Relativity

Traveling faster than light, is it possible? here are 2 contradictory answers: First off, the tachyon paradox: and here is a contradictory article: http://scienceworld.wolfram.com/physics/Tachyon.html What do u think?

*If this is in the wrong place, my apologies. I'm throwing out ideas, but they are relevant to actual physics. --------------- I was thinking, what if there is no universal rest frame? Working off of relativity, the upper limits of x,y,z velocity would be the velocity of the slowest thing in the universe + c. If it were accelerated, then the upper limits of velocity would increase. The slowest thing in the universe would be the referance frame for momenta, and thus an increase in slowest thing would transfer momentum throughout everything in the universe. This seems to lead to an acceleration of velocity towards infinity, which as best I can tell is not th…

well from what Ive read about black holes is that in them the space time curvature is infinite, because the black hole itself is in fact a singularity so it has infinite density so wouldn't one of the implications of this be that all point particles are in fact black holes?

Hi all, Newton's law of gravitation states the force between 2 masses M1 and M2 is equal to F = G M1 M2/ d^2 My question is simple: Case 1: If both masses are both travelling at relativistic speeds (referred to observer), next to each other, on parallel paths, what would the force be. Case 2: If both masses are travelling at relativistic speeds (referred to observer), on the same path, one behind the other, what would the force be. Thanks Blaze.

This is my first post, but I read most threads in the Relativity forum, and I still havent found a clear and explicit answer to the following question, concerning the Twin Paradox. When one of the twins accelerates and travels near c and then gets back, it's said that he appears younger because he has undergone some "heavy acceleration", which has made the time rate for him to pass slower. However, arent all reference frames equally valid? I know, you'd say it's not the same with acceleration and GR, but why wouldnt it be? Basically acceleration is defined as change of velocity vector in a period of time. We know that velocity is relative to the observer, so conseque…

I think the title of my thread explains what I'm going to say. If someone were to build a time machine and go back in time, and ettempted to change history by, say, telling Abraham Lincoln not to go to Ford's Theater, for he'll be shot by John Wilkes Booth. Would this change Lincolns mind about going, and thus avoid the whole thing, or would that be the cause of Lincolns going in the first place (temptation)? If the former is true, I wonder if the original timeline would have ever existed at all, and what would happen to intellegent beings of that timeline, would they all just die, or would they stay but not really exist?

I was just wondering this, because in all my contemplating about velocity and special relativity, I tend to get confused as to what physical attributes of objects get affected in what way. That is, when an object speeds up, does it's mass increase or decrease, does its length increase or decrease. Know exactly what way each attribute changes would surely resolve a lot of pseudo-paradoxes that I arrive at when I try (my damnedest) to visualize such scenarios. I also get confused when trying to remember in what way these attributes change depending on whether I'm talking about the observer or the observed, or the traveler or the stay-at-home. Also, in what way does the DIRE…

There's something I've always wonder about general relativity and what it has to say about the workings of physical laws. Here's a scenario: You're sitting in a space pod and you push on the engine throttle cause the pod to accelerate forward. You feel the force of acceleration pushing you back against your seat. Now what general relativity says about this scenario is that you can look at it two ways: 1) that the pod is accelerating forward and it is the forward moving force of the seat against your back that you feel, or 2) that there is a gravitational field behind you and all objects of the universe fall under its influence, except you and your pod because the forc…

According to general reletivity, there can be no absolute time, thererefor, there is no way to build a clock that can be the same time for everyone. Yet special theory says that light is the same speed to all observers, no matter what there speed. Why not build a clock that measures the speed of light. For example, say when light reaches point A to point B, we count that as one second, or something [of course that would be a sort of artificial time, but it would deffinitly help people never be late (of course, the time difference of moving at 2km/s and 0km/s would be so small we don't even count it)]. Every second, or what have you, a radio signal would be sen…

Hi! My second post apparently, also in the form of a question. (if u havent noticed the thread sister of this one) This time about time dilation. It's a common experiment to prove time dilation with the light reflecting a mirror, observed from a reference frame moving with velosity near c (vertical light beam path vs. horizontal movement), thus creating the right angled triangle. And I understand this. However, what would be the effects on time dilation if the movement of the observer relative to the mirrors was in the same direction as the light beam path? And what if it was the opposite direction? I forward the notion, that this way time dilation cant be proven. I…

Relativity is all about how light behaves, and from that some truth is differentiated from some myth. Light's behavior is particularly at issue because the cosmos is ever expanding... some of the very distant galaxies are receding from us at near light speed -- we find that true while looking in any direction. Getting right into it, if a fleet ("The Fleet") of spacecraft left Earth and headed out into space, moving at a significant fraction of lightspeed, then how would light (and/or radio, EM) signals behave between us and them? And how would such signals behave amongst The Fleet members themselves? Would a radio signal sent from Earth take extra time to reach T…

On the general science forum there was a thread about if we can go faster than light speed or not. I wanted to reply posting why it isnt a barrier but the thread was closed. I think no matter if it is like other threads, I come here to talk if not I will spend time on the library in silence. The point is: we can travel faster than light speed?. Yes. Speed/aceleration is acumulative, it depends on mass and energy. The lightspeed is only the barrier of the "showed" speed, faster than that is not noticiable so we dont know what move faster than light.

