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
1answer
70 views

Derivation of four-velocity using proper time?

Let us say we have an accelerating particle. 4-velocity is given by the derivative of 4-position with respect to proper time. Derivations that I have seen say that: $$d\tau=\frac{dt}{\gamma}$$ But why ...
1
vote
0answers
33 views

Electric fields and magnetic fields [closed]

I would love to know if this is roughly correct with regards magnetic fields. I recently heard someone say that there are people still looking for monopoles. I said I don't think that can be true as ...
0
votes
1answer
55 views

Lorentz contraction in continuously accelerating rod

I was having a little thought experiment about Lorentz contraction, and I couldn't really figure out what would actually happen. Note that I'm not looking for a answer 'this effect is barely ...
5
votes
4answers
262 views

Causality principle and Entropy (Second Law)

I was reading about the light cone in relativity and I got to the point where in order to avoid paradoxes one can introduce the causality principle: Causality Principle: For every inertial ...
1
vote
1answer
29 views

Matrix dimensions in the spacetime interval equation don't seem to agree? (Possible notation misunderstanding)

The spacetime interval in flat space can be expressed as $(\Delta s)^2 = g_{\alpha \beta} \Delta x^\alpha \Delta x^\beta$. I understand covariant, $x_a$, and contravariant, $x^a$, vectors to be row ...
7
votes
6answers
845 views

Is (rest) mass conserved in special relativity?

I don't understand why it is said that the (rest) mass of a system is not conserved in relativity. I mean, the momentum of a system is conserved (i.e.: it remains constant in a frame of reference ...
1
vote
2answers
95 views

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 ...
1
vote
1answer
86 views

Since the Earth is moving through space, do we experience time dilation?

What I mean is, the Earth orbits around the sun at around 30km/s, while I understand that this isn't a very high velocity does time dilation still occur to say a person who is completely stationary in ...
0
votes
1answer
58 views

Dimensionless numbers in relativistic theory

Dimensionless numbers allow physicists and engineers to extend the physical modeling landscape by reducing otherwise complex mathematics to a simple proportional relationship. For example by assuming ...
2
votes
0answers
97 views

Proof that spacetime interval is invariant

I'm trying to understand the proof that spacetime interval is invariant under for any two inertial observers. I know it's easy to arrive at the result using Lorentz transformation but I'm trying to ...
1
vote
0answers
105 views

Relativistic Momentum and Energy - Lorentz Transformations [closed]

The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Lab is colliding fully ionized gold (Au) nuclei accelerated to an energy of 200 GeV per nucleon. Each Au Nucleus contains 197 ...
0
votes
2answers
57 views

A spin on relativity's twin paradox?

What if a twin is in a rocket in a synchronous orbit with the equator of the Earth while the second twin is standing at the equator watching his twin in space. If we use 0.87c for ease of calculation ...
1
vote
2answers
71 views

Theory of relativity. Relative to what? [duplicate]

If I properly understand relativity, time ticks faster for an object sitting still than for an object passing by. So, in a universe with only two objects which have the same "age", object A is ...
-1
votes
1answer
139 views

Stone vs. Atomic Bomb

What would do more damage, a B53, a 9 megaton uranium bomb, or a medium sized stone (2 kg) stone throw at 90% the speed of light. One thing that I know that will have to be considered is that fact ...
1
vote
3answers
121 views

Dark matter: Will Special Relativity hold?

Part 1: It’s been said that dark matter makes up about 26 % of the universe. The restart of LHC would be dealing with the existence of dark matter also. Consider a situation that the results are ...
0
votes
1answer
71 views

Exactly which components of special relativity are contained in Minkowski spacetime?

In other words, which components or concepts in special relativity are reflected in Minkowski spacetime? If I'm not mistaken, Lorentz covariance is one of these concepts, correct? I'm trying to ...
0
votes
1answer
76 views

Invariance of Maxwell equations [closed]

Is there an easy way to show that the Maxwell equations $$ \partial_\alpha F_{\beta\gamma} + \partial_\gamma F_{\alpha\beta} + \partial_\beta F_{\gamma\alpha} = 0 $$ are invariant under a Lorentz ...
0
votes
1answer
85 views

Would Special Relativity Predict Time Dilation of a Geostationary Satellite Compared to an Observer on Earth?

