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Density is important in a way, but gravity is well understood as an effect of mass. If Dr Evil shot the Sun with a shrinking ray, so all its mass were compressed until it became a black hole - Earth would still orbit it the same way (same distance) it does now. The density has no effect on how "much" Gravity Earth feels from the Sun. (Especially at this distance, where we can calculate gravitational effects as being from the centre of mass). The difference would be as you get closer: if the Sun were compressed enough it could become black hole, where it would be possible to get so close you couldn't escape. That even applies to Earth. Right now we can stand - and even jump a little ... because we are far enough away from it's centre of mass. But if the mass of Earth were compressed enough (essentially, by magic, same mass but smaller radius), then standing on the "surface" we'd be squashed by the gravity - even to the point where (again, this would take magic) Earth became a black hole. This is quite different to digging down into Earth in its current un-compressed state. As we dig down, some of the mass is above us instead of below, so we'd actually feel less and less gravity.

Everything has an area of applicability. Different models are "better" or "worse" in different contexts. Say you are asked how fast you'd be running - with relation to the ground - if a train was going South at 10 km/h and you are running South along the top of the train at 10 km/h. Probably you'd say 20 km/h. You'd be wrong, but at those low speeds you'd be close enough, and there's no need to bring relativity into it. Newtonian physics is still plenty good in plenty of areas of applicability. Sure it's "wrong". But it's "good enough".

If there was anything materially significant in space, our Planet would be having to push it's way through it - we'd see the turbulent effects on our atmosphere, and our orbit would slow, and eventually we'd all drop into the Sun. Hooray for the (near) vacuum of space!

Turns out it's not that obvious. If the Universe were not flat, but curved back on itself (there are various proposed shapes) you actually could have three points where the angles don't sum to 180. http://en.wikipedia.org/wiki/Shape_of_the_universe

Relative to something else, yes, the ball gets more "relative mass". But relative to the box it's in, no. The whole point of the equivalence principle is that in looking at the box and ball we can consider them as at rest. The ball will hit the floor of the box with the same force, regardless of speed (of the box, relative to whatever else), as long as the acceleration at each time is the same.

tonyj18, to take a couple of steps back, to your OP: It's already thought that every atom has a Gravitational effect. Every atom in your body is "attracting" every atom in the Earth. If you step off a ledge and fall down to Earth, it's also falling up to you. (Just, you know, it moves much less). Your talk of "inner core" seems to imply you think Earths gravity all "comes from" the centre. That's not quite true, it's "coming from" all of Earths atoms; it's just convienient in most cases to assume it all originates from the centre of mass. Example: as you go deep under ground, you'll experience less acceleration from Gravity, as more of Earth is above you and less below. Example: the "attraction" of a nearby mountain can and has been measured. After that, I don't really understand your leap to an "explanation" of gravity.

You could look at the G-forces pilots can cope with (in flight suits) before blacking-out.

That's not a result, it's an opinion.

It seems to me you are looking for the "God of the gaps", but pointing out that the gaps may be too small to see so we need to look harder, or perhaps that the gaps are unrecognisable so we need to re-train our detectors. Still seems to go nowhere. Something will either, to current knowledge, be of "natural" origin, or it won't. You will have trouble forcing current knowledge towards being able to detect something we don't about yet. e.g. Cosmic rays were detected by chance (more or less). Nobody said "I bet there are cosmic rays, so I'll imagine what they'd look like and build a detector for them". Do you have an actual example of something that you think is from some "clever project"?

The Universe has rules. Stuff interacts in certain ways. Anything that might appear to be "cleverness" is simply an emergent property of that. A snowflake may be amazing to look at up close, but it was no "clever project" from some artist, it is simply a result of the way ice forms (the "rules" that govern ice crystals). e.g. Much like I.D. versus evolution - the simple rules of natural selection explain the life we see; we don't need to imagine an "intelligent designer". If there were some "clever project", then the cleverest part of it is making itself undetectable by providing no evidence. So the hypothetical project is so irrelevant it equals non-existant.

From the University of California, another opinion: http://math.ucr.edu/home/baez/physics/Administrivia/rel_booklist.html (Page) "Original by Chris Hillman (with contributions by Nathan Urban) September 1998." In the section that begins "Now we are starting to get to the really good stuff!" ... (My highlights): It seems to me: 1. A person can think that a book is "great" while not thinking everything in that book is "perfect". 2. Pointing out that something in a book is imperfect (or even flat out wrong), is not the same as calling the author of that book a "liar" or "crank", nor is it "denouncing" that book. 3. A book can't be listed as "acceptable as evidence", if that is intended to mean "anything quoted from it must be considered fully accurate".