Let's say you have two stations a short few miles apart, straddling the actual (not magnetic) North Pole. You shine a strong laser pointer from one station to a target positioned at the other station, employing a precalculated bearing/aim that would hit perfectly true if it weren't for Earth's rotation. Where does it hit? ..and if you're answer is "just west of true" then I question how all of a sudden there's a preferred 'aether' frame with respect to which light moves. Do you think it kind of "defaults" to the next higher 'realm', and behaves as if it's in Earth's center's inertial frame?? Duh.

Imagine a laser beam shining at the moon. if you move the beam. with enough angular velocity. due to the fact the the points speed at distance r is spped = ang. vel times r. wont that point of light be moving faster than light on the mmooons surface. And if that is true, would we see a discrete set of points like firing a machine gun while moving fast enough.

If I understand special theory of relativity right, than mass is not the amount of matter in an object, but rather the amount of energy in it. This question just came to me out of nowhere, but how much energy does it take to equal a gram?

Do any of you believe that time travel is not possible as evidenced by the Grandfather Paradox or do you believe that there is an aspect of releativity in the timeline backwards [or parallel universes] that would permit sucsessful time travel?

Yes it can be shown that say for examaple a planet orbiting a star it is the instaneous psotion of the star that is important to how a star will affect that planet grvaitionally, BUT this not what we talk about when we talk about 'the speed of gravity'. Light is an electromagnetic wave and it is produced by a 'changing' electrogmanetic field. Electromagnetism and gravity are simalir in sevral ways (the most obvious being the inverse square law), in general relativty 'changing' gravitatioanl fields produce gravitational waves which is analgous to light, it is the speed of these wave sthat we call the speed of gravity; stars generally do not produce gravtitional waves (…

Is E=mc2 only appied on the earth? I thought the gravity provide potential energy which is different from other planet.

[math]t=\frac{t}{\sqrt{1-\frac{V^2}{c^2}}}[/math] [math]m=\frac{m}{\sqrt{1-\frac{V^2}{c^2}}}[/math] [math]d=d{\sqrt{1-\frac{V^2}{c^2}}}[/math] and, of course, the famous one: [math]E=mc^2[/math] How did Einstein derive these equations?

Soz if i got the dudes name wrong, I was wondering if any body knows of any good books/sites or has any good interpretations themselves into the principle of least time/most time? I dont get what it means when "there is no change in the first order time, just a change in the second order time??? Im finding this principle very hard to pick up and would appreciate the help.

Here is an excellent compendium of links that extrapolate the mathematics of special relativity to create very interesting visualisations of the bizarre effects of travelling near the speed of light. http://ourworld.compuserve.com/homepages/anima/rfslink.htm

I know electrons have wave-particle duality but they also have mass , even if very small . When one generates electricity , is one actually doing the reverse of E = mc EE 2 & generating mass ?

If ANY mass crosses the event horizon of a black hole , it is accelerated to c ( light speed ) . The mass becomes infinite & hence the energy release becomes infinite ( even if time ( to an outside observer ) stops . Yet black holes seem to exist & must have accreted mass ( maybe the source of energy for quasars ? ). Infinite is infinite so how come the universe is still here ? Is Einstein only approximately correct ?

WARNING: THIS THREAD CONTAINS STRING THEORY AND MAY NOT BE SUITIBLE FOR CLOSE-MINDED PEOPLE. As we have seen in other threads, speed can change a circle(in this case a string). My previous examples of this dealt with rotation. Forward motion also affects a circle, only not as much. Perhaps it changes the vibrational pattern of said string enough to alter its mass.

when Relativity is quantized you get a maximum energy density a good recent paper is http://arxiv.org/gr-qc/0407074 Genericity of the Big Bounce in isotropic loop quantum cosmology Date and Hossain When it is quantized, the big bang does not contain a singularity (a place where energy density and curvature increase out of control and the model blows up) Instead of being infinite the density has a finite limit and they calculate it. when relativity is quantized so that you get a quantum model of cosmology, it approximates the classical very closely exept around the ex-singularity of the big bang----and there you get a "bounce"----a changeover from contrac…