<html><head><style type=text/css><!--
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--></style></head><body><div><span data-mailaddress="rhanson@gmu.edu" data-contactname="Robin D Hanson" class="clickable"><span title="rhanson@gmu.edu">Robin D Hanson</span><span class="detail"> <rhanson@gmu.edu></span></span> , 9/6/2014 4:31 PM:<br><blockquote class="mcnt mori" style="margin:0 0 0 .8ex;border-left:2px blue solid;padding-left:1ex;"><div class="mcnt">
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<div>Yes the way you reversibly "erase" a bit is in effect by swapping it for a bit of known value in a negentropy reservoir, and negentropy resources are in general equivalent to big memories filled with zeros. The cosmic background is in effect such a big reservoir. </div></div></div></div></blockquote></div><div><br></div><div>The background is an imperfect set of zeros. So swapping the bit for a bit from the background is reversible, but with a low probability doesn't zero it. Now, you could just test if it has become zero and if it didn't, just repeat the swap. However, this is a Maxwell demon: if the testing worked reversibly it would work for hot background radiation too. So there has to be some thermodynamic cost in the test (like erasing the result from the previous one).</div><div><br></div><br><div><blockquote class="mcnt mori" style="margin:0 0 0 .8ex;border-left:2px blue solid;padding-left:1ex;"><div class="mcnt"><div><div></div></div>
<div> So there is less obviously a reason to way to spend entropy. The max entropy usually comes via huge black holes, and those can take time to construct and then to milk. That seems to me to place the strongest limits on when we expect negentropy to get spent. </div>
</div></blockquote></div><div><br></div><div>I don't think time is the resource that is most costly if you try to maximize the overall future computations of your lightcone. Capturing dark matter with black holes seems wortwhile, but I wonder about the thermodynamic cost of doing it.</div><br><br>Anders Sandberg, Future of Humanity Institute Philosophy Faculty of Oxford University</body></html>