Blog: Science

Most of these posts were originally posted somewhere else and link to the originals. While this blog is not set up for comments, the original locations generally are, and I welcome comments there. Sorry for the inconvenience.

TIL: ophthalmology edition

I started getting noticeable floaters something like 8-9 years ago. (I see I failed to record it at the time, so I'm estimating now.) Floaters are bits of stuff in the vitreous in your eye that, as the name implies, float around and sometimes get in your way. They don't go away. They were quite annoying at first, but over time they became less invasive -- presumably my brain was learning to ignore them for the most part. I'd still see hem but they didn't get in the way as much.

A few weeks ago I noticed/realized that I've been having more trouble reading lately, whether sitting at a computer or reading a book. It wasn't a sudden change -- not the sudden onslaught that sends one for a same-day appointment to check for retinal detachment. I think it's been building for a while and finally crossed some critical threshold. I couldn't quite tell if the problem was obstruction (what floaters do) or acuity, but I'm not generally having acuity problems.

I had a checkup scheduled for earlier this week anyway, so I asked my ophthalmologist to take a look. She said yup, sure are a lot of floaters and stuff in there. I asked if she could compare what she's seeing now to the last photo she took of the inside of my eye, but that photo didn't help much. She sent me to a retina specialist just to be safe.

I saw that specialist this morning and learned some new things. Read more…

Today I learned (veterinary edition)

Orlando saw an ophthalmologist today because his pupils barely contract and my vet wanted a consultation. He's been somewhat like that since I adopted him six years ago (I've never seen pupil slits), but it's become more pronounced recently. Google had told me that this can be an age thing and it can indicate hypertension. We checked his blood pressure recently to evaluate the latter and got ambiguous results; my vet also says that measuring feline blood pressure is kind of dicey. (They took three readings in one visit, and one of them was not like the other two.)

Things I learned today:

  • Orlando is almost certainly older than we thought he was. We thought 10ish and are now bumping that up to 12ish.

  • Iris atrophy is a thing that happens in older cats where the relevant muscles just don't work as well any more. I wonder if that happens in humans too -- never heard of it before. (The ophthalmologist didn't find anything else wrong, though didn't rule out hypertension and suggested rechecking blood pressure, so this is the working theory. His optic nerve and retinas look fine.)

  • They use the same numbing drops on cats that they do on people, complete with orange dye -- which apparently makes (something) easier to see, but I've failed to retain what the (something) is.

  • Orlando's ocular pressure is the same as mine was at my ophthalmologist visit on Friday. But mine's the result of glaucoma drugs and his comes naturally. So, no worries there.

  • He has a tiny cataract forming in one eye -- something to check back on later, but nothing to do now. I giggled at the mental image of Orlando wearing glasses.

TIL: equinox, kind of

Yesterday was the equinox, but I couldn't help noticing that sunrise was at 7:07AM and sunset was at 7:16PM. That stretches the definition of "equi" a bit. Looking ahead, the day won't be within a minute of 12 hours until September 25 or 26. (One's a minute longer, one's a minute shorter.) So off to Google I went.

There are two things going on, it turns out. The first is that the equinox is relative to the center of the sun, but we count sunrise and sunset from when the top is visible. But that only accounts for 2.5-3 minutes at my latitude.

The bigger factor is atmospheric refraction: after the sun has actually set (all parts past the horizon), or the reverse in the morning, you can still see the sun. What? Yeah, apparently you can look westward at sunset and see "the sun" even though the sun is not in your line of sight; light bends. This effect varies with atmospheric conditions, but is usually good for about six extra minutes of day.

I said that I won't see a 12-hour day here for a few more days. Apparently that effect gets stronger as you move toward the equator; this site says at 5 degrees North that date isn't until October 17. It also says the day is never exactly 12 hours at the equator, when I thought the equator was the one place where you had reliable 12-hour days all year. Today I learned.

I wonder -- because I'm the sort of person who wonders about stuff like this -- what the effect is in halacha, Jewish law. The day starts at sunset, but when beginning Shabbat we add some extra time just to be safe -- 18 minutes in most communities. That's l'hatchila, what you should do from the outset, but b'dieved, after the fact, if you cut into the 18 minutes with your preparations, it's ok because it's not actually sunset yet. Except... maybe it is? If you have a bad week and light candles two minutes before (nominal) sunset -- when you can still see the sun in the sky, except it's not there -- have you kindled fire on Shabbat? Or do you go by what you can see anyway? I plan to ask this on Mi Yodeya if it's not already there, but first I have to finish Sukkot preparations.

