I'm late to the game but bringing my band geek knowledge to try and ELI5.

The white and black things you press on a piano are called keys, but that's not what it means when we talk about the KEY of a song. If you made a song using all of the strings on a guitar or all of the keys on a keyboard together randomly, it would not sound like MUSIC, it would just be noise.

If you make up a song and sing it to yourself, you could then go over to a piano and pick out what the notes are, and write them down. There will be a KEY that is most natural for that collection of notes. For instance, if the notes you wrote include a lot of B flats and E flats, your song's natural KEY is the B Flat Major Scale, which goes B flat, C, D, E flat, F, G, A, B flat. (When you are learning any instrument including voice, you will learn all the major and minor scales.)

So a song is just a series of notes with a set relationship between them. You could transpose the song you just wrote (change the notes, keep the relationship between notes the same) into any KEY, although it might change the mood of the song. Changing the key is useful for singers if the song in its original key has some high or low notes they can't hit. But if you want to play music with more than one person/instrument, you all need to be playing in the same KEY.

International athletes already have lots of opportunities to leave the country for competitions, they just have to stay once they are there. Happened literally dozens of times during the Cold War. As for visas, the US has given EB-1s to lots of athletes from other places. I'm a figure skating fan and due to the scarcity of male partners in dance and pairs, it is very common for US ladies to find partners abroad and bring them over with the EB-1. In years past, Russia didn't even quibble or try to prevent skaters from leaving, as they view individuals as disposable and easily replaced. There are more reasons than war for some athletes to want to leave Russia!

So let them defect and represent other countries.

If you live in the same place for one entire year, you will notice that the sun rises and sets in a slightly different place each day, eventually returning to about the same place it started. I notice this in my own house, because the window from which I can best see the sunset changes through the year! Agriculture, which allowed people to stay in one spot for extended periods of time, made it easier for humans to notice these changes relative to their fixed surroundings.

Lots of good explanations here. Essentially we usually want to make sure something cooks through without burning on the outside, and thermal transfer takes time. Most baking temps top out around 450F, except commercial pizza ovens, which can be as hot as 1000F and do bake a pizza in literally one or two minutes. That works because pizzas are flat and thin, and cook through quickly.

Just adding that smaller changes in time/temp are used deliberately by cooks and bakers all of the time. It's common for muffin recipes to have the first 10 minutes of cook time at 50 F higher to activate the baking powder and make them rise quickly. Then the oven gets turned down to make sure they bake through without burning. Likewise it's common to sear meat at high heat in a pan and then put it in the oven at a lower temp to cook through.

But there are actually lots of examples of the opposite of your question--cooking something longer at a lower temp. Immersion cooking (sous vide) uses pretty low temps (less than 200F) and can hold a protein at that temp for hours without overcooking. A crock pot or slow cooker also uses this "low and slow" method.