The Observer and the Observed

This essay began with a novel. Greg Bear’s Blood Music (1985) ends on a physical theory, offered late in the book by a physicist named Gogarty. Observation, he argues, is a kind of information processing. Conscious observers help set the boundaries of what happens in space and time rather than simply recording it. On this view, physical law is something we settle jointly with the universe rather than something we discover. It holds only as long as nothing contradicts it.

The trouble in the novel is biological. A biotechnologist has built intelligent cells called noocytes, and they have multiplied into the trillions. Each one is an observer. Bear’s narrator remarks that until then “the densest single unit of information processing on this planet was the human brain” (Greg Bear, Blood Music, 1985). Once that ceases to be true, the sheer density of observation begins to strain physical reality itself.

It is a striking idea, and it rests on a real feature of quantum mechanics. This essay tries to say carefully what that feature is. It then separates it from the popular versions that have grown up around it, and asks where the coupling between observer and observed genuinely shows up in biology. The short answer is that the coupling shows up everywhere, but almost never for quantum reasons. The version that matters for a person collecting data about their own body is classical and ordinary. It is also large enough to shape how such data must be gathered.

What quantum mechanics says about measurement

This section sets out the measurement problem and the ideas that have accreted around it. It matters because the novel’s premise is a dramatization of one reading of that problem. Quantum mechanics describes a system with a wavefunction, a mathematical object that evolves smoothly and deterministically under the Schrödinger equation. A wavefunction can represent a superposition, which is a state in which the system has not settled on one value of some property. When the system is measured, the theory says we obtain one definite outcome, with probabilities given by the wavefunction. The formalism therefore contains two different rules, one for evolution and one for measurement. It does not say what physically counts as a measurement, and that gap is the measurement problem.

Decoherence is the part of the answer that has been worked out in detail. Any quantum system that interacts with its environment becomes entangled with it. The environment here can be a stray photon, an air molecule, or the thermal jostling of a warm liquid. The interference between the branches of the superposition leaks into that environment, where it is effectively unrecoverable. Zurek’s review describes how this process singles out a stable set of states, the ones that survive interaction with the environment, and why they look like the ordinary classical states we see ¹. Decoherence is extraordinarily fast for anything large or warm, which is why we never see a superposed chair. What it does not do, as Zurek is careful to say, is explain why a single outcome occurs rather than another. The measurement problem is narrowed rather than dissolved.

Two experiments are usually offered as evidence that observation reaches into the physical world, and both are real. The first is the quantum Zeno effect, in which repeatedly measuring a system inhibits its transitions. Itano and colleagues demonstrated it in 1990 with beryllium ions held in a Penning trap ². Short laser pulses served as the measurements while a radiofrequency field tried to drive the ions between two hyperfine levels. The more often the pulses checked the state, the less the transition proceeded.

The second is Wheeler’s delayed-choice experiment. Here the decision to measure a photon’s path or its interference is made after the photon has already entered the apparatus. Jacques and colleagues realized this in 2007 with single photons and a quantum random number generator ³. The generator chose the configuration after the photon was in flight, in a way that no signal could have influenced. The photon behaved according to the question asked, whenever it was asked.

Wheeler took these results seriously enough to propose what he called “it from bit” ⁴. It was a working hypothesis that every physical thing derives its existence from answers to yes-or-no questions posed by measuring apparatus, and that the universe is in this sense participatory. This is the intellectual ancestor of Gogarty’s speech. Wheeler repays reading in the original, because he was precise about what he was claiming. The participant in his account is the apparatus, the polarizer and the photodetector. The claim is about how physical properties become definite, not about minds reaching out to adjust the laws of nature. He offered it as a hypothesis to be developed, and in the decades since it has been a stimulus to quantum information theory rather than an established result.

The common misreading is that consciousness collapses the wavefunction. The idea has a respectable history. Von Neumann noted that the line between measured system and measuring apparatus could be drawn anywhere, and Wigner briefly suggested that a conscious mind was where the chain had to end. Nothing in the experiments requires it. In the Zeno experiment, the measurement was a laser pulse and a photon count. In the delayed-choice experiment, the choice was made by a random number generator. Decoherence proceeds whether or not anyone is watching.

Nothing is decohered more thoroughly than warm, wet, crowded matter. That is what makes Blood Music’s premise so unlikely as physics. A living cell is about the least isolated quantum system one could design. Adding more cells adds more decoherence. The observer effect, if anything, gets smaller as the crowd grows.

Where quantum effects do appear in biology

Having narrowed the quantum story, it is fair to ask whether it appears in living systems at all. It does, in a small number of well-studied places, and this section describes the two best known.