I later asked on Mi Yodeya but didn't get an answer. Much later, I asked on Codidact.

What would be different if humans had broader visual spectrum?

Somebody on Worldbuilding (about developing fictional worlds) asked how having a broader range of vision, into the infrared and ultraviolet, would affect what people see. Having a tiny bit of relevant personal experience, I answered: Read more…

Astronomical puzzle

Unless you're on the equator, neither the earliest sunset nor the latest sunrise of the year is on the winter equinox (source). In Pittsburgh, the earliest sunset is usually around December 9 or 10. People who keep Shabbat tend to notice this.

This happens because apparent solar time doesn't line up exactly with mean solar time. The day isn't consistently (or exactly) 24 hours long, and "noon" usually isn't exactly 12:00. Plus there's some shift because of latitude. Fine.

I wondered why there wasn't a corresponding effect at the summer solstice, and played around with this slider to map it out. There actually is an effect, but it's much smaller -- the earliest sunrise was parked at the same time (rounded to the minute) from June 10-19, and the latest sunset is parked at the same time from June 23 - July 1. So in the week or so surrounding the solstice there's barely any change, while in December the boundaries more more visibly. The latest sunset is June 23 which is barely past the solstice, but it's also July 1 (and every day in between of course). And the earliest sunrise is only a couple days before, but also a week before. So what I notice is "earliest sunrise June 19, latest sunset June 23", even though those bands are wider. In the winter, on the other hand, sunset has been creeping later for a week and a half when you get to the solstice.

I guess this, too, is because of latitude, but it's still not intuitive to me. I wonder what's still wrong with my mental modeling.

Purim science?

One machine-learning technique is to pit evolving neural networks against each other in cage matches and then learn from the results. This is called Generative Adversarial Networks (GANs).

At yesterday's Purim festivities somebody described the following cutting-edge research, and I remembered just enough keywords to be able to find the paper later:

Stopping GAN Violence: Generative Unadversarial Networks Samuel Albanie, Sébastien Ehrhardt, João F. Henriques While the costs of human violence have attracted a great deal of attention from the research community, the effects of the network-on-network (NoN) violence popularised by Generative Adversarial Networks have yet to be addressed. In this work, we quantify the financial, social, spiritual, cultural, grammatical and dermatological impact of this aggression and address the issue by proposing a more peaceful approach which we term Generative Unadversarial Networks (GUNs). Under this framework, we simultaneously train two models: a generator G that does its best to capture whichever data distribution it feels it can manage, and a motivator M that helps G to achieve its dream. Fighting is strictly verboten and both models evolve by learning to respect their differences. The framework is both theoretically and electrically grounded in game theory, and can be viewed as a winner-shares-all two-player game in which both players work as a team to achieve the best score. Experiments show that by working in harmony, the proposed model is able to claim both the moral and log-likelihood high ground. Our work builds on a rich history of carefully argued position-papers, published as anonymous YouTube comments, which prove that the optimal solution to NoN violence is more GUNs.

I haven't read the full paper yet, but on a quick skim it does not disappoint. More info.

I'm delighted to see that the paper was submitted to SIGBOVIK 2017. I had no idea that Dr. Bovik had his own SIG.

ETA: Not only was that paper submitted to SIGBOVIK, but SIGBOVIK is a real thing. How did I not know about this gem from my alma mater? (Sadly, this year's conference starts at 5PM on a Friday, which would be challenging. Maybe I'll have better luck next year.)

Things I learned on the way to looking up other things

I forget how I got there, but I recently found two interesting posts about my curious-but-not-very-useful "superpower". This Guardian article (from 2002) talks about animals (and people) that can see into the ultraviolet spectrum. Did you know that raptors can see into the UV? Do you know why that's important? Because rodents -- that is, prey -- emit urine trails, and urine is visible in the UV spectrum (as anybody who's tried to find and clean pets' urine stains knows).

And then there's this fascinating post from someone who sees into the UV (due to aphakia), in which he describes and shows what he sees and talks about some cool testing he did. It's hard to evaluate such things when monitor calibration is in play (do you see what I do on my monitor? probably not), but it looks like "black lights" are lighter and more purple for him than for me.

One of the ways he tested the bounds of his vision was with a simple prism. I never thought of that. Now, where can I find a prism? :-)