What's the most surprising fact you've learned in the last couple of weeks?
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@johncarlosbaez I don't know any specifics.
Until yesterday, I believed that a "Reh" (roe, https://en.wikipedia.org/wiki/Roe_deer) was a female "Hirsch" (stag, https://en.wikipedia.org/wiki/Red_deer). But apparently they are both deer, yet different species - and not to be confused with fallow deers. Took me only shy over 40 years to learn that. 
️@johncarlosbaez Now I wonder what type of deer Bambi is.
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What's the most surprising fact you've learned in the last couple of weeks? I don't mind if it's quite technical. I just want to hear what you folks are being surprised by!
@johncarlosbaez That distilled water is completely safe to drink (contrary to what I learned in school)!
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What's the most surprising fact you've learned in the last couple of weeks? I don't mind if it's quite technical. I just want to hear what you folks are being surprised by!
One of the stars of Hacks is Laraine Newman's daughter.
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I was surprised to learn that there are small cleaner ants that clean bigger ants of a different species.
If one insect wants help with cleaning, why choose another smaller insect of the same family? One could imagine so many other willing arthropods.
Magnus (@magnus@mastodon.world)
Attached: 1 image Did ants learn this from cleaner fish? There are small ants that clean big ants without meeting any agression, just like small cleaner fish can clean sharks. https://onlinelibrary.wiley.com/doi/10.1002/ece3.73308
Mastodon (mastodon.world)
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Ancient Rome consumed lots of oil and they didn't reuse the large Dressel 20 amphora barrels. Monte Testaccio in Rome is a 'trash mountain' made of 53 million broken olive oil amphorae.
@maxpool - "53 milllion" is where I got surprised.
I wondered how long they dumped those amphorae there, so I looked it up on the Wikipedia article:
"Deposits found by excavators have been dated to a period between approximately AD 140 to 250, but it is possible that dumping could have begun on the site as early as the 1st century BC."
So, at least 110 years, but maybe over 250!
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What's the most surprising fact you've learned in the last couple of weeks? I don't mind if it's quite technical. I just want to hear what you folks are being surprised by!
@Lambo got here first with my top fact, so i'll go with this one:
transit operators in the u.s. are not authorized to question the pedigree of your 'service animal.'
as long as you identify the animal as such, you are permitted to bring it on the bus.
*any* animal.
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@buo - I should learn what this *means*. I once almost knew what a Kalman filter is, and I know it's extremely important. But I don't know what a phase-locked loop is.
I love ODE, so this is embarassing! There's always room for progress.
In phase locked loop output signal phase tracks input signal's phase. It's like automatic tuning, Frequencies synchronize through feedback.
Think tidal locking, or two pendelums in the same beam. I'm not sure 100% sure but I think Josephson effect is also like this.
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@Lambo got here first with my top fact, so i'll go with this one:
transit operators in the u.s. are not authorized to question the pedigree of your 'service animal.'
as long as you identify the animal as such, you are permitted to bring it on the bus.
*any* animal.
@saltywizard - what are the most crazy examples of service animals that have been recorded?
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@saltywizard - what are the most crazy examples of service animals that have been recorded?
i've heard local anecdotes about a pony on the bus, but i haven't researched national trends.
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i've heard local anecdotes about a pony on the bus, but i haven't researched national trends.
@saltywizard - I feel there should be YouTube videos about this....
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@isaackuo @drdrowland - I see, so colonizing it via air-filled balloon-like floating structures?
we will have to mine the surface for structural material
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@johncarlosbaez That distilled water is completely safe to drink (contrary to what I learned in school)!
@pschwahn - hmm, I never thought it was unsafe. It's just water, after all! But nobody ever told me otherwise. I wonder how common that belief is.
