Re: Questions (Space)
- From: Ric Locke <warlocke@xxxxxxxxxxxx>
- Date: Thu, 6 Sep 2007 00:43:06 -0500
On Thu, 6 Sep 2007 05:47:00 GMT+1, Tina Hall wrote:
Ric Locke <warlocke@xxxxxxxxxxxx> wrote:
Tina Hall wrote:
[...]
How are signals transported through space? I know radio bounces
around in the atmosphere (another one of those vague snippets), and
there's nothing to bounce in space. The folks that went to the moon
had contact with earth, so how did the data get from there to here?
(Link to simple information also welcome.)
I'm sorry, I don't have any links.
That's fine. Some people just like to dump links on me, and for this I'd
even reboot and look at sites. :) (My usual answer to such is known to
at least some people, so I add that it's welcome whenever it is.)
Light and radio are the same thing;
Hang on there; huh?
the general term is "electromagnetic radiation".
So you mean that it's in the same broad category, not that a radio
starts playing music if someone points a torch at its antenna.
(Electromagnetic radiation is something I can't picture.)
Don't feel bad. The scientists and engineers had a lot of problems with
the concept when it first came up, and the techniques for dealing with
radio and light look quite different. But a very bright guy called James
Clerk Maxwell came up with equations, and they work the same way for
radio as for light, and they always work, so the scientists shrugged and
went with the program. Look at it this way: an elephant and a shrew look
very different and don't appear to have much in common, but both of them
have warm blood and bear their young alive. That is, they are /mammals/.
"Electromagnetic radiation" is the "mammal" in that analogy.
Radio gets here from the moon the same way light does -- in straight
lines, through spacetime.
Waves? Those things with frequency in Hertz? (I can follow that, even
that light and radio look the same, perhaps with different frequencies,
but I can't wrap my mind around the idea that what lights stuff so I can
see it is the same that is transmitted by radio.)
Yeah, although in my opinion the whole "waves" thing tends to be a
distraction. There's one set of equations (Maxwell's) that describes
waves, and another set (from quantum physics) that describes particles,
and /both sets work/ -- a scientist or an engineer just picks the set
that works best (or is easiest to calculate) given the problem at hand.
Thinking about radio as waves and light as particles is usually the best
way to go about it, but there are exceptions, and the math works either
way. For the rest of us, it's best not to try for too concrete a
visualization; just think of something, nebulously defined, that travels
in straight lines at the speed of light, and you'll have enough to start
with.
If it helps to unify the concepts, think of radio as big and cool, while
light is little and hot. (From another very bright guy, called Stefan
Boltzman.) Do you have an electric stove or heater? When you turn it on
it's first just warm, then it starts to glow -- that is, at first it
makes electromagnetic radiation you feel as heat, then it gets hotter
and starts to make light you can see, too. Nothing changed but the
temperature. It won't make radio waves, but that's because you can't get
it cool enough.
You only need to "bounce" radio, or light, when there's something in
the way (perhaps a planet, such as the one you're standing on) and you
need to get it around the corner.
Makes sense.
You can't see the moon from everywhere on Earth at once, so the space
guys have radio receivers scattered around that are connected to
telephone lines. Whichever receiving station can see the moon can
also receive radio from there, so it receives the signals and
converts them to a telephone call back to HQ. Sometimes the receiving
stations are satellites, but the concept is the same.
Interesting.
And radio waves don't really "bounce" off the atmosphere. That's a
simplification sometimes used as jargon;
Which is just right for me. Get any more complicated and I am lost. I
need something I can picture. Shapeless theories and naked formulas
produce no image, and thus no comprehension.
people also say "hop" for the same concept.
Well, I chose 'bounce' because it sounds funny. (Think flummy. I don't
think the actual signal is anywhere ball shaped, not even a tiny dot
kind.) I could have said 'reflects back from' or something else. :)
The reality is much more complicated. I can try to explain if you
like, but it may be too much information.
If you can create a coherent image without complicated words. I doubt
that that's likely, though. (The path of comprehensive explaining
something to me is very narrow, the chance is much bigger that you miss,
I get a headache trying to understand, and both end up frustrated.)
Yes, I've noticed that. From my side -- if I try to make an explanation
too simple, sometimes people get offended at my treating them like
children. So I have to balance it out a bit, and it's hard to tell just
where the break-point might be. Causes headaches :-)
Right now I picture a wave, which looks out of place if I mentally place
that 'bouncing' off the atmosphere, or even just travelling straight,
because I don't think it physically moves that way (instead of
straight). But I can imagine (and understand) a current getting bigger
and smaller (also a wave), I just don't know what it is that gets bigger
and smaller with the radio thing (or even just sound, what it is that
hits the ear and does something in it so I interpret it as sound).
My main interest is a signal in space.
For the aliens I'd like one that's sort of stationary, covering a
certain (very, very large) area (a thick-shelled sphere, no signal
inside, no signal outside). (The weird theory thing that needn't be
humanly doable. Better understanding would of course be an advantage.
Not that I need to write an explanation, the characters aren't supposed
to find out the mechanics behind it anyway, it's just some mysterious
alien thing. But I'd like some kind of alien signal type. :) )
Stationary I can't help you with. You're right about the "shell" effect.
If you had a radio transmitter out in space somewhere, turned it on, ran
it for a while, then turned it off, what you'd get is an expanding
spherical shell. The thickness of the shell would be speed of light
times the time the transmitter was on, and the radius would be the speed
of light times the time since you switched on (outside) and off
(inside). A spaceship traveling faster than light could go somewhere
inside the thickness of the shell and receive the transmission; if it
went farther away it would get nothing because the signal hadn't reached
that point yet, and if it went closer it wouldn't hear anything because
the signal already went by.
A bright light would do the same. The spaceship inside the thickness of
the shell would see the light; outside or inside the shell, nothing.
This 'how did they send something from the moon' is for the spacefaring
human crew. I assume that travels at the speed of light. Not because you
say it's the same (I still don't get that), but it's one of those
snippets floating around in my head.
Anyway. Thanks! :)
Hope it helps. Maybe after you've digested that a bit some of the other
concepts will be easier.
Regards,
Ric
--
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