121. Exploring Physics, from Eggshells to Oceans

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My guest today, Helen Chersky, is a physicist and oceanographer at University College London.

She has a gift for seeing physics at play in the everyday world and explaining it in a way that's not only understandable, but at least for me, inspiring.

You've got one of the most sophisticated pieces of technology that humanity has ever built and you've got an egg on your kitchen table and the same bit of physics explains both of them.

Welcome to People I Mostly Admire with Steve Levitt.

I have absolutely zero intuition for physics.

I found it completely perplexing when I studied it in high school.

And when I recently flipped through my daughter's college physics textbook, all I could think was, thank God I had the good judgment never to take college-level physics.

But I've always wished I understood physics better.

I think Helen is my best chance.

You are a physicist by training, but you're not like the other physicists that I know.

The ones that I know, they're either obsessed with objects that are way too big or way too small to be directly relevant to everyday life.

So some of my physics friends are focused on how the structure of the universe looked eight-tenths of a second after the Big Bang, or they're trying to find dark matter or alien civilizations.

And others, I know, they're looking for the latest subatomic particle or trying to come up with the grand unified theory of particle interaction.

But you are so refreshingly focused on what's happening here and now.

You write about the physics of everyday life.

Well, I think the physics in the middle is underappreciated.

Partly because it's messy.

You've got surface tension and viscosity and gravity, and they're all kind of the same as each other.

So out in space, usually one or two things dominate.

But here in the real world, there's all these things jostling and one might be a little bit more important today and a little bit less important tomorrow.

And that gives you complexity and that gives you patterns and it allows for the richness of the world.

And actually, it's far less tidy physics quite a lot of the time.

The cosmologists will admit that.

But it's interesting because we can play with it.

Why would you not want to know why the world around you works?

I mean, the rest of the universe is very nice.

I don't have anything against it, but you can't really play with it.

You know, you can play it in your mind, but you can't actually pick things up and put things down and all that stuff.

And I think it's underappreciated how complex the world around us is, but also it has all these simple principles which underlie everything.

And once you understand the principles, so many things make sense.

It's not exactly a life-changing insight.

But one example that you gave in your book, Storm in a Teacup, that really sticks with me is how to use physics to figure out whether an egg is raw or whether it's been boiled.

And there have actually been a few times in my life when I've wanted to answer that question.

and I have studied the eggs and I've thought about it and I've tried and I had no idea which one was raw and which one wasn't and just ended up trying to crack them open to find out.

But you explain in the book how simple physics answers that question.

Yeah, the egg one is great because there is a difference between a raw egg and a boiled egg and it sounds really simple.

It's the raw egg is liquid.

That's what was my thought.

It's liquid.

I'll shake it.

I can tell, but you shake an egg and you really can't feel anything.

They're not so liquid that they squish around.

So if anyone's listening and you want to try this at at home, what you do is you get a raw egg and a boiled egg with their shells on, put them on a flat surface, on their side, and spin them around.

And then the interesting bit is that you just put your finger very quickly on the top and take it away.

So you stop the egg for an instant and then take your finger away.

And one of the eggs will keep spinning.

And that's the giveaway because the solid egg is all one.

So if you stop the shell, you stop the solid in the middle.

So the whole egg stops.

But the liquid, you've only actually stopped the shell.

The liquid inside, the white and the yolk, that's that's still spinning.

There's this law of the conservation of angular momentum, that's what physicists call it, that if something is spinning, it will keep spinning unless you make it stop.

And that's what happens to the inside of the raw egg.

So when you take your finger off the shell, the liquid inside pushes on the shell and pushes it round again, so it will keep spinning.

And the really great thing about the egg thing is that that's what explains what keeps the Hubble Space Telescope pointed in the same direction.

Inside of the Hubble Space Telescope, there are gyroscopes that keep spinning because there's no reason for them to stop.

And so the spacecraft can tell its orientation because it's moving around these gyroscopes so you've got one of the most sophisticated pieces of technology that humanity has ever built and you've got an egg on your kitchen table and the same bit of physics explains both of them and that's why the physics of the everyday world is interesting right because you learn a few of these basic laws and then you see they're everywhere and the really fun bit is that then you can use them as tools and that's the real power in all of this it's about showing people that physics is not beyond them it's part of their world and they do know it they just have to look at it and see the patterns.

One of the nice things about your books is that they are sprinkled with these little experiments that you can do at home to demonstrate physics in action.

And many of them are actually, I would say, at the border between experiments and magic tricks.

Sticking with eggs.

You give an example, which is how you can get an egg whose circumference is bigger than the neck of a bottle to actually nonetheless slide right through into that bottle.

Do you remember that one?

Well, this is to do with with eggs being an interesting kind of solid.

They're a very squishy kind of solid.

If you're going to try this, I advise you to boil it hard enough that the yolk is solid as well, because it'll make a lot less mess if the egg cracks.

