4 ms·

>How would you describe in a single sentence the growing precision of our calculation of the speed of light constant over the last 300 years? I don't know, fir

by mnl 9y ago

>How would you describe in a single sentence the growing precision of our calculation of the speed of light constant over the last 300 years? I don't know, first I'd talk about how it was discovered that light behaves like c really is a constant (that's not intuitive nor trivial). You could guess from Fizeau (1851) and Michelson-Morley (1887) experiments, but it wasn't really until the 1905 Einstein's paper that it was understood that you don't need aether, the speed of light can (and should) be a universal constant and it all makes sense. >How would you describe in a single sentence the way Einstein used Mercury's retrograde motion to assure himself of the advocacy of his theoretical mathematical model for gravitation? He shows (see here: http://www.gsjournal.net/old/eeuro/vankov.pdf http://www.gsjournal.net/old/eeuro/vankov.pdf) that his theory (after reasonable approximations) predicts a precession of the perihelion of Mercury that agrees with the experimental result, then he stops. That's what you do in Physics: look, my nice theory predicts this observable in agreement with the experimental data. That's a very good sign, but the data could be explained by other theory as well. Data can "prove" that a theory is wrong (if your theory has falsifiability, as it should), but they can never show that your theory is all that there is, nor your maths... There are other theories of gravitation, for instance Logunov's, that are interesting and agree with data (more or less) but have a few problems with maths. BTW, I don't think he ever really doubted his GR theory, it comes from a very simple, yet profound idea that once realised had to be right. You have to do all the technical work afterwards, that was difficult, but a few mathematicians could have done/did it (Hilbert). In any case the idea is to check your predictions with the measurements from more and more precise experiments to find out if you're wrong, not the other way around (that... well, I've met that funny epistemology a few times in social sciences.)

justifier 9y ago
Why are you relying on strawmen? > Data can "prove" that a theory is wrong (if your theory has falsifiability, as it should), but they can never show that your theory is all that there is, nor your maths. Where you got '"prove"' and 'all that there is' I am unsure My wording was: op> how well different theoretical models express experimental data Which mirrors your own reiteration of that point > the idea is to check your predictions with the measurements from more and more precise experiments Which is literally what I was asking for: measurements from .. precise experiments > predicts a precession of the perihelion of Mercury that agrees with the experimental result Right, where's the experimental data on the orbit of Mercury? If you are unable to answer the question that's fine but as is I fail to see what you are trying to accomplish with your ire and misdirection
- mnl 9y ago
  I'm sorry if I came across that way, didn't mean to. But you have to realise that it's tiresome all this new internet phenomena of laymen questioning the work ethics of actual professionals because they think they could possibly do better, if only etc. I don't usually comment on HN about Physics because... well, never mind, it really was a bad idea this time. If you're interested in the data you can browse the references, go to the libraries (as physicists have to do even at college, because it's kind of hard), find out first what exactly you are asking... even mail someone. And you can also measure things by yourself, this is a free universe and everybody can study its properties (Mercury is out there and maybe you can afford a nice telescope). What is unreasonable, very unreasonable, self-entitled in my opinion, is expecting that experimental physicists provide some kind of repository of (internal-notes redux) data for casual readers of pop sci. That would cost their time (or some overworked PhD student's) and project money, the bad news is no one is willing to do that nor paying for it. It's not that there's some kind of conspiracy, it's that people are actually busy working.
  - justifier 9y ago
    > laymen questioning the work ethics of actual professionals because they think they could possibly do better, if only etc. > What is unreasonable, very unreasonable, self-entitled in my opinion, is expecting that experimental physicists provide some kind of repository > It's not that there's some kind of conspiracy You seem to be arguing with someone else > I don't usually comment on HN about Physics because... well, never mind, it really was a bad idea this time. If you are knowledgeable on the subject I would encourage you to comment, but keep the comment on the topic being discussed
    - mnl 9y ago
      Well, I'll stay on the post topic. It's unlikely that you can get the lab notebooks from most of 20th century Physics, this is what you're really looking for. It's not that important, because once the results are published by a few different groups that don't trust each other and will scrutinize their peers' work, all relevant data have been measured again and again. If theories like Special Relativity were really wrong there would be consequences like having to close all particle accelerators because they wouldn't work. Many key experiments are routinely done as part of the university courses, and many results are also routinely used in other fields, engineering included. E.g. linearisations of Planck's distribution are done in Remote Sensing for estimating surface temperatures, they work great btw. We also understand light bulbs, pyrometers, infrared thermometers... -those work straight with Planck's Law, how else could they find the temperature-. There are GR corrections coded somewhere for your GPS to work, etc. If by seeing "how well different theoretical models express experimental data" you're planning to apply idk assorted non-linear regression models from equations you're not familiar with to see which one has the minimum chi-square or something like that, well I guess that's what hobbies are for. Differences tend to appear at the limiting cases, there you need more Physics than Levenberg–Marquardt fun, so it's better to start there. I have to warn you that your wording matches the usual stuff you get from Physics cranks (the bane of the trade), hence the knee-jerk reaction, sorry about that. I'll try harder next time.

