If you’ve been a baseball fan for any amount of time, you’ve likely already noticed a surprising little mystery we might call the “home run epidemic.” Not an official name, of course, but it says everything there is to say. Rather, it points to the question lots of insiders and even scientists have been scratching their heads over:

Where are all these home runs coming from?

Between 2014 and 2017, the number of home runs in Major League Baseball has spiked significantly. According to recent statistics, the total leapt up by 723 home runs from 2014 to 2015, an increase of 17.3 percent. This trajectory has continued up to present day … and no one really knows why.

That’s not to say we don’t have some information. In a recent article in the Chronicle of Higher Education, physics Professor Emeritus Alan M. Nathan of the University of Illinois at Urbana-Champaign explained that the secret is air resistance. Modern baseballs simply have less of it, so they can fly farther without slowing down. This leads to an increase in distance and a better chance the batter will make it all the way around the diamond.

Now the question becomes: Why? Why are baseballs exhibiting less resistance in the last few years?

“The quick answer is: We don’t know,” says Nathan. “We have looked into a number of different things; some obvious (like the height of the seams, the surface or weight of the ball), some much more subtle than that. And we have not been able to identify what feature of the ball that you can actually measure or see” that is responsible for the change.

What we do know? Neither MLB, steroids nor Rawlings is behind this, nor does there appear to be a conspiracy to make the game more “exciting” by upping home runs. Science-minded fans who want to know the answer now will be disappointed, but researchers are not giving up, so stay tuned. This mystery, much like baseball itself, will unfold in its own sweet time.