Category: Science



The Usual Colors of the Sky

Why is the sky blue? Why are sunsets red? The answers and explanations to these questions can be found fairly easily on the internet. But there are many subtle “Wait a minute…”-type questions in between the cracks that seem to necessitate subtle answers and more “difficult” searching around the internet to find those answers.

So, why is the sky blue?

No, but first, what color is sunlight?

Sunlight spectrum1, from

Visible light generally is from 390 nm (violet) to 720 nm (red). Visible sunlight is a mix of these colors at the intensities we see in the figure above.

, with maximum eye sensitivity at 555 nm (green).



Arendt, Action, and Psychological Stuff

I know next to nothing about Hannah Arendt except what I’ve read on Wikipedia and Reddit (archived).  Nevertheless, it sounds really cool.

She defined the three human activities as labor, work and action, with two mutually exclusive spheres: the political and everything else.

Arendt introduces the term “vita activa” (active life) by distinguishing it from “vita contemplativa” (contemplative life), which represents her understanding of Western society. There are only three human activities: labor, work and action. They correspond to the three basic conditions under which humans live. Action corresponds to the political actions of anyone…

What’s striking to me (and I agree with it) is the stark division between the active life and the contemplative life.  There’s action and there’s talk (so I’m already disregarding Arendt’s actual philosophical definition of “action,” but oh well.)

According to Arendt, modern life is divided between two realms: that of the public in which “action” is performed, and that of the private, site of family life where the father ruled. It is in the public realm where one distinguishes oneself through “great words and great deeds” in the same way as personal glory is attained on the battlefield.

Again, emphasizing how what you do matters.  Your private life is just for yourself.  Your public life affects you and can bring you things (reputation, resources, i.e. money, connections) that don’t really exist or have meaning with just yourself in your private, home life.

Arendt claims that her distinction is unusual and new as it has not been attempted previously by the thinkers who concerned themselves with the subject of ‘human activity’, e.g. Karl Marx. She goes on to explain that “labor” is one of the only three fundamental forms of activity that are the human condition. It is repetitive and only includes the activities that are necessary to mere living, such as the production of food and shelter as well as any material production, with nothing beyond that. The condition to which ‘labor’ corresponds is sheer biological life.

So “labor” is stuff like eating, bathing, cleaning and hygiene, and perhaps some other health and maintenance-related activities.

“Work”, on the other hand, has a clearly defined beginning and end. It leaves behind a durable object, such as a tool.

I don’t grasp the meaning of this.  I’d like to think it means the same as “work” in our normal sense, although that’s probably wrong.  But anyway, surely there’s something other than the “life maintenance” things we do (like eat, sleep, and bathe in private at home) and the political life, which I’d guess, is our normal definition of “work.”  And the point of “work” is basically accumulating resources that allow us to enrich our lives further than what bare life maintenance provides us.


On the other hand, exercise improves mood (archived), and not in a new age-y way but physiologically:

Looking deeper, Lehmann and his colleagues examined the mice’s brains. In the stimulated mice, they found evidence of increased activity in a region called the infralimbic cortex, part of the brain’s emotional processing circuit. Bullied mice that had been housed in spartan conditions had much less activity in that region. The infralimbic cortex appears to be a crucial component of the exercise effect. When Lehmann surgically cut off the region from the rest of the brain, the protective effects of exercise disappeared. Without a functioning infralimbic cortex, the environmentally enriched mice showed brain patterns and behavior similar to those of the mice who had been living in barebones cages.

Humans don’t have an infralimbic cortex, but we do have a homologous region, known as cingulate area 25 or Brodmann area 25. And in fact, this region has been previously implicated in depression. Helen Mayberg, MD, a neurologist at Emory University, and colleagues successfully alleviated depression in several treatment-resistant patients by using deep-brain stimulation to send steady, low-voltage current into their area 25 regions (Neuron, 2005). Lehmann’s studies hint that exercise may ease depression by acting on this same bit of brain.

