In the realm of logic, the principle of 'reductio ad absurdum' illustrates how faulty arguments can unravel. Yet, our peculiar Universe frequently challenges our intuitive understanding.

Historically, humanity has pursued knowledge through two primary methodologies: the top-down approach, which begins with established principles demanding logical consistency, and the bottom-up method, which involves gathering empirical evidence from the Universe to construct a cohesive model. The former, attributed to Plato, is known as a priori reasoning, where conclusions can be drawn from accurate postulates. In contrast, Aristotle, Plato's successor and opponent, championed a posteriori reasoning, starting from observable facts to build a reality model instead of deriving it from grand theories.

In scientific practice, these two approaches are intertwined. Empirical data from measurements and observations contribute to a broader theoretical framework that elucidates Universal phenomena, while theoretical insights facilitate predictions about unfamiliar scenarios. However, logical reasoning alone cannot replace empirical understanding. Time and again, science has shown that the natural world often contradicts logic, revealing rules that are more intricate than we might intuit without conducting crucial experiments. Here are three instances demonstrating that logic and reasoning can fall short in scientific inquiry.

1.) The Nature of Light. In the early 1800s, physicists debated the essence of light. Newton's corpuscular theory had successfully explained various optical phenomena, including reflection and refraction, for over a century. Light's colors, when separated by a prism, aligned with Newton's predictions. However, some phenomena, such as the double-slit experiment, required a wave-like interpretation.

In 1818, the French Academy of Sciences held a competition to explain light, where Augustin-Jean Fresnel proposed a wave theory based on Huygens' earlier work, which had its limitations. A member of the judging committee, Simeon Poisson, utilized logic to challenge Fresnel's theory, predicting an unexpected outcome.

According to Fresnel's wave theory, light passing around a spherical object should create a bright spot in the shadow due to constructive interference. Poisson deemed this prediction absurd, using it to argue against the wave theory. However, François Arago, the committee head, insisted on testing this "absurd" hypothesis experimentally.

Despite the experiment being conducted before the invention of the laser, Arago successfully demonstrated the predicted bright spot in the shadow, validating Fresnel's theory. This experiment illustrated how empirical evidence could confirm seemingly irrational predictions, showcasing the limitations of purely logical reasoning.

2.) Darwin, Kelvin, and Earth's Age. By the mid-1800s, Charles Darwin was redefining our understanding of life and the age of the Earth. He concluded that geological features, such as the Weald in southern England, required a timeframe of hundreds of millions of years, supporting his theory of evolution through natural selection.

However, physicist Lord Kelvin found this timeline implausible, arguing that if true, the Earth would have to be older than the Sun, which he considered absurd. His expertise in thermodynamics led him to calculate that the Sun's lifespan could only be 20–40 million years based on gravitational contraction, which was insufficient for the geological ages proposed by Darwin.

Despite Kelvin's logical reasoning, he overlooked the underlying process powering the Sun—nuclear fusion, which he was unaware of at the time. This misunderstanding meant that the geological timescales supported by empirical evidence were accurate, while his assumptions were flawed, stalling scientific progress for years.

3.) Einstein's Greatest Blunder. In late 1915, Einstein introduced General Relativity to address deficiencies in Newton's gravitational theory, motivated by the need to explain Mercury's orbit. He included a cosmological constant to avoid predicting an unstable Universe that would collapse due to gravity.

Years later, he deemed this constant his "greatest blunder," as it was unnecessary for a stable Universe. Instead, the Universe's expansion, as later evidenced by Hubble, was a more accurate interpretation.

In each of these cases, scientists entered with a robust understanding of natural rules. When faced with new evidence, imposing rigid logic led to conclusions that were absurd. Had they halted their inquiries at the logical impasse, they would have missed significant discoveries that reshaped our comprehension of the Universe.

The critical takeaway is that science is not merely a theoretical pursuit based on deducing principles from first concepts. Regardless of confidence in the governing rules, meaningful knowledge of the Universe emerges only through experimental inquiry and observation. As Kelvin wisely noted:

> “When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind.”

Starts With A Bang is authored by Ethan Siegel, Ph.D., who has written Beyond The Galaxy, Treknology, and The Littlest Girl Goes Inside An Atom, with more works, including the Encyclopaedia Cosmologica, on the way!