Our Universe, from the hot Big Bang until the present day, must still be explicable. Image credit: NASA / CXC / M.Weiss.

How many fundamental constants does it take to define our Universe?

And even with them all in place, what do we still not know?

Ethan Siegel
7 min readJan 6, 2017

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“The joy of life consists in the exercise of one’s energies, continual growth, constant change, the enjoyment of every new experience. To stop means simply to die. The eternal mistake of mankind is to set up an attainable ideal.” -Aleister Crowley

When we think about our Universe at a fundamental level, we think about all the particles in it and all the forces and interactions that occur between them. If you can describe those forces, interactions and particle properties, you have everything you need to reproduce our Universe, or at least a Universe virtually indistinguishable from our own, in its entirety. Because if you know the laws of physics — gravitation, quantum mechanics, electromagnetism, the nuclear forces, etc. — all you need are the relationships that tell you “by how much,” and so long as you start with the same initial conditions, you’ll wind up with a Universe with the same structures from atoms to galaxy clusters, the same processes from electron transitions to stellar explosions, the same periodic table of elements, and the same chemical combinations from hydrogen gas to proteins and hydrocarbon chains, among a great number of other similarities.

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Ethan Siegel
Starts With A Bang!

The Universe is: Expanding, cooling, and dark. It starts with a bang! #Cosmology Science writer, astrophysicist, science communicator & NASA columnist.