Relativity

Request for opinion - Do you think there are any logical problems in defining the the term "inertia" to refer to the resistance of body to a change in mometum? The fact that inertial mass is defined as m = |p|/|v| seems to suggest this definition. Pete

what experiments, if any, have been invalidated by the extinction phenomena.

Does the "speed of light" change. I just had a thought .I know that sound waves go faster when going through denser objects!! does the speed of light change when going through denser objects??? If yes, what speed do we clasify as 'speed of light'(not the actual speed)when light travels through a vacume???? thnx guys!!

Hi, new guy here. There are a couple of things I have issues with concerning the relativity theory. The first is the matter of accelerating a mass up to the speed of light. It is said that doing this would require infinite energy and that this is supported by particle accelerator experiments. When you are accelerating a particle with energy supplied from a system at rest, it is true that you would require infinite energy. It's all relative right? If the energy for acceleration was supplied from an on-board energy source on a spaceship, the mass of the energy source (and it's energy) would increase at the same rate as the mass of the spaceship. I can't see how…

Hello all members of SF, for my first post, I'd like to ask a question which has been bothering me for a while. It may be because my understanding of physics is still pretty rudimentary, but I haven't been able to figure it out, I hope one of you may be able to help. Any ideas are much appreciated. So, here it is: Two large, round magnets are placed on rods in a way that they are very close to each other and then accelerated in a circular motion (like a top spinning, not like an orbiting planet) at close to or at the speed of light, but in opposite directions. What happens? Thanks in advance.

Imagine a universe in which all that exists are three balls(one red, one blue, and one yellow). Each ball has a mass of 1kg. The red and blue balls are at rest with respect to each other, but are moving with respect to the yellow ball. From a reference frame in which the yellow ball is at rest, the red ball and the blue ball are moving and thus have kinetic energy. Now, let's move our reference frame to one in which the blue ball is at rest. The red ball at rest relative to the blue ball, so has no kinetic energy(and neither does the blue ball). The yellow ball, however, is moving and thus has kinetic energy. The red ball has more energy in the reference frame of the yell…

IF the total universe for whatever that is collectively was at zero point energy hypothetically speaking what would gravity look like?

Hi! I'm studying physics for quite some time, and some time ago a thought popped up in my head....: In classical distance measurement (Einstein, 1905) a lightsignal is emitted, and the time delay "T" is measured, it takes to reflect at a distance "X". Einstein said the observer has orientation with the starfield surrounding him. I'd like to ignore this assumption. So let's say it's dark and cloudy within a cosmic nebular. And an observer flying there wants to measure the distance to the (dark) spaceship next to him. He send a lightsignal, and gets it back, after T. All fine. But what if he recieves it from a different angle, than he emitted the lightsignal…

Equivalence Principle is absolutely wrong!!!! The "gyroscope experiment". (experiment 14, at {website link removed}) This experiment is the end of Relativity Theory...!!!! tsolkas

The physicist Tom Roberts once wrote in a trash-filled newsgroup that Einstein discussed the hidden postulates of special relativity in his "Jahrbuch" article of 1909. Today I checked a Wikipedia article (another unreliable source) on special relativity, in the section titled “Postulates”, and found that it mentions “several tacit assumptions,” one of which is “the independence of measuring rods and clocks from their past history.” The reference cited there is Einstein, "Fundamental Ideas and Methods of the Theory of Relativity", 1920. I’ve never heard of an experiment to test “the independence of measuring rods and clocks from their past history.” If this principle i…

Lets just take a moment to consider relative measurements... I'm on a train an throw a ball forward at 10m/s To me be ball is moving at 10m/s But compared to the earth the train is moving at 20m/s So compared to my friend Bill stood at the station I've thrown the ball at 30m/s. So even classically velocity measurements are all relative. One of the things that comes with more advanced physics is the lack of an absolute frame of reference, and another is that velocities don't add in the way they do classically as above.

if i were to travel to a star...say 5 light years away (10 LR round trip) at 99.99999999 percent the speed of light and then come back to earth...which of the following would occur: 1) 10 years would pass for me (the traveler) where thousands of years would pass for those back on earth or, 2) a few hours would pass for me due to time and space dilation, and 10 years would pass for those back on earth thanks

I was reading a book about General Relativity the other day, and something occured to me; there may be a serious flaw in Einstein's reasonings. What jumped out at me is that although the common analogy of a bowling ball making a dent in a trampoline is a convienient way of grasping the concept of General Relativity, the flaw lyes in the fact that that analogy deals with a 3D ball (the sun) and a 2D surface (spacetime?) but this view is not applicable in the real world because spacetime is not two dimensional, it is three dimensional. This obviously means that there is a flaw in the common understanding of General Relativity, because that would mean that a 3D object would …

