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Why Doesn't Your Butt Fall Through The Chair?
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Why Doesn't Your Butt Fall Through The Chair?

Science

Why Doesn't Your Butt Fall Through The Chair?

Why Doesn't Your Butt Fall Through The Chair?
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Woman sitting at her computer. i
Franck Camhi/iStockphoto
Woman sitting at her computer.
Franck Camhi/iStockphoto

Everyone knows that space is big and empty. To paraphrase Douglas Adams, author of Life, The Universe and Everything: "Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the pharmacy, but that's just peanuts to space."

And, as for emptiness, as a card-carrying astrophysicist I can verify that outer space is both vast and epically boring in its nothingness.

But what about inner space?

What about the space inside of solid stuff like tables, chairs and the goo of our bodies? If we zoom inward to look at solid matter on a microscopic or, better yet, a nanoscopic level, what do we find?

Surprisingly, what we find is a whole lot more empty space.

One of the strangest and least appreciated discoveries of modern physics is that solid matter is — to put it bluntly — a big fat lie.

Consider, for a moment, the chair your butt is resting on right now (or the floor, if you're standing). It's made of a squillion atoms right? And since it's a solid, all those chair atoms are packed tightly together like a vast collection of marbles in a box, right? And it's all those tightly packed atoms/marbles that are holding your butt in the chair against the force of gravity, right?

Well, actually, no. There is a tiny problem with the whole atoms-as-marbles picture.

It's entirely wrong.

Every atom has two components. There's the nucleus at the center (made of protons and neutrons) and then there's a bunch of electrons whizzing around the nucleus. When you see a picture of this (like in high school textbooks — see Figure 1), it usually looks like the nucleus is its own bunch of tightly packed marbles and the electrons are orbiting a little ways out.

Figure 1. The atom you see in high school textbooks, really, is not an atom.

Figure 1. The atom you see in high school textbooks, really, is not an atom. iStockphoto hide caption

toggle caption iStockphoto

But here's the problem with that kind of picture. You see the nucleus is only a few femtometers wide. And what's a femtometer you ask? It's a thousand million millionth of a meter, which is so incomprehensibly small to try to imagine it can blow a fuse in your imagination. But imagining such a tiny sliver of tinyness is not the real problem. The real problem is understanding where the electrons are relative to the size of the nucleus.

The average distance of an electron from the nucleus is about a ten-billionth of a meter (or what we in the biz call a tenth of a nanometer). So the nucleus is a femtometer across, and the electron is a tenth of a nanometer from the nucleus. What's the big deal? Just this: A ten-billionth of a meter is a hundred thousand times BIGGER than a femtometer. That means the electrons are a hundred thousand times farther from the nucleus than the nucleus's own width. If the nucleus were a beach ball in Midtown Manhattan, the electron would be living in an apartment in Philly.

And what does that mean? The atoms making up your chair — you know the ones supporting your booty right now — they are pretty much all empty space. Each one is a vast stretch of nothing that is lightly salted with an occasional fleck of stuff wandering in an endless void. And, as atoms go, so goes your chair — it's just empty space, too. That image you had of solid matter as tightly packed marbles? Nope. Not even close.

But now comes the $64,000 question — if atoms are nothing but deserts of empty space, how does your butt even know the chair is there? Why don't the flecks of butt-matter in the endless void just pass right through the flecks of chair-matter in their endless void?

The answer is as simple as it is weird. It's all just forces.

Cracking like lightning through the void, all the specks of electrons and the specks of nuclei are constantly interacting through a force called electromagnetism. Each interaction is carried out through the jolting exchange of particles of pure energy called photons (which is really just a nubbins of light). Each photon swapped equals a little push or a pull — a force — exerted across the emptiness. That's really what's keeping the stuff we call your butt from drifting through the stuff we call your chair.

So, the truth of the matter, dear friends, is there is no "solid" matter. Everything you think of as solid — tables, chairs, a '69 cherry red Ford Mustang, your child's noggin — none of it is really solid. Instead, there are only rapid-fire bursts of pure energy carrying forces between impossibly small flecks of somethingness. And all of it is lost in an atomic void as empty as intergalactic space.

Think about that the next time you plop down in a chair.


Adam Frank is a co-founder of the 13.7 blog, an astrophysics professor at the University of Rochester, a book author and a self-described "evangelist of science." You can keep up with more of what Adam is thinking on Facebook and Twitter: @adamfrank4.

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