So it's kind of rubbery, it's squishy.

You know, you can squeeze it and it will change shape.

So you've peeled this egg.

So this time you've peeled the egg.

You've done your spinning experiment.

You know which one was the boiled one and you've picked that one and you have taken the shell off it.

Actually, the hardest part of this is finding a bottle that's got the neck of exactly the right size.

So you want something that has a neck that's just a little bit narrower than the egg.

So, you can perch your egg, like an egg cup, on top of the bottle.

Then comes the interesting thing, because it looks like it is not going through that hole, but you can make it happen.

And what you do is into the bottom of the bottle, you drop a match, you let it burn for a little bit.

So, then what we've got is a load of hot air on the inside, which because it's hot, it's expanded.

So, inside the same amount of space, there isn't as much gas because it's expanded and the extra has been pushed out.

And then you kind of plug it with your egg, and the match will go out because it runs out of oxygen and then you've got the atmosphere on the outside and so the egg is now the sort of plug in this kind of tug of war so it's just going to go in whichever direction is pushing it hardest initially there's nice warm air down the bottom it's high pressure because those molecules are moving very quickly they're pushing on it very hard so the battle is equal and then as the gas underneath cools those molecules slow down which means they don't bump into the egg quite as hard which means they don't push quite as hard so then the outside is pushing harder than the inside and the egg will be pushed down through and into the bottle all by itself.

You can just sit and watch it because the atmosphere is pushing it there.

And then you've got the great game of trying to get it out,

which I don't think anyone has ever succeeded in doing.

This is all being caused by molecules that are far, far too small to see, billions and billions of them, but you can absolutely see their effect in the real world.

You know what's so fun for me reading your books is that every page is a reminder that I understand almost nothing about how the world actually works.

You know what I'd love to introduce you to is my friend Joshua Jay, who was a guest on this podcast a while back.

He is one of the world's greatest and most intellectual magicians.

And I bet the two of you together could create incredible illusions by taking your knowledge of everyday physics and his knowledge of perception.

And I think it could just be amazing.

But you know what's interesting about that is that I have the compulsion to explain everything, and magicians that have a rule that you never explain how it's done, right?

So, I think we might have a very interesting time, and then he would have to just like banish me so that no one could hear the explanations of how it all worked.

So, your PhD work in physics physics focused on experimental explosive physics.

That sounds almost too good to be true.

What kinds of things were you destroying during your PhD?

So I was never interested in the destruction.

I was not that kid who wanted to blow things up.

I did it because I was interested in high-speed photography and in building these experiments that let you look at something that was too small and too fast to see.

I really loved that lab work, that challenge.

And of course, the thing about explosives is that all the interesting stuff happens and then it goes bang and then you've got a mess to clear up.

and I was not very interested in the clearing up of the mess so I was interested in what made things blow up in the first place.

I was interested in the physics that happened up to that point that just before something goes pop, the material itself changes on a tiny atomic scale.

And obviously you can't look too close because it's about to all go bang.

And I couldn't wait to get away from blowing things up.

I had no intention of carrying on in that field because it's horrendous damage.

Absolutely horrendous to think of all the beautiful structures in the world around us and being able to take them apart in this incredibly violent way.

And even the day I found out that if I wanted to work in that lab, that's what I would have to do, I literally cried for a day because I didn't want to blow things up.

I didn't want to do this, but I was interested in the physics and this was the opportunity to do it.

So it was very morally difficult.

It astonished all my friends that I did it, but I was really good at building those experiments.

So explosives were interesting.

You know, I was studying secondary explosives and the mechanisms that made them go pop.

What do you mean by secondary explosives?

There's general splits in the explosives will between primary and secondary explosives.

And primary ones are things like lead azide, which is very sensitive.

So it takes very little to make it go bang, but it doesn't have very much of a kick.

It's not going to blow up a building.

But it will give enough of a kick to something else.

And the something else is a secondary explosive.

And the secondary explosive is really hard to set off.

Like it's really quite stable.

But if you can kick it hard enough to boot it into action, then it goes boom in a big way.

Could you just describe one of those experiments?

Because I'm puzzled as to how with something that's about to explode, how you would look at it at the atomic level.

What were your experiments?

So imagine a little ring molecule that's got four legs sticking off it.

And initially, those four legs are all sticking downwards like a dog.

So it's kind of standing on its four legs.

And that is one shape of this molecule.

And the other shape is that the two front legs flip up, like the dog lifted its front paws up.

And that second shape, that's the standard configuration of a secondary explosive called HMX.

You hit an explosive with a hammer, and sometimes it doesn't go bang.

The times when it does are when that molecule, those two legs, suddenly flip back down into the first configuration, and then that is a really sensitive explosive, and that's what goes pop.

So, in order to see that molecular change happening, I built this ridiculous experiment that took three rooms, has a class four laser, which is a big laser, infrared laser at one end, that was firing down through a transparent hammer made of sapphire that was about to hit the explosive.

