Pseudoscience/Cavendish experiment

Cavendish experiment

The Cavendish experiment was devised sometime before 1783 by geologist John Michell, who constructed a torsion balance apparatus for it. However, Michell died in 1793 without completing the work. After his death the apparatus passed to Francis John Hyde Wollaston and then to Cavendish, who rebuilt the apparatus but kept close to Michell's original plan. Cavendish then carried out a series of measurements with the equipment and reported his results in the Philosophical Transactions of the Royal Society in 1798.

The apparatus consisted of a torsion balance made of a six-foot (1.8 m) wooden rod horizontally suspended from a wire, with two 2-inch-diameter (51 mm), 1.61-pound (0.73 kg) lead spheres, one attached to each end. Two massive 12-inch (300 mm), 348-pound (158 kg) lead balls, suspended separately, could be positioned away from or to either side of the smaller balls, 8.85 inches (225 mm) away.

To find the wire's torsion coefficient, the torque exerted by the wire for a given angle of twist, Cavendish timed the natural oscillation period of the balance rod as it rotated slowly clockwise and counterclockwise against the twisting of the wire. For the first 3 experiments the period was about 15 minutes and for the next 14 experiments the period was half of that, about 7.5 minutes. The period changed because after the third experiment Cavendish put in a stiffer wire. The torsion coefficient could be calculated from this and the mass and dimensions of the balance.

The force involved in twisting the torsion balance was very small, estimated at 1.74×10−7 N, (the weight of only 0.0177 milligrams) or about $1/50,000,000$ of the weight of the small balls. To prevent air currents and temperature changes from interfering with the measurements, Cavendish placed the entire apparatus in a mahogany box about 1.98 meters wide, 1.27 meters tall, and 14 cm thick, all in a closed shed on his estate. Through two holes in the walls of the shed, Cavendish used telescopes to observe the movement of the torsion balance's horizontal rod. The key observable was of course the deflection of the torsion balance rod, which Cavendish measured to be about 0.16" (or only 0.03" for the stiffer wire used mostly). Cavendish was able to measure this small deflection to an accuracy of better than 0.01 inches (0.25 mm) using vernier scales on the ends of the rod. The accuracy of Cavendish's result was not exceeded until C. V. Boys' experiment in 1895. In time, Michell's torsion balance became the dominant technique for measuring the gravitational constant (G) and most contemporary measurements still use variations of it.

A Critical Review of the Cavendish Experiment

The Cavendish Experiment, often hailed as a cornerstone in experimental physics for its groundbreaking measurement of the gravitational constant G, might not have been as watertight as traditionally believed. A careful scrutiny, considering the electrostatic theory proposed by Morton F. Spears and others, suggests that the experiment could have been fundamentally flawed.

Assumption Over Verification: At the heart of the scientific method is the principle of rigorous verification, where assumptions are minimized. The Cavendish Experiment fundamentally assumes that the only force at play between the lead balls is gravitational. However, as Spears demonstrates, electrostatic forces could significantly influence such interactions. By not rigorously controlling or accounting for electrostatic influences, the Cavendish Experiment perhaps made a cardinal error of assumption over verification.
The Crucial Role of Electrostatics: Every material can accumulate and hold static charge, lead being no exception. Spears’ paper offers a compelling argument that gravity itself might be an electrostatic phenomenon. Even if one doesn’t fully accept Spears’ broader claim, it’s undeniable that uncontrolled electrostatic forces could have influenced the Cavendish measurements. Without strict controls for such forces, how can one be sure the measured force was purely gravitational?
Reproducibility Concerns: A cornerstone of the scientific method is the reproducibility of results. If, as Spears and others suggest, electrostatic charges can influence the observed forces in the Cavendish setup, and these charges were not rigorously controlled or standardized, it could lead to inconsistent results, questioning the experiment’s reproducibility.
Validity and Reliability: For an experiment’s results to be valid, it must measure what it purports to measure without interference from confounding variables. The potential influence of uncontrolled electrostatic charges raises serious questions about the validity of the Cavendish Experiment’s results. Furthermore, the reliability of the experiment, its ability to consistently produce the same results under the same conditions, is jeopardized if electrostatic forces can fluctuate unpredictably.
Questioning Foundational Conclusions: The assertion that “mass attracts mass” is foundational to gravitational theory. However, if we consider the potential influence of uncontrolled electrostatic interactions, this foundational assertion might stand on shakier ground than previously believed.