by mnl 9y ago

justifier 9y ago

Why are you relying on strawmen? > Data can "prove" that a theory is wrong (if your theory has falsifiability, as it should), but they can never show that your theory is all that there is, nor your maths. Where you got '"prove"' and 'all that there is' I am unsure My wording was: op> how well different theoretical models express experimental data Which mirrors your own reiteration of that point > the idea is to check your predictions with the measurements from more and more precise experiments Which is literally what I was asking for: measurements from .. precise experiments > predicts a precession of the perihelion of Mercury that agrees with the experimental result Right, where's the experimental data on the orbit of Mercury? If you are unable to answer the question that's fine but as is I fail to see what you are trying to accomplish with your ire and misdirection

mnl 9y ago
I'm sorry if I came across that way, didn't mean to. But you have to realise that it's tiresome all this new internet phenomena of laymen questioning the work ethics of actual professionals because they think they could possibly do better, if only etc. I don't usually comment on HN about Physics because... well, never mind, it really was a bad idea this time. If you're interested in the data you can browse the references, go to the libraries (as physicists have to do even at college, because it's kind of hard), find out first what exactly you are asking... even mail someone. And you can also measure things by yourself, this is a free universe and everybody can study its properties (Mercury is out there and maybe you can afford a nice telescope). What is unreasonable, very unreasonable, self-entitled in my opinion, is expecting that experimental physicists provide some kind of repository of (internal-notes redux) data for casual readers of pop sci. That would cost their time (or some overworked PhD student's) and project money, the bad news is no one is willing to do that nor paying for it. It's not that there's some kind of conspiracy, it's that people are actually busy working.
- justifier 9y ago
  > laymen questioning the work ethics of actual professionals because they think they could possibly do better, if only etc. > What is unreasonable, very unreasonable, self-entitled in my opinion, is expecting that experimental physicists provide some kind of repository > It's not that there's some kind of conspiracy You seem to be arguing with someone else > I don't usually comment on HN about Physics because... well, never mind, it really was a bad idea this time. If you are knowledgeable on the subject I would encourage you to comment, but keep the comment on the topic being discussed
  - mnl 9y ago
    Well, I'll stay on the post topic. It's unlikely that you can get the lab notebooks from most of 20th century Physics, this is what you're really looking for. It's not that important, because once the results are published by a few different groups that don't trust each other and will scrutinize their peers' work, all relevant data have been measured again and again. If theories like Special Relativity were really wrong there would be consequences like having to close all particle accelerators because they wouldn't work. Many key experiments are routinely done as part of the university courses, and many results are also routinely used in other fields, engineering included. E.g. linearisations of Planck's distribution are done in Remote Sensing for estimating surface temperatures, they work great btw. We also understand light bulbs, pyrometers, infrared thermometers... -those work straight with Planck's Law, how else could they find the temperature-. There are GR corrections coded somewhere for your GPS to work, etc. If by seeing "how well different theoretical models express experimental data" you're planning to apply idk assorted non-linear regression models from equations you're not familiar with to see which one has the minimum chi-square or something like that, well I guess that's what hobbies are for. Differences tend to appear at the limiting cases, there you need more Physics than Levenberg–Marquardt fun, so it's better to start there. I have to warn you that your wording matches the usual stuff you get from Physics cranks (the bane of the trade), hence the knee-jerk reaction, sorry about that. I'll try harder next time.