BYLINE: Stuart Hameroff

Introduction – A Tale of Two ORs

Newswise — The ‘think tank’ ‘Foundational Questions Institute’ (‘FQXI’) has sponsored coordinated research, articles and a press release comparing two theoretical versions of ‘objective reduction’ (‘OR’), proposals for gravity-related collapse of the quantum wavefunction.1-3 They also wrongly insinuate that the ‘Orch OR’ theory of consciousness, put forth by Sir Roger Penrose and Stuart Hameroff in the mid 1990s,4,5 has been refuted.

Orch OR depends on a particular version of OR developed by Roger Penrose (‘P-OR’).6,7 A similar version of OR was introduced by Hungarian physicist Lajos Diósi8 (‘D-OR’), who is an investigator and author on the FQXI-sponsored research and articles.

P-OR and D-OR both address the ‘measurement problem’ in quantum mechanics, the problem that quantum superpositions of multiple possibilities exist, but are not observable. Many believe the very act of measurement or of conscious observation causes quantum state reduction to definite states (“collapse of the wavefunction”). But P-OR and D-OR both suggest instead that superpositions ‘self-collapse’, and undergo reduction due to a gravity-related objective threshold (hence objective reduction, 'OR'). Both P-OR and D-OR propose reduction threshold at time t=ħ/EG, a form of the uncertainty principle (ħ is the Planck-Dirac constant, and EG the gravitational self-energy of superposition separation). Consequently, the P-OR and D-OR versions of OR are often lumped together, as ‘DP theory’.

However there are critical differences. D-OR predicts measureable radiation, heat emission with each OR event, and P-OR does not. P-OR predicts (proto-) consciousness (‘qualia’, the experiential feature of consciousness) with OR events, and D-OR is not known to have proposed it.

As radiative heat can be measured to distinguish between the two OR approaches, FQXI sponsored an impressive attempt by a well-qualified group to detect radiation from OR collapse, and thus test D-OR. But continuous experiments over two months under Gran Sasso Mountain in Italy did not find spontaneous OR-related radiation.1 D-OR appeared to be ruled out.

However, the articles and press release strangely avoided discussing the results, remained committed to radiation (D-OR), and didn’t consider P-OR (which correctly predicts no radiation). The Gran Sasso authors2 then put forth their own variant of Orch OR based on (the just-refuted) D-OR, instead of P-OR. They then refuted their own variant, but falsely implied that P-OR and Orch OR were also refuted. What is Orch OR?

Orch OR – Orchestrated objective reduction

To address the measurement problem, and consciousness, Roger Penrose6,7 considered the fundamental question of how a particle can be in quantum superposition of multiple locations simultaneously. He used ‘microscopic general relativity’, portraying quantum particles as tiny spacetime curvatures, and superpositions as separated, alternative curvatures, governed by a wavefunction (Figure 1). 

Collapse/reduction caused by subjective conscious observation (BING!!) is shown in Figure 1a (‘subjective reduction’, ‘SR’). In this view, consciousness collapses the wavefunction, but consciousness is left outside science.

Penrose proposed the precise opposite, that OR collapse occurs spontaneously at time t = ħ/EG, and (in P-OR) also causes (or is equivalent to) a conscious moment. In random microenvironments, ubiquitous P-OR moments would be experiential, but isolated, acausal and lacking memory, merely ‘proto-conscious’ (ping!!, Figure 1b), metaphorically the noise of musical instruments being tuned before a performance.

Figure 1

Figure 1. Penrose 1 described quantum particles as tiny curvatures in Planck scale spacetime geometry, and superpositions as separated curvatures. Figure 1a: a  conscious observer (BING!!) causes quantum state reduction, collapsing the wavefunction. Figure 1b: according to Penrose, separated curvatures are unstable, and reduce at time t = ħ/EG, producing a moment of phenomenal proto-conscious experience (ping!!).