And as the infrared hit the explosive, it could see which shape the molecules were.

If the flip happened, you saw green.

And then I had a high-speed camera looking to see if there was any green.

So I was looking through a sapphire hammer while a Class IV laser went pop with a high-speed camera to look for the right colour.

It was quite a production.

It was quite a complicated experiment.

I used to go in the morning and flip 47 switches and things would start buzzing and and humming, and lights would come on.

And I built the whole thing.

No one had constructed that experiment before.

So it was interesting to do.

And I did see it.

I was the first person ever to see that transition happening before it went bang.

And that's useful for safety because if you can prevent that shape change happening, basically that's a very safe explosive.

And so that then helps you in the places where you are going to use explosives, like mining or whatever, that helps you handle them safely.

Again, it's one of the things where I've never thought about how explosives work.

In our modern life, because so many brilliant people have come before us, we don't really need to know what's going on.

Although, on the other hand, as you've said, it's much more interesting once you understand a little bit more about the whys and the mechanisms.

I think it is important because the problem is if you don't understand anything of the whys, you are helpless.

Whereas if you understand a little bit of the framework, the critical thing you can do is you can ask the right question.

And that's what this is all about, really.

There's too much in the world to know.

We don't all know the answers to everything.

Having a framework for thinking about the world, it is brilliant for satisfying curiosity, but it's also phenomenally important for being able to ask the right question so that we can make judgments about the complicated world around us.

You often don't need a gigantic amount of knowledge, but you do need a framework for reality, and that's the thing that lets you ask the right question.

We'll be right back with more of my conversation with Helen Chersky after this short break.

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Honey, do not make plans Saturday, September 13th, okay?

Why, what's happening?

The Walmart wellness event.

Flu shots, health screenings, free samples from those brands you like.

All that at Walmart.

We can just walk right in.

No appointment needed.

Who knew we could cover our health and wellness needs at Walmart?

Check the calendar Saturday, September 13th.

Walmart Wellness Event.

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I knew.

Check in on your health at the same place you already shop.

Visit Walmart Saturday, September 13th for our semi-annual wellness event.

Flu shots subject to availability and applicable state law.

Age restrictions apply.

Free samples while supplies last.

So how did you switch from explosives to bubbles?

What was the path that got you to bubbles?

Well, I finished my PhD and I did not want to blow things up anymore, which came as an astonishment to every male.

The women didn't care so much.

The men were like, what?

You've got my dream job.

What are you talking about?

And I was like, you have to do the clearing up as well.

And then they went, oh.

So I was in the Cavendish Laboratory in Cambridge which is a very famous physics laboratory plenty of famous discoveries have been made there both in cosmology and in quantum mechanics including the discovery of the electron you know some really fundamental physics and I knew that there was this physics in the middle people were studying things in the real world things you could pick up and touch and I wanted to do something like that and so I spent six months kind of writing up papers and doing other things and then I literally read every edition of Nature and Scientific American and New Scientist going there must be something I can do there must be be something out there.

And, like you say, physics was so split into quantum mechanics and cosmology that there was very little in the middle back then.

And it just so happened that there had been someone in my lab who studied bubbles, and they came and gave a talk.

I was like, Oh, that's quite interesting.

And then I wrote an email to this guy, Grant Dean, at the Scripps Institution of Oceanography in California.

And I said, You know, I'm quite good at physics, got all these degrees from Cambridge in physics, don't know anything about bubbles.

Can I come and work for you?

And he said, Yes.

And so I went to Scripps in California.

I landed entirely by accident right in the middle of one of the best oceanography institutions in the world.

And then, of course, as soon as I thought about the physics of the ocean for the first time, I got it, right?

Clearly, this is important.

And then, very soon afterwards, I got extremely indignant because I was that kid that read all the things and went to all the lectures.

Like, how has nobody told me about the ocean?

This is completely ridiculous.

And so, then I learned to scuba dive because it was very obvious that if I wanted to understand what was in the ocean, I had to go in it.

So I became a scientific scuba diver.

I went to every lecture I could think of at Scripps.

I walked into people's offices and said, I don't know anything about anything.

Recommend a book for me.

And they did.

And so, you know, I was at Scripps for just over a year.

And then in my next postdoc, I went to sea for the first time.

So then I started doing field work.

So I'm curious, I've never heard the ocean and physics.

talked about together, just like you said, you hadn't heard it discussed as you were being educated.

How big is a community of scholars who focus on ocean bubbles?

There's lots of people that study the effects the bubbles have, but the number of people that actually study the bubbles, like really study the bubble physics themselves, is probably less than 10.

But bubble physics is one of those things where once you start seeing it, it's everywhere.

A bubble is an interesting thing because it's a gas and a liquid trying not to mix.

That's the reason a bubble exists, because the gas is trying to stay in a little pocket of gas and the liquid is staying on the outside of it, staying away.

