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)

0
votes
0answers
37 views

Can an event occur before or after the other one depending on what frame of reference we are in?

Two buses moving relative to each other with 30% the speed of light (4 light-min apart). Now by some mysterious way bus 1 comes to the knowledge that after 3 min-bus 2 time bus 2 is going to explode. ...
2
votes
2answers
425 views

How do I describe the order of events in spacetime?

In Newtonian mechanics, we have 3-space and time. Time allows us to order events. For example, I hold a ball in the air at time $t_0$. Then I drop it at some later time $t_1 > t_0$. Finally it hits ...
1
vote
2answers
128 views

Understanding Tensor-operations, covariance, contravariance, … in the context of Special Relativity

I'm currently learning about special relativity but I'm having a really hard time grasping the Tensor-operations. Let's take the Minkowski scalar product of 2 four-vectors: $$\pmb U . \pmb V = ...
1
vote
2answers
93 views

Rest mass energy of electron

For electron's energy why we some time use the word "REST MASS ENERGY" why we use this word as electron is always spinning? ...
0
votes
1answer
47 views

Clarification for the mutual time dilation for two observers in their inertial frame of reference

I am trying to understand the idea under the theory of special relativity recently. The time dilation predicted by special relativity baffles me. I used to think that I understand the idea underlies ...
1
vote
2answers
88 views

Special Relativity and symmetry of time dilation

I stumbled across a paradox in special relativity for which I have found no answer. In the twin paradox, the loss of symmetry in time dilation is usually explained by the reversal of movement of the ...
0
votes
0answers
20 views

relativity, light, transformations [duplicate]

is the light itself a reference frame in special relativity? Can we write the special relativity transformations between a photon and other reference frames? If we can't then what other transformation ...
1
vote
0answers
23 views

Is photon massless? [duplicate]

if photon is massless then in E2=m2c4+p2c2 is m=0 ? and p=mv1-mv2 shouldnt be zero too. if both the statements are true then does photon has no energy?
3
votes
1answer
60 views

Relativity of simultaneity subtle example [closed]

imagine three persons, Person A is standing next to a device these device is an AND gate if two photons(one from right and one from left) reaches the AND gate at the same time the device explodes and ...
2
votes
2answers
119 views

Velocity addition rule in special relativity

I just worked out a problem showing peculiarities of the velocity addition rule in special relativity. This was the statement for the problem: "Nefarious thieves flee the scene of their bank ...
3
votes
3answers
829 views

Is there an upper limit to temperature in thermodynamics or statistical mechanics

In many presentations of statistical mechanics where we have a system of particles having mass, such as the molecules of an ideal gas, the temperature is often equated to the average relative velocity ...
1
vote
0answers
35 views

Highest temperature [duplicate]

The temperature of a body varies with the KE of its particles. The maximum KE can be obtained by making the atoms move about near the speed of light. Let us take the body as a gas so that the body can ...
1
vote
1answer
47 views

determining electrostatic field using only symmetries

As an exercise, I'm trying to (rigorously) determine as much as possible about the electrostatic field due to a infinite line of charge (along the z-axis) without using Maxwell's equations or any of ...
1
vote
0answers
22 views

Observed gravity of a fast moving particle relative to observer [duplicate]

Special relativity tells us that a fast-moving object with sufficient speed will appear more massive that it would at rest relative to an observer. Since the strength of an object's gravitational ...
1
vote
0answers
26 views

Relativity collision problem [closed]

Here is the problem: A body of mass m (I assumed this is rest mass, but not 100%), and momentum p(subscript m) collides with a stationary particle of mass M. Find the available energy in the CM ...
-1
votes
1answer
68 views

Annihilation process and photons [closed]

Why should two photons produced by the annihilation process move in opposite direction? I know you would say for the conservation of momentum but why can't they move in the same direction, I want to ...
1
vote
0answers
44 views

Spacetime as a coset of a symmetry group

In the introduction to his nice PNAS paper on symmetry, David Gross said Einstein’s great advance in 1905 was to put symmetry first, to regard the symmetry principle as the primary feature of ...
1
vote
2answers
95 views

