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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Does a Michelson-Morley experiment uphold mass-energy equivalence and special relativity?

If there is an experiment that best supports $E=mc^2$, is it the Michelson-Morley experiment?
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Scalar operators In Quantum Field Theory

I am trying to learn Quantum Field Theory and I am stuck in a basic point. What is the definition of a scalar operator in QFT? That is, how does it transform under a Poincare transformation? Why do ...
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Tangent vector norm squared conservation in special relativity

I'm trying to analyse non-inertial motion in special relativity. First I'll start off with inertial motion. In my reference frame, my particle has coordinates $x^\mu = (t, x)$ And in the particle's ...
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103 views

If we could not see, would we think that nothing can go faster than sound?

And if so, then why does everybody keep asserting nothing can go faster than light speed (I'm implicitly assuming there could be something which we do not observe, which goes faster than light)?
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Can “uniform motion” (or “mutual rest”) be determined intrinsically, by members of Synge's “five-point curvature detector”?

In his description of a "five-point curvature detector" [1], J. L. Synge exhibits a Cayley-Menger determinant in terms of "optical distances" between five distinct participants; and he states that the ...
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Relativistic object impacts the earth

A familiar trope within science-fiction is that of a large relativistic object hitting a planet such as the earth. This is normally an interstellar spacecraft or a kinetic weapon with a mass in the ...
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Does mass increase at relativistic OUTSIDE of the mass's frame of reference? [duplicate]

There are other questions on here with responses saying that the mass does not change from its own frame of reference. But those answers were somewhat unclear if the mass changes to someone observing. ...
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52 views

Is it OK to see time dilation and (relativistic) mass increase as phenomena that avoid $c$ being reached? And how about length contraction?

I think I have been exposed since years ago to this line of reasoning: if $ v\to c $, then $ \Delta t \to \infty $. As $\displaystyle v=\frac{\Delta s}{\Delta t} $, it's like a natural reaction to ...
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Stress Energy Tensor of EM Field

Stress energy tensor for electromagnetic field is given by $$T^{\mu\nu}=\frac1{4\pi}(F^{\mu\alpha}F^{\nu}{}_\alpha-\frac14 g^{\mu\nu} F_{\alpha\beta}F^{\alpha\beta}).$$ My textbook (unpublished ...
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1answer
50 views

Proof of equivalence of two different covariant notations of Maxwell's equations [closed]

My homework assignment is Prove that $$\partial_\beta F_{\gamma \delta} + \partial_\gamma F_{\delta \beta} + \partial_\delta F_{\beta \gamma} = 0$$ with the electromagnetic tensor ...
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68 views

Effects of travel greater than speed of light [closed]

What will happen if a person with say weight of 100 kilograms, starts to travel with, a) equal to speed of light? b) greater than speed of light?
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2answers
161 views

Is the explanation of special relativity in Stephen Hawking's “The Grand Design” flawed?

To explain special relativity (in chapter 5 titled "the theory of everything"), Hawking starts with an example involving a flying jet, its passenger (being an observer) and an observer on the earth. ...
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2answers
61 views

What is energy of light, as we know speed of light?

1.What is total energy of EM waves, as all got same speed? If two em waves has same energy, do they have same mass? If same mass and energy, do they have same frequency or wavelength still ...
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3answers
394 views

How does a single charge produce magnetic field?

I have studied in Introduction to electrodynamics (Griffiths) that magnetic field is actually due to effects of relativity unequal Lorentz contraction of the positive charge and negative lines, a ...
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0answers
28 views

Is it possible to measure relativistic mass of a body moving towards or from an observer?

It is clear there is no problem in measuring relativistic mass via magnetic field: “Suppose you know the strength of a uniform magnetic field B. Launch a charged particle, of magnitude charge q, ...
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5answers
262 views

How do we know that photons are exactly massless and travel exactly with speed $c$ in vacuum?

I know that this question may sound stupid, but what I mean is that photons have some energy and no mass, yet the mass and energy are said to be equivalent (or maybe I got that part wrong). In an ...
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1answer
56 views

Special Relativity: Four possible time spans between events?

