My partner and I were watching National Geographic when Rainbow Mantis Shrimp we’re mentioned and how they could see polarized light.
In: Physics
Light is comprised of photons, a tiny (spatially) packets of energy. They are somehow made up of oscillating magnetic and electric field, one perpendicular to each other and to the direction of light. I can’t say I have a really good visual representation of that myself. If you imagine it like a space ship flying forward, electrical field would oscillate (for example) up-down, while magnetic field would oscillate left-right.
But, there is no UP is space. So, space ships flying together in the same direction can still be oriented in whatever direction axially. So, if you imagine a bunch of space ships moving in the same direction, and they don’t have any ordered formation, this is what unpolarized light looks like. Each photon has arbitrary orientation of electrical field.
Now, imagine that they are flying like they usually are is movies. In a formation, all oriented in the same way. That would be polarized light. While you have a bunch of photons that are completely independent of each other, their electric are oscillating in parallel planes.
It is important not to confuse polarized light with LASER. In laser, all photons have synchronized electrical fields (meaning they oscillate together). With polarized light, they just oscillate in the same direction, but they are not synchronized.
Light is an electromagnetic wave. It is the oscillation of electric and magnetic fields. So if you draw a line along which light is travelling, the electric field may oscillate up and down over the line and the magnetic field then oscillates perpendicular to that, so left and right. That’s an EM wave. In normal unpolarized light, you have many many photons and this means the electric field oscillation for example is up and down in some, left and right in another, diagonal in another, etc. So you have all sorts of orientations, of course electric and magnetic oscillations will be perpendicular to one another, but they will be as a pair in all angular orientations along this line of propagation. Linearly polarized light means we have only one orientation. You may filter out all the orientations you don’t want and retain only one like the up-down one for the electric field. Of course you can also allow two or more orientations though, and then the waves are superimposed resulting in one plane. As long as the waves are in phase (at any given point, the waves are in the same “stage” of the ocillatory cycle).
In circularly polarized light, you have two (for example) light waves in say perpendicular orientation but they are not in phase. They’re phase shifted by 90 degrees. Meaning, at any point, one wave is one quarter of the ocillatory cycle ahead of the other. When these two waves interact, they don’t result in a vector in one plane, no it actually changes orientation as the waves propagate. You get a helix. And this helix may be right handed or left handed. You can also get elliptically polarized light when the phase difference is other than a quarter.
Of course seeing polarized light is nothing special, we can do it, I think any organism with eyes can. But what is special about the mantis shrimp is that they can distinguish the difference. We can’t tell if light is polarized (actually we can, it’s a weak ability but we have it, totally shocked science when it was shown but anyway), they can, and they can tell how polarized it is.
I understand my explanation is a bit complex but I really don’t know how else to write it up. Here is a video that may help explain visually how circularly polarized light is: https://youtu.be/Fu-aYnRkUgg
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