Relativity

There's something I'm puzzling about regarding black holes: I think it's reasonable to assume that black holes exist. But we know from GPS and other evidence that clocks run slower here on earth than they do up in space. It's not an optical illusion or some kind of observer effect, it's something real, and it's down to gravity. This means time "runs slower" as you near an event horizon, whereupon it stops. Which suggests to me that collapsing stars are collapsing so slowly as far as our time experience is concerned, that they haven't finished collapsing yet. This means there can't be any actual singularities, because as far as we're concerned, the collapse takes an i…

Something occured to me earlier. If we lived in a Universe with 4 spacial dimensions instead of 3, then E=Mc(squared) would become E=Mc(cubed). I think. Would that be correct?

I was reading an archived posted in this forum from 2004 where someone asked about how space and time appear from the perspective of a photon. The common response was that such references have no meaning when refering to a photon; that it has no frame of reference. It seems at least that there should be such a thing as a photon's mathematical perspective. If it can be in the equation, it can be put on it's own side of the equal sign as it were. If nothing else, thinking of things from a photon's point of view seems to make some physical curiosities seem a lot simpler. So here's the idea: If space-time contracts to infinitessimality for a photon, then it sounds…

Does anyone have any idea of how to explain what's actually going on here, im completely lost. Id really love to understand it at last. Vector spaces; metric: Consider R3 and the orthonormal frame (0; ei), i = 1,2, 3. Let a, b and c be three vectors of that space, with contravariant components in the basis (ei) given by ai = (−1,−1, 0), bi = (0, 0,−2) and ci = (0, 1, 2). (a) Calculate the contravariant components of the vectors a, b and c in the basis e′1 = e2 + e3 e'2 = e1 + e2 + e3 e′3 = −e2. (b) Calculate the components of the metric tensor in the new basis, as well as g^1/2 and (g′)^1/2 ------------------------------------------- Vector spaces; metric…

OK, so I had no clue where to put this, so here goes nothing. In general relativity, the variational methods used, I need to figure out the variation of the (three) christoffel symbol with respect to the (three) metric tensor: [math]\frac{\delta\Gamma^{i}_{bc}}{\delta g_{bc}} = ?[/math] the reason I ask is because I'm really looking for the variation of the Ricci tensor with respect to the metric (all of this is going on in three dimensions too, only the spatial ones) [math]\frac{\delta R_{ab}}{\delta g_{ab}} = \frac{\delta\Gamma^{c}_{ab;c}}{\delta g_{ab}} - \frac{\delta\Gamma^{c}_{ac;b}}{\delta g_{ab}}[/math] that's how I would figure it to be, so I'm wondering how …

This is something that's bugged me a little bit recently. We all know that according the relativity, the speed of light is constant to all observers. The question is, why light only? There certainly are other particles (most of them theoretical) that travel at the speed of light, like gravitons. Would their speed also be constant to all observers?

But I don't see where that clashes with galilean transformations :s Hello, new here, today is the day before my physics exams and I am having a few mental problems with my relativity study . Sorry if I seem newbish, I am but a 17 year old student. Anyway, on with the question. According to one of maxwell's equations, the speed of light depends only on the electromagnetic constants of what its travelling through. No problem there, but then I dont see why this causes a clash with classic transformations. We say that A is cycling at 0.5c towards observer B, and shines a flashlight. Then we say that both see the light travelling at speed c. I can understand wh…

I understand, to an extent, that the timespace warpage is gravity. Or rather gravity is the medium we feel timespace warpage (I'm not sure how we "feel" time, but anyway...). What I don't understand is how we know about time warpage. I'm sure an experiment of some kind has proven this. The example used in the book is the rigidly rotating disk. I can see how an observer's clock on the edge of the rotating disk would run slower than the observer's clock in the center of the disk due to the speed and etc. And I can see how that is time warpage. But that's using acceleration to produce the gravity effect. How about real gravity? How do we know that time li…

I remember hearing that in conditions near absolute zero the speed of light slows down so much you could over take a laser beam on a skateboard. Now how can this be if he speed of light is constant and should apear to be traveling at c in all frames of reference. How does the temperature affect c? Is this even a plausible scenerio?

Black holes in the early universe may have circumvented a law of physics to grow rapidly to colossal size. The finding could solve a longstanding puzzle over why such massive objects appeared so soon after the universe began. The new analysis, by Marta Volonteri and Martin Rees, both at the University of Cambridge, UK, ties up all the important factors involved in the growth of a black hole and concludes rapid growth is possible. This might be because the black hole "swallows" the radiation generated as the hole gobbles up the matter around it, preventing a destructive explosion. The puzzle first arose after astronomers spotted what appear to be monster black hole…

Hi, I have some questions. I hope you guys can help me out. Gravity affects all objects in the same way right? The motion an object makes in freefall (no forces except gravity) is independent of its mass. General relativity says an object follows it's natural path (straight line, or geodesic) through a curved spacetime if no forces are acting on it. That means nothing is really 'pulling' on an object right? When I sit in a car making a strong turn I can feel the acceleration. I get pushed against the side of the car, the car pushes on me and makes me go into the other direction. My internal organs have a tendency to stay behind too, so because of the force by bod…

I am trying to grasp if a butterfly flies in Japan the air waves can create a sonami(?) some where in the world because of it? I have also heard all things in some fashion relate to something else...except a snowflake. Is this true? pljames

