Some weird stuff is going on. Dark stuff.
We can look out and calculate that galaxies are spinning too fast and should fly apart but they don’t. So we think there’s too much gravity.
And so we came up with the notion there’s some invisible undetectable stuff called dark matter making up more than 96% of the universe.
Also weird is this lensing effect astronomers see, caused, they suppose, by said dark matter.
Yet we haven’t seen it directly nor detected it even though it should be all around us.
As I said. Pretty weird stuff going on. Leaves plenty of mystery in science.