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Albert Einstein's Theory of Relativity

In Words of Four Letters or Less

[ 0 ]

So, have a seat. Put your feet up. This may take some time. Can I get you some tea? Earl Grey? You got it.

Okay. How do I want to do this? He did so much. It's hard to just dive in. You know? You pick a spot to go from, but soon you have to back up and and go over this or that item, and you get done with that only to see that you have to back up some more. So if you feel like I'm off to the side of the tale half the time, well, this is why. Just bear with me, and we'll get to the end in good time. Okay?

Okay. Let's see....

[ I ]

Say you woke up one day and your bed was gone. Your room, too. Gone. It's all gone. You wake up in an inky void. Not even a star. Okay, yes, it's a dumb idea, but just go with it. Now say you want to know if you move or not. Are you held fast in one spot? Or do you, say, list off to the left some? What I want to ask you is: Can you find out? Hell no. You can see that, sure. You don't need me to tell you. To move, you have to move to or away from ... well, from what? You'd have to say that you don't even get to use a word like "move" when you are the only body in that void. Sure. Okay.

Now, let's add the bed back. Your bed is with you in the void. But not for long -- it goes away from you. You don't have any way to get it back, so you just let it go. But so now we have a body in the void with you. So does the bed move, or do you move? Or both? Well, you can see as well as I that it can go any way you like. Flip a coin. Who's to say? It's best to just say that you move away from the bed, and that the bed goes away from you. No one can say who's held fast and who isn't.

Now, if I took the bed back but gave you the sun -- just you and the sun in the void, now -- I'll bet you'd say that the sun is so big, next to you, that odds are you move and not the sun. It's easy to move a body like ours, and not so easy to kick a sun to and fro. But that isn't the way to see it. Just like with the bed, no one can say who's held fast.

In a word, you can't find any one true "at rest". Izzy was the one who told us that. Izzy said that you can't tell if you move or are at rest at any time. You can say that you go and all else is at rest, or you can say that you are at rest and all else goes. It all adds up the same both ways. So we all knew that much from way back when.

Aha, but now wait! The sun puts off rays! So: why not look at how fast the rays go past you? From that you'd see how fast you move, yes? For you see, rays move just the same if what puts them off is held fast or not. (Make a note of that, now.) Izzy had no way to know that, back then, but it's true. Rays all move the same. We call how fast that is: c. So, you can see how fast the rays go by you, and how far off that is from c will tell you how fast you move! Hell, you don't even need the sun for that. You can just have a lamp with you -- the one by your bed that you use to read by. You can have that lamp in your hand, and see how fast the rays go by you when you turn it on. The lamp will move with you, but the rays will move at c. You will see the rays move a bit more or less than c, and that will be how fast you move. An open-and-shut case, yes?

Well, and so we went to test this idea out. Hey, you don't need to be in a void to do this test. We move all the time, even as we sit here. We spin, in fact. So they shot some rays off and took note of how fast they went east, and how fast they went west, and so on. Well, what do you know? The rays went just as fast both ways. All ways, in fact. They all went at c, just the same. Not an iota more or less.

To say that we were less than glad to find that out is to be kind. It blew the mind, is more like it. "What is up with that?" we said. And here is when old Al came in.

[ II ]

Old Al, he came out the blue and said, "Not only do rays move at c if what puts them out is held fast or not: they move at c even if you are held fast or not." Now that may not look like such a big deal on the face of it, but hold on. What this says is that you can move as fast or as slow as you want, and rays will go by you at c all the time. You can have a pal run past you and when you both look at a ray go by at the same time, you will both see the same ray go by at c! That is a bit wild, no? You, back in that void, you just can not say if you move or not -- with the lamp or no. Not that you can't tell: it can't be said. It's moot!

But for that to be true, then time also has to get in on the act. For you and your pal to see the same ray go by at the same clip, her idea of time must be off from your idea of time!

I can hear you say, "No way. That can't be!" But I tell you it is. Old Al said so. He said, here, I'll show you. Get a load of this. We have Bert and Dana. Take a bus, and put Bert on the bus. The bus goes down the road. Dana, she sits here, on the side of the road. He's in the bus and she's on her ass. And now take a rock off of the moon, and let it fall at them. It hits the air and cuts in two. The two bits burn, and then land just as Bert and Dana are side by side. One hits the dirt up the road a ways, and one hits down the road a ways. Dana sees each rock at the same time, but Bert sees one rock and then sees the next rock. Now: if Bert and Dana both see Dana as the one who is "at rest", they both will say that the two bits came down at the same time. Dana will say, "I am 'at rest', and I saw them both land at the same time, so they both did, in fact, land at the same time." And Bert will say, "I move away from the rock down the road, so when I add that fact in, I can see that if I were 'at rest', I'd have seen both land at the same time. So it must be the case that they did land at the same time." Okay, but what if Bert and Dana now see Bert as the one who is "at rest"? Eh? You get to pick who is "at rest" and who isn't, no? So make Bert be "at rest". Now Bert will say, "I am 'at rest', so the one up the road beat the one down the road, on the way to the dirt, just the way I saw it." And Dana will say, "I saw them land at the same time, but I move away from the rock up the road, so when I add that fact in, I can see that the rock up the road must have beat the one down the road."

