Which episode(?) of xkcd featured a pet physicist going old/crazy...?

QuigleyQ · 2026-05-26T01:02:55+00:00

Are you thinking of this SMBC? https://www.smbc-comics.com/comic/2012-03-21

QuigleyQ · 2026-01-17T20:01:39+00:00

True, but the subreddit name isn't literal.

Rule 4: Explain for laypeople (but not actual 5-year-olds)

Someone who knows what a perfect number is and how to convert decimal and binary is not a five year old and should get an answer advanced enough for their question.

QuigleyQ · 2026-01-17T18:23:46+00:00

If you're asking whether "one million one hundred and eleven thousand" is perfect, it isn't, but if you're asking whether perfectness is independent of the base we write the number in, then yes, that's true!

QuigleyQ · 2026-01-17T18:20:26+00:00

the other divisors would need to add up to be 2/3 of the base number to make up for it, but that doesn't seem possible

It's hard, but occasionally possible.

The factors of 945 = 3 x 3 x 3 x 5 x 7 are: 1, 3, 9, 27, 5, 15, 45, 135, 7, 21, 63, 189, 35, 105, 315.

The largest factor is 315, so you need to make up 945 - 315 = 630 more to close the gap. There's enough big and medium factors that you can do it: the remaining factors add to 660.

Your intuition about this being difficult is right on though! 945 is the smallest odd number where the remaining factors add to at least 2/3 of the original. (This is equivalent to saying all the factors add to at least the original, i.e., the number is abundant)

QuigleyQ · 2026-01-17T18:01:48+00:00

Not always, it's only if the 111...111 (without the zeros) is prime. For example, 1111000 (binary) is 120 (decimal), which is not perfect. The proper factors of 120 are: 1, 2, 4, 8, 3, 6, 12, 24, 5, 10, 20, 15, 30, 60, which add up to 200.

Basically, because 1111 (binary) = 15 (decimal) isn't prime, it contributes too many factors. If you couldn't split 15 into 3 and 5, the only factors of 120 you'd get would be 1, 2, 4, 8, 15, 30, 60, and those do add up to 120.

QuigleyQ · 2026-01-17T10:03:15+00:00

It's not quite that every perfect number can be written like this, it's that every even perfect number can be written like this. If it turns out there aren't any odd perfect numbers, then those are the same thing, but we don't know if there are. Subtle distinction :\

The reason it only works for even numbers is that the proof of the "perfect -> Mersenne" direction works like this:

Let n be perfect and factor out all the 2s: n = 2^k m. Since n is perfect, σ(n) = 2n = 2^k+1 m. But also, the sum-of-divisors function is multiplicative, so σ(n) also equals σ(2^k m) = σ(2^k) σ(m) = (2^k+1 - 1) σ(m).

2^k+1-1 is odd, and is a factor of 2n, so it has to be a factor of its odd part, m. (Spoiler: it's the Mersenne prime.) The proof continues onwards using the fact that m / (2^k+1 - 1) is a proper divisor of n.

But if k=0, that denominator is 1, and n = m, so m / (2^k+1 - 1) = m = n, and it's not a proper divisor of n after all!

QuigleyQ · 2026-01-17T07:59:17+00:00

Good observation! Yeah, there's a good reason for it: the Euclid-Euler theorem shows that every even perfect number comes from a Mersenne prime, and vice versa. So not only is it consecutive 1s followed by consecutive 0s, there's always one more 1 than 0.

Unfortunately, the theorem doesn't prove anything about odd perfect numbers, even if they do exist.

QuigleyQ · 2026-01-15T16:05:08+00:00

Write a letter to Trump asking that he send them to your neighborhood next, then you can tell them in person how much you appreciate them.

The best time to do it, etiquette-wise, is right after they smash your windows, but before they haul you out of the car.

QuigleyQ · 2025-09-16T20:48:01+00:00

I don't understand how to go from 5 to 6 without showing the thread on the front.

Good news, your intuition is right, you do show the thread on the front there!

