Hand-considered hypotheses, 101–200

Soft and biological matter, written one at a time. Colloids, polymers, gels, membranes, active matter and the physics of cells — each entry carries its own logical form, printed above it, and no two are built from the same sentence plan. None has been tested. Nothing here is a literature finding; a number in the text is an estimate, marked as such, not a measurement. These are hypotheses 101–200 of a planned 1,000, and they continue the page numbered 1–100 without reusing its subjects.

Colloids and suspensions

Misattribution
H101. The volume fraction at which a colloidal suspension is declared to jam is read off the rise of its zero-shear viscosity, but that rise contains the continuous phase's own approach to its glass transition, amplified by the particles' share of the local dissipation. If so, the apparent jamming fraction should move when the solvent's fragility changes at fixed particle chemistry, which a crowding-only picture forbids. The test is one batch of index-matched silica spheres dispersed in three solvents whose fragilities differ by roughly a factor of two (estimate), with viscosity measured against volume fraction at a single temperature.
Hidden term
H102. Depletion attractions measured between two spheres in a polymer solution are fitted with an ideal-depletant well whose depth follows the depletant's osmotic pressure, yet the depletant also adsorbs weakly on the spheres and adds a short-range attraction that does not scale with depletant size. That second term hides in the fit's baseline, where it is indistinguishable from a slightly deeper ideal well. A depletant-size series at fixed osmotic pressure separates the two, because the ideal term moves and the adsorbed term does not.
Threshold
H103. Below a certain particle roughness the rheology of a colloidal crystal stops depending on what the particles are made of and starts depending on contact adhesion, with the crossover at a few nanometres of asperity height (estimate) for micron-scale spheres. Asperities shorter than the range of the van der Waals attraction are averaged over by the contact, so the contact becomes adhesion-limited rather than geometry-limited. Seeds grown to equal radius but with controlled asperity heights, compared across two materials at one volume fraction, would locate the crossover.
Reversal
H104. Salt is expected to destabilize a charge-stabilized suspension monotonically, but at very high particle charge the trend should reverse in a narrow window, because the correlation attraction between counterion clouds is screened more weakly than the double-layer repulsion at short separation. The prediction is a second virial coefficient that is non-monotonic in salt, with the most stable point at an intermediate concentration that exists only above a charge threshold. Static light scattering across a salt series, for three particle charges, would either open that window or close the idea.
Identity
H105. The two yield stresses of an attractive colloidal gel are treated as two bond populations, but they may be one population seen at two strain rates, with the second yield being the relaxation of the first. If that is right, the ratio of the two yield strains is fixed by the ratio of the rates and not by the gel's chemistry. A strain-rate sweep on a single gel decides it: peaks that move together with rate are one process, peaks that stay pinned are two.
Count
H106. A gel built from one bond chemistry has one bond energy, so its fracture energy carries one independent structural parameter and any variation with crack speed must be kinetic rather than structural. This bounds what a fracture test can attribute to network heterogeneity. A family of gels with controlled bimodal bond distributions, counting the peaks in fracture energy against crack speed, would show whether the count follows the bond count or the rate.
Scale argument
H107. When the depletant is only a few solvent diameters across, the depletion layer is no longer a well-defined excluded-volume shell, and the force between two plates should be governed by the solvent's compressibility and become nearly independent of depletant concentration. The crossover sits at a size ratio of order three to five (estimate), where the depletant's correlation length exceeds its radius. Total internal reflection microscopy on a plate–sphere pair, walking the depletant size down to a few solvent diameters at fixed packing fraction, would show the plateau.
Inversion of standard practice
