Great question — and it looks mysterious if you only see the final numbers.
But the key is: Schrödinger did not calculate the value W/kT = 30–60.
He assumed it based on known activation energies of chemical bond rearrangements available in 1930s physical chemistry.
Let’s break it down clearly.
= activation energy needed to break or change a chemical bond (in mutation terms: a bond change in a gene).
= thermal energy per degree of freedom at body temperature (~300 K).
So is the energy barrier measured in units of thermal fluctuations.
If , thermal fluctuations almost never trigger the event spontaneously.
In the 1930s–40s, chemists like Eyring, Wigner, and Polanyi had measured typical bond activation energies:
At physiological temperature:
So:
Rounded to account for biological complexity:
So the ratio comes directly from typical chemical bond strengths.
No exotic derivation — just plugging in known physical chemistry constants.
The Polanyi–Wigner equation for spontaneous activation events is:
where is a molecular vibration frequency ~ per second.
If:
Then:
which are extremely small numbers.
Plug them in:
This yields characteristic event times of thousands of years, which is how Schrödinger arrived at:
He used this to argue that mutations are rare and discrete, leading him to propose the idea of a stable “aperiodic crystal” — what we now know as DNA.
He did not derive it mathematically.
He looked up typical bond activation energies of organic molecules and divided by .
| Quantity | Value |
|---|---|
| Activation energy | 0.6–1.2 eV |
| Thermal energy | ~0.026 eV |
| Ratio | ~25–50 (rounded to 30–60) |
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