시간이라는 것은 실재할까? 세계를 이루는 기본단위일까?
We measure time using sundials and mechanical clocks. What exactly is it that we’re measuring?
Is time something that physically exists, or is it just concept in our heads? The answer seems self-evident. Time exists. But our understanding of time started getting complicated by Einstein.
His theory of relativity tells us that time is relative to people in different situations. Einstein resolved the malleability of time by combining it with space to define space-time, which can bend but behaves in consistent, predictable ways. His theory seemed to confirm that time is the fundamental unit of the universe.
But there’s an important question it didn’t fully resolve: why we can move through space in any direction, but through time in only one? This one-way direction is called the arrow of time.
In physics, this is described by the Second Law of Thermodynamics, which says that systems will gain entropy over time. Systems in our universe move from order to more disorder, and it is the property of the universe that defines the direction of time’s arrow.
So if time is such a fundamental property, it should be in our most fundamental equations describing the universe. We currently have two equations that govern physics. General relativity describes the behavior of big things, while quantum physics explains the very small. One of the biggest goals of theoretical physicists over the last half-century has been reconciling the two into one fundamental “theory of everything.”
There have been many attempts, and some of them don’t include time at all. If a time-starved equation turned out to be true, would that mean that time doesn’t exist at the most fundamental level?
Instead of asking if time exists as a fundamental property, maybe it could exist as an emergent one. Emergent properties are things that don’t exist in individual prices of a system but do exist for the system as a whole. Each water molecule doesn’t have a wave, but the whole ocean does. Also, a movie creates change through time by images fast enough. Our brains perceive the passage of time from the sequence of still images.
The movement in movies is real, yet also an illusion. Could the physics of time somehow be a similar illusion? Physicists are still exploring these and other questions.
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