General relativity

can anyone explain to me in layman's terms what general relativity is? or more
importantly can you provide references or illustrations to explain what it is, for i have
looked on the net and its not so easy to grasp, for me anyway.

Originally posted by robbie carrobie
can anyone explain to me in layman's terms what general relativity is? or more
importantly can you provide references or illustrations to explain what it is, for i have
looked on the net and its not so easy to grasp, for me anyway.

Get the book

Relativity
The Special and General Theory

by: Albert Einstein

It states on the back of the book that It was written for the "average person". So I'd imagine If he can't explain it to you, noone can.

As a side note, I personally feel that Einstein was fairly optimistic in his assesment of what the "average person" could comfortably grasp without training, but perhaps this just means that I fall short of what he considered to be average.

Originally posted by robbie carrobie
can anyone explain to me in layman's terms what general relativity is? or more
importantly can you provide references or illustrations to explain what it is, for i have
looked on the net and its not so easy to grasp, for me anyway.

I tend to be hesitant when it comes to linking to wikipedia, but they do a good job explaining it and some of the implications of it.

http://en.wikipedia.org/wiki/General_relativity

edit: and this is it without so much of the technicals and mechanics

http://en.wikipedia.org/wiki/Introduction_to_general_relativity

and some of the observed applications of it

http://en.wikipedia.org/wiki/Tests_of_general_relativity

Originally posted by joe shmo
Get the book

Relativity
The Special and General Theory

by: Albert Einstein

It states on the back of the book that It was written for the "average person". So I'd imagine If he can't explain it to you, noone can.

As a side note, I personally feel that Einstein was fairly optimistic in his assesment of what the "average person" could comfortably ...[text shortened]... aining, but perhaps this just means that I fall short of what he considered to be average.

thanks but that was practically useless, which is not an assessment of you, more of the nature of the theory. Can it really be so hard to grasp conceptually if it is well illustrated?

Originally posted by ua41
I tend to be hesitant when it comes to linking to wikipedia, but they do a good job explaining it and some of the implications of it.

http://en.wikipedia.org/wiki/General_relativity

edit: and this is it without so much of the technicals and mechanics

http://en.wikipedia.org/wiki/Introduction_to_general_relativity

and some of the observed applications of it

http://en.wikipedia.org/wiki/Tests_of_general_relativity

thanks ill try this, but me thinks there must be a site for total noobs, general relativity for kids or something, that's more my level.

something like this

The Theory Of Relativity:

A Clerk in a Swiss patent office realized that Newton's law of gravity while right most of the time, was incorrect when talking about very large and very distant objects. This man's name was Albert Einstein. Einstein revised Newton's laws of gravity to make them more accurate. We call what he developed the theory of relativity.

It is actually two theories. The first is called Special Relativity. This theory states that it is impossible to determine whether or not you are moving unless you can look at another object.

Think about that. If you were in the middle of outer space far from any other objects how would you know whether or not you were moving? All movement is relative to other objects. For example, right now relative to your computer you are not moving at all, but relative to the distant quasars you are moving at near the speed of light. Relative to the Earth most meteorites move at about 25,000 miles an hour, but if you were standing on a meteorite looking at another meteorite going in the same direction as you, and at the same speed it would not appear to move at all.

Special Relativity also says that the speed of light is always constant. This means that no matter what you do to light it will always go the same speed. (Scientists are learning how to make light go faster but it is very difficult).

The Theory of General Relativity is the one which redefined the laws of gravity. It says that it is impossible to tell the difference between gravity and the force of inertia from a moving object.

In other words if you climb inside of a spinning spacecraft the inertia will cause you to move towards the outside walls in a way that would feel just like gravity. This is why future spacecraft designs often have large spinning cylinders attached to them.

The Theory of General Relativity also says that large objects cause outer space to bend in the same way a marble laid onto a large thin sheet of rubber would cause the rubber to bend. The larger the object, the further space bends. Just like a bowling ball would make the rubber sheet bend much more then the marble would.

http://www.kidsastronomy.com/academy/lesson210_assignment3_8.htm

there, thats my level.

Something like that. The principle of relativity states, broadly speaking, that the laws of physics are the same for all observers (for example you can play pool on a - very smoothly running - train or at a bar, it doesn't matter). This wasn't a new idea, but the new idea is the following. When Maxwell developed his equations for electromagnetism, physicists found that they violated the principle of relativity. They attempted to fix this by introducing the "ether", you can regard this as a sort of "absolute" frame. This would also imply that light moved at different speeds depending on their direction with respect to the ether. However, in the late 19th Century it was experimentally found that this is not the case.

Einstein realised that it wasn't Maxwell's equations that needed an ether, but instead the normal equations of mechanics (e.g. Newton's laws) needed to be adapted so that the principle of relativity is satisfied in both. You can do this by assuming the speed of light is constant for all observers, and this is what Special Relativity does.

General Relativity expands on the idea by connecting gravity with mechanics and unifying them, thus giving a general theory that gives rise to the bending of spacetime, black holes, etc.

Originally posted by joe shmo
Get the book

Relativity
The Special and General Theory

by: Albert Einstein

It states on the back of the book that It was written for the "average person". So I'd imagine If he can't explain it to you, noone can.

As a side note, I personally feel that Einstein was fairly optimistic in his assesment of what the "average person" could comfortably ...[text shortened]... aining, but perhaps this just means that I fall short of what he considered to be average.

I have read this book. I could not agree more with this recommendation. Einstein had the reputation of being a good teacher as long as his student was willing to put in the effort, and judging by this book, that was thoroughly deserved. Yes, you do need a decent basis in Newtonian high school physics. Yes, you need to be prepared to read through some, not all that complicated, maths formulae. But do that, and I have yet to find a book which explains the matter more clearly and more thoroughly.

