We all know there is gravity, Mrrzy. What we have theories about is what causes it and exactly how it works and whether there are any anomalies or variances in how it works. There are some very interesting theories now about gravity, and probably a great deal yet to be discovered concerning it.

Now, about "beyond reasonable doubt"....

Prior to the 1950s, the general science community felt sure beyond a reasonable doubt that continental drift did not and could not have ever occured. A scientist named Alfred Wegener thought otherwise and proposed his theory in 1905 about the breakup of an original enormous continent "Gondwanaland" into the present separate continents (plate tectonics...continental drift). He was scorned utterly by the mainstream science community who felt that it was beyond a reasonable doubt that continents do NOT move around, but have a permanent, fixed position on the globe.

They were wrong. ;-) Evidence since the 1950s has confirmed that Wegener was correct in his theory.

The conventional and popular view in any era NEVER doubts itself one iota...but it frequently turns out to be dead wrong after the passage of some time. The society of each century has the fun of debunking the sacred cows of the previous one...including the scientific sacred cows. I doubt we've seen the end of that.