Studies in science history (Chapter 3 (The little science route to fusion,…
Studies in science history
When 2 chemists (Fleischmann and Pons) working at the University of Utah discovered fusion, they launched the equivalent of a scientific gold rush. And the gold was to be found everywhere - at least in any well-equipped laboratory.
The apparatus was simple enough: a beaker of heavy water; a palladium as the cathode, and a platinum as the anode. A small amount of lithium-deuteroxide was added to the heavy water to serve as a conductor.
Though the substances are not in everyday use, and are rather expensive, they are quite famiiar to any modern scientist; there is nothing exotic about the apparatus.
Put a low voltage across this "cell" for a period of up to several hundred hours, and out should come the gold: fusion power. The heavy hydrogen atoms should fuse together into helium, releasing energy; this is the way the sun is powered.
The experiment seemed straightfoward and there were plenty of scientists willing to try it. Many did. It was wonderful to have a simple laboratory experiment on fusion to try after the decades of embarassing attempts to control hot fusion.
Scientists over the world immediately started scrambling for information about the experiment. Details were hard to come by.
Then doubts started to surface as other institutions reported that they made a mistake. Pons and Fleischmann's paper was also withdrawn from Nature. Congress decided to put the 25 million dollars on hold.
An MIT group claimed that Pons and Fleischmann had incorrectly interpreted their evidence for neutrons; CalTech also reported detailed replication attempts and all negative.
CalTech even pronounced that cold fusion was extremely improbable theoretically and accused Pons and Fleischmann of delusion and incompetence.
The little science route to fusion
It is known that palladium has a surprising ability to absorb vast quantities of hydrogen. If a piece of palladium is charged with as much hydrogen as it can absorb, then the pressure inside the crystal lattice dramatically increases.
In the 1920, two German chemists attempted to produce fusion of hydrogen using palladium, but they were not interested in fusion as a source of energy, but in the product, helium, which was used in airships.
They claimed to detect the presence of small amounts of helium. Unfortunately, they later discovered that the probable source of the helium was gas already absorbed in the glass walls of their apparatus.
In 1927, Tanberg also had similar ideas to those Pons and Fleischmann (60 years before them). The only substantial difference between Tandberg's device and the setup of Pons and Fleischmann was the use of light water as the electrolyte.
In the 1930s, Tanberg used a wire of palladium which had been saturated with deuterium. It seems he met with little success, at least in regard to the production of helium.
Pons and Fleischmann were unaware of the earlier work when they started their experiments in 1984.
While the scientific community was unfamiliar with Pons and Fleischmann's work on cold fusion, they had been following Jones' progress for several years.
In 1982, they had undertaken a major experimental effort looking for fusion triggered by sub-atomic particles produced at the Los Alamos particle accelerator. They had found far more evidence of such fusions than theory would have led them to expect, but not enough to make a source of viable energy.
The Brigham Young group pursued the idea and tried various materials as the electrodes. Soon they decidede that palladium, with its ability to absort hydrogen, was the most likely candidate.
It was these hastily carried out measurements which were later to be challenged by the MIT group; they turned out to be the Achilles heel for Pons and Fleischmann and also Jones.
It was Pons and Fleischmann's results that gave rise to the cold fusion controversy. The levels of neutrons detected by Jones were of lower orders of magnitude and he has never claimed to observe excess heat. Jones, unlike Ponns and Fleischmann, made a point of playing down the commercial application angle.
Despite his attempts to distance himself for other Utah groups, Jones has inevitably been subject to the same suspicions. There is no consensus whether he has observed fusion.
However, unlike Jones, Pons and Fleischmann had no established reputation in the field of fusion research as they were chemists, not physicists. If all the heat excess was caused by fusion, the levels of netrons produced should have been more than enough to have killed Pons and Fleischmann and other people in the close proximity.
Part of the skepticism came from fusion researchers being only too familiar with grandiose claims for breakthroughs which shortly afterwards turn out to be incorrect.