H108. Washing a suspension before use is taught as removing impurities, but it also strips the adsorbed layer that fixes the particles' effective charge, so a washed and an unwashed aliquot of one batch are not the same material. The claim worth testing is that this difference exceeds ordinary batch-to-batch variation. Split a batch, wash half against its own solvent, and compare effective charge by conductivity and by electrophoresis; a lower charge and a different modulus in the washed half make the standard practice a hidden preparation variable.
Artefact mimics effect
H109. Shear-induced re-entrant melting in suspensions has been read as a structural transition, but in a Couette cell particles migrate outward at high shear, so the scattering volume samples a lower concentration than the nominal one. The apparent melting would then track the gap's geometry rather than the suspension's phase behaviour. Spatially resolved scattering across the gap at fixed nominal concentration separates the two, since a real transition is uniform and migration is not.
Two-population mixture
H110. A sedimentation profile that looks like one species with a broad mass distribution is often two populations produced by the synthesis quench, and either model fits the profile. The populations differ in density as well as in size, which is the lever. A second run in a solvent whose density is tuned between the two buoyant densities should split one broad peak into two, and analytical ultracentrifugation makes that comparison direct.
Unit trap
H111. Crosslinker content in gel recipes is usually quoted in parts per million by mass while the mechanics depends on the molar ratio of crosslinker to monomer, so comparing gels at equal ppm across different polymer molecular weights compares different crosslink densities. A reported molecular-weight dependence of modulus in such a series is then partly a unit error. Plotting the same numbers against molar ratio either preserves the dependence, in which case it is real, or collapses it, in which case it was the unit.
Bound
H112. The stiffening a rigid filler can give a gel is bounded by the ratio of its grafted-layer thickness to its radius, because the layer and not the filler transmits stress to the matrix. This places a ceiling on reinforcement that does not care how stiff the filler is, and it would explain why nano- and micron-scale fillers of one material behave so differently. One grafted chemistry, a radius series spanning an order of magnitude, and a matched volume fraction are the whole experiment.
Sign trap
H113. The electroviscous contribution to a suspension's viscosity changes sign when the double layer grows thicker than the particle radius, because the primary and secondary electroviscous terms scale differently with that ratio. A measurement that averages across the crossover can therefore report either a rise or a fall from the same physics. A salt series at fixed volume fraction, with conductivity taken alongside viscosity, should show the sign change at a predictable ratio.
Selection effect
H114. Phase diagrams of colloidal mixtures are assembled from samples that stayed suspended long enough to be observed, which quietly removes compositions with large density contrast. The reported miscibility gap is therefore likely wider than the true one, since the near-critical compositions sediment fastest. Samples density-matched per composition, across the full range, would test whether the gap closes.
Reversal
H115. Adding a non-adsorbing polymer to an attractive colloidal gel should first weaken and then strengthen it, because at small polymer size the depletion potential competes with existing bonds and reduces their number, while at larger size it adds a second, shorter bond that carries load. The minimum strength should sit at a polymer size comparable to the gel's bond length rather than at a fixed concentration. A polymer-size series at constant osmotic pressure, with linear and nonlinear moduli both measured, tests the shape of that curve.
Time-scale mismatch
H116. Calling a colloidal aggregate irreversible usually means it did not redisperse on dilution, which is a statement about the observation window relative to the cluster's internal relaxation. A system labelled irreversible can be reversible when its internal relaxation is slower than the window, and the reverse mislabel is equally easy. Repeat the dilution at two temperatures that change the relaxation time by a known factor while leaving the attraction untouched, and see whether the label survives.
Threshold
H117. Crystallization of a sheared suspension should be bypassed entirely above a critical shear rate set by the ratio of the nucleation induction time to the shear-induced collision time. Above that rate no waiting recovers order, because nuclei are destroyed faster than they form. Fixed quench depth, a shear-rate series, and in-situ scattering followed for a hundred induction times would show whether the amorphous state is kinetic or permanent.

