Archive for the ‘Amazing Facts’ Category

Now You See It: Old Energy

Wednesday, April 7th, 2010

It was a hot day today. I told the rental office about my air conditioning, but it still isn’t working.

The light is beginning to fade now, as I write. The cool of the night will come. But even as I grumble about this heat, sitting here in a shirt I dunked in the sink, with a fan blowing on me, I have to say it could be worse. Some photons smacked into asphault and dirt, warming the air around me in this unseasonable weather. But others were captured by chlorophyll in the green alchemies outside my window, making sugar for the plants and releasing oxygen from their water so that we can all breathe. Life will continue, because of sunlight.

We take light for granted. Light is light; it’s just another bland fact of our existence. But not all light is created equal, you know. Take the light from my monitor. Without it, I couldn’t tell if I was spelling these words recognizably. The photons that make it up, little pieces of energy, are emitted from the surface of the screen and fly into my eyes in about a billionth of a second.  It is young light, and lives for only a short time, barely a tick of my 2.8 gigahertz processor’s electric heartbeat.

The light coming in the window, on the other hand, is very old.

Some of you out there in cyberspace may know that the Sun is 93 million miles away, and that light travels about 186,000 miles per second. When you do the division, that means the photons that are coming in my window left the surface of the Sun a little over 8 minutes ago.

But the energy that they carry is not a mere 8 minutes old.

They were born in the heart of the Sun, not on its surface. Atoms of hydrogen were mashed together in unthinkable heat and pressure and combined to make helium, plus the spare energy change of some photons. The Sun isn’t burning hydrogen, although physicists often say that, in a kind of shorthand. If you burn hydrogen, that is, combine it with oxygen, what you get is water. A very different process is going on inside the Sun. Instead of combining atoms to make molecules like water, the Sun is squeezing the smallest atoms (hydrogen) together to make slightly bigger atoms (helium). The light we see by is “merely” a by-product, a side effect of this solar alchemy.

Once a photon is formed in the heart of the Sun, it has to get out of the Sun. You might think this is simple, since photons are fast little buggers. The new-born photon is on its way out, of course; just as every direction you walk away from the north pole takes you south, when you are in the center of the Sun any direction you start off in is heading out. But the Sun is a crowded place. It is filled with hydrogen atoms waiting their turn to be fused into helium. So the photon cannot just fly out of the Sun. Oh, it tries, but in an extremely short time it smacks into one of these atoms and bounces off in a new direction.

After another short interval, it hits another atom and bounces off in another direction. There is no straight path out, you see, because of all of the atoms crowded inside the mass of the Sun. But it keeps trying. Eventually it reaches the surface of the sun, hits the near-vacuum of space, escapes the jostling crowds of atoms, and flies outward, perhaps to reach the Earth 8 minutes later and come in my window.

What most of you may not know is this: the average time it takes a photon to get out of the Sun is 20,000 years.

Yes, that is not a typo. Twenty thousand years. The Sun is a very crowded place. Pardon me, excuse me, please let me by, let me out of here! Imagine tying to get out of a movie theater with a million people in it milling around. Takes a lot longer than walking out of an empty building.

Twenty thousand years. Google, it if you don’t believe me. Of course, that’s an average figure. Some photons make it out in a mere ten thousand years. Some unlucky rascals are stuck in there for a million years. When we do the calculations, taking into account the densities and mean free paths, the average comes out to 20,000 years.

I should have known this a long time ago but I ran into this factoid quite recently. It blew my little mind.

When you look at the pyramids in Egypt, that some say are up to 5,000 years old…..the light you are seeing them with is far, far older. Older than any known civilization. While we have been inventing the wheel, learning how to grow crops, how to smelt copper and tin into bronze, how to write…these photons I am seeing right now were struggling to get out of the Sun. While empires rose and fell, artists painted, armies fought, a thousand generations of humans living and dying on this blue marble we call home….these poor photons were just trying to get out of the Sun.

If they could laugh, they’d laugh at the young photons streaming from my monitor to my retina. “One nanosecond? You call that a lifetime? One measly foot of travel? We’ve been on the fly for twenty thousand years. Good thing we don’t go senile.”

All the sunlight you will ever see was born thousands of years before you took your first breath. It’s been fighting its way out of the Sun for millennia just so you can look at a flower, read a book, ogle an attractive human, or walk your dog.

Think about that sometime. Sunlight is old. And we just take for granted that it will turn up every day like air.

We make our own light, of course. Candles, bonfires, street lamps, monitors, all flinging out their energy into the void, lighting the nights when our bit of the Earth is turned away from the Sun.

But they only put out young light. Our main source of light is the Sun’s ancient light. Sure, starlight takes years to get to us, far longer than the eight minutes sunlight takes. But that light, too, spent thousands of years struggling to get out of some star, so that it could streak through cold vacuum and make our night sky pretty.

We are surrounded by wonders. And they are not all in virtual space. — MRK

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