So I thought about something recently.When you move (in a super-fast spaceship) at speed close to c (say 285000 km/s) the time is slowing down relative to ouside the ship. So which means that while you are sitting there for a minute, there is actually, say, 20 hours gone outside the ship. So if you look at it and measure the distance that the ship travelled in 1 second, it wouldn't be 285000 km. It would be much less. So the paradox is - the faster you are trying to move, the slower you are actually moving. Am I right? If yes, how can it be?? It doesn't make any sense! Also I have some other questions - what is the fastest possible speed we can really reach (on a spaces…

A Dr. Murphy at cambridge has found evidence that the fine structure constant, might actually have varied billions of years ago. meaning one of the fundemental constants in physics, actually isnt so constant. The speed of light also depends on "alpha", and if one varies then the other does as well ,which means that einstein was wrong. now of course their are people who are also looking into this because physicists just can't accept their entire theory of general relavitivity is flawed, but i think Dr Murphy is right. i dont want ot go into the matho fi t all so i will offer two links: http://en.wikipedia.org/wiki/Fine_structure_constant#Is_the_fine_structure_constant…

From my understanding it is impossible to go the speed of light because as you go faster you get more massive which takes more energy so it would take an infinite amount of evergy to go the speed of light. I also just learned that as you go faster you get shorter, but I don't know how this would happen if you are getting more massive. Can someone clear this up for me?

Baby Bang experiment could open door to new dimension Monday September 11, 2006 Deep underground on the Franco-Swiss border, someone will throw a switch next year to start one of the most ambitious experiments in history, probing the secrets of the universe and possibly finding new dimensions. The Large Hadron Collider - a 27km-long circular particle accelerator at the CERN experimental facility near Geneva, will smash protons into one another at unimaginable speeds trying to replicate in miniature the events of the Big Bang. "These beams will have the kinetic energy of an aircraft carrier slammed into the size of a zero on a 20p piece," Brian Cox of Manch…

Can I ask for comments on the below qouted please:

Assume a stationary observer, sending a series of "pings" at the interval of one nanosecond toward a spaceship. The spaceship also has an identical pinging device, sending one ping a nanosecond. Furthermore, the spaceship has a transponder; every time it gets a ping from the observer, it sends back a reply. (Think of the ping as a laser flash and the reply as a reflection.) The observer receives two serieses 1. the spaceship pings, and 2. the replies. The observed interval between the spaceship pings is 1+d nanoseconds (d being the time dilation factor), and the interval between the replies is one nanosecond. As far as the spaceship is concerned, the obse…

Say we have a stable wormhole that can be used for transport and decide to move one mouth of this object some vast distance at relativistic speed - at say 0.866c to hang a figure on it – and we send a vehicle through from the ‘home’ mouth to the mouth that’s in transit… Does the vehicle undergo a huge net acceleration in the direction of travel during its passage through the wormhole? Related to this: a) When the vehicle clears the ‘transit’ mouth, is its inertial frame relative to it the same as it was relative to the ‘home’ mouth? b) Or does the vehicle – once clear of the transit mouth – get left behind by the transit mouth which is moving away at 0.866…

How it so happens that a light beam traveling through a material with -ve index moves faster then 'c'?I read that 'it emerges before it enters'.What exactly does that mean?And finally,why it does not violate relativity or will a massless particle moving faster then 'c' violate relativity?Why?Whynot?also,what are the consequences(or assosiated phenomenans) of this faster then 'c' travel. Thanks in Advance. Also,if someone is intrested,here is the news link http://news.bbc.co.uk/1/hi/sci/tech/841690.stm

"Recent research has found evidence that the value of certain fundamental parameters, such as the speed of light or the invisible glue that holds nuclei together, may have been different in the past." If this is true then I'm going give up and start going to church again... (That is if it wasn't for my golf league on Sunday morning...). http://www.space.com/scienceastronomy/060711_science_tuesday.html

If a luminous source that is a digital system, meaning it can be on or off, say a lightbulb, is turned on, but at the exact same moment is launched away from your vision at the speed of light, what would one see. I belive that observer would not see anything. The light would not have had enough time to travel to his/her retina (is it retina? im no optometrist) because the source of the light is being shot away from that persons vision as quickly as the light can travel, therefore the light emited from the lightbulb would not travel away, because those opposite rays would double the speed of light. What do you think?

Whenever somebody tries to explain curvature in spacetime, they always bring up the ol' "bowling ball on a trampoline" analogy. I'm wondering, isn't this a little like using a word in the sentence that is defining it? I saw a lecture where gravity was explained as not accellerating matter towards matter, but rather that matter "moving" in our 3 dimentions of common experience was actually at rest, and the act of resisting gravity was more like moving. I was wondering if there might be a scenario analogous to this way of thinking that doesn't involve gravity in the explanaiton. Perhaps with our medium expanding away or compressing towards our pieces of matter?

SR implies (or is interpreted as) the space contraction and time dilation depends on the relative velocity of the two reference frames. B moves at .6 c relative to A. B sees objects of known dimensions passing in the opposite direction appearing contracted to .8 their length. A accelerates to .2 c in the direction opposite of B. The relative speed of separation is now approximately .8 c. This would require the contraction B sees to be approximately .6 c. The objects moving past B do not speed up when A moves. How do you explain this?

Two light sources S simoultaneously turned on; what is the relative speed (collision speed) of both light beams when propagation wavefronts meet midway ? S---------><----------S c-(-c)=? Miguel