It¡¯s a strange old world at the moment, isn¡¯t it? With a global pandemic hanging over our heads, people are acting strangely. Irrationality is apparently on the rise, with anti-maskers claiming that the mesh size of homemade masks allows the free passage of virus particles while simultaneously preventing us from expelling carbon dioxide or inhaling sufficient oxygen. Fortunately, this is a small population, although one that happens to have a loud voice. But against this backdrop, while some of us feel continuously gaslit by the virus deniers, is it really the best time to read a book titled The End of Everything? Well, yes. Yes, it is.

Dr Katie Mack (@AstroKatie) is a prominent voice on science Twitter and a theoretical cosmologist, whose book describes the various scenarios for the end of¡­well, Everything. Granted, it won¡¯t help you set aside your more immediate concerns about things you can actually do something about, but sometimes it can be useful to take a step back and remember that, across the vast swathe of space and time, you are an entirely insignificant blip.

Mack¡¯s book is informative, occasionally wry, often entertaining and sometimes headache-inducing (in the best way). The author also occasionally gets VERY EXCITED (yes, all in caps) ¨C it¡¯s quite infectious. I am a physicist but in a completely different field from cosmology or particle physics. I work in an experimental world that is predominantly governed by Newtonian physics ¨C and I quite like it there. But Mack delves instead into the limits of quantum mechanics, general relativity, dark matter, dark energy and the research designed to produce a Grand Unifying Theory and a Theory of Everything (physicists can get a little grandiose). Many of the concepts covered in The End of Everything are familiar to me, but both cosmology and particle physics are moving so rapidly that I found it a satisfying overview, with enough detail to explain but not bamboozle. It is sufficiently cutting-edge that Mack occasionally delves into knowledge that was emerging as the book was being written. It explores the edges of the known, and dangles its feet over the precipice of where physics is broken.

The book starts with the Big Bang. Logical, because if you want to know how something ends, it¡¯s useful to explore how it started. Here we are introduced to the emergence of the fundamental physical laws that govern everything in the current known universe and for the most part explain things quite nicely. A microsecond after the birth of the universe, we think we understand how everything works, albeit with some fudges. Prior to that? It¡¯s a work in progress.

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Then we get into the meat of The End of Everything and are presented with a number of possible options. First, if the inflation and expansion of the universe reverses in a what-goes-up-must-come-down scenario, the universe may end in a Big Crunch. This prospect has been ruled out by the discovery that the expansion of the universe is accelerating ¨C Mack tells you how we know this and what it means, and introduces us to dark energy ¨C but that doesn¡¯t save the reader from an appropriately gruesome description of what a Crunch would be like. It doesn¡¯t sound like fun.

An alternative prospect is Heat Death ¨C that the universe keeps expanding, the expansion accelerates, everything spreads out, nothing is pulled in to fuel future stars, existing stars and galaxies die out, and the universe gets darker and colder. I live in Scotland and have got used to suffering the winters, but this sounds depressing even to me. Ordinary matter eventually falls apart, black holes evaporate, time itself ceases to have meaning (as in, there is no time) and then there is¡­not a lot. I think I¡¯d prefer the excitement of a Crunch.

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Related to the rather dreary Heat Death is its more exciting Big Rip cousin, which is what happens if our understanding of the accelerated expansion of the universe is wrong, even if only a little bit, and it accelerates even faster than we anticipate. The consequences are dramatic and result in the very fabric of space being ripped apart. In this chapter we learn a lot about how to measure distance in the universe, as well as the discrepancies between our particle physics ideas of the universe and our cosmological understanding ¨C the ultimate of gaps between Small and Big. We¡¯re also given some reassuring words about how if a Big Rip is destined to happen it¡¯ll be a long way into our distant future, but this is small comfort because things get worse, so much worse.

