Note (12/2015): Hi there! I'm taking some time off here to focus on other projects for a bit. As of October 2016, those other projects include a science book series for kids titled Things That Make You Go Yuck! -- available at Barnes and Noble, Amazon and (hopefully) a bookstore near you!

Co-author Jenn Dlugos and I are also doing some extremely ridiculous things over at Drinkstorm Studios, including our award-winning webseries, Magicland.

There are also a full 100 posts right here in the archives, and feel free to drop me a line at with comments, suggestions or wacky cold fusion ideas. Cheers!

· Categories: Physics
What I’ve Learned:

Uncertainty principle: you'll never be a know-it-all; you can only be a know-it-half.
“Uncertainty principle: you’ll never be a know-it-all; you can only be a know-it-half.”

The uncertainty principle is an important tenet of quantum mechanics, first stated by Werner Heisenberg in 1927. And, like most concepts in quantum mechanics, it’s best explained with an analogy to a scene in Cool Hand Luke.

(No, seriously. I’m pretty sure ninety percent of Richard Feynman’s lectures involved stories about eating fifty hard-boiled eggs. You can look it up.)

In a nutshell, what the uncertainty principle says is this: at the quantum level, there are certain pairs of properties of a particle — like position and momentum, for instance — that cannot be accurately determined at the same time. The more precisely one property in such a pair is determined, the less certain one can be about the other.

That’s a fairly textbook definition of the uncertainty principle, which means any of us who ever took a class with an intro to quantum mechanics once slept through a very similar paragraph, probably drooling on our desks. Therefore: Cool Hand Luke.

Say you’re out there in the prison yard like Luke, wearing leg irons — double irons, to be precise — and the guards have decided to break you. Boss Position says you got a bunch of your dirt in his ditch, and you’d better get it out. So you go to work, and you dig it out.

Then Boss Momentum comes up, and asks what the hell you’re doing. Get your dirt out of his yard, he says. So you shovel your dirt back into the ditch. At which point, Boss Position comes back and yells at you to get your dirt out of the ditch, and somebody smacks you with a walking stick and you get your mind right for a while until you and George Kennedy ride off in a dump truck together.

Okay, some of that bit has nothing to do with physics. It’s just a really good movie.

The point is, you’ve got a ditchful of dirt, which stands for your ability to measure. You can put all your dirt in the ditch and measure position to a T — but then you’ve got no dirt left over to measure momentum. Or you can dump all your dirt in the yard and nail down momentum, but then position is a mystery. Or you can split the dirt, half-ass an estimate for both, and then nobody’s happy. It’s your choice. But there’s no more dirt to work with.

Also, the man with no eyes will probably shoot you in the end, either way. Because in quantum physics, nobody gets their mind right for very long.

One last important thing about the uncertainty principle: it’s not solely a result of the way you do your measuring. Some people — including Heisenberg — explained the uncertainty principle in a way that made it seem the ambiguity came from the act of measuring.

(Probably because Cool Hand Luke hadn’t been made yet in 1927. I think we can all agree that would have saved everyone a lot of time.)

And while it’s true that measurement will often alter the properties of a particle under study — a photon from a microscope changing a particle’s path is a classic thought experiment example — that’s not the same thing. That’s called the “observer effect”, and beyond any ambiguity that brings to the party, there’s still a fundamental, no-getting-around-it, baked-into-the-universe uncertainty principle lurking underneath. Even in a perfect world, with a measuring device that leaves a particle entirely undisturbed, you still can’t know both the position and momentum (for instance) of a quantum particle with complete certainty.

It’s almost as though what the two properties have is… a failure to communicate. Talkin’ physics over heah, boss.

Image sources: Clear Science (uncertainty principle), Information Processing (Feynman, obviously lecturing about a hard-boiled egg), Wars and Windmills (Luke and his ditch dirt), Northwestern University and Dewey21C (Werner and Luke staring down the man with no eyes)

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What I’ve Learned:

Pauli exclusion principle: If you're anything like me, then get the hell out.
“Pauli exclusion principle: If you’re anything like me, then get the hell out.”

The Pauli exclusion principle sounds like some rule a big Italian bouncer would use to keep you out of a swanky club, or maybe the reason Hollywood doesn’t let Pauly Shore make movies any more.

(That last one doesn’t really need a special name. The reason Pauly Shore isn’t allowed to make movies any more is all of them.)