Polymers and glasses

Misattribution
H118. The drop in glass transition temperature seen in thin polymer films is credited to confinement, but a similar drop appears in bulk samples once polydispersity is matched, where the controlling variable is chain-end concentration rather than thickness. Free ends carry extra free volume, and spin-coating leaves more ends near a surface than the bulk molecular weight implies. Bulk samples with end content matched to the films, plus films at two thicknesses and the same end content, would separate the two stories.
Hidden term
H119. Plateau moduli from rheology and from neutron spin echo do not agree for the same entangled polymer, and the discrepancy tracks fragility. The missing term is the glassy contribution of the Kuhn segments: rheology sees the plateau after segmental modes have relaxed, while scattering at high momentum transfer still sees those modes frozen. Two polymers of equal chain length and different fragility, made by side-group substitution, should show a difference that scales with fragility.
Identity
H120. Physical ageing in a glassy polymer and physical gelation in the same material below its melting point may be one slowing process approached from two directions, since both are cooperative rearrangement converging on the same arrest. If so, the ageing rate at a fixed distance from the glass transition is identical whether the sample is amorphous or semicrystalline at matching amorphous fraction. An ageing-rate comparison across controlled crystallinities would test that.
Bound
H121. The drawability of a polymer fibre is bounded by the ratio of its entanglement length to its persistence length, because past that ratio the chain cannot be straightened without breaking entanglements faster than they can be pulled out. The bound belongs to the chain and not to the process, so no temperature programme can exceed it. Two polymers of one chemistry but different chain stiffness, drawn identically, should saturate at different draw ratios predictable from persistence length.
Count
H122. In a miscible blend the number of independent relaxation times is bounded by the number of components plus one, so a report of more modes is polydispersity or a hidden thermal transition wearing a mode's clothes. The bound follows from how many independent friction and modulus parameters a two-component tube picture can carry. A narrow-distribution blend, with temperature and composition varied orthogonally, shows whether the extra modes survive when polydispersity is removed.
Reversal
H123. Strong flow should first stiffen and then soften a polymer solution, because alignment removes entanglements faster than it raises backbone tension. The softening onset is expected at a Weissenberg number of order the entanglement number (estimate), a departure no single-mode constitutive law produces. Filament stretching with simultaneous birefringence would show the stress bending downward from the aligned-chain prediction at that value.
Threshold
H124. Below some thickness the glass transition temperature of a polymer film should stop depending on thickness altogether, with the floor set by the substrate's vibrational spectrum rather than by an interfacial layer. Substrate phonons supply a finite density of modes the film can couple to however thin it becomes, so the transition cannot fall indefinitely. Films of equal thickness on diamond, silicon and a soft polymer, measured by ellipsometry, would show whether the floor tracks the substrate's Debye temperature.
Dimensionless collapse
H125. Thickness-dependent glass transition shifts should collapse onto a single curve when plotted against thickness divided by the product of Kuhn length and an interfacial interaction parameter, not against thickness alone. The collapse would mean that disagreement between laboratories is a difference in interaction parameter rather than in physics, and the interaction parameter can be estimated from contact angle. If the collapse fails, the interaction parameter is the wrong variable and the interfacial-layer picture needs replacing.
Artefact mimics effect
