This pie chart shows what makes up the Universe. Amazingly, about 96% of all the mass-energy in the Universe is invisible in the form of dark matter or dark energy. I'll do posts on each of them, but briefly, dark matter is related to ordinary matter except it doesn't interact with light, so it is invisible and doesn't clump into planets and stars (unless you count these); dark energy is a mysterious energy which is causing the Universe to expand faster and faster, and may well be the inherent energy of space itself.
Of the 4% of the Universe that is in "normal" matter, most is in interstellar and intergalactic gas--only about 1/10 (0.4%) of the total is in stars like our Sun. Finally, all the elements other than hydrogen and helium make up less than 1/10 of that slice (0.03%--not shown).
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This is probably the most quoted formula. Einstein's equation changed the world. But what does it mean?
I already defined
c for you: it is
the speed of light.
The only thing you need to know about
c in this equation is that it is BIG (30 billion cm/s), and
c squared [see
Why c squared?], which is
c times
c, is VERY BIG (900 quintillion cm
2/s
2).
E stands for energy, and
m for mass (the amount of matter). So the equation is really
Energy = mass x BIG_NUMBER
Well, what the heck does that mean? It means that matter and energy are really two sides of the same coin called mass-energy. Matter can be converted into energy, and energy can be converted into matter. Before Einstein, it was thought that they were completely separate things. But they are not. They are two different manifestations of the same thing. They are like dollars and yen, except the units are grams and ergs. But there is a VERY steep exchange rate. For every gram of matter, you get 900 quintillion ergs. If you could somehow convert a pound of matter (454 grams) completely into energy, you'd have enough to power the US electrical grid for about 4 days.
Note, you can't actually convert 100% of matter into energy (since we don't have a ready supply of antimatter)—even thermonuclear fusion converts only about 1% of the matter involved into energy.
[confidence level: established, my qualifications: trained]
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I've realized that I'm not always going to have time for a full post. And perhaps some of you would like things in small bites. So I will sometimes publish short posts called factoids. This one is on the speed of light.
The constant c in Einstein's famous equation E=mc2, is the speed of light. c is 186,282 mi/sec, or 299,792 km/sec. That means light could go around the equator of the Earth (in some conduit) about 7 times in a second. On the other hand, the sun is so far away, 93 million miles, that it takes light more than 8 minutes to get here from there.
[confidence level: established, my qualifications: trained]
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