It's not New, so it's not Really News

Facebook messed with its users? I’m shocked, shocked.

Facebook tinkered with users’ feeds for a massive psychology experiment

Facebook data scientists tweaked the algorithm that determines which posts appear on users’ news feeds—specifically, researchers skewed the number of positive or negative terms seen by randomly selected users. Facebook then analyzed the future postings of those users over the course of a week to see if people responded with increased positivity or negativity of their own, thus answering the question of whether emotional states can be transmitted across a social network. Result: They can! Which is great news for Facebook data scientists hoping to prove a point about modern psychology. It’s less great for the people having their emotions secretly manipulated.

It’s Not All Black and White

Incredible art piece dances with polarized light

There’s a video in the link with the art, which is a weird combination of kinetic sculpture and optical effects from polarizers. You don’t discern the actual motion of the polarizers, but you see a motional effect from the overlap. Sort of an opto-kinetic sculpture.

One thing:

Polarizers are pieces of plastic made to only allow (or disallow) the transmission of light with certain polarizations. Natural light has a mixture of all different polarizations of light, and so any one of these polarizers only filters out a portion of the light. However, if you stack two with complementary polarizations, such as one that blocks about 50% of light and another that blocks the other 50% of light, then you end up with a totally opaque whole.

To quote a phrase: that’s not how this works! That’s not how any of this works! Simple filters don’t add linearly (they multiply — two simple 50% filters would block 75% of the light), and polarizers don’t block half each. What’s actually going on is that one polarizer sets the polarization of the light (filtering the fraction that is cross-polarized), and then the second one blocks more light, both acting according to the Law of Malus

\(I=I_0 \cos^2 \theta\)

All the light is blocked for perpendicular orientations of the polarizers, and at varying levels of light at other angles. Randomly polarized light isn’t blocked by 50% — the transmitted intensity is roughly 75%. You can see single polarizers in the video, and tell they aren’t blocked by half.

The second piece is in color but only has a still shot, so I don’t know if this is color filters or polarization with birefringent materials. I’ve posted static shots of birefringent materials before, both using a static linearly polarized source (LCD); having the background and/or foreground polarization and birefringent material move might make for an interesting display.

Go Already

I’ve been a little under the weather this week, so apologies for ignoring the blog. Catching up with my internet scouring. Here’s some Music + many illusions from OK Go

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