1922: Interferometry

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It's important to note that while the effective size of the dog can be arbitrarily large, it's not any more of a good dog than the two original dogs.
Title text: It's important to note that while the effective size of the dog can be arbitrarily large, it's not any more of a good dog than the two original dogs.


Interferometry is the practice of overlapping two different waves to get a different signal, which can be used to determine the distance between two reflecting surfaces. An astronomical interferometer uses this principle to build an array of separate telescopes that are able to work together as a single telescope, effectively providing higher resolution using a process known as aperture synthesis.

In the comic, Beret Guy and Cueball are walking Beret Guy's dogs when Beret Guy makes a comment on how interferometry is really cool. Beret Guy states that two dogs placed at a consistent interval will function as a larger dog — a play on the astronomical interferometer. While this idea works on waves, it probably won't work on dogs[citation needed] (though since h/p=λ it might), which is why Cueball is confused and starts to correct him. Before he can respond, however, Beret Guy jumps on his "large" dog and appears to be floating in midair. The existence of a large dog is further proven when it gives out a large bark. Cueball looks on speechless while Beret Guy appears to exhibit another of his strange powers.

In 1614: Kites, Beret Guy is "walking" a dog. It is possible that one of the dogs in this comic is the dog from that comic.

The title text states that the effective giant dog is not any more 'good' than the two original dogs. This is analogous to sensitivity for astronomical interferometers. Interferometry does not increase the light-gathering area, so it cannot view dim objects as well as a single large telescope could. This is also a reference generally to dog-owners calling their dogs "good dog" or "good boy/girl" when they behave well; presumably, Beret Guy's giant interferometry dog is only as well-behaved as the dogs they are derived from. (However, as interferometry does collect more light than any individual telescope used, the interferometry dog is presumably more good than either individual dog. Considering the destructive potential of a giant bad dog, this is a good thing.) It may also be a reference to the They're Good Dogs, Brent meme.


[Cueball is walking behind Beret Guy, who is walking two small dogs on two leashes.]
Beret Guy: Interferometry. Is so cool!
[They stop and Beret Guy is holding the leashes in his hand. He has taken them off the dogs and points at the dogs, which he has placed facing outward so they are standing a couple of paces apart. The distance between them is indicated by a labeled line.]
Beret Guy: If you put two small dogs a large distance apart, they can function as a single giant dog.
Line: d
[Cueball begins to speak but is cut off by Beret Guy yelling as he jumps into the space above the two dogs, with each leg a good distance above one of the dogs. (The leashes have disappeared, as well as the distance line).]
Cueball: I'm not sure that's-
Beret Guy: Hyah!
[As Cueball watches, Beret Guy floats on top of the invisible giant dog about a meter above the two small dogs, and then rides away with the two small dogs still seen below as they run to the right, leaving Cueball standing in the dust the "big" dog creates in its wake. The invisible giant dog barks from a position just in front of Beret Guy's face, far above the two small dogs.]
Invisible giant dog: WOOF
Beret Guy: Away!

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Newbie here just added the explanition and transcript, so will need editing. 16:25, 29 November 2017 (UTC)

I think we both added it at the same time; when I submitted mine it showed normally in the edit box with the captcha, but when I pressed save it spliced your explanation and mine together. Think yours is probably better researched (I was typing off the top of my head), so I reverted it again. -- 16:43, 29 November 2017 (UTC)
Seriously! A comic explanation about interferometry was created by two people at the same time, some large distance apart, resulting in interference! 04:57, 1 December 2017 (UTC)

Why is there a period after Interferometry in the first panel? 19:04, 29 November 2017 (UTC)

It has to be a mistake. Otherwise, Beret Guy sounds like he has a weird speech cadence. Dogman15 (talk) 10:17, 30 November 2017 (UTC)
Could it have something to do with the fact that it's a "period"?-- 02:41, 1 December 2017 (UTC)

I really like the [citation needed] on whether dogs can interfere with each other. I want it to stay! -- 20:05, 29 November 2017 (UTC)

Dogs certainly can interfere with each other - in fact, they often have to be restrained from doing so... 09:37, 30 November 2017 (UTC)
I agree, but feel like it would be better if the statement had more certainty. "it PROBABLY won't work on dogs". Probably? Someone is uncertain on this point??!?!? LOL! NiceGuy1 (talk) 04:19, 1 December 2017 (UTC)
If you poll a large number of theoretical physicists I'm pretty sure you'll find some who are certain it WOULD work on dogs -- It's just an engineering problem. Afterall interference has been demonstrated with molecules of over 800 atoms, which is just a few Daltons short of a yorkie. 08:25, 1 December 2017 (UTC)

Beret guy is back ! I like it... 00:05, 30 November 2017 (UTC)

