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Author Topic:   Purple dosn't beleve in relativity
Raymon
Inactive Member


Message 61 of 114 (166355)
12-08-2004 7:57 PM
Reply to: Message 19 by PurpleYouko
12-07-2004 1:29 PM


explaining the paradox
Sorry I didn't reply to this comment sooner, but I haven't been keeping a very close eye on EvC lately.
You got a lot of replies to this statment that basically said that the math works out, as well as posts that pointed out that your picture implies a 3rd observer. But there is an interesting paradox going on here that is taught to students learning relativity. Of course, it's not a real paradox. Just as the Twins paradox can be resolved, so can this notion of A's time is shorter then B's time while the converse is also true. As long as you know that length contracts at relatavistic speeds just like time slows down it's pretty straighforward. The way it is usually presented is like this-
Suppose the Flash, a man who can run at relatavistic speeds, wants to test relativity. He reasons thus: "If I have a barn that's 10m long and has doors on both ends that can be closed very quickly and a 15m long pole I can show relativity doesn't work. If I run fast enough that length contraction is 50% then I can hold the pole horizontally, run through the barn, and have the farmer try to close both doors on while I'm inside the barn. From the farmers perspective it should work because my pole is length conracted to 7.5 m. So he should be able to close both doors while I'm inside. Of course he'll have to open then again to let me out so I don't undergo acceleration and go into General Relativity's realm.
But for me, the barn is only 5m long, so there is no way I'm going to get my entire pole in there. So when the doors close at the same time they are going to hit my pole. So if the doors are able to close then the farmer's reference frame is the correct one and if they hit my pole on the way down then mine is."
This is basically the same scenario as you proposed, except instead of two times, you are comparing two lengths. So what happens?
From the farmer's reference frame, he closes the doors at the same time and Flash's pole fits inside. From Flash's reference frame, as he is running into the barn the far end closes before he gets there and then opens again to let him pass though. Then, after the entire length of the pole has passed through the near end of the barn, the near end door closes and opens. Thus we have another lesson to learn from relativity.
Simultanius events in one reference frame aren't simultanius in another.
Suppose a farmer is sitting on his porch, over-looking a long stretch of road with syncronized clocks placed every mile. Say the clocks are just striking noon as the Flash wizzes by him. To the Flash, the clocks far in front of him read to be 1pm while the ones far behind him read to be 11 am.
Personally, I think it's one of the wierdest aspects of relativity.
I hope this cleared up the "paradox".
This message has been edited by Raymon, 12-08-2004 07:59 PM

This message is a reply to:
 Message 19 by PurpleYouko, posted 12-07-2004 1:29 PM PurpleYouko has not replied

Replies to this message:
 Message 69 by The Dread Dormammu, posted 12-09-2004 10:12 PM Raymon has not replied

  
Raymon
Inactive Member


Message 88 of 114 (167923)
12-14-2004 12:15 AM
Reply to: Message 87 by contracycle
12-13-2004 10:43 AM


Re: What about 0 gravity at the bottom of the well?
I'm pretty sure you have it wrong on one point. Once you are inside a sphere of uniform density, you don't feel any gravitational force.
This fact has a neat little corralary- If you had a hole that went from one place on the surface of the earth and followed a straight line to another hole on the surface of the earth, and you dropped a ball down the hole, it would have a period of occilation of 84 minutes- even if the hole was through the center of the earth.(I'm a physisist, so I'm considering a spherical earth of uniform density)
Which means that gravitaionally speaking, every place on earth is 42 minutes away from every other place on earth. Who says Douglas Adams just wrote fiction!

This message is a reply to:
 Message 87 by contracycle, posted 12-13-2004 10:43 AM contracycle has replied

Replies to this message:
 Message 90 by jar, posted 12-14-2004 12:22 AM Raymon has replied
 Message 93 by contracycle, posted 12-14-2004 5:53 AM Raymon has replied

  
Raymon
Inactive Member


Message 89 of 114 (167924)
12-14-2004 12:15 AM
Reply to: Message 87 by contracycle
12-13-2004 10:43 AM


Re: What about 0 gravity at the bottom of the well?
dupe
This message has been edited by Raymon, 12-14-2004 12:16 AM

This message is a reply to:
 Message 87 by contracycle, posted 12-13-2004 10:43 AM contracycle has not replied

  
Raymon
Inactive Member


Message 94 of 114 (168129)
12-14-2004 2:13 PM
Reply to: Message 90 by jar
12-14-2004 12:22 AM


Sorry
:-)
Yes. And yes, presuming your hole goes through the center of the earth. It doesn't have to.

This message is a reply to:
 Message 90 by jar, posted 12-14-2004 12:22 AM jar has not replied

  
Raymon
Inactive Member


Message 95 of 114 (168137)
12-14-2004 2:22 PM
Reply to: Message 93 by contracycle
12-14-2004 5:53 AM


Re: What about 0 gravity at the bottom of the well?
Actually I misspoke. Sylas is right. You don't feel gravity inside a uniform shell. So you can only oscilate around the center if you have enough velocity to go through the other side of the shell. If you could use a rocket to reduce your speed to zero inside the shell, you would just float there, never moving.

This message is a reply to:
 Message 93 by contracycle, posted 12-14-2004 5:53 AM contracycle has not replied

  
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