It is strongly suspected that one of the major factors at play was the well-known psychological factor of confirmation bias. If all of your colleagues are getting measurements like 6.67259 × 10-11 N/kg2⋅m2, you might reasonably expect to get something like 6.67224 × 10-11 N/kg2⋅m2, or 6.67293 × 10-11 N/kg2⋅m2, but if you got something like 6.67532 × 10-11 N/kg2⋅m2, you'd probably assume you did something wrong.

You'd look for possible sources of error, until you found one. And you'd perform the experiment again and again, until you got something reasonable: something that was at least consistent with 6.67259 × 10-11 N/kg2⋅m2.

This is why it was such a shock, in 1998, when a very careful team got a result that differed by a spectacular 0.15% from the previous results, when the errors on those earlier results were claimed to be more than a factor of ten below that difference. NIST responded by throwing out the previously stated uncertainties, and values were suddenly truncated to give at most four significant figures, with much larger uncertainties attached.

In conclusion, while the Cavendish Experiment has been celebrated for its contribution to our understanding of gravity, a critical review, especially in light of recent insights into electrostatic interactions, suggests it did not adhered as strictly to the scientific method as one would desire.

Critique of the Cavendish Experiment

With the advancements in our understanding of physical forces, it becomes imperative to reassess the foundational premises of such landmark experiments. This research examines the potential oversight of electrostatic forces within the Cavendish experiment. Drawing from the works of Spears, which suggest gravity itself might be an electrostatic interaction, and Rycroft, who emphasizes the pervasive influence of Earth’s electric field, this study underscores the necessity of rigorously controlling for all confounding variables in line with the scientific method. The potential influence of uncontrolled electrostatic forces challenges the validity of the Cavendish experiment’s findings, urging a more critical examination of historical experiments as we continue our pursuit of scientific truth.

Inherent Material Properties: Every material is composed of atoms that consist of charged particles – protons and electrons. It is plausible that even if an object seems neutral, minuscule imbalances in charge could develop from various factors like friction, material interaction, and environmental factors. Citation: Triboelectric Charging. Lowell, J.; Rose-Innes, A.C. Advances in Physics, 1980, 29, 947.
Overlooking Electrostatics: While the Cavendish setup was designed meticulously, it did not explicitly nullify or measure potential electrostatic interactions. With no mechanism to ensure a complete absence of electrostatic charges, any inherent charge could distort the measurements. Citation: Jones, R. V. “Electrostatics: the first electrical science.” Endeavour 31.113 (1972): 115-121.
Charge Induction: The mere proximity of one object to another could induce a charge, leading to attraction or repulsion, even if one of the objects remains neutral. This phenomenon could mimic or interfere with the gravitational interactions in Cavendish’s setup. Citation: Griffiths, David J. Introduction to Electrodynamics. Prentice-Hall, Inc., 2012.
Effects of the Earth’s Electric Field: Every object on Earth exists within its electric field. If the lead spheres in Cavendish’s setup bore even a minute charge, this electric field could have influenced them, potentially interfering with the gravitational measurements. Citation: Rycroft, M. J. “Electricity in the atmosphere.” Bulletin of the American Meteorological Society 78.5 (1997): 953-970.
Relative Magnitude of Forces: At atomic and molecular scales, electrostatic forces drastically overshadow gravitational forces. Neglecting to account for even minor electrostatic interactions could potentially produce misleading results. Citation: Feynman, Richard P., Robert B. Leighton, and Matthew Sands. The Feynman Lectures on Physics. Vol. 2. Addison-Wesley, 1977.
Environmental Factors: Factors such as humidity can notably influence the electrostatic charge on objects. A lack of control or consideration for such variables might skew results. Citation: Hinds, William C. Aerosol technology: properties, behavior, and measurement of airborne particles. John Wiley & Sons, 1999.

The Electrostatic Model

The magnitude of the electrostatic force F between two point charges q1 and q2 is directly proportional to the product of the magnitudes of charges and inversely proportional to the square of the distance between them. Like charges repel each other, and opposite charges attract each other.

