Category Archives: Physics

Being Wrong

Posted on by

The Key to Science (and Life) Is Being Wrong

“It doesn’t make any difference how beautiful your guess is,” Feynman proclaimed, gesticulating in wide, circular, somewhat flamboyant motions. “It doesn’t make any difference how smart you are, who made the guess, or what his name is. If it disagrees with experiment, it’s wrong. That’s all there is to it.”

Feynman was absolutely right.

I agree with this; Feynman had quite a talent for being succinct. However, the converse of this is not true: just because a theory agrees with experiment is not sufficient to confirm that the theory is right — there’s the possibility that competing theories predict the same individual result in some experiment, especially if the prediction is vague. It’s one reason we like mathematical models, which give us specific predictions.

Hello Molly

Posted on by

Funneling the sun’s energy

[Molybdenum disulfide] has a crucial characteristic, known as a bandgap, that allows it to be made into solar cells or integrated circuits. But unlike silicon, now used in most solar cells, placing the film under strain in the “solar energy funnel” configuration causes its bandgap to vary across the surface, so that different parts of it respond to different colors of light.

Trivia: Molybdenum disulfide also is used as a vacuum lubricant/anti-seizing agent (its use is critical if you have metal-on-metal contact if the metals are the same); it’s similar in effect to graphite, but has a vary low vapor pressure. There’s also the fun of it being very messy — it’ll be all over you in a flash, like a toddler playing in mud.

Old Physics isn't Obsolete Physics

Posted on by

Why Are Physics Classes Full of Old Stuff?

Chad does a nice job of addressing the issue raised in a Minute-Physics video. Frankly, I thought the video was uncharacteristically naive about this particular subject.

The fact that these courses are service courses first and foremost constrains what we can teach. And much as we might wish it were otherwise, the engineering and chemistry departments don’t particular want us to teach the cool modern stuff. They want us to teach old physics from 1865, because that serves as the foundation for some of their courses. We have to teach classical mechanics first because that’s what the departments that provide most of our students want us to teach.

And, of course, foundational for more physics, as well. It’s tough to talk about things like energy and momentum in advanced discussions if the students don’t know about energy and momentum. Can you discuss what a laser is and does at 8 O’clock on day one of an introductory physics class? It’d be fun to talk about how one might do that, but I’m not seeing how we get there. It’s almost like saying “let’s go read some neat books, because that’s fun, but let’s skip over all that boring vocabulary that we spend years developing”. Like most interesting books, quantum mechanics requires more than a third-grade level of reading ability.

The thing is, I see this same issue quite a bit on the science discussion board that hosts this blog — Science Forums (dot net). People show up wanting to discuss neat new things they’ve heard about, or even propose some new model of how things work, but have no clue about the basics — meaning they don’t understand what’s going on in the article, or why their proposal won’t work, and don’t get the objections people raise.

The Name is Bond. Frictional Bond.

Posted on by

The power of science friction

Have you ever had the impression that heavy items of furniture start to take root – that after years standing in the same place, they’re harder to slide to a new position? Do your best wine glasses, after standing many months unused in the cabinet, seem slightly stuck to the shelf? Has the fine sand in the kids’ play tray set into a lump?

If so, you’re not just imagining it. The friction between two surfaces in contact with each other does slowly increase over time. But why?

Ultimate Cosmic Space Mines

Posted on by

Speed kills: Highly relativistic spaceflight would be fatal for passengers and instruments

Going slow to avoid severe H irradiation sets an upper speed limit of v ~ 0.5 c. This velocity only gives a time dilation factor of about 15%, which would not substantially assist galaxy-scale voyages. Diffuse interstellar H atoms are the ultimate cosmic space mines and represent a formidable obstacle to interstellar travel.

