[ExI] [Extropolis] Crosspost

[Keith Henson]

 On Wed, Apr 16, 2025 at 12:01 PM John Clark <johnkclark at gmail.com> wrote:

snip
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> If ET does exist, and I don't think he does, then it would be very surprising if he was only 3000 years ahead of us because the universe is 13.8 billion years old.
>
Surprising is certainly the right word, not only in the span of time
but *close* physically.  1470 ly is practically next door.  On the
other hand, it might be that ET civilizations of this kind are
relatively common, but for some reason don't communicate.

But no matter how unlikely something is, if it happens, that's reality.

>> > But I doubt they are the right experts. They are, for example, not aware of directional waste heat radiation from thermal power satellite designs which would account for the
>> impossibly low observed temperature of what they think are dust clouds.
>
> I don't know what you mean by "impossibly low observed temperature".

A natural dust cloud, like a comet tail, will be in thermal
equilibrium.  At the distance you can determine from the transit time,
it is getting a little over 100 W/m^2.  For incoming and outgoing to
balance, the cloud should be at 210 deg K.  It measures 65 K.
>
 Years ago I made a case for fast uploads sunk in the ocean for cooling
>> as the long-term fate of humanity.  That does not seem to be the only
>> solution. If you can think of a third alternative, that would be cool.
>
> The deep ocean is cold but empty space is even colder, only 2.7° kelvin.

That's true, but to get rid of 500 MW at that temperature takes
thousands of square km.  At 20 deg K, it takes 60,000 square meters to
radiate one kW.

Keith

And the Boomerang Nebula is colder yet, the dust is at only 1° kelvin;
unusual thermodynamic conditions there cause it to act like a natural
refrigerator so it's even colder than the Cosmic Microwave Background
Radiation.
>
>    John K Clark    See what's on my new list at  Extropolis
> ed6
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