Well, quite simply, we have tested it over and over again and it has always been correct.In other words, we accept it as true because of inductive logic (i.e., we went from a series of observations to a general conclusion).
This value is exceedingly useful and lets us do something really neat.For any two bodies, if we know the mass of each object and the distance between them, then we can use G to calculate the force of gravity between those two objects.These calculations will, however, only work if G is actually constant.The question is, of course, how do we know that the gravitational constant is in fact constant?” The problem is that creationists are misusing the term “assumption,” and, as usual, are completely misconstruing how science actually works.
As I will demonstrate, coral growth rates, radioactive decay rates, etc. Rather, they are the conclusions of simple inductive logic.
When we make a statement like that, we aren’t “assuming” that growth rates weren’t faster in the past; rather we are applying inductive logic.
Also, note that the argument that creationists are making here is nothing more than an ad hoc fallacy.
There is absolutely no reason to think that coral reefs grew faster in the past, or ice cores and varves formed multiple layers annually, or radioactive particles decayed faster, etc., but creationists are that those things occurred even though there is absolutely no evidence to support those notions.
That is the proper use of “assumption.” An assumption is something which you choose to accept as true despite a lack of supporting evidence.
Importantly, we can never prove that G actually is a constant, because doing that would require us to test G against every single piece of matter in the universe.