How could P-OR moments be organized in the brain to give full, rich conscious perception and action? In the mid 1990s Penrose and Hameroff proposed that orchestrated quantum computations terminating by P-OR occur in microtubules, lattice polymers of the protein 'tubulin', inside brain neurons. Dendritic-somatic superpositions would entangle, evolve, quantum compute  and collectively reach OR threshold for full conscious moments, selecting microtubule states which regulate axonal firing and behavior – ‘Orchestrated objective reduction, ‘Orch OR’ 4,5.

To accommodate Orch OR events by t = ħ/EG, a scalar brain hierarchy was described, both upward in size from neurons into networks, but also downward, inward, deeper and faster, to quantum vibrations among electron clouds inside microtubules,9 and ultimately to fundamental spacetime geometry at the Planck scale (Figures 2 and 3).

Figure 2 


Figure 2. Brain scalar hierarchy inward from 1) neuron to 2) microtubule bundles, 3) microtubules, 4) row of tubulin dipoles. Self-similar dynamics repeat every ~3 orders of magnitude.

Figure 3 

Figure 3. Brain scalar hierarchy continued. 1) tubulin protein, 2) pi resonance electron cloud dipoles, 3) atomic nuclei, and ... 4) fundamental Planck scale spacetime geometry.

The inward hierarchy was discovered by Anirban Bandyopadhyay and colleagues10,11 as self-similar patterns of microtubule quantum vibrations and resonances repeating in terahertz, gigahertz, megahertz, kilohertz and hertz frequency ranges. Orch OR conscious events are proposed as quantum computations selecting particular microtubule vibrational states, like notes and chords in music, able to control axonal firings and neuronal functions. Thus Orch OR entails ‘conscious qubits’, e.g. in and among dendritic-somatic microtubules in cortical pyramidal neurons, multiple poised alternatives that can ‘collapse’ to specific states as the ‘solution’, selecting a conscious perception or action via axonal firing directly to spinal cord.

Consider a tennis player, Roger Federer say, charging the net on a drop-shot, peeking at his opponent Rafael Nadal – shall Roger go left/cross-court, or right/down the line? He has, at that instant, a superposition of both possibilities as ‘poised alternatives’ e.g. in microtubule quantum superpositions in cortical layer V pyramidal neuron cell bodies and dendrites in his motor and pre-motor cortex. Then, Orch OR occurs, BING!!. Axons fire to spinal cord, and Federer hits down the line for a winner. Conscious quantum computing would be very useful in biological evolution.

Ample evidence exists for functional quantum states in microtubules. Bandyopadhyay’s quantum resonances,10,11 genomic, proteomic and optogenetic studies,12 and quantum optical effects in microtubules inhibited by anesthetics13-15 support the biological (‘Orch’) side of Orch OR nicely. What about P-OR?

The ‘Big Smear’

In the abstract of their paper in Nature Physics,1 the FQXI-sponsored authors say: “We then report the results of a dedicated experiment at the Gran Sasso underground laboratory to measure this radiation emission rate.”

But they then don’t report the results of the dedicated experiment (the results apparently being that radiation emission was not measured or detected). Without saying what the result was, they pivot directly to: “Our result sets a lower bound on the effective size of the mass density of nuclei, which is about three orders of magnitude larger than previous bounds. This rules out the natural parameter-free version of the Diósi–Penrose model.” (The authors clarify that the ’natural parameter-free’ version of the Diósi–Penrose model is P-OR.)

What the FQXI are they talking about?!