H126. The residual memory of a prior deformation in a polymer melt, read as slow chain retraction, can instead be the transducer's own compliance relaxing after the step. The tell is scaling: the memory amplitude should track the transducer's stiffness rather than the imposed strain. The same step on two instruments of different compliance, and on samples of two thicknesses, separates a material relaxation from an instrument one.
Inversion of standard practice
H127. Annealing above the glass transition is the standard way to erase a spin-coated film's history, but it is the wrong choice when the goal is to preserve chain conformations, because it lets the chains re-randomize while the substrate pins the surface layer. Sub-transition annealing erases stress without letting conformation relax. Permeation measurements on films annealed on either side of the transition, with identical thermal budgets elsewhere, would show which treatment actually equilibrates what matters.
Scaling group
H128. Whether a thin polymer film dewets should depend on a group combining film thickness, substrate roughness wavelength and the polymer's capillary length, not on the spreading coefficient alone. Roughness can pin a contact line only when its wavelength is shorter than the capillary length, so two polymers with equal spreading coefficients but different capillary lengths should dewet differently on one rough substrate. That is a two-polymer, one-substrate experiment.
Ergodicity break
H129. The Stokes–Einstein relation in a glassy polymer should break at the temperature where string-like cooperative motion grows longer than the chain's persistence length, which predicts that stiff chains decouple earlier than flexible ones at equal distance from the glass transition. A string longer than the persistence length carries its own internal relaxation, so diffusion no longer reports the friction that viscosity reports. Comparing tracer diffusion with viscosity for a flexible and a stiff polymer matched in transition temperature would test it.
Unit trap
H130. Crosslink densities quoted from swelling are effective chain densities that depend on an assumed interaction parameter, and that parameter is often taken from a temperature series other than the swelling temperature. The systematic error in the quoted density then tracks the extrapolation rather than the network. Re-analysing a swelling series with the parameter measured at the swelling temperature, instead of extrapolated, would shift the densities by more than the stated error.
Reversal
H131. A plasticizer can raise a semicrystalline polymer's melting point at low loading and lower it at high loading, because at low loading it anneals the crystals by raising mobility and at high loading it depresses them thermodynamically. The crossover loading is the diagnostic, and it should shift with the starting crystallinity. Calorimetry across a loading series begun from two initial crystallinities would show whether the maximum moves as predicted.
Null model
H132. A large part of what is called self-healing in polymers is explained by two cut faces simply re-wetting at the same temperature, with no interdiffusion beyond what the wetting front allows. The null model predicts recovery with the same dependence on contact time and temperature as true healing, which is why controls are rarely decisive. A sample with a non-healing but equally wetting interlayer, tested identically, should recover the same fraction if the null model is doing the work.
Topological obstruction
H133. Crystal growth under confinement should stop at a thickness of twice the lamellar period, not because nucleation is suppressed but because a confined chain cannot build a fold surface without violating the thickness constraint. This predicts a minimum thickness for crystallinity that ignores chemistry and depends only on the lamellar period. A thickness series in a neutral confining medium, with crystallinity read by ellipsometry, would show a sharp cutoff there.
Degeneracy
H134. Chain scission and crosslink scission produce the same gel fraction against dose, so a standard sol–gel analysis cannot tell them apart. What can is the molecular weight distribution of the sol, because chain scission broadens the primary distribution while crosslink scission leaves it intact and only removes material from it. Size-exclusion chromatography of the sol at several doses is the discriminating measurement.