I've got another question regarding time in special relativity. I'll start with the standard configuration: there are two observers O and O', their x-axis are aligned, in the rest frame of O observer ...
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Fundamental invariants of the electromagnetic field

It is a standard exercise in relativistic electrodynamics to show that the electromagnetic field tensor $F_{\mu\nu}$, whose components equal the electric $E^i=cF^{i0}$ and magnetic ...
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1answer
71 views

Spin statistics

I have a very intrinsic question about quantum field theory and even more general, why in 3+1-dimensional spacetime, we have only two statistics for particles to obey? Therefore why we have only two ...
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1answer
134 views

Does the passage of time effect a photons entanglement with another?

I recently read an article about "Delayed-choice entanglement swapping". Here is an excerpt from the article: Delayed-choice entanglement swapping consists of the following steps. (I use the ...
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2answers
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Relativity and acceleration-acceleration

Presummary to save expert's time! (pls see below!) "In GR, is jerk relative?" As I understand it, "Special Relativity" (special meaning, specific limited situations) applies only for (in a word) ...
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1answer
206 views

Is there a graphical representation of the Lorentz transformation equations?

I always loved theoretical physics as a kid and when I came upon this site while seeking computer advice via superuser I had to stick my silly little head into an oasis of intelligence. I have often ...
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1answer
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Interpretation of rank 2 spinors

While inspecting the $(\frac{1}{2},\frac{1}{2})$ representation of the Lorentz group and defining a right-handed spinor with upper dotted index and a left-handed spinor with lower undotted index and ...
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Problem with understanding time dilation (moving clocks can run faster?)

I ran into a serious problem with the Lorentz transformation and time dilation. In the standard configuration you have one observer S and another one S' with their x-axis aligned. I assume S to be at ...
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Energy-Time Uncertainty Principle and Photons

Heisenberg's uncertainty principle states that: $$ \Delta E \cdot \Delta t \ge \frac{\hbar}{2} $$ It is clear that this has nothing to do with the accuracy of our measurements, but rather is a ...
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2answers
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Does this proof for time dilation ignore length contraction?

A simple proof for time dilation can be found here http://en.wikipedia.org/wiki/Time_dilation#Simple_inference_of_time_dilation_due_to_relative_velocity What I am confused about is that when the ...
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Where's the energy in a boosted capacitor?

Suppose I look at a parallel plate capacitor in its rest frame and calculate the electrostatic energy, $E$. Next, I look at the same capacitor in a primed frame boosted in the direction perpendicular ...
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1answer
53 views

Relative velocity of two objects travelling at $c$ (or near $c$) [duplicate]

If two bodies are travelling at speed $0.9 \, c$ in opposite directions, what will be the speed of one, as observed by another? Newtonian mechanics won't apply at such speeds. As such, how will we ...
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1answer
33 views

Explicit Symmetry Breaking: Where do the additional d.o.f. come from?

Massless vector bosons have only two independent degrees of freedom, while massive ones have three. In spontaneous symmetry breaking, the massless vector belonging to the broken group becomes massive ...
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Is acceleration relative?

A while back in my Dynamics & Relativity lectures my lecturer mentioned that an object need not be accelerating relative to anything - he said it makes sense for an object to just be accelerating. ...
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Why does the existence of an aether go against Maxwell's equations

I am trying to determine why there is a conflict between Maxwell's equations and Galilean relativity. The standard way I have seen it explained is: The Galilean world model says velocities transform ...
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2answers
101 views

What does a relativistically moving capacitor “look” like? [duplicate]

Suppose I have a parallel plate capacitor with a vacuum between the plates, a voltage $V$ across them and a capacitance of $C$. What will this arrangement look like to an observer in a uniformly ...
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2answers
113 views

The definition of transpose of Lorentz transformation (as a mixed tensor)

In the appendix of the textbook of Group Theory in Physics by Wu-Ki Tung, the transpose of a matrix is defined as the following, Eq.(I.3-1) $${{A^T}_i}^j~=~{A^j}_i.$$ This is extremely confusing for ...
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Misuse of $\mathbf J^2$ in classifying Poincare reps

