 what you’re able to see.
Bubbles breaking apart and joining together also happens extremely quickly—and it’s extremely small—so you need those special techniques to see what’s happening. Now I study the bubbles underneath breaking waves, where lots of bubbles are breaking up in that washing machine kind of turbulence. When the bubbles go back down into the ocean they’re important for helping our oceans breathe. They’re like little packets of gas carried down into the water.
I go out on ships to measure bubbles, usually in storm season, in the Mid-Atlantic. You look out over the deck at that familiar sight of breaking waves, something seafarers have seen for centuries, but just a meter below the surface you can see something that they have never been able to see. We need to understand it because it’s part of the clockwork of our planet, one of the mechanisms making our planet run.
Some people might think of physicists as nerdy figures in lab coats remote from normal life. But your book shows us that in our everyday life we are all physicists. Give us some examples.
That’s a fantastically outdated vision of a physicist! [Laughs] Physics is all about the rules that make the world work, and we all use them every day whether we’re aware of it or not. We don’t necessarily use them systematically but we’re familiar with the way things work.
When you’re baking bread, for example, one of the main things you want is to have bubbles in your dough. You use various methods to put bubbles into bread. You can use a raising agent or yeast, or you can fold air into the bread. When you put that in a hot oven and heat the gas up, the molecules inside the bubbles will bounce off the walls like tiny bumper cars and push them outwards, which makes the bread expand and rise. That comes from something called the Ideal Gas Law: the idea that the pressure, temperature, and volume of a pocket of gas are related to each other. Once you’ve got that little bit of physics, you’ve got the internal combustion engine, winds from Antarctica, and popcorn.
One of life’s small hassles is getting ketchup out of the bottle. What does physics tell us about it—and why doesn’t banging the bottom of the bottle help?
It’s a great disappointment to me that ketchup bottles are now made out of plastic rather than glass because now you can squeeze them and you don’t get to appreciate this nice bit of physics. We’ve all been in a pub or a diner, where you have a glass bottle of ketchup. You turn it upside-down, shake it, hit the bottom, and the ketchup doesn’t come out. Then it all comes out at once! [Laughs]
That’s not random. It happens because ketchup has got this weird property known as shear thinning. What that means is, it’s really viscous until you force it to move a little bit. When you’re shaking the bottle, the ketchup can’t go anywhere, so it stays thick. Once you hit it hard enough that it has to go somewhere, then it becomes runny, so a whole load of ketchup comes out at once.
The trick is to hold the bottle at a slight angle and tap the neck of the bottle, because then you’re making it runny where you need it to be runny. Everything further up the bottle stays nice and thick. Instead of having ketchup splodge everywhere, you can control the amount that comes out.
You’re British so tea and toast play an inordinate role in your life. There’s lots of physics in them, isn’t there?
The best thing about physics for me is that the same pattern explains lots of different things. There’s no reason why you have to see that pattern in a posh lab wearing a lab coat with some expensive bit of kit. You can see those patterns in your cup of tea. When you stir milk into your tea, the white milk doesn’t just merge with the dark tea. It swirls around. Then we look up into the sky at the big, rotating storms that come past at our latitudes, and there are also two fluids mixing together, via swirling. Even though looking at your teacup is one of the most mundane things in daily life, what you see there applies in other places.
It’s the same with toast. You shouldn’t worry ab