Years ago I played the video game Portal. In this game the player has control over two different kinds of portals, one blue and one orange. As one would expect, what comes into the blue one emerges out of the orange one and the other way around. So the player has to use this portal machine to solve ingenious puzzles and eventually beat the game.
In the game a player can open a portal on the ceiling and open a second one directly underneath it. If the player then jumps into it, she (the game’s character is a girl) will come out from the one on top and again fall into the first portal repeating the process indefinitely and gaining momentum with time. At the time I asked myself the question “what happens if one were to do this in real life?” what kind of speed can an object achieve in a hypothetical scenario like this? At the time my physics knowledge was more limited and I couldn’t find a satisfactory answer. l assumed, though it seemed not entirely right, that an unfortunate girl (like the one in the game) in this situation would just keep accelerating until reaching the speed of light.
The answer came years later while watching the TV show Mythbusters. In there the term “terminal velocity” was mentioned and it reminded me of that old question. The answer apparently is that a girl performing the portal experiment on earth would keep accelerating until she reaches terminal velocity (which is about 300 Km/h) due to air resistance. Were the experiment performed in a vacuum (like empty space), then the girl would keep accelerating until she reaches the speed of light; exactly what happens to stuff falling into a black hole for example.
This just leaves me with one more question. Hypothetically, if we could build this portal experiment, how could we use it, for example to generate power?
Just something to think about…