Consider a geostationary satellite at some arbitrary distance above the Earth's equator and consider a person directly below it, standing on the Earth's equator. Both satellite and person exist on the ...
1
vote
2answers
67 views

Composition of Lorentz Transformations

If a particle is moving in the $x$-direction with velocity $c/2$, then the Lorentz transformation $\Lambda = \begin{pmatrix}\gamma & -\beta \gamma & 0 & 0 \\ -\beta \gamma & \gamma ...
1
vote
2answers
134 views

Special Relativity - Distance Not Increased?

I just watched the movie Interstellar and the question was asked of why/how high-speed travel would slow time within an area. Curious as I am, I watched several YouTube videos to quickly 'educate' ...
2
votes
0answers
26 views

Intrinsic CPT phase

Under charge conjugation C, spatial inversion P and time reversal T transformations, there are possible intrinsic phases (more for this on Chapter 9, The Quantum Theory of Field v1 by S. Weinberg): ...
0
votes
1answer
71 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 ...
3
votes
1answer
197 views

Charged particle under a uniform electric field

Suppose a charge particle $q$ starts to move without initial velocity under the influence of a uniform electric field $E$ pointing in the positive $x$ direction. Express its position vector in ...
-4
votes
2answers
73 views

Speed of light yes or no? [closed]

First off I am not a physics student: I am more of a science enthusiast. My question pertains to time and the speed of light: According to Einstein, no mass can travel at the speed of light. Now, ...
0
votes
5answers
206 views

What is the significance of the “squared” in $E =mc^2$? [duplicate]

If $c$ is just an arbitrary constant, why don't we say $E=mc$ and define the value of $c$ to be $\sqrt{299 792 458} \approx 17314$ meters per second? Or, why not use $E=mc^3$?
7
votes
2answers
159 views

Why does the minus sign in the Minkowski metric mean that nothing can move backwards in time?

I just watched this video: http://www.youtube.com/watch?v=GkCWywO93b8#t=27 and there Mr. Cox states that because of the minus sign in the Minkowski metric nothing can move backwards in time. It's ...
0
votes
1answer
32 views

SR: constant acceleration wordline simultaneity

A worldline $W$ with constant acceleration $a$ is given parametrically by $$t=\frac{c}{a} \sinh(\frac{a \tau}{c}), \quad x=\frac{c^2}{a} \cosh(\frac{a \tau}{c}).$$ Let $E=(0,0,0,0)$. I showed that for ...
1
vote
1answer
49 views

Polarization vector identity in Minkowski space?

Playing around with numerical light-like momenta $p^\mu_1,p^\mu_2$ (light-like meaning ${p_1}^\mu {p_1}_\mu={p_2}^\mu {p_2}_\mu=0$) and corresponding polarization vectors ...
8
votes
3answers
1k views

Could any object have zero mass? [duplicate]

Energy and mass are interrelated. As everything has energy could any object be massless? For example a photon is a packet of energy but still it is considered to be a massless particle. Why is it so?
0
votes
0answers
45 views

Would you be able to see yourself in a mirror in front of you as you two are in a room traveling at the speed of light? [duplicate]

Veritasium talked about this in one video. If you are in a room or a train, plane, car or whatever just a closed space traveling at the speed of light and you put a mirror in front of you, could you ...
1
vote
2answers
98 views

Special relativity mirror clock experiment inconsistency

Say I set up a relativistic mirror clock experiment in which a spaceship contains a set of mirrors with a photon bouncing between them. Say the photon's motion is parallel to the direction of motion ...
1
vote
0answers
47 views

Space and time variant? But together invariant?

I admit I'm having difficulty with spacetime. I don't understand how unifying space and time, seemingly variant quantities, results in an invariant spacetime. All texts and references talk about using ...
-1
votes
2answers
170 views

Does the speed of light have a range of speeds due to medium-dependency?