So a liquid has a set of things it does, and a gas has a set of things it does.

But when you put them together in this bubbly fluid, then you've got something which is quite different.

And so, suddenly, you open up all these possibilities in terms of behavior and what it does because it's got loads of surface area and it's quite squishy.

I mean, who thought you could have squishy water?

But bubbly water is squishy, which matters for how sound travels through it.

So, wherever bubbles are, they're doing something quite interesting because they're very different from what's around them.

So, I study mostly the bubbles caused by breaking waves at the ocean surface.

One reason I suspect that the oceans are mostly ignored by physicists is that the questions sound so hard.

Liquids in general are really complicated with fluid dynamics, but that's even in an idealized liquid where you're in a lab and you control everything about the flow and the inputs and the outputs.

It seems like it would be very difficult to do experimental work in a setting as wild as the ocean.

Yeah, but you still have to try, don't you?

No, but that's probably why not very many people have tried historically.

It's definitely the case that the people who've studied the ocean are prepared to do the difficult stuff.

Actually, lots of scientists have studied the ocean, but because it's hard to get to, it's been a very data-poor science.

And that is now starting to change.

So lots of ocean science has been done.

There have been thousands of oceanographers.

But it's interesting that the physics of the ocean has never really hit the public awareness.

Everyone loves dolphins.

dolphins are very nice, but it's a lot harder to get people interested in water that looks like other water, that looks like more water.

And I think physical oceanography kind of got stuck, which is a shame because physical oceanography basically rules the world.

So tell me, how do you collect data on bubbles in the ocean?

I have done a lot of lab experiments on bubbles.

Just understanding the fundamental acoustics and optics and how bubbles behave and break apart and join together.

You can do that in the lab because bubble physics is bubble physics wherever the bubble is.

But actually to measure that in the open ocean is trickier because if you imagine going out in a big storm and you look at these stormy seas and seafarers have looked at really stormy seas for centuries, but what's happening just half a meter beneath that surface has been completely invisible.

Almost in plain sight, but not quite.

It's just underneath the surface.

And of course, you're interested in half a meter down.

The surface is going up and down by five or six or ten meters while all this is going on.

So it's a tricky place to get to.

So what I study are the mechanisms involved in the top few meters of the ocean during storms and how they're pushing bubbles and gas downwards and how it helps the ocean take a deep breath.

So the way to do it now, we go out and research ships and these are big collaborative experiments because you need all different kinds of ocean scientists at the same time measuring all the things because there's so many things.

I just do the bubbles.

And what I do is I put floating things over the side, buoys, which have sensors for bubbles and they might be acoustic sensors or optical sensors or gas sensors.

and they can float freely in storms.

So they can effectively be the eyes and ears just in the top few meters of the ocean while these big events are going on.

So just to understand, you're saying you and a bunch of other scientists get in a boat and try to find the worst ocean storm you can find, and you ride that out while you collect data.

Yep.

Isn't that a great job to have?

Did you know whether you were prone to seasickness before you chose ocean bubbles as your specialty?

So when I started studying bubbles, I had no idea it would involve going on ships.

And actually, the first ship I went on, first month-long cruise, they call them cruises.

Any mental associations you've got with a cruise, it's not that.

It's a very functional tin can with a bunch of scientists, and there are no cocktails on the poop deck.

So I went to study bubbles with an ocean optics experiment, and it was flat calm for a month, no bubbles.

But when I did start to get out in heavier seas, I found that I did not get seasick very easily.

Everyone gets seasick sometimes.

You know, anyone who's spent time at sea who says they've never been seasick is probably fibbing, but I don't get it badly.

You know, you get used to gravity being an uncertain friend.

Having a shower on board a ship is very entertaining because you're sort of chasing the water around the shower.

You know, people shower in different ways, but normally you're kind of moving yourself around so the water gets different bits of you.

You do not have to do that at sea.

You just stand still and the ship moves and the water covers all of you.

It's great.

So I'm not sure that people generally are aware, but a huge share of the planet's CO2 is in the oceans, way more than is in the atmosphere, right?

Yes.

There is more than 60 times as much carbon in the ocean as there is in the atmosphere.

So studying how the ocean breathes is important for understanding how carbon moves around the planet, because carbon moves around naturally all the time.

But then as we put extra into the system, it's got to find extra places to go.

And so exactly where it goes and how long it takes to get there and how it's distributed and what affects that, those are big questions in chemical oceanography today.

Is your research into bubbles at all related to that issue of carbon transmission?

It is, because the gases that the bubbles are helping to move downwards, carbon dioxide is one of those gases.

A big storm is like the ocean taking a deep breath.

So for example, as wind speed increases, you tend to get more carbon dioxide crossing from the atmosphere to the ocean.

The mechanisms are what give you predictive capability.

For most of the last 10 years, what's justified the work I've done is how quickly carbon dioxide is taken up by the ocean.