The best-supported case is the radical-pair mechanism of magnetoreception. Ritz, Adem, and Schulten proposed in 2000 that migratory birds sense the Earth’s magnetic field through pairs of radicals created by light in a retinal protein ⁵. Radicals are molecules with unpaired electrons, and the authors suggested cryptochrome as the candidate protein. The magnetic field influences the spin state of the pair and therefore the yield of its chemical products. Because the effect depends on the orientation of the molecules, the bird could in principle see a pattern that shifts with heading. Hore and Mouritsen’s 2016 review lays out the chemistry and physics for biologists and the biology for physicists ⁶. It remains the leading hypothesis for how the compass works.

The radical-pair story even contains a proposed Zeno effect. Kominis argued in 2009 that the standard theory of radical-pair reactions, in use since the 1970s, hides quantum coherence ⁷. On his account a treatment based on quantum measurement theory naturally incorporates a Zeno-like inhibition and explains certain magnetic-field-dependent yields. The proposal was disputed by other spin chemists, and the question of the correct master equation is still argued over. What is notable for this essay is that the measuring apparatus in Kominis’s picture is the spin-selective chemical reaction itself. No bird is required to be aware of anything.

The other famous case has not held up as first reported. In 2007, Engel and colleagues observed long-lived oscillations in the two-dimensional electronic spectra of the Fenna-Matthews-Olson complex at 77 kelvin ⁸. That complex is a light-harvesting protein from a green sulfur bacterium, and the authors interpreted the oscillations as evidence of wavelike, coherent energy transfer. The result launched much of what is now called quantum biology. By 2020 a group of seventeen authors, several of them from the original community, had reexamined the evidence ⁹. They concluded that electronic coherences in these complexes are too short-lived to matter for energy transfer, and that the long-lived oscillations arise from molecular vibrations excited by the laser pulse. Their revised picture is instructive. Photosynthesis is efficient because the proteins are built to exploit dissipation into the environment, which is decoherence used as a tool rather than avoided.

The pattern across both cases is the same. Where quantum effects appear in biology, they live in small molecules over short times. They are confined by the warm environment rather than amplified by it, and they involve no observer in the human sense. None of this scales toward minds shaping the laws of physics.

Where measurement really disturbs the living system

If the quantum coupling is small, the classical coupling between observer and observed is not. This section describes how much of ordinary biology consists of managing that coupling.

Consider live-cell fluorescence microscopy, where the act of looking is done with light and the light does damage. Icha, Weber, Waters, and Norden describe how excitation illumination injures cellular macromolecules ¹⁰. They emphasize that the subtler consequences are the ones that quietly alter experimental conclusions, namely changes in behavior with no visible change in morphology. Their recommendations are practical acknowledgments that the observer is a participant. They advise restricting illumination to the focal plane and running explicit controls for phototoxicity. The microscopist’s problem is the physicist’s problem in a form anyone can see: the probe carries energy, and the energy changes the thing probed.

Single-cell RNA sequencing offers a starker version. The workflow, as Haque and colleagues lay it out, isolates a single cell and then lyses it ¹¹. Lysis dissolves the membrane to release the cell’s RNA for capture and sequencing. Every cell in such a dataset was observed exactly once, at the moment of its destruction. There is no way to follow one cell’s transcriptome through time. The only option is to infer trajectories from a population of cells caught at different stages.

The same review notes that even the steps before lysis can change the RNA levels one is trying to measure, since dissociating tissue into single cells is itself disruptive. A measurement that ends the thing measured is the strongest form of the observer effect there is. It is also standard practice.

At the scale of whole organisms, the classic name for the phenomenon is the Hawthorne effect. The idea is that people change their behavior because they know they are being studied. McCambridge, Witton, and Elbourne reviewed the evidence in 2014 and found that the concept is poorly defined ¹². The original factory studies do not support the clean story usually told about them. Research participation clearly can change behavior. Little is securely known about when it does, by what mechanism, or by how much. They proposed replacing the term with “research participation effects” to encourage more careful study. The effect is real enough on their reading, but it has been treated as a slogan when it deserves to be treated as a variable.

The reverse direction

The coupling also runs from the observed back to the observer. In a personal dataset the two are the same person, which is why this direction matters most here. When people measure themselves, the measurement changes them. König and colleagues reviewed thirty-one studies of reactivity to digital in-the-moment measurement, mostly wearable step counters and phone-based logging ¹³. They found small but consistent effects, with pooled effect sizes around 0.3 for physical activity. They identify three amplifiers: behaviors that are easy to change, awareness of being measured combined with social desirability, and the self-regulation that follows from seeing a gap between what one does and what one intended. A wearable is a mirror as much as an instrument.

Continuous glucose monitoring is the most direct example of the loop. A sensor under the skin reports interstitial glucose every few minutes, and the wearer sees the trace rise after a meal. Richardson and colleagues pooled twenty-five randomized trials of monitoring used as a behavior-change tool, in people with and without diabetes ¹⁴. Feedback from the monitor lowered HbA1c and increased time in the target glucose range compared with control arms. Only four of the trials measured diet, so the behavioral pathway is mostly inferred, and the review says as much.

The direction of the finding is the important thing for anyone interpreting their own glucose data. The trace records a metabolism that is being watched by someone who can act on what they see. The watching is part of what it records.