I couldn’t find anything on the following from a bit of low-effort Googling, but I think there are some who say that action helps to alleviate depression or improve moods as well.  And when I say action, I don’t mean Arendt’s political action nor physical exercise, but just general action, like doing things, instead of sitting and contemplating about doing.

Walking helps with thinking (archived), especially creative thinking.  Dipping into fanciful evolutionary psychology headcanon (or I might’ve also read this somewhere else), if we were all persistence hunters once (or simply had to walk a lot to gather berries and water for our hunter-gatherer tribe), we walked a lot daily, and the body uses this time and monotonous activity to let the brain think.  Many people talk about their subconscious helping them figure out problems – problems that they couldn’t when they were face-to-face with it at a desk – while they were doing something completely unrelated, even really smart people (archived):

Poincaré deliberately cultivated a work habit that has been compared to a bee flying from flower to flower. He observed a strict work regime of 2 hours of work in the morning and two hours in the early evening, with the intervening time left for his subconscious to carry on working on the problem in the hope of a flash of inspiration. He was a great believer in intuition, and claimed that “it is by logic that we prove, but by intuition that we discover”.

Of course, I don’t know what exactly Poincare did during his off-hours and it may not have been persistence hunting.  But even if it wasn’t, as long as it’s something habitual (archived):

To illustrate the differing thoughts and emotions involved in guiding habitual and nonhabitual behavior, 2 diary studies were conducted in which participants provided hourly reports of their ongoing experiences. When  participants  were  engaged  in  habitual  behavior,  defined  as  behavior  that  had  been  performed almost  daily  in  stable  contexts,  they  were  likely  to  think  about  issues  unrelated  to  their  behavior, presumably because they did not have to consciously guide their actions. When engaged in nonhabitual behavior,  or  actions  performed  less  often  or  in  shifting  contexts,  participants’  thoughts  tended  to correspond to their behavior, suggesting that thought was necessary to guide action. Furthermore, the self-regulatory benefits of habits were apparent in the lesser feelings of stress associated with habitual than nonhabitual behavior.


It seems that action improves mood, and I assume an improved mood improves action.  But then if the opposite might be true, why does inaction worsen mood and a worsened mood worsen action?  Again into fanciful evolutionary psychology, perhaps it’s a survival mechanism.  When circumstances are bad, you want to conserve energy and action and stay away from possibly taxing or dangerous situations.  Basically, sit tight and wait out the night/rain/drought.  Of course, when this occurs not because of a lack of resources but some internal mental reason (which is much more likely in modern life), it’s much harder or at least more mentally complex to get out of that spiral.  A modern person’s way out of inaction or depression is not the same as a hunter-gatherer seeing food for the first time in a while (some external thing happening to him) that might quickly improve his mood, spur him into action, and so on and so forth.  The tricky thing is that while action may improve mood, if an internal mental reason is what caused mood to worsen to begin with, the action isn’t targeting the source of depression.  Action in this instance is a solution that’s unrelated to the source of depression/the bad mood.  Action and its positive effects on mood might still be good enough to overcome internally-caused depression.  But I imagine that the disconnect between action and source of depression is why modern depression isn’t easily solved by action and exercise even if it undoubtedly helps physiologically.  It’s interesting and crazy that we’re such contemplative beings with such big brains but we’re still meat and water bags that are heavily influenced by physical, biological, neurochemical existence.

“In r/badhistory, the view that technology is linear gets poked fun of every once in a while. Why is the view wrong?”

In r/badhistory, the view that technology is linear gets poked fun of every once in a while. Why is the view wrong?  Isn’t technology linear? Also, why is the west so dominant when compared to other once great civilizations?


Are you familar with the idea of local maximums? Imagine in a low spot between two hills. You can climb either hill. Regardless off what hill to climb, you are increasing your elevation. But one of the hills will not reach as high as the other.

