``What is life?'' by a physicist definition

Question

The question is about defining ``What is life?'' in the field of Physics.

Whether there is any (insightful) way of defining ``What is life?'' from physicists.

There are pioneer works, including Erwin Schrödinger's nice book What is life?, cf. Wikipedia. But it will be helpful to hear from someone here if there are alternate new viewpoints. Starting from as basic concept as possible.

Probably involving concepts of entropy, thermodynamics, randomness, order-ness, emergence, aging/time-evolution, etc. But not necessary.

Since this question has been criticized being opinion based as [on hold] (I doubt there is a way to save this issue to be non-opinion-based for a less-developed frontier land like this). Let me focus on this sharp question. The sharp question, I would like to know, is that, suppose only (quantum) mechanical/physical robotic/computer measurement is available,

how can one detect whether an object is being defined as life or lifeless by some physical measurement or computer algorithm?

I imagine, if answered by a quantum physicist, perhaps it will involve with the measurement on a (ground) state wavefunction of the living/lifeless object? Detect certain electronic/magnetic/response signal, etc?

This post imported from StackExchange Physics at 2014-06-24 19:58 (UCT), posted by SE-user Idear

Answer 1

Perhaps let me try to address this question based on a discussion with Prof. Frank Wilczek. This post is not going to be complete or anything.

The punch line question I discussed with him: is there a set of mathematical equations from physical principles to distinguish life and lifeless beings? (say, hand in a system as an input, one can check its live or dead, by running algorithms/numerics/experiments in computer, which outputs the answer.)

Take virus for example may be hard to tell the "phase" difference between life or lifeless, as Brandon suggested. However, I believe, there is certainly a distinction between life and lifeless beings. An extreme example is simply the moment when life beings becoming dead (due to natural process, illness or external factors). Live or dead all concerns the same "organic" system. However, some properties changes between it is live or it is dead. So the virus example is confusing because it is about the complexity of its composition - whether it is organic enough. It is not exactly what Idear is pushing after, I thought.

There may be this distinction between life and lifeless, because the former(life) has "too many degree of freedoms" than the later(lifeless), especially in a time dependent dynamical process. The former (life one) is difficult to reconcile with Determinism.

So let me share with you, Prof. Frank Wilczek's mail response after a conversation, (I wished his generous understanding on sharing his thought to the community here, every copyright on his thought goes to his):

``Hi,

I enjoyed talking with you about this. It's an interesting question. As we discussed, I think the common notion of "life" is a vague around the edges, but of course that was (and still is) true of concepts like "symmetry", "energy", "force", "temperature" -- the scientific notions don't necessarily completely coincide with the everyday notions that inspired them, but capture what can be captured consistent with precision. Also as we touched on, I think that life may probably can only be viewed usefully in terms of how a system responds to an appropriate environment. Thus a living system, roughly, is one that grows and at some level reproduces in an appropriate class of environments. (If we want to exclude crystals, the last phrase is important.) One could attempt to make that definition more "physical" with some notion that life is connected with creating, maintaining, and amplifying entropy gradients.

All the best, Frank W.''

This post imported from StackExchange Physics at 2014-06-24 19:58 (UCT), posted by SE-user Idear