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Inevitability
james_nicoll
Threads like this one of on missiles in space are what led me to what Winchell Chung called Nicoll's Law.

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Tracking objects in Earth orbit is one of my big astronomical pastimes.

It says something about usenet that I had to check the date to make sure this was a current debate on stealth and space, and not one of the previous ones.

So is Stealth in space the Goodwin's Law for space combat? I'm inclinded to think so, as stealth in space tends to absorb all other topics in a thread.

I was wondering if it's really support for the general validity of Nicoll's Law if it's the same damn people over and over again.

It actually, in a relatively similar form, came into play on a Star Trek board I follow. There was a person who felt it was scientifically implausible that in the Trek universe, starships and starbases have sensors which can detect objects that are whole light-years away when, of course, they'd be impossible to spot from so far away.

(Of course, the Trek universe has the magic cloaking available for starships under the right circumstances, but that was left blessedly to the side of that argument despite new people jumping into it. I'm just amazed that of all the things in Trek Technology to cry foul on, he called it on sensors.)


I've been dreading going back to that thread - exactly because of Nicoll's Law.

I think that thread requires you to formulate a corollary to Nicoll's Law: Even threads that are not about stealth in space eventually become threads about stealth in space.

I suppose somehow the corollary should contain a statement that it is transitive with the original formulation of the law, but I'm not sure how to word that.

- Ken

I'm sorry to say this, but Nicoll's Law, well, it Just Ain't So. It seems to be based on a mistaken claim by one poster about the amount of heat that can be radiated through a solid angle and the size of the radiator required to do so. Lest the dispute start up again, let me just say I've already checked with someone who teaches thermo for a living, and not at a commuter college either. Also the disproof is rather easy.

What do you think Nicoll's Law says?

Your formulation assumes that stealth in space is impossible, does it not? If that's not true, then the law fails for vacuous reasons. I may be misreading the Law, but if that's the case, I would suggest you change the phrasing to "attempts to point out".

That's the argument about "perfect reflectors", no?

Do how about we concede that yes, stealth in space is perfectly plausible...if you have sufficient unobtanium in order to construct theoretical systems that border on magic.

Personally I'd just use radiators that dump the infrared directly into hyperspace, but that's just me.

Er, no. I'm pointing out that a great deal of effort has been expended to show why flashlights are impossible. That doesn't necessarily mean that stealth is 'possible'. Just that the attempt to portray it as impossible due to just plain good physics was, at best based on a complete misunderstanding of physical law, at worst, a rather pathetic attempt at intellectual bullying.

I'd also like to point at - again - that the whole stealth scenario is premised on other magical technologies, like closed-loop life support. The whole business strikes me as straining at gnats but swallowing camels, about on a par with Lister deciding his chances of snagging Wilma were zero, since Wilma would never leave Fred.

Only a whole lot less entertaining.

Sorry if I'm adding to the problem, but I just wanted to make sure I understand: you're saying the main argument for why stealth is _impossible _ was based on faulty physics, but on the other hand the major arguments from the pro-stealth side are generally based on crack science? Am I summing this up correctly?

Bruce

Um, I'm not following you on the latter bit, but yes, the idea that directional radiation is hard to do is definitely based on faulty physics. I'm not sure what the 'major arguments' are on the pro-stealth side other than this.

Anyway, to return to the main point I was making; I think Nicoll's Law should be rephrased so as not to favor one side over the other.

Hm. Closed-loop life support is a magical technology, which you can purchase for $79 plus shipping and handling from a company in Arizona.

The problem with perfect mirror arguments when applied to blackbody radiation -- and James should recognize another application of this principle -- comes from the fact that the output at the blackbody's surface is random in direction. (This fact is obscured by thinking of the blackbody as a point source, which it never is.) You can't remove this entropy from the system, no matter how ingenious your waveguide.