Gels and networks

Bound
H135. A gel's compressive strength is bounded by the osmotic pressure of the network at the concentration where it was formed, so a gel formed dense and later diluted cannot be stronger than one formed dilute and brought to the same final concentration. The bound comes from the number of load-bearing strands per unit volume, which cannot exceed what was locked in at formation. Two gels matched in final concentration but differing in formation concentration, tested in compression, would show whether the bound holds.
Reversal
H136. Gels that stiffen on heating are explained by hydrophobic association, yet a solvent that contracts thermally produces the same signature with no change in association at all. The test is a solvent series with controlled thermal expansion and matched hydrophobicity, in which the stiffening should survive even when association cannot change. If it does, part of the thermoresponsive gel record is a solvent expansion measurement wearing a gel's name.
Threshold
H137. Above a critical crosslinker valence a gel's modulus stops being proportional to crosslink density, because multifunctional crosslinkers cluster and only clusters beyond the percolation threshold carry stress. The threshold should appear as a kink for tri- and tetrafunctional crosslinkers and be absent for difunctional ones. A valence series at fixed concentration, with modulus and cluster size measured together, tests that.
Identity
H138. The negative normal force of a sheared gel and its strain stiffening may be two expressions of one nonlinearity, in which case a gel showing one at a given strain shows the other at the same strain. If they are the same, the normal force can be predicted from the stiffening with no new parameter. One experiment measuring both through a single shear history, at several strains, would show whether they share a strain scale.
Artefact mimics effect
H139. Reported self-healing in hydrogels is often the capillary adhesion of a thin water layer pulling the faces together without any chain reconnection. The signature is a healing strength that depends on humidity and disappears in an oil bath, while true healing does not. Cutting and rejoining the same gel in air, under oil, and at controlled humidity separates the two.
Conservation audit
H140. Swelling models for ionic gels hold the bath's ion chemical potential fixed while holding the internal counterion count fixed, and that conserves neither the ions nor the charge. The inconsistency surfaces as a predicted swelling maximum at intermediate salt that the measurement does not contain. Closing the ion inventory, and assaying the internal ion content directly instead of inferring it, would show whether the maximum moves or vanishes.
Count
H141. A gel's linear viscoelastic spectrum has at most as many independent modes as it has distinct mesh length scales, so a five-element model fitted to a one-mesh gel is overfitting by construction. The mode count can be obtained independently from scattering. Fitting frequency sweeps with models of increasing order, and comparing the count against the scattering-derived mesh distribution, shows whether the extra modes are real or decorative.
Time-scale mismatch
H142. A reversible covalent gel is reversible only on the timescale of its exchange reaction, so an activation energy from rheology equals the exchange energy only when the network relaxes faster than exchange. Push the stress up and the same measurement starts reporting bond rupture, with a different apparent energy. Activation energies measured at several stresses, set against a spectroscopic exchange rate, would locate the crossover.
Reversal
H143. A gel that shrinks on heating can expand again at higher temperature when the polymer has a lower critical solution temperature and the collapse expels trapped solvent, letting the elastic term win in the collapsed phase. The re-expansion is then not a second transition but a release. A slow heating ramp with mass and dimension tracked together would show the mass loss coinciding with the expansion.
Threshold
H144. Below a sample-size threshold a gel's measured fracture energy is set by its defect distribution rather than by its network, so small samples look tougher because they are less likely to hold a critical flaw. The threshold is the mesh size times a factor set by the Weibull modulus, material-specific but predictable. Fracture tests on a size series spanning it, with defect counts from imaging, would test that.
Inversion of standard practice
H145. Equilibrating a gel in a bath before mechanical testing is standard, but the bath extracts the un-crosslinked fraction, which is the component that toughens the gel. A gel tested as made is a different material from the same gel tested after equilibration, and the difference belongs in the methods section, not in a footnote. Aliquots at several equilibration times, with the extracted fraction measured, would put a number on it.
Selection effect
H146. Distributions of self-healing efficiency are conditioned on samples that survived the cut and the rejoin, so gels that fail catastrophically never enter the statistics and the reported mean is biased upward. The bias should grow with the severity of the test, which makes it measurable rather than merely acknowledged. An experiment that records every attempt on one recipe, failures included, would size the bias.
Misattribution
H147. Strain stiffening in biopolymer networks is assigned to the filaments' entropic response, but when the mesh is smaller than the persistence length the stiffening is the affine deformation of an effectively isotropic network, which has a different strain dependence. The two differ in where stiffening begins relative to the mesh size. One filament at two mesh sizes, with stiffening measured against strain, would show whether the onset scales with the mesh.
Bound
H148. The work a hydrogel actuator can do is bounded by its osmotic energy density, not by its elastic modulus, so a stiffer gel advertised as a stronger actuator may store less usable work. The bound follows because the stroke is set by swelling and the force by the same osmotic pressure, leaving no freedom in between. Actuators of equal osmotic pressure and different modulus, with work measured directly, would show whether the bound is honoured.
Hidden term
H149. A synthesized gel's measured swelling pressure includes the Donnan contribution of residual counterions from synthesis, and that term depends on washing history rather than on the network. Two gels of identical composition but different washing are therefore different materials in the osmotic sense. Swelling pressure against concentration for washed and unwashed aliquots, with residual ion content assayed, would test it.
Reversal
H150. Crosslinking can lower a gel's fracture energy at low density, because new crosslinks create short strands that break before the long ones can share load, and toughness then becomes non-monotonic with a maximum set by the strand-length distribution. The peak position, not the peak height, is the prediction. A crosslink-density series with fracture energy and strand-length distribution measured together would show the maximum and where it sits.
Derived quantity
H151. A mesh size inferred from swelling is a derived quantity only in the sense that it assumes affine deformation of the network, and at high swelling that assumption, not the measurement, is what fails. The swollen mesh is a stretched object, so setting it against a scattering mesh taken on the undeformed network compares two geometries. Measuring both on one sample at several swelling degrees, and asking whether their ratio equals the macroscopic deformation, would settle which quantity is being reported.
Aliasing
H152. Oscillatory rheology samples a relaxation spectrum at discrete frequencies, and one long relaxation can appear as two modes when the sweep is too sparse per decade. The two-process spectra reported for some gels may be one process aliased. Re-measuring the same gel at four times the point density over the same range would either split the features further or merge them, and only merging is consistent with a single mode.

