Source: Science News

Eventually, the universe will end. And it won’t be pretty.

The universe is expanding at an accelerating clip, and that evolution, physicists expect, will lead the cosmos to a conclusion. Scientists don’t know quite what that end will look like, but they have plenty of ideas. In The End of Everything, theoretical astrophysicist Katie Mack provides a tour of the admittedly bleak possibilities. But far from being depressing, Mack’s account mixes a sense of reverence for the wonders of physics with an irreverent sense of humor and a disarming dose of candor.

Some potential finales are violent: If the universe’s expansion were to reverse, the cosmos collapsing inward in a Big Crunch, extremely energetic swells of radiation would ignite the surfaces of stars, exploding them. Another version of the end is quieter but no less terrifying: The universe’s expansion could continue forever. That end, Mack writes, “like immortality, only sounds good until you really think about it.” Endless expansion would beget a state known as “heat death” — a barren universe that has reached a uniform temperature throughout. Stars will have burned out, and black holes will have evaporated until no organized structures exist. Nothing meaningful will happen anymore because energy can no longer flow from one place to another. In such a universe, time ceases to have meaning.

Perhaps more merciful than the purgatory of heat death is the possibility of a Big Rip, in which the universe’s expansion accelerates faster and faster, until stars and planets are torn apart, molecules are shredded and the very fabric of space is ripped apart.

These potential endings are all many billions of years into the future — or perhaps much further off. But there’s also the possibility that the universe could end abruptly at any moment. That demise would not be a result of expansion or contraction, but due to a phenomenon called vacuum decay. If the universe turns out to be fundamentally unstable, a tiny bubble of the cosmos could convert to a more stable state. Then, the edge of that bubble would expand across the cosmos at the speed of light, obliterating anything in its path with no warning. In a passage a bit reminiscent of a Kurt Vonnegut story, Mack writes, “Maybe it’s for the best that you don’t see it coming.”

Already known for her engaging Twitter personality, public lectures and popular science writing, Mack has well-honed scientific communication chops. Her evocative writing about some of the most violent processes in the universe, mixed with her obvious glee at the unfathomable grandness of it all, should both satisfy longtime physics fans and inspire younger generations of physicists.

Reading Mack’s prose feels like learning physics from a brilliant, quirky friend. The book is sprinkled with plenty of informal quips: “I’m not going to sugarcoat this. The universe is frickin’ weird.” Readers will find themselves good-naturedly rolling their eyes at some of the goofy footnotes and nerdy pop-culture references. At the same time, the book delves deep into gritty physics details, thoroughly explaining important concepts like the cosmic microwave background — the oldest light in the universe — and tackling esoteric topics in theoretical physics. Throughout, Mack does an excellent job of recognizing where points of confusion might trip up a reader and offers clarity instead.

Mack continues a long-standing tradition of playfulness among physicists. That’s how we got stuck with somewhat cheesy names for certain fundamental particles, such as “charm” and “strange” quarks, for example. But she also brings an emotional openness that is uncommon among scientists. Sometimes this is conveyed by declarations in all caps about how amazing the universe is. But other times, it comes when Mack makes herself vulnerable by leveling with the reader about how unnerving this topic is: “I’m trying not to get hung up on it … the end of this great experiment of existence. It’s the journey, I repeat to myself. It’s the journey.”

Yes, this is a dark subject. Yes, the universe will end, and everything that has ever happened, from the tiniest of human kindnesses to the grandest of cosmic explosions, will one day be erased from the record. Mack struggles with what the inevitable demise of everything means for humankind. By contemplating the end times, we can refine our understanding of the universe, but we can’t change its fate.

Source: Science News