Time Does Not Flow as We Think: The Evidence from Physics

The Arrow of Time: An Irreversible Journey

In classical physics, time was straightforward: Newton viewed it as an absolute, universal stream flowing equally for everyone. However, the 20th century changed everything. Albert Einstein, through his Theory of Relativity, demonstrated that time is flexible—it depends on velocity and gravity.

For an astronaut on the International Space Station (ISS), time flows a fraction of a second slower than on Earth. Experiments with atomic clocks on airplanes confirmed this in the 1970s; the difference was a mere few nanoseconds, but it was measurable.

The true mystery, however, is the “arrow of time”—the irreversible direction in which the universe flows. To understand why does time move forward, we must look at entropy, a concept introduced by Rudolf Clausius in 1850 and later expanded by Ludwig Boltzmann.

Why Time Cannot Be Reversed

Entropy measures the degree of disorder within a system. According to the Second Law of Thermodynamics, entropy in an isolated system always increases or remains constant. A spilled cup of milk will not return to its container on its own because that would require a decrease in entropy—an event that is statistically improbable.

Ludwig Boltzmann showed that processes leading to a decrease in entropy are not physically impossible, but rather extremely unlikely. Spontaneously “reversing” events, such as an egg un-breaking or milk un-spilling, would require the precise, simultaneous movement of a vast number of particles. This probability is so minuscule that it effectively never occurs in the macroscopic world.

Experiments conducted at CERN have shown that the decay of certain elementary particles (such as kaons and B mesons) violates CP-symmetry. This means the laws of physics do not act identically for matter and antimatter in a “mirror” reversal of the world. Consequently, these processes are not identical when time is reversed. While this is a specific feature of weak interactions, it proves that temporal asymmetry can exist within fundamental physical laws.

Entropy: The Force Driving Time

Entropy is not an abstraction; it is an everyday reality. In a universe that began with the Big Bang (low entropy, high order), everything tends toward maximum disorder. Stars burn out, galaxies scatter, and our bodies age. In A Brief History of Time (1988), Stephen Hawking noted that the arrow of time is thermodynamic: if entropy were to decrease, we would remember the future instead of the past.

Observations from the James Webb Space Telescope have provided detailed data on the early stages of galaxy formation, showing that complex structures appeared faster than previous models predicted. While these observations do not measure entropy directly, they reinforce the belief that the Universe began in a state of exceptionally low entropy. This remains one of the greatest paradoxes in modern cosmology: why did the universe begin in such a highly ordered state?

The Entropy of the Universe: Why Order Fades

Roger Penrose, winner of the 2020 Nobel Prize in Physics, proposed the Conformal Cyclic Cosmology hypothesis, where successive “aeons” of the Universe follow one another, and the problem of increasing entropy is resolved over vast cosmic scales.

Interestingly, 2024 experiments involving quantum simulations on IBM Quantum hardware showed that one can locally “reverse” entropy in small systems (such as qubits). However, this occurs only at the expense of increasing entropy in the surrounding environment—much like a refrigerator cools its interior while venting heat outside.

The Illusion of Time and the Brain

Even if physics describes time with precise equations, our minds experience it subjectively. Neurologists like David Eagleman show that time perception is not constant; it depends on attention, emotion, and context. In moments of stress or danger, time may seem to “slow down.” This happens not because the brain processes more information per second, but because the event is recorded with more detail, creating the retrospective impression of an extended moment.

The filmic “slow motion” effect is not merely an aesthetic choice; it accurately reflects how human consciousness interprets intense experiences. Neuroimaging shows that structures like the hippocampus and the prefrontal cortex play key roles in organizing events and providing continuity. This “extended present,” lasting a few seconds, serves as a cognitive model rather than an objective unit of time.

The Limits of Perception

Data from a 2023 experiment (repeated in 2025) showed that participants perceived time as 20% shorter during boredom and 15% longer during excitement. While this echoes the Buddhist idea that time is an illusion of the mind (maya), the scientific reality is biological. Circadian rhythms, regulated by genes such as CLOCK and PER, organize our biological time, influencing sleep and hormonal cycles, even if they do not directly determine our subjective feeling of short intervals.

The brain evolved to handle the macro-scale, not the quantum. As Carlo Rovelli writes in The Order of Time (2018):

I am convinced that time does not exist. I believe we can describe nature without using the concepts of time or space… These are just approximate concepts used by our minds to imagine reality.

In Rovelli’s theory of loop quantum gravity, time is not fundamental but emerges from interactions.

Will We Ever Truly Understand Time?

We may never fully grasp time because we are an intrinsic part of it. Immanuel Kant argued in the 18th century that time is an a priori form of perception—not a “thing in itself,” but a filter of the mind.

Modern physics partially agrees. Near the event horizon of a black hole, general relativity dictates that time slows down extremely for an outside observer, even though it remains continuous for an object falling in. Furthermore, data from the DESI project allows us to describe the expansion of the universe and dark energy with increasing precision, confirming that cosmic space expands at an accelerated rate.

Recent research into “time crystals” has shown that specific quantum systems can form periodic temporal structures that defy our intuitive ideas of a uniform flow. Whether time had an absolute beginning or is an emergent, cyclic phenomenon remains the ultimate challenge. As Hawking wrote, at least three arrows of time distinguish the past from the future. In an era where AI simulates entire universes, the question of why does time move forward remains a frontier that invites both scientific rigor and profound humility.

Read the origian article in Polish: Czas nie płynie tak, jak myślimy. Fizyka ma na to dowody