Hacker News Reader

Comment by leemailll | Hacker News Reader

Isn’t this common sense?

Common sense is, if I can see the sun through it unblocked, it must let light through, and light gives me vitamin D, right?

Common sense is a function of individual's level of knowledge. For vast majority of people, "common sense" would dictate answering this question "yes", even though in reality, the answer is "no".

I knew about this - and I think that if you have had a deficiency of Vitamin D your doctor might have told you about it.

But I'd wager to say the majority of the population that didn't consult a doctor due to a deficiency won't know this. (Unless, perhaps, when they studied something in the medical field).

Who cares if it's common sense? Common sense is a very bad way to make conclusions.

How could the fact that glass blocks UVB but allows UVA and Light be common sense?

I think it's one of those things that should be common sense but we don't generally think about it hard enough. By that I mean everyone probably could figure it out if they just gave it about 30 seconds of thought. I clearly remember the day I learned this back in high school. My physics teacher was discussing the refraction of light in materials like water and glass and the conversation moved into how materials can break up the components of light (like a prism). Another student was trying to make sense of this concept of light breaking down into frequencies and its component parts but still be light after being broken down. Forcing us to think about it ourselves, the teacher asked the class two questions: 1) Have you ever gotten a tan anywhere on your body on a long car drive in the summer? Everyone thought for a moment and answered that they hadn't even gotten so much as a farmer's tan on their arm to which he asked... 2) Why?

This forced us to think about it and realize that the window was doing more than just refraction and was stripping out or absorbing part of the light and even though it appeared as the same light to us, whatever was being removed must have been in the spectrum of light not visible to humans.

So we all intuitively know this, but never stop to actually think about it.

Doesn't seem like much intuition was had in your example, to be honest.

The teacher primed you with "Why have you never gotten burned on a long summer drive?" and then you bought that as fact and backsplained it with some basic prism experiments, the backsplanation not really mattering once you buy the fact from the teacher.

In other words, I'm not sure what 30 second thought process you think the average person can walk through to replace a teacher telling you the fact outright.

Once you know a fact, people can "intuit" any explanation. Just talk to children and listen to their bizarre theories -- but I would not call that intuition because they cannot arrive at the original fact that way.

Besides, my intuition is the opposite. My friend was a truck driver and said he'd get sunburned hands. He always kept sunscreen in the cabin.

My point was that once you learn the basic physics underlying this, you should be able to come to the proper conclusion about the vitamin D question easily enough. Every person going through the US school system is required to take a basic physics course, as far as I know. So every child who receives a HS diploma in the US should know this basic concept and, if they actually thought about it, should be able to figure it out.

I think you're confusing the underlying theory with us encountering the question on the day we learned it and then dismissing the fact that we were primed with the current conversation to know the answer. What I'm saying is that once we had that knowledge about the underlying physics, the same question(s) could have been posed weeks or months later (with no priming) and we should have been able to figure it out.

I, for one, can't really think of any daily experiences that would count as evidence for or against glass being transparent to UV. Maybe if long drives in sunny weather are a typical experience to someone, it'll be common sense to them, but I'm rarely in a car for longer than couple of hours at a time and I develop tans gradually enough I can't really notice it in span of days, let alone hours. My answer to your teacher's question 1 would be "no idea" since I wouldn't have paid attention to it in the first place.

Of course, given a premise "skin doesn't tan when sitting in a car", I think it's a good explanation for the subject.

So in a physics class, while learning about refraction, you were primed with a fact that you hadn’t personally noticed before and from that experience you deduce that this should be common sense?

It's not that we hadn't noticed it before. It's that we hadn't thought about it before. We all knew from experience that none of us had gotten any sort of tan through glass when asked. We just never thought to think about why. And before that day, we didn't know enough to answer the question. The fact that we were "primed" is just happenstance because the question came up during the learning process. Once we knew the physics (which all HS students in the US learn), the same question(s) could have been asked on another day when we weren't "primed" with the discussion and we would have been able to deduce the answer. For example - if that anecdotal evidence never came up the teacher could have put it on the final exam and we should have been able to figure it out. Again, my point is that anyone who went through the US school system and theoretically has the capability of answering the question if they actually thought about it. But most don't. That was my only point, really. It should be common sense, but isn't because no one actually gives it any consideration.

I've occasionally posed this question to people during casual conversation, and I've always received the same answer - 'of course!' (... you make vitamin D behind glass).

It's still not clear to me if there are some types of glass that do allow vitamin D synthesis or not.

From my understanding, UVB is required for vitamin D synthesizing by your body. If the glass blocks UVB then you're out of luck.

No.

Reply on news.ycombinator.com