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Please explain how "it was always like this and it will never change" does not equate to "it's been this way forever and this is how it will stay".

As it was in the beginning, is now, and always shall be: for ever and ever.

to

unchanged since Creation and would remain unchanged forever after

is a non sequitur

Before growing far toward being heliocentric, the first biorb will need to begin the defense of Earth against celestial attacks.

Kinetic energy asteroidal weapons are the most likely technology to represent the greatest threat to Earth as a result of the growing solar biorb. Once asteroid mining begins in earnest, as it will once life becomes heliocentric, asteroids can be redirected via carefully planned celestial mechanics. Within a matter of decades, a malicious interest could send a swarm of tiny asteroids toward Earth at speeds comparable to that of the Swift Tuttle comet -- a popular candidate for global disaster scenarios. Since kinetic energy goes up as the square of velocity, the important thing is to find small asteroids with the right trajectories. This would most likely be carried out on the basis of a fairly complete atlas of the trajectories of small asteroids, searching for some large number of them that could be manipulated to converge on Earth with maximum relative velocity over a fairly narrow window of time.

The most economic defense will likely be the preemptive survey, cataloging and monitoring of all celestial objects (comets as well as asteroids) large enough to survive high speed passage through Earth's atmostphere with little loss due to ablation. This means the initial prospecting for asteroidal resources will be carried out by Earth shielding entities. It is difficult to second guess the technologies that would be available for this task so far in the future, but candidate technologies are already upon us and surveys are already being done.

Perhaps the most positive aspect of this situation is that when an asteroid is identified as a threat, it is also identified as a particularly attractive source of "fuel" for space transportation. Any asteroid that has a high velocity relative to Earth, or can be easily made to have such a velocity, and which has an orbit that can be made to come near Earth, can be used as reaction mass to navigate the inner solar system. Each time this is done, however, the threat represented by such asteroids diminishes. It's as though someone had discovered a way to burn nuclear fuel in jets without pollution. The bombs would get burned up due to economic demand.

Additional global threats to Earth are most likely decreased by removing technological civilization from its biosphere.

Bullshit, you haven't given a sound reason for anything. He, on the other hand, has.

Since you wouldn't know a sound reason if it bit you on the ass, let me point you the way to clarity of thought:

Carl Sagan's Baloney Detection Kit

You are of course correct.

I was speaking in very general terms, but you do raise an interesting point, and your grasp of the theory is excellent. Still, I'm going to try to defend my generalisation, just for our own entertainment.

Assuming a robust enough power supply, even if the load impedance is not optimum, moving closer to the theoretical ideal results in increased output in proportion to load impedance.

By far the vast majority of modern audio amplifiers turn into smoke when driving Rout = Rload, though.

More typically, a loudspeaker impedance is many times the amplifier's output impedance. With transistor output stages, Damping Factor is typically at least 200 and often greater than that (Damping Factor is defined as ouput impedance divided into 8; as per AES spefication).

For whatever reason, the Anthem amp used in the example below has an unusually low output impedance, but not unbelievably so (ie 0.10 ohms is common enough amongst solid state amplifiers).

This just happens to be the first one Google game me:

Anthem PVA 2 Stereo Power Amplifier (The Anthem is a well regarded high fidelity amplifier of modern design).

[Measured Performance]
Power Output: [@1 Khz sine wave; 1% THD, 120V AC line voltage]: 8 ohms 119W/4 ohms 193W
Output impedance: [measured @ 50 Hz, 120 V line voltage]; 0.02 ohms
This particular amplifier is not specified to run into purely resistive loads of 2 ohms or less (protection circuits will trip), and the power output into 4 ohms reveals the power supply is just beginning to strain, but still it is a good result.

There are a very few designs that can do so; certainly I know of no car stereo amplifiers that can. (One hi-fi example that can is the QUAD 404 "current dumping" amplifier designed to drive electrostatic loudspeakers; the specification sheet states it can withstand a direct short for 5 minutes. If you look at the power vs impedance curve in the manual for the 404, output power at 8 ohms is 100wpc but falls with any deviation from the optimum 8 ohms; to zero at 16 or 0 ohms. Of course, it's a very unusual design, and the current dumping circuit hasn't been adopted by other makers).

You may find this link interesting;
Output Impedance Source Impedance and Load Impedance

You obviously have a better grasp of the theory than I do; all I have is 25 years of practical experience in Audio. Still, it's served me well so far.

Regards.

Australia used have such a program until the government cut the budget. So we had better hope that any planet killer doesn't approach from the south, unless South Africa or Argentina have a spaceguard project.

I played Demon Stalkers and Fire King when I was a kid. Demon Stalkers was a gauntlet clone, but better. Fire King was a real role-playing game, but based on a significantly enhanced Demon Stalkers engine (levels could now be parallel to the current one, not jus t up or down, lots of new features, etc.). I still remember it as one of my favorite games. If I recall correctly, America's Cup was very well reguarded when it came out. Enemy Infestation was a dissapointment, but it was obviously good enough to land them the Fallout Tactics contract.

