Can someone explain Einstein and gravity to me, please?

[JammieDodger]

Thanks, that clears just about everything up

 

[tagutcow]

Originally Posted by Andrewc2232

Now place your apple somewhere near the Earth. Due to the sag of space-time caused by the earth, the apple will naturally "roll" down the incline towards the earth's center.

No, it doesn't. There's an elephant in the way.

 

[ComboOrgan]

It think it would be easier to try to understand special relativity first, before you tackle general relativity. Special relativity deals with the relationship between space and time, and between momentum and mass. You'll learn the meaning of the famous E=mc^2 The book I used is this: http://www.amazon.com/Spacetime-Phys.../dp/0716723271 and I found it very easy to follow. GR adds gravity into the mix, and it makes things much more complicated Most physicists don't ever use (or even learn) general relativity, as it's simply not relevant to most fields. At my school, GR is offered as a graduate elective only, and I don't plan to ever take it. But if you want to go there, then by all means.... Some friends of mine took the class, and they enjoyed it. They said it requires a lot of math. I think you can achieve a popular understanding of special relativity with little more than high-school math, but general relativity uses things like tensors which one usually doesn't learn until until he has taken several semesters of college math and/or physics.

 

[HORNS]

Originally Posted by tagutcow

No, it doesn't. There's an elephant in the way.

ROFL - Is this a reference to what a kid wrote on his science test?

 

[clee1982]

I think the only way to know is to learn it for real, translation between science to natural language is always hard, and very prone to error. As we always need to draw analogy, and analogy doesn't really exist in such case (or at least the ones most people are familiar with).

 

[dropbeats]

thisi s some **** that woudl blow yourmind if you were stned

 

[dropbeats]

Originally Posted by dropbeats

thisi s some **** that woudl blow yourmind if you were stned

which i am right now hahah

 

[tagutcow]

Originally Posted by HORNS

ROFL - Is this a reference to what a kid wrote on his science test?
Good call.

Here's something I've always wondered... if there's no true inertial frame of reference, how does something like centrifugal force work?

 

[aKula]

Originally Posted by JammieDodger

No I was thinking of mass increasing with increasing velocity

I have a feeling reading a book written by one of the most brilliant minds ever, may lead to more confusion... but I'll certainly give it a bash.

Also, mass distorts both space and time, yes? In what manner does a massive object distort time?

I still haven't got an answer to the apple thing, btw

I think the explanations in this thread have been pretty good.

To give you a quick answer to your question, the stronger the gravitational field, the slower time moves.

So if you had a non-rotating planet and had a clock at the base and at the top of a 1km tower, the clock at the top would move faster.

I say non-rotating so we don't have to calculate any special relativistic time dilation as the relative velocity between the clocks is 0.

Just some background: I'm in my first year of a masters degree in physics now. The maths in general relativity is difficult compared to the other subjects.

 

[ComboOrgan]

Originally Posted by tagutcow

Here's something I've always wondered... if there's no true inertial frame of reference, how does something like centrifugal force work?
Centrifugal force isn't real. We define it as an outward force felt by an observer in a rotating reference frame. A rotating reference frame is not inertial, so the force isn't "real". It's simply something we use to make certain calculations easier. What people typically call "centrifugal force" is really just a superposition of centripetal force (the central force that pulls a rotating object toward the middle) and inertia.

 

[Andrewc2232]

now if only someone could explain annihilation and creation operators to me...

 

[unjung]

http://www.amazon.com/Brief-History-.../dp/0553380168 It's not a mistake that it's one of the best-selling science books of all time.

 

[yachtie]

Originally Posted by ComboOrgan

It think it would be easier to try to understand special relativity first, before you tackle general relativity. Special relativity deals with the relationship between space and time, and between momentum and mass. You'll learn the meaning of the famous E=mc^2 The book I used is this: http://www.amazon.com/Spacetime-Phys.../dp/0716723271 and I found it very easy to follow. GR adds gravity into the mix, and it makes things much more complicated Most physicists don't ever use (or even learn) general relativity, as it's simply not relevant to most fields. At my school, GR is offered as a graduate elective only, and I don't plan to ever take it. But if you want to go there, then by all means.... Some friends of mine took the class, and they enjoyed it. They said it requires a lot of math. I think you can achieve a popular understanding of special relativity with little more than high-school math, but general relativity uses things like tensors which one usually doesn't learn until until he has taken several semesters of college math and/or physics.
Not a bad nontechnical primer.

Originally Posted by unjung

http://www.amazon.com/Brief-History-.../dp/0553380168 It's not a mistake that it's one of the best-selling science books of all time.
This one sucks. I wouldn't recommend Hawking to anyone. Wanna know all about General Relativity? This is what you want: http://www.amazon.com/Gravitation-Ph...40/ref=sr_1_2? In simplest terms, the metric (or measure) for spacetime is distorted by mass to that formerly "straight" lines are curved. This plays out as a "force".