What Is Life? The Physicist Who Predicted DNA

In 1943, a physicist famous for his work on quantum mechanics gave a series of lectures asking a deceptively simple question: What is life? The resulting book, What Is Life?, predicted the molecular basis of heredity before we discovered DNA's structure. It's one of the most influential science books of the 20th century.

The Central Mystery

Schrödinger wasn’t a biologist. He was the physicist who gave us the wave equation, quantum superposition, and (infamously) that poor cat.Yes, Schrödinger’s cat — the thought experiment about quantum superposition. Same Schrödinger.

But during World War II, exiled in Dublin, he turned his attention to biology’s biggest puzzle: How does life create order from disorder?

Thermodynamics tells us entropy always increases — systems become more disordered over time. Yet living things maintain complex organization, grow, reproduce, and pass on intricate information across generations.

How?

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The Physics of Heredity

"How can the events in space and time which take place within the spatial boundary of a living organism be accounted for by physics and chemistry?" — Erwin Schrödinger

Schrödinger’s key insight: Heredity requires an “aperiodic crystal.”

Regular crystals (like salt or diamond) have repeating patterns — the same structure over and over. They can’t store much information.

But an aperiodic crystal — a crystal with an irregular structure — could encode complex information in its sequence. Different arrangements = different instructions.

He predicted, in 1943, that genetic information must be stored in a molecular structure with:

• Stability (to preserve information)
• Specificity (to encode instructions)
• Complexity (to specify an entire organism)

Nine years later, Watson and Crick discovered DNA — a double helix with exactly these properties. An aperiodic crystal made of nucleotides.

Order from Order

Schrödinger distinguished two ways to create order:

Order from disorder: Statistical mechanics. Average over millions of random particles to get predictable behavior. This is how thermodynamics works.

Order from order: Copy an existing pattern. This is how life works.DNA replication is literally copying information from one strand to another — order from order.

Life doesn’t fight entropy by organizing random chaos. It propagates existing order by copying molecular instructions.

Genes are molecular texts that copy themselves with astonishing fidelity across billions of years.

Negative Entropy

How do living things maintain order in a universe trending toward disorder?

Life doesn’t violate thermodynamics — it locally decreases entropy by increasing entropy elsewhere. We maintain our internal order by exporting disorder to our environment.

Eat breakfast → metabolize → maintain body temperature → radiate heat. You’ve increased the universe’s total entropy while maintaining your local organization.

The Impact

What Is Life? directly inspired:

• Francis Crick (co-discoverer of DNA structure)
• James Watson (co-discoverer of DNA structure)
• Maurice Wilkins (X-ray crystallography of DNA)
• Sydney Brenner (molecular biology pioneer)

All credited Schrödinger’s book as pivotal to their thinking. A physicist’s speculations helped birth molecular biology.

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What Makes This Book Special

It’s short: 90 pages. Schrödinger is concise and clear. No fluff.

It’s interdisciplinary: Physics meets biology decades before that became common. He shows how physical principles constrain biological possibilities.

It’s prescient: Writing before DNA was understood, he predicted its essential features from theoretical principles.

It’s philosophical: The final chapter asks whether consciousness can be explained physically, touching on free will and the self.

The Hard Parts

Some sections assume comfort with:

• Statistical mechanics
• Quantum mechanics basics
• Chemical bonding
• Thermodynamics

Schrödinger doesn’t hold your hand. He wrote for educated readers willing to think hard.

But he’s not showing off — he explains what’s needed, just tersely.

The Controversial Ending

The book’s final chapter, “Is Life Based on the Laws of Physics?”, ventures into consciousness and free will.

Schrödinger argues that:

• Consciousness might be singular (we’re all experiencing one consciousness)
• Free will is compatible with determinism (in a Vedantic sense)
• The barrier between subject and object is illusory

This part is… speculative. Some find it profound. Others find it confused Eastern mysticism from a physicist out of his depth.Schrödinger was deeply influenced by Vedanta philosophy and tried to reconcile it with quantum mechanics.

I lean toward “interesting but not convincing.” But the biology sections alone make the book essential.

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What Stuck With Me

Life is information: Long before Shannon’s information theory, Schrödinger saw that genes are fundamentally about encoding and transmitting information.

Physical laws enable and constrain biology: You can’t understand life without understanding the physics it’s built on. Mutations, inheritance, metabolism — all have physical bases.

Interdisciplinary thinking works: Schrödinger wasn’t an expert in biology. But his physicist’s perspective let him see patterns biologists missed.

Prediction from first principles: By asking “what must heredity be like?” he predicted molecular genetics before the evidence arrived.

Who Should Read This

Essential for:

• Anyone interested in the history of molecular biology
• People curious about life’s physical basis
• Readers who love interdisciplinary thinking
• Science students wanting to see great scientific reasoning

Skip it if you want:

• Current biology (it’s from 1943 — much is outdated)
• Easy reading (it’s dense and assumes background)
• Definitive answers (Schrödinger raises more questions than he answers)

Still Relevant?

Yes and no.

Outdated: We now know DNA’s structure, how genes work, molecular mechanisms in detail. Schrödinger was working with incomplete information.

Timeless: The questions he asked — How does physics permit life? What is special about biological organization? How is information stored and transmitted? — remain central.

And his approach — using physical principles to constrain biological possibilities — is exactly how modern systems biology works.

My Takeaway

We are, fundamentally, physical systems. Not in a reductionist “nothing but atoms” sense, but in the recognition that life must obey physical laws even as it does remarkable things within those constraints.

DNA is a technology — a molecular technology for storing and copying information, evolved over billions of years.

And the boundary between physics, chemistry, and biology? It’s useful for departments and textbooks, but nature doesn’t care. Life is physics in action.

What Is Life? is a masterclass in how to think across boundaries. In 90 pages, it changed the course of 20th-century science.

That’s not bad for a physicist asking a simple question.

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Also recommended: “The Eighth Day of Creation” by Horace Freeland Judson for the full story of molecular biology’s birth.