The Weakness of the Analogy between Machines and the Universe. What is the radius of the visible universe?… 1. To answer this, we begin by noting that the oldest light to reach us is about 14 billion light years old. 2. What is a light year?… The distance light travels in a year. 3. What is the speed of light?… Ca. 186,000 miles per second. 4. How many seconds in a minute?… 60 seconds per minute. 5. How many minutes in an hour?… 60 minutes per hour.

6. So how many seconds in an hour?... 60 X 60 = 3,600 seconds per hour. 7. How many hours in a day?… 24 hours per day. 8. So how many seconds in a day?… 24 X 36,000 = 86,400 seconds per day. 9. How many days in a year?… Ca. 365 days per year. 10. So how many seconds in a year?… 365 X 86,400 = 31,536,000 seconds per year. 11. So given that the speed of light is 186,000 miles per second, how many miles in a light year?… 186,000 X 31,536,000 = 5.865696 X 1012 = 5,865,696,000,000 miles (5 trillion, 865 billion, 696 million miles).

12. Finally, then, given that the oldest light to reach us is14 billion light years old, how far away was the oldest light when it was emitted?… (1.4 X 1010) X (5.865696 X 1012 ) = 8.2119744 X 1022 = 82,119,744,000,000,000,000,000 miles. (82 sextillion, 119 quintillion, 744 quadrillion miles). But the universe has been expanding during those 14 billion years, so the galaxies that emitted the oldest light that we can now see are actually ca. 47 billion light years away. So the radius of the visible universe is: 4.7 X 1010 X 5.865696 X 1012 = 2.75687712 X1023 = 275,687,771,200,000,000,000,000 (275 sextillion, 687 quintillion, 771 quadrillion, 200 trillion) miles. But the entire universe, including those stars whose light cannot reach us, is at least 250 times the size of the visible universe.

13. How many galaxies are there in the visible universe?… Ca. 2 trillion = 2,000,000,000,000 = 2 X 1012 galaxies 14. How many stars in the average galaxy?… Ca. 200 billion = 200,000,000,000 = 2 X 1011 stars 15. So how many stars are there in the visible universe? Ca. (2 X 1012) X (2 X 1011) = 423 = 400,000,000,000,000,000,000,000 (four hundred sextillion stars)

The original NASA release of a deep space photo from the Hubble space telescope, containing galaxies of various ages, sizes, shapes, and colors. The smallest, reddest galaxies, of which there are approximately 10,000, are some of the most distant galaxies to have been imaged by an optical telescope, probably existing shortly after the Big Bang. Their red-shifted light was emitted over 13 billion years ago, and they are now nearly 47 billion light years from the earth.

Our Galaxy The Milky Way

Drawing of Milky Way Galaxy From Above Norma

A twin of the Milky Way Galaxy, NGC 6744 is 30 million light years distant from the earth.

Approximate position of the Sun The Milky Way Galaxy Approximate position of the Sun Disk is 2,000 light years thick in vicinity of Sun 16,000 light years thick at center Ca. 27,000 light years 100,000 light years Contains at least two hundred billion stars, perhaps as many as four hundred billion stars