explain xkcd - User contributions [en]

865: Nanobots

2015-05-15T02:10:13Z

Drui: /* Trivia */ added comma

{{comic
| number = 865
| date = February 25, 2011
| title = Nanobots
| image = nanobots.png
| 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.
}}

==Explanation==
[[Megan]] and [[Ponytail]] are in orbit while nanobots are devouring the earth in a swarm. The nanobots stop after devouring 40% of the planet. This is a take on the "[https://en.wikipedia.org/wiki/Grey_goo Grey goo]" scenario in which self-replicating nanobots destroy the earth while creating more and more of themselves non-stop.

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).

IPv6 supports approximately 3.4×1038 addresses while the {{w|Earth|Earth's volume}} is around 1.08321×1012 km3 or 1.08321×1039 µm3(cubic micrometre). [[Randall]]'s guess on 40% of the planet would mean each nanobot is about 1.27331 µm3 (which is still less than "a few microns" according to [[1070: Words for Small Sets]]).

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}}.

1998 is when the [http://tools.ietf.org/html/rfc2460 IPv6 Specification (RFC 2460)] was published and IETF is the Internet Engineering Task Force.

Note that an April fool joke for [http://tools.ietf.org/html/rfc1606 IPV9] exists and would have guaranteed Earth doom in this comic's scenario.

==Trivia==

On the website, the space above the comic says "xkcd.com now has IPv6 connectivity. If you can't reach it, you or your
ISP have misconfigured equipment. Sadly, I now have no way to tell you."

==Transcript==
:[Megan and commander are on a space station.]
:Megan: Commander! Come quick! It's the nanobots—they've ''STOPPED!''

:Megan: They devoured 40% of the Earth, and then just... quit! They're just sitting there! Why?!

:Ponytail: It's a mystery. ...unless... What's the volume of each nanobot?
:Megan: A few cubic microns. Why?
:Ponytail: I think the year 1998 just bought us some time.
:[Earth's surface, covered in mountains of nanobots.]

:In the swarm:
:Nanobot: What do you mean, "Run out of addresses?"
:Other Nanobot: Look, we should've migrated away from IPv6 ''AGES'' ago...

{{comic discussion}}
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Ponytail]]
[[Category:Comics with inverted brightness]]
[[Category:Science]]

865: Nanobots

2015-05-15T02:09:34Z

Drui: /* Explanation */ added trivia

{{comic
| number = 865
| date = February 25, 2011
| title = Nanobots
| image = nanobots.png
| 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.
}}

==Explanation==
[[Megan]] and [[Ponytail]] are in orbit while nanobots are devouring the earth in a swarm. The nanobots stop after devouring 40% of the planet. This is a take on the "[https://en.wikipedia.org/wiki/Grey_goo Grey goo]" scenario in which self-replicating nanobots destroy the earth while creating more and more of themselves non-stop.

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).

IPv6 supports approximately 3.4×1038 addresses while the {{w|Earth|Earth's volume}} is around 1.08321×1012 km3 or 1.08321×1039 µm3(cubic micrometre). [[Randall]]'s guess on 40% of the planet would mean each nanobot is about 1.27331 µm3 (which is still less than "a few microns" according to [[1070: Words for Small Sets]]).

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}}.

1998 is when the [http://tools.ietf.org/html/rfc2460 IPv6 Specification (RFC 2460)] was published and IETF is the Internet Engineering Task Force.

Note that an April fool joke for [http://tools.ietf.org/html/rfc1606 IPV9] exists and would have guaranteed Earth doom in this comic's scenario.

==Trivia==

On the website the space above the comic says "xkcd.com now has IPv6 connectivity. If you can't reach it, you or your
ISP have misconfigured equipment. Sadly, I now have no way to tell you."

==Transcript==
:[Megan and commander are on a space station.]
:Megan: Commander! Come quick! It's the nanobots—they've ''STOPPED!''

:Megan: They devoured 40% of the Earth, and then just... quit! They're just sitting there! Why?!

:Ponytail: It's a mystery. ...unless... What's the volume of each nanobot?
:Megan: A few cubic microns. Why?
:Ponytail: I think the year 1998 just bought us some time.
:[Earth's surface, covered in mountains of nanobots.]

:In the swarm:
:Nanobot: What do you mean, "Run out of addresses?"
:Other Nanobot: Look, we should've migrated away from IPv6 ''AGES'' ago...

{{comic discussion}}
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Ponytail]]
[[Category:Comics with inverted brightness]]
[[Category:Science]]

970: The Important Field

2015-05-07T01:27:09Z

Drui: included green hat explanation

{{comic
| number = 970
| date = October 28, 2011
| title = The Important Field
| image = the important field.png
| titletext = I hear in some places, you need to fill one form of ID to buy a gun, but two to pay for it by check. It's interesting to see who has what incentives to care about what mistakes.
}}

==Explanation==
It is very common that online input forms demand that one's email address is typed twice, and also quite common that pasting into the second field is disabled, so that there is no escape. If a form asks for some information that is really much more crucial, and this standard routine thoughtlessly isn't used for those fields too, it would comically seem that the form-makers consider your email address to be ''hideously'' important. In the comic, the impression is that it is less important that the wrong city is not accidentally wiped out, than that the boss knows who to blame afterwards.

The title text suggests a real world parallel to this. [[Randall]] ''has heard'' about differing priorities of identifying who is purchasing a firearm (the state/locality requires one form of identification) and ensuring the payment (the store requires two forms of ID, to properly document the person, in case the check is fake or is rejected by the bank). The point is that people often care a lot about money, but a gun in the wrong hands is a potential disaster bigger than a few hundred missing dollars.

This is the only comic so far to feature [[Green Hat]].

It appears that the green hat means that he is part of the military.

==Transcript==
:[Green Hat sitting at a computer.]
:Computer: Welcome to the missile launch interface!
:''Click''
:Computer: Enter the target's coordinates.
:''Type Type''
:Computer: Enter your email address for our records.
:''Type Type''
:Computer: Enter your email again, to ensure you typed it correctly.

{{comic discussion}}
[[Category:Comics with color]]
[[Category:Sarcasm]]