What earthbound experiments show gravitation is general to all matter, and not just towards the earth?

Question

I was debating a flat earther and predictably it turned into a debate on gravitation. He said as far as we know, things fall down to the earth, not because its towards the greatest mass. The generalisation of gravitation to all matter is only a theory Newton and other physicists came up with.

and I could not answer this question(title) to me with these conditions he imposed

1.) No astronomical observations allowed.

We can't trust the demon worshipping virgin sacrificing astronomical observatories. If he allowed astronomical observations, then it would've been easy to point out the orbits of various planets and stars, and the mathematical analyses of their observed orbital mechanics, taking into account planetary masses and distances would have easily put paid to his silly objection as it would be obvious that when controlled for orbiting distance, more massive centres produces faster orbits.

2.) The classical cavendish experiment is not allowed. It measures extremely tiny masses, and even tinier "so called" gravitational effects, the entire dataset produced from such an experiment could be from either fudging the numbers or instrumental problems,and the wild uncertainties in various determinations of Big G (in the newtonian model) agree with him.

I googled for a bit about the largest scale cavendish experiment ever conducted as I think bigger masses would be more reliable, found nothing, resorted to chatGPT only for my question to completely fry it's neural network.

So i'm running out of ideas which is why i arrived here :)

Answer 1

There is some equivalence-principle literature based on free-falling retroreflectors (no air resistance) in underground boreholes, from sounding towers aboveground, and in vertical shafts in dams. The dam measurements are interesting because you can add and remove a large adjacent mass of water from the reservoir. Look for E. Fischbach's literature on "fifth force" measurements from the 1980s and 1990s, but skip ahead to the experiments which ruled out Fischbach's proposals.

The borehole and sounding-tower measurements were used by oil extraction geologists in that era to map underground density variations. This has the advantage of satisfying the economic argument for distinguishing science from pseudoscience.

Don't get too hung up on convincing your acquaintance, who may be unreachable due to an epistemological dead end. But don't miss this opportunity to dig into the literature, either — it is varied and interesting, and definitely addresses your acquaintance's concerns.

Answer 2

Every so often we get questions from flat-Earthers, people with religious convictions, or people with personal theories. Often they do not listen to other answers. It sounds like you have found such a person.

There is often no point to showing such a person evidence that convinces a physicist. That isn't where he searches for truth. His personal source of truth may be the Bible, politics, what feels right to him, or the feeling of importance he gets from being right.

It is good to show people how physicists think. But if they discount it as not the right way to find truth, you might as well stop trying.

Evidence for universal gravitation includes evidence from astronomical observatories and the Cavendish experiment. This is true regardless of his opinion. It is true regardless if classical gravity isn't totally right. Or if general relativity isn't totally right. That is still where we get evidence that illustrates how gravity behaves.

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It is easy to dismiss such people as having no experience or talent for rigorous thinking. It is often true. But it isn't always the case. It is worth watching for people who take their truth from multiple sources. They do exist. Some are very intelligent.

When I was in graduate school, one of the brighter physics students, far smarter than me, was also a fundamentalist Christian. At the time there was a big debate in the physics community over the age of the universe. Theory suggested it was 10 billion years old, but there were objects that appeared to be 20 billion years old. He was very interested. At the same time, he was studying ancient Greek so he could read early versions of the Bible. He was searching for versions without errors of translation to confirm the universe was 4000 years old. As far as I could tell, he just compartmentalized his thinking. He slowly changed his religious views, but never gave up the idea of a powerful creator.

One point is that he had two sources from which he took truth. When they were in conflict, it did not mean he could dismiss one or the other. It certainly didn't make it obvious to him that my views were right.

Another point is that he was trying to resolve the conflict. Shouting down his non-scientific side would not be helpful. It would be nice if he ultimately agreed with my thinking. But if not, he was still a bright, interesting person and a good friend.

Finally, he seems to have resolved the conflict to his satisfaction. He seems to have chosen both. This is unusual. It almost always comes down to choosing one way over the other.

If you see a question from someone trying to figure out whether physics is right, it is worth explaining as clearly and objectively as possible. Then let him wrestle and decide how he thinks. It usually does not help to point out how physics pokes holes in his other beliefs. It certainly doesn't help to be disparaging.

On the other hand if someone is already convinced and just wants to be told how right he is, there is no need to accommodate him. There is no benefit to telling him how wrong his is or what an idiot he is. We should just close the question.

This question is a meta question about how to handle such questions from such people. As such, it is probably off topic. But it has value, and doesn't deserve the down votes it is getting.