Thursday, September 08, 2005

Relativity over breakfast

I think Ben Goldacre's Bad Science column in the Guardian, sometime gets a bit lost in itself, but he's done a good summary of how media science works. We journalists misrepresent it, and then shoot at the misunderstanding. And no-one ever tries to understand it.

I read that this morning, after I'd tried explaining relativity to my daughter Kitty over breakfast.

Well, Rachel and Hannah leave earlier for secondary school, so that leaves just Kitty from 7.30 to 8.45 (plenty of time to explain relativity, I'm sure you'd agree). And she's eight, so it should be no problem!

She started it: "I'm glad I don't move too fast. Because then I'd go back in time," she said.

We'd just read her the limerick

There was a young lady named Bright
Who travelled much faster than light
She started one day
In a relative way
And came back the previous night.

Not only that, but she had other evidence: "It said so on Jackie Chan," she said.

"But do you know why time goes backwards if you go faster than light?" I asked. "It's all to do with Relativity."

"Oh no, not your science stuff. I want a hot chocolate."

"Here's the deal, you get the hot chocolate after I've told you about Relativity."

So I started in: "If you were on a train going at ten miles an hour, and started walking at ten miles an hour, how fast would you look to a person by the track?"

Speeds add up, we agreed, and then I told her that light doesn't work like that. "If you shine a torch forward, it takes a three-hundred millionth of a second to move a meter, no matter where you look from," So if the train is going at the speed of light, and you're looking from the track, you see light that can't leave the torch at all - even though the person in the track sees it leaving the torch, and going at 300 million metres per second.

That, more or less is the experimental reality - found out in the Michelson-Morley experiments.

And there's only one way to make both those viewpoints true: make time different - and make it depend on how fast you are going. So if the train is going at the speed of light, time stops (And sure, if it was possible to go faster than light, it would go backwards - stands to reason).

She listened, got her hot chocolate, and went off to school, promising not to go faster than light.

And later that day, I'm wishing I could break light speed. After the amount of time I've wasted today (trying to make a Windows 2000 boot disk for a friend if you want to know), I'd like to go back in time. Going back and doing more work would be useful.

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