Pons and Fleischmann had 2 sorts of evidence to back up their claims: excess heat and nuclear products. These had to be tested.
A careful account of the power input and ouput of the cell was kept, including all known chemical reactions that are capable of transfforming chemical energy into heat.
It is a fairly straightforward procedure to establish the power output by measuring the temperature rise, the cell first having been calibrated usign a heater of known power.
The heat excess varied between cells. Some cells showed no heat excess at all. The power sometimes came in surges. However, more routinely the heat excess was between 10% and 25%.
Despite the capricious nature of the phenomenon, Pons and Fleischmann were confident that the heat excess could not be explained by any known chemical process or reaction.
The most direct proof of fusion would be the production of neutrons correlated with the excess heat. The first neutron measurements attempted by Pons and Fleischmann were relatively crude.
A signal 3 times the background was claimed to be recorded for this one cell. This was a suggestive result, but as neither the energy of the neutrons was known.
The numbers of neutrons deteced if any were billions less than what would be expected if all the heat was produced by the deuterium fusion reaction.
Another piece of evidence for fusion having taken place would be the presence of its products, such as tritium. Pons and Fleischmann found traces of tritium in the palladium cathode of one cell. The difficulty with this finding - a problem which has beset all the claims - is that tritium is a known contaminant of heavy water.
The embarassment caused by the premature announcements from Georgia Tech and Texas A&M cautioned those scientists wo were seriously trying to repeat the experiment that they faced a long struggle.
Part of the difficult facing scientists trying to repeat the experiment was that Pons and Fleischmanns's account of what they had done was insufficiently detailed.
Some have accused Pons and Fleischmann of deliberate secrecy in order to secure patent rights or to hide their own incompetence.
Pons and Fleischmanns were initally hesitant because of their own uncertainties and their fears about the dangers of the experiment. The end product, tritium, is also one of crucial ingrediants in creating a hydrogen bomb.
While most groups saw nothing, a few had positive results. The classic problem of replication during a scientific controversy was surfacing. Negative results could be explained away by the believers due to differences in the replicating experiment.
Introduction to Part 1 and Part 2
Einstein's theory of relativity became widely known in the early part of the twentieth century. One of the reasons for its success among scientists was that it made sense of a numer of puzzling observations.
The successfulness of the theory of relativity was contrributed by:
The ending of the Great War and the unifying effect of science on a fractured continent.
The dramatic circumstances and the straightfoward nature of the 1919 "proof" of relativity.
The astonishing consequences of the theory for our common-sense understanding of the physical world.
The implication of Einstein's insight that "the velocity of light must be constant whatever the velocity of the source".
Regarding the theory of relativity
Time, mass, and length are not fixed but are relative to the speed at which things move.
Things that go very fast - at speeds near to the velocity of light - would get very heavy and short.
Light would not only travel in straight lines, but would be bent by gravitational fields to a greater extent than had been believed possible.
The atomic bomb in 1945 is not what "proved" the theory of relativity. The theory had been accepted for many years before then.
The theory is accepted due to two decisive observational proofs (Michelson-Morley, 1880s and Eddington, 1919),
Michelson-Morley "aether-drift" experiment in 1880s
Observed that light travelled at the same speed in all directions, proving the special theory of relativity.
Does the light travel at the same speed in all directions or not?
Eddington's solar eclipse observation in 1919
Observed that the starlight was bent by the sun to the right extent to prove the general theory.
Do the stars near the sun were displaced twice as far as they should have been under the old Newtonian theory or they are not?
Does the earth sail in an aetherial sea?
In 1887, Michelson and Morley carried out a very careful experiment that compared the speed of light in the direction of the earth's motion with that at right angles to the earth's motion.
In the 19th century, it was believed that light travels through a universal medium caled "the aether". If this was true, then the velocity of light would appear to vary as the earth moves throught the eather in its orbit around the sun.
