The estimate of the number of stars in just our Milky Way galaxy is pegged at about 400 billion.  The latest estimates based on data collected by the Hubble and other ground based instruments puts the number of galaxies in the universe, which currently has a estimated diameter of about 78 billion light years—at 500 billion at the least.  Our galaxy is an average size galaxy.  So, we can do the math easily enough.  The final number of the stars in the universe turns out to be the number 7—with 24 zeros after it.  It is estimated that there are over 1000 stars for each grain of sand on the world’s beaches and deserts.

            And yet, biology can give us even larger numbers.  One could say that the Earth is infested with life.  Crawling with it even.  Recently, scientists have estimated the total number of bacteria on Earth.  William B. Whitman of the University of Georgia led a group of microbiologists who conducted the study and they determined that there are approximately five million trillion trillion bacteria on planet Earth.  That number is a five followed by thirty zeros.  If each microbe were a United States copper penny, and you stacked them one on top of the other, the stack of pennies would be a trillion light years high.  That’s more than ten times higher than the whole known universe.

            And that’s only counting the bacteria, not any of the millions of other species of life on the planet, ranging from all the microbes that are not bacteria, such as amebas and paramecia, to the more than six billion human beings that stroll around the surface of our globe.  Life is abundant and fills every nook and cranny, every crevice that there is.  There is no spot on our world that doesn’t have life on it, whether it is the hottest, driest desert, the coldest spot in Antarctica, or the boiling volcanic vents in the deepest ocean. 

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            The United Nations Determinants and Consequences of Population Trends assume that modern homo sapiens first appeared about 150,000 years ago.  If we go with that assumption, then the total number of human beings who have ever lived is about 107 billion, meaning that the current population of the world, which is now over 6 billion, accounts for maybe 6 per cent of all the people who have ever been born.  We could give a star in the Milky Way galaxy to every human being who has ever lived and still have nearly three hundred billion stars left over, just in our galaxy alone. 



            There are 57.5 million square miles of dry land on Earth.  If all the human beings who have ever lived were spread evenly upon the surface of the world—just the dry land—each person would have just about a third of an acre of land to himself or herself.  If we only parceled out the land to the currently living, each human being would get a six acre spread.

            Although the average individual human being is made up of somewhere around fifty trillion cells, when we want to talk about extremely large numbers, we don’t talk about “biological” numbers.  We still talk about astronomical numbers, even though the numbers employed in astronomy are actually smaller—that is, don’t have as many zeros—as those involving life.

            How come?  Because the sheer size of the universe dwarfs biology.  It’s what makes astronomical numbers astronomical. 

            A human red blood cell is a mere 0.00003 inches across.  Meanwhile, an average adult male is 72 inches tall.  It would take 2.4 million blood cells, stacked end to end, to equal the height of such a human being. 

            A mile is 5280 feet—or 880 men long.  The distance to the moon is about 240,000 miles.  That means that the moon is about 1.27  billion feet away.  If we stacked six foot tall human beings end to end, we would need more than 211 million men—more than all the men in the United States—in order to reach the moon.  And so the size difference between you and the distance to the moon is far greater than the distance between a blood cell and you—by nearly a hundred times. 

            The distance to the sun is 93 million miles.   If you could drive that distance in your car, keeping your speed at 60 miles per hour, it would take you nearly 177 years to get there if you never stopped (it would only take you about 166 days of non-stop driving to get to the moon).  The distance from the Earth to the Sun is the distance from the Earth to the Moon multiplied by 387.5 times. That’s the equivalent of 82 billion six foot tall men stacked head to toe: more than ten times the current population of the world and about 80 per cent of all the human beings who have ever lived. 

            The brightest star in the sky, other than our own sun, is Sirius, the Dog Star, near the constellation of Orion.  It is about 8.6 light years away.  A light year is the distance light, moving at 186,000 miles per second, can travel in a year: about 5.878 trillion miles.  So the bright star Sirius, at 8.6 light years from Earth, is about 50 and a half trillion miles away.  Multiply that by 880 to get the number of six foot tall human beings you’d need stacked head to toe to reach that distance.

            As far as that might seem, Sirius is in our local neighborhood, astronomically speaking.  The Milky Way, our home galaxy, is at least 100,000 light years in diameter: the distance from the Sun to Sirus multiplied by 12,500.  The next closest galaxy, the Andromeda Galaxy, is 2.5 million light years away, or the distance from the Sun to Sirius multiplied by 312,500 times.  That’s 1.58 x 1011 times the 93 million mile distance between the Earth and our Sun that would take you 177 years to travel at sixty miles per hour.   Of course, that mind boggling number of miles is still less than half the number of bacteria living on Earth.

            Astronomical—and biological—numbers therefore are not only greater than we imagine, they are greater than we can imagine.


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