# Tagged Questions

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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### How time and speed of light are related? [closed]

I want to know how speed and light and time are related? How will motion with highspeed effect time? I am not a physics student. I want an answer which is free of mathematical relations. I want an ...
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### How does SUSY avoid to create non-Lorentz interactions?

A three-legs fermion interaction or boson absorbing a fermion are things we do not see in QFT because the corresponding terms in the Lagrangian are not Lorentz invariant. But in susy, naively, such ...
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### Gradient of $ct'$ axis in spacetime diagrams

This is either an unimportant piece of information or it's meant to be obvious, but I can't find anywhere what the gradient of the $ct'$ axis in a spacetime diagram should be. I know that the $ct'=1$ ...
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### What's the problem with light traveling at speed higher than $c$?

I'm trying to understand how Einstein concluded that time is relative based on thought experiments such as a torch attached to the end of a rocket. Based on answers to questions like this one, this ...
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We say that any function $f(t,x,y,z)$ is a tensor of rank {0 0} because it takes no vectors or one-forms in order to give a real number. But couldn't we have just written the same function as $f(t,x,y,... 1answer 33 views ### Multiple Objects at Constant Speed Imagine 1 million objects travelling in space, at a constant speed, along an imaginary line. They don't deviate from that line for the sake of this argument. Now, object 1 has a velocity of$v_{1}=1$... 1answer 51 views ### How does time dilation occur due to velocity and gravity [duplicate] I am trying to understand and clarify the way time dilation occurs due to general and special relativity and for which reason. In the case where an object is approaching a planet in free-fall how does ... 1answer 79 views ### Different definitions of the parity transformation for the Dirac spinors There are two definitions of the parity transformation acting on the Dirac spinors:$\Psi_P = \eta \gamma^0 \Psi$with$\eta = i$($P^2=-1$as in Srednicki) and$\eta=1$($P^2=+1$as in Peskin & ... 3answers 266 views ### How can we prove charge invariance under Lorentz Transformation? We have gravitational force between two massive particles and we have electromagnetic force between two charged particles. When special relativity suggests that mass is not an invariant quantity why ... 3answers 79 views ### Mass and frequency of photons [duplicate] Light is affected by gravity which means light has got mass. Quantum theory tells us that light consists of discrete quanta of energy, which we call photons. These photons have a rest mass of zero (as ... 1answer 162 views ### Can special relativity be derived from the invariance of the interval? As far as I know, the classical approach to special relativity is to take Einstein's postulates as the starting point of the logical sequence, then to derive the Lorentz transformations from them, and ... 3answers 173 views ### Why did Einstein took speed of light unit or constant in his equation of relativity? We can find that no object can have speed more than light from Einstein's equation of relativity because if anything have speed more than light then we get -ve value within square root. But why did ... 2answers 67 views ### Planes of Simultaneity on Minkowski diagrams As seen from a "stationary" reference frame, Why do lines of simultaneity for fast-moving observers run parallel to distance axis instead of perpendicular to the time axis. Obviously, in a regular t ... 2answers 383 views ### How to achieve speeds faster than light? [duplicate] So, I heard that all speed is relative. And that nothing can travel faster than light. Then I guess it is OK for a spaceship to leave Earth at 0.6c constant speed. And what if an other spaceship were ... 0answers 32 views ### Helicity of massive particle at high enengy We know that massless spin-1 particle like photon only has two helicity state (-1,1), what about the helicity of massive spin-1 particle (W boson) at very high energy? Does it have helicity 0 state ... 0answers 36 views ### How do I make a slowly rotating neutron star using fortran code? I make a slowly rotating neutron star code but I am little bit confuse, when I solved the coupled differential equation using runga-kutta 4th order method. These coupled differential equations as ... 0answers 74 views ### Derive Galilean transformation. (The meaning of the relativity) In the book The meaning of the relativity Einstein says that in classic mechanics two postulates are previously supposed: 1.- The time is absolute. 2.- The longitude is absolute. And this implies ... 1answer 96 views ### Does there exist finite dimensional irreducible rep. of Poincare group where translations act nontrivially? I read several textbooks of QFT and find that there are two ways to classify the particles or fields. The first one is to study the irreducible representation of Lorentz group (or exactly the ... 3answers 99 views ### Confusion on relativistic electromagnetism of two charge particles When I was introduced to the relativistic nature of electromagnetism, the following scenario is introduced: Two protons are fired such that they travel at the same velocity in parallel directions ... 0answers 11 views ### How can I do a nested lightcone integral? I want to do an integral of the form$I(x-y)=\int d^{D+1}z_1...d^{D+1}z_n f(x-z_1)...f(z_n-y)$where$x,z_1,...z_n,y$are all (D+1) vectors and$f$depends only on the proper times between them.$z_i$... 1answer 82 views ### Signification of “finite but unbounded universe”? I recently read Einstein's book about relativity and he says that his theory predicts the shape of the universe. It would be finite but unbounded. But how is this possible? What's the difference ... 