Review: Cosmos by Carl Sagan

This book was developed co-developed with the TV show of the same name. If you’ve seen the show, there’s not that much new in here. But then again, if you enjoyed the show, you’ll find much of the same enjoyable content here. Carl Sagan’s writing is excellent, and the book offers an interesting, sweeping look at physics, astronomy, biology, science, history, technology, and much more.

A few fun facts / insights I jotted down while reading:

• The clever way in which Eratosthenes estimated the circumference of the earth: you go to two cities between which the distance is known, put two sticks vertically in the ground, and measure the angle of the shadows they cast at the same time of day. That difference in the shadows is due to the curvature of the earth, and Eratosthenes found it to be about 7 degrees between Alexandria and Syene, or about 1/50th the circumference of a circle. He knew that Alexandria and Syene were about 5,000 stadia apart (1 stadia is about 157.5 metres), so 5,000 stadia * 50 = 250,000 stadia, or 39,375 km. This estimate turns out to be within 2% of the real value.

• The Library of Alexandria was the largest library of the ancient world, but everything in it was completely lost. For example, one of the volumes it contained apparently talked about how the earth was but one of many planets and how the stars we see in the night sky are exceptionally far away—an extraordinary idea for ~300BC! After the library was burned down, it took nearly two thousand years to re-discover these ideas. And this was but one volume of hundreds of thousands that were burned. It’s staggering to imagine the loss of knowledge and human progress from this.

• Venus is astonishingly hostile to any sort of life or exploration. The surface of the planet is nearly 900 degrees Fahrenheit (~450 degrees Celsius); the atmospheric pressure is 90 times that of earth; it is covered with dense clouds that block out the sun; but these clouds don’t provide any water, as they are made of sulfuric acid, and this corrosive substance rains down in the upper atmosphere, though due to the heat, it evaporates long before reaching the surface; and this entire atmosphere is spinning extremely quickly, generating winds of up to 200 mph (~300 kph).

• When we measure the red shift, we see that the entire universe seems to be moving away from the earth, in all directions. But what makes the earth so special? It turns out, it’s not (there are no privileged reference frames); instead, the universe is expanding in all directions. So everything is moving away from everything. It’s a bit like a balloon being inflated: if you were floating at some point within the balloon, no matter which point you were at, it would seem like all the other points were moving away from you in all directions.

• But if the universe is expanding, is there some sort of boundary? E.g., If the universe is like an inflating balloon, what represents the rubber part of the balloon? What is happening at the “edge”? Well, it’s possible that there are no edges; instead, the universe loops around on itself. To imagine this, imagine first a 2D universe, where everything lives on a 2D sheet of paper, a bit like in the story Flatland. Now, take the ends of the paper, and connect them together in the third dimension so they form a loop. For a 2D being living in the plane of the paper who can’t perceive the third dimension, they would start moving forward in the plane, and after along time, they’d end up right back where they started, even though at all times they were moving forward. Now take this analogy up one dimension: we are beings who live in a 3D world that, through a 4th dimension that we can’t perceive, loops back around on itself. If we could go far enough straight in one direction, we’d eventually find ourselves right back where we started.

• The word museum derives from the word muse.

• Math and science may be the Rosetta Stone of the universe.

I also saved a few of my favorite quotes from the book:

“The surface of the Earth is the shore of the cosmic ocean. On this shore, we’ve learned most of what we know. Recently, we’ve waded a little way out, maybe ankle-deep, and the water seems inviting. Some part of our being knows this is where we came from. We long to return, and we can, because the cosmos is also within us. We’re made of star stuff. We are a way for the cosmos to know itself.”

“The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars. We are made of star stuff.”

“If you wish to make an apple pie from scratch, you must first invent the universe.”

“What an astonishing thing a book is. It’s a flat object made from a tree with flexible parts on which are imprinted lots of funny dark squiggles. But one glance at it and you’re inside the mind of another person, maybe somebody dead for thousands of years. Across the millennia, an author is speaking clearly and silently inside your head, directly to you. Writing is perhaps the greatest of human inventions, binding together people who never knew each other, citizens of distant epochs. Books break the shackles of time. A book is proof that humans are capable of working magic.”

“We are like butterflies who flutter for a day and think it is forever.”

“Exploration is in our nature. We began as wanderers, and we are wanderers still. We have lingered long enough on the shores of the cosmic ocean. We are ready at last to set sail for the stars.”

“National boundaries are not evident when we view the Earth from space. Fanatical ethnic or religious or national chauvinisms are a little difficult to maintain when we see our planet as a fragile blue crescent fading to become an inconspicuous point of light against the bastion and citadel of the stars.”

“I am a collection of water, calcium and organic molecules called Carl Sagan. You are a collection of almost identical molecules with a different collective label. But is that all? Is there nothing in here but molecules? Some people find this idea somehow demeaning to human dignity. For myself, I find it elevating that our universe permits the evolution of molecular machines as intricate and subtle as we. But the essence of life is not so much the atoms and simple molecules that make us up as the way in which they are put together.”

Rating: 4 stars