And a big share of human emissions to date have been absorbed by the oceans, right?

The carbon dioxide in the atmosphere would be much higher if the oceans weren't doing heavy duty pulling carbon dioxide out on net.

The ocean has done us a gigantic favor, basically, because if it wasn't for the ocean taking up carbon dioxide, we would be way past the Paris climate targets already, quite a while ago.

It's acted as a buffer.

And that's one of the reasons the ocean is important on planet Earth is because it is the big buffer.

You know, it's a buffer for temperature, which means you add an extra little bit of heat.

You don't immediately get a spike in temperature.

You've got somewhere to store it.

And so it's the same with the carbon dioxide, that as there's been more in the atmosphere, more has been pushed down into the ocean.

And of course, it causes problems in the ocean.

It makes the ocean less alkaline, and that's got implications for life in the ocean.

There's no such thing as a free lunch, but there's no doubt that it has done us an enormous favor by taking up so much.

But the question is whether that's going to continue, because as the oceans warm, gas is more likely to come out than go in.

You know, if you have warmer water, it will tend to give gas back to the atmosphere, and that would be very serious.

Warming is just one of the reasons that might happen.

But we need to keep an eye on that because we're sort of assuming that the ocean is going to continue helping us out.

Well, what if it doesn't?

We should be able to track that.

The way you say that, it sounds like the scientific community doesn't have a very good idea about how the oceans will behave in a different scenario where temperatures are two degrees Celsius higher.

Is that a fair thing to say?

No, well, you know, no one's got a crystal ball, right?

So we don't have models that we can say with 100% certainty this is what's going to happen.

We do have a very good idea of some of the big influences.

We know as the oceans warm, for example, what's mostly warming is the top layer.

And that makes the top layer more buoyant.

and that increased stratification makes it harder for the top to connect to the deep ocean so there's things like that where you can be pretty certain that's going to happen we can see actually the ocean is deoxygenating so it's lost about two percent of its oxygen since the 1960s that's not because of carbon dioxide is it is it the warming or what's happening Changes in ocean currents, changes in life and where life is living, those all make a difference.

And changes in the amount of oxygen that is taken in from the atmosphere in some of the places that feed the deep ocean.

And then, of course, you've you've got things like eutrophication, where the outflow of rivers, you know, Mississippi, for example, there's a huge amount of fertilizer comes down that river.

You get these enormous blooms of phytoplankton, and then what comes along to eat them consumes all the oxygen.

And the big debates are about how the big ocean currents and how the overturning circulation will be affected.

Generally, currents in the ocean go sideways.

The ocean is layered, so things tend to go horizontally.

But there are places in the ocean where the surface is connected down into the deep.

And so if it goes down there, it goes a long way down and slither around in the deep for maybe a few hundred years and it will slowly come back up somewhere else.

And so there are questions about whether that overturning circulation might slow down.

The problem with all of these things is that we're talking about massive processes.

This is an engine that runs on scales of decades or centuries.

And we've got, depending on what you're looking at, perhaps 20 years of really detailed data.

And so we can make some predictions and we know the physics, but exactly how it's all going to play out is still not clear.

We're studying how the system worked at the same time as it's changing.

So it's difficult to separate how much is this just natural variability and then where's this extra trend that is due to climate change?

And it's not that we can't do that science, it's just that no one's got complete confidence in that predictive power yet.

But any of these changes are big and serious and we should worry about them because it's the physics of the ocean engine that sets the environment of planet Earth.

It's not just, oh, the water's a couple of degrees warmer.

That sounds quite nice.

If it changes the shape of the engine, that's a problem.

The oceans are cold, and maybe it's just a warped human perspective, but it seems like the fish and the phytoplane, all of them might like it a little warmer down there, but it sounds like that's a pretty naive view of what's going on.

I think that's a lot of anthropomorphism there.

Like, oh, that cute little fish would love a nice warm jacket because it looks cold.

It's not quite as simple as that, partly because ocean creatures are very well adapted to the environments they're they're in.

And also they might use temperature to navigate, for example, to know where to go to find food at different times of year.

But also it's patchy.

It's not like the whole ocean is warming evenly.

The way to think about all of this is that this ocean engine, which the water is doing lots of things.

It's moving heat around.

It's moving natural chemicals around.

It's doing things all the time.

And it's got a shape.

And the shape of that engine and the way it flows, that's what means it's quite warm in Britain and quite cold in Nova Scotia, for example, even though we're more or less the same latitude.

And the the thing about climate change is that in some respects, it's going to change the shape of the engine, and therefore, the heat will be distributed differently.

The biggest problem with that is that everything we know on this planet is very well adapted to things being as it is now.

And that's both the animals and us.

You know, where we trade, where our agriculture is, where we live, where we get our water from.

All of that depends on it working as it does now.

It's changed in the past, it's not changed this quickly, and that's the problem.