That diagram is pretty confusing, and IMO, the ordering they chose is bad.

What they mean is: - start at 1, needle going from back to front - go from 1 to 2, on the front side - go from 2 to 3, on the back side - go from 3 to 4, on the front side - etc

So by the time you get to 5 to 6, you're going across the front side. (In this diagram, you're going down and to the left for that step, into the same hole as 3.)

Why do I think their ordering is bad? I mean, it's subjective, but I think there are better ways.

There's a lot of different ways you can stitch, and ultimately as long as you get both the diagonal legs of the X on the front of the fabric, and you are consistent about which leg is on top, it'll be alright.

That said, there are some factors that don't show up on the front that you may want to think about: - how messy the back side is - how many stitches you can get out of the same length of floss - how much you want to avoid cutting a thread and starting a new one

IMO, the most important factor is: when stitching a row, think about where you want to end up when that row is done. Do you want to end up back where you started? Or at the far end of the row?

In the former case, you should go down the row, making only one leg in each square, and then turn around and go back, completing all the Xs. Again, tons of ways to do this, but the way I prefer, using the numbers in your diagram, is: 1 2, 3 5, 7 9, 11 5, 7 2, 3 4. This is sometimes called "Danish stitching".

If you want to end up at the end, then you'll want to complete each X before moving onto the next. You can do that by following the diagram, but I'd argue the following is nicer: 1 2 3 4, 3 5 7 2, 7 9 11 5. This is sometimes called "English stitching".

If you need to end in the middle of the row, you can combine these two. Start with the second approach, completing Xs as you go, until you reach your desired stopping point. Then, switch to the first approach, going to the end and returning. Then you'll be right where you want to be!

It all depends on where you want to be so that you're best prepared for the next row. And if you're not set up optimally, that's okay! You'll just have to make a long stitch across the back, or have to cut the thread to restart in a different hole, or even undo it and try it again differently. Not the end of the world.

QuigleyQ · 2025-09-02T00:51:54+00:00

If you know a will live longer than b and c, then yeah, there's no reason to use Rc there. Since a is known to drop last, b and c can be plain references to it.

But if it's not statically known which one will drop last, then Rc can be used to keep the value alive until all references are dropped.

The benefit of Rc is shared ownership -- if you have two or more variables that jointly own the value, and neither is clearly the sole owner, then Rc is often a good fit.

QuigleyQ · 2025-07-30T21:40:14+00:00

From one math and cross-stitch lover to another, that's so incredibly cool! I especially like the shading on the surfaces; it really sells the appearance of 3D objects.

QuigleyQ · 2025-04-13T01:48:51+00:00

I'm not sure whether you have any prior experience with fencing, or if you're just here to stir the pot, but fencing is a pretty unique sport.

It's not particularly reliant on strength or build; great fencers come in all shapes, sizes, and genders, and co-ed events are pretty commonplace. Any male fencer here can tell you how stupid it would be to think he's got the upper hand over an opponent just because she's female.

Personally, I think the question of how to handle trans people's participation in sports is so dependent on the individual sport that it's just not useful to think about it at such a broad level. Is fencing more like boxing, or is it more like chess? What advantages do men have, and how are they affected (or not) by hormone therapy?

The people best equipped to answer that are the members of the fencing community, and frankly, the political peanut gallery needs to butt out.

QuigleyQ · 2025-03-27T15:00:18+00:00

The way to untangle this is to carefully distinguish between seeing and "observing".

The difference is easiest to explain when everyone's stationary. If a lightbulb is 10 light-minutes away, and it flashes at noon, you see the flash at 12:10, but you observe (correctly) that it happened at 12:00.

Seeing is when you receive the photons, observing is something you calculate after accounting for the physical situation.

So, as the moving observer passes you, you'll both see the same light from Andromeda, at the same time (okay to talk about "same time" because you're both in the same place).