Membranes and interfaces

Identity
H153. The hydration force between lipid bilayers and the steric force between bilayers carrying sugar headgroups may be one force, since both come from water structuring that the headgroup perturbs. If that is so they share a decay length, and the chemical distinction between them is a naming convention. Force–distance measurements on bilayers with headgroups of graded size, at matched hydration, would show whether the decay length is common.
Misattribution
H154. Membrane tension from a tether pull is assigned to the bilayer, but in a living cell most of the resistance to a tether comes from cytoskeletal prestress transmitted at attachment points. The discriminating experiment is a tether pull before and after a mild depolymerization that leaves the bilayer's composition and area intact; if tension falls by most of its value, the measurement was of the cytoskeleton.
Threshold
H155. Above a critical membrane tension a protein's hydrophobic mismatch is accommodated by tilting the protein rather than by deforming lipids, because beyond some tension tilt becomes the cheaper mode. The threshold should depend on the protein's aspect ratio rather than on its hydrophobic length alone. Proteins of matched mismatch and different aspect ratio, reconstituted in tension-controlled vesicles, would test that.
Reversal
H156. Cholesterol can order or disorder a bilayer depending on how its length matches the phospholipid's, so one cholesterol fraction can raise or lower the area compressibility. The mechanism is free-volume filling when cholesterol is shorter than the lipid and mismatch when it is longer. A lipid series of graded chain length at fixed cholesterol fraction, with compressibility measured, would show the crossover.
Artefact mimics effect
H157. A pore reported in a free-standing membrane from electrical conductance is sometimes a wetting film between membrane and aperture edge, conducting along a circumference rather than through an area. The tell is geometry: conductance scales with the aperture's circumference, not its area. Two aperture diameters with the same membrane separate the two cleanly.
Bound
H158. A nanopore's selectivity between two ions is bounded by the ratio of their dehydration energies to the pore's own electrostatic energy, so no geometry separates ions whose dehydration energies differ by less than the pore's thermal roughness. This is a bound on chemistry, independent of fabrication quality. Two ions of known dehydration difference, across a pore-diameter series, would show whether selectivity saturates at the predicted value.
Scale argument
H159. Below a pore diameter of roughly two hydration shells (estimate), continuum electrostatics is undefined because the dielectric constant is not a local property, and conductance should collapse onto one curve when scaled by the hydration-shell diameter. The collapse would say the relevant variable is the number of water molecules across the pore, not the pore's charge. Sub- nanometre pores of different chemistry, measured in one apparatus, would test the collapse.
Count
H160. A membrane has two bending moduli, mean and Gaussian, but a bilayer on a curved support has an effectively different pair because the support breaks the symmetry; a claim to measure both from one curved-support experiment is therefore underdetermined. The geometry, not the model, sets how many independent numbers exist. The same bilayer on supports of two curvatures would show whether the fitted pair is geometry-independent.
Hidden variable
H161. The flicker spectrum of a red-cell membrane carries a contribution from spectrin-network thermal motion with the same spectral slope as the bilayer's, so the spectrum alone cannot separate them. Separation requires changing network density while holding the bilayer fixed. Cells with partially depleted spectrin, or resealed ghosts with titrated spectrin, would show whether the amplitude tracks network density or bilayer rigidity.
Inversion of standard practice
H162. Blocking non-specific binding with a protein such as BSA is standard in membrane assays, but the blocker adsorbs to the bilayer and changes its tension and permeability, so a blocker-free control is not the same experiment. Part of a "specific" signal may be the blocker's own effect. Running the assay with and without the blocker, on a bilayer whose tension is measured independently, would size the contribution.
Reversal
H163. Raising membrane fluidity can lower permeability to a small solute when partitioning rather than diffusion controls permeation, so the usual expectation that fluid membranes leak more fails near the free-volume cavity size. The crossover sits at a solute radius relative to the cavity distribution. A homologous solute series across a fluidity series, with partitioning measured separately, would locate it.
Threshold
H164. There is a critical curvature above which a protein's preferred curvature dominates its localization more than its hydrophobic mismatch, and below which mismatch wins. That would explain why one protein sorts differently in vesicles of different size. Vesicles of graded radius, with a protein of known mismatch and preferred curvature, would show the crossover.
Null model
H165. Domains in ternary lipid vesicles may be the mixture's equilibrium phases, in which case their sizes should follow classical nucleation and coarsening, and the null model explains most reported sizes without any active pinning. The test is whether domain size grows after a quench as the null model requires, followed on one vesicle for hours. Pinning would appear as a plateau the null model cannot produce.
Artefact mimics effect
H166. Reported negative tension in some membrane systems is an artefact of an aspiration-pressure sign convention or of a membrane fold drawn into the pipette, both of which invert the geometry without changing any physics. Withdrawing and re-aspirating the same membrane would remove the anomaly if it is geometric. Recording the full aspiration sequence rather than only the final state would expose it.
Unit trap
H167. Permeability coefficients circulate in both centimetres per second and metres per second, and the factor of a hundred occasionally gets absorbed into a claimed anomalous resistance. Two studies disagreeing by roughly two orders of magnitude should be checked for that conversion before any physical explanation is attempted. The test is bookkeeping against the method sections, and it is the cheapest test on this page.

