I won't subject you to quantum mechanics because I'm not even sure how much I understand it, but I have decided that I shall inundate you all with a Brief Overview of Relativity.
Mostly because I feel like it. And the times that I've tried to explain it to my mom left me unsatisfied (hi mummy!) so I'm going to see if it works better in writing.
Oh, and it might be helpful to adopt a thoughtful pose as you read the screen.
Anyway, the general setup goes thusly: James Clerk Maxwell discovered some extremely fancy equations for how electricity and magnetism work. [For anybody who knows some calculus: they're partial differential equations that relate EM fields to current and charge density.] Anyway, when you put these equations together, you come out with the equation for how light travels.
At this point physicists widely believed that light traveled through the "ether" - just like water waves travel through water and sound waves travel through air (or whatever else), physicists believed that light waves needed a medium to travel through. However, experiments around the turn of the century (that is, the 20th) showed that the Earth was stationary relative to the ether - i.e. it's not wooshing past us as one would expect as we orbited the Sun. Several people (such as Hendrik Lorentz) came up with reasons this might be, but the physics community wasn't really satisfied with this approach because we don't really like making excuses for our theories when things don't turn out how they should have.
ANYWAY, this is the state of the theories for electricity and magnetism at the time Einstein came around. Einstein was a huge fan of Maxwell's equations. He decided to approach the problem from a different way: if we take Maxwell's equations as the absolute reality, rather than the ether, what do we come up with?
The first thing that comes up is that light will always travel at a constant speed: c (about 300,000,000 meters per second, or 671,000,000 miles per hour). At first this doesn't seem like much of a "miraculous discovery" but the thing of it is that you will measure light going at this speed no matter how fast you're going.
The most popular way of getting people to be confused by this (because if you're not confused by the end of this post, I'm not explaining it right :D ) involves a tennis balls, but I'm going to step it up a notch and use a cannon.
Because I can.
So for some reason, you've acquired a cannon and want to find out the speed at which it fires the cannonballs. So you set up the necessary equipment, fire the cannon past the equipment, and get some number out. Not extremely exciting. Next, you put the cannon on a truck (you can never have too much heavy machinery) and have the truck drive at high speeds, then fire the cannon again. This time, the cannonball will be going faster: it will be traveling with its original speed PLUS the speed of the truck. Not so bad, yes?
Well, now we get interesting. Because you are in a scientific mood (this happens to everyone, right?) you want to modify your equipment to measure the speed of a light beam as it goes past. So you do. Then you take a flashlight, shine it past the equipment, and it will say that the light passed by at about 670,000,000 miles per hour. For the next step, since a flashlight really isn't very exciting, you decide to go all out: strap the flashlight to a car that can go at half the speed of light (You were so fascinated with this experiment that you created an engine capable of attaining such a speed. Just play along.) Now, taking the cannon example above, one might predict that now the light beam will travel past the detector at 670,000,000 miles per hour PLUS the speed of the car: 335,000,000 miles per hour. Lo and behold, when the number pops out of the machine, it is once again 670,000,000 miles per hour.
At this point you might be tempted to think that there must be something wrong with your machinery (since you designed and built it in the space of one sentence.) So you double check all of the connections and programs, crank up the car to travel at 99% the speed of light, and run the experiment again.
Still 670,000,000 miles per hour.
This is the conclusion that Einstein arrived at. No matter how fast you're going, the speed of light will always be constant. But he didn't stop there. The reason that relativity was so controversial, and why it is such a monumental theory, is the implications it has. This is the point where the author has to be reassuring and yell dramatically, "STAY WITH ME!!"
So what happens is this. That conclusion, which is known as the Second Postulate of Special Relativity (we are ignoring the first postulate because it doesn't really add to this conversation) makes absolutely no sense in the traditional way of explaining things (i.e. the Cannonball Principle). So the point where Einstein really freaked everyone out with his genius is coming up with why light would act that way. What happens is that for someone standing on the ground next to the detector and looking at the car as it speeds past at 99% of the speed of light, they will see that time is unfolding inside the car
more slowly than what they measure - that is, the driver of the car's watch will be ticking about a tenth as fast as your watch as you stand at rest by the machine. That effect, called time dilation, ends up exactly compensating for the speed that the car would add to the light from the flashlight - time goes slower, so it takes the light a longer amount of time to travel the same distance - which explains how we measure it to have the same speed.
At this point somebody stood up and said "Why my good sir, that is simply preposterous! Suppose we have two twins - if one travels around the world at nearly the speed of light, surely one will not age
slower than its twin! Then one would be older, even though they were born at the same time!" The people sitting nearby (for we are imagining this taking place in an auditorium.) nodded conspiratorially and looked to Einstein for his rebuttal. His rebuttal was this: "Yeah, isn't that weird?"
The author at this point will assure his readers that all of this has been thoroughly tested. For example, at one point a pair of atomic clocks, accurate to the nanosecond, were created. One was put on a very fast plane, which flew around the world. Even though the speed of the plane wasn't even close to the speed of light, the effects of time dilation would be evident simply because of how accurate the clocks were. Lo and behold, the clock that was on the plane was lagging behind the one that remained on the ground by precisely the amount predicted by relativity.
Taking this consequence further by leaps and bounds, Einstein then showed that lengths will also contract at high velocities, mass will increase, and all sorts of other things. At one point, the equations fell out in such a way to produce that ever so clichéd relation: E=mc
2. The gist of this is that mass is just another form of energy; from this idea sprung the atomic bomb, which works on the principle that destroying some of the mass releases a COLOSSAL amount of energy (since the speed of light squared is, in fact, a very large number).
So that is special relativity in a very inadequate nutshell. Perhaps at some point I'll also add general relativity, but for now I will leave you alone. Have fun mulling these over :D