But the Pauli exclusion principle is something else entirely. In the 1920s, physicists kinda-sorta understood something about the nature of atoms, and the electrons whizzing around them. They knew how many electrons the atoms of each element contained — one for hydrogen, two for helium, five for Milla Jovovich, et cetera — and they knew that some of those elements were more “stable” than others.

In physics terms, this stability meant that atoms of these elements didn’t share electrons with other atoms. They had no extras to give, and no empty electron-sized holes on their knickknack shelves to fill. These elements seemed to have atoms that were “full” of electrons — but no one knew exactly what that meant, or what kept the atoms in that “full” state.

A lot of people guessed it was those godawful Carl’s Jr. Thickburgers. But those didn’t exist yet — so it was probably something else.

Enter physicist Wolfgang Pauli, who simplified matters by making things more complicated. Because this is quantum physics, and that’s how it works most of the time.

At the time, electrons in an atom were characterized by three characteristics, or “quantum numbers”. Together, the values for these numbers described (roughly) the distance, shape and orientation of the electron’s orbit around the atom. And it took a hell of a lot of work to figure those three coordinates out.

Pauli decided that wasn’t enough, and added a fourth. He didn’t know what it was, exactly, but it was some characteristic with one of two possible values, like “on” or “off”. “Shirts” or “skins”. “Team Edward” or “Team Jacob”. Take your pick.

To make up for all the extra math, he then tacked on his Pauli exclusion principle: taking all four characteristics into account, no two electrons in an atom can have the same values. An electron orbital is “full” with two electrons in it — one with each possible value for Pauli’s fourth number. They can’t have the same number — and a third wheel can’t slip in, because both possible numbers are taken.

With that, it all came together. Atoms have different numbers and types and sizes of orbitals, but applying the Pauli exclusion principle explains which ones are “full”, and when the whole atom is “full”. The predictions lined up exactly with what scientists had already observed about atomic behavior. With one simple rule (well, relatively simple, for physics), Pauli gave physics a cornerstone of quantum mechanics and atomic physics. And in 1945, physics gave him back a Nobel Prize for it.

In the following years, Pauli’s fourth quantum number was identified as the “spin” of the electron, which for typically-complicated reasons has a value of either 1/2 or -1/2, but never anything else. All those physicists who bet on “boxers” versus “briefs” were apparently wrong.

But the impact of the Pauli exclusion principle didn’t end with electrons and atoms. The rule applies to all fermions (subatomic particles with half-integer spin), and also explains the characteristics of conductors and semiconductors, shows why matter is stable and takes up volume, and helps astrophysicists describe why white dwarf and neutron stars don’t collapse into black holes. Not bad for a scientific idea that basically started out with electrons picking “heads” or “tails”.

Image sources: StudyBlue (Pauli exclusion principle), Vevo (Pauly Shore, outside looking in), Kristy Lish (Leeloo / Fifth Element), Synotrip (Paris with a mouthful of Carl)

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What I’ve Learned:

Nucleation: Once you start, you REALLY can't stop.
“Nucleation: Once you start, you REALLY can’t stop.”

Everybody has to start somewhere. If you’re a corporate lackey, you start at the bottom. If you’re a gravedigger, you start at the top. And if you’re a phase transition, you start with nucleation.

Phase transitions are the change of a substance from gas to liquid, or from liquid to solid. But transitions don’t magically happen everywhere at once; you never see a swimming pool full of water freeze in an instant.

Not outside of a Vegas Penn and Teller show, anyway. Preferably with David Blaine chained down in the deep end.

Instead, the process — in this case, the formation of ice crystals — starts in one or more places called nucleation sites. In pure substances, these sites may occur randomly; where materials are mixed or in an irregular container, the nucleation sites usually form where different surfaces meet. Like by a leaf floating in the swimming pool. Or the tip of David Blaine’s nose. Just for instance.

Once formed, the nucleation sites provide an anchor for the transition process. That process speeds up, piling onto the sites like tacklers on a running back, until the entire team is on the pig pile and the system comes back into equilibrium. In the example above, that would be when all the water on the surface that’s cold enough has frozen into solid ice. Or when they fish the David Blaine-cicle out with a pool noodle.

The magic-but-actually-science of nucleation is not limited to freezing water, however. It’s also a crucial part of other natural processes, like crystallization, cloud formation and elongation of biological polymers like actin filaments. Some quantum cosmologists have even hypothesized that our entire universe is the result of a sort of bubble nucleation in the vacuum of whatever it is that lies outside the universe we observe.

(My guess for what’s out there? That girl from the Wendy’s commercials. Because she seems to be every-fricking-where else these days.)

