The End of Everything (Astrophysically Speaking)

by Katie Mack

Because we don’t know whether it’s really a cosmological constant or not, we generally call any hypothesized phenomenon that could make the universe accelerate in its expansion dark energy. To throw some more terminology into the mix, an evolving (i.e., nonconstant) dark energy is often called quintessence, after the “fifth element,” a mysterious something-or-other that was popular to philosophize about in the Middle Ages and is not really much more precisely specified now. A nice thing about the quintessence hypothesis is that it could lead us to a theory with some parallels to the cosmic inflation at the beginning of time. We know that whatever it was that caused cosmic inflation eventually turned off, so perhaps a similar accelerated-expansion-causing field could have turned on since then, causing the acceleration we see today.