I read the paper on "The Loeb Scale" and had only a couple of further thoughts:
1) Loeb seems to place an inordinate stress on "non-gravitational acceleration", when it seems more likely that non-gravitational DECELERATION would be more cause for concern. They would have to decelerate to rendezvous with Earth either for an invasion or peaceful contact. Accelerating will just harmlessly fling them right out of the solar system, back into the black once again.
2) ALL 3 of the highest levels of the scale, which encompass confirmed technological origin, concern themselves mostly with the likelihood and magnitude of an Earth impact. Why would aliens travel for thousands of years in generational starships just to drive them into the Earth in a suicide mission? Even Heinlein's "Bugs" in Starship Troopers flung regular, run of the mill natural asteroids at Earth as weapons - they didn't send any technologically enhanced marvels. Why bother with that when simply chucking a rock would do?
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1) Loeb seems to place an inordinate stress on "non-gravitational acceleration", when it seems more likely that non-gravitational DECELERATION would be more cause for concern. They would have to decelerate to rendezvous with Earth either for an invasion or peaceful contact. Accelerating will just harmlessly fling them right out of the solar system, back into the black once again.
2) ALL 3 of the highest levels of the scale, which encompass confirmed technological origin, concern themselves mostly with the likelihood and magnitude of an Earth impact. Why would aliens travel for thousands of years in generational starships just to drive them into the Earth in a suicide mission? Even Heinlein's "Bugs" in Starship Troopers flung regular, run of the mill natural asteroids at Earth as weapons - they didn't send any technologically enhanced marvels. Why bother with that when simply chucking a rock would do?
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“Trouble rather the tiger in his lair than the sage among his books. For to you kingdoms and their armies are things mighty and enduring, but to him they are but toys of the moment, to be overturned with the flick of a finger.”
― Gordon R. Dickson, Tactics of Mistake
― Gordon R. Dickson, Tactics of Mistake