Science nerds, unite!
I got an email this morning saying my first issue of Astronomy is in the mail!
Woo! "When Black Holes Collide" - could I have joined at a more perfect issue?? I used to get this mag back in the day, but have somehow let all my subscriptions die over the past couple of years.
So I was reading the other day and found out this little fascinating piece of information. It seems that the effects of relativity (as in, Einstein's Theory of), are what give gold its unusual color. Bear with me; I'm going to explain it to you because it's kind of awesome that the hard-core and often elusive concepts that describe the space-time continuum are involved in making that shiny ring you're wearing, but I'll try to keep the jargon to a minimum. (Though if you're into that kind of thing, I found a good explanation here.)
Most metals have a silvery-grey appearance, right? So it should seem strange that gold is a shiny yellow instead. See, gold is a very heavy atom (Au - 79), much heavier than, say, nickel, iron, or silver. We have to discuss how atoms work, so let's use an analogy first - the solar system. Earth, for example, has to orbit the sun at a certain speed. If it slows down, it won't have enough orbital velocity to keep from resisting the sun's massive gravitational force and spiraling down into it. (Now, if you know anything about particle physics, you know that's not a perfect analogy to describe the movements inside an atom, but for our purposes, it'll do.)
So inside an atom, the electrons must orbit the nucleus at a certain speed, lest they fall into the center. The more massive the nucleus, the faster the electron must orbit to have enough momentum to 'counter-act' the higher gravitational force pulling in. Make sense? So in a heavy atom like gold, the electrons in a particular orbit level are moving with much greater speed than those in a lighter atom like silver.
What's the point? Well, when the electrons start moving at the kind of speeds required for a gold atom, they are traveling at an appreciable percentage of the speed of light - over half, actually. Relativistic effects - where velocity and mass become intertwined - come into play and mean that the orbiting electron actually becomes heavier. The greater mass affects the radius (and thus, the energy level) of its orbit, which will become important in a second.
Now we have to jump over to quantum mechanics for a minute (don't leave yet!). Materials get their color when the electrons in each atom absorb light. This absorption gives the electrons energy, which makes them jump to new orbits. But because orbits only exist at certain energy levels (and not in between), electrons are very picky about what they absorb. When light hits a silver atom, the electrons only accept the energy at a particular point in the spectrum - in silver's case, this exists around the UV point. So the electrons in silver don't absorb any visible light; therefore, it's all reflected, giving it that colorless appearance.
But in gold, remember, the relativistic effects have made the electrons heavier and, thus, changed the location (energy) of its orbit levels. The electrons in gold, then, are going to absorb light at a different part of the spectrum, which happens to be in the blue-green part of visible light. That means it reflects the yellow, reddish light, giving gold it's golden color! Were it not for these relativistic effects, gold would look just like silver!
I think there are a few unanswered questions here - like why mercury, which is right next to gold on the periodic table, is just as silvery colored as silver.
Maybe you're not as fascinated by this as I am, but think about it - look at some piece of gold jewelry you have and realize that the tiny, tiny particles inside are moving over half the speed of light! The theory of relativity says that, at this speed, the time that those particles exist in is passing by slower than the time that's passing by the tick of the clock on your wall. The electrons hanging out on your finger are aging more slowly than you!
Your ring that's worth so much because of its shiny golden gleam, exists in a different kind of space-time than you do! Well, parts of it are anyway, and that's freaking awesome.