The universe is in movement

Our universe is defined by its motion, and one way to describe the history of science is our increasing awareness of the restlessness of the cosmos.

For thousands of years, the brightest scientists of Europe and the Middle East believed that the Earth stood perfectly still and the heavens revolved around it, with a series of nested crystal spheres supporting the celestial bodies. These early astronomers engaged in attempts to explain and predict the motion of these objects – the Sun, the Moon, all known planets, and the stars. These predictions were excellent, and their systems were able to explain the data well into the 16th century.

But this cosmological system of motion, developed by Claudius Ptolemy in the 2nd century, was not perfect. In fact, it was a clumsy mathematical mess based on small circular orbits embedded within larger ones, some with the Earth as their center and others with other points. On his deathbed in 1543, the Polish astronomer Nicolaus Copernicus published On the Orbits of the Heavenly Bodies, a radical reformulation of the old Ptolemaic system, which placed the Sun at the center of the universe – still and motionless – and set the Earth in motion along with all the other planets around it.

Reactions to Copernicus' work were mixed and muted. On the one hand, it was a bold and controversial redesign of the universe. On the other, it was arguably just as messy and complicated as the Ptolemaic system it was meant to replace. And it raised more than a few questions that had no easy answers. First of all, if the Earth was moving, how could we tell?

We know we are moving on the surface of the Earth in a number of ways. We can feel the wind on our face as we walk, or watch a distant target approach. So why don't we feel a strong gust of wind as the Earth orbits the Sun? Or why are we not being hurled into the void of space due to our planet's incredible rotation?

There were no ready answers to all of this. It took another century and the development of Newton's theory of gravity to get the whole picture and make the Earth's movement understandable. Today we know that we do not feel the Earth's movement because we move with it, and since the vacuum of space is just that – a vacuum – there is nothing we can fight against and betray this movement.

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