<div dir="ltr"><div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><span style="font-family:arial,sans-serif">On Sun, Jan 24, 2016 at 7:28 AM, Anders Sandberg </span><span dir="ltr" style="font-family:arial,sans-serif"><<a href="mailto:anders@aleph.se" target="_blank">anders@aleph.se</a>></span><span style="font-family:arial,sans-serif"> wrote:</span><br></div><div class="gmail_extra"><div class="gmail_quote"><br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"></blockquote><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;display:inline">></div> I originally argued that the star is unlikely to be a Dyson because of the rapid construction (or decay); the chance of seeing that moment in history is small:<br>
<a href="http://aleph.se/andart2/space/likely-not-even-a-microdyson/" rel="noreferrer" target="_blank">http://aleph.se/andart2/space/likely-not-even-a-microdyson/</a><br>
So I was happy with the comet hypothesis. But the dimming doesn't fit at all, so it has to be something stranger.<br>
Meanwhile Phil Plait claimed the dimming was too *fast* to be Dyson construction, and I felt obliged to calculate some limits on Dyson construction:<br>
<a href="http://aleph.se/andart2/space/what-is-the-natural-timescale-for-making-a-dyson-shell/" rel="noreferrer" target="_blank">http://aleph.se/andart2/space/what-is-the-natural-timescale-for-making-a-dyson-shell/</a><br>
So what do I think it is? I suspect it is natural, but perhaps a rare phenomenon. Maybe there is a small and dense cloud of interstellar dust drifting past?</blockquote><div><br></div><div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;display:inline"></div><font size="4">I agree, I<div class="gmail_default" style="font-family:arial,helvetica,sans-serif;display:inline"> </div>think it's probably<div class="gmail_default" style="font-family:arial,helvetica,sans-serif;display:inline"> </div>something odd but natural. It's a F3 star that is brighter than our G2 sun and as a result it has a shorter lifetime.<div class="gmail_default" style="font-family:arial,helvetica,sans-serif;display:inline"> </div>The sun will remain on the main sequence for about 10 billion years but a F3 will leave the main sequence in only<div class="gmail_default" style="font-family:arial,helvetica,sans-serif;display:inline"> </div>about<div class="gmail_default" style="font-family:arial,helvetica,sans-serif;display:inline"> </div>2.5 billion years and become unstable. If the sun were a F3 and the Earth were in a larger orbit around it in the habitable zone Evolution would have had enough time to produce bacteria but then the sun would have vaporized the<div class="gmail_default" style="font-family:arial,helvetica,sans-serif;display:inline"> </div>bacteria and the <div class="gmail_default" style="font-family:arial,helvetica,sans-serif;display:inline"></div>entire planet<div class="gmail_default" style="font-family:arial,helvetica,sans-serif;display:inline"> </div>as well<div class="gmail_default" style="font-family:arial,helvetica,sans-serif;display:inline"> </div>a billion years before the Cambrian Explosion even started.<div class="gmail_default" style="font-family:arial,helvetica,sans-serif;display:inline"></div></font></div><div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;display:inline"></div></div><div><font size="4">And if it's a Dyson Sphere it's odd we can't pick up any intelligent radio signals from it; the star is only 1<div class="gmail_default" style="font-family:arial,helvetica,sans-serif;display:inline">,</div>480 light years away and the Arecibo Observatory could detect a similar instrument 50,000 light years away but we don't hear a peep. People have looked with optical telescopes <div class="gmail_default" style="font-family:arial,helvetica,sans-serif;display:inline">for</div> flashes of LASER light coming from the vicinity of the star and haven't found those either.</font></div><div><font size="4"><br> John K Clark </font></div></div></div></div>