Explain It Like I'm Five (ELI5) Thread

I got this idea from @LDoBe’s excellent Everyday Engineering thread:

I tried showing my roommate the Engineered Earth video I posted and realized that she didn’t know what frictional forces were. She found the video infinitely less interesting because she didn’t understand the fundamentals. Obviously everyone knows what friction is, but she couldn’t make sense of the free-body diagrams used in the video to illustrate the point despite understanding the significance of the concept to everyday life. I figured there would be more than a few people who are like, “I’m sure this is cool, but I don’t understand any of it.”

What I’ve found is that people don’t like to ask questions because they’re afraid of being patronized for not knowing 100% of the things. The point of “explaining it to me like I’m five” is to get childish pride out of the way and focus on the wonderful things we can all learn together.

There are a lot of people here with diverse backgrounds and differing levels of expertise, so ask a question, and maybe someone will pick up the phone.

To the answerers, assume people lack the basic knowledge to understand what they want to understand. Jargon is your enemy. Define terms. Assume the questioner knows what a five year old would know. Be patient.

The questioner, try to be equally patient. Sometimes when you know a lot about something, it’s hard to figure out how to get other people to know what you’re on about.

#On this hallowed thread, none shall be shamed for not knowing things.


Thanks for starting this. I always learn a lot when I read Reddit’s /r/eli5 group. I’m hoping that the fine Mutants here will facilitate some great learning as well.

To kick things off here, I’ll start.

Someone, please ELI5: voxels.

I hear about them all the time as a construct for 3D graphics and imaging but I’m not really sure what they are. I found the Wikipedia article to be mind numbing. Are they just essentially like 3D sprites?


Okay, I’ll start (well, after @ficuswhisperer of course), since I’ve outgrown most manifestations of shame about my manifold spheres of ignorance.

I’ve always wondered: what exactly is a bond? How do bond markets work? I once had a savings bond that was apparently worth $100 upon maturity. Wasn’t sure how that worked. And every time I’ve voted for some bond measure I’ve imagined it’s like buying a new school on layaway, but I’ve never known who buys them or how anything gets funded that way. Please explain to little Donnie Petersen, age five.

Thank you!


3D space is modeled in a computer using a coordinate system. Like how on a regular 2D graph in math class you have an X-Axis that goes horizontally, and a Y-axis that goes vertically. In graphics, you take that grid, and each square made by the crossing of an X-coordinate and a Y-coordinate is a pixel.

So, while pixels quantize 2-d space, a voxel extends the idea into the third dimension, so that, instead of having a quantized 2-d area (a pixel) you have a 3-d volume of space, a voxel. And you can do all the same transformations on voxels as you can on 2-d images.

If you’d like more detail, maybe I can go further. But yeah, that’s the basics. A voxel is pretty much no different than a pixel, except it’s a 3d volume, instead of a 2d area.

The single best-known use of voxels that laypeople encounter has got to be Minecraft. Typically you want your voxels to be small, so the surfaces of objects aren’t all jagged when they’re rendered. But in Minecraft a voxel is a meter on a side. So you have 1x1x1m cubes that are the “minimum size”.


There’s nothing wrong with not knowing something.

It’s when a person feigns being knowledgeable to the detriment of others that’s problematic.


Say I want to borrow $10,000. Rather than asking for a loan, I offer to sell people bonds. The bond is a promise that I will give them $100 ten years from now. I sell the bonds for just $50. So you pay $50 now for $100 later.

Between now and when ten years from now, you might decide you’d rather have money than a bond, so you might sell it to someone else. Presumably you’ll want more than $50 for it since it’s closer to the time the bond pays out, and presumably no one will pay you $100 or more for it. That’s what bond markets are, places where people buy and sell bonds.

There are plenty of different kinds of bonds out there but ultimately they are just a way of paying interest.


So is it like a series of 2D “points” along an x/y/z axis that represent a 3D object when “combined”?


This thread is going to be a blast. I especially look forward to any macroecon 'splainers, as the finance and economics section of The Economist is still foreign to me even though I’ve been reading it for more than a decade.

A five year old’s knowledge is expressed in a five year-old’s vocabulary. Whenever possible, abide by the Top 10,000 Words guideline. Randall Munroe, who demonstrated mastery of this in his book Thing Explainer, has provided a handy online text editor for such writing.


