Microtubules

#+BEGIN_SRC text BLOCK A — Microtubules as “quantum antennas” deep dive: what the physics allows, what is observed, and what remains speculative

Premise Microtubules are 25 nm–diameter protein cylinders comprising 13 protofilaments with neuronal lengths from microns to tens of microns, which constrains any EM resonance or guiding claim by subwavelength cross-section physics. Knossow 2020 Prota 2023. oai_citation:0‡ScienceDirect oai_citation:1‡PMC

Key numbers you can trust Outer diameter ≈25 nm, lumen ≈15 nm, axial repeat ≈8 nm per dimer, neurite lengths often 1–20 µm. Use these for mode cutoffs, exciton hopping lengths, and half-wave estimates. Knossow 2020 Prota 2023. oai_citation:2‡ScienceDirect oai_citation:3‡PMC

Why the “metal half-wave antenna” metaphor fails Microtubules are high-index dielectrics in water, not metallic rods. At UV/visible frequencies you do not get free-electron currents; guidance is by dielectric waveguide or localized excitations. For a dielectric rod with radius a≈12.5 nm, n_core≈1.6 in aqueous cladding, the normalized frequency V at 280–300 nm is far below single-mode cutoff V≈2.405, so only weak or leaky guidance is plausible. MIT OCW 2006 RP Photonics. oai_citation:4‡MIT OpenCourseWare oai_citation:5‡RP Photonics

Tubulin refractive index and optical regime Best current measurements give n_tubulin≈1.64 at 589 nm, consistent with protein optics and correcting earlier inflated reports; use n_eff≈1.6 as a baseline in half-wave or cutoff estimates. Krivosudský 2016/2017. oai_citation:6‡arXiv

UV half-wave sanity check Half-wave in a dielectric is L≈λ0/(2n_eff). For λ0=280–300 nm and n_eff≈1.6, L≈87–94 nm. A 1 µm MT can host ~10 half-waves along its length, yet the deeply subwavelength radius keeps one in weakly guided or localized regimes rather than efficient radiation. MIT OCW 2006 RP Photonics Krivosudský 2016/2017. oai_citation:7‡MIT OpenCourseWare oai_citation:8‡RP Photonics oai_citation:9‡arXiv

What actually transports near-UV energy in tubulin Credible UV transport is exciton migration across aromatic networks, mainly tryptophans. Experiments show electronic energy diffusion length ≈6.6 nm in MTs with dynamics that challenge simple Förster pictures, supporting short-range quantum transport rather than long-range waveguiding. Kalra 2023 Kalra 2023 PMC Babcock 2024. oai_citation:10‡ACS Publications oai_citation:11‡PMC

THz regime and collective vibrational coupling At f≈20 THz the free-space wavelength is ≈15 µm; in hydrated media with n≈2 the half-wave is ≈3.8 µm, comparable to MT lengths. Intense picosecond THz pulses disassemble MTs within minutes, indicating strong coupling to collective modes. This is evidence of interaction and possible mode selectivity, not of long-lived coherence. Hough 2021 Schroer 2021. oai_citation:12‡PMC oai_citation:13‡Nature

MHz–GHz resonance claims Reports of MHz–GHz resonances in isolated MTs exist but have debated reproducibility and potential instrumentation artifacts; treat as suggestive and contested. Sahu 2013. oai_citation:14‡CORE

Decoherence timescales in brain tissue Order-of-magnitude estimates yield τ_decoh≈10^−13 to 10^−20 s for brain-relevant degrees of freedom, far below neural timescales. Re-estimates argue screening and distances can extend coherence toward ~10^−5 to 10^−4 s, still many orders below synaptic milliseconds unless you posit rapid, local bursts chaining into cognition. Tegmark 2000 Hagan 2002. oai_citation:15‡Physical Review

Updated synthesis to replace “quantum crystals” Microtubules are quantum-sensitive bio-dielectrics: they host transient UV excitons on tryptophan networks and couple strongly to THz mechanical or polar modes. That is real and testable. What is not yet supported is robust, brain-scale quantum coherence that survives the warm, wet, noisy neuron at cognition-relevant scales. Frame this as “short-lived quantum effects plus classical cytoskeletal dynamics,” not as persistent quantum computers. Kalra 2023 Babcock 2024 Hough 2021 Tegmark 2000 Hagan 2002. oai_citation:16‡ACS Publications oai_citation:17‡PMC oai_citation:18‡Physical Review

Practical experiments that would move the needle

In-cell two-color pump–probe around 280 nm with MT tracking to test directed exciton migration beyond Förster expectations and dose-dependent anesthetic perturbations at Trp sites. Kalra 2023. oai_citation:19‡ACS Publications
THz pump with ultrafast structural readout on neurites to map mode-selective amplification and thresholds for disassembly versus reversible modulation. Hough 2021 Schroer 2021. oai_citation:20‡PMC oai_citation:21‡Nature
Pre-registered replication of MHz–GHz MT resonances using shielded fixtures, blind analysis, and independent labs. Sahu 2013. oai_citation:22‡CORE #+END_SRC

#+BEGIN_SRC python

half-wave in a dielectric and THz wavelength helper

def half_wave_nm(lambda0_nm, n_eff): return lambda0_nm/(2*n_eff)

def half_wave_um_from_thz(f_thz, n_eff): c = 299792458.0 lambda0_um = (c/(f_thz*1e12))1e6 return lambda0_um/(2n_eff)

print(“UV 280 nm, n=1.6 -> half-wave ≈”, round(half_wave_nm(280,1.6),1), “nm”) print(“UV 300 nm, n=1.6 -> half-wave ≈”, round(half_wave_nm(300,1.6),1), “nm”) print(“THz 20 THz, n=2.0 -> half-wave ≈”, round(half_wave_um_from_thz(20,2.0),2), “µm”) #+END_SRC MIT OCW 2006 RP Photonics Krivosudský 2016/2017. oai_citation:23‡MIT OpenCourseWare oai_citation:24‡RP Photonics oai_citation:25‡arXiv

#+BEGIN_SRC text Back-of-the-envelope V-number intuition (cylindrical fiber surrogate) V ≈ (2πa/λ0) * sqrt(n_core^2 − n_clad^2). With a≈12.5 nm, λ0≈0.28 µm, n_core≈1.64, n_clad≈1.33–1.38, V is well below single-mode cutoff ≈2.405, implying at most weakly guided or leaky modes at near-UV. MIT OCW 2006 RP Photonics Krivosudský 2016/2017. oai_citation:26‡MIT OpenCourseWare oai_citation:27‡RP Photonics oai_citation:28‡arXiv #+END_SRC

#+BEGIN_mermaid flowchart LR A[UV photon ~280 nm] —> B[Trp network exciton
ps–ns over ~7 nm] B —> C[Energy dissipation or local coupling] A -. weak dielectric guiding .-> D[Weak standing fields
subwavelength radius] E[Metabolic pumping] —> F[Collective THz modes
elastic or polaritonic] F —> C note right of D: Strong leakage, not a rod antenna note right of F: Interaction shown by THz-induced disassembly #+END_mermaid Kalra 2023 Babcock 2024 Hough 2021. oai_citation:29‡ACS Publications oai_citation:30‡PMC