Could someone please explain to me what the theory of relativity is to me?

I have googled the theory of relativity and have read information about it on many links and I still don't get the meaning or concept of it. Could someone please explain to me what it is and how it is related towards objects in the universe?





I will choose a best answer.|||In short:


You are moving. Someone else is not. When both of you look at some external event, the two of you see different things. This is because of time.


Imagine you are moving very swiftly down a railroad track, sitting on a flatcar.


You are facing sideways. You hold two mirrors, so you can see both in back of you and in front of you. An observer is sitting beside the track. Just when you pass one light pole, and approach another light pole, and are exactly equidistant between the two poles, lightning bolts strike both poles at the same instant.


What does the observer see? He sees the double lightning strikes on the two poles and swears that they happened at the same time.


But you look in your mirrors and see the front pole is struck first. The pole behind is struck later. Why?


Light traveling from the poles to you takes time. You don't see simultaneous strikes. The light from the poles travel equal distances to the observer, the two times are equal. For you, the times are not equal. As light moves from the poles to you, you are changing position. You travel closer to the front pole, and farther from the rear pole. You will see the light from the front pole before you see the light from the rear pole.


Now Einstein took this rather obvious idea farther. What happens to a person who is moving at the speed of light? Does he see nothing from behind? And everything all at once from the front (direction of travel). And if he shines a flashlight forward, does the beam not exit?


And what about gravity? If Einstein was in a falling elevator, and he was falling as fast as it, would he be without gravity? And is this like being in space? And if he was in space, in an elevator that was rising faster and faster, being pressed down to the floor at one G, would this be just like he was standing motionless on Earth? These ideas and others will confound you and me for a long time.|||General Relativity


General relativity is a theory of space and time created by Albert Einstein and published in 1915. The central idea of general relativity is that space and time are two aspects of something called spacetime, which is curved in the presence of matter, energy, and momentum, (picture a funnel where a planet or star is at the bottom of the funnel and the funnell is made of "spacetime")


http://simple.wikipedia.org/wiki/General鈥?/a>





Special Relativity


Suppose you are moving toward something that is moving toward you. If you measure its speed, it will seem to be moving faster than if you were stopped. Now suppose you are moving away from something that is moving toward you. If you measure its speed again, it will seem to be moving more slowly. This is the idea of "relative speed."





Before Einstein, scientists were trying to measure the "relative speed" of light. They were doing this by measuring the speed of starlight reaching the Earth. If the Earth were moving toward a star, the starlight from it should seem faster than normal. If the Earth were moving away from a star, the starlight from it should seem slower than normal.





They noticed that no matter who performed the experiments, where they were performed, or what starlight they used, the "relative speed" of light was always the same.





Einstein said this happens because there is something odd about distance and time. He thought that as the Earth moves through space, our clocks slow down (ever so slightly). So, any clock used to measure the speed of light is off by exactly the right amount to make light seem to be moving at its regular speed.





Also, Einstein said that as the Earth moves through space, our measuring devices change length (ever so slightly). So, any measuring device used to measure the speed of light is off by exactly the right amount to make the starlight seem to be moving at its regular speed.





Other scientists before Einstein had written about light seeming to go the same speed no matter how it was observed. The idea that made Einstein's relativity so revolutionary is that light does not just seem to go the same speed, it is always going the same speed no matter how an observer is moving.


http://simple.wikipedia.org/wiki/Special鈥?/a>





If you type:


simple explanation relativity





into any search engine you can find good stuff





http://www.squidoo.com/relativity_explan鈥?/a>





or go to youtube, I think that would be your best bet. Just type in relatvity, there are some vids in there|||Both special and general relativity are surprisingly simple. They fall from these statements:





Special Relativity:


(A) The speed of light is c.


(B) All observers in uniform motion (straight line, no acceleration) observe the same laws of physics. There is no "special" frame of reference, no absolute rest.





General Relativity:


(A) All observers in any motion observe the same laes of physics. This is a generalisation of the special relativity (A).


or equivalently:


(A') Acceleration and Gravity are indistinguishable. In fact, they arent pysically real effects but merely two sides of the same underlying physical entity... space-time curvature.





