Physics Help Forum A probably stupid question.
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 Aug 11th 2011, 07:34 AM #1 Junior Member   Join Date: Aug 2011 Location: North Yorkshire, England Posts: 1 A probably stupid question. I've got a fairly new founded interest in Relativity, so although I'm keen I know very little. Therefore this is probably an excruciatingly obvious question, but... Imagine that two objects are fired past each other, each at a fraction of the speed of light higher than a half - let's say three quarters of c. They are both in steady motion (not accelerating or decelerating), so according to Relativity are both perfectly entitled to believe that they are at rest and that the other object is moving. If this were true, it would appear to each object that the one fast approaching them was going at the sum of their speeds, i.e. one and a half times the speed of light. I'm clearly thinking about this the wrong way, as one and a half c makes no sense, so what am I missing?
 Aug 11th 2011, 10:15 AM #2 Physics Team     Join Date: Jun 2010 Location: Mauritius Posts: 609 I'm not well versed in it, but that thread might interest you: Do you think gravity shells, around a mass ... __________________ Jerry (Got my results!) It is easier to protect your feet with slippers than to cover the earth with carpet. No one can go back and change a bad beginning; but anyone can start now and create a successful ending. If a problem can be solved, no need to worry about it. If it cannot be solved what is the use of worrying?
Aug 12th 2011, 07:37 AM   #3
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Hi and welcome to the forum!
 Originally Posted by ToTheWareMobile I've got a fairly new founded interest in Relativity, so although I'm keen I know very little. Therefore this is probably an excruciatingly obvious question, but... Imagine that two objects are fired past each other, each at a fraction of the speed of light higher than a half - let's say three quarters of c. They are both in steady motion (not accelerating or decelerating), so according to Relativity are both perfectly entitled to believe that they are at rest and that the other object is moving. If this were true,
so far so good, all is ok.
 it would appear to each object that the one fast approaching them was going at the sum of their speeds, i.e. one and a half times the speed of light. I'm clearly thinking about this the wrong way, as one and a half c makes no sense, so what am I missing?
Your reasoning here is "Galilean" or the one of classical mechanics. See http://www.physicshelpforum.com/phys...er-than-c.html. And why not Einstein velocity addition.
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