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Hi David;
My fault for creating confusion from the start of the thread.
OK so I’ll apologise if I’ve annoyed anyone with this thread.
I’m happy to bury it and move on.
This will be my last post on it, so I’ll have a go at answering my own questions to clear up any mystery I’ve created.
Here goes:
Question #1:
So if black is the lack of light, can something ever be truly black?
No. In science we call something that is black, a blackbody.
It absorbs light. As it does this, it heats up.
As it heats up, it then gives back the light it originally absorbed.
When it does this, we can see it, so it’s not black any more !
Question #2:
Is outer space black ?
No. Even though when you look up at the sky at night, you are looking at outer space and it might look black .. but its not really.
Space is pretty empty but there’s always a very small amount of stuff there.
So is there a perfect vacuum that has nothing in it ?
(See question #3 for the answer)
Question #3:
Is space truly empty ?
Space is never truly empty. Even in ‘voids’.
So, even if you choose say, a dice-sized piece of space that has no matter in it, it still isn’t empty. It has energy. On average, every cubic centimetre of deep space has about one photon (light particle) passing through it (more photons, if they have lower energy).
What if you block this photon so it can’t pass through the dice-sized piece of space ?
Space itself has energy. Einstein’s theory of Relativity tells us this.
Question #4:
How much energy does space have ?
No one knows but if they did, they’d win the Nobel Prize.
Perhaps a tiny a amount (adults: 10∧15 Joules per cc.), but if you consider a large volume of space, this can be a very big number. For a volume the size of the Solar system enough to power a country for tens of billions of years (adults: ~ 10∧30 Joules).
And that’s the presently thought to be about the lower limit.
Question #5:
What does question #4 mean ?
The energy in Question #4 could be considered dark energy which speeds up the expansion of the universe.
It also means that there is no such thing as a perfect vacuum.
… So, these simple questions have led to a complex issue – Dark Energy.
If Primary School kids can ask questions about dark matter (and they understand enough about it to ask the questions we have seen), then I can see no reason why they wouldn’t ask about dark energy. So how would we answer questions about it ?
I think this is an easy way to give them some of the concepts behind it, whilst keeping it fairly simple.
Sorry for the confusion .. a bit of a crazy idea, I know !
It’s the rain, and an over-active mind, y’know !
(I was actually inspired by reading an article about dark energy. I kinda liked the simplicity of the above approach).
Cheers & Rgds
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