Relativity

FAQ article development, feel free to ask questions or make suggestions. (I'm still working on the Einstein field equation section. Probably keep that portion seperate to minimize length) This question is amongst one of the most commonly asked questions in relativity. Numerous articles both in pop media and peer reviewed articles refer to terms such as space time fabric, space time curvature. This leads the new learners with a common misconception that space has some mysterious fabric or material like property. To answer this properly we need to describe a few principles. A) gravity influences mass B) energy is a property of particles, or physical configura…

General relativity is rather solved in time symmetric way, like the least action principle condition in Einstein's field equations, what as in e.g. Wheeler-Feynman absorber theory requires symmetrically both retarded and advanced solutions. So why seems there are only considered retarded gravitational waves? Can we exclude being advanced wave for all observed events ( https://en.wikipedia.org/wiki/List_of_gravitational_wave_observations )? If not, should they use original chirp shapes, or maybe time reversed?

I have been lately interested black holes and wanted to ask about some very hypothetical scenario. Let's say we have some kind of an extremely massive black hole (my understanding is that it enables you to cross the event horizon without being completely torn apart. Now let's say we are on some strange planet that is painted in a continuous gradient by the longitude, say red on north pole and blue on south pole and then some spectrum of colors in between. Let's now imagine it is being pulled towards the black hole with the south pole of the planet being the closest. Furthermore let's say I am on the equator with a flashlight pointing towards the ground. I'm really curious…

If an object is moving at a significant (reativistic) velocity wrt a particular frame of reference then that frame will see it as length contracted in the direction of motion. Not only "see" it but the object will actually. be. length contracted in that frame of reference. (Hope I am correct so far) In the frame of the object itself no such contraction is observed or experienced. So my question is ,are there any objects where this lack of symmetry would be a problem? Are some objects required to be perfectly symmetrical along all 3 physical axes so that they could not physically exist "squashed up" in another frame of reference ? (I presume the answer must be "no"…

In physics, the amount of force an object has is described as \[ F = dp/dt \], so one could take the derivative of relativistic momentum to find the relativistic force by using the product rule. Given the equation for relativistic momentum, \[ p = mv \gamma \], we could assume that the mass is constant, and it is the only variable that doesn't change due to a relative velocity. Then we can find the derivative using the product rule on the two remaining variables. \[ F = \frac{dp}{dt} = m \frac{d}{dt} (\gamma v) \] -> \[ F = m (\frac{d \gamma}{dt} v + \gamma a) \] from \[ a = \frac{dv}{dt} \] Then \[ F = ma \gamma + mv \frac{d \gamma}{dt} \] by distribution and rearran…

I am proposing a rigorous thought experiment at the intersection of physics and the philosophy of science. The goal is to test whether we can, by applying a set of strict methodological constraints, arrive at a single, fundamental formulation of physical laws. This challenge is not based on new physics, but on "Mathematical Hygiene" (MH) - a principle demanding absolute correspondence between mathematical symbols and their operational, relational meaning. Part 1: The Rules of the Experiment (The Principles of "Mathematical Hygiene")For this experiment to be pure, we must temporarily agree to follow four disciplines. (I will refer to them as A.1–A.4). * A.1. The Principle…

They say: even if our spaceships can go at the speed of light, our spaceship may take many years to reach the other star/ other side of the galaxy/universe. Fact is: if you go (near) at the speed of light, you will be there in (almost) no time. (according to your own clock) Thanks to realtivity. That's our wormhole, right there.

The constancy of the speed of light is a fundamental assumption in modern physics, built into both relativity and the SI system of measurement. I’ve been wondering: to what extent is this a fundamental property of nature, and to what extent is it a convention tied to our choice of units and measurement definitions? And does our current measurement framework even allow us to establish the possibility of it to vary in the first place? The Issue of Measurement The SI second is defined using atomic clocks based on the frequency of a cesium transition. The meter is defined in terms of the speed of light, which is fixed at 299,792,458 m/s by defini…

Suppose we have 2 spacecraft and one of them (B) is following the other (A) towards a region of greater spacetime curvature. In A ,which has its own artificial gravity an elctrician(E) climbs a ladder to a fuse box loses his or her balance and falls to the ground . A backup electician (F) repeats the procedure and again falls to the floor. B observes that F takes longer to follow the same trajectory than E . Is this because B actually observes this via a light(or other) signal or because B calculates it from a GR model? Is this a distinction with no difference or does it have any significance? (Hope my setup had no holes in it) Also are the time measured to …

Basically we are talking about pole barn paradox of Einstein. Fundamental is Lorentz length contraction. The faster the speed of the object te more contracted it appears. So there is a pole there is a barn and a person. From perspective of pole, barn appears to be contracted and pole doesn't fit from the perspective of barn pole appears to be contracted and does fit. From perspective of a person standing outside pole appears to be contracted and fort. Note that pole travels at 99 percent speed of light and we cam use formula of length contraction. Basically I am a curious student trying to learn this relativity and want to know from experts whether or not I am right

Hello, Is it conceivable that there is a fundamental flaw in GR like this: Could it be that it is as impossible to curve spacetime in GR to the point of reducing the size of objects to 0 as it is for matter in motion to reach the speed of light and be contracted to a length of 0. The curvature would have to be non-linear, and it would be increasingly difficult to curve space to the point that the formation of a black hole is not possible because it would require infinite energy. This would mean that Einstein's equations would not be good. What is wrong would not be the form of the curvature but the coupling between energy and curvature, which in…

