Why does time slow down as you go faster? Time slows down as we go faster because our perception of time gets distorted.
This all comes down to the fact that the speed of light in a vacuum is constant. Light, in a vacuum always travels at C, which is 299,792,458 m/s. The difficulty comes because the speed of light is always that speed, no matter what your viewpoint is. For example, imagine someone called Frank sitting on a rollercoaster that goes through the station at speed and imagine someone else called Lucy standing on the station watching the rollercoaster. The rollercoaster goes through the station at 50 km/h, so Lucy on the platform sees Frank in the rollercoaster moving at 50 km/h. Let’s say that when the rollercoaster goes through the station, Frank throws his smartphone (for whatever reason) forward at 50 km/h. From the perspective of Frank, he is stationary and the phone is moving forward at 50 km/h. From the perspective Lucy, Frank is moving forward at 50 km/h and the smartphone is now moving at 100 km/h. This makes sense and we don’t have any trouble understanding it. The two speeds add together. If you want to throw a ball faster, you run up first because your speed will add to the speed of the ball. The problem comes when we talk about light. Imagine the rollercoaster is now traveling at the speed of light and Frank throws his smartphone at the speed of light. Frank will see his phone moving at the speed of light, but Lucy will see the train moving at the speed of light and the smartphone also moving at the speed of light, not twice the speed of light. How can Frank and Lucy both see the smartphone moving at the speed of light? The only way is if their perceptions of time have been distorted. This is called “time dilation”.
So, the actual answer to the question “why does time slow down the faster you go?” is that it doesn’t. Time slows down from the perspective of another observer.
Let’s go back to our rollercoaster person, Frank, but put him in a car with windows and roof so there is no wind. As he goes through the station, he throws his smartphone up in the air and catches it. The phone goes straight up and straight down because he is moving with the rollercoaster and all of the air in the rollercoaster is moving as well. His phone goes up 1 m and down 1 m in 1 second and he catches it. It has travelled 2 m in one second, or 2 m/s. However, from the perspective of Lucy on the platform, the phone goes up and down in a big arc because the rollercoaster is moving. The rollercoaster moves 5 m forward in the 1 second it takes to throw and catch the phone, so the phone moves in an arc that is roughly 5.4 meters long, which is 5.4 m/s. So, the same thrown smartphone has moved at 2 m/s and 5.4 m/s at the same time. The only difference is the viewpoint of the person doing the observing. And the only way the same object can travel further from one perspective than from another is if it is travelling more slowly.
The important distinction that we need to make here is that time in each place doesn’t slow down, but from another viewpoint, it does slow down. Let’s put Frank on a spaceship that can travel at the speed of light and let’s put Lucy on Earth. They both have a grandfather clock that ticks once a second. As Frank’s spaceship moves away from Earth at the speed of light, to them, both of their clocks are ticking normally. Lucy sees her clock tick once a second on Earth and Frank sees his clock tick once a second on his spaceship. The difference comes if Lucy looks at Frank’s clock. To her, it has virtually frozen, along with Frank and his spaceship.
This is technically a way that time travel into the future could be possible, but it is all moot, really, because there is no way that Frank and his spaceship with the clock could ever reach light speed. Only something with no mass, such as a light photon, can travel at light speed. This is because as something gets faster, its mass increases, requiring more energy to go faster. For something with mass to go at the speed of light would require infinite energy. And this is what I learned today.
Sources
https://en.wikipedia.org/wiki/Time_dilation
Photo by Stas Knop: https://www.pexels.com/photo/white-clock-reading-at-2-12-1537268/