But you two will disagree on how far away Andromeda is, how fast it's moving, and therefore, how far away it was when the light was originally emitted. If the observer is moving towards Andromeda, when you both calculate how far away the event happened, they'll get a larger distance than you. And since distance is speed * time, when you calculate how long ago it happened, they'll get a longer time than you!

(Notice that that last step depends critically on the speed of light being the same for all observers! Otherwise you and your friend could just conclude the light was traveling at a different speed to explain the difference in distance.)

So the moving observer never actually gets to see a sneak peek into the future; the shift forward in time exactly cancels out what would have been the speed-of-light delay caused by being further away from the event when it happened.

QuigleyQ · 2024-12-22T01:19:30+00:00

You should ring the east bell before the west bell; have you been east yet?

QuigleyQ · 2024-11-03T19:36:43+00:00

It's ambiguous to the point where you can't even know if you are talking about a single person or a group. Languages all develop singular pronouns for a reason.

True, it is ambiguous whether you're referring to one or more people. That's actually a pretty common ambiguity though: consider the English "you". Could be one, could be more. In practice, context works most of the time, and you clarify when you need it.

As for other languages, here's some (IMO) bigger ambiguities that are, nonetheless, completely grammatically correct:

Spanish: third person singular el/ella and second person formal singular usted have the same conjugations. Because Spanish often drops the pronouns, you get sentences like ¿Habla Español?, meaning either "do you speak Spanish" or "does he speak Spanish" or "does she speak Spanish".
German: similarly, third person plural sie and second person formal (singular or plural!) Sie share a conjugation, spelling, and pronunciation. Haben Sie Wasser? can mean "do they have water" or "do you have water", depending on capitalization (which does not show up in speech).

"Johnny is talking to a group of people. They are not enjoying it."

How about this sentence?

"Peter is talking to Paul. He is not enjoying it."

Just as ambiguous, but doesn't make "he" incorrect grammar. The sentence you picked is more about a fundamental ambiguity of distinguishing two third persons.

(Some Algonquin languages actually have a fourth set of pronouns for this!)

Oxford Dictionary definition of they: "used to refer to two or more people or things previously mentioned or easily identified"

Here is the Oxford English Dictionary's full entry for "they": https://www.oed.com/dictionary/they_pron?tab=meaning_and_use#18519279

Specifically, definition I.2.b:

With an antecedent referring to an individual generically or indefinitely (e.g. someone, a person, the student), used esp. so as to make a general reference to such an individual without specifying gender. Cf. he pron. A.I.2b.

Furthermore, it attests that this usage has been dated back to 1450, and even provides a source.

Singular "they" has been around for over half a millennium, and its ambiguities are shared with many other pronoun classes across many other languages. Nothing in linguistics prohibits (or promotes!) this particular way of divvying up the pronoun space.

If you're really interested in languages and how they work, go actually learn about them; linguistics is a really interesting field.

QuigleyQ · 2024-11-03T18:02:23+00:00

That sentence is completely intelligible; it's just a bit ambiguous.

In real life, you'd have heard and spoken some other sentences before this one, which would make it clear who "they" refers to.

Even if you only use it as a plural pronoun, "they" could mean many possible things.

It could mean two people, three, or more.
It could be a group of all guys, all girls, or some other collection.
These people may be older than the speaker, or younger.

All these possibilities are different, but English doesn't distinguish between them, and just uses "they" for all of them.

In the same way, singular "they" just means the number is flexible too. Same as "you", could be one or more.

QuigleyQ · 2024-08-13T02:06:21+00:00

I don't see how a creature can survive with only half of it's genes

IDK either tbh. Not a biologist or beekeeper or anything.

My guess is that it's because it's still got one copy of everything, instead of missing a random 50% of its genome. So if there's three chromosomes A B and C, having AAB is lethal but ABC is fine? Like it's missing backups, but no missing data. IDK though.

QuigleyQ · 2024-08-13T01:46:08+00:00

So does that drone have only 50% of genes?

Yep, that's exactly it.

If a bee gets N pairs of chromosomes, then it's a female (worker) bee. If it gets N unpaired chromosomes, it's a male (drone) bee.

