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#81
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Microgravity parable
From stmx3:
Stuf4 wrote: [snip] "NASA scientists call this microgravity... The term is apt since Albert Einstein said that acceleration caused by gravity is equivalent to any other push." The principle is about _mass_ equivalence, not acceleration equivalence. [snip] That is incorrect. It was the happiest moment in Einstein's life when he realized that an accelerated reference frame was equivalent to a frame in a uniform gravitational field. From this basis, Einstein could later show the equivalence of intertial and gravitational mass. But the first preceded the second. It's called a thought experiment. I suspect a primary reason is because Einstein was well aware that there's no such thing as a "uniform gravitational field". Gravity follows an inverse square decay (not uniform linear decay). Gravity extends radially (not uniformly linear once again). These are the extremely fine ways to distinguish gravity from uniform linear acceleration (the "moving elevator"). To repeat the easy way: Just look out the window. In the following, Einstein discusses how he came to believe there should be *no* preferred reference frame for the description of physical phenomena: "Then there occurred to me the ... happiest though of my life, in the following form. The gravitational field has only a relative existence in a way similar to the electric field generated by magnetoelectric induction. *Because for an observer falling freely from the roof of a house there exists--at least in his immediate surroundings--no gravitational field* [his emphasis in italics]. Indded, if the observer drops some bodies then these remain relative to him in a state of rest or of uniform motion, independent of their particular chemical or physical nature (in this consideration the air resistance is, of course, ignored). The observer therefore has the right to interpret his state as 'at rest.' Here are two possible explanations for the above italics: - Einstein was misquoted. - Einstein was mistaken. Let's not fall into the trap that, "Einstein said it then it must be true". I don't know of anyone who is(/was) infallible. Of course, a third explanation of the highlighted quote is that the position I've been backing here is in error and that somehow gravity ceases to exist when an object is in freefall ("there exists...no gravitational field" in the immediate surroundings). Both positions appear to be very well defined. We are all free to reject what strikes us as absurd and to accept that which seems logical. Because of this idea, the uncommonly peculiar experimental law that in the gravitational field all bodies fall with the same acceleration attained at once a deep physical meaning. Namely, if there were to exist just one single object that falls in the gravitational field in a way different from all others, then with its help the observer could realize that he is in a gravitational field and is falling in it. If such an object does not exist, however--as experience has shown with great accuracy--then the observer lacks any objective means of perceiving himself as falling in a gravitational field. Rather he has the right to consider his state as one of rest and his environment as field-free relative to gravitation. The experimentally known matter independence of the acceleration of fall is therefore a powerful argument for the fact that the relativity postulate has to be extended to coordinate systems which, relative to each other, are in non-uniform motion." (Pais, A. (1982). 'Subtle is the Lord...': The Science and the Life of Albert Einsteing. Oxford: Oxford University Press. p. 178) So, Einstein would say that an ISS crewmember has the right to say he/she is in zero gravity. If Albert isn't turning in his grave over the use (nay, the popularity) of that term, I am certain that Isaac is. (my opinion) ~ CT |
#82
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Microgravity parable
From Peter Smith:
Mike Hanson wrote... Out in space and accelerating at 9.81 m/s^2, the man also has weight: he feels exactly the same force pushing up on the soles of his feet. These two 'forms' of weight are qualitatively identical, and this is where you have gone wrong: looking out of the window doesn't count. The key word is 'locally', and the question is: can you distinguish between the first and second cases *if you don't know where you are*? And the answer is: no. Mike, I fail to see your reasoning as to why looking out the window doesn't count as a simple way to tell that you are in a very strong gravitational field (due to the planet Earth, the Sun, the Moon, etc) as opposed to a "zero gravitation" field (no gravity). You ask whether one can distinguish between gravity and acceleration. But the question of whether one can distinguish between 'orbital microgravity' and a 'microgravity field' is a different question. Peter, please check "orbital microgravity" as a self-contradictory oxymoron. Orbits require gravity in order to be orbits. (I would be interested to hear an official explanation of how NASA resolves this blatant contradiction.) ~ CT |
#83
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Microgravity parable