However, They found that light seemed to move at the same velocity in all directions.
According to the theory of relativity, light should have a constant velocity in all directions, but the theory did not surface until some 2-5 years after Michelson began his observation.
However, Michelson was disappointed because he failed to find the speed of the earth. Michelson did not even complete the experiements properly; he went straight on to other things after publishing the initial findings.
To measure the velocity of the earth, Michelson needed to measure the velocity of light in a variety of directions. Initally, the speed of light was estimated around 18.5 miles per second.
The used mehod was what we now call "interfermotery". The same beam of light is split into two and recombined. When the split beam recombines, it will give rise to "interference fringes": a series of light and dark bands.
Since the ather wind was expected to change depend on the orientation of the apparatus due to the earth rotation on its axist, the experiment had to be repeaated at different times of the year.
Note that if the velocity of the solar system through the aether was similar to the veloctiy of the earth in its orbit, there would be times of the year when the earth's movement in its orbit would nearly cancel the sub's movement. To prove this theory, the observations should be done during two seasons of the year.
The need for temperature and vibration control indicated that the experimental apparatus be heavily built on massive foundations in hte cellars of strong, well insulated buildings.
6 elements in the experiment by Michelson-Morley
(1) The light rays must be split and reflected along paths at right angles
(2) Observations of fringes must be made at a number of points as the whole apparatus is rotated on its axis
(3) The observations must be repeated at different times of the day to take account of earth's rotation on its axis
(4) The observations must be repeated at different seasons to take account of the earth's changing direction of movement with respect to the solar system
(5) The experiment, it might be argued, should be argued, should be carried out in a light, open, or transparent building
(6) Likewise, the experiment should be carried out on a high hill or a mountain
The 1881 experiment
According to his calculations, an aether wind having something in the region of the earth's orbital velocity would ive rise to a displacement of about a tent of the width of a fringe as the apparatus turned. He felt that he would be able to observe this easily if it were there.
He published the results of his observations, whihc were that no movement of the earth through the aether could be detected.
After publication, his results were analyzed and pointed that he had neglected to take account of the non-zero effect of the wind on the transverse arm of the apparatuus. This led him to design and build an improved apparatus.
The 1887 experiment
After the usual trials and tribulations, Michelson and Morley were ready to observe again. However, they found no effects related to the speed of the aether wind.
To be a test of relativity, the experiment needs to demonstrate not that the earth is not moving with anything like the expected velocity, but that there is absolutely no difference in the velocity of light in whichever direction it is measured.
the 1887 experiment was not a very good test of relativity, even though it was adequate as a test of what Michelson and Morley wanted to know. Only after Einstein's famous papers were published, the experiment become "retrospectively reconstructed" as a famous and decisive proof of relativity.
Morley and Miller in the 1900s
Numerous explanations were put forward in an attempt to show how the existence of an aether was compatible with the null results.
Still unsettled with the idea that the aether was trapped, Morley and Millor built an improved interferometer.
They again found what could only be counted as a null result when compared with what might be expected from the earth's orbital velocity.
As they completed their work, Einstein's papers were becoming recognised. However, Einstein's ideas were not uniformly accepted upon their publication. The debates on the theory of relativity lasted for several decades.
Miller experiments in 1920s
As a result of encouragement from Einstein and Lorentz, Miller decided to continue his work. There was a small effect in the earlier experiments, however, for relativity, any real effect, although small, was crucial.
In 1925, Miller concluded that he had found an observed motion of the earth of about 10 km per second (about 1/3 of the original Michelson experimetns).
Although the famous MIchelson-Morley in 1887 is regularly taken as the first, the experiment in 1925 is a more refined and complete version of the experiment was widely hailed as disproving relativity.
There were a number of experimental responses to Miller's finding, all of them claiming a null result. The biggest effort was made by Michelson himself.
