One of the biggest questions facing astrophysicists in the 21st century is the most obvious: What is the stuff of the universe -- the black space between the stars and planets -- made of?

We usually call that black stuff "dark matter." Scientists believe it holds the universe together despite the furious and unprecedented amounts of energy unleashed during the violent, universe-forming singularity known as the Big Bang.

Though it is an imperfect analogy, it helps to think of dark matter the way we think about gravity when contemplating the role it plays in the scheme of things.

Even while trying to get one's head around that mystery, we're also forced to ponder the conundrum scientists call "dark energy" -- the cosmic accelerant that accounts for the rapid expansion of the universe.

Scientists have no idea how dark matter and dark energy interact, but thanks to a gift of more than $5 million from Bruce McWilliams, a Carnegie Mellon alumnus and trustee and the chairman and CEO of Tessera Technologies, Carnegie Mellon University will be able to put additional professors in endowed chairs to beef up its already stellar lineup of astrophysicists in the search for answers.

The donation of Mr. McWilliams and his wife, Astrid, will make it possible for Carnegie Mellon scientists to delve more deeply into the 13.7-billion-year mystery that is the universe. Pittsburgh -- and all of humanity -- applauds their multimillion-dollar investment in what may be a never-ending search for knowledge.