[ExI] extropy-chat Digest, Vol 148, Issue 11

[John Clark]

On Tue, Jan 26, 2016 at 6:26 AM, Anders Sandberg <anders at aleph.se> wrote:

>
​> ​
> Actually, the Webb telescope is radiating a lot of IR in most directions.
> It is only the the business end that is cold.
>

​
I don't see why that would be. A parabolic dish will focus the IR light
hitting the dish from the outside but it won't focus the blackbody IR
emitted by the dish itself due to its temperature. from a distance a dish
should look indistinguishable from a disk provided they were both at the
same temperature and size and they were both silver, or if they were both
black. With the Webb the outside
​IR​
 will be reflected and will heat the detector at the focus and thus
creating more blackbody IR that the  distant observer will see, although I
concede at a
​​
*slightly* longer wavelength.  So OK it would look slightly cooler because a
​t​
the business end
​ ​
the detector would be in the distant observer's
​
 line of sight and at other directions it would no
​t be​
, but I think the reflected IR would be far weaker than the blackbody IR.
​ So they'd be *almost* indistinguishable. ​

​ John K Clark​
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