The Doppler Effect, which relates changes in wave frequency to the distance between an observer and the source of the waves, was first utilized in astronomy by none other than Edwin Hubble. Observing the spectra of nearby galaxies, he noticed a trend in redshifts. The obvious conclusion was that these galaxies were moving away from us. The larger picture seemed to indicate the expansion of the universe at an accelerating rate. That is how we currently view the universe. But what other models preceded this one?
Tracing astronomy back to its roots, the earliest model of the universe, called the Brahmanda ‘’Cosmic Egg’’ Universe, possibly evolved around 3000 B.C. in the Hindu Rigveda, a compilation of Vedic Sanskrit hymns. This model pivots around a single speck called a Bindu, whereby all of interplanetary space continuously oscillates between states of expansion and contraction.
The next major model was the Aristotelian universe, theorized by Aristotle around 300 B.C., a ‘’steady-state’’ cosmos. This model was geocentric (i.e. considered the Earth to be the center of the universe), with planets and stars encompassing the center. Through Aristotle’s gaze, the universe was static and finite. It did not have a beginning nor an end and remained constant in size. Aristotle’s universe added a fifth element, ether, to the four classical elements: fire, air, Earth, and water. Ether fills the abyss that encircling the universe beyond Earth’s peripheries.
Around 200 A.D., Ptolemy disclosed yet another geocentric model of the universe. This Ptolemaic model was composed of a stationary Earth around which planets and other celestial objects moved in epicycles. This was dubbed the ‘’most successful cosmological model’’, as it offered the basis to the first lunar model (curated by Ibn Al-Shatir). It was also the relatively most complex model of its time and empowered astronomers to accurately project the whereabouts of nearby planets.
The most popular ancient model of the universe is that of Copernicus. The Copernican universe was, in contrast, heliocentric (i.e. placing the Sun in the center of the universe). Copernicus falsely suggested that stars remain in fixed positions. Nevertheless, his theory revolutionized astronomy as it did not treat the Earth as a static central point but as a planet in motion, following physical laws that other planets follow as well.
Newton’s ‘’Principia Mathematica’’ described yet another ‘’steady-state’’, gravitationally-bound universe. Matter was uniformly distributed throughout the cosmos. Despite its gravitational balance, this Newtonian universe was fundamentally unstable and volatile. Einstein’s theory of relativity depicted a universe similar to that of Newton’s. The only improvement was the addition of a ‘’cosmological constant’’, which acts as a counterpart to gravity, as Einstein saw that the existence of gravity alone would lead to the ultimate contraction of the universe.
In line with the universe’s accelerating expansion, our grasp of the cosmos continues to grow throughout the eons. That can be attributed to developments and improvements in scientific discoveries. It is both discerning and critical to keep in mind that our current model of the universe may be rectified by a future model with better supporting evidence. In the meantime, our collective understanding of the universe remains as the spacetime continuum accelerating in expansion.