5 ms·

The Origin of Mass (2003) [pdf]

87 points by lainon 9y ago

lisper 9y ago
Should add [2003] to the title.
amelius 9y ago
> Finally, the most basic feature of mass in classical mechanics is that it is conserved. For example, when you bring together two bodies, the total mass is just the sum of the individual masses. This assumption is so deeply ingrained that it was not even explicitly formulated as a law. (Though I teach it as Newton’s Zeroth Law.) The author may wish to check [1] for historical reference. [1] https://en.wikipedia.org/wiki/Conservation_of_mass https://en.wikipedia.org/wiki/Conservation_of_mass
- pvg 9y ago
  The author is a Nobel laureate in Physics.
  - mowenz 9y ago
    So what's wrong with Lavoisier being credited with the Law of Conservation of Mass? He is famous enough for it that I, having no formal training in physics, am aware of him discovering it independently. The author may be right (or wrong) but he is not right or wrong due to whatever epaulletes he is wearing on his uniform. It does signal he is likely right, but in that case we should point to the reason and not just point to at the epaulettes.
    - pvg 9y ago
      Nothing, other than the fact the author is not talking about Lavoisier's law and that it's more than a little presumptuous to be telling someone who teaches physics at MIT, beside collecting a Nobel prize, that they might wish to check Wikipedia (ceremoniously [1]-footnoting it, in two lines of text) for the historical perspective they might lack. Yes of course the author can be wrong about something - the comment isn't pointing out anything wrong, just sententiously insinuating he is uninformed.
      - mowenz 9y ago
        Then you can enlighten us because as far as we can tell what we think you are saying is the author's discussion of conservation of mass has nothing to do with the Law of Conservation of Mass (as opposed to some mystic qualities of matter believed prior to the discovery of this law of nature--in classical physics). Don't just point to the epaulettes and tell him to be respectful--it's ok to question authority (granted it was done a little bit presumptiously, you are right there, but I'd recommend letting it go--be the bigger person and be the teacher).
        pvg 9y ago
        I'm not 'pointing to epaulettes. I am pointing out the silly and unwarranted assumption Frank Wilczek is unaware of the basic, Wikipedia-page-level history of the science in question. I think it's obvious and a given that he is. If you don't think that's the case, fair enough but it's up to you to find some concrete way to support that rather odd view - it's not for me to refute it from first principles.
        mowenz 9y ago
        We're not asking you to defend this physicist. There's an obviously confusing bit about conservation of mass here, which lead to the user citing the Law of Conservation of Mass, that I already asked about, and which you are now ignoring. That's the thing to focus on, not on Frank Wilczek. We already know the poster (unwittingly) was a bit presumptious, but in my opinion I think it would be better to focus on the ideas and let the presumptiousness just slide.
        pvg 9y ago
        What's the confusing bit?
        mowenz 9y ago
        What's remarkable about conservation of mass in the author's example that's not already formulized in the Law of Conservation of Mass?
    - andars 9y ago