This has a design consequence. A longitudinal dataset about a person is a record of a system with feedback, and the feedback is the person. The first weeks of a glucose trace are different in kind from the twentieth. By then the wearer has learned which meals produce spikes and has quietly changed them. A blood panel drawn the morning after someone read their previous results measures a different person from the one who gave the earlier sample.

This is a property of the system rather than a defect to be engineered away. The practical response is to record enough context that the effect can be seen. That means noting when results were shown, what changed afterward, and which measurements were taken before the subject had any information to react to. A baseline is only a baseline if it precedes the feedback.

Back to the novel

Bear’s Gogarty is not wrong about everything, and the novel deserves credit for building its ending on a live question in physics rather than on nothing. Observation does fix properties that were not fixed before it. Repeated observation does inhibit change. The choice of what to ask does determine what the world can answer. All of that is in the record.

What does not follow is the scaling. The effects are confined to small, cold, isolated systems. Adding trillions of warm observers only speeds the decoherence. The universe has been observed for a very long time by a great many things without anyone noticing the boundaries shift.

The coupling that shapes biology is the older kind. Light damages what it illuminates. Sequencing consumes what it reads, and people change when they watch themselves. Bear used quantum measurement as a metaphor for a truth that is broader than physics, that observer and observed are never fully separable. A person building a record of their own body should take the metaphor seriously in its classical form. You are both the instrument and the subject. The data will be better if they are gathered by someone who knows that.

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Footnotes

1. Wojciech Hubert Zurek. Decoherence, einselection, and the quantum origins of the classical. Reviews of Modern Physics, 2003. https://doi.org/10.1103/RevModPhys.75.715 ↩

2. Wayne M. Itano, D. J. Heinzen, J. J. Bollinger, D. J. Wineland. Quantum Zeno effect. Physical Review A, 1990. https://doi.org/10.1103/PhysRevA.41.2295 ↩

3. Vincent Jacques, E Wu, Frédéric Grosshans, et al. Experimental Realization of Wheeler’s Delayed-Choice Gedanken Experiment. Science, 2007. https://doi.org/10.1126/science.1136303 ↩

4. John Archibald Wheeler. Information, physics, quantum: the search for links. In W. H. Zurek (ed.), Complexity, Entropy, and the Physics of Information, Addison-Wesley, 1990. https://philpapers.org/rec/WHEIPQ ↩

5. Thorsten Ritz, Salih Adem, Klaus Schulten. A Model for Photoreceptor-Based Magnetoreception in Birds. Biophysical Journal, 2000. https://doi.org/10.1016/S0006-3495(00)76629-X ↩

6. P. J. Hore, Henrik Mouritsen. The Radical-Pair Mechanism of Magnetoreception. Annual Review of Biophysics, 2016. https://doi.org/10.1146/annurev-biophys-032116-094545 ↩

7. I. K. Kominis. Quantum Zeno effect explains magnetic-sensitive radical-ion-pair reactions. Physical Review E, 2009. https://doi.org/10.1103/PhysRevE.80.056115 ↩

8. Gregory S. Engel, Tessa R. Calhoun, Elizabeth L. Read, et al. Evidence for wavelike energy transfer through quantum coherence in photosynthetic systems. Nature, 2007. https://doi.org/10.1038/nature05678 ↩

9. Jianshu Cao, Richard J. Cogdell, David F. Coker, et al. Quantum biology revisited. Science Advances, 2020. https://doi.org/10.1126/sciadv.aaz4888 ↩

10. Jaroslav Icha, Michael Weber, Jennifer C. Waters, Caren Norden. Phototoxicity in live fluorescence microscopy, and how to avoid it. BioEssays, 2017. https://doi.org/10.1002/bies.201700003 ↩

11. Ashraful Haque, Jessica Engel, Sarah A. Teichmann, Tapio Lönnberg. A practical guide to single-cell RNA-sequencing for biomedical research and clinical applications. Genome Medicine, 2017. https://doi.org/10.1186/s13073-017-0467-4 ↩

12. Jim McCambridge, John Witton, Diana R. Elbourne. Systematic review of the Hawthorne effect: New concepts are needed to study research participation effects. Journal of Clinical Epidemiology, 2014. https://doi.org/10.1016/j.jclinepi.2013.08.015 ↩

13. Laura M. König, Anila Allmeta, Nora Christlein, et al. A systematic review and meta-analysis of studies of reactivity to digital in-the-moment measurement of health behaviour. Health Psychology Review, 2022. https://doi.org/10.1080/17437199.2022.2047096 ↩

14. Kelli M. Richardson, Michelle R. Jospe, Lauren C. Bohlen, et al. The efficacy of using continuous glucose monitoring as a behaviour change tool in populations with and without diabetes: a systematic review and meta-analysis of randomised controlled trials. International Journal of Behavioral Nutrition and Physical Activity, 2024. https://doi.org/10.1186/s12966-024-01692-6 ↩