[Math] reason why $\log \phi \approx (\log 2)^2$

approximationgolden ratiologarithms

With $\phi=\frac{\sqrt5+1}2$ the golden ratio, we have
$$\log_2 \phi = 0.6942\ldots\\
\,\log_e 2 = 0.6931\ldots$$

Equivalently,

$$2^{\log 2} =1.6168\ldots\\
\quad\;\phi = 1.6180\ldots$$

Is it a simple coincidence or is there a deeper reason for this?

To give an idea of the sort of thing I'm looking for, the identity $\frac{1/\sqrt2}2 = \sinh \frac{\log 2}{2}$ is a very good explanation of the observation that $1/\sqrt2 \approx \log 2$. It also allows estimating the error term by expanding the series for $\sinh$.

Edit: Expanding on infinitylord's remark, this equivalent to the observation

$$0.49915\ldots = \sinh\left((\log 2)^2\right)\approx 1/2$$

Best Answer

Take a few well-known constants such as $\gamma,1,\phi,2,e,3,\pi$, a few functions $\log,\exp,\sin,\cos$ and the six basic operations $+,-,\times,\div,a^b,\sqrt[b]a$. Form as many simple expressions as you can by combining them. For example, there are more than $6000$ expressions of the form $f(x)\text{ op }g(y)$ many of which fall in a small range, say $[0.1,10]$. Hence you can expect a few pseudo-coincidences.

Below a plot of the values of $2717$ such expressions with a value in the above range.

enter image description here

This exhaustive search reveals the interesting

$$\frac{e^\gamma}{e^e}\approx\frac{e}{e^\pi}$$ $$0.117529\approx0.117467$$

which is nothing but $$\gamma-e+\pi\approx 1.$$ (Actually $1.00052649003$.)

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