Active matter

Misattribution
H168. Giant number fluctuations are assigned to activity itself, but in a dense suspension the same exponent can arise from a broad distribution of swimming speeds, which produces the same variance without any collective effect. The two are distinguishable because a population engineered to one speed should show a different exponent at the same density. Speed-sorted swimmers, with the exponent measured across sorted fractions, would test it.
Threshold
H169. Motility-induced phase separation has a critical density set by the ratio of run length to persistence length, which makes tumbling frequency and density interchangeable knobs. The prediction is a single curve when density is plotted against that ratio for swimmers of different tumbling rates. A strain with tunable tumbling, plus a density series at fixed run length, would test the collapse.
Reversal
H170. More activity can mean a colder tracer: at high activity the swimmers' collisions become correlated and a passive tracer turns subdiffusive, so the effective temperature read from its long-time diffusion falls even as the bath's energy input rises. The non-monotonicity should survive at fixed tracer size. Tracers of two sizes in baths of graded activity, with short- and long-time diffusion both measured, would show it.
Hidden term
H171. A measured active stress always contains the stresslet of the swimmer's own body, which scales with shape anisotropy rather than with propulsion, so two swimmers of equal speed and different shape give different measured stresses. Only varying shape at fixed speed isolates the propulsion term. A swimmer family of graded aspect ratio at matched speed, in a stress-measuring geometry, would separate them.
Scale argument
H172. Active turbulence has a characteristic length set by the swimmer's length only when confinement exceeds a threshold ratio of system size to swimmer length; below it, the pattern wavelength is set by the box. This predicts that the same suspension in two cells shows two vortex sizes, which is a statement about boundary conditions rather than biology. A confinement series with in-situ imaging would test it.
Identity
H173. Bacterial turbulence and the mesoscale turbulence of synthetic swimmers may be one instability, since both are driven by the same advective nonlinearity and both should relate vortex size to reorientation time in the same way. If so, a scaling measured in one predicts the other with no biological parameter. Comparing the vortex-size scaling in a bacterial and a synthetic suspension at matched density and reorientation time would test that.
Count
H174. An active nematic has at most three independent elastic constants once activity is allowed to renormalize them, so a measurement reporting four has folded a flow-alignment term into one of the three. The count is bookkeeping about which deformations cost energy independently. Fitting the same defect structures with three- and four-constant models, and comparing residuals, shows whether the fourth is required or merely absorbed.
Selection effect
H175. Motility assays select for swimmers that stay in the focal plane, which biases measured speed distributions toward slow, in-plane cells, and the bias is worst for the fastest and most persistent ones because they leave the plane before they can be tracked. A thicker chamber imaged with a light sheet, compared against the thin-chamber distribution, would measure the bias rather than assume it away.
Artefact mimics effect
H176. Phase separation reported in some bacterial suspensions can be oxygen depletion at the coverslip, which slows metabolism in a layer and creates a motility gradient that looks like a phase boundary. The tell is that a perfused chamber cannot establish the gradient, so the pattern should vanish. Perfused and sealed chambers imaged identically separate metabolism from mechanics.
Conservation audit
H177. The stress in an active gel should balance the traction its motors exert on their surroundings, and measured stress fields generally do not balance once the motor-density gradient is included. That gradient is rarely imaged, so the missing term gets absorbed into a phenomenological activity parameter. Imaging motor density and stress simultaneously in one sample would show whether the balance closes without it.
Threshold
H178. Traction forces stop rising with substrate stiffness above a critical value that is set by adhesion-cluster size rather than by cytoskeletal stiffness. A cluster transmits force only up to the load at which it ruptures, so the plateau should move with cluster size and not with myosin activity. Cells with clusters of different size on stiffness gradients, read by traction microscopy, would test that.
Reversal
H179. A faster swimmer can disperse more slowly in a crowded medium, because higher speed raises the collision rate with obstacles and shortens persistence. The crossover is where collision time equals persistence time, and it should show as a turnover in the dispersion coefficient rather than a monotonic rise. Swimmer–tracer mixtures at graded speed, in a fixed obstacle density, would expose it.
Hidden term
H180. An effective temperature read from a tracer's diffusion and mobility assumes the fluctuation–dissipation relation with the tracer's bare friction, but swimmers renormalize that friction as well as the noise. The ratio then reports the modified friction rather than the activity, and the error grows with swimmer density. Dragging the same tracer with optical tweezers in the active bath, to measure its friction independently, would separate the two.
Degeneracy
H181. Alignment and propulsion generate identical steady-state nematic order-parameter fields, so the order parameter cannot identify which is operating. The degeneracy breaks only in defect dynamics, which differ between the two. Defect annihilation rates in a system where alignment and propulsion can be varied independently would test it.
Bound
H182. A low-Reynolds-number swimmer's efficiency is bounded by its shape's slenderness rather than by its waveform, so a sperm cell and a helical bacterium of equal slenderness share the same maximum efficiency. The bound comes from the resistance matrix's structure, which a waveform can approach but not exceed. Measured efficiencies across swimmers matched in slenderness and varied in waveform would test it.
Topological obstruction
H183. An active nematic confined to a sphere cannot reach a defect-free steady state, because the Euler characteristic forces a net topological charge whatever the activity. The defect number is fixed by geometry and activity only sets their motion. Spherical active nematics at two radii, with defect counts measured, would show whether the count is quantized as predicted.
Null model
H184. Flocking in synthetic active colloids may be alignment induced by the container's walls, since a wall organises swimmers without any particle–particle alignment. The null model of wall-induced ordering reproduces the reported order parameter, which makes the transition possibly a boundary effect. The same suspension in a wide and a narrow chamber at matched density would show whether the order parameter tracks the wall.

