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Post by speakertoanimals on Oct 20, 2010 15:09:21 GMT 1
Wrong. We also have the simple fact that one object is higher than the other (i.e., we have to do work to lift one object to the position of the second), which means they are at points of different gravitational potential. And the fact still remains that general relativity predicts a time dilation based on he difference in gravitational potential, NOT the difference in field strength, and all experiments agree with relativity. Mind you, doesn't help that popular science articles such as this one: www.physorg.com/news204470740.htmlalso state incorrectly (or imply at least) that the effect is due to a reduced pull of gravity at a height. It isn't.
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Post by abacus9900 on Oct 20, 2010 15:29:15 GMT 1
It's a strange position to take to think you must either hold a professional degree in something or other or completely give up asking questions about it. Most people are by nature curious and some are more able than others so you cannot simply condemn everybody who does not, at a given stage, have the knowledge of a professor - that is just plain bonkers. How would anyone become interested and fired by a subject if they could not ask questions about it and perhaps go on to develop their knowledge further? In fact, this argument could be used to completely scrap state education since no child is born an expert in anything! What an eccentric person you are STA.
However, it's rather odd that you have not as yet presented this MB with any scientific basis for regarding creation ex nihilo as a legitimate theory. All you have asserted is that it is one of a number of possible solutions to the known data but have not told us why? I suppose you would use, yet again, the flimsy excuse that it's all way beyond our rather feeble intellects to grasp so why bother anyway? If so, I think this would be more of a cop-out than a valid reason for not justifying your claims.
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Post by carnyx on Oct 20, 2010 15:37:24 GMT 1
STA;
From the POV of the objects, all they know is that they feel less 'g' .. they are lighter.
So where and how does this potential energy of yours get stored within the object?
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Post by abacus9900 on Oct 20, 2010 15:41:41 GMT 1
Yes but you see, you have still failed miserably to get the key ideas over, preferring instead to couch it all in jargon (yet again).
Why don't you explain to people that gravitation is just another form of acceleration so that a direct parallel can be seen between gravitational time dilation and time dilation due to an accelerating body far out in space well away from gravitational fields? You should explain that the Equivalence Principle states that you cannot tell the difference between standing on the earth and standing in a lift which is being accelerated out in free space. You should also have made it clearer that the gravitational potential of an object is equivalent to the energy needed to move that object up against the earth's gravitation pull which is 'given back' when such an object is released, such as, for example, when water is raised to a given height in order to store the energy used in raising it for use in driving a hydroelectric plant. Analogies again, STA, try to use more of them next time. It's all about presentation, STA, Savvy?
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Post by abacus9900 on Oct 20, 2010 15:48:05 GMT 1
carnyx, I'm really beginning to consider the possibility that, in reality, STA is some old codger with a science textbook in front of her quoting it word for word without really having grasped the underlying principles. This would at least explain why she seems unable to convey ideas in a relatively straightforward way. It's really not rocket science but basic physics so how in the world she manages to tutor her (alleged) students just confounds me!
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Post by carnyx on Oct 20, 2010 16:45:17 GMT 1
Abacus9900,
I had 'her' down as a whole JCR, but your explanation seems more plausible. I think it also fits Olmy, who apparently does not even understand basic logic.
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Post by olmy on Oct 20, 2010 16:58:53 GMT 1
...Olmy, who apparently does not even understand basic logic.... Oh dear, another military grade irony meter reduced to smouldering wreckage! I'm quite convinced you wouldn't know logic if it gave you a haircut..... [Have you noticed I'm now taking your approach to 'argument' and not actually tackling the points but just saying you are wrong. I can see the attraction, it's much easier....] ;D ;D ;D ;D
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Post by abacus9900 on Oct 20, 2010 17:06:38 GMT 1
Abacus9900, I had 'her' down as a whole JCR, but your explanation seems more plausible. I think it also fits Olmy, who apparently does not even understand basic logic. Well, I think with Olmy, he seems very mathematical, which isn't to everyone's way of thinking. I think some people think mathematically, others think in other ways; you play to your strengths I suppose.
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Post by abacus9900 on Oct 20, 2010 17:10:59 GMT 1
Abacus9900, I had 'her' down as a whole JCR... JCR?
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Post by olmy on Oct 20, 2010 17:11:03 GMT 1
It's a strange position to take to think you must either hold a professional degree in something or other or completely give up asking questions about it. I've been searching back through the thread for someone who said that. No luck. All that I could find was the blatantly obvious point that there are limitations to understanding complicated subjects unless you are both able and willing to study them in depth. People seem to accept that when it comes to (say) brain surgery or aeroplane design - you don't get endless amateurs who've watched some telly program telling the experts they are wrong. Neither do you get complaints that said experts cannot explain their specialism to the point that said amateurs can see the detailed problems and immediately contribute to the subjects.....
