Chapter 3: The Relation of Physics to Other Sciences

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Welcome to the Deep Dive.

Today, we're really getting into some foundational ideas looking at Richard Feynman's view on physics.

Specifically, how physics sort of acts as the basic layer for almost all the other sciences.

Yeah, it's a really compelling way to frame it.

He positions physics as the modern successor to natural philosophy.

The core idea is that everything, chemistry, biology,

even geology and astronomy, ultimately comes down to the jiggling and wiggling of atoms, as he put it.

Right.

So our mission today is to kind of trace those connections, see how these sister sciences, as Feynman calls them, rely on physics.

But interestingly, before he even gets into the natural sciences, he makes a really key distinction.

He does.

Yeah, right off the bat, he separates mathematics.

Math is absolutely crucial for physics, no doubt, but it's not a natural science.

Because it's not tested by experiment.

Exactly.

Math is tested by logic, by proof.

Physics has to face the judgment of observation, of experiment.

That's the dividing line.

Okay, that makes sense.

Methodology is key.

But what about things that aren't science at all, like art or, you know, feelings?

Well, that's another important point he makes.

Just because something like love or appreciating beauty isn't testable by experiment doesn't mean it's wrong or bad.

It just means it's, well, it's non -science.

It lives in a different category.

Got it.

A useful clarification.

Okay, so let's start unpacking the sciences themselves.

Maybe chemistry first.

That seems like the most direct connection.

Historically, chemistry really drove home the idea of atoms, right?

Especially early inorganic chemistry.

That's right.

You had people like Mendeley finding these incredible patterns, the periodic table, but they were finding empirical rules.

What physics, specifically quantum mechanics, did later was explain why those rules exist.

So Feynman argues that, in principle, all of theoretical chemistry is contained within physics.

Ah, but that, in principle, is doing a lot of work there.

If physics explains it all, why do we still need chemists?

It's his great analogy.

Knowing the rules of chess doesn't make you a grandmaster.

We know the fundamental quantum laws governing atoms and electrons, but predicting the outcome, when you have billions of them interacting in a complex reaction, that's incredibly hard.

The complexity is staggering.

Okay, which leads naturally to statistical mechanics, I suppose, dealing with those huge numbers.

Precisely.

That field really grew up at the boundary of physics and chemistry.

It's the mathematical toolkit for handling systems with vast numbers of particles moving randomly, you know, the jiggling.

It lets us talk about average behaviors, which gives us concepts like heat and temperature thermodynamics.

Right.

You can't track every atom, so you look at the statistics.

Exactly.

And then chemistry gets even more complex when it moves toward living things, organic chemistry.

There used to be this idea that substances from life were somehow special.

Yeah, the idea of a vital force.

But we now understand that organic molecules are just incredibly complex arrangements of the same atoms found in inorganic stuff.

Carbon, hydrogen, oxygen, just put together in much more intricate ways.

There's no fundamental difference, just complexity.

And that takes us right to the doorstep of biology.

And it's fascinating that early link you mentioned, biology, actually helping physics with the conservation of energy through Mayer's work on animals.

A really neat historical feedback loop.

But if we look inside the body now with our modern understanding, we see these incredible physical systems.

Take nerves, for example.

Okay, nerves.

Biologists found they're like tiny tubes with complex walls.

Exactly.

And those walls are crucial.

They act like the plates of a capacitor.

What's the cell doing?

The cell is actively pumping ions across that membrane.

It uses energy to push positive ions out and keep negative ions mostly inside.

That creates an electrical potential difference.

Like charging up the capacitor.

Right.

And the nerve impulse, it's essentially a wave of breakdown.

The membrane suddenly becomes permeable at one spot.

The ions rush across, discharging that little section.

And that triggers the next section.

Feynman's vertical dominoes analogy.

Perfect analogy.

One falls, triggers the next, and the wave travels down the nerve fiber.

But the dominoes need resetting.

And that's the slower part.

The cell has to pump those ions back out again using energy to get the nerve ready to fire again.

Okay, so that's the electrical signal.

What happens when it reaches, say, a muscle?

Ah, then it switches to a chemical signal.

At the nerve ending, these tiny packets of a chemical, acetylcholine, are released.

And those affect the muscle fiber.

We know muscles have proteins like myosin and actomyosin.

Right.

