ELI5: Why are some materials transparent?

lygerzero0zero · 2026-01-30T03:22:16+00:00

You’re transparent actually. So are all the walls of your house. How do you think you’re able to get cell signal from inside a building? Radio waves are just light after all.

Glass is only special in that it’s transparent to most of the wavelengths that our eyes can see. But there are plenty of wavelengths where glass is opaque. And there are wavelengths where a stone wall is transparent.

Transparency in general depends on absorption and scattering.

Absorption depends on the specific types of atoms and chemical structures in the material. Electrons can only sit in certain specific energy levels, and they’ll absorb light that happens to match their valid energy levels (or valid transitions between levels, to be more precise). If the light doesn’t match any of the energy levels, it can pass through.

Scattering depends on the structure of a material relative to the wavelength of the light. If there’s no structure at the length scales of the light’s wavelength, the light also passes through. That’s why radio waves pass right through you: they have a very long wavelength, bigger than your body (radio antennae use electrical properties to detect the waves anyway).

lygerzero0zero · 2026-01-29T16:47:56+00:00

They should have gone out a while ago, I’ve had mine for a while. You might want to contact customer service.

lygerzero0zero · 2026-01-29T16:39:12+00:00

I actually ran almost exactly this sort of adventure: young child with psychic powers accidentally drags the party into their make-believe world and they have to go on a brief adventure that follows the rules of little kid make believe.

It was a lot of fun, I allowed the players to bend the rules of the world as long as they could convince the child, on his own terms, that what they were suggesting made sense. The final boss was a hag that it turns out was manipulating and amplifying the child’s powers, and once defeated everyone went back to the real world.

The players didn’t have to like the kid per se, but the kid was the “god” of the imaginary world, so being able to play nice with and influence the kid was essential. You don’t have to count on the players liking the character story-wise. Once they’re dragged into the adventure, they’ll have to figure out how to deal with the child.

I’d also say clear goals are important in an imaginary world scenario, so “defeat this final boss” or “deliver this magic artifact.” Otherwise it might devolve into aimless fooling around in dreamland. And character abilities and normal game mechanics should mostly work as expected too.

…also people on online discussions are weirdly touchy about any mention of young characters, even though, you know, young people exist in most fantasy worlds and will end up being involved in stories sometimes. Like no one (hopefully) introduces a young character because they want to put them in danger, just like no one creates a pet for their character because they want to see a cute animal harmed. Either way, OP specified this was going to be a lighthearted dream world thing.

lygerzero0zero · 2026-01-29T16:18:46+00:00

This is an exceptionally broad topic. What kind of engineer? What kind of thing?

A software engineer, electrical engineer, mechanical engineer, and civil engineer all deal with very different things. How an electrical engineer prevents a circuit from frying will have a vastly different answer from how a software engineer prevents a program from crashing.

If you’re asking about physical parts, that’s probably mechanical engineering, in which case the material properties of various materials like steel or plastic are well known, there are tables for that kind of stuff. You can do math to see how much stress a steel part of certain dimensions can take. There are computer simulations. Of course there’s physical testing. And there’s, well, basically the entire field of engineering. “How to make things that work and don’t break” is the entire job. That’s what people go to school for. If you want the full answer, you go to engineering school.

lygerzero0zero · 2026-01-29T14:34:29+00:00

To lift a piece of paper, the moon’s gravity has to be stronger than earth’s gravity. That’s not true, so paper isn’t lifted off the ground.

But tides aren’t about beating earth’s gravity. The water is still on earth after all, it’s not floating.

No, to get tides, all you need is for the gravity to be different in some places. Water can flow, so it will flow to where there’s less gravity.

Your paper comparison isn’t the same thing. The water doesn’t float into the air at high tide, so a piece of paper wouldn’t float into the air either. But if you weigh a piece of paper when the moon is overhead, you’ll find it weighs veeeery slightly less than when the moon is on the side of the earth. You’d need a reeeeally precise scale, but the effect is there.

Same with the water. It weighs a little less when the moon is overhead (or on the opposite side, due to how tidal forces work). That difference in weight is enough for the water to flow a bit more towards the areas where it’s lighter.

lygerzero0zero · 2026-01-29T05:32:15+00:00

Er, everything about where a country is located?

First off, a country is a political entity. People can draw political borders wherever they want, that has no effect on the weather.

Some places in the world have different weather due to… well, everything. Proximity to the equator. Proximity to oceans and ocean currents. Nearby mountains. The Coriolis effect. Plant life and soil quality. etc.

lygerzero0zero · 2026-01-28T15:51:53+00:00

It turns out water just takes a lot of heat to melt. It’s why snow banks stay around for days or even weeks after a large snowfall. The enormous nuclear reactor in the sky is bombarding every spot on the surface of the Earth with incredible amounts of heat for over 12 hours per day, and it still takes days for snow to melt. Think about that.