Two different formulas

My problem is simple : given a particle of mass $m$, charge $q$ and velocity $\bf{v}$. If $\bf{A}$ denotes the magnetic potential satisfying $\bf{B}= \nabla \times \bf{A}$. I want to etablish the ...
0
votes
1answer
35 views

Deduction of four-acceleration vector

Consider an Euclidean metric. The four-accelation vector can be obtained from the time derivative of four-velocity: $$a^k=\frac{du^k}{d\tau}=\gamma \frac{du^k}{dt}$$ We have that $u^k=(\gamma ...
0
votes
1answer
52 views

Question 17 in section 2.9 in Schutz's A First Course in General Relativity [closed]

The question is as follows: Prove that any timelike vector for which $U^0>0$ and $\vec{U}\cdot \vec{U} = -1$ is the 4-velocity of some world line. I need to show that there exists a 4-vector ...
0
votes
1answer
24 views

Demonstration of non orthogonality of time-like vectors on Minkowski space

I want to demonstrate that if two 4-vectors, $A^k$ and $B^k$ are orthogonal, then they aren't time-like. So, if we suppose that $A^k$ and $B^k$ are time-like, we have that: $$\sum_k A^k A_k <0, ...
25
votes
5answers
3k views

Hole-and-nail paradox in special relativity

Yesterday we started relativity on our physics class, and my professor taught us a few concepts. We did some examples on how things changed by looking them from different reference systems, and a ...
1
vote
1answer
95 views

Does a spaceship travelling at near lightspeed see the universe aging slow or fast?

Now I know this probably is well trodden territory, but this question has bugged me for some time, and I couldn't find a similar question in the archives (although plenty about relativistic time ...
3
votes
1answer
149 views

What is the deep reason of length contractions and time dilations? [duplicate]

In the theory of relativity, a spacetime can have length contractions or length expansions and time can have time dilations or expansions. In theory of special relativity, any physical object with ...
1
vote
2answers
150 views

Doubts regarding Einstein's 1905 derivation of mass-energy equivalence

This is a follow up on this question. In his [paper][2] under the title:Does the inertia of a body depend upon its energy-content, Einstein drives the famous $E=mc^2$ equation. His argument can be ...
3
votes
2answers
54 views

what happens to a magnetic field when it moves relative to an observer at relativistic velocities?

what happens to a magnetic field when it moves relative to an observer at relativistic velocities? Does it become an electrical field?
2
votes
1answer
289 views

Perfect fluid and Cauchy momentum equation

The stress-energy tensor of a perfect fluid is given by $$T^{\mu\nu}=\left(\rho+pc^{-2}\right)u^\mu u^\nu+pg^{\mu\nu}$$ The divergence of the stress-energy tensor is zero: $\nabla_\mu T^{\mu\nu}=0$. ...
0
votes
2answers
107 views

What is the basic concept of four-dimensions in physics?

I have been reading a few books lately and browsing the internet for an explanation on the concept of "four-dimensional" space (or, space-time, as some of them have been calling it). But, what those ...
0
votes
0answers
27 views

Length Contraction and Acceleration [duplicate]

Say that I have a spaceship that needs to travel 490 lightyears to the exoplanet Kepler 186f. Half the way of the trip the spaceship accelerates with a constant acceleration of 1G and on the other ...
4
votes
5answers
554 views

Speed of light as a universal speed limit

It follows from special relativity that nothing can travel faster than light. Einstein believed this would have to hold so generally that he assumed the Einstein-Podolsky-Rosen paradox to indicate a ...
2
votes
3answers
631 views

Faster than light signals and the price to be paid if we accept them : a very simple protocol

Some physicists currently understand entanglement as transferring information instantaneously, yet not violating causality. Is this really a satisfactory explanation, or should be look for something ...
0
votes
1answer
34 views

How to calculate relativistic mass versus time?

I know that relativistic mass is calculated as: But when mass m0 gets bigger, also mass of the accelerating body mass m gets bigger so m0 gets bigger and so on. So if body accelerates with ...
3
votes
1answer
255 views

Who aobserves length contraction?

