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One of the weirdest things I have learned about science is that time doesn’t literally move at the same speed for everyone. How in the world could this be possible?
It is possible for time to both speed up and slow down under certain conditions. It can even almost stop. This isn’t something out of a science fiction book; it’s how physics works.
The theory of relativity can be a bit difficult to grasp. There are complicated equations, advanced physics, and something that is impossible to completely understand. I know I had to do a lot of reading and research to grasp a little bit of the theory of relativity, so it isn’t just you having trouble understanding it. A lot of people don’t understand it.
One aspect of it is that time and space depend on motion and gravity.
Time Isn’t Absolute
Many of us picture time as something that is constant. A minute is a minute and an hour is an hour. Then comes along relativity to tell us that this isn’t true.
One example would be to imagine two people. One person is standing still on the Earth while the other is traveling in a very fast spaceship. From the person’s perspective standing on the Earth: The person on the spaceship experiences time more slowly than the person standing on Earth. Weird huh? This is known as time dilation
Motion Changes Time
So basically, the faster you move, the slower time passes for you relative to someone else who is moving slower. You may not feel it, and everything would seem normal; however, it has been proven. If someone could travel at the speed of light, time would pause for the person going this fast. However, only things with no mass can travel that fast.
Gravity Also Changes Time
Now to make things more bizarre, not only does speed affect time, but also gravity.
For example, compare a clock near the Earth and a clock out in space. The clock closer to the Earth moves more slowly. This is because gravity affects the structure of spacetime.
Space and Time Are Connected
Before relativity was figured out, people thought that space and time were unconnected. However, Einstein came up with the idea that they are part of the same system.
This means that you can’t change space without affecting time, and you can’t change time without affecting space.
Why This Matters
It isn’t only a theory but it has an affect on real life. Satellites that orbit the Earth move very fast, but they experience less gravity. The clocks on satellites run quite differently from the clocks on Earth. In other words, if we didn’t adjust for this, GSP would be inaccurate within minutes. Time isn’t universal, but there is no single “now” that everyone shares.
Part 6: The Bigger Implication
If time depends on motion and gravity, then reality itself depends on perspective. Two observers can measure different times and experience events differently. That seems to mean that no one’s perspective is the same. We are all experiencing time differently, and none of us is wrong.
Final Summary
Let’s put this all together. Time is inconsistent since motion and gravity slow time. Since space and time are connected, reality depends on perspective.
So when you look at a clock, it’s not measuring something that is universal. It is measuring time from your perspective. How’s that for something to think about?
Further Reading (Affiliate Links)
The Fabric of the Cosmos by Brian Greene
Relativity: The Special and the General Theory by Albert Einstein
Einstein’s Clocks, Poincaré’s Maps by Peter Galison
A Brief History of Time by Stephen Hawkings
Black Holes and Time Warps by Kip S. Thorne
Spacetime Physics by Edwin F. Taylor and John Archibald Wheeler
Gravity by James B. Hartle
The Order of Time by Carlo Rovelli
Welcome to the Universe by Neil deGrasse Tyson, Michael A. Strauss, and J.Richard Gott
A First Course in General Relativity by Bernard Schutz
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See Also
Black Holes in Astronomy: The Dark Engines of the Universe
Why is the Universe Bigger Than it Should be