4 ms·

From the abstract: "Most people believed that fat is converted to energy or heat, which violates the law of conservation of mass."

orblivion 9y ago
But not the conservation mass-energy. What's to say we're not burning off our fat in a nuclear reaction? :-D
- colechristensen 9y ago
  Chemical reactions undergo the same mass loss as nuclear reactions. A fat molecule weighs very slightly more than the sum of it's parts. The resulting water and carbon dioxide products will weigh less than the reactants by exactly the amount of energy released. It's just much more difficult to notice because the amount of energy released is as much less.
  - gwright 9y ago
    Is this true? I was under the impression that the excess energy is due to the different bond energies of the input and output molecules and not due to mass to energy conversion.
    - colechristensen 9y ago
      The mass that's converted to energy in both chemical and nuclear reactions comes from differences in bond energies. Nuclear chemistry is about the bonds between subatomic particles, ordinary chemistry is about the bonds between atoms. Mass-energy conversion isn't a special thing, it's universal. All energy has mass. When energy moves, mass moves, always.
      - andrewla 9y ago
        I'm reasonably certain that this is not correct; this was a viewpoint held fairly briefly in the post-Einsteinian physics community, but abandoned because of a lack of evidence. For the purposes of general relativity, stress-energy is the mass/energy hybrid quantity, but the equivalence is not literal in the sense that in a given inertial reference frame momentum does not attach to energy, but only to mass.
  - orblivion 9y ago
    I've heard of this as well. However, I assume this means that mass turns into kinetic energy specifically, right? And potential energy actually increases with mass? (This isn't something I've heard, it's just the only way I can make sense of things.)
smsm42 9y ago
Converting mass to energy does not violate conservation of mass. But if anybody on the planet managed to convert a pound of mass into energy, we'd hear about it pretty quickly - it's roughly as much energy as a Castle Bravo thermonuclear weapon released. But chemical reactions of course do not involve any significant change of mass, too low energy levels.

orblivion 9y ago

But not the conservation mass-energy. What's to say we're not burning off our fat in a nuclear reaction? :-D

colechristensen 9y ago
Chemical reactions undergo the same mass loss as nuclear reactions. A fat molecule weighs very slightly more than the sum of it's parts. The resulting water and carbon dioxide products will weigh less than the reactants by exactly the amount of energy released. It's just much more difficult to notice because the amount of energy released is as much less.
- gwright 9y ago
  Is this true? I was under the impression that the excess energy is due to the different bond energies of the input and output molecules and not due to mass to energy conversion.
  - colechristensen 9y ago
    The mass that's converted to energy in both chemical and nuclear reactions comes from differences in bond energies. Nuclear chemistry is about the bonds between subatomic particles, ordinary chemistry is about the bonds between atoms. Mass-energy conversion isn't a special thing, it's universal. All energy has mass. When energy moves, mass moves, always.
    - andrewla 9y ago
      I'm reasonably certain that this is not correct; this was a viewpoint held fairly briefly in the post-Einsteinian physics community, but abandoned because of a lack of evidence. For the purposes of general relativity, stress-energy is the mass/energy hybrid quantity, but the equivalence is not literal in the sense that in a given inertial reference frame momentum does not attach to energy, but only to mass.
- orblivion 9y ago
  I've heard of this as well. However, I assume this means that mass turns into kinetic energy specifically, right? And potential energy actually increases with mass? (This isn't something I've heard, it's just the only way I can make sense of things.)

smsm42 9y ago

Converting mass to energy does not violate conservation of mass. But if anybody on the planet managed to convert a pound of mass into energy, we'd hear about it pretty quickly - it's roughly as much energy as a Castle Bravo thermonuclear weapon released. But chemical reactions of course do not involve any significant change of mass, too low energy levels.