More Cavendish mythology
Published by admin August 14th, 2007 in Uncategorized, Cavendish ExperimentNigel Cook writes in Quantum gravity mechanism and prediction that
Cavendish produced a more accurate evaluation of G by measuring the twisting force (torsion) in a quartz fibre due to the gravitational attraction of two heavy balls of known mass located a known distance apart.
1. Cavendish did not know about G.
2. Cavendish never measured the Newtonian occult force
3. Cavendish used a copper wire, not quartz
4. Cavendish failed to give the distance between the “two heavy balls.”
See Cavendish’s original paper.
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Pioneer1,
Thanks for the criticism of this historical sentence in my blog post, but see:
http://www.fas.harvard.edu/~scdiroff/lds/NewtonianMechanics/CavendishExperiment/CavendishExperiment.html
“The Cavendish apparatus basically consists of two pairs of spheres, each pair forming dumbbells … One dumbbell is suspended from a quartz fiber and is free to rotate by twisting the fiber; the amount of twist measured by the position of a reflected light spot from a mirror attached to the fiber. … the gravitational attraction between two sets of spheres twists the fiber, and it is the measure of this twist that allows the magnitude of the gravitational force to be calculated. … The apparatus was originally invented by the Rev. John Michell in 1795 to measure the density of the Earth. It was modified by Henry Cavendish in 1798 to measure G and subsequently by Coulomb to measure electrical and magnetic attraction and repulsion. Apart from the historical significance of the experiment, it’s really neat to see that you can measure such an incredibly weak force using such a simple device.”
Maybe you can direct some fire at them, and also the publishers of Dr Asimov’s books which say Cavendish used a quartz fibre to measure G?
I know from practical experience of this and other experiments that when you are doing this kind of thing, developments occur in stages. Cavendish in his first experiments may have used a copper wire, but that gave way to a quartz fibre for greater accuracy. Similarly, in his first paper he may not have calculated or used the symbol G = (Fr^2)/(mM). However, G is just a letter representing the proportionality factor and thus relative strength of the gravitational interaction. Cavendish measured all the values in (Fr^2)/(mM).
The exact history of when the quartz fibre and the ratio for G were introduced into the experiment is trivial for the my purposes. If you can produce evidence that none of these (quartz fibre and G calculation) developments to Cavendish’s experiment were his own doing, and can identify who actually did them, then maybe I can add their names to the discussion of the outline history.
If you want to attack historical inaccuracy which is actually damaging mainstream science today, may I suggest that you take a look at Maxwell’s theory of electromagnetism: Maxwell got the equations wrong, he never wrote what are called the vector calculus “Maxwell’s equations” which were written by Oliver Heaviside in 1893.
Nobody worries about the physics of Maxwell’s “displacement current” equation although Schwinger’s threshold of 1.3*10^18 volts/metre as the minimum electric field required for pair-production of polarizable charges in the vacuum prevents any “displacement current” in the vacuum in weak electric fields, such as those measurable in all radio waves which according to Maxwell’s theory are waves of vacuum displacement current which are caused by, and in turn cause, electromagnetic fields. Maxwell’s theory of light is expressed as the Faraday induction equation curl.E = -dB/dt and Maxwell’s “displacement current” equation curl.B = x*dE/dt. As a result, the classical-quantum Maxwell-Yang-Mills electromagnetic unification is totally misunderstood today, which has serious implications for electroweak theory. Correct the photon theory, and you automatically get an accurate of what the electromagnetic force-field vector boson is (with its 4 rather than 2 polarizations).
Re: the errors in Maxwell’s equations. See Chalmers, http://www.iop.org/EJ/abstract/0031-9120/10/1/011 quoted at http://electrogravity.blogspot.com/2006/04/maxwells-displacement-and-einsteins.html Dr Alan F. Chalmers’ article, ‘Maxwell and the Displacement Current’ (Physics Education, vol. 10, 1975, pp. 45-9). Chalmers states that Orwell’s novel 1984 helps to illustrate how the tale was fabricated: ‘… history was constantly rewritten in such a way that it invariably appeared consistent with the reigning ideology.’ Maxwell tried to fix his original calculation deliberately in order to obtain the anticipated value for the speed of light, proven by Part 3 of his paper, ‘On Physical Lines of Force’ (January 1862), as Chalmers explains: ‘Maxwell’s derivation contains an error, due to a faulty application of elasticity theory. If this error is corrected, we find that Maxwell’s model in fact yields a velocity of propagation in the electromagnetic medium which is a factor of [root 2] smaller than the velocity of light.’
