The timers click on a little after five. You can watch it happen if you are driving the neighborhoods off Rollingbrook at the right minute in December: one house, then three, then the whole street, the strings along the eaves and the wire deer on the lawn and the inflatable snowman lurching upright as its fan kicks in. Nobody is standing at a switch. A cheap plastic box in a garage outlet decided the sun was down, and the street lit up.
There is a pleasure in it that does not need explaining, and I am not going to explain it away. But I want to follow the glow backward for a while, because it goes a long way back, and the road it takes runs right past this town.
Start with the bulb. If the string is old, it is a filament: a hair of tungsten sealed in glass, with the air pumped out so it will not burn. Push a current through the hair and it fights the current, and the fighting heats it, and at a couple of thousand degrees it glows the way a stove eye glows, only whiter. Nine parts of the electricity go out as heat you cannot see, and about one part, or less, goes out as light you can. That is why the old strings were warm to the touch and why your grandmother's tree was a small fire hazard. It is also why they looked the way they looked. A hot thing glows every color at once, more red than blue, and the eye reads that as warm.
If the string is the kind on most store shelves, each bulb is a diode, which works by nothing like the same trick. A diode is a sliver of crystal, a semiconductor, grown so that one side has a few electrons too many and the other side a few too few. The side with too few is best pictured as having holes in it, places where an electron could sit and does not. Where the two sides meet there is a step, a small cliff in the energy landscape. Push a current across and electrons from the crowded side go over the cliff and drop into holes on the other, and each one, on landing, gives up the height it lost as a single packet of light. One electron, one hole, one photon. The color of the photon is the height of the cliff, and the height of the cliff is set by what the crystal is made of. There is no filament and nothing gets hot on purpose. Most of the electricity comes out as light. That is why a string of a hundred of them draws a few watts and a string of a hundred filaments drew a few dozen, and why you can leave the diodes on all night and not feel it in the bill.
Red diodes were easy, relatively; the first one that gave off light you could see was made in 1962. Blue ones were not. For decades the crystal that would make a blue photon refused to be grown clean enough to work, and without blue you cannot make white, and without white the diode was a thing for calculator displays and not for the eaves of a house. The people who finally grew it, in Japan, using a compound of gallium and nitrogen, got a Nobel Prize in physics in 2014 for it. The white diodes on your string are blue ones wearing a coat of phosphor that soaks up some of the blue and lets it back out as yellow. Blue plus yellow reads to the eye as white. You are looking at a physics prize every time you look at a porch in December.
Now follow the wire. This is where people's picture of electricity usually goes wrong, and I want to get it right. The electrons in the wire do not come from the power plant. They are the copper's own electrons, and they have been in that copper since it was smelted. When you plug in the string they do not race down the cord. They shuffle. In a household wire under a normal load the electrons drift at something like a fraction of a millimeter a second, slower than a snail. And because the wall current reverses direction sixty times a second, they do not even get that far. They rock back and forth in place, like a crowd swaying. What moves fast is not the electrons but the push, the field, which sets up along the whole wire at a good fraction of the speed of light. What the plant sends you is the shove, and the shove gets passed down the line from electron to electron the way a shove gets passed through a packed room, and at the end of the line a few electrons in a sliver of crystal go over a cliff and a photon comes out.
The shove comes from a spinning thing. Most of the electricity on the grid is made by turning a magnet inside a coil of wire. The panels on a few roofs on the street are the exception, and at half past five in December they have already quit for the night; everything else is something turning. Some of the turning is wind pushing on blades longer than a bus, far out west of here. More of it is steam or hot gas pushing on blades in a building, and in this part of the world more of that is natural gas than anything else. The gas comes out of the ground wet, with its heavier cousins riding along in it, ethane and propane and butane, and a processing plant strips those out. Those liquids are what sit in the salt caverns under Mont Belvieu fifteen minutes up the road, waiting for a cracker or a pipeline. What is left after the stripping, nearly pure methane, is the dry gas that goes down the line to a generating station and burns in a turbine, and the turbine turns a shaft and the shaft turns a magnet and the magnet drags on the electrons in a coil and the shove starts. Sixty times a second. Every generator on the grid turning in step with every other one, across most of the state, so that the swaying crowd in every wire sways together. If one big plant drops off, the rest feel it as a drag on their shafts and slow down a hair, and every clock that keeps time by the wall current loses a hair with them. The Texas grid is its own machine, an island, tied to the rest of the country by only a few thin connections. You are plugged into a thing nearly the size of Texas.
That is the road from the diode back to the well. It passes Baytown in more than one place. The gas that turns the turbines is the dry cousin of the gas the plants on the channel take apart for feedstock. The wire is insulated with plastic, and the plastic is made from ethylene, and ethylene is made here by the ton. The little plastic socket and the cord and the timer box in the garage and the vinyl skin of the snowman: petrochemistry, all of it, from a drum on the ship channel or a drum very like it. The glow on the eaves is a long argument that starts with a molecule.
But the road does not stop at the well. Go back further. The gas in the pipeline is the oldest thing on the street by a margin that is hard to hold in the head. It was alive once, as small things in a warm sea, and when they died the energy they had spent their short lives gathering was left behind in the bonds between their carbon and their hydrogen, and it stayed there, in the dark, under a growing weight of rock, while the continents drifted into their present places. Burn the gas and you break the bond and what was held in it comes out as heat. The heat pushes the blades. The blades turn the magnet. The magnet shoves the electrons. The electrons go over the cliff in the crystal, and something that was gathered in a sea a few hundred million years ago comes out of a porch in Baytown as a photon at half past five on a December evening and travels the last few yards across a lawn into an eye.
And the eye is the part I cannot get over. The photon lands on the back of the eye, on a cell that has been waiting for exactly that, and a molecule in the cell bends, and a nerve fires, and a brain made of the same carbon that was in the sea builds a picture of a house with lights on it, and something in that brain says: pretty. I do not know a way to say what that is without sounding grander than a porch deserves. Carbon that was mud is looking at carbon that was gas and finding it beautiful. The universe grew an eye, somewhere along the line, and this is one of the things it points the eye at.
I know a man who runs the night shift on one of the units on the channel, or I know enough of them that I can make one up without lying. He gets home a little after six in the morning in December, which is before the timers click off, so the last thing he sees on his street before he goes in to sleep is the neighbor's eaves still lit against a sky that is just starting to gray. He does not think about turbines. He has been thinking about pressures and flows for twelve hours and he is done thinking. He thinks the lights are pretty and that the neighbor has the timer set wrong, and he goes in.
A house on the street goes dark at midnight, on its own schedule, and the grid does not notice. A few watts less on a machine the size of Texas. Somewhere a shaft turns a hair easier and nobody's clock moves. The last photons out of that string of diodes are already past the fence, past the street, and most of them end in a wall or a leaf or a windshield. A few go straight up, miss everything, clear the sea breeze and the clouds and the thin top of the air, and keep going. They will be past the moon in a little over a second, and out of the reach of anything that could catch them a long time before the house is gone.