Miller's paper in 1933
In 1933, MIller published a paper reviewing the field and concluding that the evidence for an aether wind was still strong. We have then a classic stiuation of so-called replication in physics.
Miller claimed a positive result, critics claimed negative results, but Miller was able to show that the conditions under which negative experiments were conducted were not the same as the conditions of his own experiment as his experiment was the only one that was done at altitude and with a minimum of the kind of shielding.
However, the argument in physics was over. Other tests of relativity showed that the theory of relativity is correct and the velocity of light must be constant in all directions.
The notion of "anomaly" is used in science in 2 ways: (1) describing a nuisance and (2) signifying a serious problem.
Are the stars displaced in the heavens?
The bending of light rays by a gravitational field was a central prediction of Einstein's theory.
This was observed by Eddington during a sun eclipse in 1919 when the bending of starlight by the sun was measured and found to agree with the theoretical value calculated by Einstein.
The curious interrelation of theory, prediction and observation
The general theory of relativity is a complicated business. Even in 1919, only Einstein and Eddington who fully understood it.
However, based on Newton and Einstein theories, a strong gravitational field would have an effect on light rays, but the Einsteinian effect should be greater than the Newtonian effect. The problem was to find out which theory was correct.
The earth's gravitational field is too small, but the sun's gravitational field is much greater. The light coming from stars should be bent as the rays pass through the sun's gravitational field. To us, it should appear that stars close to the sun are slightly displaced from their usual position.
In figures, the expeced displacements were 0.8 second of arc and about 1.7 seconds of arc for the two theories, a second being 1/3600 of a degree.
Einstein's theoretical derivation of the maximum apparent deflection of light rays is somewhat problematic. As in many delicate experiments, the derivations, though unclear at the time, came to be seen to be correct after the observations had "verified" Einstein's prediction.
Science does not really proceed by having clearly stated theoretical predictions which are then verified or falsified. The validity given to theoretical derivations is intimately tied up with our ability to make measurements. Theory and measurement go hand-in-hand in a much more subtle way that is usually evident.
One has to separate the theory from the prediction derived from that theory. In case of Eddington, he obtained measurements that concurred with Einstein's derived prediction, but the results were taken as confirming not only the prediction, but also Einstein's theory.
Eddington seemed to confirm not only Einstein's prediction about the actual displacement, but also his method of deriving the prediction from his theory - something that no experiment can do.
As we see, Einstein's theory and Eddington's prediction are very inexact and some of them conflicted with others. When deciding which data should be kept or discarded, Eddington had Einstein's theory in mind. Therefore, Eddington could only claim to have confirmed Einstein because he used Einstein's derivation in deciding what his observations really were, while Einstein's derivations only became accepted because Eddington's observation seemed to confirm them.
In this case, observation and prediction were linked in a circle of mutual confirmation rather than being independent of each other as we would expect according to the conventional idea of an experimental test. When we descirbe Eddington's observations, we will see just how much he needed Einstein's theory in order to know what his observations were.
The nature of the experiment
The size of displacement - Newtonian or Einsteinian - is so small that the only possible chance of measuring it is by comparing photographs of a region of sky with and without the sun present. For the crucial observations, one must await a total eclipse, but the photographs must be taken several months before or after, when the sun is absent from that region of the sky.
For an experiment of such delicacy, it is important that as much as possible is kept constant between the observations and the background comparisons.
The trouble is that the observation photographs and the comparison plates have to be obtained at different seasons of the year. This means lots of other things have time to change. Furthermure, observation plates made in the daytime will use a warm telescope, while at night, the camera looks through a cold telescope. The difference in focal length between hot and cold telescopes will disturb the apparent position of the starts to a degree which is comparable with the effect that is being measured.
What makes matters worse is that eclipses can usually be seen only from remote corners of the world. It is not possible to take major telescopes, with all their controlling mechanisms, to such locations. This means the telescopes will be relatively small, with low light-gathering power.
