Umm - thinks - is it possible to radiate in one direction only, or only in a few? Or is 'radiate in all directions' an absolute tautology, in all circumstances? Answer on one side of the interweb only...
It's certainly possible to radiate in one direction only. Your nearest flashlight should provide an example. Or, if you want to be picky about the bulb in the flashlight, the nearest laser pointer.
Mm, I was definitely thinking that the source radiates all around, and then you can grab that and focus it after; I have no idea how lasers work, but I'll take your word for it gladly.
The second question, of course, that then arises: does that answer apply in a more primitive society where it may be physically true but no one knows that, because they only have candles and lamps and no lasers at all; can a phrase be tautological in context, where it's not in physics...?
You can read the Wikipedia article about lasers if you really want to know. But the fact that they send out all their light in exactly the same direction is one of the major things that make them so useful.
And since a tautology is a semantic thing, it doesn't have to care about physics. But I suspect that the lamp that shines in one direction only is an old enough concept (all it takes is a flame and a box with only one opening, after all) that "radiate" doesn't necessarily mean that stuff is being sent out in all directions. Far from sure, though.
Radiation is usually isotropic, but a radiation source can be partly shielded so it only radiates on one side. (Think of a charcoal grill. Light and heat radiate up and sideways, but the base of the grill mostly prevents it from going down.) An individual piece of charcoal may be radiating in all directions, but a person looking at the whole grill from across the yard would not perceive it on that scale.
Clear as unshielded glass, thank you - and a new word, too (isotropic - I have almost no scientific vocabulary at all. And yet I aspire to write SF. That's 'aspire' in the standing-at-the-bottom-of-the-mountain, gazing-up-in-awe-and-wonder sort of sense...).
"Isotropic" is a great word, if you're just starting to build your scientific vocabulary. It means something is the same in all directions. If there is more in one direction than others, it is "anisotropic." If you're looking from a distance, the way we look at stars, radiation is isotropic. But if we were close enough, there might be enough anisotropy to matter, like with the grill example.
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Date: 2006-07-06 05:54 pm (UTC)(no subject)
Date: 2006-07-06 06:09 pm (UTC)The second question, of course, that then arises: does that answer apply in a more primitive society where it may be physically true but no one knows that, because they only have candles and lamps and no lasers at all; can a phrase be tautological in context, where it's not in physics...?
(no subject)
Date: 2006-07-06 06:18 pm (UTC)And since a tautology is a semantic thing, it doesn't have to care about physics. But I suspect that the lamp that shines in one direction only is an old enough concept (all it takes is a flame and a box with only one opening, after all) that "radiate" doesn't necessarily mean that stuff is being sent out in all directions. Far from sure, though.
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Date: 2006-07-06 09:52 pm (UTC)(no subject)
Date: 2006-07-06 05:59 pm (UTC)(no subject)
Date: 2006-07-06 09:57 pm (UTC)(no subject)
Date: 2006-07-07 01:42 am (UTC)(no subject)
Date: 2006-07-07 01:57 pm (UTC)