The acetylcholine triggers something in the muscle fiber involving those proteins.

We know the chemicals.

We know the fiber contracts.

But the exact physical mechanism, the specific molecular machinery that converts that chemical interaction into a physical shortening of the muscle, that's still a bit of a black box.

We don't know the precise details of how the dimensions change.

So even there, at the muscle level, there are physical unknowns.

To get deeper, we need to go inside the cell to the biochemistry.

Yes, into the real engine room.

And that's where you encounter these incredibly complex chemical pathways, like the Krebs cycle.

Which Feynman shows as a figure, just this complex chart of molecules changing.

Yeah, rather than getting lost in the specific names on the chart, think about the process.

It's like a factory production line, taking molecules in, transforming them through many steps, and generating useful energy barriers.

But the really key insight here, underpinning all these biological reactions, is something called the activation energy barrier.

The energy hill you have to get over to start a chemical reaction.

Exactly.

Most chemical reactions left to themselves wouldn't happen easily at body temperature.

They need a significant energy kick to get started.

Think about striking a match.

But life does these reactions constantly, without getting hot.

How?

Enzymes.

That's the secret.

Enzymes are large protein molecules, and they act like highly specific machines or jigs.

Okay, so what do they do?

They grab onto the reactant molecules, holding them in exactly the right position relative to each other.

This specific alignment allows the reaction to happen via a different pathway.

One that completely bypasses that high energy hill.

It's like finding a tunnel through the mountain instead of climbing over it.

And crucially, the enzyme itself isn't used up in the reaction.

It lets go and is ready for the next set of molecules.

Like a catalyst, but a very sophisticated biological one.

Precisely.

A biological catalyst.

And some of these biochemical cycles are about energy itself, right?

Like the GDP to GDP conversion he mentions.

Right.

That's one example of the cell's energy currency, much like the more famous ATP -ADP system.

GDP -gronassine triphosphate holds significantly more chemical energy in its bonds than GDP.

When specific enzymes facilitate it, the energy released by converting GDP back to GDP can be used to power other cellular processes,

such as muscle contraction.

He notes that you need GDP, along with the right enzymes, for muscle fibers to actually contract in water.

That energy release drives the mechanical work.

It's amazing how interlinked it is, but figuring out these incredibly complex cycles must be a nightmare.

How did they even track what was happening?

Ah, well that's where physics provides essential tools.

Experimental techniques are crucial.

The different versions of carbon.

Exactly.

Carbon usually has an atomic weight of 12, but there's a stable isotope, carbon -13, and a radioactive one, carbon -14.

Chemically, they behave almost identically because they have the same electron structure, but because they have different masses or are radioactive.

You can track them.

So you feed a cell molecule with, say, carbon -14, and then you can follow where those specific atoms end up in the complex reaction chains, like putting a tracer on them.

Precisely.

You can trace the path of the marked atoms through the Krebs cycle or any other biochemical process.

It was absolutely fundamental to mapping out this intricate chemistry.

Okay, let's talk about the things making these enzymes, the proteins themselves, and the blueprint.

DNA.

Proteins first.

He says they're chains of amino acids.

20 different kinds.

Yes, 20 standard amino acids, and they link up in And different amino acids have different chemical properties.

Some have sulfur atoms that can link up, creating loops or cross -links in the chain.

Some are acidic, some basic.

One called proline actually puts a definite kink in the chain.

So the sequence determines how this long chain folds up into a specific complex 3D shape.

Exactly.

And achieving that shape is vital for its function, like the enzyme holding reactant molecules just right.

He mentions solving the hemoglobin is this monumental achievement.

Finding where every single atom is in 3D space.

A huge triumph of physics -based techniques like x -ray crystallography.

Thousands and thousands of atoms precisely located.

But then comes the kicker.

Yeah.

The problem is, even knowing the exact structure, we often still don't fully understand why that particular arrangement of atoms performs its specific function.

We see the machine, but we don't always understand how it works.

We know the what, but not the how or why.

In many cases, yes.

Which brings us to the blueprint itself.

DNA.

Deoxyribonucleic acid.

That's the molecule, primarily in the cell nucleus, that carries the instructions for making all those proteins, including the enzymes.

And these instructions get passed down, right?

Through reproduction.

Yes.

DNA has two main jobs.

Store the information and replicate itself accurately so the information can be passed on.

