RE: The Extinction Challenge (fwd)

Billy Brown (
Sun, 1 Aug 1999 00:38:46 -0500

Robert J. Bradbury wrote:
> You can't comment very much on the IR/UV exposure without knowing
> exactly how much dust is between you and the radiation source.
> UV/Visible will be absorbed by dust and re-emitted in the IR.


> To be perfectly frank, I don't think it can be done (without a huge
> amount of work). You have to determine the particle types that result
> from SN/GRB, determine their density when they reach Earth, determine
> their reduction (and byproduct production) for intervening mass,
> determine their interaction rates with the elements in the human
> body, determine the mutation rates resulting from those exposures, etc.
> You could come up with numbers, but the assumptions would probably be
> open to question. The best you can probably do is a simple calculation
> that says SN/GRB are harmless at greater distance X, and SN/GRB are
> guaranteed to be fatal when closer than distance Y.

If I were trying to construct a detailed, realistic model of the effects of some particular supernova, you would be correct. Fortunately, I'm not trying to do astronomy here. I think that even the most pessimistic assumptions you can make will give you an event that has little or no effect on a technological civilization, even at very close distances.

My preliminary calculation made the following very pessimistic assumptions:

  1. perfectly transparent interstellar space
  2. all the energy arrives at the same time
  3. you get to presume that 100% of it is whatever form of energy you think would be the most deadly

I still get completely trivial exposure numbers at a distance of only 1 light year. Now, everyone seems to have this "deadly supernova" meme so firmly fixed in their heads that they still aren't convinced, despite the fact that virtually everything that has ever been published on the topic was *science fiction* (which typically has only a distant relationship with scientific fact). I guess I'll have to find some authoritative references for my starting numbers, and include all the details of the calculations this time.

Stay tuned, I'll post the URL in a week or so.

Billy Brown, MCSE+I