We typically think of the universe as being mostly empty space, and that informs our understanding of how alone, and how adrift, we sometimes feel our planet to be. But what if the universe can be better understood as a liquid? According to the recent work of European physicists Stefano Liberati and Luca Maccione, there's a good chance that it can—that the spacetime we think of as empty is actually a "low-viscosity superfluid." And if this new theory holds water (so to speak), it may finally solve the mystery of quantum gravity.
Cambridge theoretical physicist Benjamin Bahr explains quantum gravity—or, rather, explains why we can't explain quantum gravity, and why it'd be a good thing if we could—here:
You can read the Liberati-Maccione study, published in the April 2014 issue of Physical Review Letters, here.
The practical implications of the universe functioning as a superfluid may be limited for now, but the idea raises some interesting possibilities. In addition to providing a vehicle for finally reconciling the theories of gravity and quantum mechanics, it may help to explain what dark matter and dark energy are, how the universe formed, and so forth.
Or it may turn out to be one of the many unfalsifiable hypotheses proposed to answer cosmology's the big unanswered questions—and that would be OK, too.