You're listening to People I Mostly Admire with Steve Levitt and his conversation with Helen Chersky.

After this short break, they'll return to talk about how ocean waves may have changed the course of history.

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Helen Chersky has the ability to make complex ideas feel simple and also relevant to our lives.

That's a really powerful kind of storytelling.

In the time we have left, I want to ask her how she thinks about telling those kinds of stories.

So a lot of what we're talking about is coming from your new book.

It's called The Blue Machine.

And I have to say, when I heard that you were going to write a book about the physics of the ocean, I was skeptical.

And I was skeptical because good books are almost always full of good good stories.

And good stories almost always revolve around people, not things.

It's hard to tell a good story about a wave or an ocean current.

Did that give you any pause as you embarked on this latest book?

No, because I thought someone should do it.

Because you're exactly right that there's this problem of how do you relate to water.

We are very...

committed to things that we can relate to and that have big cute eyes and fluffy ears.

But I knew the stories were there because I could see them.

The way the ocean engine turns has affected so many animals, plants, structures, civilization, history, cultures.

It's all there.

You just have to do a bit of digging.

It was more time-consuming digging than I anticipated.

I'll give you that.

So, literally, the book plan for my last book was actually 10 post-it notes on one piece of paper, and each of the post-it notes had three words on it.

This one was this gigantic document that covered a wall because there's so many stories.

I never had any doubt that the stories were there, but it did take a lot of digging because no one really talks about those stories in this way.

You tell a lot of interesting stories in the book about guns and war, perhaps in homage to your early PhD work on explosives.

For instance, you tell a fascinating story about oceanography in D-Day that I've never heard before.

And I asked my father, who knows...

everything about World War II, and he didn't know that story either.

Could you tell the story?

Was the guy's name Walter Monk?

Walter Monk, yeah.

So Walter Monk was an extremely famous oceanographer.

He died just a couple of years ago at age 101, I think.

And he was working right up to the end.

But he started out during the Second World War, right at this period when people were really looking at the ocean for the purposes of war.

So if you turned up somewhere with a load of soldiers on a ship, you had to somehow get them onto the shore.

And so there were these things called landing craft, kind of flat, wide barges.

And the problem that these things had is that if the waves were very big, these were terrible boats.

They floated, they could carry people a short distance, but they weren't very good.

So if there was any swell coming in, they got tipped over.

And Walter was looking at the conditions initially off the coast of Africa where these things were being used.

And as far as they were concerned, then it was kind of like magic.

Like, oh, today there's really large swell and these boats are getting tipped over.

And tomorrow it's totally fine.

So he started working on how do you predict where the waves are going to be.

Even then, they knew the basic mechanism.

Walter Monk understood that you had to predict the storm.

So you you needed a weather forecast.

You needed to understand what waves were generated.

You need to understand how they traveled and how long it would take them to get somewhere.

And then you could make a prediction.

So they worked on that and they got better at it.

And then D-Day was coming up, the sort of critical day in the Second World War, where a load of boats had to arrive on the coast of France.

And it was either going to be, I think it was the 5th or the 6th of June.

And the moon had to be right, so there was light to see.

And the weather had to be right.

Then they, of course, wanted the element of surprise.

So they didn't want to just sit there and wait because the Germans would know they were coming and so they did wave predictions and the answer came back from the models that if you go on the first day on June the 5th there is going to be so much swell everything will be a disaster and Eisenhower made the decision to delay D-Day by a day and then history as we know it followed.

That was one of the first instances of predicting the ocean in order to change a decision about how humans acted.

One thing you do masterfully in the Blue Machine is you tell stories where animals rather than humans are the central characters.

I'd never heard of a Greenland shark before, but they are amazing creatures.

I think everyone should be talking about them all the time.

They're kind of a baggy sweater pretending to be a shark.

They live in cold places.

So sharks don't tend to live in cold places.

These ones do up near Greenland, as you might expect.

And they can be huge, you know, four to five meters long when they're fully grown.

And they swim incredibly slowly.

Most of them are blind because they've got this kind of horrible parasitic worm hanging out of one of their eyes or both.

But since they live in the dark, it doesn't seem to make much difference.

No one's ever seen one eat, I don't think, but their stomachs have, you know, seals and fish.

So it seems that what they do is kind of just slide along as a piece of darkness and then chomp.

But the thing about the Greenland shark is that they can live up to 450 years old.

They don't reach sexual maturity until they're 150.

That's unbelievable.

It's yeah, it's patient lifestyle, isn't it?

But the reason they can live so long is because it's cold.

You know, they have a slow, cold lifestyle and they just live slowly.

And the way it comes up in the book is that a few years ago, there was a research ship in the Gulf of Mexico, where the surface temperature is obviously very, very warm.

And they were studying the aftermath of the deepwater horizon oil spill.

So they were putting down baited hooks to do surveys of what was living down there.