In evolution, its called a fitness landscape. Paths of technological development can be similar.

A recent question on ask historians involved the development of iron weapons. The answer involved metallurgy – iron is frequently inferior to bronze, and it was only the development of consistant alloys and better techniques that gave iron an edge (a better edge in this case). Focusing on bronze is advantageous – until another civilization manages to be able to alloy a superior form of iron. Local maximums.


What I think is interesting is that once people discover that a new technique for metallurgy creates iron that is better than bronze, everyone starts to adopt it. This is some sort of direction to technology, is it not? One society goes in one direction and discovers a local maximum and another society goes in another direction and discovers a different local maximum. But if these two societies intermingle (whether it’s a peaceful or violent intermingling, take your pick), if the people in the two societies discover that one of the local maxima is higher than the other, then they’ve discovered a local maximum of a larger region and have made a step in the direction of the global maximum. Keep repeating this and as your map gets larger and more societies intermingle, your greatest local maximum gets higher and higher.

At the danger of summoning the hatred of Jared Diamond-critics, I think he mentioned in one of his works that one way he “measures” a civilization is its ability to dominate another civilization and avoid being dominated by other civilizations (whether it’s violent, peaceful, economic, diplomatic, or cultural domination). What I’m saying is, when two societies – each having discovered a different local maximum – intermingle, if one dominates another, they will have succeeded in that domination for some reason. That “some reason” is their local maximum. Once news of this knowledge spreads (if that “reason” can be identified and is made into knowledge), other societies will pursue that local maximum as well. As long as societies have enough knowledge of the past to pursue higher and higher maxima, they will be acquiring more and more things that enable them to “dominate other civilizations or avoid being dominated by other civilizations.” Could this suffice as a kind of definition for “technological progress?” If there is a “linear” component to it, it’s that as our “map” expands, our local maximum of that map increases or at least doesn’t decrease.

Of course, this assumes that knowledge of the past remains and there are no catastrophes that set back civilizations in general. But I think catastrophes setting back technologies isn’t something that goes against the belief of “linear technological progress.” I think even staunch “linear progress” believers allow for the fact that unseen catastrophes can cause set backs, or even that scientific knowledge is not a smooth process. I think the key question that both sides wrestle with is how progress seems to happen over generations, even if key inventions seem to happen by chance (like fermented foods or penicillin being discovered fortuitously by leaving things too long or less hygienic than intended). So could “societal domination leads to the adoption of more ‘dominating’ technologies” be a satisfactory explanation? This does mean that if societies that get dominated had wonderful, advanced technologies that get lost to time, it may be a long time until those technologies are rediscovered again, if at all. That’s just a matter of us not finding those directions in the map that could lead to undiscovered local maxima. The key is that as more people interact and more societies intermingle, as long as we would rather dominate than be dominated, “dominating” technologies are going to be adopted more and more. We could try to describe what exactly are more “dominating” technologies (e.g. faster, cheaper mobility for people, more crops per area of land produced that is sustainable, etc.), but I think it’s easier to fall into incorrect claims with details like that. The key is “What technologies help you dominate other societies (or people) or avoid being dominated by other societies (or people)?”




Jordi Alba ”I sleep for 12 to 13 hours at night. Then I nap for two, three or four hours more. It’s one of the keys to my strength.”

The more you sleep, up to some limit (maybe 8 hours, maybe 12 hours, maybe 17 hours), the more effective you are when you are awake.  I wonder if there is an “optimal” amount of sleep to awake ratio depending on what your daytime activities are.  For professional athletes (though it would depend on their sport), perhaps the optimal sleep : awake ratio is higher than average.  For intellectual activities (though this would also depend on what kind of intellectual activity: logical, creative, using knowledge you already know, or learning and then using knowledge that you never knew before), I wonder what the optimal ratio is.  (Of course there would be individual differences, but let’s say we can average those out.)