# relaitivity Definition and Topics - 75 Discussions

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1. ### I Question regarding space diagram transformation in special relativity

While learning about Special Relativity I learnt that we use the Transformation matrix to alter the space .This matrix differs for Contravariant and Covariant vectors.Why does it happen?,Why one kind of matrix (Jacobian) for basis vectors and other kind(Inverse Jacobian) for gradient ,divergence...
2. ### I Refractive index of a medium in relativistic motion

I once naively think that the speed of light is also a constant in a medium in all inertial frames which is not the case. I tried to derive the result yet there is a discrepancy from the results I read in some articles. For example, from [Link to unpublished paper redacted by the Mentors], the...
3. ### I The center of mass & relativistic collisions

In special relativity (especially relativistic collisions), is the center of mass frame as useful as Newtonian mechanics?
4. ### Spaceship is approaching the Earth with an unknown speed

I started by finding the main events: Sending the first message Receipt the first message Sending the second message Receipt the second message Now, what we know is the time by ##S'## (comoving frame with the spaceship) ##T_1'## and ##T_2'## remaining to arrive to the earth measured at...
5. ### I Four Velocity Vector: why divide by time according to the particle?

So I understand that time is now part of the four vector, and so dividing delta X by delta t (time according to me), would produce just c as the first dimension of the vector, which gives us no intuition as to how fast time is moving for the observer, so is not useful. I understand why we...
6. ### I Relativistic energy equation applied to a double-slit experiment

My question: How do the values for the velocity, momentum and energy of an electron in a double-slit experiment are altered by the observation? Probably,energy is altered. Given that energy is a function of momentum and velocity, either or both of these must have been changed. However, I am...
7. ### A A doubt about time measurement in an MT traversable wormhole

I am reading this article now :http://www.cmp.caltech.edu/refael/league/thorne-morris.pdf. And i am a little bit confused about the Eq.(38a)and Eq.(38b), which means the time measured by traverller and people in the sataion, and I just think the time measured by traveller should be his proper...
8. ### Why does the speed of light change in different media?

In relativity, the speed of light in vacuum is a universal constant. Also, it has wave-particle duality. So if the speed of light slows down in a different media other than vacuum, what exactly is slowing down? Macroscopically speaking, the speed of light does slow down. What about in the...
9. ### Prerequisites for General Relativity (Advice needed)

Summary: At this point, I am thorough with single variable, multivariable calculus, differential equations, linear algebra and basic concepts of point-set topology and tensor analysis. To learn General Relativity along-with its mathematical rigor, what are the topics I should first be thorough...
10. ### Other Which math skills to learn for understanding relativity?

Summarized: Which mathematical fields should you focus on if your goal is to gain a better understanding of relativity and related subjects? (My apologies if there are already other threads asking this question, but 'math' and 'relativity' aren't really useful search terms on this forum.) Hi...
11. ### I Calculate mass from time dilation

Based on the exponential growth of time dilation 0.0 - 1.0 if given the radius of an object how do you calculate the mass of the object? Time dilation is a function of gravity. Which can be thought of as escape velocity from a gravitational field. So if you have to achieve .866 c to escape...
12. ### I Escape velocity - General relativity

Hi, Do we obtain the same escape velocity equation: Ve = sqrt(2GM/r) using both Newtonian and Relativistic approach?
13. ### Relativity Thoughts on General Relativity by Hobson?

Background: I'm about to graduate with a mathematics degree(in the US), hence I have exposure to multivariable calculus, real analysis, abstract algebra, complex variables etc (no differential geometry however). I have also taken a class on QM(using Griffiths) and I saw some SR during a Modern...
14. ### B Is our Universe a single point for a photon?

I have come across a questions which reads "Why does even photon travel?". After reading special and general theory of relativity, this one bugs me all over. For a particle moving closer to speed of light, clock slows down and the space around it contracts. I see a photon travel and I see things...
15. ### B Gravitational mass and Inertial mass in relativistic physics

In Newtonian mechanics, both gravitational mass and inertial mass is m. This principle is known as the principle of equivalence. However, I heard that in Relativity, gravitational mass is γm instead of m because total energy of the particle is γmc2. But in special relativity, it is widely known...
16. ### I Trying some physics i don't even know about.

