We begin with the stars, then ascend up and away out to the galaxy, the universe, and beyond. What did Buzz Lightyear say in Toy Story? âTo Infinity and Beyond!â
Itâs a big universe. I want to introduce you to the size and scale of the cosmos, which is bigger than you think. Itâs hotter than you think. It is denser than you think. Itâs more rarified than you think. Everything you think about the universe is less exotic than it actually is. Letâs get some machinery together before we begin. I want to take you on a tour of numbers small and large, just so we can loosen up our vocabulary, loosen up our sense of the sizes of things in the universe. Let me just start out with the number 1. Youâve seen this number before. There are no zeros in it. If we wrote this in exponential notation, it is ten to the zero power, 100. The number 1 has no zeros to the right of that 1, as indicated by the zero exponent. Of course, 10 can be written as 10 to the first power, 101. Letâs go to a thousandâ103. Whatâs the metric prefix for a thousand? Kilo- kilogramâa thousand grams; kilometerâa thousand meters. Letâs go up another 3 zeros, to a million, 106, whose prefix is mega-. Maybe this is the highest they had learned how to count at the time they invented the megaphone; perhaps if they had known about a billion, by appending three more zeroes, giving 109, they would have called them âgigaphones.â If you study file sizes on your computer, then youâre familiar with these two words, âmegabytesâ and âgigabytes.â A gigabyte is a billion bytes.1 Iâm not convinced you know how big a billion actually is. Letâs look around the world and ask what kinds of things come in billions.
First, there are 7 billion people in the world.
Bill Gates? Whatâs he up to? Last I checked, heâs up to about 80 billion dollars. Heâs the patron saint of geeks; for the first time, geeks actually control the world. For most of human history that was not the case. Times have changed. Where have you seen 100 billion? Well, not quite 100 billion. McDonaldâs. âOver 99 Billion Served.â Thatâs the biggest number you ever see in the street. I remember when they started counting. My childhood McDonaldâs proudly displayed âOver 8 Billion Served.â The McDonaldâs sign never displayed 100 billion, because they allocated only two numerical slots for their burger count, and so, they just stopped at 99 billion. Then they pulled a Carl Sagan on us all and now say, âbillions and billions served.â
Take 100 billion hamburgers, and lay them end to end. Start at New York City, and go west. Will you get to Chicago? Of course. Will you get to California? Yes, of course. Find some way to float them. This calculation works for the diameter of the bun (4 inches), because the burger itself is somewhat smaller than the bun. So for this calculation, itâs all about the bun. Now float them across the ocean, along a great circle route, and you will cross the Pacific, pass Australia, Africa, and come back across the Atlantic Ocean, finally arriving back in New York City with your 100 billion hamburgers. Thatâs a lot of hamburgers. But in fact you have some left over after you have circled the circumference of Earth. Do you know what you do with what you have left over? You make the trip all over again, 215 more times! Now you still have some left over. Youâre bored going around Earth, so what do you do? You stack them. So after youâve gone around Earth 216 times, then you stack them. How high do you go? Youâll go to the Moon, and back, with stacked hamburgers (each 2 inches tall) after youâve already been around the world 216 times, and only then will you have used your 100 billion hamburgers. Thatâs why cows are scared of McDonaldâs. By comparison, the Milky Way galaxy has about 300 billion stars. So McDonaldâs is gearing up for the cosmos.
When you are 31 years, 7 months, 9 hours, 4 minutes, and 20 seconds old, youâve lived your billionth second. I celebrated with a bottle of champagne when I reached that age. It was a tiny bottle. You donât encounter a billion very often.
Letâs keep going. Whatâs the next one up? A trillion: 1012. We have a metric prefix for that: tera-. You canât count to a trillion. Of course you could try. But if you counted one number every second, it would take you a thousand times 31 yearsâ31,000 years, which is why I donât recommend doing this, even at home. A trillion seconds ago, cave dwellersâtroglodytesâwere drawing pictures on their living room walls.
At New York Cityâs Rose Center of Earth and Space, we display a timeline spiral of the Universe that begins at the Big Bang and unfolds 13.8 billion years. Uncurled, itâs the length of a football field. Every step you take spans 50 million years. You get to the end of the ramp, and you ask, where are we? Where is the history of our human species? The entire period of time, from a trillion seconds ago to today, from graffiti-prone cave dwellers until now, occupies only the thickness of a single strand of human hair, which we have mounted at the end of that timeline. You think we live long lives, you think civilizations last a long time, but not from the view of the cosmos itself.
Whatâs next? 1015. Thatâs a quadrillion, with the metric prefix peta-. Itâs one of my favorite numbers. Between 1 and 10 quadrillion ants live on (and in) Earth, according to ant expert E. O. Wilson.