These principles are very common and everybody can agree to them. For example, you wouldnt want to make an entirely new set of physical laws for someone living on Venus, just because Venus moves rapidly relative to Earth. Physics there is the same as it is here... including the speed of light, the boiling temperature of water, the spectral lines of atoms and so on... Also, the physics of a person in a freely falling elevator is the same physics as the physics of someone floating in spaces with zero gravity. If you agree to and understand these, you already understand relativity. No math needed at all.|||the simple meaning is,every physical measurements we measure are relative to other things.there is no any absolute measurement. if we measure the speed of bus relative to bus halt,and relative to


other moving vehicle,the results are different that mean there is no any absolute speed to bus.


relativity says every ting is relative to speed.|||basicly einstein said in his special theory of relativity that the speed of light is always constant in a vaccuum and time and space are not absolute, they are relative. his general theory of releativity says that gravity warps space and time|||Theory of Relativity-


Relativity as is clear from the word means "Relative to something"


The theory of relativity tells us how we can interpet observations made by us under a particular set of conditions , relative to the ones made under another.


Theory of relativity has two parts:


1-Theory of special relativity- SPECIAL means that this theory works with those objects that are NOT accelerating.Its a special case of zero acceleration.


It tells us TWO things:


1-Speed of light is constant ,no matter from where you look at it.


2-Laws of physics are same for a particular frame of reference(m not sure of this one)


This is strange,consider it this way:


When you are driving a car and look at another car which is travelling in the same direction with the same speed,you will feel that the other car is not moving at all with respect to u!


Because the two velocitties got cancelled..


Its not so with energy. Imagine that you r driving the car and a beam of light rays passes parallel to you, if you measure its speed by experiment you will find it to be exactly same as the value you obtain when you were not moving and then measured velocity. You would have expected to get a somewhat lower velocity of light as judged from the moving car but its NOT so.


since speed=dist/time


and speed of light=constant


Consider a case where you are travelling in a train ,it has a mirror fixed on its roof ,a friend of yours is standing on the platform and can see inside the train. Your train is moving.


You switch on and then off a torch aiming at the mirror. The rays of light would go up, get reflected and come back so they'll cover(according to you) a distance of say 3metres(height of the roof from the torch)


but you, the torch all are inside the train and are moving with a speed relative to your friend on platform,so your friend will see that the beam of light rays will not just go up but also move horizontly covering an additional distance let this total distance be= 5metres.


Now relativity tells us that speed of light is constant no matter where you measure it from so u and ur friend both will percieve velocity=c for the light beam ,now:


speed=dist/time


so time=dist/speed


since both of you experience the same speed but different distance covered by the beam so naturally the eqn tells us that both of you will measure a different time-interval between the start of light beam and its coming back!!


This means that rate of passing of time can vary accroding to the velocity you have relative to the other. However in order for this effect to be large enough to be experienced directly , we need to travel not at the velocity of train but at a velocity comparable to the veloctiy of light say 99% the speed of light then the difference in time interval for the two persons will be so much that like say one would have aged just 5 yrs while the other one at the platform would have aged 20 yrs! (remember he will measure greater distance so greater time).





Theory of General Relativity includes accelerating bodies and is much moe complex and difficult.


It tells us that particles having mass modifies/warps the space and time around it.


Its like ...when you throw a heavy ball on a streched rubber sheet, the ball would create a depression on the sheet. the same way mass is like the ball and the sheet is analogous to sapce and time. The bending of space around a mass results in gravitational force because other nearby masses(even energy) follow the bending of space and consequently fall into the depression. just like a smaller ball would fall into the depression created by the heavy ball on the sheet!


The theory also tells us that mass modifies time around it so that time is slowed down near a mass relative to the flow of time away from the mass!


Einstein gave the equivalence principle in which he said that gravity and acceleration are equivalent.


i.e. acceleration can provide the same thing which gravity provides and vice versa.





Check out this video and follow the sequence of videos(1,2,3,4,5):


http://www.youtube.com/watch?v=IM5rCpnBR鈥?/a>