And they put a hook down, they pulled up on deck a juvenile Greenland shark.

And they weren't super surprised because down in the depths of the ocean, even in the Gulf of Mexico, the water is cold.

And And so when they pulled it on deck, it was warmer in death than it had ever been in life.

So it was out of place.

It was probably struggling to feed a bit, but it wasn't that far out of its temperature range because the ocean has structure.

The ocean has anatomy.

And so you can tell the story of the anatomy of the ocean, partly through the creatures that navigate through it and use that anatomy.

It's not just water and more water.

It's features.

And you can navigate through those features to find the best feeding places.

Now, most of the time, I would expect that descriptions of physical systems without stories, that would be on the boring side.

But the facts that you have about the ocean are so startling to me that I was simply blown away.

Could you talk a little bit about the physics of sound in the ocean?

For instance, how far can a whale transmit a sound?

What really makes some whale calls travel a long way is the physics of the ocean.

So the ocean has this kind of channel on the inside of it, a kind of flat layer.

And if sound, deep sounds especially, go into that layer, they sort of bounce up and down within the layer.

And so they don't reach the surface and they don't reach the floor and they don't spread out very much.

They just go out sideways.

So they can travel a very, very long way without being attenuated.

And there's this extraordinary experiment that was done to demonstrate just how far sound can travel through the ocean called the Heard Island Experiment, 1991.

Walter Monk pops up again.

It had been noticed that somebody had set off some explosives in one part of the ocean and someone someone else had heard it thousands of kilometers away.

And Walter Monk said, we know that if the ocean temperature is different, sound travels at a different speed.

So what if we made a loud noise deliberately and then we listened all around the world and we could sort of take an average temperature?

of the whole ocean all in one go just from one measurement because they knew that climate change was coming back in 1991 so they thought well maybe as the ocean warms we can use this to track climate change so they set up this experiment with two ships that went down to the southern ocean so kind of where all the global ocean connects.

And they had these really massive speakers that made really deep noises.

And they set up listening posts all around the world, you know, in Bermuda and in the Indian Ocean and on both sides of the Americas and all these places.

And they were just listening.

And the sounds traveled through this channel.

And it was heard several hours later.

And they could time it with incredible precision.

So it worked as a listening experiment.

And then all their speakers blew up because it's quite hard to make really deep noises.

So you're literally saying they made a sound on one ship

and two hours later, halfway across the world, that sound was heard.

That's right.

And they could also learn stuff from the way it arrived.

They made a clever kind of signal so they could learn exactly what the path was as it traveled through the ocean.

So there was a lot of subtlety.

And it was the days of faxes.

So there was a fax machine on the ship.

So they're getting these faxes from the other side of the world saying, oh, you know, we heard you this morning.

So it was a really interesting idea.

Obviously, and this is much more obvious now than it was then.

There were concerns about marine mammals.

And now, of course, the idea of making extremely loud noises right in the channel that big animals use to communicate is a no-no.

So it sort of died a death, but now it's coming back because there are proposals to use natural sound.

You know, if a glacier cracks or there's an earthquake, there's something kind of natural, loud noise.

People have said, well, maybe you could use that natural loud noise and play the same game.

And so there is some work going into it.

Again, but yeah, sound can literally travel around the globe.

In addition to thinking about bubbles and everyday physics, you've also thought a lot about the role of science and scientists in society.

And people often say things like, public policy should follow the science, which sounds really sensible, but it's a statement you totally disagree with, right?

Yeah, yeah.

I have to be careful because it's easy to get sort of misquoted on this.

But the thing is that science doesn't tell us what to do.

Your values tell you the direction you want to go in.

So maybe during a pandemic, you don't want people to die.

Or maybe if climate is changing, you want to minimize the damage that's going to cause.

There's some kind of decision you make based on values.

And the science will tell you how to put that into action.

From a probabilistic point of view, because no one's got a crystal ball, if you want that outcome, these are the things you need to do to get there.

And I think one of the problems with a lot of the debates we're having in society at the moment is that we're mixing up values and science.

Everyone wants the science to be on their side, right?

But actually the science isn't on anyone's side.

You have to have your debate about your values, and then the science will tell you how to get there.

And maybe the science can tell you, these are the sorts of questions that you should apply your values to, right?

Here's a thing that's coming down the line.

Can we have a think about this as a society?

What do we choose to do about this?

It's not the case that science tells you what to do unless you've already sorted your values out.

So you are both a scientist and you're a citizen.

And an interesting question arises with the role that scientists, especially in the environmental movement, play as advocates.

It's my impression that you don't do so much advocacy that you tend to stick to science more so than other people who are involved in the study of things like the oceans.

Is that something you've done intentionally?

I don't really think that's true.

What I don't do is get involved in debates on social media very much.

But I think there's a kind of advocacy which is making sure we are asking the right question.

I was a student environmental activist right the way through from when I was 13.

I had a sort of notice board at my school that had all the environmental things people could do on it.