It is, I agree, not really a book for the average person. Rather, it's a book for the average already interested layman, which is a higher standard. But it's not a book for the expert by any means.

Richard

Originally posted by KazetNagorra
Something like that. The principle of relativity states, broadly speaking, that the laws of physics are the same for all observers (for example you can play pool on a - very smoothly running - train or at a bar, it doesn't matter). This wasn't a new idea, but the new idea is the following. When Maxwell developed his equations for electromagnetism, physi ...[text shortened]... giving a general theory that gives rise to the bending of spacetime, black holes, etc.

Thanks KazetNagorra, i find it utterly fascinating although a total noob and not that brainy either, how can space bend though? its not like its made of anything, is it? is it? I mean, how can gravity push or pull something that doesn't exist, or is not tangible? surely it must have some mass for gravity to work?

Originally posted by Shallow Blue
I have read this book. I could not agree more with this recommendation. Einstein had the reputation of being a good teacher as long as his student was willing to put in the effort, and judging by this book, that was thoroughly deserved. Yes, you do need a decent basis in Newtonian high school physics. Yes, you need to be prepared to read through some, n ...[text shortened]... ayman, which is a higher standard. But it's not a book for the expert by any means.

Richard

do you have any illustrations about travelling at the speed of light and what it would appear like, would everything be frozen to a standstill? or any illustrations that helps me grasp the principles for naturally the mathematics will be quite beyond a noob like me.

Originally posted by robbie carrobie
can anyone explain to me in layman's terms what general relativity is? or more
importantly can you provide references or illustrations to explain what it is, for i have
looked on the net and its not so easy to grasp, for me anyway.

I will have a go at explaining general relativity in rather over simplistic terms but in terms that I hope any layperson would understand:

firstly, there are two parts of relativity: “special relativity” and “general relativity”.
The one thing they both have in common is that they are both, at least in part, derived from assuming that the speed of light is always the same for all observers. ( More importantly, they also both assume that the “principle of relativity” is correct which is the requirement that the equations describing the laws of physics have the same form in all frames of reference but, in case you get confused by the meaning of “ frames of reference”, I will avoid that term here. Where the two theories differ in the most fundamental way is that “special relativity” is derived from considering only non-accelerating frames of reference while “general relativity” is derived from considering only accelerating frames of reference )

But “general relativity” mainly deals with the effects of gravity and acceleration while “special relativity” doesn't.

General relativity explains gravity by saying that, when you fall to the Earth, although in a three-dimensional sense you ARE accelerating towards the Earth, in a forth-dimentional sense it is not you that is accelerating towards the Earth but the surface of the Earth that is accelerating toward you! That is because three dimensional space is curved in four dimensions.
That does not mean that the Earth is acceleration outwards and thus expanding in three dimensions because, remember, Earth is not accelerating this way three-dimensionaly but forth-dimensionaly.

I have carefully avoided how time relates to this above (which it does) to make it easier to understand.
If you take into account how time relates to this above then one prediction general relativity makes is that the planet Mercury's orbit should appear to wobble as seen from the Earth due to it being much further into the gravity well of the sun -and, indeed, it does and it has been observed to have exactly the amount of wobble predicted by general relativity! -that is very powerful evidence!

Originally posted by Andrew Hamilton
I will have a go at explaining general relativity in rather over simplistic terms but in terms that I hope any layperson would understand:

firstly, there are two parts of relativity: “special relativity” and “general relativity”.
The one thing they both have in common is that they are both, at least in part, derived from assuming that the speed o exactly the amount of wobble predicted by general relativity! -that is very powerful evidence!

actually i think you are confusing simplicity with clarity, never the less, i thank you for
drawing the distinction between special and general relativity, although as yet, you
leave the matter of the fourth dimension unresolved, indeed what is this fourth
dimension which you cite and which has such an effect on the other three dimensions.
Once i can understand what this fourth dimension is, then we can talk of its effects on time.

Originally posted by robbie carrobie
Thanks KazetNagorra, i find it utterly fascinating although a total noob and not that brainy either, how can space bend though? its not like its made of anything, is it? is it? I mean, how can gravity push or pull something that doesn't exist, or is not tangible? surely it must have some mass for gravity to work?

The "bending" of spacetime is a way to visualize what is going on mathematically. What it means is that e.g. a light ray passing near the sun will bend.

Originally posted by KazetNagorra
The "bending" of spacetime is a way to visualize what is going on mathematically. What it means is that e.g. a light ray passing near the sun will bend.

ok, i found this,

The theory explained

When Einstein wrote his general theory of relativity in 1915, he found a new way to describe gravity. It was not a force, as Sir Isaac Newton had supposed, but a consequence of the distortion of space and time, conceived together in his theory as 'space-time'. Any object distorts the fabric of space-time and the bigger it is, the greater the effect.

Just as a bowling ball placed on a trampoline stretches the fabric and causes it to sag, so planets and stars warp space-time - a phenomenon known as the 'geodetic effect'. A marble moving along the trampoline will be drawn inexorably towards the ball.

Thus the planets orbiting the Sun are not being pulled by the Sun; they are following the curved space-time deformation caused by the Sun. The reason the planets never fall into the Sun is because of the speed at which they are travelling.

According to the theory, matter and energy distort space-time, curving it around themselves. 'Frame dragging' theoretically occurs when the rotation of a large body 'twists' nearby space and time.

this was also pretty awesome,

http://www.youtube.com/watch?v=0rocNtnD-yI