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Originally Posted by renormalised
That's true, the reason why we feel it here on Earth is because we're living inside Earth's gravitational well. We feel an acceleration towards the Earth's centre as the "pull" of gravity. The Sun, being so far away, has minimal effect (although tell astrologers that  ) |
I don't think you understood my resoponse. We are actually much deeper inside the gravity well of the Sun than that of the Earth. The reason we don't feel the effect of the Sun's gravity is that we live on the surface of the Earth which is in free-fall around the Sun.
This is the same reason that an astronaut on the Space Shuttle doesn't feel the gravitational effects of the Earth even though they are only a couple of hundred kilometers above the surface of the Earth - they are in free-fall around the Earth - in Einsien's language they are in an inertial reference frame.
From our reference frame on the surface of the Earth, we are not in free-fall relative to the Earth. In Einstein's language: we are not in an inertial reference frame. The space-time curvature induced by the mass of the Earth is thus experienced in this frame of reference as an acceleration which we call gravity.
To repeat: the gravity well of the Sun is vastly larger than that of the Earth at our position. We just don't experience it from our frame of reference in free-fall around the Sun. Likewise, the gravity well of the galaxy is vastly larger here than that of the Sun: we just don't experience it from this frame of reference because the whole Solar System is in fee-fall around the centre of the galaxy.
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Originally Posted by renormalised
I wouldn't exactly call jumping off a cliff as being in free fall!!!! The result at the end is never free  |
Well the example Einstein used himself was being in an evelator car when the cable breaks. He realised that the occupants would be unable to determine if they were in free-fall or in intergalactic space.
In the same way, if you jump off a cliff, you feel weightless as you are in free-fall (neglecting effects of air resistance obviously). When you hit the ground, you are obviously no longer in free-fall. (Einstien himself only bothered to mention this obvious fact in his little book on relativity for the general public:
http://en.wikisource.org/wiki/Relati...General_Theory).
This is the fundamental line of reasoning on which the general theory of relativity is based. Einstein realised this in 1907 but it wasn't until 1915 that he had got his head around the math enough to publish a complete physical theory theory of gravity, electomagnetics and motion - the General Theory of Relativity.
Quote:
Originally Posted by renormalised
That's a given, greater mass = much larger curvature of space.
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You have this correct.
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Originally Posted by renormalised
I'm just as concerned about pseudo-science as you are, however I'm more careful about whom I address as being one who talks pseudo-science. Much of particle physics and cosmology these days sounds like pseudo-science but you'd never address someone like Neil Turok as being a crackpot!!!! (even if he looks like the proverbial mad scientist ). |
I have never said that Neil Turok is a crackpot. The Chair of Mathematical Physics at Cambridge University is most certainly not a "pseudo" or "fringe" scientist.
All of the things I have mentioned here (and the laws of termodynamics) were covered in a course called PY101 that I studied in my first year at university about 15 years ago. If you are genuinely concerned about psedo-science, I implore you to get your basic scientific facts straight before confronting the more "cutting-edge" areas of physics.
I assure you I am far from arrogant and I mean no disrespect to you. I do have the greatest respect for the scientific tradition as first described by Descartes and perfected by Newton and will jump to it's defense when provoked.
Take care,
Doug