Nigel, thanks for the comments.
Harvard’s Lab Tutorial for the Cavendish experiment contains many inaccuracies and highlights how widespread Cavendish mythology is. The confusion arises because they refer to the toy pendulum they use in the lab as “Cavendish apparatus” as if it were a replica of Cavendish’s pendulum.
This is a good example of how physicists confuse themselves by naming important concepts multiple times and using the same label for many different concepts. Most concepts in physics are context sensitive. This is a characteristic sign of pre-scientific fields.
Yes. That’s one of my ongoing projects. The page did not have contact info but I will write to some people at Harvard physics department to see if they reply.
Previously, I have written to Britannica and Nature asking them to correct mythological statements about the Cavendish experiment. If more people wrote to them that would be helpful. Here’s the letter I wrote to Nature. (Nature email: correspondence@nature.com) and also to Britannica (Britannica email: CustomerService@us.britannica.com). If you communicate with them please let me know their response so that I can include it in my blog.
True. I agree.
Yes, exactly. C.V. Boys, an assistant professor of physics in Royal College of Science, first introduced the quartz fibre in order to build a smaller apparatus circa 1889. This site has the historical details.
I dispute that Cavendish measured F. He measured the excursion of the pendulum arm. He supplied some of the constants of the pendulum precisely and others he ignored. But the values of the constants of the pendulum are not relevant to the experiment because Cavendish never measured F. He never claimed that he did.
I agree that it is irrelevant to your discussion if Cavendish used copper or quartz but it may be relevant if he did not measure force.
My claim is that Newtonian force is occult. Occult does not exist in nature. Therefore, force is not a magnitude and cannot be measured. Consequently, Cavendish never measured the Newtonian force. More info about the history of G can be found in my wiki.
To me the occult nature of the Newtonian force is definitive proof of its non-existence. But occult is not enough evidence to discredit a Newtonian concept in the framework of Newtonian physics. Failing to measure the Newtonian force physicists defined the Cavendish experiment as the posthumous measurement of it.
Today, physicists own the Cavendish experiment and they define it to prove their Newtonian doctrine. Only when the Cavendish experiment is freed from the ownership of physicists it will be understood as what it really is: a computation of the mean density of the Earth by an application of Kepler’s rule. The apparatus is redundant.
Yes. I agree.
Yes. I can produce evidence for both. I think the Oxford site referenced above should be good evidence that quartz was introduced in the 19th century. Cavendish gave the wire’s specification as “the wire by which the arm was suspended was 39 1/4 inches long, and was of copper silvered…”
It is well known that G was first defined in 1894 by C.V. Boys. Cavendish did not know about it and he did not use it. B.E. Clotfelter’s 1987 article Cavendish experiment as Cavendish knew it covers the issue in detail. Here’s another link where a physicist from University of Texas states that the Cavendish did not measure G.
Many thanks for your reference to Maxwell’s fabrication. Maxwell did the same regarding the Cavendish experiment. He is the source of the mythology that Cavendish apparatus has a mirror attached to it.
The same exact process of rewriting history to make Maxwell’s equations “consistent with reigning ideology” also happened with the Cavendish experiment.
“Reigning ideology” of Newtonian physics is Newtonism. Force is the faith of Newtonism. Force cannot be questioned within physics. So physicists simply rewrote history to match their Newtonian doctrine.
In the 19th century, about two hundred years after Newton’s definition of force, this force had not yet been observed even though physicists have been trying constantly to observe it. C. V. Boys solved the problem by defining the Cavendish experiment as the first measurement of the Newtonian force by defining a unit he called G. Boys is practicing Newtonian Whig history. He is fixing history to fit it into the Newtonian doctrine in order to save Newton’s sacred authority. He was very succesfull. To this day Cavendish experiment is believed by physicists to be the first measurement of the Newtonian force. It is a crime against science.
I believe this shows that science and history are the same. My goal is not to “attack historical inaccuracies damaging to mainstream science.” I agree with you that it is trivial to correct what kind of wire Cavendish used. But what Cavendish measured or did not measure is not trivial. And that’s revealed by historical analysis. In this sense history and science are synonyms. Physics, in this sense, is not science. Because physicists took an experiment to “Determine the Density of the Earth” and rebranded it as “the first measurement of the Newtonian force.”
