[dwaltrip]

A common measure of complexity is the amount of information required to fully describe or recreate some system.

If you simply gather a very large number of hydrogen atoms into a region of space at a certain density, you will create star. From this angle, it isn't terribly complex.

The instructions for creating a cell from scratch are... immensely more complicated.

The star's behavior, .e.g. the movement and changes of the convection zones, fusion dynamics, how the magnetic fields change over time, coronal mass ejections, sunspots, etc. may be extremely complex. I think few people who know much about stars would disagree on that.

But I would wager there are many more orders of magnitude of complexity going on in a human cell, from an information theory perspective. Even just describing individual proteins themselves and how they fold is phenomenally difficult.

Of course, I may be wrong about the cell's behavior having higher complexity. The important take away is that it is possible to make such comparisons in a meaningful way.

[JabavuAdams]

Good points, but there's still something missing in the comparison. It's the difference between the initial information content, and the dynamics. Suppose we had to fix some problem in a star such that we need to precisely manipulate the magnetic fields, and perhaps things at a quantum scale. At that point, we are concerned with the fine-scale configuration of that particular star. Your proposed star creation algorithm only gives an ensemble over all stars of that particular mass and initial composition. It has less information content, because it doesn't create a particular star. I.e. we are willing to accept a huge class of individuals that we call "stars".

So, we're back to comparing thing A that we need to understand at the finest scale, to thing B where we ignore its individual complexity in favour of the stereotypical version. It's easy to estimate the gravitational attraction or mass of a cell. It's this fine-scale manipulation that causes these severe requirements for deep understanding.

EDIT> :) The instructions for creating life are even simpler. 1) Have a Big Bang. 2) Wait.

[dwaltrip]

Hmm. You are making me think hard, which I like. Given that any human description of a system is going to be an approximation of reality, I suppose the one of the key difficulties is determining which aspects of the system are more important for our model to more closely match.

Even if the information theory metric of complexity is somewhat flawed, given our limitations, I think it is a useful tool. I'm not sure what would be a better way of comparing complexity.

At the very least, I think I can make statements such as: "a closed container of hydrogen gas at room temperature and pressure is a much simpler system than a Swiss watch", which we could roughly quantify in a somewhat robust way. The hydrogen part is easy, as the atoms are indistinguishable, and their movements can be closely approximated with simple formulas.

P.S. I just remembered a good (and short) minutephysics video on entropy & complexity, perhaps it is worth linking: https://youtu.be/MTFY0H4EZx4

[rgejman]

Is it possible that no individual star OR individual cell can be sufficiently described because of quantum uncertainty effects that would affect any "object" with electrons (speaking as a biologist; not a physicist).

Also: this is a really great, really stellar thread.

[JabavuAdams]

Not sure how electrons enter into it. Quantum Mechanics (QM) isn't limited to electrons. Chemistry is largely focused on electrons, so maybe that's where you were first introduced to QM?