LASERS: GOING VEEERRRYYYY SLLLOOOWWWLLYYYYY

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Any good fiction needs conflict, and what better conflict than war! But with war, comes weapons. Thankfully, our science fiction writes have brought us into the future with the invention of lasers as a means of giant, wonderful, fiery explosions. Unfortunately, some of them go about it completely wrong.

The idea behind a laser begins with atoms themselves. In most cases, atoms are surrounded by electrons, and these electrons orbit atoms at specific orbitals. Each electron can enter higher states of energy whenever energy is added to the electron. The electrons are then considered to be in an “excited” state.



An atom.

Once they come back down to their original state after being in an excited one, they emit a photon. Most of the time, these photons are emitted in a somewhat random direction. A flashlight, for example, has photons going in random directions, so that in a sense they are unorganized. If those photons are bounced back and forth until they are in a line between two mirrors, the photons line up and are “organized.”

Line them up and watch them go! An "organized" stream of electrons.

That is an extremely simplified version of what actually happens in a laser. Using excited electrons to emit photons, and then making each of those photons move back and forth in an organized pattern creates the beam we know so well in science fiction. But in order for us to do any damage with these beams, they need to be at extremely high power when emitted.

Now, as for relevance, Star Wars is the easiest comparison. Pick any fight scene in any of the movies that involves either a laser gun or a light-saber. If we assume that these weapons are in fact lasers, and not some extremely odd electron-photon magic, none of them should work, or at least appear to work as they do.

Slowest moving lasers EVER.

The first example has to do with the way we see the lasers. In Star Wars, lasers are “shot” in short bursts that we can see as short beams that fly through space. Unfortunately, the only way for this to happen is to disregard one of the most basic concepts of physics itself: the speed of light, which in a vacuum is 299,792,458 meters per second. The only way for our eyes to see the lasers in Star Wars is if you were to slow light down enough to make it travel through space MUCH slower than it actually travels.

Our other example is even more physics breaking. The light saber, a weapon that arguably defines the Star Wars universe, asserts that a small hand held device can emit a laser that not only stops at a certain distance and continues to maintain its shape, but also has the ability to deflect other lasers that have been already shown to be against the laws of physics in the paragraph above.


Darth Vader, just ignoring the breaking of physics.

First, in order for a laser to “stop”, it must be reflected back to the source or be absorbed completely. This requires something physically at the endpoint of the laser that has the capability to reflect the photons back, such as a mirror. Even if that were possible, there would have to be some way to reflect the laser again to keep it from tearing apart the emission device.

This also comes into play when deflecting lasers, as shown in the Star Wars films. Even if it were possible to slow down the photons from a laser in the way we see them in the films, there would still need to be some sort of reflective surface (black holes aside) to be able to make them change their direction.

With all this said, many come up with other arguments to allow for the light saber to work. First, some argue that the photons from a laser don't necessarily need to be "reflected" if they can be bent. If we assume that a light saber has the technology to actually bend photons back to create an ellipse, thus showing that the light never actually stops and does not need to be reflected, then the light saber can have a working model.

Another argument is that the light saber isn't actually light, it's a plasma. We use plasma cutters today, and they have been shown to work. The biggest problem the plasma theory has is the supply of power and fuel. Plasma cutters rely on a gas, such as nitrogen or oxygen, to be superheated to a point where it becomes a plasma. In order for a plasma saber to work, we first need the power required to superheat the gas to a plasma, then have a seemingly unlimited gas supply, all packed into a hand held device.






Thomas Edwards - Physics 211x - FH1 - 2010