Thanks for the inspirational comments.
Pioneer1,
Thanks. I’m interested in your statement above:
The word “force” to me is just rate of change of momentum or approximately the product, mass*acceleration, i.e., F = dp/dt ~ ma.
Mass can be measured, momentum can be measured, and acceleration can be measured.
So I don’t see a deep problem, really. If you don’t like F = GmM/r^2, then employ F=ma and you can write down acceleration a = GM/r^2, so your problem is sorted: acceleration is definitely measurable.
Force might be occult in one sense, but you can measure both of the things you need to calculate it’s value.
If you are going to attack force as being occult, then you could also attack momentum and energy.
The problem with momentum occurs when you ask what momentum a photon of light has. If light hits a surface and is absorbed, it imparts a momentum of p = E/c, but if the light is reflected from the surface (say a rigid mirror), the total momentum imparted to the surface is p = 2E/c. The difference is because the reflection process can be considered as two events: the absorption of the photon (giving momentum p = E/c to the mirror) and then the re-emission of the photon in the opposite direction (giving a recoil to the mirror which - because of the reversed direction of the photon - adds a second p = E/c to the first impulse, so the total momentum is p = 2E/c.
Therefore, the amount of momentum a photon is able to deliver to a target depends on whether the photon is absorbed or reflected back the way it came. [Obviously, there is a snag in my simple argument here, because in deriving p = 2E/c for reflection, I’m assuming that the mirror is perfectly rigid. If it really is perfectly rigid (i.e., of infinite mass) then it won’t actually recoil at all. If it is not perfectly rigid, then the reflection factor will be less than 2, because some of the incident energy will be lost before the photon is re-emitted and the new photon will have a longer wavelength and less energy, giving less recoil.]
The occult problem with energy is the problem of the reference frame in which a collision process is viewed. This is well known in particle physics, of course, where the conventional reference frame is that of the centre of mass for the system under consideration:
Consider two colliding toy cars, and the occult nature of energy becomes clear.
(1) Take two cars each 1 kg in mass and have them each travelling at 5 metres/second towards each other (total impact speed 10 metres/second). The total kinetic energy release is E = 2[(1/2)mv^2] = 25 Joules.
(2) Take the same two cars but keep one stationary and have the other hit it at 10 metres/second. The total kinetic energy release is E = (1/2)mv^2 = 50 Joules.
Now why the difference? When two 1 kg masses collide at a total speed of 10 m/s you get 25 Joules if the centre-of-mass is the reference frame, but you get 50 Joules for the same masses hitting at the same relative speed when you view the collision in the reference frame of one mass!
Clearly the difference is due to the fact that kinetic energy is proportional to the square of velocity, so you get disproportionately more energy when one body is considered to have all the motion, than you do when you consider the motion to be equally distributed.
But surely conservation of energy is violated? Of course, it is not violated.
I’ve had a long correspondence by email with Dr Mario Rabinowitz over various things, often consisting of politely worded arguments. One problem he had with my work was my argument that in the expanding universe, radiation being exchanged between charges (in the case of gravitational force, the charge is mass) is redshifted to lower energies. This means that masses receding from one another at immense distances will exchange redshifted radiation, including redshifted “gravitons” in any Yang-Mills quantum field theory of gravity. As a result, at extreme redshifts, quantum gravity should be reduced in strength in an expanding universe, because redshifted gravitons have lower energy (E=hf). Mario suggested that this would violate conservation of energy. However, it is just usual redshift theory.
If you think about the redshift of any radiation in an expanding universe, say the most severely redshifted radiation there is - the cosmic background radiation - what has happened to the principle of conservation of energy there?
It’s fairly obvious that energy is conserved, and what happens is that photons get “stretched out” longitudinally in the expanding universe, so the radiation expands in length as the universe expands, filling the same proportion of the volume of the universe.
The total energy present remails the same, it is just that the transverse frequency falls because the photon gets longer. What is occurring as the universe expands is that the energy density of radiation in space falls (because the same energy is distributed over a bigger volume), but the total energy remains constant. However, it gets redshifted to lower frequency, so its entropy increases and it is a less useful form of energy.
