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Thanks for sharing those stories. It sounds like you pay quite a bit of attention to the sky and stars! > Why are you not able to make similar empirical tests?

Thanks for sharing those stories. It sounds like you pay quite a bit of attention to the sky and stars! > Why are you not able to make similar empirical tests? If you are able to carry them out, why are they not enough for you? I'm guessing you meant these as rhetorical questions. They're indeed good for introspection. For clarity though, I'm perfectly satisfied with a globe Earth. Seems to be a pretty good model for my needs. I was actually hoping sidestep discussions of Flat Earth vs Round Earth since, as you point out, the empirical observations aren't to hard to think up as a lay person. They're not quite trivial enough to be done in your backyard though. What I'm more interested in, personally, are questions like "What is the structure of the Earth's interior?" I learned an answer from a textbook and am vaguely aware of how seismic data has been used to extrapolate this, but I'm not quite sure how to come up with a Core + Mantle + Crust model myself. Instead of brute forcing these things, I'd really like to hear some clever reasoning and Fermi estimation capable of rederiving these standard results. Perhaps easier to answer would be "Does the moon have an atmosphere?" One idea I had was to point a telescope on a line of site tangent to the lunar surface and look for abberations in starlight compared to stars a large angular distance away. This seems doable in your backyard with relatively cheap hardware.