Sometimes I get so bored that I just try to calculate certain experiments I've heard without know the solution. Like using the basic formula to calculate the speed of the moon around the Earth. This time I tried to calculate the differences between 2 clocks, on put on the highest building in the...
17. ### I How does the speed of light affect clocks?

If the speed of light would change in the universe without any other natural constant changing, would all clocks be affected in the same way by this? This is implied by Einstein in this paper on page 368 http://myweb.rz.uni-augsburg.de/~eckern/adp/history/einstein-papers/1912_38_355-369.pdf...
18. ### Consolidating maxwells equation with relativity

Hello I know that maxwells equations are consistent with relativity. The following thought experiment seems to imply otherwise so I am wondering where my mistake lies. Lets say we have some very large conductor loop(with a radius of many lightyears). At the center of the loop is some magnet...
19. ### Electromagnetic waves

I have learned about the electric fields of static charges and those of moving charges. From what I gather(although I have not really learned the specifics) when charges are accelerated they emit electromagntic waves which are essentialy an electromagnetic field progagating through space. My...
20. ### B Does the size of the Universe change with motion?

This is a question I was looking at based on Relativity and John Wheeler's one-electron universe theory. https://en.wikipedia.org/wiki/One-electron_universe My question is this. The faster you move towards the speed of light, wouldn't everything in the universe contract to a single particle...
21. ### Relativity Books for learning the maths used in learning Relativity

Can anyone suggest a book from where I can learn the math used in relativity like Tensors,Minkowski spacetime metric ,etc ? A suggestion of pdfs would also be appreciated?
22. ### Special relativity and Lorentz factor problem

Homework Statement There are 2 particles(1,2) separated ∆x=L moving with the same velocity u_x in frame of reference S , there's an other reference S' moving at v . I have to calculate ∆x'. GAMMA(LORENTZ'S FACTOR) Homework Equations The Attempt at a Solution I have done x1=0 when t=0 So...
23. ### I Magnetic field measured in a rotating frame

Consider that we have a magnet and a magnetometer (a fluxgate magnetometer with a single coil), standing still as shown in fig 1. In fig 1, the magnetic field measured at the axis z1 of the magnetometer coil is B1. But if everything (magnet, magnetometer and the axes) was rotating together...
24. ### A Sufficient conditions for Rayleigh-Taylor instability

I was reading the paper entitled "The Rayleigh—Taylor instability in astrophysical fluids" by Allen & Hughes (1984), and they discuss relativistically hot plasmas in the context of weak magnetic fields which are presumed to have no dynamic influence, so they take a fluid approach. In this paper...
25. ### I Covariance and invariance

Can anyone briefly explain the difference between covariance and invariance in terms of special relativity? My understanding is that an invariant quantity is a value which does not change regardless of frame of reference it is being measured in. Covariance is a value which when measured in...
26. ### I The relativistic de Broglie equation

I'm having trouble understanding how the 4-wave vector is derived, and also how it is then used alongside the 4-momentum vector to formulate the relativistic de Broglie equation. The inner product of the 4-momentum vector with itself, is an invariant quantity. If we define the 4-momentum...
27. ### Body decay on the axis of an infinite wedge

Homework Statement On the axis of an infinite wedge that moves with velocity ##\vec{V}##, the body decays with the formation of a lot of splinters that fly away uniformly in all directions with velocity ##\vec{u}##. What should be the angle of the wedge that half of the splinters fall on its...
28. ### Fringe-Shift in Michelson Interferometer with a Moving Source

Homework Statement The Michelson interferometer in the figure below can be used to study properties of light emitted by distant sources A source ##S_1##, when at rest, is known to emit light at wavelength ##632.8~ \rm nm##. In this case, if the movable mirror is translated through a...
29. ### I Questions about the general principle of relativity

One of the founding principles in GR is the principle of general relativity, which loosely states that all coordinate frames (inertial and non-inertial) are equivalent in the sense that the laws of physics are invariant. My question is, does the justification for this come from Einstein's...
30. C

### I Electrical Current Repelling Magnets Due to Relativity

I recently watched this Varitasium video where he explains the magnetic field due to a current carrying wire. In the video he explains how what we see and describe as the magnetic field produced by a current carrying wire is actually just a electric force caused by the an imbalance of charges...