Electrons, Ants and Nebulas

The tale of how our intuitions are not scale invariant

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Lorentz Factor

“There is little evidence that Newtonian gravity is accurate on scales much larger than 0.1pc” -Scott Tremaine

Despite what Star Wars would have you think, pc, or parsec, is a unit of length. 1 parsec is equal to approximately 3.26 light years, or 30 trillion kilometers. Once again, as we move far out from the human bubble, our intuition begins to break down. One of our formulations of gravity — Newton’s inverse square relation, does not hold at far out distances. The postulated existence of Dark Matter is a direct consequence of this. Suppose we take a typical galactic cluster, and calculate the masses of all the visible objects. From here, we can derive the gravitational forces involved. Surprisingly, given the velocity of these galaxies, the force is not enough to bind them and the cluster should scatter. Yet, the clusters remain tightly bound, and so there must be something else contributing to the gravitational attraction. Similar failures of classical gravity occur when observing distant galaxies, clusters and nebulas. At the aforementioned cosmic scales, our notions of gravity breakdown, and new theoretical entities are required to make this anomalous behaviour intelligible. Another alternative: rewrite the equations that govern acceleration and gravity at these galactic distances, and decide upon a critical point when these new laws become valid.

“Say not, ‘I have found the truth,’ but rather, ‘I have found a truth’. Say not, ‘I have found the path of the soul.’ Say rather, ‘I have met the soul walking upon my path.’
For the soul walks upon all paths.
The soul walks not upon a line, neither does it grow like a reed.
The soul unfolds itself, like a lotus of countless petals.”

-Khalil Gibran

Written by

Insatiably curious student of life | Writing about Physics, Philosophy, & Dharma | Newsletter @ apsis.substack.com | Personal Site @ sashamanu.com

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