eesmith 9y ago
I was responding to your statement "It's not actually so trivial. There are simple observations that are consistent with a Round Earth model, but it's pretty difficult to nail things down rigorously and precisely." I object to the idea that additional rigor and precision is needed for the specific case you were responding to. As to your overall topic, one step is to watch that miniseries I mentioned earlier, "The Ring of Truth: An Inquiry into How We Know What We Know". It gives several examples of working things out from scratch. For example, drop a measured and small amount of olive oil onto a still pond. It produces an oil patch. The volume of the oil divided by the size of the patch gives an upper bound for the size of the molecules in olive oil. What you might not know is that there is a large amount of literature in repeating some of the classic experiments. For example, physics undergraduate lab courses may have the students measure the strength of the Earth's local magnetic field, or the value of the gravitational constant G (not g, which is the acceleration due to gravity), and do so using basic equipment you can gather or make yourself. Detecting the Earth's structure on your own is difficult. You will need a seismometer, and learn how to interpret it. A quick search shows there are many hobby plans for building your own seismometer, or you can buy ones made for schools. The harder part is to come to trust that P-waves and S-waves are different, that they have different speeds, that one cannot go through liquid, and that observations of many earthquakes from around the world can be combined with an understanding of material science and thermodynamics to produce a model of the interior of the Earth. If your purpose is to avoid what you consider to be appeals to authoritative sources, you will have to redo from scratch what took others several lifetimes to develop. One of these is Francis Birch, https://en.wikipedia.org/wiki/Francis_Birch_(geophysicist) https://en.wikipedia.org/wiki/Francis_Birch_(geophysicist) . Quoting that Wikipedia page, "In 1952 he demonstrated that Earth's mantle is chiefly composed of silicate minerals, with an inner and outer core of molten iron." Concerning the round earth model, what you can do given limited travel is to create a Foucault pendulum, or visit somewhere which has one set up. In principle this can be done in a backyard, but it required a long pendulum wire and still air - do you have an empty corn silo in your backyard? The time it takes to go around can be used to calculate your latitude. However, this only shows that you are in a rotating reference frame. You then need to repeat what the ancient Greeks did, and look at lunar eclipses to see that the shadow of the earth is always a circle, no matter where the Moon is in the sky. These together mean that from your backyard you could (in principle) determine that the Earth is a rotating round object. Concerning your question "Does the moon have an atmosphere?", the problem is, the Moon does have an atmosphere. It's very thin - https://en.wikipedia.org/wiki/Atmosphere_of_the_Moon https://en.wikipedia.org/wiki/Atmosphere_of_the_Moon . A naked eye view of the Moon is enough to determine that it does not have an extremely thick atmosphere. So with a backyard telescope all you can do is set an upper bound for the thickness of the atmosphere. But to do that, you need some way to predict what those aberrations might look like. For example, if it had a CO2 atmosphere that was 0.1 bar at the surface, would you be able to detect it? Have you measured the index of refraction of different gasses, or are you willing to trust the measurements of others. I'm not saying it's impossible, but rather that you have to decide at some point where you can trust the results of others.
- xelxebar 9y ago
  Wow. Thank you for you thoughtful and long replies. > ...you have to decide at some point where you can trust the results of others. Exactly. My personal attitude in asking is very much in the "hacker spirit"; mainly I point out appeals to authority as an identification of an opportunity to dig deeper. > Foucault pendulum Oh! That's a thing I had forgotten. Back in the day, I remeber using several of these and correlating their positions against rotation rates to estimate the Earth's radius. Not quite a backyard experiment though. > "The Ring of Truth" miniseries It seems this is on YouTube. Thanks for the pointer! The oil drop experiment sounds really cool. > Moon does have an atmosphere... all you can do is set an upper bound for the thickness of the atmosphere. Fair enough. You're speaking more precisely than I. I'm also wondering at what point the variance drops beneath the noise from Earth's atmosphere. This is something that's worth taking a top-down approach by initially trusting our Handbook of Physics and Chemistry and slowly working our way back. Anyway, thanks again for your in-depth replies. You must be an amazing conversation partner!
  - dwaltrip 9y ago
    I really like everything eesmith wrote. I'm all about understanding on a deeper level how things work and how pieces of the world fit together. I also think re-proving fundamental knowledge with simple experiments is awesome. For the general question of knowing how we can trust modern knowledge, there is another useful angle. We can look at the technological devices and items in the world, and try to imagine how they work so reliably and precisely. For example, things like digital cameras, microwaves, mcat machines, gps devices, weather predictions, infrared goggles, sunblock, pneumatic machinery, one-way mirrors, miniature electronics, etc... the list goes on Why are these things so reliable? How do they work? It's very hard to imagine a world in which these countless devices exist, and yet the corresponding science is not very well-understood or robust, at least without jumping too far off the deep end. Of course, it's a fantastic exercise to try to research and understand which individual bits of scientific knowledge are required for the various modern technological devices that we encounter. I know you don't think that the foundations of modern knowledge are shaky. I just thought that your questions were considerate and genuine, and that you might appreciate this additional way of analyzing things. Edit: Watching the Ring of Truth right now... very cool program. Makes me want to do some observations myself.

