Relativity

would something as massive as the earth fall at g or 2g towards the earth?

I was thinking about escape velocities and I ended up thinking about black holes and what would happen if someone or something fell into one. In particular, I asked myself: if something was to start still at the event horizon and then, drawn by the gravitational force, was start "falling" toward the center, at what speed would it reach the singularity? Does it even make sense to ask a question like that? I have some calculus that may make no sense, but I wanted to show it to you to know what you thought: Probably you all know how to calculate the escape velocity: E® is the initial kinetic and gravitational potential energy, on the surface of the planet E(infin…

It is said that, Speed of light is c, locally. What does locally mean here?

My brother asks me this question for which I have no answer. If gravitational effects are propagated as waves at light speed, and light cannot escape from a black hole, how do the g-waves escape?

Hi, I tried to explain relativity to somebody, and I thought of a newtonian situation where relativity would appear. And strangly It seems to be enough to generate relativity effects (without any spacetime involved).. here is the exemple : If we have a group of ships immobile on the ocean (far enough that they can see each others), and they have to communicate. So they use flying birds to carry messages from one ship to another. Birds are perfect they are never tired and always fly at the same speed according to the ocean. If one ship want's to get an information about something, in every case, it have to send a bird, and wait for the bird carrying the answer to com…

So heres my conundrum- if light can bend, doesn't that mean its velocity is changing, and therefor accelerating? My theory is that when it hits a gravity field the gravitons fragment the light, which makes it break up in multiple directions without slowing down. Am i right? Im confused because if it was the idea that its following the curveture in space then wouldnt that mean their are perpendicular curvetures to it that cancel it out?

(Sorry, I wall o' text. For ease of skipping to the question Blue text is a remedial preface. Orange text is the explanation someone else gave for the problem in the blue text. Black text is my question about the orange explanation of the blue problem.) I saw an explanation of the twin paradox online that tried to explain the twin paradox. I understand the theory that relative motion dilates time. Hense, a twin travels at .8c to an object 5 lightyears away. From their perspective about 15 years has passed, but when they come back to earth, everyone else has experienced closer to 25 years. The problem comes from the notion that all frames of reference are equall…

Recently it has been shown that Alcubierre drives can be created with orders of magnitude less energy than previously thought if they are done with the negative energy in a certain pattern. In Alcubierre's original paper, he points out that the Casimir effect could perform the job of the negative energy: So, why hasn't there been small-scale tests using plates to try to get the required spacetime geometry using negative energy provided by the Casimir effect? Or have there been such tests? I suspect there haven't, otherwise it would have been bigger news and would have shown up in my search for material. So, there's got to be a reason. Is is the rocket …

This idea came to me at work earlier today and I thought I'd post a topic about it and see what people had to say. Would it be possible to construct a large space station far away from Earth (and any other planets') gravitational pull, so that whoever on-board the station would experience a speed-up of time dilation. This dilation so great, that we could send research teams and engineers on-board these stations to research and produce cutting edge technological achievements, which will pass at a normal pace of time for the researchers, but for us dwellers on Earth, we will receive these newly advanced technologies in half the time (generally speaking)! Is this…

Hi, I’m not a physicist but I’m very curious about relativity, I read and studied a little and I have one big issue I can’t understand. Let’s make an example, it would be easier for me to explain my point as English is not my first language: There are 2 old friends Mr.Green and Mr.Red who are in their own space-ships in the middle of the universe, at this moment the 2 spaceships are connected through a door and Mr.Green and Mr.Red can meet each other. From the windows they can’t see anything, it’s all dark and they don’t have any reference point. Moreover the 2 space ships are moving forward at a low constant speed (let’s say 50km/h) in a straight line. The 2…

Ok, now first of all I never really had a clear or *satisfiable* definition or explanation for any of 12 or (13/18/........) Dimensions Out there. So I took the time to get your help Now is there any dimensions called *imaginary dimensions* the one in which ( the events occur with respect it your thaughts //the events occur as you imagine them ) How do you explain or prove the very existence of each dimensions that are out there. Discus the basic concept of dimensions ie. What is a space dimension What's a temporal dimension How many dimensions do we exist in ( I aynt talking about the 3 dimensions ¤ I was referring to the space dimension…

Can the detection of gravity waves lead to anti-gravity?

From a thread in the astronomy forum: I just want to disagree with the statement that "the reason why they agree that the train doesn't get smashed is different," which I've seen stated before in these forums. The reason the train doesn't get smashed is the same in all frames: The front guillotine comes down before the front of the train reaches it, and the the back guillotine comes down after the back of the train passes by. Each of these two things describes an event that happens at a single respective location (the location of the respective guillotine), and all observers agree on those statements. The fact that the two events are simultaneous in the tun…

Hi, I imagined a hyper sphere in spacetime (an spherical event) that would be invariant by Lorentz transformation. Given a length R in a (x,y,z,t) space (around any event point) I considere the hypersphere given by : x²+y²+z²+(t*c)² = R Isn't it invariant by Lorentz transformation ?

