# The End of Everything (Astrophysically Speaking)

**Katie Mack**

★★★★★

An engaging read for the general audience about what we currently know about the history and structure of the universe and what that knowledge – and the pieces we don’t know – might mean for its future and eventual end. Katie Mack writes in a casual, entertaining style. It’s clear she finds all of this *absolutely fascinating*. And she sprinkles the writing with funny stories and quotes and side notes to get across the basics of quantum mechanics, Higgs fields, high-energy physics and the like without delving too much into the math. But the math, and the measurements, are important, because as it turns out, very small changes in how things work at the quantum level can have *major* implications on the universe’s ultimate fate.

The last time I read about this topic in anything resembling depth was about a decade ago. Since then there’ve been major discoveries in both quantum physics (chiefly confirming the existence of the Higgs boson) and astronomy, where we’ve found ways to look at ever more distant galaxies, and effectively farther and farther back in time.

Dr. Mack goes through the easier to grasp possibilities first, the ones based on what we *do* know about the universe. Big crunch, heat death, big rip - these are almost tangible, and which is more likely depends on things we can measure right now. Then she gets into the more esoteric possibilities, the ones based on the uncertainties. Like, if this quantum field we’ve measured is a little bit off one way or the other, reality might be unstable, so it would be really helpful to get better measurements. Or some of the multidimensional theories that have been proposed to unify relativistic gravity with quantum mechanics. If our 3D universe is just one of many in a larger-dimensional space, colliding with another one would probably be bad news for both!

She finishes up with a quick round-up of upcoming lines of research and some new theories in development that could fill in the gaps, or could shift to a new paradigm. (One theorist she spoke to suggested that even space and time might not be fundamental aspects of the universe, but built on something else)

## Random thoughts:

I’ve known about the cosmic microwave background radiation for a long time. But I’d always thought of it as “leftover radiation,” like a lightbulb fading as it cools down. I hadn’t thought of it in terms of looking so far back in time that we’re effectively seeing the big bang itself (or at least the point when the universe was still on fire)!

Dark energy as a cosmological constant, something Einstein put in his equations because they wouldn’t balance otherwise, then someone else figured out how to get the math to work without it… and then later observations found this weird discrepancy that could be best explained by adding this constant to the equations. Einstein was right even when he was wrong!

I still can’t wrap my head around the concept of vacuum decay. It’s like an ICE-9 scenario for the laws of physics.

We know more about dark matter than we used to. We can map it. We know roughly how much there is and roughly where. We know what it does. We just don’t know what it *is* yet.

And yet calculations indicate that dark matter and dark energy – whatever they turn out to be – make up vastly more of the universe than our own kind of matter!

**Online at**The End of Everything (Astrophysically Speaking).

**Available from**AstroKatie, Bookshop.org.