Science with Richard Bleil
Some years ago, the pope purchased a new “pope mobile”. It was basically a truck with a bullet-proof case designed to be high enough for him to stand up in so he can wave to the crowds as they passed. It was quite an expensive vehicle, and, of course, the late-night comedians had a field day with it. Among the myriad of jokes was one that I remember (although who said it has since escaped my mind) who claimed that the single most expensive piece of equipment on the vehicle was the GPS system that placed the pope at the center of the universe.
Yes, there was a time that scientists believed the earth (and Rome more specifically) to be the center of the universe. The reality is that they were right. Well, kind of. The fact is that we can define the center of the universe to be anywhere we want, but there’s no particular point in making the center of the universe Earth. In so doing, the mass of the universe is off balance. But more than that, the equations describing the motion of the other celestial bodies just becomes far more complex.
Honestly, we’re used to arbitrarily placing, and even moving, the center of the universe. If we’re describing the rotation of the earth, the axis is the center (line) of the universe. If we’re describing the orbit of the moon, the earth becomes the center of the universe. If we’re describing the orbit of the earth, the sun becomes the center of the universe. Then it’s the galactic center, and finally the universe center as we continue to go further and further out to larger and larger orbits.
I find it a weird and rather humbling thought, that the “center” can be chosen to be whatever is most convenient. As I sit here, am I moving, or am I still? The answer is that it depends on my point of reference. Relative to the galactic center (or the sun, or the center of the earth), yes, I’m moving at a variety of speeds depending on which one I choose. Relative to the walls of this little prison and I laughingly call a home, no, I’m sadly and pathetically going nowhere. Driving home tonight, relative to a fixed point on the road ahead of me I was driving sixty miles per hour. Relative to me, that car approaching me was traveling one hundred and twenty.
This is the start of Einstein’s relativity. Seems pretty simple, doesn’t it? But like so many things in life that are supposed to be simple, the complications quickly stack up. One of the strangest ides is that the speed of light, even in relativity, is always fixed in a vacuum. The Doppler effect is something of which we are quite familiar. The classic example is the horn from a train, where the pitch shifts from high as it is approaching us to low as it passes and is moving away. Light is the same way. It always moves in a vacuum at six-hundred and seventy million miles per hour, and this does not change whether the observer is moving towards it, away from it, or is even emitting it. Shoot a cannon from a train and the train’s speed will be added (or subtracted depending on the direction you are shooting relative to the motion of the train). But for light, the speed does not change. But it can shift.
This is called the “blue shift” or the “red shift”. The speed remains constant, but the frequency, that is the number of waves that pass a fixed point in space per second, will shift. If you’re moving towards the light, even though its relative speed is fixed, you’ll pass more waves per second, and the light will appear to be bluer (blue shift). If the source is moving away from you, you’ll pass fewer waves per second, and the light will appear redder (red shift). This is actually how astronomers measure the velocity of distance stars relative to that of the earth. If they are moving towards us, the light (as measured instrumentally using a spectrophotometer) will appear more blue that it should be, and red if its moving away. The bluer, the faster the object is moving towards us and vice versa for red.
Now I’ll blow your mind. No matter how we measure the speed of light, no matter how accurately and precisely, the speed of the light will be exactly the same whether we are passing more waves per second, or fewer. Therein lies the mystery that physicists like Einstein fought with. Me? I’m good, thanks.
Bleil's Banter 