What I've Learned

Long-time readers of this column will be aware of my fascination with large numbers. Back in 2005, I calculated how many ways there are to arrange the first 30 words of the Gettysburg Address. (The answer is 265 followed by 30 zeros, or 265 nonillion)

Later that year, I wrote about comparing the number of grains of sand on earth to the number of stars in the universe. The heavens won handily, there being ten times more stars than grains of sand.

Early in 2009, I investigated this bit of narrative from the movie, Amelie: "Meanwhile, on a bench in Villette Square, Felix Lerbier learns there are more links in his brain than atoms in the universe."

It turned out that the idea in this quote was correct. The human brain has so many more possible links between cells than there are atoms in the universe, it is no contest.

Since writing those columns, things have changed. Not my love of large numbers, of course, but man's knowledge of the size of the universe and of the potential connections in the brain.

In 2005, when I wrote about grains of sand versus stars in the universe, there were estimated to be seven sextillion grains of sand on earth. That's seven followed by 21 zeros. And there were estimated to be 70 sextillion stars, ten times the number of grains of sand on all of earth's deserts, beaches, and icy roadways.

Now, five years later, the number of grains remains the same, but the number of stars has risen to 300 sextillion. Why? Because scientists couldn't see dwarf stars (a class of small, cool stars) in other galaxies, so counted the number of bright stars and assumed (almost always a dangerous thing to do) that other galaxies had the same ratio of dwarf stars to stars as ours does. The Milky Way is a spiral galaxy with around 400 billion stars and has about 100 dwarf stars for every star that's like our Sun. Many other galaxies are not spiral shaped. Thirty percent, for example, are elliptical and have, scientists now realize, 1,000 to 2,000 dwarfs for every Sun-like star.

So, does this increased estimate of stars mean that there are, in fact, more atoms than potential brain connections? Rest easy. Your brain still dwarfs the universe.

My 2009 column underestimated the number of potential connections in the brain by such a degree as to be laughable. I assumed (there it is again) that there are around one billion neurons (nerve cells) in the human brain. There are actually around 200 billion. Also, I tried to estimate the number of possible connections by considering only the neurons and not the trillions of synapses that connect them.

A single neuron can have tens of thousands of synapses connecting it to other neurons. Until recently, a synapse was thought to be a simple on/off switch. A new understanding of synapses and the ways they process and relay information reveals the human brain to be frighteningly powerful.

Stephen Smith, a professor of molecular and cellular physiology at Stanford University School of Medicine, made a recent statement that will wow you:

"One synapse, by itself, is more like a microprocessor--with both memory-storage and information-processing elements--than a mere on/off switch. In fact, one synapse may contain on the order of 1,000 molecular-scale switches. A single human brain has more switches than all the computers and routers and Internet connections on Earth."

And it has more links and connections then there are atoms--atoms, not stars--in the universe. In 2005, the number of atoms in the universe was estimated to be one followed by 81 zeros. If we triple that number, it would be three followed by 81 zeros. That's three sexvigintillion.

How does the brain match up? If we go with my 2009 estimate using a count of one billion neurons--ignoring new estimates of neurons and ignoring what we now know about synapses--the number of possible connections in the brain is three followed by 5,000,000,000 zeros.

That's a number so large, it doesn't even have a name.