The replication mechanism he described sounds

almost simple.

Conceptually.

It's incredibly elegant.

The DNA molecule is famously a double helix, two long chains twisted around each other.

Think of it like a twisted ladder.

The sides of the ladder are sugar and phosphate groups.

The rungs are pairs of four chemical bases.

Let's just call them A, B, C, and D for simplicity.

And the key is how they pair up.

Absolutely key.

A always pairs with B, and C always pairs with D across the ladder rung.

Or, more accurately, adenine with the man, glonium with cytosine, but A, B, C, D gets the idea across.

So the sequence along one side dictates the sequence on the other.

Exactly.

So for replication, the ladder unzips down the middle.

Each single strand then acts as a template.

Because A only pairs with B, and C with D, free -floating As, Bs, Cs, and Ds in the cell nucleus line up along each template strand, creating two identical new double helices.

It's beautiful self -assembly.

Okay, that covers replication.

But what about the other job?

Using the DNA sequence to build a protein.

That's where we hit a wall, right?

That's what Feynman identifies as the central unsolved problem of biology at the time he was writing.

We know that a copy of a segment of DNA called RNA carries the message out of the nucleus to the ribosome, the cell's protein factories.

So the ribosome reads the RNA message.

Yes, it reads the sequence of A, B, C, D, well, U replaces B in RNA, but same idea, on the RNA strand.

But how does that linear sequence of four letters translate into the specific sequence of 20 different amino acids needed to build a particular protein?

The genetic code.

Exactly.

What is the code?

How many RNA letters specify one amino acid?

What's the dictionary that translates the nucleic acid language into the protein language?

That was the great mystery.

Of course, we know much more about this now, but at the time Feynman was speaking, it was the frontier.

Right.

But even with that huge unknown,

the fundamental belief driving the research was clear.

Absolutely unwavering.

The core assumption is that all things are made of atoms and everything that living things do, thinking, moving, replicating everything can ultimately be understood in terms of the physics of those atoms interacting, jiggling, and wiggling.

Okay.

Let's zoom out dramatically now from the cell to the cosmos astronomy.

Ah, astronomy.

In a way, physics began there with understanding the elegant clockwork of the solar system.

But Feynman highlights a different, maybe even more profound discovery from astronomy.

Yes.

The realization, thanks to the spectroscope, that stars are made of the exact same stuff as the earth, the same atoms.

How did the spectroscope show that?

By analyzing the light from stars.

Each type of atom, when heated, emits or absorbs light only at very specific frequencies, like a unique fingerprint or musical chord.

The spectroscope breaks starlight down into its frequencies, and we saw the fingerprints of hydrogen, helium, iron,

all the elements we know here.

It was mind -blowing.

The stuff up there is the same as the stuff down here.

He even notes that helium and technetium were actually found in the spectra of stars before they were definitively isolated on earth.

Amazing.

And physics helps here because we can take those known atoms and apply things like statistical mechanics.

Exactly.

We know the atoms, we can estimate the temperatures and pressures in stars, very hot, but often quite low density overall, and we can calculate how those atoms should behave.

This led directly to understanding where stars get their energy.

Nuclear fusion.

Nuclear burning, yes.

Primarily fusing hydrogen into helium, releasing enormous energy.

And this process, happening over billions of years and generations of stars, is what created all the heavier elements.

The carbon, oxygen, iron, everything that makes up planets like Earth and us was cooked inside stars and then thrown out into space in stellar explosions like NOVAE and SUPERNOVAE.

We're literally stardust.

We are.

And the evidence is even in the details, like the relative proportions of isotopes, say carbon -12 versus carbon -13.

Those ratios are like fossil clues telling us about the conditions inside the stellar furnaces where they were made.

So physics gives us a pretty good handle on stars, which are incredibly distant and extreme.

But paradoxically, when we look closer to home at Earth itself, geology and meteorology, things get murkier.

It's a fascinating contrast, isn't it?

For meteorology, weather prediction, the instruments we use are all based on physics, of course, thermometers, barometers.

But the theory struggles badly.

Why?

Because the atmosphere is a fluid in motion and it's inherently unstable and turbulent.

Like water flowing over a rough surface.

Exactly.

Feynman uses the analogy of water flowing smoothly over a dam, then suddenly breaking up into chaotic drops and eddies.