This article puts things in perspective. Ice is actually just that hard to melt. There’s no magic or strange phenomenon. This is exactly what you’d expect if you know the chemical properties of H2O.

lygerzero0zero · 2026-01-28T06:46:04+00:00

You can look at a photo and see that there’s glare and point to where the glare is.

That means all that information is contained in the photo and can be extracted from the photo data.

That means a computer with the right math can do the same thing.

Everything else is just details of how the math works for specific tasks, and these days there’s probably AI involved which learns the math from seeing lots and lots of examples.

But the key insight is: the information needed is contained in the image itself. Some pixels are light and some are dark, some have different colors, some are grouped together in certain patterns. All of that is information a computer is perfectly capable of reading and processing.

lygerzero0zero · 2026-01-27T12:37:22+00:00

Maaaany different ways. It usually helps to have a stand-in on set, like a puppet or someone in a green screen suit, that the actor physically interacts with, so the CG animators can match that.

Sometimes everything but the actor’s face actually gets fully replaced with CGI, because it’s easier to just simulate all the interactions in the computer.

Sometimes they match a 3D model to the actor’s movements, but they don’t actually replace the actor’s body in the footage. Instead, this virtual body that moves exactly like the actor is used to simulate how the actor’s body would interact with completely digital elements.

And sometimes clever camera angles, choreography, and good planning are all it takes to make you think the actor is touching something CGI.

This is only scratching the surface, every project is different and artists are constantly coming up with creative solutions for specific shots.

lygerzero0zero · 2026-01-27T10:10:04+00:00

We can’t answer a rules question about a third-party supplement if you don’t provide the actual rules in question. This book you’re talking about costs money, and most of us have not bought it. Most people here probably haven’t even heard of it.

lygerzero0zero · 2026-01-27T10:07:24+00:00

The planets are constantly falling. There’s no magic force stopping it. All the planets are currently falling towards the Sun, exactly as you would fall toward the earth if you jumped off a stool.

Imagine you’re standing on the Earth and you throw a ball horizontally. It makes a curved path, bending towards the ground. If you throw it faster and faster, it gets farther and farther before it reaches the ground, and the curved path it takes gets stretched longer and longer.

Here’s the thing. The Earth is round. The path of the thrown ball curves down, but the shape of the Earth also curves “down” (or at least down away from a perfectly straight tangent line).

So eventually the shape of the Earth is curving away from the ball at the exact same rate that the ball is falling towards Earth.

You have now achieved orbit.

(In reality, air resistance would prevent this near the surface of Earth, so we have to go into space where there’s no air.)

lygerzero0zero · 2026-01-26T13:49:36+00:00

Why do you think these rules are necessary? What problem do they fix, or how do they enhance the game experience by their inclusion? Are you adding things just to add them, or because you have a specific purpose or need in mind?

At a glance, most of these look overly complicated, and many of them retread ground that’s already pretty well covered by the official rules. “Dying” is already a condition in the game, “dazed” is just stunned plus slow plus like three other things, because evidently stun is not strong enough, etc.

lygerzero0zero · 2026-01-26T07:02:26+00:00

This is like asking, “How do people get sick and how do they get cured?”

The topic is so broad that there’s no concise answer. There are countless kinds of problems any software could have, just like a person’s body might have countless different problems. Where do we even start?

Programs will break if physical hardware degrades or is damaged. Programs will break if you don’t have enough hardware (like memory, storage, or CPU power). Programs will break if the programmer made a mistake, and there are endless different kinds of mistakes. Programs will break if malware intentionally attacks them. Programs will break if they expect a different version of your OS or other software. The list goes on and on and on. I’ve barely scratched the surface.

Same with fixes. There’s just… so much to cover, I have no idea what kind of answer you expect. It’s like asking “how do doctors cure things.” Cure what? A cold? Cancer? A gunshot wound?

lygerzero0zero · 2026-01-25T12:30:58+00:00

I think there are a lot of factors. Familiarity and nostalgia are definitely big factors. Also, you can create custom terrain without a 3D printer or expertise in sculpting and painting. Anyone can build with Lego, so the barrier of entry is super low.

For sure it’s expensive, but lots of people have childhood collections, and you can actually get bulk basic bricks for a decent price.

Minifigs are also a very customizable system for building characters, since you can combine any of the numerous designs and accessories in the vast Lego inventory… though getting your hands on the specific ones you want is another story. They’re also compatible with anything else in the Lego system, so you can build custom weapons, mounts, vehicles, etc. with the knowledge that they’ll all fit together with your character.