I have a homework in our nuclear physics class. The question is "An astronaut whose height in the earth is exactly 6ft is lying parallel to the axis of a spacecraft moving at a 0.9C relative to the ...
1
vote
0answers
44 views

Special Relativity and Space travel [closed]

I'm doing a science project on space travel where I have to include a part about special relativity and how time acts when you're traveling in space with high speed. I'm not really sure where to start ...
0
votes
1answer
61 views

Restrictions on the form of a function imposed by Lorentz invariance

I need help proving a couple of theorems regarding the most general form of a function with some particular Lorentz-transformation properties. By the way, the question is possibly (though not ...
0
votes
2answers
70 views

At what speed is the conservation of angular momentum carried out?

If the sun suddenly slowed down would pluto's orbit immediately speed up? If so, then isn't the information pertaining to the sun's angular momentum change being carried to Pluto faster than light? ...
-4
votes
2answers
139 views

is following alternative interpretation of total energy possible? E=m'v^2 instead of E=m'c^2 [closed]

I have read the paper, http://arxiv.org/pdf/physics/0206061.pdf "Fundamental Disagreement of Wave Mechanics with Relativity", some time ago, in which the author claims that there is another way to ...
8
votes
4answers
816 views

Special Relativistic approximation to GR

Some time ago I was talking to a professor in college about some of the fundamental aspects and origin of General Relativity. I was surprised to learn, in fact, that a pretty good approximation to GR ...
1
vote
0answers
18 views

Basic Special Relativity Problem [closed]

A cylindrical rocket 10 m long and 2 m in diameter moves at a speed $ V=0.9c $ with respect to earth, where $c$ is the speed of light in vacuum. I. Knowing that the pilot's heart beats 70 times per ...
0
votes
0answers
28 views

Real and relative velocity formula

What i need is a thing more complicated than the usual relative velocity formula. Imagine a radar. You are at the center, moving at some angle, but lets make it clear, you are always at the center. ...
0
votes
0answers
35 views

Why do we sum relativistic intervals in relativistic action of a massive point-particle, and not a function from it?

Relativistic action as follows (which should explain relativistic motion of a classical particle): $$ S = C \Delta s=C\int ds $$ Where $C$ is some constant and $\Delta s$ is relativistic interval. ...
6
votes
1answer
208 views

The effect of relativistic near misses

Alice and Bob are both floating in free, empty space. Alice does not like Bob very much. Thus one day, believing that there is no such thing as overkill, Alice takes her programmable hyper-energetic ...
1
vote
1answer
184 views

How can I prove that D'Alembert operator is invariant under Lorentz transformations?

I'm currently taking a course on Classical Electrodynamics and I'm trying to prove that the D'Alembert operator ($\square=\eta^{\mu \nu} \partial_{\mu} \partial_{\nu}$) is invariant under Lorentz-like ...
4
votes
2answers
283 views

Spacetime and uncertainty principle

I only have limited knowledge of relativity and quantumphysics but as far as I know, the uncertainty principle relates the uncertainty of space and momentum of a particle. Einstein however, explained ...
1
vote
1answer
78 views

How is time dilation invariant of observer?

From one observer's perspective, on all moving objects time will run slower. But from the perspective of one of those objects, it's the observer who's slow. And the answer seems to be that both are ...
1
vote
1answer
45 views

Can we see ourselves slower due to time relativity?

Please bear with me because I'm noob at physics. Numbers don't have to be calculated, these are just examples, I'm just asking conceptual stuff. Just double check: Objects traveling at $0.99c$ in ...
3
votes
1answer
103 views

What is the difference between scalar and vector mesons?

My understanding is that vectors and pseudooscalars change sign under parity operation and pseudovectors and scalars do not. However, I don't understand what the difference between a vector and ...
1
vote
2answers
129 views

Classical physics in curved space

I'm trying to learn General Relativity. As a stepping-stone between classic (Newtonian) physics and complete relativity, imagine a universe where space is curved, but time is perfectly flat. Also, the ...
0
votes
2answers
50 views

Travel by Earth rotation [closed]

why we can't go outside the atmosphere and travel with earth rotation .. and can we travel in the opposite direction of atmosphere by the same speed of atmosphere it’s moving at about 1,000 miles an ...
4
votes
2answers
281 views

Dimensional Paradox Demonstrated by Light Moving Between Parallel Mirrors

In a thought experiment, there are two parallel mirrors which are very long which also face each other. One has a hole in it and one flash from a strobe light shines into that hole. One observer in ...