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Post by speakertoanimals on Oct 20, 2010 18:01:11 GMT 1
No scientific basis? Did I not refer readers to the quantum cosmology pages at Cambridge? If people don't think that DAMTP at Cambridge constitutes a scientific basis for a theory, then that is their problem, not mine.........
As regards the equivalence principle, I did indeed bring that up early on in the very thread where I pointed out that gravitational time dilation depends on potential, not force of gravity...........
As regards questions about where a body stores its gravitational potential energy.............Well, asking that and thinking it is some sort of clincher just shows that the asker has no idea about the very basics, and had really better understand those before trying to make ANY statements about gravitational time dilation.
Short answer -- where does a body store its kinetic energy, especially since whether or not a body has any kinetic energy depends on your point of view! Similarly, the exact amount of gravitational potential energy of a body depends on where you chose to define the zero (since as I keep saying, the zero of potential is arbitrary!).
But you can give the concept a physical meaning, but not in terms of the body, but the spacetime. So, what do a whole load of rocks suspended above the earth want to do? They want to fall. When they do, they lose GPE, and gain kinetic energy.
But there is another way to look at this. Think of the rocks that make up the earth spread out over space. Then we have zero gravitational field, if evenly spread, and zero kinetic energy. Now nudge it a little bit, so one region is just that little bit more dense than elsewhere. Now you will have started a gravitational collapse, and if you wait long enough, you will end up with all the rocks in a big lump (probably quite hot as well!), and a gravitational field around the lump.
So, where did all that energy come from? What else has changed? The gravitational field. We went from spread out rocks and FLAT spacetime, to hot rocks in a lump, and curved spacetime. To make energy budget fit, the answer is rather than thinking of GPE, we instead have energy in curved space, but that energy is NEGATIVE, and the more curved, the more negative.
SO, we start with zero energy,and end up with a large negative energy in the curved spacetime, cancelled out by the large positive energy that the rocks had as they gained kinetic energy as they fell.
So, GPE is not in the rock, but in the effect that rock has on the spacetime around it, and on the way that spacetime gets more curved as the rock approaches earth, since adding the rock increases the gravitational pull of the earth just a little bit.
And that is why rocks fall, because curved spacetime has negative energy compared to flat spacetime.
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Post by speakertoanimals on Oct 20, 2010 18:06:46 GMT 1
And when my students write what you wrote, that's called plagiarism (i refer people to my own posts on the equivalence principle), but in this case, really bad plagiarism in that you neither explained your basic terms, and managed to use more jargon than myself.........
And that's the problem with failing students as well, they can't see the difference between an actual explanation, and their garbled attempt at one.
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Post by carnyx on Oct 20, 2010 18:23:16 GMT 1
Olmy ... teill us what the JCR is ....
And where is anybody telling anybody that they are wrong ... (apart from that gravity gradient bollocks) ... except in posts from you and STA.
And, speaking as an actual ex-expert in aircraft design, there was no problem in answering comments by interested people ... the problem is, that it was much fun that one could get seriously distracted!
(And as a matter of fact, I learned from Barnes Wallis himself that this ought to be the proper attitude for designers to take, because they might learn something of value, which was refreshing after experiencing years of accidié-ridden academics and teachers ....)
And with regared to a singular lack of understanding of logical argument. olmy is in a world of his own. I have yet to see a logical sequence of arguments that make sense from him .. other than outbusts of bluster.
Olmy ... STA ......can either of you actually start a thread?
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Post by abacus9900 on Oct 20, 2010 18:33:17 GMT 1
It's a strange position to take to think you must either hold a professional degree in something or other or completely give up asking questions about it. I've been searching back through the thread for someone who said that. No luck. You did not look very hard, did you Olmy? STA distinctly stated that the information given in popular TV or radio shows or perhaps on MB's such as this when not presented in technical detail was fairly worthless, which is complete codswallop because it is the value or the potential value to the person receiving it that is of value. STA herself admitted that when she was a kid such information as was available took her interest in subjects like physics and inspired her to go on to higher learning. Why she and you have a problem with this is quite mysterious, unless, of course, it is your view that STA is an Oxford don and as such is infallible and to be worshipped. Get the blinkers off Olmy, please.
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Post by abacus9900 on Oct 20, 2010 18:43:21 GMT 1
No scientific basis? Did I not refer readers to the quantum cosmology pages at Cambridge? If people don't think that DAMTP at Cambridge constitutes a scientific basis for a theory, then that is their problem, not mine......... Probably expressed in so much jargon as to be virtually incomprehensible to most people! STA, the reason you are supposed to come on here is to explain things to us mere mortals, remember? Yes, ok, but why confuse things by looking at them backwards? Negative energy indeed!.
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