There is still a bit of mystery here when you consider a single photon that is redshifted due to the expansion of the universe. How can the frequency of a single photon in the cosmic background radiation get shifted to a lower value as the universe expands, without violating conservation of energy, E = hf?
If individual photons in the cosmic background do lose energy as they get more and more redshifted, where does that energy go? Clearly the answer is has to do with reference frames. The cosmic background radiation we see is coming from a vast difference associated with a massive recession velocity. So the paradox in energy when considering a single photon is that we’re comparing dissimilar energy, because the reference frames are different. When we consider a single photon before redshift, we’re calculating its energy in a reference frame far from us, receding at a massive rate. When we consider the redshifted photon arriving here on earth, we’re changing reference frames to one in which (to us) the photon appears to be severely redshifted.
In order to understand conservation of energy, it’s only conserved in a similar reference frame. So to get into the reference frame of a photon of the cosmic background radiation, you’d need to be in a spaceship travelling outward from the earth at the same speed that the gaseous fireball matter (at the location where the cosmic background radiation originated from) was receding at.
Once you get up to that speed into the radiation so you are in the same reference frame, the photons of cosmic background radiation will no longer be redshifted to 2.7 K, they will have a temperature of 3000 K or so (just as they did at 400,000 years after the big bang). This is because the radiation hitting you head on is (to you) blueshifted to higher energy as you accelerate to higher speeds. So if you get in the same frame of reference as the radiation when it was emitted, energy is perfectly conserved.
It’s really shameful how hard it is to get clear explanations of physics from textbooks and lecturers on some things. You end up having to try to work answers out for yourself. Another problem with reference frames regards Newton’s gravitational force law:
(a) Suppose you have an apple falling to earth, then the law is F = GmM/r^2 where m is mass of apple and M is mass of earth. Here, the force F is due to the earth upon the apple (the gravitational field around an apple is trivial). This is proved because F = ma, so F = GmM/r^2 is due to simply the acceleration field around the big mass M, acceleration a = GM/r^2.
(b) Now suppose you have two planets of approximately equal mass, m and M. In that case F = GmM/r^2 is wrong. The reason is that each mass M then has its own significant gravitational acceleration field around it so and the total acceleration is then
a = (Gm/r^2) GM/r^2
= G(m M)/r^2.
Hence the total force of one planet with respect to the other is generally given by:
F = Ma = GM(m M)/r^2.
This is substantially different from Newton’s law because for identical masses m = M gives the solution:
F = 2GMM/r^2
This is obviously twice what Newton’s law says! The inaccuracy in Newton’s law is not a substantial problem because in the solar system, the mass of one body is always much smaller than the other, so for instance the acceleration of the sun towards the earth’s mass can be excluded and the only significant acceleration is a = MG/r^2 where M is sun’s mass, giving F = ma = mMG/r^2 which is Newton’s law.
It’s only where both masses are similar (which would be the case in certain binary stars) that Newton’s law is wrong.
This is maybe useful evidence that force, as defined in Newton’s law for gravity, is occult, and it is far less confusing to consider the accelerative field surrounding a mass than to consider the “force”. There are also problems with a = MG/r^2 due to modifications introduced by general relativity. Because radial coordinates are contracted around a mass in general relativity (just as masses in motion are contracted in the direction of motion), the effective strength of gravity gets altered.
The reason for this effect in general relativity is that when Newton’s a = MG/r^2 is converted into tensor mathematics notation you get R_(ab) = 4*Pi*GT_(ab), which “when combined with the contracted Bianchi identity … leads to the conclusion that the trace T of the energy-momentum tensor … has to be constant throughout spacetime. This is blatently inconsistent with ordinary (non-gravitational) physics. Accordingly Einstein … came up with [a correction factor to the Newtonian tensor model] we now know as Einstein’s field equation R_(ab) - (1/2)Rg_(ab) = 8*Pi*GT_(ab).” (Quoted from Penrose, Road to Reality, ch. 19, section 7. Penrose includes a minus sign on the source term, right hand side, for the direction of arrows on the gravitational field lines drawn between masses, but that is just convention and confuses the story for quantum gravity where the field lines represent the paths of gravitons being exchanged between masses, i.e. gravitons are travelling in both directions along such lines.)
