Einstein thought time dilation was both real and not – he was right
What even is time? Columnist Karmela Padavic-Callaghan takes on this mind-bending question by exploring the proof we have that time dilation is both a physical phenomenon and a psychological one
Albert Einstein's theory of relativity introduced the concept of time dilation, which can be both real and apparent. According to general relativity, clocks closer to Earth's center of gravity, such as those at sea level, tick more slowly than those higher up. Additionally, clocks moving at extremely fast speeds also experience time dilation.
This phenomenon has been confirmed through decades of experiments, but the exact nature of time dilation and what it means for a physical effect to be real has been the subject of philosophical debates since Einstein's initial formulation in 1905.
To illustrate time dilation, imagine you and a friend each possessing an identical clock and a one-meter-long rod. If your friend travels in a spaceship moving at an incredibly high speed, their clock will tick more slowly, and their rod will appear shorter compared to yours. The degree of the difference in time dilation and rod contraction can be calculated using Einstein's equations, which he derived over a century ago.
If another friend travels at a slightly slower speed, the same effects will occur, but to a lesser extent. When you later catch up with either friend's spaceship, your clocks will synchronize, and your rods will appear the same length again.
Physicists use the concept of "inertial frames" to describe these effects. An inertial frame is akin to comparing a stationary room (or rest frame) with a spaceship traveling at a constant speed (a moving frame). In your individual frames, you and your friends can establish coordinate systems with familiar dimensions of width, depth, and height.
When one friend moves faster than the others, their coordinate system deforms, contracting in the direction of motion. This detail puzzled Einstein's contemporaries, as it seemed the change in rod length was closely tied to the coordinate system used to position it. Critics argued that an effect dependent on a coordinate system cannot be considered real.
However, coordinate systems are merely tools humans created to organize our understanding of the physical world.
Written by urgent.news from New Scientist's reporting — not their text. Machine-written — may contain errors; check the original before relying on it.
