It’s energy/matter leakage from other dimensions.
If we lived in a two dimensional universe (think sheet of paper) and we were getting warmer because the desk lamp was shining on us, we would be wondering, “where’s all this heat coming from?” And we’d feel dark, compressed areas left by a pencil and wonder what caused that, too.
You’ve come to the same conclusion I have. With string theory and all of the extra dimensions involved other complete University could be stacked upon ours like some fourth dimensional book. It would explain why gravity is so weak with it reaching across more dimensions than light does.