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How was the size of Earth first measured? (2015)

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Re: How was the size of Earth first measured? (2015)

#101

5% error is incredible. I wonder what Eratosthenes thought of his own measurement. Did he believe it was accurate? Or questioned if unknown factors could have thrown off his calculation?

He measured it in "stadia" and there was no consensus about exactly how long a stadion was. The definitions ranged widely, from ~150m to ~210m. The low error assessment comes from magnanimously (but baselessly) choosing to use the definition of a stadion which assigns Eratosthenes the lowest error. https://en.wikipedia.org/wiki/Stadion_(unit)

Even if he only measured Earth's radius with 50% accuracy, that's still pretty impressive for the 2nd Century BC.

Re: How was the size of Earth first measured? (2015)

#102
post #80
post #11

Terrence Tao has an old excellent presentation on the “cosmic ladder” which shows how from this measurement you can build up to measure the largest distances in the visible universe: https://terrytao.files.wordpress.com/2010/10/cosmic-distance...

The thing that stood out to me was the second rung of the ladder, the Moon. Having a large companion satellite is not a prerequisite for life (probably), so how would aliens without one bridge this gap? It seems like it would take a lot more physical theory beyond simple geometry to get there.

Aliens might live on a planet without a large moon but it’s pretty unlikely for their planet to be the only object in orbit around their star. The easy way to measure the Earth-Sun distance today is to use radar to precisely measure our distance from Venus and triangulate our position from that. Aliens with radar could do the same trick using other objects in their home planetary system.

But even before radar, we had parallax methods for figuring this stuff out. Radar just brings the error down into the low parts-per-billion territory.

Re: How was the size of Earth first measured? (2015)

#103

Earlier quoted context omitted.

I'm not convinced until the pyramids encode the Meter and the Kilogram and Mole. ...in Hex.

make enough measurements and you can probably find those "encoded" there, too

write a program to prove your point.

I'm not saying this with sarcasm. Maybe you could take over my attempts at coming up with a custom set of equations for a pyramid, or any other platonic shape, using symbolic regression / genetic algorithms.

https://pastebin.com/9CEU76K6

Re: How was the size of Earth first measured? (2015)

#104

Earlier quoted context omitted.

You can get to the absolute dimensions of the pyramid from the crackpot equations though: https://pasteboard.co/cIMzn8KktEZy.png https://tobeornottobe.org/the-great-pyramid-intro/math-const... https://pastebin.com/TsUtcWAa I just found a great recap on this topic that also fits nicely with the points your link brings up, shedding a better light on the number 43,200 in other cultures (the scaling factor between the py…

I'm not convinced until the pyramids encode the Meter and the Kilogram and Mole. ...in Hex.

"The pyramids give us the dimensions of our planet on a scale defined by the planet itself." - Hancock

It's a bit as if we had never seen a poem and stumble upon some text that harbors rhymes. You'd argue there's no intrinsic link between, say, pickle and tickle, you'd dig in each word etymology to show they wouldn't rhyme in their past forms. And beyond that you would deny the fact words rhymes because they are not in succession, and when I'd point out it's because the rhymes are crossed, you'd laugh it off.

It's not about convincing you (of what ? of some secret intent ? I'm not even sure this is the case). It's about how convincing it is. For that you need to model the cognitive process that interprets these coincidences.

Algorithmic Simplicity and Relevance - Jean-Louis Dessalles

https://telecom-paris.hal.science/hal-03814119/document

4.1 First-order Relevance Relevance cannot be equated with failure to anticipate [16]: white noise is ‘boring’, although it impossible to predict and is thus always ‘surprising’, even for an optimal learner. Our definition of unexpectedness, given by (1), correctly declares white noise uninteresting, as its value s at a given time is hard to describe but also equally hard to generate (since a white noise amounts to a uniform lottery), and therefore U(s) = 0. Following definition (1), some situations can be ‘more than expected’. For instance, if s is about the death last week of a 40-year old woman who lived in a far place hardly known to the observer, then U(s) is likely to be negative, as the minimal description of the woman will exceed in length the minimal parameter settings that the world requires to generate her death. If death is compared with a uniform lottery, then Cw(s) is the number of bits required to ‘choose’ the week of her death: Cw(s)  log2(52×40) = 11 bits. If we must discriminate the woman among all currently living humans, we need C(s) = log2(7×109 ) = 33 bits, and U(s) = 11 – 33 = –22 is negative. Relevant situations are unexpected situations.

s is relevant if U(s) = Cw(s) – C(s) > 0 (2)

Relevant situations are thus simpler to describe than to generate. In our previous example, this would happen if the dying woman lives in the vicinity, or is an acquaintance, or is a celebrity. Relevance is detected either because the world generates a situation that turns out to be simple for the observer, or because the situation that is observed was thought by the observer to be ‘impossible’ (i.e. hard to generate).

