitting in one of ...
-2
votes
1answer
64 views

Constancy of speed of light in vacuum? [closed]

Have scientists tried their best to calculate speed of light in vacuum? It seems very absurd to me that light of all frequencies have same velocity in space. Can someone find in future if this speed ...
1
vote
1answer
41 views

Are there certain reference frames where proper length of proper time are supposed to be measured?

Let's say we have two frames: Bob on Earth and Alice in a rocketship. Let's say Alice is traveling at a relativistic speed away from Bob. With that in mind. Is there a certain frame where we should ...
0
votes
0answers
28 views

Doppler and Special Relativity [on hold]

I am on the tip of a spaceship going close to the speed of light. According to doppler, when I look forward, light will be shifted blue. According to Einstein, my time has slowed so the frequency of ...
-1
votes
0answers
26 views

Generalizated Lorentz transformation [closed]

Given $S$ and $S'$ inertial reference system with the same coordinate origin at $t=t'=0$, if $S'$ has a velocity $(v,0,0)$ about $S$ the Lorentz's transformation is defined by: ...
4
votes
2answers
561 views

Introduction to relativity books for an engineer [duplicate]

Possible Duplicate: Getting started general relativity I am an engineer who loves to read science fiction books especially when there's more science than fiction but usually I see that I ...
3
votes
3answers
273 views

Why isn't a Photon justified in concluding that it is at rest and everything else is moving past it at c? [duplicate]

Why isn't a photon moving at c not justified in concluding that it is at rest and everything else is moving past it at c since relativity postulates that the laws of physics are invariant (i.e. ...
2
votes
1answer
50 views

Visual pictures of Lorentz transformations

How can I visualize Lorentz transformations? I know it's four dimensional, but without a visual picture in my mind I can't understand any of this. For example how do: Time reflection Space ...
1
vote
0answers
51 views

QFT: Ground State Momentum - Normalisation of States

In my notes I have, $$ \left\langle \mathbf{p} \left| \mathbf{q} \right.\right\rangle = \left\langle 0 \left| {a(\mathbf{p})}\ {a(\mathbf{q})}^{\dagger} \right| 0 \right\rangle $$ I am not sure how ...
0
votes
0answers
27 views

Wikipedia page in pair production kinematics [closed]

There is a term $E^2/c^2$ there. Shouldn't the sign of it be negative? Source
-1
votes
0answers
16 views

Show that an isolated photon cannot undergo pair production [duplicate]

I need to see the mathematical details as how the conservation of four momentum is violated.
0
votes
0answers
70 views

Equation of motion of a free particle

We know that the equation of motion of particle can be derived from the respective action. But in the book I am reading, the author is saying: ... timelike worldline of a massive particle is ...
0
votes
0answers
43 views

Can something appear to be faster than the speed of light? [closed]

I thought of this interesting thought experiment. Imagine I have two space monkeys, George and Gracie, both unconscious. I place them far off in space so that they may not see anything in any ...
1
vote
1answer
111 views

The norm of the vector sum of two 4-momentum vectors before and after pair production

Two photons traveling along the x-axis (in a lab frame of reference) of different frequencies are about to collide. Their 4-momentum vectors are (h$\nu_1$/c , h$\nu_1$/c , 0, 0) and (h$\nu_2$/c , ...
1
vote
2answers
115 views

What does diagonalization mean here?

In a gravity theory in spacetime, the metric has signature $− + +· · ·+$. Concretely this means that the metric tensor $g_{μν}$ may be diagonalized by an orthogonal transformation, i.e. ...
2
votes
1answer
211 views

Watching a LIVE stream in spaceship traveling away from earth close to speed of light

My name is Dennis. This might sound just straight up ignorant of basic concepts of physics. I was having a conversation with my friend in regards to streaming a LIVE event on earth to a spaceship ...
0
votes
0answers
20 views

What should I do to calculate the force between to moving parallel planes? [closed]

I'm trying to understand the force between two parallel moving planes. One of them is moving parallel to itself and the other one is moving away from the first one. I thought at first to consider ...
1
vote
1answer
93 views

What does it look like for a ball falling to the event horizon observed by distant static observer?

Here is the picture used in susskind&Lindesay's book ''An Introduction to Black Holes, Information and String Theory Revolution'' I understand very well that the ball will be contracted at the ...
1
vote
1answer
51 views

Implication of Relativity [duplicate]

According to relativity, no useful matter can travel faster than light. Suppose that your are a light beam travelling. Now you have a parallel light beam travelling beside you. Suppose you look at the ...
1
vote
1answer
285 views

Time-reversed twin paradox

This started with wondering about the nature of certain physical quantities under time-reversal - chiefly, that acceleration retains its magnitude and direction at a given time regardless of the ...
157
votes
18answers
24k views

Do we know why there is a speed limit in our universe?

This question is about why we have a universal speed limit (the speed of light in vacuum). Is there a more fundamental law that tells us why this is? I'm not asking why the speed limit is equal to ...
9
votes
2answers
4k views

How Special Relativity causes magnetism

So my physics teacher assigned us an article about how special relativity causes magnetism in a wire with a current, even with the low drift velocities of electrons in a current. It seemed that the ...
1
vote
3answers
101 views

Observing a point 13.82b ly away, 1b years ago

I understand that we can observe far away galaxies to get an idea how the universe looked like in the past. Assuming the universe is 13.82b years old, would it be correct to say that if we looked at ...
3
votes
1answer
60 views

Most efficient speed to travel at, considering the effects of time dilation; according to Special Relativity

I understand that this question has recently been asked, and yet not answered to the greatest and most understandable extent, but I was wondering whether travelling at the speed of light is really the ...
0
votes
1answer
315 views

Relativistic Kinematics - 2-Body Particle Decay

Consider the scenario where a particle of mass $M$ decays into two lighter particles of mass $m_1$ and $m_2$. In the center of mass frame (i.e. $\mathbf{p}_1$ and $\mathbf{p}_2$, the momenta of the ...