Whatâs next? 1018, a quintillion, with metric prefix exa-. Thatâs the estimated number of grains of sand on 10 large beaches. The most famous beach in the world is Copacabana Beach in Rio de Janeiro. It is 4.2 kilometers long, and was 55 meters wide before they widened it to 140 meters by dumping 3.5 million cubic meters of sand on it. The median size of grains of sand on Copacabana Beach at sea level is 1/3 of a millimeter. Thatâs 27 grains of sand per cubic millimeter, so 3.5 million cubic meters of that kind of sand is about 1017 grains of sand. Thatâs most of the sand there today. So about 10 Copacabana beaches should have about 1018 grains of sand on them.
Up another factor of a thousand and we arrive at 1021, a sextillion. We have ascended from kilometers to megaphones to McDonaldâs hamburgers to Cro-Magnon artists to ants to grains of sand on beaches until finally arriving here: 10 sextillionâ
the number of stars in the observable universe.
There are people, who walk around every day, asserting that we are alone in this cosmos. They simply have no concept of large numbers, no concept of the size of the cosmos. Later, weâll learn more about what we mean by the observable universe, the part of the universe we can see.
While weâre at it, let me jump beyond this. Letâs take a number much larger than 1 sextillionâhow about 1081? As far as I know, this number has no name. Itâs the number of atoms in the observable universe. Why then would you ever need a number bigger than that? What âon Earthâ could you be counting? How about 10100, a nice round-looking number. This is called a googol. Not to be confused with Google, the internet company that misspelled âgoogolâ on purpose.
There are no objects to count in the observable universe to apply a googol to. It is just a fun number. We can write it as 10100, or if you donât have superscripts, this works too: 10^100. But you can still use such big numbers for some situations: donât count things, but instead count the ways things can happen. For example, how many possible chess games can be played? A game can be declared a draw by either player after a triple repetition of a position, or when each has made 50 moves in a row without a pawn move or a capture, or when there are not enough pieces left to produce a checkmate. If we say that one of the two players must take advantage of this rule in every game where it comes up, then we can calculate the number of possible chess games. Rich Gott did this and found the answer was a number less than 10^(10^4.4). Thatâs a lot bigger than a googol, which is 10^(10^2). Youâre not counting things, but you are counting possible ways to do something. In that way, numbers can get very large.
I have a number still bigger than this. If a googol is 1 followed by 100 zeros, then how about 10 to the googol power? That has a name too: a googolplex. It is 1, with a googol of zeroes after it. Can you even write out this number? Nope. Because it has a googol of zeroes, and a googol is larger than the number of atoms in the universe. So youâre stuck writing it this way: 10googol, or 1010^100 or 10^(10^100). If you were so motivated, I suppose you could attempt to write 1019 zeros, on every atom in the universe. But you surely have better things to do.
Iâm not doing this just to waste your time. Iâve got a number thatâs bigger than a googolplex. Jacob Bekenstein invented a formula allowing us to estimate the maximum number of different quantum states that could have a mass and size comparable to our observable universe. Given the quantum fuzziness we observe, that would be the maximum number of distinct observable universes like ours. Itâs 10^(10^124), a number that has 1024 times as many zeros as a googolplex. These 10^(10^124) universes range from ones that are scary, filled with mostly black holes, to ones that are exactly like ours but where your nostril is missing one oxygen molecule and some space alienâs nostril has one more.
So, in fact, we do have some uses for some very large numbers. I know of no utility for numbers larger than this one, but mathematicians surely do. A theorem once contained the badass number 10^(10^(10^34)). Itâs called Skeweâs number. Mathematicians derive pleasure from thinking far beyond physical realities.
Let me give you a sense of other extremes in the universe.
How about density? You intuitively know what density is, but letâs think about density in the cosmos. First, explore the air around us. Youâre breathing 2.5 Ă 1019 molecules per cubic centimeterâ78% nitrogen and 21% oxygen.
A density of 2.5 Ă 1019 molecules per cubic centimeter is likely higher than you thought. But letâs look at our best laboratory vacuums. We do pretty well today, bringing the density down to about 100 molecules per cubic centimeter. How about interplanetary space? The solar wind at Earthâs distance from the Sun has about 10 protons per cubic centimeter. When I talk about density here, Iâm referencing the number of molecules, atoms, or free particles that compose the gas. How about interstellar space, between the stars? Its density fluctuates, depending on where youâre hanging out, but regions in which the density falls to 1 atom per cubic centimeter are not uncommon. In intergalactic space, that number is going to be much less: 1 per cubic meter.
We canât get vacuums that empty in our best laboratories. There is an old saying, âNature abhors a vacuum.â The people who said that never left Earthâs surface. In fact, N...