The most powerful form of activism for me, and it's different for different people, is doing things.

And of course, a debate is part of that.

But I think that what I can do is help frame debates and help make sure those debates are well informed.

I do express strong views, especially on climate change and what people should do about this, but I don't spend a lot of time waving flags, partly because I'm really busy, but partly also because I think I can put my effort into actually doing things, into making things change, rather than just complaining about the system.

I do do a lot of complaining about the system, but I think if you help people see how the system works, you're giving everyone a bigger lever to change it.

And what matters is that that lever moves.

I definitely would count myself as an environmental activist, but not the sort that gets involved in protests.

I prefer to focus on what are the constructive routes to action.

And that's my form of activism.

If you couldn't tell, I really enjoyed my conversation today with Helen Chersky.

And if you did too, I'd think you'd like her books.

Her first book about everyday physics is called Storm in a Teacup.

And her most recent book about the physics physics of the ocean is called The Blue Machine.

And now is the time of the show where we take a listener question.

And as always, I'm joined by our producer, Morgan.

So we have a question from a listener named Ed.

And Ed writes, I've always wondered if it would be possible to flip the prison incentive structure to where prisons get more money for inmates that don't reoffend.

It would incentivize correctional facilities to actually focus on correcting the issues that cause criminals to keep being criminals.

What do you think, Steve?

In principle, yes, it's almost always a good idea if you can tie any institution's compensation, their incentives, to the quality of the service that they provide.

But in practical purposes, I would say the chances that we would ever figure out a way to get prisons compensated so when the inmates didn't come back, they were rewarded.

I think it's just completely out of the question because it is so hard to change anything in public policy, especially in prisons.

We talked with Clementine Jacobi, and she and her team have worked years just to get data to be able to tell the prisons that they should be letting the people out who are in there because they've already completed their terms.

Whenever you give strong incentives, you have to be careful you don't elicit a kind of behavior you don't want.

So what could happen here?

If you start incentivizing prisons not to have the inmates come back, it might be easier to make life miserable in the prisons than it is to actually give the inmates the skills and the capabilities that will help them do better on the outside.

I think this is one of those ideas that looks good on paper, but I can't even imagine a pathway to making it a reality.

Are you aware of any programs?

that don't emulate this, but are alternative ways of helping keep prisoners from coming back to prison?

Are you aware of any research along those lines?

It's been really hard to do good research.

The area I know best is in prison education.

And there are just, to my knowledge, are not many good studies that really compellingly tell a causal story about education working or not working.

I'm not saying that education in prisons doesn't work.

And we had Dwayne Betts on not that long ago.

He's putting libraries in prisons with the hope that it will both make prisoners' time better, but also maybe influence what happens to them when they go back to the outside world.

I'm 100% in favor of giving education to prisoners.

It's just that the research thus far that I've seen hasn't been particularly convincing.

I still believe 100% in doing it.

I still think it's got to help, but to a skeptic who didn't think it was going to work, I don't think the research would change their mind.

Ed, thank you so much for writing.

If you have a question or comment, our email is pima at freakonomics.com.

That's p-im-a at freakonomics.com.

It's an acronym for a show.

We read every email that's sent, and we look forward to reading yours.

In two weeks, we're back with a brand new episode featuring Arnold Schwarzenegger.

I'm so excited to have the chance to talk with him.

When I was asked, Arnold, what do you think about someone threw an egg at you?

Then I said, Well, I hope the next time he also throws some bacon, so I have a complete breakfast.

As always, thanks for listening, and we'll see you back soon.

People I Mostly Admire is part of the Freakonomics Radio Network, which also includes Freakonomics Radio, No Stupid Questions, and The Economics of Everyday Things.

All our shows are produced by Stitcher and Renbud Radio.

This episode was produced by Julie Canfer with help from Lyric Bauditch and mixed by Jasmine Klinger.

We had research assistance from Daniel Moritz Rabson.

Our Our theme music was composed by Louise Scara.

We can be reached at Pima at freakonomics.com.

That's P-I-M-A at freakonomics.com.

Thanks for listening.

You were in London a little while ago, right?

No, that must have been Dubner.

I don't think I've been in London in ages.

One of the Steves or Stevens was in London.

The Freakonomics Radio Network, the hidden side of everything.

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Honey, do not make plans Saturday, September 13th, okay?

Why?

What's happening?

The Walmart Wellness Event.

Flu shots, health screenings, free samples from those brands you like.

All that at Walmart.

We can just walk right in.

No appointment needed.

Who knew we could cover our health and wellness needs at Walmart?

Check the calendar Saturday, September 13th.

Walmart Wellness Event.

You knew.

I knew.

Check in on your health at the same place you already shop.

Visit Walmart Saturday, September 13th for our semi-annual wellness event.

Flu shots subject to availability and applicable state law.

Age restrictions apply.

Free samples while supplies last.