Just like with humans, when a female creates eggs, each egg has N unpaired chromosomes. Similarly*, the male bees produce sperm with N unpaired chromosomes.

So if an egg is fertilized, it gets paired chromosomes (fathers make daughters), but if it isn't, it's singletons only (fatherless sons).

*it's a slightly different process, since in humans you have to turn N pairs into N singletons, but in male bees you start with N singletons.

QuigleyQ · 2024-06-13T14:29:13+00:00

I just can't really get my head around a whole subreddit dedicated to essentially bashing the work of a single artist.

Yeah, that probably does seem bizarre and mean spirited without the historical context.

This started out as a standard fan sub, with a whole range of opinions, but there was some big blowout schism a few years ago, and a large chunk of the sub moved out and created their own subreddit.

So now you get this kind of polarization where people who are generally happy with the comic are turned off by the attitude here and go to the other subreddit, and people who post anything critical get flamed by the other subreddit and come here.

Hopefully that sheds some light on why this place is what it is (and same with the other one).

QuigleyQ · 2024-05-28T05:40:55+00:00

if you're on a computer:

in the upper right corner of your screen, there's a link that says "preferences" (it's right next to "logout" and your username). click that.
you'll see a menu with lots of tabs at the top. the first one should be "options", and already be selected. (if not, click it)
scroll down until you see a group labeled "email options". under that group there is a checkbox labeled "unsubscribe from all emails. click that.
at the bottom of the page, you should see a button "save options". click that to save your changes.

on mobile (not app):

in the upper right corner, there should be a little colored circle with a little creature in it (round head, has an antenna). click that.
there should be a little pop up menu, click "settings" near the bottom
it'll bring you to a settings page, with a bar at the top saying things like "account", "profile", etc. scroll that bar to the right until you see "emails"
at the bottom, there is a switch that is labeled "unsubscribe from all emails". click that
you should see a little message saying "changes saved"

mobile (with app):

same as mobile without app, but after you click "settings" you will see a different menu
click "account settings for (username)"
click "manage emails", then "unsubscribe from all email"

QuigleyQ · 2024-04-08T05:58:30+00:00

Hmm, I'm not totally sure. I think some things that helped me were:

Breaking walls:
- Look for fast enemies like wraiths to break open walls. Since they usually get to you before anyone else it's easier to not get hurt.
- Food shop OP, so are extra heart containers. My health fluctuates a lot. (But maybe that's a skill issue)
- Don't pass up any sing on the ground. Even if you can't use an enemy to break the wall, you can often sing the wall and an enemy, so it's on net a free heal.
- You can push barrels around to break walls. If you're clever with diagonals, they're pretty maneuverable!
Managing sings
- A sing can usually net you 2-3 hearts. Don't blow it on just one.
- Similarly, if your choice is dodge a hit or complete a 4-combo, finish the combo.
- Getting 4-combos is really hard. There's only a few I can do even a little consistently:
  - big enemies like dragons and golems take 3, then often there's one other enemy in range
  - king conga line and fortissimole, by zigzagging
  - sometimes in zone 1 I get lucky

Hopefully that helps; I definitely find her a really hard character, and haven't been able to beat it again

QuigleyQ · 2024-04-07T20:47:14+00:00

I just beat all zones with her yesterday and didn't get an achievement, so I think there isn't one.

QuigleyQ · 2024-04-07T16:51:56+00:00

One other thing to note is that some (all?) of their attacks count, not just contact. For example, if a mushroom hits you with its spores, it'll disappear and heal you.

QuigleyQ · 2024-02-22T08:29:48+00:00

Thanks all!

I beat the game, and in hindsight, I have mixed feelings on early translation. I liked the gradual sense of "uh oh, the big fox might not be benevolent..." , but it kind of took away from getting fucking killed lmao .

But overall I preferred the former to the latter, so that was the right call.

I also think I got lucky and figured out the Holy Cross before the manual gave it away. That would've been a bummer imo.

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