If 2 masses are moving apart or towards each other, does the force of gravity between them vary relativistically? If a gravitational field propagates at C, and a mass originating the field is moving relative to another mass, then is a Lorentz factor needed to describe their gravitational interaction? That is: The Force of attraction given by the simple Newtonian equation: Can be rewritten by substituting: If this is mathematically correct, then 2 objects moving away from each other at velocity greater than C should experience repulsive (or anti) gravity, and in a galaxy where there are many mass pairs where v2/c2 is non-trivial, there will be s…

A lot of the older physics says information itself doesn't travel faster than light. In nearly every local frame and on its own even with entanglement, this is true. However, I have seen a lot of news like this http://www.forbes.com/sites/alexknapp/2012/09/06/physicists-quantum-teleport-photons-over-88-miles/ in the last few years and even older references to older entanglement experiments, . Even if information doesn't travel faster than light outside of certain curvatures of space, could have an entangled pair, put one component of the pair inside a black hole and potentially teleport a photon to the outside component of the pair? And why not?

I've learned through many youtube videos on things like special relativity and just general physics that there is no way to send information faster than light, because objects cannot move faster than light. This feels like a bit of a naive question but.. surely in the future it's possible for some loophole around the speed barrier to be found, or some kind of particle that does go faster (maybe a tachyon) to be found, and then could you send information faster than light? Just saying it seems like a pretty useful thing to do if it could be done

Does accelerated particle recieve the same momentum per second in particle accelerator? Does electromagnetic force have 'red shift' to accelerated particle?

Something about red/blue shifting seems illusionary, or in a way physically non-nonsensical. If I travel towards a photon that's a light year away with 0 matter and energy in between me and the photon, and a source another light-year away said before the experiment began that the photon is red, when I finally run into it, I will measure it has blue shifted. But, where did it gain the energy? If I knew it gained the energy, how did I not measure it before the amount of time it would have taken light and violate causality? The only way I can think it works is some way of modeling is the energy you put into moving towards the photon is in some way proportional to the relativ…

I read Einstein’s twins paradox (http://www.einstein-online.info/spotlights/Twins) and I found it very hard to believe. How can the traveling twin returns to find his brother older when he comes back to earth? If the aging is calculated by heart beats then both of them had the same count of heart beats during this trip. What will happen when someone is traveling with a speed as near as speed of light? Let’s think about the following scenario to understand more. If you are driving your car and look in the mirror on a car that has the same speed, then it will look like as if the car is not moving. If the speed of the other car is higher, then it will be moving towar…

With my telescope I can see a distant clock, keeping 'normal' time. (taking both time dilation and doppler into account), What do I SEE if I move away from the clock at high speed, say 3/4 speed of light ? What do I see if my speed approaches c ? On the other hand, what do I SEE if I move quickly, say 3/4 c, towards the clock ? What do I see if my speed approaches the speed of light ? Four questions . . . Thank you.

Can water be compressed? I have heard multiple conflicting views on this. Assuming that you could compress water, could you compress it to a point where any further compression would not be possible? If so then could you make a tube, full of water, and push the water from one end and have the force traverse the length of the tube instantaneously? Compression waves can't happen in water, unless I'm mistaken. I'm more then a bit confused on this and wasn't entirely sure where to post this. I hope posting this here is alright, as it has to do with faster then light data sending and the physics of water.

Suppose we do a constant Jacobian transformation (but not Lorentz) of a SR (inertial) frame by using four linear change of variables (coordinates) equations. This defines an apparent gravity field with a constant metric (but not the SR metric) in which there is apparent relative acceleration of separation and where the field clocks record unsynchronized time. From the geodesic metric equation we see that the acceleration vector depends on the first partial derivatives of this constant metric and so these derivatives must therefore be non-zero ???? Also, the velocity vector along a geodesic is constant but it defines some sort of accelerated motion. How can this be ?? …

I am driving my car at the speed of light and I turn on my headlights. What do I see?

From Wikipedia: In physics, length contraction is the phenomenon of a decrease in length measured by an observer of objects which are traveling at any non-zero velocity relative to the observer. http://en.wikipedia.org/wiki/Length_contraction Or perhaps its the grammer ?? IE: traveling ------------>at any non-zero velocity HOW CAN YOU TRAVEL IF YOU HAVE NON ZERO MOTION TO SELECT FROM????? Does velocity also work like a CREDIT CARD??? looks like it to me. Is that the observer at the very end point of this Cone?? Are They: a: laying down b: looking up c: sideways??? Does this also relate to the observer's dream…