GoKawiilFive hundred years ago, Nicolaus Copernicus proposed that the Earth might be one of several planets orbiting the Sun, rather than the centre of the universe. He compared the geocentric model to a monstrous form assembled from parts of different bodies, like the Creature Mary Shelley brought to life three centuries later in Frankenstein — each part appearing human on its own, but as a whole a grotesque patchwork.
The geocentric model was built to directly match the sky: where a planet paused against the background stars and looped into retrograde, a dial was added so the planet would pause in its orbit around the Earth and loop backwards a while before resuming its normal course. In contrast, Copernicus recognised that the outer planets — Mars, Jupiter, and Saturn were known at the time — might enter retrograde loops due to parallax, their apparent positions shifting relative to the background stars as our orbit brings us near and then we pass them on our way around the Sun.
Copernicus had no idea of the physics that Isaac Newton or Albert Einstein would eventually use to explain planetary motion. Nor did he imagine this motion resulted from the same phenomenon that causes apples to fall from trees, or paths of light to bend around the Sun. His model ended up with as many knobs and dials as the geocentric system due to his use of circles rather than ellipses to describe orbits.
Even so, Copernicus recognised that a Sun-centred theory afforded the possibility that it might eventually explain why phenomena like retrograde motion should appear as they do to us, despite the planets’ motion being continuously in one direction only. And in doing so, he paved the way for others like Newton and Einstein, who later fleshed out both the underlying concepts and formal mathematical descriptions of a solar system in which planetary motion is expected to appear with all the complexity we observe.
In hindsight, the discovery Copernicus’s proposal prompted was that broken symmetries — our off-centre perspective from a planet orbiting the Sun, and the non-uniform motions of all planets including ours — would complicate appearances within an ontological framework that is nonetheless simpler.
In a similar sense, it may be argued that the standard cosmological model today — which gives an accurate description of phenomena but is nevertheless an amalgam of ad hoc patches, each inserted to unnaturally force the evolution of a universe that is otherwise expected to be different from the way it appears — bears a closer resemblance to Frankenstein’s monster than it does the simple explanations of planetary motion given by Newton and Einstein. For despite all the dials and knobs that have been added to ensure the standard model does directly resemble appearances, after a century of development it still affords no explanation of why our universe should be expected to expand, as it appears to do.
Why should our universe expand?
In the Copernican tradition, we ought to ask why our universe should expand. The standard cosmological model affords no such explanation. It is based on a principle, famously promoted by Einstein together with his colleague Willem de Sitter, that characterises the universe as expanding in spite of a tendency to decelerate because it is filled with everything we see. This is important: according to the basic Einstein-de Sitter framework for describing cosmic expansion, all the galaxies and light we see across the universe are thought to work against the universe’s expansion, slowing it down; and anything driving expansion is an ad hoc dial we’ve added so that base model fits appearances better than it naturally should.
In fact, this tendency for light and matter to slow cosmic expansion mathematically blows up to an infinite amount at the Big Bang. Therefore, the model’s only “explanation” for why our universe even could be expanding today is that it began with such a tremendous rate that momentum carried it against its natural tendency towards the opposite. For this reason, a century ago British astronomer Arthur Stanley Eddington complained of the Einstein-de Sitter model that would dominate twentieth century cosmology, “One cannot deny the possibility, but it is difficult to see what mental satisfaction such a theory is supposed to afford.”
Much like its Ptolemaic predecessor, this model has since been augmented with various features allowing it to fit the data with impressive accuracy. First, there is an inflationary epoch, thought to have occurred a moment after the Big Bang, which would drive a fleeting period of exponential expansion and erase several tensions the Einstein-de Sitter model otherwise leaves unresolved — though leaving the initial expansion problem untouched. Then for a long while the universe is thought to have decelerated, its slowing rate driven primarily by radiation in the early universe followed later by matter, in good alignment with Einstein-de Sitter. Finally, after several billion years a component we’ve come to call dark energy, which does tend to drive expansion, is thought to have become significant enough that the expansion rate eventually began to accelerate.
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