8 ms·
Ole Roemer and the Speed of Light
- prezjordan 14y agoVery thorough explanation, awesome! What I'm more curious of is, how did astronomers measure the radius of the earth and moon several hundred (1000?) years ago?
- CUViper 14y agoI don't know for the Moon, but for the Earth try this: https://en.wikipedia.org/wiki/Eratosthenes#Eratosthenes.27_measurement_of_the_Earth.27s_circumference https://en.wikipedia.org/wiki/Eratosthenes#Eratosthenes.27_m...
- rcthompson 14y agoGiven the radius of the Earth, they could probably get the radius of the moon by looking at the curvature of the edge of the Earth's shadow upon the moon during a lunar eclipse.
- abecedarius 14y agoFind the moon's distance by parallax, then the radius follows from the angle it subtends.
- dalke 14y agoFor parallax you need to take two measurements at the same time. Given that the distance to the moon is about 384,400 km, a 1,000 km baseline gives an angle of 1/384 radians = 0.15 degree. This requires some a rather sophisticated methods, such as clocks with good precision and a telescope. The method of Aristarchus is much more clever than that. At 1/2 moon, the earth/moon/sun forms a right angle. The angle moon/earth/sun could be measured as about 3 degrees - something that the ancient Greeks could measure. This gives a ratio of earth-moon/sun-moon distances between 18 and 20. Then during a lunar eclipse, you can measure the width of the cone of the earth's shadow vs. the moon's width. During a solar eclipse you can see that the moon's angular width is about that of the sun. That information, plus the measured radius of the earth, and a bit of geometry, gives you an estimate of the size of the moon. http://en.wikipedia.org/wiki/On_the_Sizes_and_Distances_%28Aristarchus%29 http://en.wikipedia.org/wiki/On_the_Sizes_and_Distances_%28A...
- stargazer-3 14y agoThe coolest thing about it is that more than 2200 years ago it was already possible to measure Earth's circumference with only 2% error. If not for the dark ages, who knows what world we'd live in now?
- arethuza 14y agoThe term "Dark Age" to describe the time after the fall of the Western Roman Empire seems, as far as I can tell, to be rather frowned upon by historians. After all, the Eastern Roman Empire continued a lot longer in the form of the Byzantines up to the fall of Constanople in 1453 and, more importantly, there was the rise of Islamic culture - which reach a very high level of civilization during this time. Having said that, I am personally fascinated by history during this time as it led to the genesis of a lot of our current nation states and the very paucity of the historical record from these times just adds to the romance for me!
- teeja 14y agoMichael S. Malone explores the "dark ages" idea in his new book "The Guardian of All Things:The Epic Story of Human Memory". His conclusion was that it was pretty dark for 5 or 6 centuries after Rome fell - then the "high Middle Ages" began and learning and writing and schools and scholarship were rampant all over Europe and the Middle East. Really opened my eyes on that period.
- vorg 14y agoIslamic civilization took over from Roman civilization from about 632 AD in the Middle East, centered around North Africa, Iraq/Persia, and Turkey at various times over the next 1300 yrs. Perhaps more important was the Sui/Tang dynasties in China around 600 AD kicking off over 1000 yrs of being the most developed place on Earth. They built the Grand Canal connecting the Yellow and Yangtse rivers, turning them into a single economy based on trading rice for coal.
- ef4 14y agoIt's not so much that the "dark ages" intervened in some linear progression of scientific discovery. Rather, it seems to require a precise and finicky set of conditions to get a real scientific & industrial revolution going. The hard part isn't really the basic scientific discoveries. It's the society-wide political and economic conditions that let capital accumulation go exponential. The ancient Greeks had working toy steam engines. They could have started the industrial revolution right there. Why didn't they? There are lots of theories. Maybe they hadn't invented good enough ideas about banking and property. Maybe their reliance on slave labor blinded them to the value of mechanization. Maybe their class system kept people with scientific knowledge too far away from people with practical working knowledge. The bottom line is that scientific knowledge is probably not the limiting factor.