We know the fundamental laws governing air and water flow.

But predicting the behavior of these turbulent, unstable systems is incredibly difficult mathematically.

Small changes can lead to huge, unpredictable differences later.

The butterfly effect, basically.

In essence, yes.

And geology faces similar, though perhaps deeper, challenges regarding Earth's interior.

We understand surface processes like erosion fairly well.

Yes, that's relatively straightforward physics and chemistry.

But the really big geological questions, what causes mountains to form?

What drives volcanoes and earthquakes?

Why do continents drift?

Those are much harder.

There's the theory of convection currents in the mantle.

Right.

The idea of slow, circulating currents of hot rock deep inside the Earth, pushing and pulling the crust around, it makes sense conceptually.

But the problem for physicists is trying to figure out the actual properties of rock under the conditions deep inside the Earth, millions of times atmospheric pressure,

incredibly high temperatures.

How dense is it?

How quickly does it deform or give?

How does it flow?

We can't exactly replicate those conditions easily in a lab.

Not easily, no.

So modeling those deep Earth currents accurately remains a huge challenge.

Our understanding of the Earth's engine is still quite incomplete.

Okay, last stop on this tour.

Psychology.

How does Feynman view its connection to physics?

He seems skeptical of some approaches.

He is quite direct, particularly about psychoanalysis.

He categorizes it as non -science, not necessarily because a subject matter is invalid, but because historically, its claims weren't rigorously tested against experimental evidence in a verifiable way.

But what about the parts of psychology that do connect to biology and physiology, like how the brain works?

Ah, there he sees it as a science, albeit a very young and incredibly difficult one.

We're making slow progress understanding things like vision, how the eye processes light, how the signals travel to the brain.

But the core mystery remains memory, doesn't it?

Absolutely.

That's the giant elephant in the room problem.

What physically changes in our brain cells are the connections between them when we learn something.

When a memory is formed, we simply don't know the mechanism.

We don't understand the physical basis of learning and memory storage.

Feynman says, forget humans, we can't even really figure out how a dog works at that fundamental level yet.

It's a humbling perspective.

It seems like many of these complex problems across different sciences bump up against a similar kind of difficulty.

They often do.

And Feynman points out one specific, very old physical problem that underlies the difficulties in several of these fields.

It's a problem physicists themselves haven't solved mathematically.

Which is?

The analysis of circulating or turbulent fluids.

That came up with weather and geology.

And astrophysics modeling exploding stars or accretion disks.

Even basic engineering calculating the drag on an airplane, or just how water flows through a pipe accurately under all conditions.

Whenever you have a fluid gas or liquid flowing in a complex, swirling, turbulent way, our mathematical tools struggle to provide precise, predictive answers.

We know the basic equations, Navier -Stokes, but solving them for turbulence is monstrously hard.

So this one unsolved problem in fundamental physics acts as a roadblock for progress in meteorology, geology, astrophysics engineering.

Pretty much anywhere complex fluid flow is important.

It's been a major challenge for over a century.

If we could crack turbulence, it would unlock understanding across an incredible range of scientific fields.

Wow.

Okay, that really brings it all together.

Feynman's final image, the glass of wine, seems like a perfect summary.

It is.

He looks at the glass and sees everything.

The physics and the evaporating alcohol, the reflections on the glass.

The geology and the silicon atoms of the glass itself forged from ancient rocks.

The chemistry and the complex organic molecules, the fermentation products, the enzymes.

And even history and biology, the evolution of the grape, the processes that made the elements in the first place within stars.

It's all there.

It's a powerful reminder that these divisions we make, physics, chemistry, biology,

they're convenient for us, for learning and research, but nature itself doesn't recognize them.

Not at all.

It's all one interconnected system, ultimately governed by the same fundamental physical laws.

So, thinking about this interconnectedness, what's the big takeaway for you listening right now?

I think it's that the real frontier isn't just discovering new fundamental laws, maybe.

It's understanding the incredible, almost baffling complexity that arises from the laws we already know, that problem of turbulence.

It's not about missing laws.

It's about the sheer difficulty of calculating the consequences of the laws we have.

Solving that century -old puzzle could arguably trigger more progress across science than discovering a new particle.

So, knowing where these deep interconnected challenges lie,

what part of this vast complex puzzle are you inspired to think about tackling next?