Hack and Shill Went Up the Hill

Posted on by

Why Nate Silver’s Gambling Streak Makes Me Trust Him More

America is filled with people who think its okay to lie, bullshit, or otherwise misrepresent the truth in order to advance the electoral prospects of a politician or the cause of a governing coalition. Let’s call them shills. Other people aren’t necessarily aware that they’re misrepresenting the truth, but their work is so shaped by what would advance the causes of a candidate or governing coalition that it’s often indistinguishable from the shills. We’ll call them hacks. In a better world, journalists would be sworn enemies of shills and hacks, and the best are. Unfortunately, the press, especially the political press, has more than its share of shills and hacks.

I’m not sure if you’ve been following the Nate Silver hullaballoo this past week or so, but the short version is this: he has used statistics to show that Obama had (at the time of the linked article) a 75% chance of winning, based on a model that weights different polls according to past accuracy, instead of using the very blunt national polls. Advanced stuff. But because those on the right don’t like the answer, they are crying, “foul!”

A) this isn’t surprising, given how the GOP tends to treat science the way a baby treats a diaper. But B) this is actually an example of how science works. (A and B being somewhat related)

Taken by itself, a 75% chance of winning isn’t testable for a single-outcome event like an election. You can win even if your probability is low — unlikely events happen all the time. (and 1 in 4, or the current 1 in 6, is not all that unlikely. Clearly, you can roll a 6 on a standard die, even though there’s only a 1 in 6 chance of doing so) In the long run we see truly unlikely events because there are a lot of events. But that’s what you need in science in order to test your model — lots of events, so that you may gather statistics. This is why it’s important that Silver not only uses his model(s) to predict the result of the presidential election. There are more results

In 2008, he correctly predicted the outcome of the presidential election in 49 of 50 states, and accurately identified the winner in all 35 Senate races.

So there’s more to it than simply picking an overall winner. When your model accurately predicts outcomes, you have confidence that the model is a good one. Just like in science. We aren’t satisfied if all we can do explain past events; it’s the predictive power, and the possibility that the model can be falsified, that is one of the things that sets science apart from any wannabes.

Glow in the Dark … Roads

Posted on by

Netherlands highways will glow in the dark from mid-2013

The studio has developed a photo-luminising powder that will replace road markings — it charges up in sunlight, giving it up to ten hours of glow-in-the-dark time come nightfall. “It’s like the glow in the dark paint you and I had when we were children,” designer Roosegaarde explained, “but we teamed up with a paint manufacture and pushed the development. Now, it’s almost radioactive”.

Special paint will also be used to paint markers like snowflakes across the road’s surface — when temperatures fall to a certain point, these images will become visible, indicating that the surface will likely be slippery.

That's a Big Twinkie

Posted on by

I’ve been reading about some people expressing frustration that they are still in a bad way after hurricane Sandy — no power, long lines for gasoline, etc. Yes, it’s tough and you have my sympathy and empathy (90 hours without power this summer after being hit with a derecho gives me an inkling of the troubles)

But this was no small thing. The NOAA website discusses the energy released in a hurricane

It turns out that the vast majority of the heat released in the condensation process is used to cause rising motions in the thunderstorms and only a small portion drives the storm’s horizontal winds.

A typical hurricane releases an average of 6 x 10^14 Watts of power — it’ll be higher where there is more rainfall — which is 200 times the electrical energy generation in the world. The wind energy is a fraction of a percent of that, but is still half the world’s electricity generation level. And Sandy was bigger, so the numbers will be higher. All of that, focused on the mid-Atlantic/Northeast coastal areas.

The point is that there was a lot of fury unleashed last week, and it takes some time to recover from that. Gasoline in short supply indicates some of the logistical problems going on. A lot of people, requiring a lot of energy, all of it needing to be imported somehow. All of the behind-the-scenes things we take for granted, until a disruption occurs.

Sculpting the Answer

Posted on by

Three Tips for Solving Physics Problems

I began with the Feynman algorithm for solving physics problems:

Write down the problem.
Think very hard.
Write down the answer.

This is reminiscent of the old joke about how to sculpt an elephant:
1. Get a huge block of marble
2. Chip away everything that doesn’t look like an elephant

… but the post then goes on to explain how this is very useful advice.