Gravity

Lift a pétanque boule and throw it straight up. It will ascend for a while but soon it will fall to the ground. What can be deduced from it?

There is a force affecting the boule that slows it down and accelerates downwards. Otherwise, in accordance with the law of inertia, it would move at a constant velocity.

This effect cannot be explained by mere environmental resistance. Firstly, the relatively aerodynamic sphere would slow down much longer. Secondly, the air resistance along with the inertia would block the boule, not force it to fall. There must be something else going on. The Flat Earth Society offers three explanations: hydrostatic buoyancy, acceleration of the Earth, or electromagnetism.

Let's start with the electromagnetic theory. It is based on paramagnetism. Paramagnetic materials, such as aluminum, barium and calcium, are attracted by (any) external magnetic field. So, in theory, the Earth would not have to be gravitational but rather it would attract objects with its own magnetic field.

However, some substances, such as water, copper or bismuth, are purely diamagnetic. They behave exactly the opposite way - they are repelled by (any) external magnetic field. Thus, if gravity did not exist and paramagnetic phenomena was strong enough the Earth could attract some objects magnetically but others would simply shoot off.

Let's move to the buoyancy theory. The hydrostatic (and aerostatic) buoyancy results from the difference in hydrostatic pressure below and above a body; below it is larger than above it. Therefore, there is a pressure exerted on the body from below which manifests itself as an ascending force. However, several problems would appear in a situation where there would be no gravity serving as an opposing force.

Firstly, the force buoying the body up would be greater than what we can observe in reality. Secondly, greater pressure is verifiably always present under the body so the hydrostatic force always aims upwards. In a world without gravity, each and every object would always rise whereas in our world some levitate or even fall.

Not only does the hydrostatic force fail to imitate gravity, it cannot exist without the presence of Earth's attractive force. Something must be constantly compressing the fluid otherwise no pressure would be created or it would spread evenly. Therefore, no difference in pressure and no hydrostatic force would exist. Moreover, the attractive force must always point downwards otherwise the observed hydrostatic force's direction would also change.

These claims are also supported by experiments. In certain environments, such as during a parabolic flight or in Space, a lack of hydrostatic pressure and hydrostatic lift power is proven although there would be no reason for it without the existence of gravity.

You could also let objects fall in a vacuum chamber. In such an environment there cannot be any lift therefore there must another force present. Could it be possible that pressure and buoyancy exist even in vacuum? Firstly, there is no evidence for such a phenomenon. Secondly, the vacuostatic gravitational theory would still face the same troubles as the hydrostatic theory (see above). And thirdly, the intesity of vacuostatic pressure would vary on differently dense objects so they would fall at different speeds. However, in reality, all objects in vacuum fall at the same speed.

What about the theory of the ever-accelerating Earth? Firstly, all objects in the weightless state would have an acceleration of about 10 m/s² relative to Earth. However, this is ruled out by the existence of spaceships and space stations (such as the well-observable ISS) which, without a doubt, even after the considerable time spent in the state of weightlessness, haven't fallen on Earth.

Secondly, it cannot explain different gravitational accelerations. Even if the individual latitudes would accelerate differently, the gravitational acceleration also depends on your altitude, whether you are moving west or east (the Eötvös effect), and so on.

Furthermore, even a slight difference would soon tear the Earth apart. For you to get an idea: in not even 15 minutes of accelerating from zero velocity the elevation difference between Mount Huascaran and the Arctic Ocean, the areas with the most extreme gravitational accelerations, would be larger than between the bottom of the Mariana Trench and Mt Everest on the stationary Earth and in 29 hours it would be 384 000 km, the same as the mean distance between the Earth and the Moon in the heliocentric model.

In result, there must be a force attracting objects to the Earth, which is not caused by hydrostatic buoyancy or the theoretical acceleration of the Earth or electromagnetism.

What leads me to the conclusion that it is the "Newtonian" gravity? Firstly, massive objects are provably attracted to each other (see, for example, the Cavendish or the Shiehallion experiments). Secondly, the force of Earth's attractive force decreases with a second power of the distance, in accordance with the Newton's law of universal gravitation. Thirdly, the force of "Newton's" gravity corresponds to the observed Earth's attractive force. Fourthly, gravity explains a number of natural phenomena, such as tidal forces and proven phenomena predicted by Einstein's general theory of relativity.

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