This means that the exposures have to be long. Long exposures bring with them another range of problems. Not only does the telescope have to be held steady, but it has to be moved to compensate for the rotation of the earth.
On top of all these problems, there are also the contigencies of the weather. If clouds cover the sky then all the preparations are wasted.
One can understand that Eddington observations were not just a matter of looking through a telescope and seeing a displacement; they rested on a complex foundation of assumptions, calculations, and interpolations from two sets of photographs. And this is the case even if the photographs are clear and sharp - which they were not.
The expeditions and their observations
The Eddington observations were actuallmy made by 2 separate parties: 1 with 2 telescopes, the other party with 1 telescope. The 2 parties went to 2 different locations.
The best photographs, though they were not completely in focus, were taken by the Sobral 4-inch telescope.Crommelin and Davidson calculated that the deflection of starlight at the edge of the sun would be between 1.86 and 2.1 seconds of the arc, compared to the Einstein prediction of 1.7 seconds.
In very broad terms, one of the Sobral instruments supported the Newtonian theory, while the other leaned towards Einstein's prediction for his own theory. However, the photographs that support Newton was problematic since the results from the astrographic telescope were poor.
The 2 plates from the Principe expedition were the worst of all, but Eddington obtained a result from these plates using a complex technique that assumed a value for the gravitational effect.
At first, he used a value half-way between Einstein's and Newton's and then repeated the procedure using Einstein's figures. It was not clear what difference these assumptions made though it is worth noting that, in Eddington's method, Einstein's derivation played a part even in the initial calculation of the apparent displacement.
If we forget about the theory and the derivations, we might argue that the 2 sets of poor plates cancel each other out, and that the remaining evidence showed that the displacement was higher than 1.7. Nonetheless, it would be difficult to be able to provide a clear answer. Nevertheless, in 1919, the Astronomer Royal announced that the observations had confirmed Einstein's theory.
Interpretation of the results
Even to have the results bear upon the question it had to be established that there were only 3 horses in the race: no deflection, the Newtonian deflection, or the Einstein deflection.
To make the observations come out to support Einstein, Eddington and the others took the Sobral 4-inch results as the main finding and used the 2 Principe plates as supporting evidence while ignoring the other 18 plates taken by the Sobral astrographic.
In the debate which followed the Astronomer Royal's announcement, it appears that issues of authority were much to the fore. In the end, Eddington won the day by writing the standard works which described the expeditions and their meaning.
10 more eclipse observations were conducted between 1922 and 1952. Only 1, in 1929, managed to observe a start that was closer than 2 solar radii from the edge of the sun, and this suggested that the displacement at the edge would be 2.24 seconds of arc.
Most of other 9 results were also on the high side. Although there are other reasons to believe the Einstein value, the evidence on the bending of visible star light by the sun, at least up to 1952, was either indecisive or indicated too high a value to agree with the theory.
Conclusion to part 1 and part 2
The picture of a quasi-logical deduction of a prediction, followed by a straightforward observational test is simply wrong.
What we have seen are the theoretical and experimental contributions to a cultural change, a change which was just as much a license for observing the world in a certain way as a consequence of those observations.
After the interpretation of the eclipse observations had come firmly down on the side of Einstein, scientists suddenly began to see confirmation of the red-shift prediction where before they had seen only confusion.
Eddington and the Astronomer Royal did their own throwing out and ignoring of discrepancies, which in turn licensed another set of ignoring and throwing out discprepancies, which led to conclusions about the red-shift that justified the first set of throwing out still further.
No test viewed on its own was decisive or clear cut, but taken together they acted as an overwhelming movement. Thus was the culutre of science changed into what we now count as the truth about space, time, and gravity,
We have no reason to think that relativity is anything but the truth, but it is a truth which came into being as a result of decisions, about how we should license our scientific observations; it was a truth brought about by agreement to agree about new things.