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@johncarlosbaez @pigworker I learned the same thing but the other way round (this is not a coincidence, we were in the same place when it happened). I knew this operation was a monad but didn't know it was the free monad monad
Said in terms of just polynomial functors, the operation p* defined as the least fixpoint of p*(y) = y + p(p*(y)) (that's the least fixpoint of an endofunctor on Poly) is both a monad -* on Poly, and also has the property that p* is a monad on Set for every p
@julesh @pigworker - I don't even know what a "container" is. It's my own fault. There's this repository of computer sciency category theory terminology that's different from the mathy category theory terminology, and I've never been tempted to explore it. There must be something about it that repulses me. I guess my love of math fizzles out when it starts getting too close to computer science. I apologize.
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@pschwahn - hmm, I never thought it was unsafe. It's just water, after all! But nobody ever told me otherwise. I wonder how common that belief is.
@johncarlosbaez @pschwahn I heard this in chemistry class in school. Well, "distilled water is not for drinking" was the rule, the justification was that it lacked some of the essential stuff found in tapwater.
Presumably, it was also to prevent students from drinking the distilled water, which parents donated to the chemistry class.
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@julesh @pigworker - I don't even know what a "container" is. It's my own fault. There's this repository of computer sciency category theory terminology that's different from the mathy category theory terminology, and I've never been tempted to explore it. There must be something about it that repulses me. I guess my love of math fizzles out when it starts getting too close to computer science. I apologize.
@johncarlosbaez @julesh @pigworker Mathematicians tend to call containers "polynomial functors". David Spivak has written a lot about them under this name.
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@johncarlosbaez @julesh @pigworker Mathematicians tend to call containers "polynomial functors". David Spivak has written a lot about them under this name.
@eigil True. I'm a touch old-fashioned in this respect. I note that renaming all the things is the number one strategy when it comes to ignoring prior art. @johncarlosbaez @julesh
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@foldworks - special relativity manages to make good use of a story involving *both* twins and something akin to time travel. The Twin (Non)Paradox.
@johncarlosbaez @foldworks well akSHUallY I think you mean "general relativity" because only non-inertial reference frames could lead to the twins being different ages when reunited.
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@johncarlosbaez @pschwahn I heard this in chemistry class in school. Well, "distilled water is not for drinking" was the rule, the justification was that it lacked some of the essential stuff found in tapwater.
Presumably, it was also to prevent students from drinking the distilled water, which parents donated to the chemistry class.
@thmprover @johncarlosbaez @pschwahn
The reason I heard is that it reverses the direction of osmosis in your gut, leaching nutrients from your body instead of distributing them.
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What's the most surprising fact you've learned in the last couple of weeks? I don't mind if it's quite technical. I just want to hear what you folks are being surprised by!
Here's my big recent surprise: the number
F = (2221564096 + 283748 sqrt(462)) / 491993569
plays a fundamental role in number theory!
For any irrational x, we define its 'Lagrange number' to be the supremum of c such that
|(p/q) - x| < 1/cq²
has infinitely many solutions for rationals p/q. So, the bigger the Lagrange number is, the easier x is to approximate by rational numbers. Quite famously, the golden ratio has the smallest possible Lagrange number, namely √5.
Here's the shocking fact: every real number ≥ F is a Lagrange number, and F is the smallest number with this property!
F is called 'Freiman's constant', because he proved this fact. His proof is 100 pages, and I don't want to read it... but some people have.
There's a lot more crazy stuff about the set of all Lagrange numbers. A tiny bit is here:
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Here's my big recent surprise: the number
F = (2221564096 + 283748 sqrt(462)) / 491993569
plays a fundamental role in number theory!
For any irrational x, we define its 'Lagrange number' to be the supremum of c such that
|(p/q) - x| < 1/cq²
has infinitely many solutions for rationals p/q. So, the bigger the Lagrange number is, the easier x is to approximate by rational numbers. Quite famously, the golden ratio has the smallest possible Lagrange number, namely √5.
Here's the shocking fact: every real number ≥ F is a Lagrange number, and F is the smallest number with this property!
F is called 'Freiman's constant', because he proved this fact. His proof is 100 pages, and I don't want to read it... but some people have.
There's a lot more crazy stuff about the set of all Lagrange numbers. A tiny bit is here:
@johncarlosbaez
Somehow I missed this in the past. It's believable, but not particularly intuitive.
