By Huzayfa Mallick
All About Time!
Time is an idea we think we know well. To be fair, it can’t be that complicated right? 60 seconds in a minute. 60 minutes in an hour. 24 hours in a day and 365 days in a year. An 11:59 PM deadline is a time we all know well too! Sounds pretty universal, doesn’t it? In a rapidly changing universe filled with mysteries beyond our understanding, time seems to be the only thing that doesn’t change. It just keeps ticking forward, and there’s nothing we can really do about it.
However, like any field of science, there’s much more to unpack about the mysteries of time than people think. In reality, the concept of time turns out to be one of the more complex ideas in our universe, needing Einstein’s theory of special/general relativity (and a ton of foundational work from other scientists) to help us understand its place in the universe. To begin developing an understanding of the concept of time, we need to take a look at how physics has evolved over several centuries to produce our modern-day knowledge of this concept.
Sir Isaac Newton was a famous physicist from the 17th century, and is widely regarded as one of the best scientists of all time. You may know him for his work on the force of gravity (and the laws of motion!), yet he also made contributions to our initial understanding of time as well. Newton thought that time was a ‘constant’ – something universal. A variable that does not change across the universe. For instance, the idea implies that one second on Earth represents one second across the universe. On the other hand, Newton believed that the speed of light was variable, and did not function as the constant we know today.
Contrasting Newton’s ideas came scientists such as Einstein and Minkowski, who introduced new theories into our understanding of the physics behind space, time and light. For one, it was put forth that the speed of light is a constant, as recognized by our world today to be 3.0 x 108 m/s. Thus, it was then proposed that time was relative, and therefore, not a constant as previously thought. In essence, the perception of time can differ based on one’s frame of reference, which formed the basis of Einstein’s theory of special relativity.
The concepts of space and time were also reimagined within this era of science. The three dimensions of space are commonly referred to as the x, y, and z coordinates of a particular object in space. The creation of a space-time continuum validated the addition of time as a ‘4th dimension’ to the already existing three, and thus, interconnected the concepts of space and time. You can think of it like a 4-point coordinate system. Instead of simply having an x, y, z coordinate to describe an object’s location, you have now added a coordinate for time, essentially describing an event in time and space.
Within these contrasting ideas, one fact remains constant; time always goes forwards. This idea can be attributed to two theories. For one, it must abide by the law of entropy, which states that the universe tends to go from low to high entropy. In other words, it tends towards a higher degree of disorder at all times. Thus, going backwards in time would violate this law, and is thus, impossible. Second, the universe is expanding at a rapidly increasing rate. As both space and time are ‘connected’ (explained above), the expansion of space would not allow time to go in the ‘backwards direction.’
Revisiting Einstein’s theory of special relativity, the perception of time can change based on a person’s frame of reference. What exactly does this mean? Well, we can look at two important scenarios to discuss its implications: when someone is accelerating near the speed of light and when someone is near a massive celestial object.
Revisiting Einstein’s theory of special relativity, the perception of time can change based on one’s frame of reference. To further clarify this idea, we can take a look at two important scenarios to discuss its implications.
A person on earth versus a person in space accelerating near the speed of light
A person in close proximity to a massive celestial object (ex. A black hole)
For the first scenario, we can take a look at an example commonly used in today’s world: the one with two twins! In this scenario, there is one twin located on the surface of the Earth, while the other is accelerating near the speed of light on a rocket ship. Let’s say that the person on the rocket ship started the timer for 30 years and returned to Earth soon afterwards. While they would have aged 30 years, their twin on Earth would be much older, due to the perception of time in both frames of reference. In essence, near the speed of light, time appears to go slower relative to the person on the surface of the Earth.
The second scenario occurs when a person is at close proximity to a massive celestial object, such as a black hole. Think of the movie Interstellar. When the spaceship of the crew is near a black hole, their ‘clock’ runs much slower than the people on Earth due to time dilation. This phenomenon can be explained using the space-time continuum, as all objects in the universe warp the fabric of space-time to some degree. Massive objects such as black holes completely bend and distort the space-time continuum around them, and thus, have an impact on the perception of time. Near black holes (as an example) a person’s ‘clock’ will tick much slower relative to the surface of the Earth, thereby causing them to age at a much slower rate.
That concludes my attempt to understand and explain the concept of time and relativity.
Get ready for an awesome article on the science of the brain for next week!
Thank you for reading!
Works Cited
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