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Drakkith
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I'm sorry, Harry, but I can't figure out how anything from post 23 onward is related to the discussion on how gravity works.
This discussion: "the gravity [what causes it?] "Drakkith said:I'm sorry, Harry, but I can't figure out how anything from post 23 onward is related to the discussion on how gravity works.
In the sense of the Equivalence Principle, they are exactly the same. The key of the EP is that the experimenter cannot look outside, so he cannot tell if his lab is...harrylin said:It's partially the same as you say,
You are the one introducing unnecessary complications, by making a physically irrelevant distinction between active and reactive forces.harrylin said:and the unnecessary complication for the analysis that you introduced
I'll mention this a last time, as repetition becomes tiring: the ground is held up by pressure forces within the Earth. There is thus no upward (and thus outward) flying ground which idea leads the unaware to imagine expanding space or things like that as cause of gravity, as illustrated in thread https://www.physicsforums.com/threads/poincares-space-dilemma.821480/A.T. said:[..] The role of the rocket thrust is equivalent to the role of the contact force from the ground [..]
A.T. said:The role of the rocket thrust is equivalent to the role of the contact force from the ground,
Just like the chest in case b) is held up by pressure forces in the combustion chamber.harrylin said:the ground is held up by pressure forces within the Earth.
The chest in case b) also isn't flying outward. So the equivalence I state above still holds true.harrylin said:There is thus no upward (and thus outward) flying ground
On the surface of the Earth, what cause the lines of longitude, parallel at the equator, to come together at the pole?thecosmos123456 said:what causes the particles to come together
This reasoning is incorrect in curved spacetime. In a flat spacetime it would indeed be correct that the surface of the Earth could not be accelerating (proper acceleration) outwards while retaining a constant radius, but spacetime is curved and so it can indeed accelerate (proper acceleration) outwards while retaining a constant radius.harrylin said:as we know, the surface of the Earth cannot be flying upward as the radius of the Earth is constant.
Locally we can pretend that the effect is caused by the upward flying of the ground in an inertial frame in flat spacetime. Globally the effect is still caused by the upward flying (proper acceleration) of the ground, but we cannot ignore the curvature of spacetime and there are no global inertial frames.harrylin said:Yes, locally we can pretend that the effect is caused by the upward flying of the ground.
Hmm, so does a debunking of a debunking equal a rebunking or just a bunking?harrylin said:It was even the explanation of gravity that was debunked in the other thread; the Earth is not expanding (as it should, to make it work for falling observers from all sides).
Actually, the prime objection is that it does not work in general, but it only works in the Schwarzschild and Kerr spacetimes.Rob Benham said:After almost a lifetime's interest in gravity, and some years ago, this forum gave me a steer to a paper being reviewed by an American professor. It was all about the inflow into matter of some kind of fluid spacetime, and was uncannily like the notion I'd had in my student days. The prime objection to the hypothesis was something like: 'I'm not sure where all this spacetime is going.'
PF is not for personal theory development. The published "flowing spacetime" model works only for Schwarzschild and Kerr spacetimes, and specifically does not work for cosmological spacetimes.Rob Benham said:I've always felt that the concept of the Universe changing scale* is no harder to accept than learning it was expanding. Both take quite a leap of faith. In such a universe, spacetime - whatever it turns out to be - would have a limitless sink-hole and limitless energy proportional to the mass it was flowing into. *every part of every nucleon as well as the space between.
Clear nice example. I agree.DaleSpam said:To understand the importance of curvature, consider two latitude lines on a sphere. For simplicity consider the latitude lines 5° N and 5° S. As you follow those lines around the sphere, they maintain a constant distance from each other. However, the 5° N line is constantly turning (covariant derivative) to the north and the 5° S line is constantly turning (covariant derivative) to the south. So they are turning away from each other but maintaining constant distance. This is impossible on a flat surface, but possible in a curved surface.