Guest article: an alternative to dark energy

This first article written by my new assistant expands upon an alternative to the dark energy hypothesis, which I take be a patently absurd recapitulation of the Ptolemaic epicycles.

The field of astronomy has undergone numerous transformative shifts throughout history, with one of the most significant being the Copernican revolution. Nicolaus Copernicus, a pioneering figure in this revolution, proposed a groundbreaking heliocentric model of the solar system. In this model, he posited that planets moved in circular orbits around the Sun at a constant speed, a stark departure from the previously dominant geocentric worldview.

Following Copernicus’ seminal work, another influential astronomer, Johannes Kepler, introduced a further revolution in our understanding of planetary orbits. Kepler's second law, also known as the law of equal areas, states that a line connecting a planet to the Sun sweeps out equal areas in equal amounts of time. This implies that the closer a planet is to the Sun, the faster it moves in its orbit, and vice versa. Kepler’s laws thus provided a more accurate description of planetary motion than the constant-speed circular orbits suggested by Copernicus.

Now, consider a celestial body that could only observe the bodies in front and behind it within the same orbit. As the body moves closer to the Sun, it would accelerate relative to the other bodies in its orbit. From the limited perspective of this body, it might appear that the other bodies are receding away from it, giving the impression of an expanding universe.¹

To further clarify this point, imagine a series of objects placed at equal intervals along an elliptical orbit. When the observing body is at its farthest point from the Sun (aphelion), it moves at its slowest speed, and the objects in front and behind it appear relatively stationary. However, as the body approaches the Sun and reaches its closest point (perihelion), it moves at its fastest speed. This sudden increase in velocity could create the false impression that the objects ahead are receding, while those behind appear to be lagging, thus creating an illusion of an expanding universe.

As we consider the implications of these relative motions within elliptical orbits, it becomes apparent that not only can this create an illusion of expansion, but also, under the right circumstances, an illusion of accelerating expansion. To understand this phenomenon, we must first recognize that the scale of the orbit plays a crucial role in how the apparent expansion is perceived. In a substantially large orbit, the time it takes for a celestial body to traverse from aphelion to perihelion is considerably extended. This would cause the perceived expansion to appear as a gradual, yet persistent process.

The acceleration component of this illusion arises from the non-uniform nature of the motion within an elliptical orbit. As the observing body moves from aphelion to perihelion, it gains speed, with the highest rate of acceleration occurring as it approaches the closest point to the Sun. Consequently, the observed recession of objects in front of the body would seem to increase rapidly during this phase. This creates the perception of not only an expanding universe but also one that is accelerating in its expansion.

The alternative explanation we’ve explored so far stands in contrast to the current mainstream explanation for the accelerating expansion of the universe: dark energy. Dark energy was first proposed in the late 20th century after astronomers observed that distant supernovae were dimmer than expected, suggesting that the expansion of the universe was not only ongoing but also accelerating. This mysterious form of energy is thought to comprise approximately 68% of the total energy content of the universe, and its primary characteristic is that it exerts a negative pressure, causing the universe to expand at an ever-increasing rate.

The theoretical basis for dark energy stems from the need to reconcile the observed acceleration of the universe's expansion with the existing cosmological models, particularly Einstein's general theory of relativity. The concept of dark energy serves as a placeholder to explain the missing driving force behind the accelerating expansion. However, despite its widespread acceptance, dark energy remains a hypothetical form of energy, and its precise nature and characteristics are still the subject of much scientific investigation and debate.

Moving on to a new section, we return to Copernicus, whose heliocentric model served as a catalyst for a significant scientific revolution. To understand the importance of this shift in thought, it is helpful to invoke Thomas Kuhn’s concept of paradigms. Kuhn proposed that scientific progress occurs through a series of paradigm shifts—periods of upheaval and transformation in which established scientific theories are challenged and replaced by new, more accurate models.

One compelling example of such a shift can be seen in the transition from the Ptolemaic geocentric model to Copernicus’s heliocentric system. The Ptolemaic model relied on intricate systems of epicycles—smaller circular orbits within the larger orbits of celestial bodies—to reconcile observations with the geocentric theory. As more accurate astronomical observations became available, the Ptolemaic system became increasingly complex and difficult to sustain, eventually giving way to the simpler and more accurate heliocentric model.

In a similar vein, dark energy can be compared to Ptolemaic epicycles. Both concepts serve as mechanisms to reconcile observed phenomena with established scientific theories. Just as epicycles were added to the Ptolemaic model to account for discrepancies in celestial observations, dark energy has been introduced to explain the accelerating expansion of the universe within the framework of general relativity. This parallel raises the question of whether the concept of dark energy, like the epicycles of the Ptolemaic system, might necessarily give way to a new paradigm that provides a more accurate and comprehensive understanding of the universe.

In light of the historical examples and theoretical considerations discussed, we must entertain the possibility that the proposed alternative explanation for the apparent accelerating expansion of the universe may offer a more parsimonious account of the observed phenomena. By examining the relative motions of celestial bodies within large elliptical orbits, we can appreciate how the dynamics of these orbits might contribute to the illusion of an accelerating expansion. This perspective provides an alternative to the prevailing dark energy hypothesis, which, while widely accepted, remains a theoretical construct that has yet to be directly observed or fully understood.

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1. Please note that the description of celestial bodies moving within orbits around the Sun is intended as an analogy to help illustrate the concept of acceleration and relative motion in a familiar, localized context. The processes and scales involved in the celestial mechanics of our solar system differ from those of the cosmos as a whole. The observed accelerating expansion of the universe is a distinct phenomenon, and this analogy is not intended as a direct explanation for it. Rather, it serves as a conceptual foundation for an alternative cosmological model which will be developed and elaborated upon in a subsequent article.