- mfn 14y agoThis set of slides goes over how some astronomical measurements were made hundreds of years ago: http://terrytao.files.wordpress.com/2010/10/cosmic-distance-ladder.pdf http://terrytao.files.wordpress.com/2010/10/cosmic-distance-...
- hencq 14y agoWow, that's absolutely brilliant. Thanks for sharing. It's particularly impressive to see how old (and accurate) some of these measurements are.
- chii 14y agoi got goosebumps - i mean, the people of old are really intelligent! they used whatever piece of data they can scrunge together to piece the truth out. I feel like these days, we aren't putting in as much effort in these endeavours as the days of old. I wonder why...
- StavrosK 14y agoThat's easy! Rosy retrospection, positivity effect, there are a few biases going on here.
- 205guy 14y agoThe "people of old" were just as intelligent as humans today, they just didn't have the same access to technology or stored knowledge (which is why Wikipedia is so revolutionary in some ways). If you look at the statuary from Classical times or the cathedrals of medieval Europe, you come to realize these people were just like us. Some went through life unthinking, others probably had unrealized gifts, and a few were able to show their talents. Also, I'm no anthropologist, but I believe modern humans have existed longer than wrting and the historical record, so I would conjecture that humans up to 10,000 years ago--perhaps all the way back to the Cro-Magnons of 40Kya--were just as intelligent as people today, just they didn't have the means to express it the way we do. In some ways, the wasted educations and wasted talent of today is apalling. I was in the Sainte Chapelle in Paris recently and realized no one has created anything like it in 800 years.
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- rcthompson 14y agoThe distinction between philosophy and science (and math, engineering, etc.) is a very recent one (less than 200 years old). You may have heard the term "natural philosophy" as an old term for science, but it betrays that fact that what we now call science was just another branch of philosophy. Remember that Descartes also authored major mathematical works. Philosophers of that day could and did do a little bit of everything. Anyway, his argument, and the other arguments of them time, were based on things like the fact that if the speed of light were finite, you would notice things like the sun, moon, and earth being out of alignment during an eclipse, since the earth's shadow would lag behind it. Since no such misalignment was observed, the speed of light must be infinite. Later philosophers pointed out, of course, that it was also possible that the speed of light was finite but very fast, and the eclipse lag time was immeasurably small. Then Roemer settled things once and for all.
- chii 14y agoit'd be interesting to have recounts of what people's thoughts were of the speed of light, when it was found out that it's so damn fast.
- acqq 14y agoTo put it in perspective, Newton's "Philosophiæ Naturalis Principia Mathematica" was first published 11 years later.
- vishal0123 14y agoFor those who don't know, a more accurate calculation of speed of light was done in ancient india and had been mentioned in rigveda: http://www.hitxp.com/articles/veda/light-speed-rigveda/ http://www.hitxp.com/articles/veda/light-speed-rigveda/
- carbocation 14y agoIn case you are serious, there is no mention of how this calculation was empirically made. It seems much more likely that this is fortuitous teleological translation rather than an actual discovery of the speed of light cryptically hidden away in the Vedas.
- pitchups 14y agoThe original article referenced by the link above has more information on why the calculation may be authentic and can be found at http://www.infinityfoundation.com/mandala/t_es/t_es_kak-s_light_frameset.htm http://www.infinityfoundation.com/mandala/t_es/t_es_kak-s_li...
- carbocation 14y agoNo, those add no empirical support. They mention no derivation of the numbers, no explanation for how they were measured. They don't clarify, beyond the blog post, whether this should be accepted as a discovery or treated as coincidence. They just restate the same coincidence.
- chubbard 14y ago"...Sun (light) traverses 2,202 yojanas in half a nimisha" Yes, but how did he measure it?
- shmerl 14y agoHe could know that from someone else. But from whom - is a separate question.
