Re: Why Would Aliens Hide?

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On Fri, 26 Nov 1999, Amara Graps wrote:

> The ISO observations of the amount of dust in our Galaxy being off by
> about a factor 100 from what the scientists count (currently) as dust
> sources is a problem.

Amara, I presume the ISO observations to which you refer are the measurements of IR from diffuse background dust. A few questions:

• Is this IR *known* to be primarily from the local dust cloud, the rest of the galaxy, or some combination of both?
• If from the local cloud, what are the estimates for the temperature of the cloud as a whole? [This has an impact on where SIs decide to live in the long run. Will humanity need to construct (or move) its SI to some other location to achieve the best thermodynamic efficiency, have the best telescope conditions, etc.? This of course goes back to why the Dark Matter (if SIs) would be in the halo, which I've assumed to be a radiation avoidence strategy. It may be more for thermodynamic and/or observational reasons.]
• Does the article you mention (or other sources) breakdown the dust abundance into actual particle masses and *densities*? [The densities are important because they impact on the speed at which interstellar travel can occur. The current literature seems fairly conflicting on whether interstellar probes, particularly nanoprobes lacking extensive shielding, can survive gas or dust impacts at speeds like 0.1c.]
• After a star forms within a dust cloud, how long does it typically remain in the dust cloud, i.e. does it ever orbit out of or blow the dust cloud away?

Also, could you provide a little interpretation of the gas/dust ratio value? Is this this an atom[molecule]/dust grain # abundance or is it a mass ratio?

It is worth noting that none of the [primary] papers that I have seen regarding interstellar colonization and/or the Fermi Paradox seems to have been concerned with the hazards posed by interstellar gas & dust. I would expect that the gas/dust ratio in the galaxy should over time decline. The gas, if dominated by uncharged molecules, could not easily be repelled by magnetic methods. On the other hand if much of the dust carries a charge it might be more easily pushed out of the way. [If I've got this really wrong, someone please correct me.] So it may be that interstellar travel is easy early in galactic history but gets progressively more difficult. (Of course the argument could be reversed if the gas hitting you is like raindrops, and the dust hitting you is like cannonballs).

Thanks,
Robert

• [ Next ][ Previous ] In reply to: Amara Graps