Rossdavidh's Reviews > Dark Matter and the Dinosaurs: The Astounding Interconnectedness of the Universe

Dark Matter and the Dinosaurs by Lisa Randall
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This book is fascinating on many levels.

First of all, Lisa Randall is a good writer, and she knows how to tell a good story of scientific discover. There are a couple, she thinks intertwined, stories of discovery here.

The first, is the story of how one of the Great Unsolved Mysteries of my childhood (how did the dinosaurs die) got solved (the big ones were killed by a meteor, and the little ones turned into birds). This led naturally to the question, how many of our planet's mass extinctions have been caused by impacts of extra-planetary objects? Answer: we have a new Great Unsolved Mystery, but maybe some of them.

The second story of scientific discovery, if you want to call it that, is dark matter, which Lisa Randall apparently considers a bit of a misnomer since it's really more like invisible matter. Others apparently think "dark" is more apropos, since we are almost totally in the dark about what it is. It is affected by gravity (and other matter is affected by its mass through gravity), but other than that never seems to interact with anything else (e.g. no light reflects off of, or is blocked by, it).

So, given that dark matter pulls on the rest of the (visible) universe via gravity, but it isn't distributed in the same way (e.g. it is not as much of a flat disk), one could imagine that it might have an impact on how things like meteors, asteroids, etc. (I can never keeps straight which one is which without looking up the definitions) whiz around the galaxy. This, in turn, could theoretically alter how often Earth gets clobbered by a big one. Randall thinks that some of the Milky Way's dark matter is in a relatively thin disc, rather than all of it being more or less in a spherical blob. When the Sun passes through this disk, it would get a bit

In addition to being two interesting stories about how science works, the book is itself an interesting example of how science works. Randall's thesis is novel, and in an unusual turn of events for anything to do with dark matter, they are falsifiable.

Being falsifiable, while it sounds like a bad thing when you first hear of it, is actually a very good thing. If a theory is falsifiable, then you can imagine evidence or data that would prove it false. That means, in turn, that if the theory is true you can actually make predictions with it. You can predict that the events which you imagined which would prove it false, won't happen. If no possible turn of events you could imagine could ever prove your theory false, then your theory doesn't actually give you the ability to predict anything with confidence. If it can explain anything, it can't rule anything out. Randall's theory is not only falsifiable, it actually points out that an astronomical satellite Gaia, already launched at the time she wrote the book, would provide data (on the path of thousands of stars over time) that would be able to prove or disprove her hypothesis. After all, if a dark matter disk can tug on asteroids and comets via gravity, it can also tug on stars.

Well, it turns out, Randall's theory is not just falsifiable, it is falsified. Earlier this year, the first big paper resulting from Gaia was published, and it was not kind to Randall's theory. Although the authors of the paper spoke highly of how exciting and cool it would have been if her theory were correct, the universe decided otherwise.

Now, one might think that this makes the book unimportant, but actually I disagree. For one thing, a great deal of it was about dinosaurs (and the impact that killed them) and dark matter (why we believe it exists, and how little we've been able to find out about it). That part is all still sound, and it is the bulk of the book.

Also, though, I enjoyed reading about Randall's thinking as she and her colleagues put together this (falsified) theory, because it is a look at how science actually happens. All too often the story of science looks only at the winning theories, the ones that turn out to be true. For each one of those, there are countless others that require nearly as much painstaking work to piece together, and then test, which turn out not to be true. Science is not great because of its ability to generate true theories. Science is great because of its willingness to put its theories to a test that the theory's creator cannot control. Science is great not because of how often it gets things right, but because of how well it tests them to see which are wrong.

Even without that, though, it's a good book, filled with a lot of (not falsified) science. I look forward to her next book (and her next theory).

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Reading Progress

Finished Reading
May 22, 2018 – Shelved
May 22, 2018 – Shelved as: black

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