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I know I'm dumb, but can someone explain this part? "Dana sees each rock at the same time, but Bert sees one rock and then sees the next rock." How would anyo

I know I'm dumb, but can someone explain this part? "Dana sees each rock at the same time, but Bert sees one rock and then sees the next rock." How would anyone's movement, or lack of it, affect their perception of whether the rocks landed at the same time or not?

breadbox 13y ago
You're not dumb. It's a subtle point, otherwise special relativity wouldn't have been necessary to invent. (You may find it worthwhile to read a more normal article on special relativity -- it's much easier to understand than general relativity.) The two rocks land just as Bert and Dana are closest to each other. The two rocks are equally distant from that point. But as the light propagates towards them, Bert continues to move towards the light from the impact ahead of him, and away from the impact behind him. Thus he will see the light from the former impact before the latter. (The traditional thought experiment is described in terms of trains and lightning, instead of buses and moon rocks. If you do a web search for that plus "special relativity", you should find plenty of descriptions that are closer to the original.)
gjm11 13y ago
The rays that come from each rock move only so fast. They take time to get from the rock to Dana or Bert. And it is only by when those rays get to Dana or Bert that they can say if they were at the same time, or one and then the next. Now. Bert is on the bus. It goes, let us say, from west to east on the road. Bert is half way from the west rock to the east rock when each rock hits land -- but he is on the move, and when the rays from the east rock hit his eyes he has gone some way east. The rays from the west rock have not yet got to him. Then, just a tad more time, and the rays from the west rock get to Bert's eyes. But Dana does not move. She sits by the road. The rays from the west rock and the east rock hit her at the same time: each rock is, say, a yard from her, one west and one east. So Dana sits and does not move; she sees the rays from each rock at the same time. Bert is on the bus, and goes from west to east; he sees the rays from the east rock and then the rays from the west rock. And all that is fine. They both know that Dana does not move and Bert does. So they will say that each rock hit at the same time, for Dana (who did not move) saw them hit at the same time. But (and this is the bit that may fry your mind) we can just as well say that Bert does not move and Dana does move! And then we will have to say that the east rock hit and then the west rock! How can that be? We must say, even if you find it odd, that "did the east rock hit, then the west? or the west, then the east? or both at once?" just goes one way for Dana and not that way for Bert. Just like "is this rock to the east or to the west?" may not go the same way for both, if they are not at the same site. (You are not dumb. This is hard. It took Al to work it out!)
- breadbox 13y ago
  Yes, you have the idea. You put down just a word or two, no more. But then you add to it, and then some more, and then the next you know, you have a page full of such text. It can be hard to stop once you get into it!
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- deleted 13y ago
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boburhedRAGTOP 13y ago
Thanks to the both of you for taking the time to answer! Makes a lot more sense! I feel relatively smarter now

breadbox 13y ago

You're not dumb. It's a subtle point, otherwise special relativity wouldn't have been necessary to invent. (You may find it worthwhile to read a more normal article on special relativity -- it's much easier to understand than general relativity.) The two rocks land just as Bert and Dana are closest to each other. The two rocks are equally distant from that point. But as the light propagates towards them, Bert continues to move towards the light from the impact ahead of him, and away from the impact behind him. Thus he will see the light from the former impact before the latter. (The traditional thought experiment is described in terms of trains and lightning, instead of buses and moon rocks. If you do a web search for that plus "special relativity", you should find plenty of descriptions that are closer to the original.)

gjm11 13y ago

The rays that come from each rock move only so fast. They take time to get from the rock to Dana or Bert. And it is only by when those rays get to Dana or Bert that they can say if they were at the same time, or one and then the next. Now. Bert is on the bus. It goes, let us say, from west to east on the road. Bert is half way from the west rock to the east rock when each rock hits land -- but he is on the move, and when the rays from the east rock hit his eyes he has gone some way east. The rays from the west rock have not yet got to him. Then, just a tad more time, and the rays from the west rock get to Bert's eyes. But Dana does not move. She sits by the road. The rays from the west rock and the east rock hit her at the same time: each rock is, say, a yard from her, one west and one east. So Dana sits and does not move; she sees the rays from each rock at the same time. Bert is on the bus, and goes from west to east; he sees the rays from the east rock and then the rays from the west rock. And all that is fine. They both know that Dana does not move and Bert does. So they will say that each rock hit at the same time, for Dana (who did not move) saw them hit at the same time. But (and this is the bit that may fry your mind) we can just as well say that Bert does not move and Dana does move! And then we will have to say that the east rock hit and then the west rock! How can that be? We must say, even if you find it odd, that "did the east rock hit, then the west? or the west, then the east? or both at once?" just goes one way for Dana and not that way for Bert. Just like "is this rock to the east or to the west?" may not go the same way for both, if they are not at the same site. (You are not dumb. This is hard. It took Al to work it out!)

breadbox 13y ago
Yes, you have the idea. You put down just a word or two, no more. But then you add to it, and then some more, and then the next you know, you have a page full of such text. It can be hard to stop once you get into it!
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deleted 13y ago
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boburhedRAGTOP 13y ago

Thanks to the both of you for taking the time to answer! Makes a lot more sense! I feel relatively smarter now