$SO(1,3)$ has an infinite number of representations, classified by the Casimir invariant $p^2$. $SO(3)$ also has an infinite number of representations, classified by the Casimir invariant $\mathbf ...
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Shouldn't we use a Hamiltonian that doesn't give special treatment to time? [duplicate]

If we have a Lagrangian $\mathcal L$ that depends on some scalar field $\phi$, we define the momentum as $\pi \doteqdot {\partial \mathcal L \over \partial \dot \phi}$. The Hamiltonian then is ...
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1answer
51 views

Importance of Powers of Velocity in Classical Mechanics

Is there any general significance to calculated quantities that depend purely on general powers of the velocity of a particle/system/etc? The first power being momentum and the second being kinetic ...
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2answers
56 views

When talking about atomic mass, how is $E=mc^2$ factored in? [duplicate]

When talking about atomic mass in the periodic table of elements, is this number the mass of the element at rest? If I understand correctly, the (relativistic) mass of an element will increase as the ...
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1answer
80 views

Electromagnetism in flat space

I want to get a deeper understanding of how Electric and Magnetic fields transform under Lorentz transformation. That is how to start from gauge transformation of Electric and Magnetic fields $$E= ...
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78 views

Mathematical Definition of Locality

What is the mathematically precise definition of principle of locality in physics for a continuous space-time in the sense that an object is only directly influenced by its immediate surroundings?
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134 views

Magnetic force as a relativistic effect?

There is something I am confused about when it comes to the force between two parallel wires carrying current, specifically why when they carry current in the same direction the wires are always ...
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0answers
72 views

Does a mass gain inertia against movement in all directions as it approaches the speed of light?

If a mass moves along the x axis at near the speed of light, does it take as much energy to additionally accelerate the mass along the y axis as it does to accelerate it along the x axis by the same ...
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4answers
312 views

Is $E^2=(mc^2)^2+(pc)^2$ correct, or is $E=mc^2$ the correct one?

I have been having trouble distinguishing these two equations and figuring out which one is correct. I have watched a video that says that $E^2=(mc^2)^2+(pc)^2$ is correct, but I do not know why. It ...
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0answers
86 views

What is the derivation of $E=mc^2$? [duplicate]

How did Einstein derive his most famous equation: $$E=mc^2$$ Is the above equation a special case of $$E^2=m^2c^4+p^2c^2$$ Its derivation? What is the difference between them?
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Is it a postulate or a well proven fact that speed of light remains constant w.r.t any observer?

We usually heard that speed of light in vacuum $c$ remains same no matter how observer is moving? I am wondering whether is it taken as a postulate or a proven phenomenon that $c$ is constant ...
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3answers
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Why are we not able to move at the speed of light again? [duplicate]

In many many answers here and papers everywhere, it's often stated that no object can move faster than light. Why is that again?
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4answers
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Why is there a controversy on whether mass increases with speed?

Some people say that mass increases with speed, some people say that the mass of an object is independent of its speed. I understand how some (though not many) things in physics are a matter of ...
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2answers
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Is reflection instantaneous?

I was wondering while reading "On the Electrodynamics of moving bodies" by Albert Einstein (1905) (Translated to English). In the paper, he describes the time as being: by definition that the ...
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Time dilation: faster or slower?

I was wondering about Time-dilation in Special Relativity. I am still a middle school student who wonders so please excuse me if I missed any important aspects. Let us assume we have a system of ...
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3answers
219 views

A vertical variation of modern versions of Michelson-Morley

For almost a year now, I have been in the uncomfortable position of having an idea. However, there is one nice thing about this idea. It makes a concrete, exact and relatively easy to test physical ...
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4answers
344 views

What's so special about the speed of light? [duplicate]

What's so special about the speed of light? Why do many equations in physics include the speed of light in vacuum $c$? Why do so many thing depend upon it? Why can't it be the speed of sound? ...