3 ms·

> I find it astounding that a theory like quantum mechanics can have inside it another theory, an approximation, also extremely beautiful mathematically, but ra

by dvt 7y ago

> I find it astounding that a theory like quantum mechanics can have inside it another theory, an approximation, also extremely beautiful mathematically, but radically different. It’s like taking Bach, adding some noise, and getting the best of the Beatles out. I wish I understood better why this can happen. This isn't really the case. Author should've probably mentioned the Ehrenfest theorem[0]. It's not exactly accurate to say that Newtonian mechanics is "embedded" in quantum (or rather Hamiltonian) mechanics. In fact, we need to do some "artificial" re-jigging to make quantum mechanics work at Newtonian scales. [0] https://en.wikipedia.org/wiki/Ehrenfest_theorem https://en.wikipedia.org/wiki/Ehrenfest_theorem

gus_massa 7y ago
>> It’s like taking Bach, adding some noise, and getting the best of the Beatles out. It's a very bad analogy. It's difficult to find a good one. Let's try anyway: Imagine that QM is a real piano and CM is how you expect a piano to sound in normal conditions. If you press a C key, you get a C sound. You can modify the sound releasing the key or keeping it pressed, or pressing the pedals. There are some effect where you press another keys so the sound of the original string make the other strings move and modify the sound. You can hit the wood part of the piano to make some drum like sounds. Most of this can be simulate in an electric keyboard and get an accurate piano-like sound. This is like Classic Mechanics. Quantum Mechanics is like the real piano. You can open or close the top. You can fill the piano with a different gas to make the sound slightly different. Or fill it with water or liquid nitrogen. Use drumstick to hit the strings directly. Use a hammer to hit the wood walls. These create a more wide set of sounds that are nor reproducible in a electric keyboard. An electric keyboard is only an approximation of an idealized real piano. (An experiment where the waviness of the particles is the most important part is like dropping a piano from a 8th floor to hear the sound of the crash, or using the piano as firewood to hear the crispy sound of fire in a winter night. I'm not happy with these examples because they are too destructive, but I wanted too examples of sounds that are very far away from the sounds you expect in an electric keyboard.) (For some reason, musicians do more weird destructive acts with guitar than with pianos. Perhaps it would be a better instrument for the analogy. But it is more difficult to make an idealized model of a guitar. A piano is almost discrete.)
- daxfohl 7y ago
  Better analogy would be chemicals adding up to life. Life adding up to ecosystems. Bargaining adding up to economics. D flip flops adding up to the internet. But all of this stuff is real.
  - gus_massa 7y ago
    I disagree. My idea is that with some common assumptions and simplifications, QM looks like CM when the mass is big and other usual conditions. Like a real piano can be under normal conditions simulated by an electric keyboard. Life is like an emergent phenomena based in chemistry. In some special cases, the chemistry is very complicated and it's better to have special name for this situation and call it life. Anyway, the problem with analogies is that each one thinks that their own one are better.
    - daxfohl 7y ago
      Oh well, I'm more of a rolling stones fan anyway. (smiley face)

by dvt 7y ago

gus_massa 7y ago

>> It’s like taking Bach, adding some noise, and getting the best of the Beatles out. It's a very bad analogy. It's difficult to find a good one. Let's try anyway: Imagine that QM is a real piano and CM is how you expect a piano to sound in normal conditions. If you press a C key, you get a C sound. You can modify the sound releasing the key or keeping it pressed, or pressing the pedals. There are some effect where you press another keys so the sound of the original string make the other strings move and modify the sound. You can hit the wood part of the piano to make some drum like sounds. Most of this can be simulate in an electric keyboard and get an accurate piano-like sound. This is like Classic Mechanics. Quantum Mechanics is like the real piano. You can open or close the top. You can fill the piano with a different gas to make the sound slightly different. Or fill it with water or liquid nitrogen. Use drumstick to hit the strings directly. Use a hammer to hit the wood walls. These create a more wide set of sounds that are nor reproducible in a electric keyboard. An electric keyboard is only an approximation of an idealized real piano. (An experiment where the waviness of the particles is the most important part is like dropping a piano from a 8th floor to hear the sound of the crash, or using the piano as firewood to hear the crispy sound of fire in a winter night. I'm not happy with these examples because they are too destructive, but I wanted too examples of sounds that are very far away from the sounds you expect in an electric keyboard.) (For some reason, musicians do more weird destructive acts with guitar than with pianos. Perhaps it would be a better instrument for the analogy. But it is more difficult to make an idealized model of a guitar. A piano is almost discrete.)

daxfohl 7y ago
Better analogy would be chemicals adding up to life. Life adding up to ecosystems. Bargaining adding up to economics. D flip flops adding up to the internet. But all of this stuff is real.
- gus_massa 7y ago
  I disagree. My idea is that with some common assumptions and simplifications, QM looks like CM when the mass is big and other usual conditions. Like a real piano can be under normal conditions simulated by an electric keyboard. Life is like an emergent phenomena based in chemistry. In some special cases, the chemistry is very complicated and it's better to have special name for this situation and call it life. Anyway, the problem with analogies is that each one thinks that their own one are better.
  - daxfohl 7y ago
    Oh well, I'm more of a rolling stones fan anyway. (smiley face)