      The key words are "in classical mechanics." Nobody wondered whether the mass of two stacked bricks was equal to the sum of the masses of the individual bricks. On the other hand, burning cloth seems to "leave behind" a lot less than you started with. Lavoisier's contribution was to demonstrate that even in chemical reactions, with shocking changes in color, state of matter, etc, mass was conserved. Wilczek is discussing the ingrained assumption about the bricks.
      - mowenz 9y ago
        We're familiar with Lavoisier's Law. So when you are suggesting CM, many of us probably know that Lavoisier's Law would show small errors at high energy states in CM... But then your explanation offers some perspective on Lavoisier's Law... So what are you suggesting with your key word?
    - Mvandenbergh 9y ago
      In the context of chemistry, conservation of mass is not at all obvious which is why it is a big deal that Lavoisier proved it to be the case. To determine that burning wood into ash (for instance) doesn't change the total mass of the system requires precise measurement and an intuitive leap on what constitute the boundaries of the system. In mechanics there is historically no such law precisely because no-one would ever have thought that it wasn't obviously true.
      - mowenz 9y ago
        Yes I am aware. The issue is that in our current understanding we now know in chemistry we are adding element1+element2=element1+element2... (classically at least). So while Lavoisier led us to the above, the author is pointing to the fact that e1+e2=e1+e2 but to the reader this can be confusing because Lavoisier's Law also states the same... Though once you understand that you are just rearranging chemical bonds b/w elements there's nothing different about it. I don't have any intuition about how you would theoretically prove the assumption in Lavoisier's Law--Newton's 0th Law. It seems if Lavoisier's Law is true it implies Newton's 0 must also, at least intuitively... It's a reasonable source of confusion and I think it's ok the above poster was misguided about it as everyone agrees from the start on this: almost no one questioned such an assumption.
- pfortuny 9y ago
  That is the superposition principle for scalars.
zentiggr 9y ago
That was a very understandable outline of the basic concepts... well written and almost convinces me that I could step off the end of the Theoretical Minimum math and into further QM. Oh my.
kqr 9y ago
> it derives m=E/c², not E=mc². Einstein was thinking about fundamental physics, not bombs. Although I know the E=mc² formulation makes more sense from an "E²=(pc)²+(mc²)²" point of view, the author had a kind of striking way to put their point. It's as if the war managed to intertwine itself in culture so strongly it twisted the perception of the entire general public on issues of fundamental physics!
- tinalumfoil 9y ago
  F=ma was originally a=F/m. Although the former seemed more useful at the time the latter nowadays is more intuitive. The bomb shaped culture and physics, sure, but rewriting equations into more useful and intuitive forms isn't a new or uncommon phenomenon.
  - bykovich2 9y ago
    Yeah, I think it's inherently more striking to think about mass "becoming" energy, or the "energy content" of mass, than about the converse. Imagining energy "condensing" into mass is wild, but we spend a lot more time around mass qua mass than around pure energy.
empath75 9y ago
Interesting that he doesn't mention the Higgs.