I have put together 3 configurations, the first (config a) depicting gravity's strongest point, I am assuming the answer is "A", but if its not, please explain why. the second (config b) depicting light of sight, again, I am assuming the answer is "A" (nevermind where the sun is in the image), but if its not, please explain why. the third (config c) is depicting both of what config a and b did, I am assuming "A" is the correct answer for both. either way, if the answers are "A" why is the spacetime curved like such? if the answers are "B" then why is the line of sight way off? for example, I wanted to be sure to use a black hole in config c, to show the exaggerated eff…

I was doing some new learning as I do from time to time the other day learning a little about the history of neutrino's. The thing that stood out the most for me was the discussion on whether they oscillated or not and the reasoning behind it. It was once thought they had no mass, and without mass it was impossible for them to oscillate, so therefor either there were different types of neutrino's or they had mass to allow them to oscillate. In return, this gets the blood flowing on the thought of speed of light vs time. The argument against the neutrino's not having mass was that they would experience no time because they would be restricted to moving at the speed of lig…

If we want to accelerate very long train, instantly accelerating each railway carryage into a moving frame at v, then we should accelerate them simultaneously in neutral simultaneity. t =to + (gamma -1)*x/(v*gamma)

Falsifiability Falsifiability, a core principle in the philosophy of science, means a theory or hypothesis is scientific only if it can be potentially proven wrong through empirical evidence or logical contradiction Question: Would re-run of Hafele–Keating experiment with a twist, where different types of clocks are being used, disprove relativity if depending on a clock you would observe significant differences in time loss or gain? For example: Cesium, Rubidium, Maser. Or even no gain or loss when clock with different mechanisms would be used. Would that be enough to prove that relativit…

Consider a current carrying circuit with a straight side. Because of length contraction, in the straight side the moving electrons will appear closer together than they would be if there were no current. This gives a greater charge density, so the straight side should have a negative charge. But this is not observed. How come?

Why do scientist always say that mass bends space, and not that mass is product of bending of space? To me it makes much more sense that mass and energy is caused by curvaton of space time and not the other way around. They are simultaneous phenomena's and its is impossible to say what was first. Maybe the mass is manifestation of space curvaton over some level and energy is manifestation of space under some level. I think that evidence of this hypothesis can be observed in experiment where same amount of mater and antimatter collide. If we presume that mater is a manifestation of space curvaton in one direction and antimatter manifestation of space curvaton in …

Do you have a favorite warp drive theory / direction? and / or Are you aware of a mechanism to measure bending spacetime in a laboratory? This question is based on the idea that there is not enough known information to construct a testable theory of faster than light travel, so a better path may be to see if spacetime can be bent in a laboratory, & construct theory if something works. In the movie, "Oppenheimer" the scientists working on the atomic bomb discussed advancing with both a theoretical & empirical strategy. So if there is not enough information to construct a viable theory, then maybe empirical options can lead to a breakthrough.

Hello to everyone. I have questions, if you don't mind me asking. Are we moving or standing still in relation to light? And what about light in relation to the Earth? And what about the Earth in relation to light?

A photon is emitted in a vacuum some arbitrary distance above a spatially isolated spherical mass equal to Earth. The photon is emitted in a parallel direction to the surface. Will the photon orbit at the same height continuously, fall to Earth or just continue out along an increasingly flat space/geodesic?

I might not be a good physist but I'm surely not dumb [ ok maybe i might]. We all know the theory of pragmatism, stated by James Sidis who advanced this theory, that makes people work through their lives, we wake up everyday, the sun is up, we know the time is either 7 or 8 in the morning according to our circadian rythyms. What if time is a construct of the mind that evolved in us over thousands of years, I meanit is true we can calculate the speed of a moving object with the help of time, but what if we constructed that into our belief, there is a reason why we cannot calculate the exact the exact speed of the springs that make up the electrons just vibrating. …

What is the nature of the motion of light with respect to itself? Does it experience time and displacement?

I have a spaceship the Millennium Falcon 2. She can travel upto 99%c, and I want to take my girlfriend Joanne to Alpha Centauri which is about 4LY away. Obviously we can't start off at 99%c, so we will be accelerating at 1G from 0 and when we get to 99%c we will switch off the engines and cruise at a constant speed until we need to turn the ship around and fire the nuclear fusion engines to slow down the ship at a comfortable deceleration rate of 1G. What maths do I need to calculate our total journey time ship's time taking into account relativistic effects? I think the factor tau has something to do with it but I'm not sure how exactly Joanne wants …

I've seen this posted on this site many times over the years and I think it's wrong but never saw a correction or explanation. It's repeated often in posts labelled "expert" but I don't understand what it means. As a Lorentz transformation doesn't a boost imply constant velocity? How can a measure of velocity be called an acceleration? How is a measure of velocity a type of Lorentz transformation? Is there some sensible meaning to what I quoted that I'm just not comprehending?

Suppose we have 2 systems ,one of which derives from the other how can one measure the difference between them (the amount of "change")? Can we assume that the first system is comprised of n constituent parts and the other m constituent parts since these parts can interact and destroy/create themselves? Do we have to connect the two systems with an array of "lines of causality "?