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Enter the Relativity Challenge
An anonymous reader writes "Any slashdotters wanna pick up a lazy 25,000 Euros? All you have to do is explain Einstein's theory of relativity in a five minute multimedia presentation. The Pirelli Group have laid down this 'Relativity Challenge' to anyone as part of the International Year of Physics. Entries close on 31 March 2005."
It's a stepping-stone towards the ultimate goal: explaining Special Relativity in a haiku.
OK, let's see if I can help.
Maxwell's equations of electro-magnetic theory show the speed of light in a medium to be determined by 2 properties of that medium. For vacuum, those two properties are fundimental constants - thus the speed of light is fixed.
Now, if I take a squirt gun with a fixed exit velocity and squirt it at you, the water will be moving slower if I am backing away from you and quicker if I am running at you. That fits with our day-to-day experience.
But for light in a vacuum that does not happen - if I now use a light-gun, you will measure the speed of all three beams of light (me backing away, me standing still relative to you, me running at you) as the same.
And curiously, so will I - I will measure the speed of light leaving my light-gun as the same, no matter what.
Now, the ONLY way you can get both my measurements and yours to agree is if things like length, mass, and time change based upon my motion relative to you - hence the need for the Lorentz transformation.
Then, you get into the "twins paradox" - Take 2 twins. Kick one of them up to nearly the speed of light. Wait till the other one has aged 10 years. Bring the high-speed twin back.
From the stationary twin's perspective, the high speed twin slowed down. From the high speed twin's perspective, the stationary twin (who wasn't stationary from the high speed twin's perspective) slowed down. Yet both cannot be true.
So Einstein reasoned out that the ONLY difference between the twins was who felt the acceleration - that twin would slow down.
But if I lock you in a box, you cannot tell if you are setting on a planet or in free space being accelerated - so gravity must be like acceleration.
That's GR in a nutshel.
www.eFax.com are spammers
I'll take that challenge:
Light goes the same speed
For everyone everywhere
Funkiness ensues
When you are courting a nice girl an hour seems like a second. When you sit on a red-hot cinder a second seems like an hour. That's relativity. -Einstein
I don't think it can be said much better.
The best relativity resource I've found is an in-depth online book called "Reflections on Relativity". Be warned, it's the real deal; read it slowly and carefully. Intro calculus should suffice to get you through chapter one (which took me about two weeks spare time in the evening to read and digest), after that it gets tougher, although I'm finding the subjects don't build on each other so much after that so you can skip something you can't follow and keep going. (On the other hand, I only just finished Chapter 2, of 9.)
:-)
About the only thing I can tell you, short of linking the book as I did or quoting it more extensively than Slashdot will allow, is that nearly everything physics fanboys think they know is wrong. Don't rely on Star Trek for your physics, get the real deal; it'll only take as much time as a few episodes of Star Trek and you'll feel much better about your expanding horizons
You can't just wave it off saying the one that experienced the accelleration will have their clock slow down. If you want to calculate how much less one person aged, you go by how long (time and distance) they were travelling at that speed. For example, if I accellerate to 0.999999c in about a year (I think that's about 1g accelleration) and travel 10 light-years and back, then 24 years will have passed on Earth (20 travel + 4 for accelleration), but I will have aged only about 4. If I undergo the same accelleration but travel 10,000 light-years and back, then 20,004 years will have passed on Earth, but I will still have aged only about 4. The accelleration didn't make time pass more slowly, it was the period while I was tavelling at high speed that made it pass more slowly. Take both examples together and the one would seem to have 4 years pass and the other would seem to have 19,984 years pass, even though they experienced the same accellerations.
This also leads to an absurd result from my point of view. I will have only seen 2 years go by, but I will have travelled 20,000 light-years. From my point of view I would have been travelling 10,000 times the speed of light. How can this be?
I think it has to do with contraction. Lorentz contraction is one thing I haven't understood, how you can measure the length of something that is going nearly the speed of light? Apparently, when you are going nearly the speed of light, everything else contracts in the direction of your travel. For instance, if you were going a certain speed and passed a meter stick, it would appear to be only 1 millimeter long, although a stationary observer by the meter stick would see it as 1 meter long.
Now as for how fast you are going, that is all relative as well. If I take off from earth and accellerate to 0.999999c for about a year and travel 10 light-years, I don't think I'm going 10 light years. Space and the galaxy will seem to contract along the direction of my motion. When I get 10 light-years in space, it will appear to me like I have travelled a much shorter distance.
Here's a more concrete example. Let's say that I pass Earth going at velocity V, which slows down time for me to 1/10th normal. Then I travel to a space buoy that you have measured from earth as 10 light years away. Not only will I reach that buoy in about a year, but I will think I have travelled much less than 1 light-year because space along my direction of motion has contracted. During that time, an earth-based observer thinks 10 years have passed. The reason that his clock doesn't appear to slow down for me is because I don't think he's travelling that fast. To me, he has travelled much less than 1 light-year because space contracted and I think it was in 1 year, so he is travelling much slower than the speed of light and subject only to minor relativistic effects.
I have a poster of Einstein on my wall, with a quote:
"Do not worry about your troubles in mathematics. I assure you, mine are much greater."
I might not have that exactly right, but as I understand it he was struggling with the math too.