Imagine this: You leave Earth at age 15 in a spaceship traveling at the speed of light and spend 5 years in space. When you return to Earth you will be 20 years old, but all of your friends who were 15 when you left will be 65. That might sound far-fetched, but modern physics tells us that time is relative and the phenomenon you just imagined is called Time Dilation.
What exactly is time dilation?
Time dilation is a fundamental concept in Einstein’s theory of relativity. It states that the progression of time is relative and depends on the observer's frame of reference. The idea behind this is that as you move through space, time is measured differently for you compared to someone stationary. The faster you move, the slower time passes for you compared to someone standing still. The same effect is observed if you are in a stronger gravitational field. Time dilation is a proven phenomenon, observed in high-speed particle physics experiments and GPS technology, which must account for time dilation to maintain accuracy.
Time dilation and velocity
Special relativity is how speed affects mass, time, and space. It arises from the nature of time and space; it is what causes time dilation. The passage of time slows down at high speeds. The faster an object moves, the greater the time dilation experienced. For a real-world example, we can look at how moving clocks are slowed down by motion.
The image above shows two light clocks, one is stationary and the other is in motion. For the light clock in motion, it appears that time has slowed down; that is time dilation. Velocity and time dilation are connected through the Lorentz factor, which is dependent on velocity and the speed of light.
Time dilation and gravity
Spacetime is a unified thing. Hence when you affect space you also affect time. Gravitational forces bend space and in turn bend time. Massive objects warp spacetime causing time dilation within their gravitational fields. This effect is known as gravitational time dilation. GPS satellites experience this due to their higher altitude and weaker gravitational field. They run about 38 microseconds faster than Earth clocks per day. Gravitational time dilation is a relativistic effect, meaning it will depend on the observer's frame of reference, Time will pass normally for an observer in the gravitational field but appears to pass faster to a distant observer.
The Twin Paradox
This is one of the most famous thought experiments in special relativity. It goes like this:
Twin A stays on Earth while Twin B travels at almost light speed to a distant star and back. The paradox arises when considering time dilation from both the observers’ frames of reference,
Twin A’s perspective (on Earth):
Twin B is traveling at high speed, so time dilation occurs.
Twin B’s clock appears to run slower during the journey.
When Twin B returns, their clock will be behind Twin A’s clock.
Twin B’s perspective (in the spaceship):
Twin A is moving away from them at a high speed.
Time dilation occurs for Twin A, so their clock appears to run slower.
When I return my clock will be ahead of Twin A’s clock.
The paradox: Each twin thinks the other’s clock is running slower!
The twin paradox illustrates the strange implications of time dilation in special relativity. It is a mind-bending concept that challenges our classic perception of time and space.
Watch this video for more information.
Reference list
Jones, A. and Robbins, D. (2016). Slowing Time to a Standstill with Relativity - dummies. [online] Dummies.com. Available at: https://www.dummies.com/article/academics-the-arts/science/physics/slowing-time-to-a-standstill-with-relativity-193289/ [Accessed 30 Oct. 2024].
Logsdon, T. (n.d.). Time dilation | Definition, Equation, Examples, & Facts. [online] Encyclopedia Britannica. Available at: https://www.britannica.com/science/time-dilation [Accessed 30 Oct. 2024].
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