Still another problem with Newton’s a = MG/r^2 introduced by general relativity is that for light speed radiation crossing the radial gravitational field lines at right angles, the deflection of the radiation is not given by a = MG/r^2 but by a = 2MG/r^2. This is because a low speed object has its electric field lines extending in 3 spatial dimensions, but a light speed object is contracted in the direction of motion so it’s electric field lines in the direction of propagation have zero magnitude. All of the electric field lines from a light velocity object are in the transverse direction (at right angles to the line of propagation). The geometry of how the electric field lines from a photon and a slow moving object interact with gravitational field lines then shows that for a given number of electric field lines, you get twice the interaction if the object is going at light velocity (a photon) than if it is going at low speed.
So there are many failures in Newton’s law, although the usual way the corrections are handed out does not inspire much understanding.
Nigel,
Thanks for the comment.
I would say that, the way you read it, “rate of change of momentum” and “mass*acceleration” and “force” are synonyms.
The way I read F = dp/dt = ma all these terms F, dp, dt, m and a are placeholders that must be cancelled when we want to compute orbits. The placeholders are not magnitudes, instead they hide the two magnitudes, R=radius of the orbit and T=the period of the orbit.
What remains after placeholders are eliminated is half of Kepler’s law R/T^2. Newton labeled this half of Kepler’s law “Force.” He also labeled the other half 1/R^2 “Force.” Since orbits cannot be computed with expressions containing placeholders Newton cancelled force terms to recover Kepler’s rule and used Kepler’s rule for astronomical calculations. Newton called Kepler’s rule Newton’s laws. Physicists still read Kepler’s rule as Newton’s law.
You just cancelled force. It is irrelevant if I measure acceleration and assign it to GM/r^2. In a = GM/r^2 there is no force. Force terms are eliminated. What remains is
R/T^2 = (some constant) 1/R^2
This is Kepler’s rule. Yes. R and T are magnitudes and can be measured. Force was a placeholder not magnitude and it cancelled. You cannot cancel R or T without destroying the proportionality.
When you eliminate the occult Newtonian force to obtain the working proportionality the force terms are gone.
Not true. The working equation has no force terms in it. Only non-working definitions F=R/T^2 and F=1/R^2 do.
Why discuss momentum and energy? In this context momentum is a placeholder. We can reduce momentum to its constituents. There is no reason to discuss the small m, it gets eliminated. What remains is velocity v=R/T. I have no problem with R/T.
But for the moment let’s think in terms of Cavendish experiment because in physics Cavendish experiment is given as the first measurement of the Newtonian force.
What did Cavendish measure? He measured the excursion of the pendulum arm.
Cavendish did not measure momentum. He did not measure mass and he did not measure acceleration. He measured distance. How can we claim that Cavendish measured force?
In order to claim that Cavendish measured force we need to look at the formula he used to compute the density of the earth. This is the formula:
N^2/10844 D
N is the period and D is the divisions the arm moved as Cavendish changed the position of the weights.
There is no term for force in this expression.
The pendulum itself did not contain something called force. Cavendish did not measure a quantity called force. The experimental equation that Cavendish used to obtain mean density of the earth did not contain a term for force either. If so, how can we claim that Cavendish measured force?
The pendulum arm oscillates as simple harmonic motion. No force term enters into the description of the pendulum’s motion. If you know such an expression please let me know.
What is the effect of the Newtonian force emanating from the so-called attracting weight?
If we assume that the attracting weight indeed attracts the pendulum arm, it does so in an intelligent way: the lead weight calculates the attraction necessary according to Newtonian laws and sends that information instantaneously to the small weight attached to the arm of the pendulum. The small weight does its own intelligent calculations and sends it back to the attracting weight and it moves legally according to Newtonian laws. All this happens instantaneously in zero time.
This is occult.
The motion of the pendulum is not described with an equation which includes force. If we write down F=GmM/r^2 and F=ma and then equate them and eliminate Fs this means that the motion does not require force. Fs canceled. Fs were put there to save Newton’s authority.
Again, Newton’s law is nothing other than Kepler’s rule. Newton defined 1/R^2 = F and T/R^2 = F. When he wanted to do astronomical calculations he canceled Fs and used Kepler’s law. In this sense Newton’s force is not even occult. It is a placeholder which is written to save Newton’s authority then eliminated.
So I would like to find an equation describing the motion of the Cavendish pendulum which has a term for force in it.
Thanks for this comment. Plenty of good information. I’ll reply to other points you make as well.