## 6.1 Introduction to Waves and Sound

There is a secret about waves. It is the kind of secret that, if you fully understand it and its implications, may well blow your mind and leave you scribbling paranoid manifestos on attic walls.

Or worse, you might only think you understand this secret, and go off and make some horrible and misleading movie like What The Bleep Do We Know1 based on your flawed understanding.

It is the kind of secret that has a lot in common with some of the best conspiracy theories: it’s far-fetched and far-reaching, and for many years it attracted only a small handful of dedicated believers trying in vain to convince everyone else that it was true.

1. Just don’t even bother googling it, seriously.

## To Stir, Or Not To Stir

In my physics undergrad, we had one prof who seemed a bit strange. Actually, being only a bit strange seems something of an accomplishment for a physics professor, as most of them ran the gamut from odd to unintelligibly bizarre. But the one I’m talking about here was a younger guy who taught us about thermodynamics.

He was odd in a number of ways, but one sticks out in my memory: one day, in class, he said he couldn’t understand why anyone would ever stir a hot cup of tea, because stirring adds energy, which would only make the liquid hotter. He also said that people switched from wooden spoons to metal ones for the sole reason that they conducted heat out of hot liquids, allowing them to cool down more quickly.

Both of these comments were strange because they seemed to betray a pretty deep misunderstanding of the physical world – something that would cause problems for, say, a physics professor.

Luckily for us, Randall Munroe of xkcd fame has tackled the issue of stirring hot drinks in his latest instalment of What If: Stirring Tea. The question asked:

‘I was absentmindedly stirring a cup of hot tea, when I got to thinking, “aren’t I actually adding kinetic energy into this cup?” I know that stirring does help to cool down the tea, but what if I were to stir it faster? Would I be able to boil a cup of water by stirring?’

## Wired: The Experiments Most Likely to Shake Up the Future of Physics

If you’ve been following Pop Physics (especially if you’ve stuck through the overlong and unannounced hiatus that started with the new school year) and are still in school, there’s an excellent chance that you’ll end up working for one of these projects someday!
The Experiments Most Likely to Shake Up the Future of Physics

Here’s one of my favourites:

“NOvA will attempt to figure out this mass hierarchy by shooting a beam of neutrinos from Fermilab near Chicago 810 kilometers away to a detector in Ash River, Minnesota. A similar experiment in Japan called T2K is also sending neutrinos across 295 kilometers. As they pass through the Earth, neutrinos oscillate between their three different types. By comparing how the neutrinos look when they are first shot out versus how they appear at the distant detector, NOvA and T2K will be able to determine their properties with high precision.”

Science!

## Free Energy! Only \$7610

Earlier this year, I posted about why perpetual motion and “Free Energy” machines are impossible. Soon after, I found someone trying to sell their own perpetual motion device on YouTube.

Today, I’m going to do one better: an indiegogo campaign called “Home Quantum Energy Generator” has raised \$16,902 (far surpassing its oddly specific goal of \$7,610) to build a protoype Free Energy device. This thing features several of the hallmarks of modern physics quackery:

1. An inventor who is specifically not a trained physicist, but a “career Electronics Engineer”
2. Layperson explanations that defy logic
3. The word “Quantum” thrown in for good measure

Here are a few of my favourite quotes: (more…)

## Two Games That Mess With Relativity

When you start to learn about Special (or General) Relativity, one of the first question you’re almost guaranteed to ask is, “Why do things get so weird when you approach the speed of light?” My favourite answer to this question is to say that if we lived our lives at relativistic speeds, our current low-speed, “normal” world would seem just as bizarre.

Unfortunately, most of us don’t have access to the kinds of energies required to experience relativistic effects first-hand. Luckily, modern technology has provided us two glimpses into the kinds of mind-bending phenomena described by Albert Einstein.

First off, there’s the 3D, MIT-created, graphically beautiful game called A Slower Speed of Light. This first-person non-shooter, developed at MIT’s Game Lab, is free to download, so go try it out now. The goal of the game is to navigate a 3D world and collect spheres, which incrementally reduce the speed of ligh, amplifying effects like time dilation, Lorentz contraction, and the Doppler shift. Or in lay terms, stuff just keeps getting crazier.

## This Martian Life

Well, it’s now just over a year since Curiosity landed on Mars. What better way to celebrate than a stop-motion video with a hard-rockin’ soundtrack?

Here you can see this excellent robot wandering around the dunes, grabbing soil samples, and generally having a marvellous time, all through the fish-eye lens mounted on the front of the Rover.

## 5.7 Entropy, Part 2: Efficiency

Critical Questions:

• Why can’t we build a machine with 100% efficiency?

After a shamefully long delay, let’s take a look at the consequences of entropy. In the previous section, I described entropy as a measure of the statistical probability of a state.

One of the most significant results of this kind of thinking is that, because high-entropy states are more likely than low-entropy ones, the total entropy of the universe will always tend to increase over time. We have to say “tend to” here because things like all of the air particles in a room jumping to one side can, technically, happen. But if every process obeys this statistical reasoning, then instances of spontaneous entropy decrease are so unlikely that they are essentially impossible, so the total entropy of everything will always be naturally increasing.

Here’s where we can connect things back to energy. First of all, if you want to reduce the amount of entropy in a certain area – like arranging the bricks into a wall – you have to expend some energy.

## Size of a Neutron Star Compared to NYC

Yes, it turns out the two things in the title of this post have comparable sizes. Who knew?

A neutron star is a very old star that has burned off most of its energy and then collapsed into itself. As a younger star (such as our sun) undergoes the nuclear fission reactions that make it glow, the energy released keeps all of that matter spread out to a very large distance. But if those reactions cease, the intense gravitational forces compress everything down to a shockingly small volume.

In the image above, that blue ball contains the equivalent of 500,000 Earths worth of matter, giving it an unimaginable density: a teaspoonful of the stuff would weigh a couple billion tons.

And yes, that shadow makes no sense whatsoever. But it looks good, and that’s what’s really important.