Life is Physics

For some in the field, finding a theory starts with upending how biologists describe living systems. “When I go to a biology conference, somebody always stands up and says, ‘life is chemistry,’ and then shows a whole bunch of putative reactions,” says Nigel Goldenfeld, a physicist at the University of Illinois at Urbana–Champaign who studies problems related to evolution and ecology. “I don’t think life is chemistry.” Chemistry provides information on the molecules needed to make life, but not on how to get a functioning cell, for example. Instead, he says, “life is physics,” and researchers should think of living organisms as condensed-matter systems with thermodynamic constraints.

I’m not sure I completely agree. I am certain there is much we might learn by applying physics to biology, but it’s not clear that physics is the whole story. My own field of statistics is a mathematical discipline, but in application requires a certain “art” of using key information from other fields. A person can understand the math but not the application.

I’m betting that others will have their own reasons to think physics is not the whole story. :wink:


It is the typical conceit of @physicists to see everything as physics, chemists to see everything as chemistry, mathematicians to see everything as math, economists to see everything economics. Though, I’m not sure biologists see everything as biology. Evolutionists, however, might see everything as evolution…

Reminds of our interminable conversation about motors and flagella. There is value in seeing things from a physics perspective, but let’s not collapse life down to an identity with physics.

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I tend to see everything as one big joke, so that isn’t unique to scientists. :grin:


But only the physicists are right…though I could argue math’s case too. :wink:

One reason is the efficiency we gain in making predictions using biology, rather than relying on quantum physics for everything, even though in theory, QM could predict future quantum configurations of the world at a given time on its own (ignoring measurement problem issues).

There is a nice discussion of that in the Emergence video from this playlist (the fourth one in the playlist at the right of the displayed YT page). The first four minutes of the video set the stage, then Sean Carroll and especially Dan Dennett explain why a (quantum) Laplace’s demon would be mystified about how we could do as well as it* in making predictions from the from other sciences than physics.

Caorse Graining YT Playlist

  • And without a halting oracle up our sleeves!

At the most fundamental level, why everything is not physics is covered in this piece by Ed Feser.

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I normally do not read Feser. However, I made an exception in this case. And that was my mistake. Or, rather, that resulted in my reading Feser’s mistakes.

Feser’s post is against materialism. Much of physics is about time and space, which are immaterial. But Feser fails to understand that.

That’s not what most scientists mean by “matter”.

There’s another point of disagreement. Feser thinks that everything is describable with logic. In my view, only the abstract is describable with formal logic. Yes, we use logic for things in the world. But, in order do do that, we first construct our own logical models. And then we apply the logic to those models. Logic, by itself, cannot refer to anything in the actual world. It takes human mediation to connect logic to reality.

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No one else posted this, so I guess it’s up to me …


XKCD: Purity


This is an admittedly naive question from a physicist: in what way is life not reducible to physics? In my “typically conceited” physicist mind, all of natural science is a subset of physics, i.e. a biologist is a type of physicist.

This is because I think there is no clear difference between a biologist, who studies emergence phenomena resulting from more basic foundational physics, and say a condensed matter physicist, who studies emergence phenomena resulting from more basic foundational physics.


As a biologist, that is how I view the situation. Physics describes the interaction between atoms and energy, and this is what is understood to be the root causes of everything within the science of biology. This is especially true when you start digging into the basics of molecular biology.

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And here’s my naive answer from a mathematician.

Life is about behavior. The physics is a mere implementation detail.


I suppose this would depend on what one thinks about consciousness. I believe that one’s behavior is just an emergent phenomenon resulting in the physical state of one’s brain, i.e. ultimately caused by the particular configuration and motion of the brain’s physical constituents (e.g. quarks and so on).

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It depends what you mean by ‘reducible’.

If you mean that the explanations of all other sciences can be replaced by explanations using only the language and theories of physics, I think the answer is no.

If you mean the explanations of other sciences cannot violate the laws of physics, I think the answer is yes. (I’m leaving what is meant by laws of physics for another thread!).

If you mean that only the entities postulated by fundamental physics are real, and all other entities are reducible to them metaphysically, then that is a good question.


I mean this one. I don’t mean all other sciences, as depending on the definition this can include mathematics, but biology in particular. Why is biology not reducible to physics in this sense?

