Katie Mack
Katie Mack, a theoretical astrophysicist and cosmologist, is an assistant professor at North Carolina State University and a member of the Leadership in Public Science Cluster. Mack studies the universe from its origin to its demise and - in this book - speculates about the cosmos' ultimate end, which is inevitable.
Though the universe isn't likely to terminate for many trillions of years, there are scenarios in which the end is mere seconds away. The evolution and demise of the cosmos is a fascinating subject, and Mack makes it even better with her wit and sense of humor.
Mack starts by providing a brief description of the creation of the universe and how it got to where it is now. In short, there was the Big Bang; a brief period of Cosmic Inflation (10⁻³⁴ seconds); the Quark Era, when subatomic particles formed; a period of cooling, during which the subatomic particles condensed into electrons, protons, and the like; and finally the formation of stars, galaxies, black holes, etc. The universe was expanding the entire time, and in fact the expansion is accelerating. But what goes up must come down (so to speak) and the universe will inevitably come to an end.
In this book Mack explores five possibilities for the termination of the universe. These are the Big Crunch, Heat Death, the Big Rip, Vacuum Decay, and the Bounce. Mack explains the physics of each scenario, and for the real nitty-gritty, illustrated by sketches and graphs, you'll have to read the book.
❃ The Big Crunch
The Big Bang starts the universe's expansion, and from that point onward the gravity of all the material in the universe (gases, galaxies, stars, black holes, etc.) works against the expansion, trying to slow it down and pull everything back together again. This could lead to a contracting universe that ends in a Big Crunch.
Mack describes the climax of the Big Crunch as follows: The collected radiation from stars and high-energy particle jets, when suddenly condensed to even higher energies by the collapse, will be so intense it will begin to ignite the surface of stars long before the stars themselves collide. Nuclear explosions tear through stellar atmospheres, ripping apart the stars and filling space with hot plasma. No celestial entities could possibly exist un-incinerated......and ultimately nothing will survive.
We don't need to get in a lather, though, because it will be at least tens of billions of years before a Big Crunch reversal could occur.
❃ Heat Death
A second possibility is that the expansion of the universe will counteract gravity, and the cosmos will continue to inflate indefinitely. In this scenario, SPACE ITSELF - in the form of dark energy - overcomes gravity and fuels the growth of the universe. (Dark energy is defined as a theoretical repulsive force that counteracts gravity and causes the universe to expand at an accelerating rate.)
If the cosmos continues to enlarge, every galaxy will ultimately be completely alone. The stars already shining will burn out, exploding as supernovae or, more often, sloughing off outer layers....gradually cooling for billions or trillions of years. Black holes will evaporate (via Hawking radiation), fade, and disappear. Ordinary matter, which makes up stars and planets, will suffer a similar fate. Eventually nothing will be left. This occurrence is termed 'Heat Death', a physics term that refers to the fact that entropy - which is ALWAYS INCREASING - causes progressive disorder.
Don't be too concerned, because we probably have 10¹⁰⁰⁰ years or so before Heat Death would occur.
❃ Big Rip
Dark Energy might also finish off the universe by tearing it apart. Physicists have determined that certain values for Dark Energy, IF THEY EXIST, will cause the space WITHIN structures - within atoms, molecules, planets, stars, human bodies, etc. - to expand, and everything will come apart. Molecules will crack open and structures will be torn apart, atom from atom, from within.
Don't sweat too much because no BIG RIP could be less than a hundred billion years off.
❃ Vacuum Decay
Vacuum Decay has to do with the Higgs Field, the theoretical field of energy that permeates the universe and imparts mass to the fundamental particles. The physical state we live in is called our 'Higgs vacuum', and the laws of physics in the Higgs vacuum allow us to exist. If the Higgs vacuum should suddenly acquire some other, more stable value (which apparently is theoretically possible), there would be different laws of physics, and everything we know would be destroyed.
Mack observes that for us, this would be so sudden that we'd never see it coming. She writes, "In fact, it's entirely possible that, as we sit here now, drinking our tea, vacuum decay has already occurred....Maybe it is, cosmically speaking, right next door, quietly approaching with relativistic stealth, destined to catch us unawares, between breaths."
On the upside, if this should happen, it won't hurt.
❃ The Bounce
The Bounce has to do with the possibility of other dimensions. We think of the universe as having three dimensions, east-west, north-south, up-down, with the added dimension of time to form space-time. We call our 3-dimensional universe a 3-D 'brane.' Physicists speculate there may be other branes, in other dimensions, that we can't access.
The idea of the Bounce is that our universe formed when two branes - both filled with hot dense plasma - collided. This would be the Big Bang, and our universe would go on to evolve as described above. (We don't know what's going on in the other brane(s).)
In the Bounce scenario, the collisions are cyclic, That is, the branes collide again and again. Each time, the collision destroys our universe and simultaneously sets off a Big Bang. This is also called an ekpyrotic universe, "caught in an eternal cycle of fiery birth, cooling and rebirth."
No one knows which, if any, of the above scenarios is most correct, and Mack observes that we still have a lot to learn. Right now, though, the most popular paradigm for the cosmos is called the Concordance Model. In this picture, the universe has four basic components - radiation, regular matter, dark matter, and dark energy - plus gravity. If physicists have their facts correct about all these things (which is by no means certain), we're headed for a Heat Death.
More research is required, and Mack observes, 'If we want to learn anything about the future of the cosmos, we'd better address the giant, invisible ever-expanding killer elephant in the room: dark energy. In a dark energy dominated future, one in which the cosmos gets progressively emptier, colder, and darker until all structure decays, we reach the ultimate Heat Death. But this is predicated on dark energy being an unchanging cosmological constant. If dark energy somehow changes over time, the implications for the cosmos are drastically different.'
Since (at the current time) it's almost impossible to learn anything about dark energy, physicists have their work cut out for them.
In Mack's epilog, she addresses what's probably most important to people, which is that - when the universe terminates - our legacy as a species just ends. Mack says, "At some point, in a cosmic sense, it will not have mattered that we ever lived." This is sad. Professor Hiranya Peiris, an astrophysicist, admits, "I give talks where I mention that [termination] is probably the fate of the universe, and people have cried."
Hiranya Peiris
I think we all feel a little bit like crying when we contemplate the end of the universe. 😥
Though one doesn't like to contemplate the end of everything (as we know it), this is a very interesting book, highly recommended.
Rating: 4 stars
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