Oh, I can explain macroecon to you:

It’s bullshit.



A bond was (sometimes still is) a pretty piece of paper with a dollar amount and a date on it. If you wait until that date, you will get the amount of money listed. That date is when the bond “matures”.

Someone (maybe you, maybe your grandparents) bought this bond for less than the money amount listed. Over time, the value of that bond goes from what it cost to buy until the printed date at which time it’s worth the full printed (mature) amount. So, if you’re really desperate for money, you can cash in your bond early, you just won’t get the full amount.

Now, most bonds aren’t actually printed on paper, so you have to look at your online account to buy, sell, or find out when it was bought (and for how much) and when it matures (and for how much).

From a tax perspective, the money difference is not considered interest, and in fact in many cases the money is not taxable at all. Municipal bonds are usually non-taxable.

Municipal means a city, county, state, federal, or other public entity (school district, etc.) creates the bond. They’re raising money for a new school, roads, Olympic stadium, B-1B Lancer, etc.

Bonds are considered safer – less risky – than investing in the stock market or directly in a company because they are issued by municipalities, which have a tendency to not go bankrupt as often as companies do, and/or are considered first in line to be paid off if there is a financial crisis (ahead of stock holders, for example). Also, the tax-free aspect for many of them means you don’t have to make as much profit to cover the taxes as well. Thus, bond rates are usually much lower than the stock market average at any given time.

That’s a start…what are your follow-up questions?


No, they’re literally like a series of 3D volumes. They’re the quanta of a 3D volume, like how a pixel is the quanta of a 2D area. The pixel “fills” the area, while a voxel “fills” the volume.

So if pixels are like the pieces in a fesco mosaic, then voxels are like legos in a replica statue of liberty:

Made of pixels:

Made of voxels:

Although, it gets tricky. For the sake of saving space and also just to make coder’s jobs easier, you typically only model the voxels at the outer surface of the object. Like an infinitely thin orangepeel. So it’s more like you get a 2D surface that “bulges” into 3D space. When you get to HD games modeling of objects, then actually, what you said is pretty close to correct. At fine enough scales, it’s more like a series of volume-less points in space defining the texture and shape of the object’s surface as a cloud of points.


During clinicals, our instructors would always remind us: “Never be afraid to say ‘I don’t know’. We can always correct knowledge and thinking processes. We can’t always correct mistakes—especially grave ones.”


Ha, I typed up almost exactly this, right down to the $50 now for $100 ten years later. Spooky.

I would add the basic definition: that a bond is just a promise to pay a set amount after a set time. And that the promiser is usually a government.


What happens if the bond issuer goes bankrupt? Are you SOL at that point?

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Also yes. It’s tricky. Depending on what’s being modeled, voxels can be either point-like, or particle-like. I like thinking of them in terms of particles personally, because that’s easier for me to visualize. But the point-like application of defining surface shapes is the same thing. Just not so thick and chunky.


Yeah – as a programmer I like thinking in particles. Thinking in 3D arrays makes sense to me.

I do enterprise and system programming and such and rarely need to think of things like voxels but it’s one of those things that I’ve always wondered about. Thanks for helping to explain them to me.


Yeah, what happens then? @anon50609448 and @chgoliz, if Municipal Entity X issues those $100 bonds for $50, they’d need to sell 200 of 'em to get the $10k they need to build that really cheap footbridge on the main highway out of town. And they’re on the hook to pay back $20k on those 200 bonds in ten years. Do they just pay for those bonds with some other source of dough (parking tickets, whatever) that they have ten years to slap together? And are those bonds guaranteed by some other entity if Entity X goes belly-up or something?


“Pimping” used to be a thing in British medical education, and for all I know still is. Instructors would trap students with questions that the student couldn’t possibly know how to answer and then call them out when they tried to pretend they knew. The point was to humble the student and make sure that the student understood the inportance of having real knowledge before undertaking an action. I don’t know if it showed real utility in practice but I like the thought of formally teaching people the value of the phrase, “I don’t know.”

ETA: Against “pimping.”


And by the way, yes, that $100 bond of mine was, in fact, a pretty piece of paper. I think it was a gift from an aunt. Or… no, I tell a lie, I think it was prize money for coming in second place in the 1984 San Diego County Spelling Bee. I also got a combination trophy/desk lamp.


Man, med school in the UK sounds very different than the curriculum here in the US.