Thus, at the system's aperture, you have a bundle of light rays with at minimum the same entropy they began with. In practice, this would mean the rays must spill out in all directions, including nearly tangent to the aperture, creating a hemisphere of light... not very different than simply putting the perfect mirror behind the blackbody source to begin with.

This is related to Feynman's problem with the lawn sprinkler at the bottom of a swimming pool.

Really? For $79 you can buy a closed loop life-support system where people rely only on recycled oxygen, recycled water, recycled food? With only small quantities of oxygen, food, and water for emergencies? Wow! I must have been asleep when that was announced.

Uh . . . you got some cites handy?

Oh, btw, your argument about entropy doesn't make sense; all we require is that the mirror arrangement be at least as large as the radiating surface (if it's smaller that _will_ violate the Second law.)

Sorta like the reflector in a two-dollar flashlight.

Ah, I see.

They've been making commercial closed loop ecosystems for twenty years. Some of them are quite large. I will let you do the difficult task of Googling the firm. Also, this new specification of "people" is moving the goal posts, and I will ignore it as beneath you.

I'm afraid I don't understand your objection to a -- standard -- entropy argument. It has nothing to do with area, but with the vector distribution of light rays at the radiating surface and aperture. No set of mirrors is capable of decreasing their net entropy. Basic thermodynamics, in the same way you generally can't use a set of mirrors to focus sunlight hotter than the Sun.

Your flashlight, incidentally, is a poor counterexample, since it emits light at a tangent to the edge of the aperture, exactly as one would expect.

Feel free to use math in your explanation.

Sigh. The point is to have spaceships that need to be stealthed (so I have to add another requirement, that the life-support package be small enough to fit into one.) You're the one moving the goalposts by claiming it's enough to show the concept works for things much smaller than people. No, for the scenarios under discussion, it's not. You might as well claim that a bucket of pond water 'proves' that closed life-support is possible. Or the entire Earth, for that matter.

btw, I'm saying that directive radiation doesn't 'violate entropy'. And no, a flashlight is an excellent example, since it's cone of radiation is rather narrow, certainly far narrower than stealth opponents would have us believe - even though the principle is _exactly_ the same.

I'll let you have the last word, since your tone is definitely rather hostile, and I'm not going to discuss this with anyone who has that particular attitude.

"btw, I'm saying that directive radiation doesn't 'violate entropy'. And no, a flashlight is an excellent example, since it's cone of radiation is rather narrow, certainly far narrower than stealth opponents would have us believe - even though the principle is _exactly_ the same."

But does a flashlight radiate in a cone for all frequencies? I'd be willing to bet not.

Stephen Shevlin

I've been more patient with you than you deserve, silly. A flashlight doesn't radiate light in a cone. There's a simple experiment you can do at home to prove this. Go into a dark room, with a standard utility flashlight. Press the flashlight so that the cylinder of its head rests against the wall. Turn it on. You'll see light emitted from right above the rim of the head against the wall.

A simple thought experiment about the geometry involved is sufficient. Since the radiator isn't a point source (far from it, to be efficient), some of the photons are coming from something that by definition can't be the focus, therefore won't emerge from the mirror as parallel rays. There will be by necessity divergence. The larger the photon source compared to the mirror, the more the divergence. Minimizing the effect starts requiring a honking great mirror, which sort of starts defeating the purpose of trying to hide.

Of course, this also points out a significant problem with this setup: the non-point source radiator is going to be hit by reflected photons itself, which will reduce it's capacity to radiate.

So once again we're back to the point where it's theoretically possible given a perfect reflector and a point-source radiator. Which makes it practically impossible.

Incidentally, I think this proves that any objections "scentofviolets" might make are not necessarily based in physical reality.

I'll call the Board of Irony.

Um, you really can't see the difference between 'Points out', and 'Attempts to point out'? I'm perfectly happy with the latter - it doesn't tilt in either direction. The former definitely does. I'm assuming English is your first language, correct?

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