December 20, 2023

Claire Story

11th Grade

Dominican Academy

Time and space have remained a perplexing question for generations of scientists, particularly how time behaves differently on Earth, in outer space, or the distant universe. According to A Briefer History of Time, written by Stephen Hawking,  time is a “personal concept, relative to the observer who measured it” and is not absolute (Hawking 106). People observe time based on the individual clocks that they carry, and not all clocks may agree (Hawking 106). Renowned physicist Albert Einstein proposed the theory of relativity, saying that the laws of science and the speed of light should be equal for every freely moving observer regardless of their current speed (Hawking 44). As described in relativity simultaneity, it is time that passes at different rates for everyone and it “depends on our state of motion relative to each other” (Al-Khalili 61). Time moves slower when near a body with a high gravitational pull. For example, because Mars has less gravity than Earth, time passes ever so slightly faster (Hamer). 

An object’s location can usually be described in three coordinates (longitude, latitude, and height above sea level). However, the spacetime of relativity has four coordinates, including one for space and time (they are indistinguishable from each other) (Hawking 33-35). According to Neel Patel in the MIT Technology Review article, the faster an object moves through three-dimensional space, the more slowly it will move through the fourth dimension, time, relative to other matter; thus, nearing the speed of light will slow clocks tremendously (Patel). The speed of light is constant, proving that time is not absolute but depends on gravity and spacetime (O’Callaghan). Nothing can move at the speed of light (except, of course, light) because, according to Einstein’s well-known equation E = mc2, an infinite increase in speed would involve infinite mass and energy (Hawking 36).

Additionally, it takes time to even see the light of a star from Earth. The light of the star the traveling twin was on would take one year to reach the twin on Earth; on the other hand, the twin in space would see the Earth’s clock as one year behind because its current light had not reached him/her yet. Therefore, on the trip to space, both twins see their own clocks as running twice as fast as the other’s; however, on the trip back from space, both twins would see the other’s clock as running twice as fast. At the end of the trip, the Earth’s clock would be ahead of the clock in space, proving that the twin in space is now younger. Time passed more slowly due to the traveler's high speed (Lasky). 

One thing is certain across the universe: time can only move forward. As presented in the Second Law of Thermodynamics, matter must go from low to high entropy. According to Jonathan O’Gallaghan in the article “What is time?”, beginning with the uniformity of the Big Bang, galaxies naturally move towards disorder. This is called the “arrow of time” and is dictated by the fact that entropy cannot reverse. While equations may show that time can run backward, this would be impossible as it would violate the Second Law (O’Callaghan).

In conclusion, the perception of time depends on the current speed of an object, the distance from its destination, and if it nears an expansive body involving gravity. Time will always seem unchanged to the traveling object because of the “arrow of time” that is always moving forward. These are all only theories, however, as we can never accurately observe time in distant parts of the universe.