# Physical Constants in Python

# Physical Constants in Python

### Python and SciPy library are pretty powerful scientific tools. In this post, we put this to the test using a famous problem from the world of physics.

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You can find a large collection of physical constants in `scipy.constants`

. The most frequently used constants are available directly, and hundreds more are in a dictionary `physical_constants`

.

The fine structure constant α is defined as a function of other physical constants:

The following code shows that the fine structure constant and the other constants that go into it are available in `scipy.constants`

.

```
import scipy.constants as sc
a = sc.elementary_charge**2
b = 4 * sc.pi * sc.epsilon_0 * sc.hbar * sc.c
assert( abs(a/b - sc.fine_structure) < 1e-13 )
```

## Eddington's Constant

In the 1930s, Arthur Eddington believed that the number of photons in the observable universe was *exactly* the Eddington number:

Since at the time the fine structure constant was thought to be 1/136, this made the number of photons a nice even 136 × 2 ^{256}. Later he revised his number when it looked like the fine structure constant was 1/137. According to the Python code above, the current estimate is more like 1/137.036.

Eddington was a very accomplished scientist, though he had some ideas that seem odd today. His number is a not a bad estimate, though nobody believes it could be exact.

## Related Posts

The constants in `scipy.constants`

have come up in a couple previous blog posts.

The post on Koide's coincidence shows how to use the `physical_constants`

dictionary, which includes not just the physical constant values but also their units and uncertainty.

The post on Benford's law shows that the leading digits of the constants in `scipy.constants`

follow the logarithmic distribution observed by Frank Benford (and earlier by Simon Newcomb).

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