Without evidence, there is no knowledge

Albert Einstein’s theory of knowledge can teach us a lot about how we (should) understand the world

My then 8-yr old daughter, Caley, in 2005 during a trip to Yellowstone National Park. She asked a good question, and wouldn’t accept for an answer anything that wouldn’t have also satisfied Einstein. Photo by the Author.

Many years ago, while driving through Yellowstone National Park with my eight-year-old daughter Caley, I mentioned we would soon need to stop for gas. She turned to me and asked, “How do you know?” I explained that she had just asked one of life’s most essential questions—one worth treasuring and cultivating. When I described the car’s fuel sensor system, she pressed further: “What if the sensor doesn’t work?” Even in this seemingly simple case, the reliability of empirical evidence raised complex questions.

As a scientist, I have always recognized the importance of theory while understanding its limitations without empirical evidence. Einstein himself developed a sophisticated framework for understanding the relationship between theory and evidence. In 1934, Einstein articulated a principle fundamental to both scientific inquiry and general knowledge:

“Experience is the alpha and omega of all our knowledge of reality.” [1]

This strikes me as exactly right, though we’re going to unpack this a bit with the help of a delightful paper published several years ago by Sarah Glenn, in which she explores the relationship between experience and reason in Einstein [2]. Contemporary physicists and science communicators, including Stephen Hawking and Neil deGrasse Tyson, have dismissed philosophy as irrelevant to modern scientific inquiry. Einstein, however, considered philosophy fundamental to scientific understanding. In a 1944 letter to Robert Thorton, he argued:

“So many people today—and even professional scientists—seem to me like someone who has seen thousands of trees but has never seen a forest. A knowledge of the historic and philosophical background gives that kind of independence from prejudices of his generation from which most scientists are suffering. This independence created by philosophical insight is—in my opinion—the mark of distinction between a mere artisan or specialist and a real seeker after truth.” [3]

The philosophical inquiry into the nature of knowledge has historically centered on two main approaches: rationalism and empiricism. Rationalists argue that human reason alone can discover fundamental truths about the universe. Empiricists, conversely, maintain that knowledge derives primarily from sensory experience and empirical observation, including data gathered through scientific instrumentation.

Pythagoras of Samos (570-495 BCE) established an early rationalist framework by asserting that numbers constitute the fundamental nature of reality—a position that continues to resonate with some contemporary mathematicians.

[Pythagoras writing in a book, detail from Raphael’s School of Athens. Image from Wikimedia, CC license.]

The Eleatic school, led by Parmenides of Elea and including Zeno of the famous paradoxes (not the Stoic one), represented another significant early rationalist tradition. In his poem On Nature, Parmenides distinguished between two paths to understanding reality: doxa (opinion), which perceives the world through appearances, and aletheia (truth), which transcends appearances through rational inquiry. Parmenides privileged the rational path to truth over mere sensory perception.

Plato, influenced by Pythagorean mathematics, reportedly inscribed 'Let no one ignorant of geometry enter' at his Academy's gate. His attempt to ground philosophy in mathematical rigor—what I have called Plato's error—reflected his belief that philosophical truth could be established with geometric certainty.

René Descartes, renowned for his cogito ergo sum (“I think, therefore I am”), represents a pivotal figure in early modern rationalism. Though his methodological skepticism sought to establish philosophical certainty by questioning all existing knowledge, his reliance on the cogito as a foundation proved fundamentally problematic. Descartes’s subsequent appeal to divine veracity to validate human reason compromised his epistemological framework, exposing a fundamental weakness in pure rationalist methodology.

The empiricist tradition found early expression in Thales of Miletus and the Milesian school, which emphasized experiential knowledge. Thales demonstrated the practical value of this approach by predicting the 585 BCE solar eclipse and successfully speculating in olive presses through meteorological forecasting.

[Urania, the Muse of Astronomy, reveals to Thales the secrets of the skies, by Antonio Canova. Image from Wikimedia, CC license.]

Aristotle’s empiricist leanings emerged from his extensive biological investigations, aligning him with later Epicurean and Pyrrhonian approaches. The Stoics developed a more integrated methodology, synthesizing empirical observation (physis) with logical analysis.

Francis Bacon, Descartes’s contemporary, advanced empiricist methodology, which the British philosophers Thomas Hobbes, John Locke, George Berkeley, and David Hume later refined into a comprehensive epistemological framework.

Hume’s skeptical empiricism prompted Kant’s philosophical awakening, leading to his transcendental idealism—a synthesis that challenged both rationalist and empiricist approaches as unduly limited in their accounts of knowledge.

While contemporary rationalism largely persists in non-academic contexts such as the LessWrong community, empiricism evolved through post-Kantian movements including logical positivism—developed by the Vienna Circle—and American pragmatism as articulated by Charles Sanders Peirce and William James.

This was a very rapid historical overview, but I felt it may help the curious to dig deeper. Let’s return to Einstein, shall we?