# ­xkcd thread **URL:** \ **Category:** Cafe Society\ **Tags:** comic-strips\ **Created:** [May 28, 2020, 12:57am UTC](https://boards.straightdope.com/t/xkcd-thread/854574 "2020-05-28T00:57:03Z")\ **Posts on this page:** 20\ **Page:** 318
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 5, 2026, 1:19am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/6343 "2026-09-05T01:19:50Z")
> [@Pardel-Lux](#): > > I wonder what would happen if you turned noclip back off in the exact moment the asteroid passes through the center of the Earth. It’d either be able to move back out but not in again, or it’d instantly teleport out to the nearest open space. Depends on the engine reality is running on. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [September 7, 2026, 7:12pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/6344 "2026-09-07T19:12:31Z")
> **[Semaphore](https://xkcd.com/3295/)** [![](https://imgs.xkcd.com/comics/semaphore.png) ](https://imgs.xkcd.com/comics/semaphore.png) “The speed of light in air is 50% faster than in fiber, but it’s a challenge to get the arms to move fast enough to realize the latency advantage.” ---
**Author:** ![Pleonast](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pleonast/32/1183_2.png) [@Pleonast](https://boards.straightdope.com/u/Pleonast)\ **Post date:** [September 8, 2026, 3:19pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/6345 "2026-09-08T15:19:41Z")
It’s a prototype of > **[Laser communication in space](https://en.wikipedia.org/wiki/Laser_communication_in_space)** > > Laser communication in space is the use of free-space optical communication in outer space. Communication may be fully in space (an inter-satellite laser link) or in a ground-to-satellite or satellite-to-ground application. The main advantage of using laser communications over radio waves is increased bandwidth, enabling the transfer of more data in less time. In outer space, the communication range of free-space optical communication is currently of the order of hundreds of thousands of kilom... ---
**Author:** ![Marvin\_the\_Martian](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/marvin_the_martian/32/2898_2.png) [@Marvin\_the\_Martian](https://boards.straightdope.com/u/Marvin_the_Martian)\ **Post date:** [September 8, 2026, 11:53pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/6346 "2026-09-08T23:53:55Z")
> [@Frodo](#): > > The proverbial Earth-Shattering Kaboom? Stick to your little rings and leave Earth-shattering kabooms to us experts. ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [September 9, 2026, 12:44am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/6347 "2026-09-09T00:44:00Z")
Totally aside from the silliness of a semaphore-to-digital and back interface, how is this supposed to prevent unauthorized access to either computer? ---
**Author:** ![abcdefghij](https://avatars.discourse-cdn.com/v4/letter/a/43a26b/32.png) [@abcdefghij](https://boards.straightdope.com/u/abcdefghij)\ **Post date:** [September 9, 2026, 12:46am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/6348 "2026-09-09T00:46:14Z")
Where’s a hacker gonna get ahold of flags in this day and age? ---
**Author:** ![Frodo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/frodo/32/302_2.png) [@Frodo](https://boards.straightdope.com/u/Frodo)\ **Post date:** [September 9, 2026, 12:57am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/6349 "2026-09-09T00:57:31Z")
I think there’s a rabbit in your Uranium PU-36 Explosive Space Modulator. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 9, 2026, 1:26am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/6350 "2026-09-09T01:26:50Z")
The same way as any other airgap, of course. ---
**Author:** ![Pleonast](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pleonast/32/1183_2.png) [@Pleonast](https://boards.straightdope.com/u/Pleonast)\ **Post date:** [September 9, 2026, 1:42am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/6351 "2026-09-09T01:42:24Z")
> [@Lumpy](#): > > Totally aside from the silliness of a semaphore-to-digital and back interface, how is this supposed to prevent unauthorized access to either computer? It’s not about _security_ sensitivity, but about _electrical_ sensitivity. ---
**Author:** ![kferr](https://avatars.discourse-cdn.com/v4/letter/k/71e660/32.png) [@kferr](https://boards.straightdope.com/u/kferr)\ **Post date:** [September 9, 2026, 11:01am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/6352 "2026-09-09T11:01:33Z")
He may have borrowed/stole the idea from the Clacks in the Discworld book _Going Postal_. ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [September 9, 2026, 11:08am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/6353 "2026-09-09T11:08:09Z")