Let's unpack this. ‘Mass density of nuclei’ refers to the degree of superposition, or ‘smearing out’ of mass ‘separated from itself’. The more the smearing, the lower the mass density, and the lower the EG, given by EG = Gm2/a(where G is the gravitational constant, m is the mass, and ‘ac’ a measure of superposition separation length, or ‘smear factor’). A 'smear factor' length value for ac is necessary to calculate EG

To calculate EG for tubulin, the component protein in microtubules, Hameroff and Penrose4 determined ac for tubulin in 3 possible ways -  1) partial separation of the entire protein, 2) complete separation at the level of the protein's atomic nuclei, and 3) complete separation at the level of its protons and neutrons. The dominant effect was 2) complete separation at the level of (carbon) atomic nuclei – each nucleus separated from itself by its radius 2.5 femtometers (2.5 x 10-15 m, 2.5 fermi lengths). (And ac of 2.5 femtometers theoretically enables electronic-nuclear quantum coupling.) This smear factor ac = 2.5 femtometers was used to calculate tubulin EG to then relate the number of superpositioned tubulins for Orch OR moments to occur by t = ħ/Eat various times and frequencies .

Anirban Bandyopadhyay had already shown quantum resonances in microtubules in megahertz and gigahertz experimentally,10,11 so 10 megahertz (t = 10-7 secs) was selected as a likely frequency for Orch OR events, brief enough to avoid decoherence. By t = ħ/EG, Hameroff and Penrose calculated that to reach Orch OR threshold at time t = 10-7 secs (potentially repeating at 107 Hz, 10 megahertz),  EG of 1015 superpositioned entangled tubulins would be required. With a total of about 1020 tubulins in a human brain, 10 megahertz Orch OR events would involve 10-5 of total brain tubulins, a seemingly reasonable fraction (1/10,000) which could change dynamically. Hameroff and Penrose5 further suggested that Orch OR events in megahertz and other frequencies negatively resonate, interfere and change scale to give ‘beats’ at slower kilohertz and hertz frequencies, including EEG and cognitive epochs. See the scalar hierarchy in Figure 2.

Back to the ‘Big Smear’. D-OR predicts that small superposition smear values (such as 2.5 femtometers ac) result in high levels of radiation (large EG), and that large smear values result in low levels of radiation (small EG), or if large enough, none at all. The Gran Sasso authors then assert that the absence of radiation in their experiments was because the smear value must have been too large. They then ‘dry-labbed’ a smear factor big enough to give zero radiation (‘R0’) to match their negative results. This is their ‘lower bound’ R0 = ~0.5 x 10-10 m, half an angstrom. (With a carbon atom nucleus smeared to half an angstrom, a single carbon atom would be microns, larger than some entire biological cells!)

Apparently to test their R0, the Gran Sasso authors2 then concocted a variant of Orch OR based on D-OR constraints, further smearing the 2.5 femtometer ac smear factor 3 to 4 orders of magnitude larger! They then calculated times t = ħ/EG, and, not surprisingly, got bizarre results. For example EG of 1015 tubulins with their smeared out R0 would reach threshold only after 12 days, rather than 10-7 secs with the 2.5 femtometers ac factor (12 day response time not very helpful in tennis, for example). They thus successfully disproved their own D-OR variant of Orch OR, but have absolutely no reason to “rule out the natural parameter-free version of the Diósi–Penrose model” if that implies P-OR. This would be like saying: “Sorry Einstein, you were wrong. We changed your equation to e=mc5 and it doesn’t work.” 

The Gran Sasso authors and FQXI press release1-3 don't actually criticize, accuse or find fault with P-OR, or Orch OR, whatsoever. But they repeatedly insinuate they've been refuted by conflating P-OR and D-OR.

They say2:

“…Orch OR based on the DP theory is definitively ruled out…”

Reply: ‘DP theory’ lumps together D-OR and P-OR, but only the D-OR variant of Orch OR was ruled out. Authentic Orch OR based on P-OR remains perfectly viable.

And they say2:

“Orch OR theory, when based on the simplist version of gravity-related dynamical collapse, is highly implausible…”

Reply: The “simplist version…” (according to the authors) is Diósi OR. Their Orch OR variant based on D-OR doesn’t work. Authentic Orch OR based on P-OR remains completely plausible.

