
#1
Jan1813, 02:41 PM

P: 10

Hi all,
I'm having a discussion with someone who believes they understand GR, here is their understanding of how gravity works... "The time and space at your feet are different from the time and space at your head. This has been experimentally verified, especially in terms of the time component. We have the technology to measure time accurately enough to actually make these kinds of experiments, and they have been made. A clock placed at your feet will run slower than a clock sitting on your shoulder. It is the dilation in spacetime (both space and time) between your head and your feet that cause your body to accelerate downward toward the massive earth. And because this is indeed the cause of gravity on the Earth, this means that you body is actually exerting a downward force onto the Earth's surface." 



#2
Jan1813, 03:16 PM

P: 70

We do exert a gravitational force on the earth, if you look up the equation you can establish how much the earth is "pulled" up towards you if you were to jump... it's obviously negligible, but it does happen. 



#3
Jan1813, 03:23 PM

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#4
Jan1813, 03:35 PM

P: 10

Understanding General RelativityHow can a body in free fall be exerting a force? Isn't the surface of the earth an accelerated frame, hence it is the surface accelerating upwards towards the body in free fall? 



#5
Jan1813, 03:42 PM

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#6
Jan1813, 04:18 PM

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#7
Jan1813, 04:39 PM

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There is a precise geometric sense in which we are "travelling" through time (or rather spacetime), and the fact that the clock at your feet is "rotating" slower means that your path through spacetime is "turning". The only way to stop "turning" is to go into freefall where you wouldn't detect any difference in time between your head and your feet, but the force of the ground on your feet makes you keep "turning". 



#8
Jan1813, 04:50 PM

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#9
Jan1813, 04:59 PM

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#10
Jan1913, 09:19 AM

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#11
Jan1913, 09:25 AM

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#12
Jan1913, 09:30 AM

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#13
Jan1913, 10:32 AM

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#14
Jan1913, 10:51 AM

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Jan1913, 11:00 AM

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#16
Jan1913, 11:02 AM

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So I am sitting here perfectly still but accelerating towards the Earth at 9.8m/s^2. How does classical mechanics or GR explain that? Newton certainly knew about it. 



#17
Jan1913, 11:07 AM

C. Spirit
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#18
Jan1913, 11:20 AM

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