Hmm, appeal to authority. ;)

Still, a good page nonetheless, Sagan is certainly missed. I also note Sagan included "Appeal to ignorance (absence of evidence is not evidence of absence)" as one of his common fallacies of logic. Nonetheless, ad hominem attacks on theists seem rampant on /.

This post only slightly tongue in cheek.

Please read Carl Sagan's baloney detection kit:

"Everything in the Bible is literally true [Argument from "authority"] except where it's obviously intended as a parable or metaphor [Observational selection (counting the hits and forgetting the misses)]. In this case, of course God created the world in 7 days - 7 of His days [Special pleading (typically referring to god's will)]. From our point of view, 7 of His days looks like a mighty long time. Don't get hung up on literalism and legalism. They are mere intellectual cudgels used in meaningless verbal battles between self-important idiots [Ad hominem - attacking the arguer and not the argument] furiously engaged in competitive but highly transient mental masturbation."

From the "Disperse Life" pages:

(An "inforb" is an orbit occupied by informational entities. A "biorb" is an orbit occupied by biological entities.)

The first biorb is likely to be around Earth growing out of the . It will grow Before growing far toward being heliocentric, the first biorb will need to begin the defense of Earth against celestial attacks.

Kinetic energy asteroidal weapons are the most likely technology to represent the greatest threat to Earth as a result of the growing solar biorb. Once asteroid mining begins in earnest, as it will once life becomes heliocentric, asteroids can be redirected via carefully planned celestial mechanics. Within a matter of decades, a malicious interest could send a swarm of tiny asteroids toward Earth at speeds comparable to that of the Swift Tuttle comet -- a popular candidate for global disaster scenarios. Since kinetic energy goes up as the square of velocity, the important thing is to find small asteroids with the right trajectories. This would most likely be carried out on the basis of a fairly complete atlas of the trajectories of small asteroids, searching for some large number of them that could be manipulated to converge on Earth with maximum relative velocity over a fairly narrow window of time.

The most economic defense will likely be the preemptive survey, cataloging and monitoring of all celestial objects (comets as well as asteroids) large enough to survive high speed passage through Earth's atmostphere with little loss due to ablation. This means the initial prospecting for asteroidal resources will be carried out by Earth shielding entities. It is difficult to second guess the technologies that would be available for this task so far in the future, but candidate technologies are already upon us and surveys are already being done.

Perhaps the most positive aspect of this situation is that when an asteroid is identified as a threat, it is also identified as a particularly attractive source of "fuel" for space transportation. Any asteroid that has a high velocity relative to Earth, or can be easily made to have such a velocity, and which has an orbit that can be made to come near Earth, can be used as reaction mass to navigate the inner solar system. Each time this is done, the threat represented by such asteroids diminishes. It's as though someone had discovered a way to burn nuclear fuel in jets without pollution. The bombs would get burned up due to economic demand.

Additional global threats to Earth are most likely decreased by removing technological civilization from its biosphere.

In a related note Segan's "Deamon Haunted World", published a few years before his death, is wonderful.

"Wonderful" is clearly the understatement of the year. The book took me 3 months to read, and its not all that long of a book. It took me some time because the book does what few can, and it actually makes you think.

The chapters that are my particular favorites are "The Baloney Detection Kit" and "Dragon in my Garage" The Baloney Detection Kit can be found on the internet as well here is one link. Anyone whom I respect has a grasp of the kit and how it works, while they may not know of the kit directly, they use its rules just the same.

But we can't feed everyone in the world on an average western diet.

It's recently been estimated that each person in Sydney requires 4.5 hectares of productive land. If all the world's people were to live as people in Sydney do, we would need three times all the productive land on the planet ( Radio interview with Dr Ted Trainer, UNSW)

This is mainly due to the enormous amount of land needed to grain to feed to cattle for beef. Genetic engineering might help here, but perhaps more importantly, we need some social engineering to reduce the high meat diet of most of the western world. (That said, I'm not a vegetarian myself...).

Of course efficient communication is an vital tool for education, which might be able to encourage this sort of social change. So Freeman Dyson might have a point here regarding the internet.

Having mentioned Internet and Genome, I suppose I should comment on the Sun too :) One of the major problems with western culture is it's phenomenal energy consumption. I don't think relying on solar power (or fusion) is neccesarily the answer. We need to reduce energy consumption. Don't panic. I'm not suggesting we turn off all our computers to save energy. In fact, computers and the internet could (and should) actually reduce the energy consumption of our society.

A large percentage of western energy consumption is spent on transport (heating and cooling are also big factors - use proper insulation!). But of course we can now cut at least our own transport cost to almost zero: Telecommute to work!

The cost of transporting food is a pretty amazing. Did you know that the for each litre of milk consumed in the US, half a litre of diesel is used to get it there?

Ted Trainer provides fairly radical suggestion for reducing both the amount of land we use, and our energy consumption. Live Simply ... so that others can simply live. It involves changing what we define and expect of our standard of living, and restructuring our cities with things such as more local food production (permaculture, urban market gardens), and decentralised business/industrial districts.