87 points by lainon 9y ago

Should add [2003] to the title.

> Finally, the most basic feature of mass in classical mechanics is that it is conserved. For example, when you bring together two bodies, the total mass is just the sum of the individual masses. This assumption is so deeply ingrained that it was not even explicitly formulated as a law. (Though I teach it as Newton’s Zeroth Law.) The author may wish to check [1] for historical reference. [1] https://en.wikipedia.org/wiki/Conservation_of_mass https://en.wikipedia.org/wiki/Conservation_of_mass

pvg 9y ago
The author is a Nobel laureate in Physics.
- mowenz 9y ago
  So what's wrong with Lavoisier being credited with the Law of Conservation of Mass? He is famous enough for it that I, having no formal training in physics, am aware of him discovering it independently. The author may be right (or wrong) but he is not right or wrong due to whatever epaulletes he is wearing on his uniform. It does signal he is likely right, but in that case we should point to the reason and not just point to at the epaulettes.
  - pvg 9y ago
    Nothing, other than the fact the author is not talking about Lavoisier's law and that it's more than a little presumptuous to be telling someone who teaches physics at MIT, beside collecting a Nobel prize, that they might wish to check Wikipedia (ceremoniously [1]-footnoting it, in two lines of text) for the historical perspective they might lack. Yes of course the author can be wrong about something - the comment isn't pointing out anything wrong, just sententiously insinuating he is uninformed.
    - mowenz 9y ago
      Then you can enlighten us because as far as we can tell what we think you are saying is the author's discussion of conservation of mass has nothing to do with the Law of Conservation of Mass (as opposed to some mystic qualities of matter believed prior to the discovery of this law of nature--in classical physics). Don't just point to the epaulettes and tell him to be respectful--it's ok to question authority (granted it was done a little bit presumptiously, you are right there, but I'd recommend letting it go--be the bigger person and be the teacher).
      - pvg 9y ago
        I'm not 'pointing to epaulettes. I am pointing out the silly and unwarranted assumption Frank Wilczek is unaware of the basic, Wikipedia-page-level history of the science in question. I think it's obvious and a given that he is. If you don't think that's the case, fair enough but it's up to you to find some concrete way to support that rather odd view - it's not for me to refute it from first principles.
        mowenz 9y ago
        We're not asking you to defend this physicist. There's an obviously confusing bit about conservation of mass here, which lead to the user citing the Law of Conservation of Mass, that I already asked about, and which you are now ignoring. That's the thing to focus on, not on Frank Wilczek. We already know the poster (unwittingly) was a bit presumptious, but in my opinion I think it would be better to focus on the ideas and let the presumptiousness just slide.
        pvg 9y ago
        What's the confusing bit?
        mowenz 9y ago
        What's remarkable about conservation of mass in the author's example that's not already formulized in the Law of Conservation of Mass?
  - andars 9y ago
    The key words are "in classical mechanics." Nobody wondered whether the mass of two stacked bricks was equal to the sum of the masses of the individual bricks. On the other hand, burning cloth seems to "leave behind" a lot less than you started with. Lavoisier's contribution was to demonstrate that even in chemical reactions, with shocking changes in color, state of matter, etc, mass was conserved. Wilczek is discussing the ingrained assumption about the bricks.
    - mowenz 9y ago
      We're familiar with Lavoisier's Law. So when you are suggesting CM, many of us probably know that Lavoisier's Law would show small errors at high energy states in CM... But then your explanation offers some perspective on Lavoisier's Law... So what are you suggesting with your key word?
  - Mvandenbergh 9y ago
    In the context of chemistry, conservation of mass is not at all obvious which is why it is a big deal that Lavoisier proved it to be the case. To determine that burning wood into ash (for instance) doesn't change the total mass of the system requires precise measurement and an intuitive leap on what constitute the boundaries of the system. In mechanics there is historically no such law precisely because no-one would ever have thought that it wasn't obviously true.
    - mowenz 9y ago
      Yes I am aware. The issue is that in our current understanding we now know in chemistry we are adding element1+element2=element1+element2... (classically at least). So while Lavoisier led us to the above, the author is pointing to the fact that e1+e2=e1+e2 but to the reader this can be confusing because Lavoisier's Law also states the same... Though once you understand that you are just rearranging chemical bonds b/w elements there's nothing different about it. I don't have any intuition about how you would theoretically prove the assumption in Lavoisier's Law--Newton's 0th Law. It seems if Lavoisier's Law is true it implies Newton's 0 must also, at least intuitively... It's a reasonable source of confusion and I think it's ok the above poster was misguided about it as everyone agrees from the start on this: almost no one questioned such an assumption.
pfortuny 9y ago
That is the superposition principle for scalars.

zentiggr 9y ago

That was a very understandable outline of the basic concepts... well written and almost convinces me that I could step off the end of the Theoretical Minimum math and into further QM. Oh my.

kqr 9y ago

> it derives m=E/c², not E=mc². Einstein was thinking about fundamental physics, not bombs. Although I know the E=mc² formulation makes more sense from an "E²=(pc)²+(mc²)²" point of view, the author had a kind of striking way to put their point. It's as if the war managed to intertwine itself in culture so strongly it twisted the perception of the entire general public on issues of fundamental physics!

tinalumfoil 9y ago
F=ma was originally a=F/m. Although the former seemed more useful at the time the latter nowadays is more intuitive. The bomb shaped culture and physics, sure, but rewriting equations into more useful and intuitive forms isn't a new or uncommon phenomenon.
- bykovich2 9y ago
  Yeah, I think it's inherently more striking to think about mass "becoming" energy, or the "energy content" of mass, than about the converse. Imagining energy "condensing" into mass is wild, but we spend a lot more time around mass qua mass than around pure energy.

empath75 9y ago

Interesting that he doesn't mention the Higgs.