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Side note about Newton and occult. Newton was not just a physicist who dabbled with occult. He turned occult into physics. Before Newton scientists and natur

Side note about Newton and occult. Newton was not just a physicist who dabbled with occult. He turned occult into physics. Before Newton scientists and natural philosophers like Descartes believed that movements were caused by physical contact. Newton started traditionally and proposed the existence of ether that transmits forces. When he became interested in alchemy, he replaced ether with occult forces that repel and attract each other. Newton received criticism for his theory that gravity was worked through "action at a distance", because that is occult quality. His theory was not seen as physical theory at first, because 'physical theories' at the time were physical in the intuitive common sense meaning. Action at a distance, across a vacuum, was occultism. Keynes called Newton the last magician. He was able to make similar leap as Einstein did.

0x445442 7y ago
I'm always amazed when I'm reminded of the genesis of Einstein's Special Theory of Relativity. Whether you think it sprung solely from his mind or not, the thought experiment is so simple a young child can understand but look at the ramifications which follow. Just remarkable.
- ralfd 7y ago
  Which thought experiment?
  - WhompingWindows 7y ago
    What would it be like to ride on a beam of light? What would happen if you're on a motorcycle that's going the speed of light, that then has a headlight that's throwing light forward at the speed of light?
    - cperciva 7y ago
      There is no ride. From the photon's perspective, it is emitted and instantaneous absorbed at its destination.
    - PeterisP 7y ago
      It's not possible even in a though experiment, as nothing that has mass (i.e. a motorcycle) can be going at the speed of light. It can be going (theoretically) at 99.999999% of lightspeed, but that's conceptually different.
  - brilee 7y ago
    Special relativity is the set of equations that arises when you take a hypothesis: "you always perceive light as traveling at a speed `c`, no matter how fast you're going" and work out what would have to change in order to allow this statement to hold true.
    - carapace 7y ago
      Sorry to be pedantic, it was: 1.) Maxwell's equations permit no other speed for light than c. 2.) All physical laws (such as Maxwell's) are the same in all inertial reference frames. From those two the rest flows.
      - ralfd 7y ago
        I found that useful. But why is 2 true? Was that proven by experiment or by math equations? It doesn’t seem intuitively true to me.
        carapace 7y ago
        I think both, I'm not a physicist, so I may get this wrong. If it wasn't true, if there was a difference in some physical law due to your motion, you would be able to detect the One True Frame of the Universe. Now here's where I get a little fuzzy, I think it was up for grabs, and then they tried (Michelson–Morley experiment https://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment https://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_exper... ) and couldn't do it. (See also Mach https://en.wikipedia.org/wiki/Ernst_Mach#Philosophy_of_science https://en.wikipedia.org/wiki/Ernst_Mach#Philosophy_of_scien... ) If you're in a spaceship with no windows, out in space, and you are in free-fall (not accelerating), there's no experiment you can do that will tell you whether you are moving or not. If your spaceship has a window, and you look out and see another spaceship passing by (but nothing else) you can't tell whether you're still and it's moving, or you're moving and it's still, or you're both moving. You can detect the relative velocity between you and the other ship, but not the absolute velocity (because there isn't one.) Intuitively we are used to a "absolute" reference frame provided by the bulk of the Earth but that's just a (highly) local context. In space (which is to say, in our Universe) there's no absolute reference frame, so you literally cannot have an absolute velocity, and obviously you can't have a physical law described by an equation that includes a term that doesn't exist, n'est-ce pas? Cheers!
  - 0x445442 7y ago
