Secondhand Science

“The Doppler Effect: yet another reason to run from screaming children.”

Most science happens in a laboratory or a particle accelerathingy or inside the brain of some bushy-eyebrowed theory geek. The applications don’t make it far into the real world. Like, why do we never see nonhomologous recombination in the newspapers? Or a cartoon starring Schrodinger’s cat?

Which would presumably be a fan of lasagna, but not so much of Mondays. Just based on previous observations of animated feline behavior.

But once in a while, we’re thrown a bone — a science bone — and we get to see what the eggheads are talking about in their fancy journals and proceedings. Like the Doppler effect, which we can observe on a regular basis — or daily, depending on your neighborhood — and also hear about on the local six o’clock news. That’s more public exposure than Jeremy Piven gets.

Although, to be fair: it’s Jeremy Piven. So.

Anyway, the Doppler effect has to do with waves, and the way they change in frequency relative to motion. Sound waves, for instance. Imagine a toddler in a mall throwing a tantrum, and screaming “MOMMY!” at one-second intervals. As toddlers do.

Now, if you’re moving toward the child — maybe you’re “MOMMY”, and you have the binky that will end this meltdown — the sound of those one-per-second screams will reach your ears faster. If you could run fast enough (and please do; we’re trying to shop here, ma’am) in the direction of the kid, you’d notice the frequency of those screams getting closer together. The child’s still shrieking them once a second, but you’re plowing toward them, so you get to the next one faster than, say, some guy just sitting in the food court with breadsticks shoved in his ears.

That change in frequency is the Doppler effect, and it’s a result of relative movement between the source and the receiver of the waves in question. So if you’re sitting still — because “Mommy’s tired”, obviously — but the squirt comes screaming toward you, the effect will be the same. On your ears, anyway. If not necessarily your Xanax prescription.

The Doppler effect works in the receding direction, too. If your relative motion is away from a wave source, the frequency will decrease as you move further away. With sound waves, pitch varies with frequency, which is why sirens — or toddlers — coming toward you sound high-pitched as they approach, then normal as they pass and lower-pitched as they speed past.

But autotuning ambulance noises and screaming tots isn’t the only trick up the Doppler effect’s sleeve. Light is a wave, too — depending on the time of day and which theoretical physicist you’re talking to — and astronomers can use observations of starlight to determine whether those stars are moving toward us or away from us. But rather than changing pitch, light undergoing a Doppler effect shifts color instead. So light sources coming at us skew toward blue wavelengths, or are “blueshifted”, while light from stars streaking away shows a “redshift”.

And what about the Doppler effect horning in on the local news? Well, radar is another type of electromagnetic wave, and works just the same as light and sound. That “Doppler radar” the weatherman gets so excited about determines the speed and direction that storms are moving by measuring the Doppler effect on radar waves bounced around the atmosphere.

There are plenty more examples, but you get the idea. Also, that kid’s not going to cram his own binky in his mouth, apparently, so maybe you could take care of that now, mommy. Mommy. MOMMY!