I feel it should be noted that these are good dogs, Brent. -- 04:49, 30 November 2017 (UTC)

I think the good dog part in the title text is related to the new t-shirt from Questionable Content. I think there has been guest comics one way or the other before. 06:25, 30 November 2017 (UTC)

It's different and probably unrelated, but the comic made me think of the science fiction classic _A Fire Upon The Deep_ in which there are intelligent hive mind dog packs. One dog isn't intelligent, but put 4-6 together and the pack forms a single person with human-level intelligence. 07:52, 30 November 2017 (UTC)

The latest research shows you'd need about 30 dogs to equate to one human in terms of neuron quantity (https://newatlas.com/dogs-smarter-cats-neuron-density-study/52416/), but I wouldn't expect human-level intelligence with just 30 dogs because that ignores the amount of overhead needed to control the 30 dog bodies. 11:20, 30 November 2017 (UTC)
Note that while Tines are similar to dogs, they are not actual earth dogs and are likely more intelligent or at least having more mental capacity even separately. -- Hkmaly (talk) 23:42, 30 November 2017 (UTC)

A large bark does not prove a large dog - dog size and bark size are not proportionately related. The fact that the bark is apparently emanating from mid-air would be more of an indication (though this could be an auditory illusion caused by the combination of barks from the two dogs). 09:37, 30 November 2017 (UTC)

Well, barks can make interference much easier than dogs themselves ... -- Hkmaly (talk) 23:42, 30 November 2017 (UTC)

While I get the gist of the comic, my borderline completionism won't let me completely enjoy it unless I can understand the logical connection between astronomy and dogs. How are dogs and telescopes isomorphic in the realm of interferometry? Just another random brilliant leap that only makes sense to Beret Guy (i.e., not logical to any other being on Earth)? -- 14:53, 30 November 2017 (UTC)

I get the sense that this is it, there's no connection between dogs and astronomy except the one Beret Guy just created. NiceGuy1 (talk) 04:19, 1 December 2017 (UTC)
Have you never heard of the Dog Star? 10:16, 1 December 2017 (UTC)
True... Except the Dog Star is something to observe, while the concept being linked is about what's doing the observing. :) Connection seems shaky at best. Now, if there was some recent article about someone using Interferometry to observe the Dog Star, we'd have our connection. NiceGuy1 (talk) 04:56, 5 December 2017 (UTC)
Here's the connection: https://en.wikipedia.org/wiki/Canis_Major 10:52, 1 December 2017 (UTC)
Srs answer - interferometers have other uses besides astronomy, including quantum physics, radio antennas, direction-finding, and precision measurement. They function by measuring a signal (radio wave, laser beam, w/ever) at two distant points simultaneously, or else by splitting a signal so it travels two different paths to reach a detector. If the difference between the points/paths is such that the wavefronts reach the detector(s) at exactly the same moment, you get "constructive" interference - the waves' peaks and troughs add together and produce a signal of twice the strength. In the context of the comic, the dogs are the signal*, and Beret Guy the detector. Note that if the wavefronts do not arrive in sync you will get partial addition, and/or partial cancellation, or may even produce a perfect cancellation, and get no signal at all. So, presumably if Beret Guy were to move one of the small dogs a little to the left or right, all the dogs would disappear completely.
(*We may assume that both dogs are at the same frequency and therefore constitute one signal for our purposes. It is unclear to me if the dogs are more properly thought of as signal emitters or are simply the measured output of a single wavefront at two different points, but if I think too much harder about this metaphor I may lose my mind.) 22:29, 1 December 2017 (UTC)

Does anyone else notice how in the third panel, HYAH seems to be coming from BG's beret button? What if the beret is controlling him?MrBookBoy (talk) 15:03, 30 November 2017 (UTC)

I love the observational skills of the XKCD fandom, makes me feel right at home. LOL! You're right, I don't see how there can be any question that it seems like the button is doing the talking. NiceGuy1 (talk) 04:19, 1 December 2017 (UTC)

Senstivity WILL be greater than for a single telescope, because you ARE gathering more light. You're not doing it at one detector, but processing both the measurements will allow you to add the images together and then lead to some sort of coherent integration! 03:29, 26 December 2017 (UTC)

There could be another layer of joke here with the invisible dog representing a nod to the things which interferometers measure: visibilities (ref: https://en.wikipedia.org/wiki/Interferometric_visibility ). 20:42, 21 January 2019 (UTC)

Y'all realize that there's a period between the words "interferometry" and "is?" Z1mp0st0rz (talk) 17:04, 12 April 2024 (UTC)

It's in the Transcript, so I imagine that it's indeed known... 20:36, 12 April 2024 (UTC)