    The one I learned was this: Person A is on a moving train and tosses a ball into the air of height H. To this person the ball travels a distance of 2H to in a time T to return to his hand. Person B is beside the tracks and sees the same event. To this person the ball travels 2 * (x^2 + H^2)^1/2, which we'll later call D, in the same time T where x is the distance the train traveled during this time. Since velocity is a measure distance divided by time the velocity of the ball in Person A's frame of reference is 2H/T (V1). The velocity of the ball in Person B's frame of reference is 2D/T (V2). Obviously V2 is greater because the distance traveled is greater for the same amount of time. Now suppose instead of tossing a ball into the air of height H, Person A shines a flashlight to a mirror at height H. The new constraint is this; the velocity of light is a constant and cannot be faster for Person B. Now what? Length contraction / time dilation is what.
- kkylin 7y ago
  Not a physicist, but my understanding (from having glanced at one of Einstein's 1905 papers a long time ago) was that the genesis of SR has a context. Specifically, the following observations bothered Einstein (below are my words, don't think anyone from 1905 would say it this way): 1. Maxwell's equations did not permit information to propagate faster than some finite velocity c, which (for many good reasons) can be identified with the speed of light in vaccuum. 2. Closely related mathemaical fact: Maxwell's equations were Lorentz invariant. 3. On the other hand if one envisioned a charged particle moving in a field, then Newtonian theory says the particle dynamics were galilean invariant. But the particle and the field really are part of one system, and it would be odd for the two parts to have different symmetry properties, as this would mean for example that when one changes between two coordinate systems their equations of motion would transform in different ways. I know lots of you know way more physics & history of physics than I. Please jump in!
gerikson 7y ago
I kind of enjoyed Gleick's bio of Newton: https://www.goodreads.com/book/show/17098.Isaac_Newton https://www.goodreads.com/book/show/17098.Isaac_Newton It doesn't shy away from what later hagiographies deride as "religious superstition", but what according to Gleick was integral to Newton's worldview.
ken 7y ago
Here's something I'd love for someone to explain about "magicians". I've read that Einstein was a great physicist for his work on relativity. I still don't know what he actually did. Did he have some mountain of experimental data, to which he found a model which fit? Did he have sub-models which he unified, or simplified? What exactly were his inputs and outputs? In school we're taught that the scientific method involves hypothesis, and experimentation, and confirmation or rejection, but in Einstein's case all I hear about are fully-formed theories -- and then confirmation by others, years after his death. Did he eliminate other possible theories through experimentation, or did he happen to get it right from the start? Was relativity the only possible solution, or was there also some luck involved?
- ajkjk 7y ago
  Einstein's inputs were a bunch of scattered theories about electromagnetism and thermodynamics -- particularly, Maxwell's equations for the electromagnetic field, and the empirical description of the photoelectric effect, and Planck's description of blackbody radiation. His outputs were deducing models that elegantly explained these phenomena: that a constant speed of light in all reference frames, as unintuitive as that is, would lead to the equations of relativity, and that energy being transmitted only in discrete quanta would lead to the photoelectric effect and blackbody radiation effects that were observed by others. This was largely not a feat of producing theories on data. It was coming up with a simpler explanation for phenomena which had already been known, but for which existing explanations were far too complex. The amazing part is that he did this four times in one year (1905): https://en.wikipedia.org/wiki/Annus_Mirabilis_papers https://en.wikipedia.org/wiki/Annus_Mirabilis_papers
- monocasa 7y ago
  For one, Mercury's orbit was pretty confusing, and needed a fudge factor when calculated with existing Newtonian methods. This is why some were so convinced that there had to be a tiny planet Vulcan between it and the sun. When you use Relativistic equations rather than Newtonian, the math just works out clean without a fudge factor.