Speaking of bubbles, a lot of people have been having fun with nucleation, possibly without realizing it. The key to the explosive foaming mess you can make by dropping a Mentos candy into a bottle of diet soda is indeed nucleation. Small pores in the Mentos allow bubbles of gas from the soda to form, which attract more bubbles and more bubbles — and they tell two friends, and so on and so on until there’s foam all over your kitchen and mom’s asking why there’s half a dissolved mint embedded in the ceiling.

Of course, bubble nucleation doesn’t require all those theatrics to be useful. Microscopic irregularities in champagne glasses nucleate those nose-tickling bubbles in the bubbly everyone loves. Nucleation also explains why it’s harder to pour a beer into a used glass without foaming up the place; the remnants of the previous pint’s suds provide sites for bubble-making that a fresh clean glass would not.

So that’s nucleation in a nutshell. It’ll help you pour a good beer, it makes Mentos much more interesting, and it might help us get rid of David Blaine. Honestly, what more could you ask of science?

Image sources: ASEPTEC (nucleation diagram), YouTube (cold, wet but sadly unfrozen David Blaine), (football pig pile), New York Times (science ‘n’ Mentos)

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What I’ve Learned:

Double-slit experiments: where two holes make a 'whaaaat?'
“Double-slit experiments: where two holes make a ‘whaaaat?'”

Have you ever dated someone who wouldn’t make a damned decision? Where should we eat? “I dunno.” Which movie are we watching? “Whichever.” Should we get married and have kids and live happily ever after? “Meh. We’ll decide later.”

Well, that’s what the universe is like. And the double-slit experiment is one of the clearest proofs.

Think about light. Light is kind of an important part of the universe; it’s the whipped cream on the cosmic sundae. Without light, there’d be no suntans or iPads, and we’d all be stubbing our toes in the dark every time we turned around.

So light is kind of a big deal, and physicists have studied it for hundreds of years. Back in the 1600’s, Isaac Newton — he of the fabulous hair and apple-induced concussions — thought that light was made up of tiny little particles, which eventually became known as photons.

And for a hundred-plus years, the universe said, “Yeah, sure, whatever.”

Every time scientists studied light, it behaved like a beam of little particles. Up until the early 1800s, that is, when physicist Thomas Young shone light through a pair of slits in a barrier, and watched the universe get wishy-washy.

Here’s the issue: if light is made up of particles — like a stream of paintballs, say — and you fire a bunch of those at a wall with two holes in it, then you’ll end up with just two spots of paint on the other side, right behind the holes.

Also, you’ll have a very messy wall. Mom is going to be pissed.

But what if light was made up of waves? Imagine water flowing through a dam with two holes. The water would only make it through the gaps — but then it would spread out, with the ripples from each side flopping into each other, creating a network of peaks and troughs called an interference pattern. That’s the pattern Young saw in his double-slit experiment, and he proclaimed that light is composed of waves.

To which the universe replied, “Eh, maybe.”

This is where things get really goofy. First of all, it’s not just light that behaves in this waffly way; double-slit experiments work with electrons, atoms and some molecules — or basically all the stuff our toes and iPads and suntans are made of.

But worse — what happens when you push, for instance, a single electron at a wall with two slits? Why, you get a single spot on the other side, just like the damned thing was a microscopic stupid paintball.

The universe doesn’t know which tie looks better. You decide.

And if you shoot a bunch of electrons at those slits, one by one — do you get two patches of light on the other side, since those individual electrons clearly act like particles? Nope. Eventually you get the very same interference pattern you would if you opened the floodgates up front.

Now the universe is just shrugging at you. And laughing behind your back.

In many ways, double-slit experiments — both physical and thought-experiment variations like those proposed by Richard Feynman — have helped to shape modern ideas about quantum mechanics, and the probabilistic nature of reality those theories suggest.

All of which is to say, if you’re ever stuck on a really important life decision like where to live or which job to take or whether that toe you stubbed in the dark might be broken — don’t ask the universe.

It hasn’t made a damned decision in three hundred years.

Actual Science:
Florida State University / Optical Microscopy PrimerThomas Young’s double-slit experiment
University of Oregon / 21st Century ScienceTwo-slit experiments
PhysicsWorldFeynman’s double-slit experiment gets a makeover
Physics arXiv Blog / MediumPhysicists smash record for wave-particle duality
io9An experiment that might let us control events millions of years ago

Image sources: Physics World (double-slit pattern), SweetJack (splatter wall), GearCrave (“Which tie, universe?”), QuickMeme (unsure Fry [standing in for the universe])

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