An EM particle-wave propagates in a vacuum at a constant speed $c$, independent of the source/receiver but dependent on most mediums it moves through. Since the vacuum is a medium, and if logically ...
1
vote
2answers
59 views

Is there experimental evidence supporting the equivalence principle between different particles?

Knowing virtually nothing of GR, and only hints of particle theory, this might be something of a naive question. If I've misunderstood somethings, I would gladly like to know why. Perhaps a more ...
4
votes
5answers
154 views

How can we justify dropping the absolute time hypothesis?

In some approaches to Special Relativity the theory is motivated talking about the Michelson-Morley experiment and how this relates to the postulate that the speed of light is the same in every ...
0
votes
1answer
86 views

Deriving the Lorentz factor

Recently, I learned how to derive E = mc^2. However, to do so, one must accept the relativistic mass equation. How does one derive this?
2
votes
1answer
69 views

Rindler and Minkowski space future/past infinity

In my black holes course, we are looking at the Penrose diagram for 1+1 D Minkowski space. My notes don't specifically describe $i^{\pm}$ (future/past timelike infinity) but do say all timelike curves ...
1
vote
0answers
35 views

SR: vector field and change of reference [closed]

If $U$ and $V$ are vector fields, then the derivative of $U$ along $V$ is the vector field $\nabla _V U$ with components $$\nabla _V U^a=V^b \frac{\partial U^a}{\partial x^b}.$$ I would like to verify ...
2
votes
4answers
133 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 ...
1
vote
3answers
80 views

What is $E$ in the Planck-Einstein relation?

The Planck-Einstein relation was first given for photons $$E = h\nu$$ But later, de Broglie extended it to matter waves, and showed that it would hold for all particles as well. The $E$ for a photon ...
2
votes
2answers
131 views

Propagation speed of photons when taking higher-order QFT corrections into account

In our group of experimental physicist who have nothing to do with and know very little about quantum field theory, we recently had a question concerning the propagation speed of photons in vacuum: ...
-5
votes
2answers
118 views

Einstein's mass-energy equivalence [closed]

Einstein's wonder equation $E=m c^2$,if we take energy is proportional to the mass, we can put single constant to make that equivalent equation. We all know that ...
1
vote
2answers
186 views

Why are the proper time and the proper length not defined in the same frame of reference?

I've just read this interesting Wikipedia article about time dilation and length contraction in special relativity. . Derivation of time dilation Applying the above postulates, consider the ...
-1
votes
2answers
55 views

Relativity asymmetry?

If you have two bodies that move towards each other at a constant velocity, each body will observe the other body experience time faster. This does not make sense to me because if you had a person ...
0
votes
2answers
65 views

What is the difference between these two equation dealing with time dilation?

In my textbook, the time dilation equation is presented as $\Delta t' = \gamma \Delta t,$ where $ \gamma = 1/ \sqrt{1 - v^2/c^2} $. My understanding of this equation is as follows (correct me if I'm ...
0
votes
0answers
26 views

Relativistic doppler effect in three dimensions

Consider a sphere that travels through space with a velocity $v$. I wish to investigate the relative intensities of the CMB on all points on the sphere. For the microwaves approaching from the direct ...
1
vote
1answer
78 views

How to motivate this approach on Special Relativity?

One of the most common approaches to Special Relativity is that based on the two Einstein's postulates: The laws of Physics are invariant in every inertial reference frame The speed of light ...
1
vote
1answer
34 views

Perception at relatavistic speeds

If one were to be traveling at near the speed of light, their mass would be $m_{rel}= m_0 / \sqrt{1 - \frac{v^2}{c^2}}$. For the mass to double the speed would have to be $86.6\%c$ [edit] To better ...
0
votes
2answers
61 views

About Lorentz Group

In definition of orthogonal matrices we say that the a matrix $A$ is orthogonal if $A^TA = I$, while for Lorentz Group it is written as $\Lambda^Tg\Lambda = g $. And we say that Lorentz transformation ...
0
votes
0answers
24 views

Threshold energy, does this indicate particle annihilation?

If we have a question on threshold energy like the following: Two particles A and B collide to create C and D. Find the threshold energy required for particle A given that particle B is at rest. ...