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Ask Slashdot: How Would You Explain Einstein's Theories To a Nine-Year-Old?
SiggyRadiation writes: A few days ago, my 9-year-old son asked me why Albert Einstein was so famous. I decided not just to start with the famous formula E=mc^2, because that just seemed to be the easy way out. So I tried to explain what mass and energy are. Then I asked him to try to explain gravity to me. The earth pulls at you because it has a lot of mass. But how can the earth influence your body, pull your feet to the ground, without actually touching you? Why is it that one thing (the earth) can influence something else (you) without actually being connected? Isn't that weird? Einstein figured out how energy, mass and gravity work and are related to each other. This is where our conversation ended.
Afterwards I thought: this might be a nice question to ask on Slashdot; how would I continue this discussion to explain it to him further? Of course, with the goal of further feeding his interest in physics.
Afterwards I thought: this might be a nice question to ask on Slashdot; how would I continue this discussion to explain it to him further? Of course, with the goal of further feeding his interest in physics.
next.
"Einstein figured out how energy, mass and gravity work and are related to each other. "
That would be Newton. Einstein tweaked Newton to cover the extremes.
To acquaint someone with Einstein, start with some of his thought experiments which break Newtonian physics.
"National Security is the chief cause of national insecurity." - Celine's First Law
General Relativity took me 5 years to get my head around as an adult. I taught my daughter, now 11alot about current cosmology. She now has nightmares about asteroid hits and the heat death of the universe, But she loves maths and wants to be an engineer, so I've done pretty well.
I wouldn't try to do it directly. Plenty of other people have covered these areas, and on a level that makes it accessible. For time dilation, Carl Sagan's original Cosmos series had an excellent depiction of time dilation and travel approaching the speed of light. IIRC, part of it was based on a "what if" scenario in which c was something you could approach by peddling a bicycle really hard. When you returned from the ride, all your friends were grey-haired old people.
I'm sure there is some other good programming out there.
For all intensive purposes, "whom" is no longer a word. That begs the question, "who cares"?
By your own account, your son is not asking you about relativity: he is asking why Einstein is so famous (and he is 9 year old).
The proper answer is, then, because he ranked to the top of his field, just like (put here whatever TV competition he is fan of, Disney young singers or whatever). When you get to the top of your field, you get famous. Full stop.
Now, if you really want to introduce him into Einstein's, I can tell how I introduced myself, but I was eleven or twelve back then, which I think makes the situation a world apart.
I happened to start thinking about the relativity principle, the original one, Galileo's (no memory of how I stumbled onto it, though) and felt fascinated by the old man in his ship, trying to decide from within his cabin if the ship was moving or not. From there I moved to the "known fact" that nothing, and I mean NOTHING, can go faster than light in a vacuum (you can disgress a bit here talking about Mach's aether and Michelson-Morley experiment if you want to), and how would the world look like if that were true (I probably had read some of the old mental experiments about trains and watches coming and going, but I've forgotten when or where, probably because all this became obscured on my memory by my read, years later, of both Russell's 'ABC of Relativity' and Einstein's 'The meaning of Relativity' -*you* should read them and you would probably wouldn't be asking this question.
Once I got satisfied about special, I moved to the general starting also on"known" facts (taken by me as granted, back then): energy and mass are somehow equivalent (E=m*c^2) and gravity and acceleration look very much the same but can they in fact be set appart? (hint: gravitity looks "spherical" from the perspective of an observer under a heavy field). Oh, another interesting fact: there can also be black holes under newtonian physics, as long as C stands constant and nothing can run faster than light (in a vacuum -oh! and why does light runs faster in a vacuum than through transparent matter? does something can go faster than light -on said matter? Mr Cerenkov left a message).
The fact is, that though you cannot *demonstrate* Einstein's Special or General theories of Relativity without advanced maths (you can't demonstrate Newton's either), you can *exhibit* them on a credible manner, specially the special one (pun intended), on a two dimensional field, just using basic geometry, so a child can have a grasp of them.
"If you can't explain it simply, you don't understand it well enough.""
-- Albert Einstein
I would ask my nephew that when he was around that age, he starts at MIT next year at 16. I would explain to him that in one year, Albert Einstein changed the face of the world, and made all our lives better. He used his imagination to do it. He wasn't the best mathematician, in face, there were better ones hot on his heels, but he had the ability to imagine how little things work as well as the entire universe. He then set out to prove it. I think kids respond to encouraging their creativity with stories like Einstein's and how he built his ideas on other's ideas. Exposing them to Julius Sumner Miller, Brian Greene and Richard Feynman is also a lot of fun, because they had lots of fun with science. I enjoy talking to kids about science, and seeing their eyes light up. These videos are pretty good. https://www.youtube.com/watch?...
Two twins orbit around each other and then meet. They are both older than each other.
Sounds like you're the one who doesn't understand relativity.
Two twins are set into motion relative to each other, and then left to coast inertially like that. Time passes. Each twin thinks more time has passed for the other than for themselves since they were set into motion. Neither is objectively correct; a third observer could find the same amount of time to have passed for both, or any different ratio of time to have passed for either, depending on how that observer is moving.
But then the twins are set back into motion toward each other. Again, after being set into motion like that, they disagree about how much time is passing for each other, but then, so does every other observer, and about everything else in the universe too. Observers in different states of motion disagree about how much time is passing how quickly where.
The twins come back together and are brought to a stop relative to each other. They have definitive ages relative to each other that they both agree on, as does every other observer in the universe.
The trick is that when they're being set into motion apart, turned around and sent back together, and stopped at the end, time is also passing differently for each of them not just because of their different states of motion, which nobody can agree upon, but depending on whose motion is being changed how much, which is something that every observer can agree upon even if they can't agree on the absolute measure of that motion. (That is, while observers may disagree about which twin is stationary and which is moving, they will all agree that one twin is moving more [or less] now than it was before).
If one twin stayed in the same state of motion the whole time, while the other got sped away, turned around, and then stopped when he got back, then the one who stayed behind is older, and everybody agrees.
In your scenario, it sounds like they both underwent the same acceleration, just mirrored from each other, so both would be the same age when they came back together, and both would agree on that, as would every other observer in the universe.
Other observers moving differently than the twins would disagree on what age they are, but they'd all agree that they're the same age as each other, whatever that age is.
-Forrest Cameranesi, Geek of all Trades
"I am Sam. Sam I am. I do not like trolls, flames, or spam."
I once read an account of a thought experiment where there are a line of cows side by side with their noses all touching a long, straight fence. The farmer attaches an electric fence shocker to one end of the fence and it makes all the cows jump as they feel the shock.
The farmer sees the cows jump one after the other as the electricity reaches each nose
But to a visitor from a nearby city, who happens to be standing at the other end of the fence at the time, the cows all seem to jump up in unison, since the light bringing the image of the far cow arrives at the same time as the electricity arrives to shock the nearest cow.
When the farmer and the passerby meet they find they have different first hand accounts of the same events, proving to the farmer that city folk are ignorant of country ways, and proving to the city slicker that country folk tell tall stories
Nullius in verba