To be fair, they also say:2 “…the results of this paper do not rule out Orch OR theory in general. Rather, they rule out variants of Orch OR based on the simplist version of the DP theory of gravity-related dynamical wavefunction collapse.”

Reply: Yes, they say this twice in the 3 papers, but 7 times say that Orch OR based on DP theory is ruled out, or implausible.

Finally, the FQXI Press release3 title: “Collapsing a leading theory for the quantum origin of consciousness”

Reply: The ‘leading theory’ is presumably authentic Orch OR based on P-OR and, as a scientific theory, is most definitely not collapsing. The two peer-reviewed papers made deceptive insinuations, but the FQXI press release headline did the dirty work, and wrongly declared Orch OR demise.

Does ‘retroactivity’ explain the missing radiation?

Could both views on OR radiation be correct? Penrose has maintained such radiation would not be detected, but has also proposed retro-active effects of OR, time symmetry being an essential feature of quantum mechanics. For example in The emperor’s new mind,6 Penrose described seemingly backward time effects in brain sensory processing, as discovered by Ben Libet in the late 1970s,16 as retro-active effects of OR. Many other examples of apparent backward time effects in consciousness include the ‘color phi’ effect, and pre-cognition. And real-time conscious behavior and free will may depend on retro-activity, avoiding the apparent problem of consciousness ‘coming too late’.17

In principle, retro-activity can ‘erase’ the unselected superposition curvature, as if it never happened, preventing observable radiation in OR. What is retro-activity? Penrose develops the idea in his chapter in a book Quantum mechanics and consciousness edited by Shan Gao (~October, 2022, Oxford Press).18

Retro-active influence from near-future events could be beneficial in predator-prey relations, and evolution in general. Let’s return to Roger Federer charging the net on a drop-shot, peeking at his opponent Nadal – shall he go cross-court, or down the line? With retro-activity, perhaps Federer sees Nadal leaning to his right, expecting Roger to hit cross-court. Orch OR occurs (BING!!), axons fire and Federer hits to Nadal’s left, down the line for a winner.


Insinuations by FQXI and the Gran Sasso team that Penrose OR, and/or Orch OR had been disproven are deceptive, misleading and false. Penrose OR is the first, and as yet only truly scientific mechanism for conscious experience yet put forth. It cannot simply be replaced in the Orch OR theory by D-OR or anything else.

But new avenues of research interest have been highlighted, for example quantum optical pharmacology, the brain's microtubule-based scalar hierarchy, and Roger’s retro-activity in physics and consciousness. Among theories of consciousness, Orch OR has the 1) greatest explanatory power, 2) tightest connection to brain biology, and 3) most supportive evidence. We welcome constructive criticism and collaboration.


  1. Donadi et al (2021) Nat. Phys. 17, 74–78.
  2. Derakhshani et al (2022) Phys Life Revs 42:8-14
  3. FQXI Press release June 13,2022
  4. Hameroff, S., Penrose, R. (1996).
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  5. Hameroff, S., Penrose, R. (2014). Physics of Life Reviews 11 (1), 39–78
  6. Penrose, R (1989). The Emperor's New Mind (Oxford Press).
  7. Penrose, R (1996). Gen. Rel. Grav. 28, 581-600.
  8. Diósi L (1984) Phys Lett A 105, 199-202
  9. Hameroff, S. (2022) Front. Mol. Neurosci
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  11. Saxena et al (2020) Fractal and Fractional 4(11)
  12. Emerson et al (2013) J Am Chem Soc. 135, 5389–5398.
  13. Lewton (2022) New Scientist, April, 8
  14. Kalra et al (2022)
  15. Celardo et al (2019) New J Phys 2630/aaf839
  16. Libet et al (1979) Brain 102, 193–224.
  17. Hameroff, S (2012) Front Integr Neurosci (6) 1-17, 10.3389/fnint.2012.00093.
  18. Penrose, R (2022), in Quantum mechanics and consciousness, Ed. Shan Gao, Oxford Press (in press)