The death of the universe by Vacuum Decay is by far my favourite, partly because it could happen at any time, we won¡¯t know anything about it, it¡¯s currently plausible ¨C and it involves something that looks like a phase transition, which is in my own domain. Imagine heating a pot of water to cook pasta, and you realise you¡¯ve forgotten to add salt. The moment you add the salt, the water boils. The water has undergone a liquid-to-vapour phase transition.

Now imagine this on the scale of the universe. The physics isn¡¯t quite the same, but this is an analogy so we¡¯ll run with it. The fundamental physical laws that govern matter represent one possibility (in my imperfect analogy: hot water). But Mack tells us that current evidence suggests this isn¡¯t actually the optimal configuration. It may surprise you to know that, in our current understanding of fundamental physics, the universe is imperfect ¨C or this may not surprise you at all, depending on your opinion of ¡°Monday¡±. Unfortunately, if we optimise the models, the universe as we know it breaks, or at least matter does. To return to my pasta analogy, if we throw a large handful of salt into the universe, all of matter turns into so much vapour; the laws that currently hold it together no longer work. Game over, everywhere. Just to reiterate: this could happen at any time. But don¡¯t worry, you won¡¯t feel a thing.

Mack goes on to describe a further cyclic scenario with the repeated creation and destruction of the cosmos and the introduction of other dimensions. This is where it gets difficult to come up with real-world analogues for mathematical constructs and Mack introduces actual hand-waving to illustrate multiple universes.

The book then briefly summarises the prospects for future measurements of fundamental particles that could help either patch up a few holes in our current understanding of the universe or point us in a whole new direction. Mack also describes the possibilities emerging from observations of the cosmos using the latest telescopes and measurements of gravitational waves.

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The final chapter explores what it all means, for us. Does knowing that Everything Ends make us feel better or not? You may have seen widespread reports of a preprint published on PsyArXiv suggesting that fans of horror and disaster movies are more resilient to the current pandemic uncertainty. Now that is only a preprint and so may turn out to be wrong, but here¡¯s your chance to test it yourself. Reading The End of Everything may boost your pandemic resilience: Mack describes what is, after all, the ultimate in disasters.

Oh, and wear a mask.

Cait MacPhee is professor of biological physics at the University of Edinburgh.

The End of Everything (Astrophysically Speaking)
By Katie Mack
Allen Lane, 240pp, ?20.00
ISBN 9780241372333
Published 4 August 2020

The author

Katie Mack, assistant professor of physics at North Carolina State University, grew up in Long Beach, California, outside Los Angeles. Although she ¡°didn¡¯t live at all close to the beach¡±, she recalls, she ¡°spent a lot of time there anyway; I?loved the ocean air in the evening¡±.

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She studied at the California Institute of Technology in Pasadena, which she experienced as ¡°a?very, very intense place. I?had to work extremely hard, and I?learned a?lot.¡± What proved particularly valuable was that she ¡°was able to do physics research throughout my undergraduate years, so I?knew what I?was getting into before I?got to grad school¡±.

Along with her cutting-edge research, Mack has a huge following on Twitter and enjoys engaging with a wide, non-specialist audience. So how does outreach enrich her work in a highly technical field?

¡°I work in cosmology, with a strong connection to particle physics,¡± she replies, ¡°so the problems I¡¯m working on tend to be very broad and to be best approached through making new creative connections between topics. One of the things I?get out of outreach is that I?end up talking about topics far outside any kind of narrow focus, and that helps me come up with new ideas in my?work.¡±

In her new book, Mack explores the ultimate in cosmic disasters. So what was it like to be thinking about that in the midst of a global pandemic?

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¡°I think it kind of helps, weirdly,¡± she reflects. ¡°During the pandemic, we¡¯re locked away in our small spaces, being anxious about what¡¯s going on in the world. Thinking about ultimate cosmic destruction takes me far away from that. It¡¯s not exactly a?cheerful topic, but it¡¯s so far removed from any day-to-day worries that there¡¯s something kind of calming about that change in perspective.¡±

Matthew Reisz