The nature, possibility, and current extent of scientific reduction is the subject of ongoing research and controversy in philosophy of science. I’ve provided some links below; the IEP one is best as an introduction but the SEP links provide deeper summaries. I could try to rehearse some of the basic ideas here, but I am hardly an expert, and I suspect you would get more out of at least the introductory sections of each. In particular, the SEP article on intertheoretic relations of physics might be of direct interest given your training.

Although I was aware of these controversies, I had actual something simpler in mind when I said I doubted reduction of explanation: namely, the psychological nature of explanation. It seems to me that even if (eg) biological evolution could somehow be restated in the language and theories of physics, one could not call the result an explanation in the sense that it would be something a human could grasp. This is related to what I was trying to get at in my reply to Dan Eastwood at the top of this thread in the discussion of emergence and efficiency of prediction.

Here are the links for philosophical details:
IEP Introl

SEP Intro

SEP On physics and intertheory reduction

SEP on biology and intertheory reduction

I quite like the Nagel-Schaffner reduction. However I think I would go further, that even prior to reduction, biology is already physics. To me, there is no clear boundary where physics stops. I don’t understand why:

  • Bob studies jellyfishes, which are aggregates of particles. Therefore, Bob studies emergent properties from a bunch of particles.
  • Alice studies neutrons, which are aggregates of particles. Therefore, Alice studies emergent properties from a bunch of particles.
  • Somehow, Bob is a biologist while Alice is a physicist.

How is it not the case that both of them are physicists? Just that Bob studies biology (a subfield of physics) while Alice studies subatomic physics (also a subfield of physics).

I agree they both study emergent patterns of fundamental physics entities. To me, that is expressing something ontological: what the world is. If you think that is enough to say that are both doing subfields of physics, then I cannot argue with you under that assumption. But I think there is more to it.

What I am trying to focus on is how emergence affects how they express their results. That to me is where explanation enters. Biologists don’t express their results in the language of fundamental physics (which I take to be for now something involving QFT, assuming GR is not relevant for biology).

Whether those explanations and theories of biology could in principle be re-expressed using only fundamental physics is the philosophical controversy about intertheoretic reduction.

But my further point is that the explanations are only graspable because they are expressed in and take advantage of higher level (ie emergent) regularities that are noted in my post from four days ago.

These regularities also underlie by favored approach to ontology. I think these regularities are worthy of being called ‘real’. that is as part of the basic furniture of the world. I like the way David Wallace quotes Dennett to this end in his book on the The Emergent Multiverse: Quantum Theory according to the Everett Interpretation

The idea can be formalized to rid it of any overtones of subjectivity inherent in the concept of usefulness.

I think there might be an analogy of this approach to the ontology associated with renormalization in physics, but since I have only the haziest understanding of renormalization, that analogy could be a figment of my imagination.

(ETA Off-topic: I see Dr Loeb had what comes across to me as a rather testy interview with the New Yorker on the Oumuamua object New Yorker Interview)

The quarks come and go, as we eat, exhale, etc. But the kind of behavior is more persistent.

I should perhaps clarify, though. When I say “behavior”, I am not restricting that to gross behavior. I also include cognitive behavior, perceptual behavior, etc. And, looked at that way, I take a person to be a bundle of behavior that happens to have a dynamically changing physical implementation.

To me QFT is not any more the language of physics than whatever is used in biology is. After all, plasma physics is solidly in the realm of physics, yet we don’t talk about plasma physics by reducing it to QCD. To me, the relation between (biology → particle physics) is the same as the relation between (plasma physics → QCD).

No one demands a box of plasma to be expressed by QCD for it to be called a subfield of physics. Why do we demand biology to be expressed by QFT for it to be called a subfield of physics?

Also, whether explanations are graspable by humans or not does not matter to me. Explaining a box of plasma in terms of QCD is not graspable by anyone, yet studying boxes of plasma is solidly in the realm of physics.

I understand, but even the time evolution of these particles are governed by physics. The emergent behavior of an open system of quarks is still part of physics.

Fair enough. But that evolution of particle includes the possibility of the particles no longer being part of the person.

Biology carves up the world into organisms. Physics carves it up into particles (and fields, etc). The way that biology carves up the world is incommensurable with the way that physics carves up the world. That’s why biology is not reducible to physics.