Monday, August 29, 2016

Why You Shouldn't Have Fallen for That "Helium Beer" Video

A little over a year ago, a video of two giggling, drinking Germans started making its way around the internet. As they take sips of their beers, the giggles rise sharply in pitch, thanks to the helium that's taken the place of the CO2 which ordinarily gives beer its carbonated bounce. Each burst of laughter sounds more ridiculous than the last, and the two lose themselves in a chain-reaction of such high-pitched hilarity that it's impossible not to be drawn in and find yourself laughing along. You can check out the video below.

The video is, as you might have guessed from our post's title, a fake of sorts. I will say that it's a remarkably well-acted one; the way the Bierprobierers react to one another—and to hearing their own voices—makes for a convincing performance that's even duped a few of our physicists (at least for a moment). But now that we've had our fun, it's time to dig in to how you can tell that helium beer is a hoax, aside from the fact that the video was posted on March 31st of last year.
Our first clue that the voice modulation was added in after filming comes from understanding just how helium raises the apparent pitch of your voice. When you go to hum a note, your vocal folds (pictured right) pinch together, and the air moving over them causes them to vibrate at a certain frequency that depends on the tension in them. Somewhat surprisingly, this vibration frequency doesn't change when helium is inhaled. Instead, helium—which is less dense and has a higher speed of sound than air—picks up higher-frequency resonances more easily than air does. The upshot of this is that a lungful of helium will create a wacky pitch-bending effect, but only until it's been exhaled, which means you usually get one or two good breaths in before your voice goes back to normal, and it gradually descends in pitch as the helium in your lungs mixes with air on the inhale. The Bierprobierers' voices stay roughly the same through multiple gasps of laughter, which is a solid clue that some trickery is afoot here.

But what if it's a time-release thing? you might have thought. After all, the gas has to pass over the vocal cords to raise their voices, so maybe it's diffusing slowly through the esophagus into the lungs to provide a steady supply of giggle-inducing helium. Whether or not this is possible might be a little difficult to deduce from first principles, but we can hazard a guess based on the simple fact that ordinary beer doesn't make you feel like you're suffocating when you drink it. (If it did, it probably wouldn't be nearly as popular, but who knows?)

There's a particularly unpleasant feeling you get when you hold your breath too long—it's a unique, visceral, panicked sensation; the suffocation response. It's your body's way of telling you "Surface. Now." Curiously, the suffocation response in humans and other mammals isn't triggered by a lack of oxygen; instead, it's an excess of carbon dioxide that produces this sensation. From a practical standpoint, they're basically the same thing: for our entire evolutionary history, if you weren't getting enough oxygen, it was because you were holding on to "stale" air that had already had its Oconverted into CO2. (This peculiarity of evolution is also why pure helium, nitrogen, and other inert gases can be very dangerous to humans—you won't necessarily realize you're not getting oxygen until it's too late. I've heard horror stories of a pair of physics students who took an open dewar of liquid nitrogen into an elevator, not realizing that the rapidly evaporating gas was displacing the elevator's oxygen. Fortunately, they were discovered and revived shortly after passing out when the elevator's doors opened in a suitably dramatic roll of fog.)

Now, most beer is full of CO2, either produced naturally by the yeasts that ferment the brew or added after the fact to help drive the beer out of its keg once it's tapped and give it a nice, foamy head. If the gases in beer were capable of making it from the GI tract to the respiratory tract, drinking soda and beer would trip this suffocation response and wouldn't be nearly as pleasant an experience as it is.

There's a far more obvious (but accordingly less fun) way to tell whether or not helium-infused beer is a possibility, though: solubility. Any number of online data tables will tell you with a quick glance that helium is about one one-hundredth as soluble in water as CO2, owing to its small molecular size, relative non-polarity, and status as a noble gas. Obviously we're talking about beer rather than water, but the two are similar enough that the hundred-fold difference in solubility more than accounts for any discrepancies introduced by the alcohol, sugars, etc. This insolubility means that you can pump as much helium as you want into a bottle, but when you open it up it'll all bubble to the surface. (Note that nitrogen gas has a similarly low solubility—this is why "Nitro" beers tend to have a thick head of fine bubbles but a relatively "flat" body compared to ordinary brews.)

That about wraps it up for helium beer, unfortunately—it's a wonderful, but impossible, idea. Like all impossibilities, however, it's a great opportunity to learn and teach about the universe we live in: in asking "Why not?", we learn about boundaries, the rules that are responsible for the properties and processes going on around us. At the very least, it's a study in quality acting: knowing that it's a hoax makes a second watch positively strange, as two grown men fake-giggle their way to viral fame.

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