0answers 18 views ### Compressed length of a moving body [closed] This question is on behalf of someone else without access to a computer so any further clarification or responses may be delayed. The question comes in the form of photos of the original questions as ... 1answer 44 views ### Speed of light in vacuum in special relativity In special relativity, the speed of visible light is defined as a constant. But visible light is only a small part of the electromagnetism field. So why? 0answers 43 views ### Thought experiment on special relativity If we were travelling in a spaceship, accelerating (arbitrary value) from a velocity 0, and we assumed that times and distances outside of the spaceship remained the same as that of ours, would we be ... 1answer 66 views ### Can information be sent faster than speed of light [duplicate] I just had this idea one day and I decided upon a thought experiment to verify it. Imagine 2 people A & B sitting on two sides of a pipe which is stretched to a length of 3x10^8 m. The pipe is ... 1answer 69 views ### Are Coulomb's Law and Lorentz force always true for all phenomenon in physics? I saw two equation about charge: Coulomb's law $$\mathbf F=k \frac{q_1q_2}{ r_{12}^{2} }\, \mathbf{\hat r}$$ and magnetic Force $$\mathbf F=q \, \mathbf v\times \mathbf B$$ My question is:... 1answer 52 views ### Stacked motors thought experiment first of all, I'm not a mathematician, just curious about something that came up to my mind and maybe you can help me out. Scenario: I have a motor that spins let's say at 20K revolutions per minutes.... 2answers 122 views ### Where do I begin in order to study relativity? [duplicate] I am in high school now and I want to get the basic idea of what relativity. Can anyone suggest me a book or website for it? I am also curious about the mathematics behind it. Is it possible for me to ... 0answers 42 views ### Why is there a minus in the Gauge Field Lagrangian kinetic term? [duplicate] For vector Gauge fields we usually write the kinetic term: $$\mathcal{L} ~=~ - \frac{1}{4} F_{\mu \nu} F^{\mu \nu}$$ while for matter fields e.g. for a real scalar:$$\mathcal{L} ~=~ \frac{1}{2} ... 0answers 53 views ### What is wrong with this derivation of the lorentz factor in attempting to derive the lorentz contraction, I assumed that light speed is measured the same from all inertial reference frames. The situation set up is object A is standing still, whilst object B ... 2answers 298 views ### Is there a limit to how hot an object can get? If heat is the measure of how fast the atoms are moving in an object, than isn't there a limit to how hot that object can get as nothing can go as faster than the speed of light. So because the atoms ... 0answers 26 views ### Value of$E_x$through an$X-\textrm{boost}$Suppose I'm standing at the (0,0,0) point of a coordinate system and I see an electric field where$E_x=f(t,x,y,z)=\sin(x\cdot y\cdot z\cdot t)$and at time$t_0=0$I start moving on the x-axis at ... 0answers 45 views ### Electromagnetic Tensor under Lorentz transformation,$F'(\Lambda x)= \Lambda F(x) \Lambda^T$?) Suppose we have a configuration of electric and magnetic fields$E(x1,x2,x3,x4)$and$B(x1,x2,x3,x4)$, they depend of position and time for a fixed coordinate system. And I want to know how someone in ... 2answers 224 views ### Presentism: doesn't everything exist at the same moment? [closed] The Help Center recommends I 'fix' this question: (original question) "It seems self-evident that everything exist in the Now. Notwithstanding time-dilation and different rates of the passage of ... 1answer 89 views ### “Spacetime tells matter how to move; matter tells spacetime how to curve” and acceleration in flat space-time? [closed] John Wheeler stated "Spacetime tells matter how to move; matter tells spacetime how to curve." Does this contradict with the assumption that mass can be accelerated in flat space-time (see i.e. this ... 0answers 53 views ### Lorentz invariance of the Heaviside function [duplicate] Consider the Heaviside function$\Theta(k^{0})$. This function is Lorentz invariant if$\text{sign}\ (k^{0})$is invariant under a Lorentz transformation. I have been told that only orthochronous ... 1answer 71 views ### Rest Mass Clarification I would like to know about the Rest Mass? Why we need the phrase "rest mass"? Because, mass is a constant quantity? Or Is the Mass varying with velocity? How can we understand that mass varying with ... 2answers 966 views ### Does rest exist? I initially thought that the concept of rest depended on an inertial frame of reference. So for example, if the Earth and everything on it were the only things in the universe, and the Earth was ... 0answers 33 views ### question dealing with time dilation and length contraction In Einstein's theory of relativity and reference frames, It states that an observer on earth watching a spaceship fly at close to the speed of light heading away going towards a distance star that the ... 0answers 32 views ### How does length contraction map from a macro size object to its individual sub-atomic parts? If an object consisting of many atoms is traveling close to the speed of light, explanations of length contraction seem to indicate the whole structure contracts. It seems easy to imagine an electron,... 4answers 233 views ### Rapid acceleration does what to inertial frame clocks? I'm 10 light years from Earth and see Earth's clock/calendar reading 2000, including light travel time. In other words, I assume it's 2010 on Earth, but what I actually see is the year 2000 due to ... 0answers 54 views ### Finding an explicit expression for inverse of Lorentz transformation${\Lambda^\mu}_{\nu}\$

I'm studying in a module titled "Symmetries and Action Principles in Physics." I'm having a small trouble with the notation, I think, of special relativity. We have in the text In fact we may ...
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### What do observers in relative motion agree on?

What are the measurements on which two observer in relative motion will agree? Other than the speed of light.