Imagining Special Relativity: Why Time is Weird
While typing this article, my fingers are moving through time more slowly than the rest of my body. This is because things in motion move through time more slowly than things at rest. Don’t believe me? Keep reading.
For starters, let’s perform a thought experiment. Imagine two reference frames which are not accelerating (inertial reference frames). We’ll call the first one “A” and the second “B.” (For the sake of simplicity, lets imagine “A” & “B” are both spaceships) Relative to A, B is moving at a constant velocity of V. (It is important to note here that if these frames of reference are the only observable objects, it is impossible to determine which object is actually moving doing the moving.)
Back to our spaceships: Imagine B is above A, and on the bottom of B is a dangling wire. On the top of A, there is an erect wire, so that when B passes A, the wires make contact, and the clocks on both ships begin counting time (t=0).
Now, imagine a light flashes in front of both ships. By this time, B has moved forward relative to A. (We know that an object’s velocity is measured by calculating how much distance it covers in a certain amount of time.) Both A and B observe this flash of light and each can use their own frame of reference to determine how far away the light flash is. A will say that the flash occurred when A was a distance of d away from the light, and when A’s clock read a time of t. B will say that the flash occurred when B was a distance of d’ away, and when B’s clock read a time of t’.
Simple enough, right? Now, I want all of you to imagine you are on a spaceship that is moving close to the speed of light. On the bottom of the ship is a mirror with a light attached to it. Dangling from this mirror is another mirror placed so that, when the light shines, it will reflect from mirror to mirror as the ship travels. From your frame of reference, that is from the viewpoint of the ship, the light appears to move directly up and down. Sitting on a meteor outside the ship is an alien. It observes your ship passing by and, in turn, observes the light traveling between the mirrors. However, the alien does not see the light travel straight up and down. Because the light is traveling with the ship, the alien sees the light make its trips at an angle. Because of this, our extraterrestrial observer calculates the time between trips to be different than we do inside the ship.
To summarize, nothing can travel at or above the speed of light. (about 300,000,000 meters per second) but light itself (or similarly massless particles), This gives us meters – a unit of distance in space – and seconds, a unit of time. Special relativity is, in essence, a unification of space and time. The two are intertwined. Since we can’t travel at or above the speed of light, as we approach c, space and time bend around us to prevent us from traveling the amount of space required to be covered in the amount of time that would place our speed at or above the speed of light.
The phenomenon involving time’s bending is known as “time dilation.” Because space and time are tied together, as time bends around you (as you approach the speed of light), space does as well. This causes you also become skinnier as you approach the speed of light. (This bending of space around an object is known as “length contraction.”)
This concept probably sounds incredibly foreign, if not downright strange. After all, we live our lives not traveling near the speed of light, so we’ve always experienced time as if it were a constant. Time dilation is a reality of our physical universe though. We even witness it with our space-based satellites!)
Now. If we wanted to validate the effects on humans, think of it this way. This is why if you fly a plane, while you may be traveling at fast speeds relative to those who aren’t flying, you aren’t moving close at all to the speed of light, so the effects of time dilation don’t apply to you. However, if you were to travel at 90% of the speed of light, or .9c, you would be traveling at “relativistic” speeds, and you would age much slower than those who aren’t traveling with you. If you travel for ten years in this way, when your journey is over, you will have arrived in a world far different from the one you left. Because you were moving through time much slower than those who weren’t accompanying you, you will have aged ten years, while those you left behind will all be deceased. You will have traveled through time.
So, I wasn’t lying when I said that my fingers were moving through time more slowly than the rest of my body…technically. While they’re moving closer to the speed of light than the rest of my body, they aren’t moving anywhere near fast enough to make any difference at all.
Read the full article (equipped with digestible illustrations)
- Chace aka cosmophilia (via Quarks and Quasars)
"Physical Consequences of Lightspeed Travel":
"What Does it Mean to be Traveling Through Space & Time?"
"The Subjectiveness of Time"
"Effects of Time Dilation on our Satellites:"
Image Source: http://tinyurl.com/opc7ybw