- nikcub 14y agoA solution to an accurate measurement of longitude for shipping was one of the biggest scientific problems of the time and involved some of the brightest minds in the world working over decades and centuries. After losing almost 2,000 sailors and 4 Navy ships in an accident attributed to poor navigation, the British government offered the Longitude Prize - which was worth millions of dollars in todays money. From Gallileo and his method of timekeeping by tracking the moons of Jupiter, through to John Harrison and his invention of the chronometer - which ended up winning most of the Longitude Prize - the effort that went into finding a solution had many side effects for science and the solution opened up the world to better navigation and the eventual colonization. The entire story is chronicled in the book 'Longitude'[0], which was a best seller in 1998. It is well worth a read. Wikipedia is also a good starting point for finding out more.[1] [0] http://www.amazon.com/Longitude-Genius-Greatest-Scientific-Problem/dp/080271529X http://www.amazon.com/Longitude-Genius-Greatest-Scientific-P... [1] http://en.wikipedia.org/wiki/History_of_longitude http://en.wikipedia.org/wiki/History_of_longitude
- damian2000 14y agoGreat book. There was also a BBC TV doco about it - http://news.bbc.co.uk/2/hi/science/nature/241228.stm http://news.bbc.co.uk/2/hi/science/nature/241228.stm
- carlob 14y agoAnother interesting read is "The island of the day before" by Umberto Eco. A 1995 novel about the problem of longitude and time zones. http://en.wikipedia.org/wiki/The_Island_of_the_Day_Before http://en.wikipedia.org/wiki/The_Island_of_the_Day_Before
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- mhandley 14y agoAnd if you're ever in London, I'd thoroughly recommend visiting Harrison's clocks at the Greenwich Observatory: http://www.rmg.co.uk/harrison http://www.rmg.co.uk/harrison
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- Pr0 14y agoVery impressive!
- axomhacker 14y agoI love these kind of stories. Such stories fills me up with an immense sense of appreciation for scientists/philosophers/thinkers from the post-middle-ages. Also, why I'm absolutely loving the coursera class on astronomy: https://class.coursera.org/introastro-2012-001/ https://class.coursera.org/introastro-2012-001/. If you have not peaked into it yet, the way Dr. Plesser explains concepts and bridges them with the historical advances leaves a lasting impression. I wish we had classes like this back in school.
- notimetorelax 14y agoSounds interesting, thank you for the suggestion. Here's the direct link to course description: https://www.coursera.org/course/introastro https://www.coursera.org/course/introastro Although course started a while ago they still give access to the materials is you subscribe now.
- axomhacker 14y agoAlso, if you like the "Introduction to Astronomy" course, there's a follow-up (although from a different university, Caltech) coming up: "Galaxies and Cosmology": https://www.coursera.org/course/cosmo https://www.coursera.org/course/cosmo
- JonnieCache 14y agoAnd if that isn't enough for you there's a complete series of stanford cosmology lectures from Leonard Susskind (!) starting here: http://www.youtube.com/watch?gl=GB&hl=en-GB&v=32wIKaLkvc4 http://www.youtube.com/watch?gl=GB&hl=en-GB&v=32wIKa... It's part of a comprehensive course in modern physics, all taught by susskind, and all on that same youtube channel. There's classical mechanics, quantum mechanics, the aforementioned cosmology and more iirc. He's a great teacher, it's amazing that you can just dial up tens of thousands of dollars worth of education like this.
- robolav 14y agoAdam Savage explains how light was measured in a ingenious experiment in 1849: http://ed.ted.com/lessons/how-simple-ideas-lead-to-scientific-discoveries http://ed.ted.com/lessons/how-simple-ideas-lead-to-scientifi...
- guillaume__ 14y agoMeasuring the speed of light only with a cog, a piece of glass and a mirror is so clever. The relevant part of the video starts at 4:06. A history of measurement of the speed of light can be found there https://en.wikipedia.org/wiki/Speed_of_light#History https://en.wikipedia.org/wiki/Speed_of_light#History
- notdrunkatall 14y agoThat was a fantastic presentation, thanks!
- Florin_Andrei 14y agoIt's quite doable today at the level of a "garage physicist". I keep thinking to try it. Maybe one of these days.
- rimantas 14y agoIs there a book with collection of stories like this?
- andrewcooke 14y agoa couple of good, but old, anthologies are "a random walk in science" (and whatever the follow-up was called - perhaps "more random walks..."). this search has the first one as a pdf in the first hit - https://www.google.cl/search?q=a+random+walk+in+science&oq=a+random+walk+in+science&aqs=chrome.0.57j62l3j64l2.6612&sourceid=chrome&ie=UTF-8 https://www.google.cl/search?q=a+random+walk+in+science&...