Stuf4 wrote... You ask whether one can distinguish between gravity and acceleration. But the question of whether one can distinguish between 'orbital microgravity' and a 'microgravity field' is a different question. Peter, please check "orbital microgravity" as a self-contradictory oxymoron. Orbits require gravity in order to be orbits. duuh - that's why I used the quote marks, Stuf4. I went on to explain how you could (if you were in a sealed box with no windows and experiencing no obvious gravitational effects), how you could differentiate between orbit and absence of (significant) gravity. By the way, if you looked out the window, how would you detect a black hole? - Peter |
#84
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Microgravity parable
Peter Smith wrote:
Stuf4 wrote... You ask whether one can distinguish between gravity and acceleration. But the question of whether one can distinguish between 'orbital microgravity' and a 'microgravity field' is a different question. Peter, please check "orbital microgravity" as a self-contradictory oxymoron. Orbits require gravity in order to be orbits. duuh - that's why I used the quote marks, Stuf4. I went on to explain how you could (if you were in a sealed box with no windows and experiencing no obvious gravitational effects), how you could differentiate between orbit and absence of (significant) gravity. By the way, if you looked out the window, how would you detect a black hole? - Peter Apparently, according to Stuf4, you can see acceleration, but you can't see gravitation. |
#85
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Microgravity parable
Peter Smith wrote:
I went on to explain how you could (if you were in a sealed box with no windows and experiencing no obvious gravitational effects), how you could differentiate between orbit and absence of (significant) gravity. There are ways to fool the human body into thinking a plane is falling even though it is still climbing (by gradually reducing climb rate by a certain amount). There are ways to simulate 0g in a plane even though it isn't in orbit. On the ISS, your senses may be fooled into thinking that there is no gravity because you fall at the same rate as the walls, ceiling, floor. But a cell doesn't really have senses, nor do crystals, light waves etc. It is only in recent history that we found out that gravity also affects light. Before that, humans thought gravity only affected "matter" and didn't think light could be affected. Until we understand gravity 100%, it is wrong and/or arrogant for anyone to state that all the effects of gravity are cancelled if you are in the right spot on the ISS. |
#86
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Microgravity parable
Neelix wrote...
Until we understand gravity 100%, it is wrong and/or arrogant for anyone to state that all the effects of gravity are cancelled if you are in the right spot on the ISS. Of course. And a previous post of mine showed how to easily demontrate that they are *not* cancelled. - Peter |
#87
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Microgravity parable
From Peter Smith:
Stuf4 wrote... You ask whether one can distinguish between gravity and acceleration. But the question of whether one can distinguish between 'orbital microgravity' and a 'microgravity field' is a different question. Peter, please check "orbital microgravity" as a self-contradictory oxymoron. Orbits require gravity in order to be orbits. duuh - that's why I used the quote marks, Stuf4. (A perfectly accurate term is "micro-g". No contradiction.) I went on to explain how you could (if you were in a sealed box with no windows and experiencing no obvious gravitational effects), how you could differentiate between orbit and absence of (significant) gravity. I agree with your point there. There are other ways to tell that an astronaut is in a strong gravitational field (vice "zero gravity") beside just the windows. By the way, if you looked out the window, how would you detect a black hole? One way would be to observe the patch of blackness that defines the black hole's event horizon circled by a haloed grouping of apparent stars created by the gravitational lens effect. ~ CT |
#88
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Microgravity parable
Stuf4 wrote... By the way, if you looked out the window, how would you detect a black hole? One way would be to observe the patch of blackness that defines the black hole's event horizon circled by a haloed grouping of apparent stars created by the gravitational lens effect. If the Sun became a black hole, its event horison would have a 6km diameter. To see the black disc, I would have to be at most 350km away. At this distance the gravitational gradient would be significant, and I would be orbiting at 1.9kHz. I would be feeling like LooseChanj is about now I guess Pass me a iBuzz Aldrin/i Hic! - Peter |
#89
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Microgravity parable
"Peter Smith" wrote in message
... Pass me a iBuzz Aldrin/i Hic! We know that Drew Carey is a space fan- after all, he named the results from his garage brewery *Buzz* Beer! -- If you have had problems with Illinois Student Assistance Commission (ISAC), please contact shredder at bellsouth dot net. There may be a class-action lawsuit in the works. |
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