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Archive for February, 2012

This is part 2 of my review of The Cosmic Landscape by Leonard Susskind. Part 3 is here.

Here is the dilemma. You’re a well-respected scientist. You decide that you want to write a popular science book to bring your field and your research to the masses. However, a straight, logical presentation of the facts and the theories is too dry. We need to break it up a bit, add a bit of human interest.

So tell a story! Stories make us want to keep reading to find out how it ends. You decide to give some anecdotes, or even a historical overview. For the period of time during which you were in the field, this is easy – you can simply give a personal history of your interactions with the scientists involved, the ideas proposed, and their reception by the community. However, if you want to go back before your career started then you’ll need to rely on historical sources. Here lies the problem: you’re not a historian. As a scientist, if you read a paper published 20, 50, 100 years before you entered the field, you do it because the information is still relevant to your work. You don’t do it to get a fair and balanced sample of the intellectual climate at the time.

Your popular science book has now strayed out of your field and into the history of science. History is a very subtle subject – it deals with people, lots of people. People are complicated. If you’re not careful, you might end up repeating convenient, popular myths that reduce personalities to caricatures and events to fables.

Given the title of this post, you may have guessed that I’m about to accuse Susskind of precisely this allegation. Keep in mind – overall, his book is highly recommended. I am literally taking issue with a couple of footnotes. And, as I keep reminding you, I’m no historian either. I’ll do my best to quote from actual historians of science.

Around the Medieval World

Repeat after me: people in the Middle Ages did not think that the Earth was flat. Twice in his book, Susskind suggests that people only started believing that the Earth was round when it was circumnavigated, either by Magellan (page 67) or Columbus (page 160). This myth has been debunked so many times. It’s on Wikipedia’s “List of common misconceptions”. The best TV show ever joined the cause. The ancient Greeks not only knew it was round, but Eratosthenes made a very good estimate of the Earth’s diameter in 240 BC. In 1945, the “Members of the Historical Association” published a series of pamphlets titled “Common Errors in History”, the second of which says: (more…)

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I’m a great fan a popular science books, particularly when the topic is cosmology or fundamental physics. Susskind’s “The Cosmic Landscape” was particularly enjoyable, though I will take issue with a few things in later posts. For now, here are a few highlights:

I love a good illustration:

A rocket-propelled lemon moving away from you might have the color of an orange or even a tomato if it were going fast enough. While its moving toward you, you might mistake it for a lime.

This is simply the Doppler effect, which we’ve all observed for sound as an ambulance drives past. It works for light as well, but you have to be going close to the speed of light. Using the right formula from Einstein’s special relativity, we find that you must fire a lemon at a tenth of the speed of light to make it look red. About the same speed, but moving toward you, will make it look green.

Susskind gives an excellent account of the fine-tuning of the universe for intelligent life.

[T]he Laws of Physics may not only be variable but are almost always deadly. In a sense the laws of nature are like East Coast weather: tremendously variable, almost always awful, but on rare occasions, perfectly lovely. … One theme has threaded its way through our long and winding tour from Feynman diagrams to bubbling universes: our own universe is an extraordinary place that appears to be fantastically well designed for our own existence. This specialness is not something that we can attribute to lucky accidents, which is far too unlikely. The apparent coincidences cry out for an explanation.

In particular, he takes the discussion to the cutting edge of particle physics, discussing the gauge hierarchy problem:

Physicists puzzled for some time about why the top-quark is so heavy, but recently we have come to understand that it’s not the top-quark that is abnormal: it’s the up- and down-quarks that are absurdly light. The fact that they are roughly twenty thousand times lighter than particles like the Z-boson and the W-boson is what needs an explanation. The Standard Model has not provided one. Thus, we can ask what the world would be like is the up- and down-quarks were much heavier than they are. Once again – disaster!

… the cosmological constant problem:

Throughout the years many people, including some of the illustrious names in physics, have tried to explain why the cosmological constant is small or zero. The overwhelming consensus is that these attempts have not been successful.

… fine-tuning of cosmic inflation needed to give the universe the right amount of lumpiness:

A lumpiness of about 10^-5 is essential for life to get a start. But is it easy to arrange this amount of density contrast? The answer is most decidedly no! The various parameters governing the inflating universe must be chosen with great care in order to get the desired result.

… and even supersymmetry:

The biggest threat to life in an exactly supersymmetric universe [has to do] with chemistry. In a supersymmetric universe every fermion has a boson partner with exactly the same mass, and therein lies the trouble. The culprits are the supersymmetric partners of the electron and the photon. These two particles, called the selectron (ugh!) and the photino, conspire to destroy all ordinary atoms. … in a supersymmetric world, an outer electron can emit a photino and turn into a selectron. … That’s a big problem: the selectron, being a boson, is not blocked (by the Pauli exclusion principle) from dropping down to lower energy orbits near the nucleus. … Goodbye to the chemical properties of carbon – and every other molecule needed by life.

Susskind is also clear to distinguish between the landscape of string theory and a multiverse (or megaverse):

The two concepts – Landscape and megaverse [a.k.a. multiverse] – should not be confused. The Landscape is not a real place. Think of it as a list of all the possible designs of hypothetical universes. Each valley represents one such design. … The megaverse, by contrast, is quite real. The pocket universes that fill it are actual existing places, not hypothetical possibilities.

All in all, the Susskind’s book is highly recommended.

Part 2 of my review is here.

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