- srathi 14y agoSlightly off-topic: there is a story-like narrative description of development of quantum mechanics in a book by Manjit Kumar. I don't recall the title, though.
- Avalaxy 14y agoI was just about to post this, but 'A short history of nearly everything' by Bill Bryson has a LOT of these stories. It explains how we determined the circumference and the weight of the earth, the distance to the moon and the sun, etc. In fact the whole book is about this, it explains all the important scientific breakthroughs from the past and how we've gotten to them.
- maeon3 14y agoWhat I take away from these stories is not how to calculate the speed of light, but how to discover things previously not known. Observe something on the edge of what is known, (the orbital period of IO), take better measurements than ever before (creating new measurement technologies), observe unexplained phenomenon (the annual increase/decrease in the orbital period of IO), and apply tried and true mathematical principles: (given the distance between planets, and the observed orbital period, solve for speed of light). It's this process that will answer other unanswered questions in our physics engine, another one for example being whether or not photons degrade, or if it is possible to remove the higgs boson from matter, rendering it with no mass.
- tripzilch 14y agoInteresting. Put it like that the large hadron collider is just a natural consequence :)
- gus_massa 14y agoThe Higgs bosons don't live inside the matter, so it's not possible to remove them. It's more complicated, and difficult to explain without a few algebra and physics study years, but let's try with another broken analogy: The Higgs field is like an invisible background. When the particles bounce against this background the effective effect is that the particles have apparent mass. Sometimes, the particles create bumps in the background; these bumps can move and they are the Higgs bosons. It's (probably) not possible to remove the background to make the particles "lighter". (The equations are so clear, the analogy explanations are so confusing. :( )
- imglorp 14y agoI'm a little unclear on how was the +/- 11 minutes variation measured throughout the year? Huygen's clocks lost about 15s/day, which would give them around an hour and a half a year. source: http://www.americanscientist.org/issues/pub/huygenss-clocks-revisited http://www.americanscientist.org/issues/pub/huygenss-clocks-...
- redwood 14y agoLove this: "He later served as mayor and prefect of police of Copenhagen and ultimately as head of the State Council." A real renaissance (or post-renaissance) man! I love imagining a scientist heading up a bunch if police!
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- lectrick 14y agoLoved this. Interesting how it was an accidental discovery based on a different pursuit at the time. That is almost a trope of life itself...
- lectrick 14y agoThe NOVA series was good, for anyone curious. http://www.amazon.com/NOVA-Lost-Sea-Search-Longitude/dp/B000XBPDXK/ref=sr_1_cc_2?s=aps&ie=UTF8&qid=1355505396&sr=1-2-catcorr http://www.amazon.com/NOVA-Lost-Sea-Search-Longitude/dp/B000...
- lmm 14y agoArrgh. The original, better title had stood for at least four hours, and was the name under which I knew the discussion. Is there any kind of site/extension that displays hacker news, but gives stories the titles they were originally submitted under? If not I guess I'll do it myself.
- bjornsing 14y agoOur little startup started it's life at Ole Römers väg (Ole Roemer's road) in Lund, so I've looked up a few versions of this story. The one I like the best* has a more dismal tone: Ole discovered the finite speed of light, but was outmaneuvered by Jean-Dominique Cassini who had a complex theory based on tables. I sometimes use it when I want to explain how important it is to try and see past "social truth" to find the real one. I can's say which version is more accurate, but there's a scientific inaccuracy in the OP that makes me a bit skeptical of the author: The distance between Jupiter and the Earth will have no impact on how long Io is hidden behind Jupiter. It's the change in distance been Jupiter and Earth from when Io disappears behind Jupiter to when it reappears some minutes later that will affect the timing. So IMHO the illustration in the OP is wrong, the timing will be approximately the same in position 1 and 2. Position 2 should be moved so that it is at the far right (or left) of Earths orbit. (*) http://www.pbs.org/wgbh/nova/physics/ancestors-einstein.html http://www.pbs.org/wgbh/nova/physics/ancestors-einstein.html