I found this video talking about time slowing down the faster you travel. Is it possible that this video is real? http://www.metacafe.com/watch/1366485/stop_watch_this/ I kinda think it's fake ...but I dont know. Richard

why would it matter? it seems people think that you can go back in time by exceeding the speed of light. why? wouldn't you just arrive at your location faster than the light would? as far as my logic goes, the only difference is that it'd be dark when you stopped. and if going faster than light does enable us to go back in time, shouldn't we also de-age? if we age going slower than lightspeed, shouldn't we stop aging at lightspeed, and de-age if we exceed lightspeed?

Hello, newbie here from Washington DC, no background in physics or higher mathematics, but very curious about theoretical physics nonetheless. I've been reading various articles about the speed-of-light and I came across a statement that intrigued me: Everything travels at the speed of light. Now, I realize that most of this motion for everyday objects is diverted in both the time and space directions, so that theoretically an object at rest is travelling through spacetime at light-speed through the time direction while light travels at this speed through space. But my question is this: "objects at rest" that travel at the speed-of-light through time DO NOT app…

need some clarity does light travel in a straight line? does it bend with different mediums? is light speed constant through different mediums or does ir slow down? what changes the wave length of light as red has the longest and purple the shortest? when you answer are they the same when light is exposed to gravity (except black holes)?

How does special relativity affect a gravitational field? I'd think that because the radius becomes smaller and the masses become bigger, the field is magnified by a factor of gamma^4. Is that right? =Uncool-

Am doing problems at the end of a chapter on "Vector Analysis in SR" Got stuck when asked to find the "elapsed proper time for the body as a function of t (Integrate d[math]\tau[/math] along its world line)" The body concerned here is "uniformly accelerated" ie "its acceleration four vector has constant spacial direction and magnitude" Ignoring y and z for the moment is the world line given by x = 1/2at^2? If so how do I get from there to [math]\tau[/math] as a function of t? As v is increasing the [math]\gamma[/math] is of course a function of time too - hence the integration I think. Have already found the relationships for speed and distance as functions …

Both of the books I have only derive the LT for motion of the frames parallel to the x axis. OK, this keeps the maths simple and also covers motion parallel to any other axis. But nowhere have I seen the LT for a relative velocity v which has components in each of the 3 spacial dimensions. I understand that the x values will only be effected by the x component of the velocity - and similarly for y and z. But what about t? So I guess my question is what is the "t" transform in this case? John

General Relativity Einstein worked (from) Newton’s equations describing matter and gravity: And he also changed a lot of it too, describing gravity in whole new terms to physicists. Newton’s law of gravitation is given as: F = G M_1M_2/d^2 Where G is the gravitational constant, m1 is mass one, and m2 is the second body with mass, and F was the force distributed between them. Also, Einstein worked with the already existing equation describing the laws between two masses m_1 and m_2, finding a square force that weakened over greater factors: Charles Augustine de Coulomb in 1785 showed that the force of attraction and the force of repulsion between two electrica…

In physics, when we consider a particle and its past, present and future path throughout the universe, we call its definite path a ‘’worldline.’’ A particle will always try to move in straight lines throughout spacetime, but because space and time are curved into each other, most of the time, they follow curved paths through space. This is what we mean by a warped space, or distorted spacetime. We find that these distortions are in fact just gravity, or curved spacetime. And gravity is the presence of matter itself. Even light cannot escape the wrath of gravity at very strong levels, but usually, a tiny photon traveling in empty space will almost definitely travel i…

Einstein first derived his transformations of coordinates and times in section I-3 of ON THE ELECTRODYNAMICS OF MOVING BODIES. The physical predicates of that derivation were his two Postulates, which Einstein believed were "only apparently irreconcilable". The implicit purpose of all that follows was to remove that irreconcilability. Einstein's First Postulate: "...to the first order of small quantities, the same laws of electrodynamics and optics will be valid for all frames of reference for which the equations of mechanics hold good*i.e. to the first approximation." Einstein's Second Postulate: "...that light is always propagated in empty space with a definite…

Events have allready occured in the past,and have not yet occured in the future. They can only occur "now". But how long is "now" ?

As a layman, I have a few questions about the Michelson-Morley experiment that proved the nonexistence of an ether. In the experiment, what was the nature of the supposed ether? Was it assumed to be stationary or in motion? Was it considered to be a substance or an energy?