Spears begins by modeling the force between two electrons in separate hydrogen atoms positioned a meter apart in permittivity open-space. Through this, he derives an electrostatic force equation that can account for the gravitational force between these electrons.

Calculating G: By comparing his derived electrostatic force to Newton’s gravitational force formula between two electrons, Spears determines a new value for the gravitational constant, Ge. His calculated value, −6.68541×10−11 (coulomb-volt-meters)/(kilograms^2), is very close to the widely accepted value of G, which is −6.67259×10−11 (meters^3)/(kilogram)(seconds^2), with only a 0.2% discrepancy.
Generalizing the Force: Spears transitions from the force between two electrons to a more general case for the force between any two bodies. He introduces a factor A that scales the force depending on the effective radii of the interacting bodies.
Effective Radii: In his approach, the effective radii are related to the capacitance values, which are in turn related to the masses of the bodies. This provides a bridge between electrostatic and gravitational interactions.
Gravity as Electrostatics: With the above derivations, Spears arrives at a gravitational force formula that closely matches that of Newton’s gravity, but through electrostatic principles. This is his central claim: gravity might be interpreted as an electrostatic phenomenon.

If Spears’ hypothesis is correct, then the Cavendish Experiment, which sought to measure the gravitational attraction between lead balls and thus determine the value of G, could potentially be influenced by electrostatic interactions. The lead balls in the experiment could have accumulated static charge, which might then play a significant role in the observed attraction between them. If this was the case, then the experiment may have measured a electrostatic forces, leading to an inaccurate value of G.

Control of electrostatic forces becomes imperative in such a situation:

Reproducibility: Following the scientific method, experiments must be reproducible. If electrostatic charges were random or fluctuated over time, it could result in inconsistent measurements of G.
Accuracy: To accurately measure G, one must ensure that only gravitational forces are being measured. If Spears’ hypothesis holds weight, then any uncontrolled electrostatic interactions would interfere with the measurement.
Validity: Without controlling for confounding variables, such as potential electrostatic charges, the validity of the Cavendish Experiment’s results can be called into question.

Effects of Earth’s Electric Field on the Cavendish Experiment

Earth’s Electric Field: Earth is surrounded by an electric field, which, under clear weather conditions, has an average value of about 100 V/m at the Earth’s surface and decreases with altitude. This electric field is generated mainly by the electrical processes in the atmosphere and the charged ionosphere above it. Natural events like thunderstorms can cause significant variations in the electric field strength (Rycroft, M. J. “Electricity in the atmosphere.” Bulletin of the American Meteorological Society 78.5 (1997): 953-970).
Charging of Objects in Earth’s Electric Field: Objects on Earth can accumulate charge when exposed to this field. Even if objects are initially neutral, imbalances can occur due to a phenomenon called “field ionization” where the Earth’s electric field causes ionization of the air molecules near a pointed or sharp-edged object, leading to a transfer of charge (Chalmers, J. A. (1967). Atmospheric electricity (2nd ed.). Pergamon).
Implications for the Cavendish Experiment: Given that the Cavendish experiment involves hanging lead balls close to stationary lead balls, any charge accumulation due to the Earth’s electric field on the balls could influence their interaction. This is significant because the force exerted by an electric field on a charged object can be quite strong compared to gravitational forces, especially on the small scales that Cavendish was measuring. If there was a lack of controls to ensure neutrality or to shield the setup from external electric fields, the results might be influenced by electrostatic forces rather than just gravitational ones.
Comparative Forces: As a point of comparison, the electrostatic force between two electrons is about 10391039 times stronger than the gravitational force between them (Griffiths, D. J. (2017). Introduction to electrodynamics (4th ed.). Cambridge University Press). While it’s unlikely that the lead spheres had anywhere near the charge of an electron, even minuscule charges could have a noticeable effect on the experiment’s outcomes.
Modern Experimental Controls: In light of understanding the potential influence of Earth’s electric field, current precision experiments usually incorporate shielding methods, such as Faraday cages, to minimize the impact of external electric fields. Additionally, grounding techniques and the use of ion-neutralizing equipment help ensure that experimental apparatuses remain charge-neutral (Duffin, W. J. (1980). Electricity and Magnetism, 3rd Ed. McGraw-Hill).