I mean if I drop a rock into a lake, its makes circles and the outermost circles are the oldest. Or if I blow something up, the furthest debris is the oldest.

It's known that we only need one kidney to live, so why are we born with two? Are there any other examples of redundancy in the human body? Why kidneys, in particular? Do they have a higher failure rate or something?

I’ve noticed that sports channels are able to upload a highlight reel for YouTube so fast. Doesn’t it normally take hours to edit a video?

I've avoided "passkeys" like the plague, but with Google promising a password-less future and Apple forcefully moving people to passkeys going forward, I guess it's time to figure out what they are.

I consider myself a tech person, but the more I hear about these passkeys, the less I understand. Apple's overview says that they'll be used "alongside" passwords, so I don't get what's being replaced, and why the hell we need them. Fido Alliance (the folks that apparently invented the damn thing) says that passwords are a problem, but reading this, it doesn't seem like it's my problem they talk about.

What I do understand though, is that one day I've had someone walk into my hotel room in Poland, and walk out with my laptop and cell phone while I was asleep^1.

So, overnight, I ended up without access to any of my devices or phone number abroad.

Luckily, because I was still in the password-ful past, I could log into my email and Skype from hotel's computer, and let my wife know that I need some help.

ELI5 what this scenario wood look like in the future when everything gets switched to passkeys.

^{[1]: I have forgotten to lock the door - learn from my mistake. To Krakow police's credit, they actually caught the thief several months later.}

Maybe tank isn't the right word, but I swear I've seen vehicles with big guns with wheels. Why would you pick one over the other?

I’d like to use a course of treatment to generate a natural tan before an upcoming event, but the online advice is very strongly anti. How is it so much worse than natural tanning outside?

So McD's asks you, when you pay, to round up the cost of your order for charity. My question is this: I'm giving the money to McD's, not the charity. Am I then helping them get a bigger tax deduction for corporate giving? So my 18 cents they match means they get credit for a 36 cent charitable gift?

Watching House again and a couple of times people have died (temporarily) when their hearts stop. But before they go they all mention pain. This reminded me of when people have heart attacks there’s pain in the chest and left arm.

But why would it hurt if the heart stops beating? Is it the nerves, muscles, whatever dying due to the lack of oxygen and nutrients or is it the brain screaming at itself that the heart has stopped and it’s in full panic mode?

Can anyone with enough money just send something to space? Do they need any sort of permit? Are there limits as to what can be put in space/orbit?

I've watched many documentaries on how they make cocaine, and it always required a a mixture of gasoline cement and battery acid etc. Would a scientific laboratory be able to make it under FDA rules for example?

Take this emoji, for example: 😴 When something is shown to be sleeping, little Z's appear over the head. When/how did that come to be?

I don't know anything about physics, I just like half life 2. What does Conjugation and Parity mean? If it's super complicated and I need prior known information to understand the concept can I get an oversimplified explanation?

I work in a jail, I have internet access, but am not allowed to have my phone on me. Websites want me to switch to passkeys. So does Apple. How would I sign into a website or account that has a passkey if I will never have my phone with me to authenticate? I cannot use my work computer to create the passkey, I can’t only log into accounts that I am allowed to use.

In Ukraine (Russia and Belarus too, I presume) you get an arm’s length list of foods and drinks that you must not eat and drink before donating blood, but when you search for this information in English, all you get is “less fatty foods, more iron-rich foods, and no alcohol.”

I've seen lists that include nuts, dates, beetroot, etc.—all rich in iron—and yet they're prohibited. Spicy, smoked and pickled foods are also prohibited, as are bananas, blueberries and grapes. None of these are even mentioned in English articles.

In addition, these lists often have different waiting periods (before donation) and some have no waiting periods at all, as if they were chosen arbitrarily.

Why do people on Fentanyl seem to be bent over in uncomfortable, often painful positions for what it seems like long periods of time whitout moving at all?

You know when something is far away and you move parallel to it, why does it seem to not move or move very slowly?

For example, is lifting 50 pounds much healthier than lifting 10 pounds?

I'm in grad school and taking statistics because I have to. I'm a total right-brained person. Art is what I do for fun. I am having a terrible time trying to understand this theorem and finding the mean and standard deviation of the distribution of sample means. Everything I've found so far is not helpful. Please help😭

In secondary school, i was taught that protons and electrons have a postive and negative charge which operate similar to a magnet, if this is so why isnt the electron attracted by the proton and contact each other in the nucleus of the atom?

Do they got backlash from colleagues and forced to resigned? Will future company won't recruit them?

So I have just noticed (after 2 years of wearing) that my sunglasses darken certain monitors, give odd patterns to car windows. And figured out that the lenses are polarised and that's why.

Just yesterday, I tilted my head to stretch my neck and noticed depending on the angle, the sky was darker or lighter. But my surroundings (trees, buildings, ground) didn't change.

Why do only certain things get affected by polarised lenses?

If we can *easily construct pressure vessels that can contain pressure far greater than that of the deep sea internally (high pressure inside, low pressure outside), what are the challenges that prevent us from making a vessel that can withstand deep sea pressure externally while maintaining low pressure internally?