In other contexts, some authors have noticed the relation between interestingness and unexpectedness [9, 16], or suggested that the originality of an idea could be measured by the complexity of its description using previous knowledge ([10], p. 545). All these definitions compare the complexity of the actual situation s to some reference, which represents the observer’s expectations. For instance, the notion of randomness deficiency ([8], ch. 4 p. 280) compares actual situation to the output of a uniform lottery. The present proposal differs by making the notion of expectation (here: generation) explicit, and by contrasting its complexity Cw(s) with description complexity C(s).

Re: How was the size of Earth first measured? (2015)

#105
post #87
post #85

Earlier quoted context omitted.

Because spheres are the best Platonic solid and so Earth must be a sphere, naturally.

Spheres aren't Platonic solids.

Whoops, I was thinking "solids that were highly significant to Plato" (for which spheres definitely qualify) but of course, as you point out, they're not actually Platonic solids. Still Plato relate-o though:

> Plato's Timaeus proposed that the body of the cosmos was made in the most perfect and uniform shape, that of a sphere containing the fixed stars.

(Wikipedia, referencing F. M. Cornford, Plato's Cosmology: The Timaeus of Plato)

Re: How was the size of Earth first measured? (2015)

#106

The Greeks (or, more precisely, the Eastern Mediterraneans, since a ton of these guys were Phoenician) were jaw-droppingly awesome at this stuff. I wish I could have seen it. It makes you wonder how much knowledge from other places - places with wetter climates, and/or further from the colonial powers of the 19th C - has been lost. One of the contributing reasons heliocentrism disappeared from view was that a large q…

I had a history prof address these feats-of-observation of these primordial scientists: you've got a group of totally idle wealthy, with up to 16 hours of day time to fill, across millions of people and thousands of years. Eratosthenes could've thought about this problem — and nothing else — for a thousand hours in just six months, with plenty of time off to pursue other hobbies. When's the last time you dedicated 1000 hours to a single problem?

Re: How was the size of Earth first measured? (2015)

#107

This estimation method would only work under the assumption that earth is a spherical. Now that we do know that it's a sphere. But how could you figure that out back in 2000 years ago?

The Earth must be a sphere because during lunar eclipses its shadow is always a circle.

Re: How was the size of Earth first measured? (2015)

#108
post #8

Given the large distance between the cities, how did they communicate to confirm that the sun was indeed overhead at particular time and date?

Thank you! I've wondered that, can't wait to see what he answer is.

The communication requirements are minimal. The only real requirement is that we agree on which day to perform the measurement.

You and I could sit at Christmas dinner, and conspire to measure the shadow of a 1metre pole at solar noon on Easter Sunday, at our respective locations.

We could then compare those measurements when we meet next Christmas.

Re: How was the size of Earth first measured? (2015)

#109

Earlier quoted context omitted.

Of course it's fundamentally unlearnable. No matter what we do know, we can never prove there wasn't someone else who figured it out even earlier but never wrote it down, or they did but it and all references to it were lost. Most "firsts" carry an implicit asterisk that isn't worth mentioning. The first person to run a 4 minute mile did so in 1954. With the asterisk that somebody else might have already done that mi…

In that case then "earliest known" is the only thing that should ever be said and there is no justification for claiming "first".

Logically, sure. Practically, we've collectively decided to skip words that are redundant in context.

Kind of the same way you don't usually include the country code of your phone number when someone asks for your number (unless you're in an international context).

In all areas of life, we give technically incomplete information, but reasonably expect people to know what we mean. Because we're humans, not computers. And we do it all day long, every day.

Re: How was the size of Earth first measured? (2015)

#110
post #73
post #42

Earlier quoted context omitted.

pages 156-158: “Ironically, when Aristarchus proposed the heliocentric model, his contemporaries dismissed it, on the grounds that they did not observe any parallax effects...” “ so the heliocentric model would have implied that the stars were an absurdly large distance away.” “[Which, of course, they are.]”

Knowing this makes me perplexed whenever someone treats geocentrists as idiots. Sometimes science really can get only as far as our "eyes" can see.

If we had to prove which is right without access to prior wisdom, most of us would fail miserably. Our current understanding of the world can't be built in any single person's lifetime.

But it's easier than ever to do your own research in the modern age. Heliocentrism vs. geocentrism is a well established topic. It doesn't take a genius to reach the right information. You can even conduct your own experiment if you want to.

The only thing stopping people from learning besides poverty is their own free will. I think the reputation is well deserved.

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