https://www.explainxkcd.com/wiki/api.php?action=feedcontributions&feedformat=atom&user=Mocramisexplain xkcd - User contributions [en]2026-04-05T04:53:29ZUser contributionsMediaWiki 1.30.0https://www.explainxkcd.com/wiki/index.php?title=865:_Nanobots&diff=55869865: Nanobots2013-12-24T15:42:49Z<p>Mocramis: </p>
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<div>{{comic<br />
| number = 865<br />
| date = February 25, 2011<br />
| title = Nanobots<br />
| image = nanobots.png<br />
| imagesize = <br />
| titletext = I think the IETF hit the right balance with the 128 bits thing. We can fit MAC addresses in a /64 subnet, and the nanobots will only be able to devour half the planet.<br />
}}<br />
<br />
==Explanation==<br />
[[Megan]] and [[Ponytail]] are in orbit while evil nanobots are devouring the earth in a swarm. The nanobots stop after devouring 40% of the planet. This is a take on the "gray goo" scenario in which self-replicating nanobots destroy the earth while creating more and more of themselves non-stop.<br />
<br />
However, the nanobots are only able to destroy 40% of the planet because 40% of the earth volume = (# of {{w|IPv6}} addresses) x (A few cubic microns). Without more IP addresses, the nanobots cannot continue to replicate (assuming that each nanobot must be individually addressable).<br />
<br />
IPv6 supports approximately 3.4×10<sup>38</sup> addresses while the earth volume is around 1.08321×10<sup>12</sup> km<sup>3</sup>[http://en.wikipedia.org/wiki/Earth] or 1.08321×10<sup>39</sup> µm<sup>3</sup>(cubic micrometre). <br />
[[Randall]]'s guess on 40% of the planet would mean each nanobot is about 1.27331 µm<sup>3</sup> (which is still less than "a few microns" according to [[1070: Words for Small Sets]]).<br />
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This is a joke on the shortage of IPv4 addresses. The only difference is that we are on {{w|IPv4}} and the nanobots are on {{w|IPv6}}.<br />
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1998 is when the [http://tools.ietf.org/html/rfc2460 IPv6 Specification (RFC 2460)] was published and IETF is the Internet Engineering Task Force.<br />
<br />
Note that an april fool joke for [http://tools.ietf.org/html/rfc1606 IPV9] exists and would have guaranteed earth doom in this comic' scenario. <br />
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==Transcript==<br />
:[Megan and commander are on a space station.]<br />
:Megan: Commander! Come quick! It's the nanobots—they've ''STOPPED!''<br />
<br />
:Megan: They devoured 40% of the Earth, and then just ... quit! They're just sitting there! Why?!<br />
<br />
:Ponytail: It's a mystery. ...unless... What's the volume of each nanobot?<br />
:Megan: A few cubic microns. Why?<br />
:Ponytail: I think the year 1998 just bought us some time.<br />
:[Earth's surface, covered in mountains of nanobots.]<br />
<br />
:In the swarm:<br />
:Nanobot: What do you mean, "Run out of addresses?"<br />
:Other Nanobot: Look, we should've migrated away from IPv6 ''AGES'' ago ...<br />
<br />
{{comic discussion}} <br />
[[Category:Comics featuring Megan]]<br />
[[Category:Comics featuring Ponytail]]<br />
[[Category:Science]]</div>Mocramis