eesmith 9y ago

I was responding to your statement "It's not actually so trivial. There are simple observations that are consistent with a Round Earth model, but it's pretty difficult to nail things down rigorously and precisely." I object to the idea that additional rigor and precision is needed for the specific case you were responding to. As to your overall topic, one step is to watch that miniseries I mentioned earlier, "The Ring of Truth: An Inquiry into How We Know What We Know". It gives several examples of working things out from scratch. For example, drop a measured and small amount of olive oil onto a still pond. It produces an oil patch. The volume of the oil divided by the size of the patch gives an upper bound for the size of the molecules in olive oil. What you might not know is that there is a large amount of literature in repeating some of the classic experiments. For example, physics undergraduate lab courses may have the students measure the strength of the Earth's local magnetic field, or the value of the gravitational constant G (not g, which is the acceleration due to gravity), and do so using basic equipment you can gather or make yourself. Detecting the Earth's structure on your own is difficult. You will need a seismometer, and learn how to interpret it. A quick search shows there are many hobby plans for building your own seismometer, or you can buy ones made for schools. The harder part is to come to trust that P-waves and S-waves are different, that they have different speeds, that one cannot go through liquid, and that observations of many earthquakes from around the world can be combined with an understanding of material science and thermodynamics to produce a model of the interior of the Earth. If your purpose is to avoid what you consider to be appeals to authoritative sources, you will have to redo from scratch what took others several lifetimes to develop. One of these is Francis Birch, https://en.wikipedia.org/wiki/Francis_Birch_(geophysicist) https://en.wikipedia.org/wiki/Francis_Birch_(geophysicist) . Quoting that Wikipedia page, "In 1952 he demonstrated that Earth's mantle is chiefly composed of silicate minerals, with an inner and outer core of molten iron." Concerning the round earth model, what you can do given limited travel is to create a Foucault pendulum, or visit somewhere which has one set up. In principle this can be done in a backyard, but it required a long pendulum wire and still air - do you have an empty corn silo in your backyard? The time it takes to go around can be used to calculate your latitude. However, this only shows that you are in a rotating reference frame. You then need to repeat what the ancient Greeks did, and look at lunar eclipses to see that the shadow of the earth is always a circle, no matter where the Moon is in the sky. These together mean that from your backyard you could (in principle) determine that the Earth is a rotating round object. Concerning your question "Does the moon have an atmosphere?", the problem is, the Moon does have an atmosphere. It's very thin - https://en.wikipedia.org/wiki/Atmosphere_of_the_Moon https://en.wikipedia.org/wiki/Atmosphere_of_the_Moon . A naked eye view of the Moon is enough to determine that it does not have an extremely thick atmosphere. So with a backyard telescope all you can do is set an upper bound for the thickness of the atmosphere. But to do that, you need some way to predict what those aberrations might look like. For example, if it had a CO2 atmosphere that was 0.1 bar at the surface, would you be able to detect it? Have you measured the index of refraction of different gasses, or are you willing to trust the measurements of others. I'm not saying it's impossible, but rather that you have to decide at some point where you can trust the results of others.

xelxebar 9y ago
Wow. Thank you for you thoughtful and long replies. > ...you have to decide at some point where you can trust the results of others. Exactly. My personal attitude in asking is very much in the "hacker spirit"; mainly I point out appeals to authority as an identification of an opportunity to dig deeper. > Foucault pendulum Oh! That's a thing I had forgotten. Back in the day, I remeber using several of these and correlating their positions against rotation rates to estimate the Earth's radius. Not quite a backyard experiment though. > "The Ring of Truth" miniseries It seems this is on YouTube. Thanks for the pointer! The oil drop experiment sounds really cool. > Moon does have an atmosphere... all you can do is set an upper bound for the thickness of the atmosphere. Fair enough. You're speaking more precisely than I. I'm also wondering at what point the variance drops beneath the noise from Earth's atmosphere. This is something that's worth taking a top-down approach by initially trusting our Handbook of Physics and Chemistry and slowly working our way back. Anyway, thanks again for your in-depth replies. You must be an amazing conversation partner!
- dwaltrip 9y ago
  I really like everything eesmith wrote. I'm all about understanding on a deeper level how things work and how pieces of the world fit together. I also think re-proving fundamental knowledge with simple experiments is awesome. For the general question of knowing how we can trust modern knowledge, there is another useful angle. We can look at the technological devices and items in the world, and try to imagine how they work so reliably and precisely. For example, things like digital cameras, microwaves, mcat machines, gps devices, weather predictions, infrared goggles, sunblock, pneumatic machinery, one-way mirrors, miniature electronics, etc... the list goes on Why are these things so reliable? How do they work? It's very hard to imagine a world in which these countless devices exist, and yet the corresponding science is not very well-understood or robust, at least without jumping too far off the deep end. Of course, it's a fantastic exercise to try to research and understand which individual bits of scientific knowledge are required for the various modern technological devices that we encounter. I know you don't think that the foundations of modern knowledge are shaky. I just thought that your questions were considerate and genuine, and that you might appreciate this additional way of analyzing things. Edit: Watching the Ring of Truth right now... very cool program. Makes me want to do some observations myself.