So you see, when you give up on the idea of a one true "at rest", then you have to give up on the idea of a one true time as well! And even that is not the end of it. If you lose your one true way to see time, then you also lose your one true way to see size and your one true way to see mass. You can't talk of any of that, if you don't also say what it is you call "at rest". If you don't, then Bert or Dana can pick an "at rest" that isn't the same as what you used, and then what they will get for time and size and mass won't be the same.

What a snag, eh? I hope you can see how that gave some of them the fits, back when old Al told us that one. But even so, that ain't the half of it. I mean, most of us know that if old Al had got hit by a bus at age ten, we'd have got this far on our own in good time. No, it was what came next that was the real slap in the face.

[ III ]

Now, I've said a lot here on how to see (or how not to see) how fast you "move". What I need to tell you now is just what I mean by that word "move". When I say "move", I also mean that you don't slow down or get sped up at any time, and that you don't veer to one side at all. When you move, you just keep all that the same as you go. How we say it is, you don't have any "pull". Why do I make a big deal out of that, you ask? Okay, let me tell you.

Cast your mind back to Ari, from way way back when. He's the one who said that if you are at rest, you tend to stay at rest, and if you move, you tend to come to rest. He was off, you know, as he had no way to know that it was the air that has you come to rest. We had to wait a long time for Izzy to come by and say, "No, Ari: if you move, you tend to just go on and on. To come to rest, you need to have a pull." The air will give you a pull, a pull that has you come to rest. Then we also have the big pull, the one that says what is down and what is up, the one that has all of us in its grip. Izzy saw that this pull was the same pull that has the moon in its grip, too. I said that a pull can be a veer, yes? That is what the pull on the moon does. The moon has to veer all the time for it to stay with us. Were it not for that pull, it'd just go off in a line -- no veer -- and we'd just sit here and wave bye bye. Same with us and the sun. We veer, each hour, or else we'd get real cold real fast.

But then, see, Izzy had to deal with the way that the pull acts. If a body has more mass, then it also has more pull, yes? That is why the sun is the axis we spin upon, and we are not the axis for the sun. But then why can't it go both ways? You take your ball of lead and your ball of wood and drop them, they land at the same time. But the lead ball has more mass, so it must get more pull. Izzy said, "Well, see, a body has one more kind of pull. This pull is such that it will want to stay put all the time. And the more mass it has, the more it will want to stay put. That pull is the 'a body at rest will tend to stay at rest' part of the deal. So you see, that pull and the big pull are in a tug-of-war, and they work out so that any mass will fall just as fast."

I call it a "new kind of pull", but it isn't so new: you feel it all the time. Get in a car and step on the gas -- you feel a pull back into your seat. Let up on the gas a bit, and the pull goes away. Make a left, and you feel a pull to the side. Stop, and you feel a pull out of your seat as you slow down. Or, go to the fair and get on a ride. As you spin, you feel a pull out, away from the ride. You spin: that is to say you veer, and veer and veer and veer, just like the moon. If you had no seat belt, you'd fly off the ride, and you'd fly off in a line. (Well, that is to say, you'd fly off in a line as a bird sees it. To be fair you'd also arc down at the same time. But put that to one side.)

Okay but now, see, old Al's big idea did not work when you look at pull. Go back to when you were lost in the void. You can't say if you move or not, yeah, but you sure can say if you have a pull on you or not. If you did, you'd feel it, no? Sure. So then you have no one true "at rest", no one true way to look at time, or mass, or size, but you do have one true way to look at a pull? Old Al said, "Erm. I don't buy that." We all said, "Aah, why not? Just give it a rest, Al." You can see why Al did not want to give it a rest, I bet. But this one was not such an easy nut.

[ IV ]

Izzy once said, Look here: say you have a disk that can spin, and so you put a pail of milk on it and you make it spin. You will see the milk go up the side of the pail, and fly over and out onto the disk. No big deal, eh? The spin will make a pull. But now what if you said that the pail of milk is your "at rest"? Then you have you and the sky and all that in a big huge ...

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