I have to break it to you that semaphore was absolutely non-fictional: [![](https://thumb.wikimedia.org/wikipedia/commons/thumb/f/f6/P1060531_Telegraphe_de_Chappe_Marly.JPG/500px-P1060531_Telegraphe_de_Chappe_Marly.JPG) ](https://thumb.wikimedia.org/wikipedia/commons/thumb/f/f6/P1060531_Telegraphe_de_Chappe_Marly.JPG/500px-P1060531_Telegraphe_de_Chappe_Marly.JPG) Also, so are opto-isolators: [![](https://thumb.wikimedia.org/wikipedia/commons/thumb/a/ac/Optocoupler_cross_section.jpg/960px-Optocoupler_cross_section.jpg) ](https://thumb.wikimedia.org/wikipedia/commons/thumb/a/ac/Optocoupler_cross_section.jpg/960px-Optocoupler_cross_section.jpg) ---
**Author:** ![puzzlegal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/puzzlegal/32/3827_2.png) [@puzzlegal](https://boards.straightdope.com/u/puzzlegal)\ **Post date:** [September 9, 2026, 11:09am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/6354 "2026-09-09T11:09:30Z")
My husband says there was a news item recently (that i looked for, but didn’t find) about traders getting a microsecond advantage by using encrypted radio instead of sending their trades over glad phone lines. I suspect that was part of the inspiration. ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [September 9, 2026, 11:24pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/6355 "2026-09-09T23:24:51Z")
Yeah, Pratchett based his semaphores on the real ones that were all over the world in the 19th century > **[Optical telegraph](https://en.wikipedia.org/wiki/Optical_telegraph)** > > An optical telegraph is a line of stations, typically towers, for the purpose of conveying textual information by means of visual signals (a form of optical communication). There are two main types of such systems: the semaphore telegraph which uses pivoted indicator arms and conveys information according to the direction the indicators point, and the shutter telegraph which uses panels that can be rotated to block or pass the light from the sky behind to convey information. The most widely used... _Telegraph Hill_ in San Fransisco is named for the optical telegraph that was there ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [September 9, 2026, 11:27pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/6356 "2026-09-09T23:27:22Z")
> **[Fault Taunting](https://xkcd.com/3296/)** [![](https://imgs.xkcd.com/comics/fault_taunting.png) ](https://imgs.xkcd.com/comics/fault_taunting.png) “One of the first things they teach you is to NEVER play with the geology toy over a mantle hotspot.” ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [September 10, 2026, 9:36am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/6357 "2026-09-10T09:36:57Z")
Another nice geology one, I feel seen. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [September 11, 2026, 6:32pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/6358 "2026-09-11T18:32:21Z")
> **[OH Scale](https://xkcd.com/3297/)** [![](https://imgs.xkcd.com/comics/oh_scale.png) ](https://imgs.xkcd.com/comics/oh_scale.png) “To access distant parts of the project, I ended up building a regular-scale passenger train inside each rail.” ---
**Author:** ![thorny\_locust](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/thorny_locust/32/431_2.png) [@thorny\_locust](https://boards.straightdope.com/u/thorny_locust)\ **Post date:** [September 12, 2026, 11:35pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/6359 "2026-09-12T23:35:46Z")
That’s probably in violation of the zoning — ---
**Author:** ![BigT](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bigt/32/12044_2.png) [@BigT](https://boards.straightdope.com/u/BigT)\ **Post date:** [September 13, 2026, 4:27am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/6360 "2026-09-13T04:27:07Z")
> [@Chronos](#): > > The same way as any other airgap, of course. It would slow it down, but they are still connected, unlike a proper airgap. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 13, 2026, 11:26am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/6361 "2026-09-13T11:26:10Z")
Proper airgaps are still connected, too. Computers are useless if they’re not connected. You have to have some way of getting input to the computer, and getting output from the computer, in order for it to do its job (whatever that is), and so long as there’s input and output, there exists the possibility to use those inputs and outputs to compromise the computer. ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [September 13, 2026, 6:02pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/6362 "2026-09-13T18:02:52Z")
Yes, but the standard air gap involves a mandatory human vetting of the input/output process. [Previous page](https://boards.straightdope.com/t/xkcd-thread/854574.md?page=317) [Next page](https://boards.straightdope.com/t/xkcd-thread/854574.md?page=319)