Sorry if this is a dumb question, recently I have been interested in the question of how "life" should be defined and got a specific question:

If we compare a live body of a person and a dead body of someone who just died, what is the difference in term of their molecule? Say for example, when the heart stops beating, the blood won't cycle through the body, but if we focus on individual cells, say the blood cell, which has hemoglobin molecules, it stops carrying oxygen when the person dies, but if we dig further, the hemoglobin molecule is defined as:

A hemoglobin molecule is made up of four polypeptide chains, two alpha chains of 141 amino acid residues each and two beta chains of 146 amino acid residues each.

A bit more further we would reach the microscopic world, where there are atoms, protons, electrons, etc, AFAIK, these things would still obey the rule of thermal motion, although the motion may be less active due to the reduced temperature of the dead body.

So from the atom's perspective, what is the difference between a live person and a dead body?

Thanks and sorry again for this dumb question!

  • 4
    $\begingroup$ From atoms prospective there is no difference. It is like a car that has crashed: from the atomic (and even material) perspective it is still a pile of metal, glass, and plastic... but the shape of the parts and their position in respect to each other are such that it cannot function anymore as a car. One could say that being a car is more than just being a collection of atoms - it is an emergent property. You can search this site for emergence. $\endgroup$ Jul 28 at 11:46
  • $\begingroup$ Thanks @RogerVadim to me the car example feels a bit different, a dead body can be lifeless without any damage or deformation, yet there is no life in it, the atoms, molecules, organs, skins, etc, are still in good shape, it's more like a machine that runs our of power and no power can be provided to it for some reason, and comparing such a machine with a running machine that does have power supply, there's no difference even between parts / components. $\endgroup$
    – hzxu
    Jul 28 at 13:04
  • $\begingroup$ @hzhu What you say is correct. The difference is that car materials are stable, soone can restart it long time after it stopped, whereas the molecules in an organism start to degrade. If new molecules are not synthesized, this degradation becomes irreversible. In other words, there is damage, even though it is not immediately visible. Although forensic scientists are trained to see even insignificant markers. $\endgroup$ Jul 28 at 13:12

None. Say you were to take a skin sample from a living individual, and a skin sample from a deceased person. If you were then to somehow extract and isolate a single atom from each sample, they would be indistinguishable. In other words, if you were to mix up the two atoms, there would be no way if telling which came from the deceased individual.


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