Ask MetaFilter questions tagged with einstein

How was it proved that mass exerts the gravitic forces?

Lorc — Mon, 06 Jul 2009 11:00:14 -0800

How was it proved that gravitation was a function of mass? If we can estimate planetary masses from the strength of their gravity, including that of the earth, then we must be pretty confident that we've nailed the relationship between the two.

I know that the force of gravity is proportional to the mass of an object and inversely proportional to the distance. And certainly when we look at the universe there's evidence of strong gravity wherever we see a lot of mass. But I also know that science is robust and does not just accept obvious observations without testing them to destruction. How do we know that there's a causal relationship rather than it being circumstantial? And that it exists at all scales, not just with planetary masses?

It seems to me that you'd have to test known masses and be able to measure that object's gravity in order to prove anything. Is that what they did, and if so, how was it done? Is there a gravitational equivalent of Rutherford's gold foil and Robert Millikan's oil-drops?

Learning General Relativity

DU — Mon, 06 Jul 2009 06:06:12 -0800

What textbook can I use to learn General Relativity, including the associated math? What I have so far

I'm pretty firm on calculus and basic physics (and of course Euclidean geometry, etc). Less firm or polished, but technically familiar with vector calculus. I recognize words such as "laplacian" from electromagnetics, but really only have a vague understanding of the actual concepts.

What I'm interested in

I'd like to learn GR. And of course to learn GR, I need to learn some of the underlying mathematics such as differential geometry. I'm also interested in learning perhaps 10% more diff geo than is strictly required for GR.

The field

I have access to a largish technical library covering stuff from math to programming to astronomy to thermodynamics to engineering. "Classics" are probably in the catalog, but may be permanently checked out.

The requirements

Requirement 0 is really more of a guideline: I'd like something that teaches both GR and the needed math together. However, if there are N books that otherwise qualify and teach the subjects separately, I'm open to the idea.

1) Not overly formalized. I prefer a conversational, readable textbook.
2) Good problem sets. (I.e. not just one or two per chapter)
3) Answer key.
4) Not a "bible" or an "elegant reformulation". I need to be able to learn from it, not marvel at the comprehensiveness or elegance from a position of already knowing the subject.

An example of a nearly great suggestion is Gravity: An Introduction to Einstein's General Relativity by James Hartle. Why only "nearly" great? No answer key. Unfortunately, as perfect as the book otherwise appears, this renders it useless to me.

Some examples of actually great suggestions, but on different topics. If you know (of) these books, you will know the kind of thing I'm looking for:

Fundamentals of Physics by Halliday, Resnick and Walker
Div, Grad, Curl And All That by Schey.

BEC in popular media

Lesium — Mon, 01 Jun 2009 19:41:15 -0800

References to Bose Einstein Condensates in popular media I am giving a general talk on BEC's (I am doing my PhD in the field), i am looking for any references to them in popular media, movies and tv shows and the like (but not science shows).

So far I know about the reference in Numb3rs and The Big Bang theory, does anybody know of any others?

How to get Mad Scientist Hair.

BrianBoyko — Thu, 01 May 2008 12:59:37 -0800

Anyone know how to get "mad scientist hair?" I've actually found that I like the look that I get when I get up in the morning and my hair sticks out like a mad scientist. It doesn't hurt any that I'm the resident "evil genius" where I work and I'm quite fond of the "mad scientist chic" myself. But trying gels and sprays to get the hair to stay like that just doesn't work. Anyone got any advice on how to get the "mad scientist hair" look?

Why can nothing go faster than the speed of light?

complience — Thu, 14 Feb 2008 04:24:08 -0800

How does Einstein prove nothing can go faster than the speed of light and that Atoms exist? I've never understood Einstein's theory's on light, How does he prove that the speed of light is Constant and that nothing can go faster than this speed?

And while we are on Einstenion theory's can someone also explain how Brownian motion of pollen seeds in fluid proves that atoms exist? If atoms are moving the pollen whats moving the atoms?

E=MC². So?

markovich — Wed, 14 Feb 2007 00:59:43 -0800

What did Einstein actually contribute to the modern world? With some scientists, you could say - he made the lightbulb, the other would be - without his help, the computer would not be possible, yet another - he made the first prototype of the airplane. Well, what did Einstein actually do? We always hear that Albert is one of the greatest scientists in the world, however, the only thing I can think of that his theories actually bore relevance to would be Nuclear Energy. Even with that, I'm not really sure how much he was responsible for, and if the nuclear program would perhaps have been possible without him.

What I'd like is a list of practical tools right now that would possibly not exist, had Albert never been born.

Time dilation and relative speed

seanyboy — Tue, 13 Jul 2004 04:53:52 -0800

Time dilation and relative speed. If the speed we travel is relative to the thing we're travelling away from, then how does the universe know which of the two things is actually moving? (so time dilation can occur) Is there a known universal "zero-speed"? If so, at what speed is the earth moving, and would it make a difference to the time dilation depending on the direction a spaceship moved away from the earth?

Explain Theory of Relativity

xmutex — Tue, 06 Jul 2004 14:12:46 -0800

trying to get my head around special relativity filter: Can someone explain to me, in terms as devoid of mathematical formulae as possible, how something traveling less than the speed of light cannot be accelerated to the speed of light?