0x445442 7y ago

I'm always amazed when I'm reminded of the genesis of Einstein's Special Theory of Relativity. Whether you think it sprung solely from his mind or not, the thought experiment is so simple a young child can understand but look at the ramifications which follow. Just remarkable.

ralfd 7y ago
Which thought experiment?
- WhompingWindows 7y ago
  What would it be like to ride on a beam of light? What would happen if you're on a motorcycle that's going the speed of light, that then has a headlight that's throwing light forward at the speed of light?
  - cperciva 7y ago
    There is no ride. From the photon's perspective, it is emitted and instantaneous absorbed at its destination.
  - PeterisP 7y ago
    It's not possible even in a though experiment, as nothing that has mass (i.e. a motorcycle) can be going at the speed of light. It can be going (theoretically) at 99.999999% of lightspeed, but that's conceptually different.
- brilee 7y ago
  Special relativity is the set of equations that arises when you take a hypothesis: "you always perceive light as traveling at a speed `c`, no matter how fast you're going" and work out what would have to change in order to allow this statement to hold true.
  - carapace 7y ago
    Sorry to be pedantic, it was: 1.) Maxwell's equations permit no other speed for light than c. 2.) All physical laws (such as Maxwell's) are the same in all inertial reference frames. From those two the rest flows.
    - ralfd 7y ago
      I found that useful. But why is 2 true? Was that proven by experiment or by math equations? It doesn’t seem intuitively true to me.
      - carapace 7y ago
        I think both, I'm not a physicist, so I may get this wrong. If it wasn't true, if there was a difference in some physical law due to your motion, you would be able to detect the One True Frame of the Universe. Now here's where I get a little fuzzy, I think it was up for grabs, and then they tried (Michelson–Morley experiment https://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment https://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_exper... ) and couldn't do it. (See also Mach https://en.wikipedia.org/wiki/Ernst_Mach#Philosophy_of_science https://en.wikipedia.org/wiki/Ernst_Mach#Philosophy_of_scien... ) If you're in a spaceship with no windows, out in space, and you are in free-fall (not accelerating), there's no experiment you can do that will tell you whether you are moving or not. If your spaceship has a window, and you look out and see another spaceship passing by (but nothing else) you can't tell whether you're still and it's moving, or you're moving and it's still, or you're both moving. You can detect the relative velocity between you and the other ship, but not the absolute velocity (because there isn't one.) Intuitively we are used to a "absolute" reference frame provided by the bulk of the Earth but that's just a (highly) local context. In space (which is to say, in our Universe) there's no absolute reference frame, so you literally cannot have an absolute velocity, and obviously you can't have a physical law described by an equation that includes a term that doesn't exist, n'est-ce pas? Cheers!
- 0x445442 7y ago
  The one I learned was this: Person A is on a moving train and tosses a ball into the air of height H. To this person the ball travels a distance of 2H to in a time T to return to his hand. Person B is beside the tracks and sees the same event. To this person the ball travels 2 * (x^2 + H^2)^1/2, which we'll later call D, in the same time T where x is the distance the train traveled during this time. Since velocity is a measure distance divided by time the velocity of the ball in Person A's frame of reference is 2H/T (V1). The velocity of the ball in Person B's frame of reference is 2D/T (V2). Obviously V2 is greater because the distance traveled is greater for the same amount of time. Now suppose instead of tossing a ball into the air of height H, Person A shines a flashlight to a mirror at height H. The new constraint is this; the velocity of light is a constant and cannot be faster for Person B. Now what? Length contraction / time dilation is what.
kkylin 7y ago
Not a physicist, but my understanding (from having glanced at one of Einstein's 1905 papers a long time ago) was that the genesis of SR has a context. Specifically, the following observations bothered Einstein (below are my words, don't think anyone from 1905 would say it this way): 1. Maxwell's equations did not permit information to propagate faster than some finite velocity c, which (for many good reasons) can be identified with the speed of light in vaccuum. 2. Closely related mathemaical fact: Maxwell's equations were Lorentz invariant. 3. On the other hand if one envisioned a charged particle moving in a field, then Newtonian theory says the particle dynamics were galilean invariant. But the particle and the field really are part of one system, and it would be odd for the two parts to have different symmetry properties, as this would mean for example that when one changes between two coordinate systems their equations of motion would transform in different ways. I know lots of you know way more physics & history of physics than I. Please jump in!

gerikson 7y ago

I kind of enjoyed Gleick's bio of Newton: https://www.goodreads.com/book/show/17098.Isaac_Newton https://www.goodreads.com/book/show/17098.Isaac_Newton It doesn't shy away from what later hagiographies deride as "religious superstition", but what according to Gleick was integral to Newton's worldview.

ken 7y ago

Here's something I'd love for someone to explain about "magicians". I've read that Einstein was a great physicist for his work on relativity. I still don't know what he actually did. Did he have some mountain of experimental data, to which he found a model which fit? Did he have sub-models which he unified, or simplified? What exactly were his inputs and outputs? In school we're taught that the scientific method involves hypothesis, and experimentation, and confirmation or rejection, but in Einstein's case all I hear about are fully-formed theories -- and then confirmation by others, years after his death. Did he eliminate other possible theories through experimentation, or did he happen to get it right from the start? Was relativity the only possible solution, or was there also some luck involved?

ajkjk 7y ago
Einstein's inputs were a bunch of scattered theories about electromagnetism and thermodynamics -- particularly, Maxwell's equations for the electromagnetic field, and the empirical description of the photoelectric effect, and Planck's description of blackbody radiation. His outputs were deducing models that elegantly explained these phenomena: that a constant speed of light in all reference frames, as unintuitive as that is, would lead to the equations of relativity, and that energy being transmitted only in discrete quanta would lead to the photoelectric effect and blackbody radiation effects that were observed by others. This was largely not a feat of producing theories on data. It was coming up with a simpler explanation for phenomena which had already been known, but for which existing explanations were far too complex. The amazing part is that he did this four times in one year (1905): https://en.wikipedia.org/wiki/Annus_Mirabilis_papers https://en.wikipedia.org/wiki/Annus_Mirabilis_papers
monocasa 7y ago
For one, Mercury's orbit was pretty confusing, and needed a fudge factor when calculated with existing Newtonian methods. This is why some were so convinced that there had to be a tiny planet Vulcan between it and the sun. When you use Relativistic equations rather than Newtonian, the math just works out clean without a fudge factor.