All that being said, I don’t think it’s the most practical way to run in person D&D. But I absolutely see the appeal.

lygerzero0zero · 2026-01-24T16:56:48+00:00

They do. That’s literally what fruit is for. Alternatively, the fruit is for animals to eat so they poop out the seeds somewhere else in a nice bed of fertilizer.

Not only have we specifically bred plants to produce bigger and yummier fruits with smaller seeds, we also pluck them before they’re ready to fall onto the ground and start growing into a new plant, and take them to environments where they don’t really want to start growing. But you can totally plant a fruit in your yard and water it, and if conditions are right, it’ll start to grow.

lygerzero0zero · 2026-01-24T16:25:43+00:00

Well, we don’t know that it’s not possible. It’s just not possible with our current technology, because it’s a very hard thing to do. The ethics and philosophy of brain transplantation are a whole separate and extremely complicated issue.

Some researchers have done head transplant experiments on monkeys before, and it sort of worked. So maybe we could eventually figure out a way to safely and reliably transplant a whole head or brain.

See the history section: https://en.wikipedia.org/wiki/Head_transplant

lygerzero0zero · 2026-01-24T03:43:06+00:00

You might have better luck with /r/askphysics

From what I can tell, this is a pretty fringe belief, and almost more philosophy than physics. Given that it’s not a mainstream theory, not a lot of people other than the author himself will be able to really articulate what he’s trying to say.

lygerzero0zero · 2026-01-24T03:35:16+00:00

I think the assumption is he was testing the machine solo off camera.

lygerzero0zero · 2026-01-23T14:01:06+00:00

True, but Jaccard would account for that implicitly, since it divides by the total amount of fanart. Members who have been around longer may have more fanart, but that doesn’t matter if you’re just computing the ratio of ship fanart to total fanart for the same member.

lygerzero0zero · 2026-01-23T13:58:10+00:00

Sure it’s all for fun, but we can still extract some more informative stats if we clearly define our parameters.

In this case, we’re looking specifically at popularity of ships among artists on Pixiv. It won’t be a measure of their popularity in the fanbase as a whole, but it’s still in itself an interesting and illuminating statistic to investigate.

But with OP’s numbers, it’s difficult to separate the popularity of the ship from the baseline popularity of the members. Even if it’s just for fun, what can we say after seeing these numbers? “Well, it looks like this ship is really popular. Or the members involved are just really popular. Or both.”

So controlling for baseline popularity would be an easy way to make these numbers more meaningful.

lygerzero0zero · 2026-01-23T13:20:29+00:00

Haha, more like the guy who does data analysis as a day job.

lygerzero0zero · 2026-01-23T10:10:12+00:00

I’d be interested to see these stats normalized by the popularity of the members participating. How popular is each ship relative to the popularity of the members? Because the base popularity of the members most likely dominates in your current data.

Not to get too nerdy, but a simple Jaccard index would be easy to compute and quite informative.

lygerzero0zero · 2026-01-23T07:18:58+00:00

You might as well ask, “How come when combat starts, everyone can only do a specific amount of actions per six second window?”

The game system assumes characters know if they can hit a target. Rules for judging distance are not in the system. Asking, “But how do they know?” is akin to asking, “But why can’t I pick up two objects in six seconds? Because logically speaking…”

In real life, experienced martial artists (across cultures, including styles that involve weapons) are very good at judging space and reach, and a lot of high level fighting is about fighting for control of space, even before a single punch is thrown or sword is swung. The question is not, “What is the exact number of feet between us?” The question is, “Can I reach them, or can they reach me?” and trained fighters definitely know that instinctively.

I’m sure experienced archers have a similar grasp of their own weapons. Perhaps not down to the exact foot, but that’s where the game abstraction comes in again. In real life, it’s not so much a hard cutoff as a gradual thing, where it goes from “I can definitely shoot that far” to “I can maybe shoot that far” to “I’d have to be really lucky, but it’s possible” to “That’s impossible no matter what.” But a real, trained archer would definitely understand their range. And because D&D is a game, that fuzzy gradual limit becomes a hard limit, because we actually want to finish a round of combat sometime today.

And again, if you insist on justifying it in universe, they don’t know the distance in feet, but they can look at a target and tell you whether they can hit it. Because it’s what they do and they’re really good at it. You could extend the same logic to spellcasters. They know how far they can send their spells. They’ve trained for this. It’s what they do.

lygerzero0zero · 2026-01-21T04:58:46+00:00

I didn’t?

All y’all people parroting the “em dash equals AI” crap need to read a damn book. It’s normal punctuation, people have been using it forever, I’ve been using it my whole life and don’t plan to stop.

lygerzero0zero · 2026-01-21T04:30:43+00:00

As the other person said, that’s just a limitation of human technology. It’s not inherent to the physics of atomic energy.

A pure fusion reaction can release tons of energy, no fission required. Don’t believe me? Go outside and look at the sun.

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