Biological physics at the physical level

Misattribution
H185. Cell stiffness from atomic force microscopy is assigned to the cytoskeleton, but in a thin cell the indentation curve includes the substrate through the finite-thickness correction, so cells on stiff substrates look stiffer with no change of their own modulus. The correction is the usual suspect and the usual omission. Indenting cells of two heights on two substrates, fitted with a model that carries the substrate term, would separate the contributions.
Identity
H186. The poroelastic and viscoelastic responses of a cell may be one response at two rates, with the crossover at the diffusion time of cytosol through the mesh. A cell that looks poroelastic at one loading rate would then look viscoelastic at another, with no constituent changing. Indentation at several rates spanning the predicted crossover, on cells whose mesh size is measured independently, would test it.
Threshold
H187. Below a critical cell size the nucleus sets the mechanical response instead of the cytoskeleton, at roughly the nuclear diameter (estimate). The prediction is that cells of one type but different ploidy, and therefore different nuclear size, cross the threshold at different cell sizes. Micropipette aspiration on cells of graded size, with nuclear size measured, would test that.
Reversal
H188. Adding crosslinkers to an actin network should stiffen it and then soften it, because dense crosslinking suppresses the filament bending that stores elastic energy once the crosslink spacing falls below the persistence length. The maximum should therefore sit at a spacing comparable to the persistence length. Titrated crosslinker with mesh size from scattering would show whether the peak is there.
Bound
H189. A molecular motor's stall force is bounded by the ratio of step size to compliance, so two motors of equal free energy and different compliance have different stall forces. The bound exists because a compliant motor loses part of its chemical step to elastic storage before it can act on the load. Optical-trap measurements on motors of known compliance, matched in free energy, would test it.
Hidden term
H190. The diffusion coefficient of a membrane protein measured in a cell includes hydrodynamic drag from the glycocalyx, which a reconstituted liposome does not have, so the same protein diffuses faster in a vesicle for a reason that is not the membrane. Stripping the glycocalyx enzymatically and measuring diffusion in the same cell before and after would isolate the term.
Artefact mimics effect
H191. Superdiffusion reported for particles inside cells is often the drift of the whole cell or of the stage, which adds a ballistic component that no intracellular transport produced. The tell is a fixed fiducial marker drifting the same way. Tracking an immobile marker alongside the particles, and subtracting the common mode, would test it.
Count
H192. A molecular machine's cycle has at most as many independent rates as it has distinct conformational states minus one, so a model with more rates is underdetermined by dwell-time data alone. The bound concerns identifiability, not mechanism. Fitting dwell-time distributions with increasing numbers of states, and asking whether the data constrain the extra rates, would test it.
Scale argument
H193. A biological membrane is thin enough that continuum elasticity fails at the scale of a protein, with the crossover at a protein diameter comparable to the membrane thickness divided by the square root of the bending rigidity in thermal units. Above that size a protein sees an effective medium, below it individual lipids. Proteins of graded diameter in bilayers of two thicknesses would test the crossover.
Inversion of standard practice
H194. Clamping cytosolic pH is standard in reconstitution, but cellular pH fluctuates with metabolism and those fluctuations may be the control signal for assembly, so a clamped reconstitution removes the signal and can build something the cell never builds. A reconstitution with a controlled pH oscillation at the same mean pH would test whether the dynamics matter.
Selection effect
H195. Single-molecule studies keep the motors that stay bound long enough to be seen, which biases dwell-time distributions toward long times, and the bias grows as the observation window shortens relative to the mean dwell. Comparing single-molecule dwell times with a bulk assay at identical conditions, with the window varied deliberately, would measure the selection rather than correct it by guesswork.
Threshold
H196. There is a critical filament length below which a cytoskeletal network cannot transmit stress across a cell, set by the ratio of mesh size to the cell's smallest dimension. Below it the membrane, not the network, dominates the cell's mechanics. Cells whose filaments are cut to controlled lengths, with mechanics probed locally, would show the crossover.
Reversal
H197. A stiffer matrix can lower a cell's traction forces when the matrix's ligand density is sparse, because stiffness and ligand density push adhesion maturation in opposite directions. The crossover sits at a ligand spacing comparable to the integrin cluster's size. Substrates varying stiffness and ligand spacing independently, with traction microscopy, would show the inversion.

Cross-cutting

Unit trap
H198. Mesh sizes from scattering and from rheology are in different units by construction, and the conversion between them assumes a model, so a cross-paper comparison compares models as much as materials. The trap is that both are printed in nanometres and therefore look commensurable. Recomputing a set of published pairs with one model would show whether the disagreement is real or imported by the conversion.
Order-of-limits
H199. Whether a soft material is called poroelastic or viscoelastic depends on the order in which the limits of frequency and sample size are taken, and the two standard protocols take opposite orders: one sweeps frequency at fixed size, the other sweeps size at fixed frequency. The protocols then disagree not because the material is inconsistent but because the limits do not commute. Running both on one sample in one apparatus would show the disagreement and its size.
Ensemble inequivalence
H200. Preparing a soft material by quench and by slow cooling can give the same structure factor and different mechanics, which means structure is not a state variable for soft matter. If that holds, matching structures before comparing mechanical data is not enough, and two samples should be matched in history as well. A pair matched in scattering and compared in rheology, with preparation histories recorded, would test it.

Status and plan

200 of 1,000. The first hundred covered instruments, materials and inference; this hundred stays inside soft and biological matter and tries to make each entry a separate argument rather than a slot in a grid. The forms are printed so that a reader can check the claim of variety instead of taking it.

The next hundred will move to the physics of living systems at the tissue scale and to the boundary between soft matter and physiology, still one at a time, with the forms tracked. The rate is the point: a thousand in one pass would be a template, and a template is what the first rule forbids. None of the two hundred has been tested; the value of the list is the ideas, and the value of a test is separate from it.

If one of these is worth an experiment, it is H199 — that the poroelastic and viscoelastic readings of one material disagree only because two protocols take the limits in opposite orders. It needs one apparatus, one sample and two sweeps, and it would either explain a decade of scattered numbers or close the question cheaply.

Incoprea Research · hand-considered hypotheses 101–200 · soft and biological matter · 3 November 2026 · ~/Desktop/Nov3/