AP Syllabus focus:
'Developments in physics and psychology challenged the Newtonian universe and weakened confidence in objective knowledge.'
Around 1900, European thinkers increasingly questioned whether the universe was orderly, predictable, and fully knowable. New ideas in physics and psychology unsettled older assumptions about nature, reason, and the human mind.
The older scientific worldview
Before 1900, many educated Europeans assumed that science revealed a stable, orderly universe. The legacy of the Scientific Revolution and the Enlightenment encouraged faith in reason, measurement, and universal laws. Nature seemed intelligible, and the human observer seemed capable of describing it accurately.
Newtonian universe — a mechanistic view of nature, derived from Isaac Newton, that pictured the universe as governed by fixed laws operating in absolute space and time.
Classical physics also implied determinism, the idea that if the laws of motion were known, future events could in principle be predicted. That assumption gave enormous prestige to precise observation and mathematical description. The scientist appeared to be a neutral investigator standing outside what was being studied.
This outlook supported confidence in objective knowledge, the belief that truth existed independently of the observer and could be discovered through rational investigation. Late nineteenth-century science had strengthened that confidence, but around 1900 new theories began to expose limits in both the external world and the human mind.
Physics and the end of absolutes
Einstein and relativity
Albert Einstein’s work was especially important. In special relativity (1905), time and space were not absolute containers within which events occurred. Measurements of time, length, and motion depended on the position and movement of the observer. In general relativity (1915), gravity was no longer simply a force acting at a distance in Newtonian fashion; it reflected the curvature of space-time itself.
Artistic but conceptually standard visualization of general relativity: massive bodies deform a “spacetime surface,” and motion follows the geometry of that curved space. The image supports the notes’ point that Einstein replaced Newton’s force-based gravity with a geometric account of gravity in spacetime. Source
For educated Europeans, this suggested that even basic categories once treated as fixed were more complex and less intuitive than previously believed. The confirmation of relativity during the 1919 solar eclipse gave the theory public visibility, but it also deepened the sense that modern science had moved beyond ordinary common sense.
Quantum theory and probability
At the same time, quantum theory challenged the old mechanistic picture from another direction. Max Planck, Niels Bohr, and Werner Heisenberg helped show that matter and energy at the subatomic level did not behave in the smooth, predictable way imagined by classical physics. Instead of strict certainty, physicists increasingly used probabilities.
Heisenberg’s uncertainty principle implied limits to how precisely certain properties could be known simultaneously.
The universe still had order, but that order no longer looked fully deterministic or completely transparent to human observers. Physics remained powerful, yet it no longer seemed to guarantee absolute certainty in the older Newtonian sense.
Psychology and the divided self
Developments in psychology were equally disruptive because they challenged assumptions about the self. If physics questioned whether nature could be known in an absolute way, psychology questioned whether the human mind was itself rational, unified, and fully knowable.
Psychoanalysis — a psychological theory and method, associated especially with Sigmund Freud, that emphasized the influence of the unconscious mind on human behavior.
Its reliance on interpretation rather than simple measurement also suggested that understanding human beings required decoding symbols and conflicts, not merely recording observable behavior.
Freud argued that human behavior was shaped not just by conscious thought but also by hidden desires, memories, fears, and conflicts. Dreams, slips of the tongue, and neurotic symptoms suggested that the mind contained layers beyond rational control. This undermined the older Enlightenment image of individuals as primarily reasonable beings who understood their own motives.
Self-knowledge now seemed partial and unstable. If people could misunderstand themselves, then claims to detached and objective judgment became harder to maintain. Freud’s ideas were controversial, but their influence was wide. Intellectuals increasingly took seriously the possibility that civilization, morality, and politics might be shaped by irrational drives as much as by deliberate reason.
The broader challenge to certainty
Together, new physics and new psychology transformed European intellectual life. They did not destroy science; instead, they changed what many Europeans thought science could do. Certainty gave way to complexity, and explanation became less about fixed truths that simply waited to be discovered.
These developments weakened confidence in objective knowledge in several connected ways:
The observer mattered more than the Newtonian model had suggested.
The universe appeared less like a clockwork mechanism and more like a system that required revised concepts, probability, and interpretation.
The mind itself was no longer a fully reliable instrument of reason.
As a result, early twentieth-century Europe became more receptive to skepticism about universal truths. Philosophers, scientists, and educated readers increasingly accepted that knowledge might be conditioned by perspective, language, hidden motives, or the limits of observation. The challenge to certainty came from within the most prestigious fields of modern thought, which made it especially powerful. Knowledge could still advance, but it now seemed more provisional than absolute.
FAQ
During the eclipse, astronomers tested whether light from distant stars bent as it passed the sun, as general relativity predicted.
When the observations appeared to support Einstein, newspapers presented the result as a dramatic overturning of old physics. The event mattered politically as well: British scientists publicly confirming a German-born scientist’s theory just after the First World War gave the discovery unusual international symbolism.
Ordinary error suggests that better instruments or methods could eventually remove the problem.
Quantum uncertainty was more unsettling because it implied a built-in limit:
the issue was not simply clumsy measurement
nature itself placed constraints on what could be known exactly at the same time
uncertainty therefore became a principle, not merely a technical defect
Vienna combined a strong medical culture with intense debate about identity, sexuality, family life, and social tension in a multi-ethnic imperial capital.
That setting helped psychoanalysis grow. Freud worked within a world of doctors, educated middle-class patients, and intellectual networks that were unusually open to discussing nervous disorders, repression, and the hidden pressures of modern urban life.
Critics argued that psychoanalysis relied heavily on case studies and interpretation rather than controlled experiment.
They also doubted whether many Freudian claims could be tested or falsified in a rigorous scientific way. Supporters saw this as a misunderstanding of the complexity of the mind, but sceptics thought psychoanalysis often explained too much too easily and lacked clear standards of proof.
They pushed philosophers to rethink what counted as knowledge.
Some movements, such as logical positivism, tried to tighten standards of verification and language in response to scientific complexity. Others, including phenomenology, focused more closely on consciousness and lived experience. In both cases, the older confidence that reality could be described in a simple, transparent, universally agreed way became much harder to sustain.
Practice Questions
Identify one way developments in psychology weakened confidence in objective knowledge in early twentieth-century Europe. (2 marks)
1 mark for identifying that Freud or psychoanalysis argued that unconscious drives, repression, or hidden motives shaped human behavior.
1 mark for explaining that this meant people could not fully know themselves through reason alone, weakening confidence in objective knowledge.
Explain how developments in both physics and psychology challenged the Newtonian universe and weakened confidence in objective knowledge in early twentieth-century Europe. (6 marks)
Award 1 mark for each valid point, up to 6 marks:
Describes the Newtonian universe as orderly, mechanistic, and governed by fixed laws in absolute space and time.
Explains that Einstein’s relativity challenged the idea of absolute space and time.
Explains that quantum theory introduced probability or uncertainty instead of strict determinism.
Explains that Freud or psychoanalysis emphasized the unconscious, repression, or irrational motives.
Links new physics to limits on detached observation or absolute certainty.
Links new psychology to limits on rational self-knowledge or objective judgment.
