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We begin the publication of an article by Manuel Carreira already published in its day by the Spanish Center of Sindonology. In it he makes a very interesting approach to look at the syndone with the eyes of a physicist. Manuel M. Carreira, a Jesuit priest, had a degree in Philosophy (Universidad Pontificia Comillas, Madrid), a degree in Theology (Loyola University, Chicago), a Master in Physics (John Carroll University, Cleveland) and a PhD in Physics (The Catholic University of America, Washington). His thesis was on cosmic rays and was supervised by Dr. Clyde Cowan (co-discoverer of the neutrino and Nobel Prize in Physics). Dr. Carreira has been a member of the board of directors of the Vatican Observatory for fifteen years. In addition to research on astrophysics and the relationship between science, philosophy and theology, he has worked on several NASA-funded technology development projects in the aerospace area. He will die in February 2020.

The study of the Shroud of Turin covers aspects as diverse as the relationship with the iconography of centuries, the textile examination of the cloth, the medical analysis of the blood stains, the history of its possible itineraries until it reached France, the determination of the origin of the multiple wounds, the information contained in the image, the age of the cloth and the possible process of forming the image on it. Various authors, specialists in each of the sciences and techniques applicable in each case, have on many occasions dealt with these aspects and continue to present their evaluation of results with a competence that is always worthy of admiration and which is subjected to the criticism of scientists of comparable professionalism.

I am not among the small number of those who have had direct access to the Shroud or to samples taken from it for laboratory studies, although I have had the satisfaction of dealing directly with those who have made such studies, as well as reading with interest a large number of publications on the subject. Because of my training as a physicist, I have a special interest in two problems that, independently of all other aspects, need to be discussed and resolved within the scope of this discipline: the age of the Shroud announced as a result of measurements of its C14 content, and the hypotheses formulated to explain the characteristics and formation of the image. I only want to deal with these two problems in this article, and I wish to do it in a systematic way and always with the criterion of using the endorsement of comparison with the facts: physics is ultimately self-defined by the contrast of its theories with the real and observable behavior of matter.

1. Dating of the fabric by radiocarbon dating

The result announced in 1988 is well known to all: three different laboratories jointly affirmed that the C14 dating technique indicated that the Turin canvas was from the 14th century, around the time when we have historical evidence of its existence in France. The immediate reaction of the media, and even of ecclesiastical circles, was to declare the matter closed, and to deny any possible connection of the Shroud with the crucifixion of Jesus fourteen centuries earlier.

With only one piece of information against it, although it was a piece of information with all the prestige of modern nuclear science, the whole previous study of dozens of scientists from all disciplines and all the concordant results pointing to the archaeological authenticity of the cloth were considered invalid. Without answering the obvious questions of how someone in the Middle Ages could have the medical or historical knowledge to produce an impression that astonishes for its anatomical, pathological and cultural accuracy, and without indicating how that unique image could appear on the canvas, the case was closed with more or less lukewarm references to a symbolic value of that "icon", or with a scornful attack on the credulity and opportunism of those who venerated it for centuries.

I believe, as a physicist, that the reaction was premature, hasty and excessive. It is not the first time, nor will it be the last, that a discordant fact has perplexed researchers for some time. We can recall that, at the beginning of the century, the duration of the Sun by the known processes of energy production was totally incompatible with the age of the Earth and its rocks, with clear traces of life well before the calculable age of our star. Also the age of the universe according to Hubble's data in the 1930s was lower than the age of the Earth's rocks, and today the problem arises again with ages of stars that seem to exceed the most accepted estimates of the expansion since the initial Big Bang. In each case, it was necessary to re-calibrate dating methods or to extend the physical processes to be taken into account. But in no case was any of the scientific data denied or considered worthless because they conflicted. The same has happened in the field of particle physics, with problems as serious as the apparent non-conservation of mass and energy (which led to the prediction and discovery of the neutrino) or, at present, with the lack of solar neutrinos, which forces us to a far-reaching revision in our theories of nuclear reactions in stars or in the properties of elementary particles.

Science advances by solving problems, not by denying them. By overcoming "common sense" with its obvious conclusions, Einstein gave us relativity. Quantum mechanics, despite its undoubted success, continues to challenge all our notions of reality and what "must" happen; to the point that it is even said in textbooks that we should not ask ourselves how things can really be so, if we want to advance in our study. It is always to be feared that our simplifications of problems to make them solvable will leave us with the false impression that we have taken into account all the important factors.

In the case of C14 dating, it is well known that discordant results occur with some frequency, and that a single datum is not enough to be certain. We need to know precisely the amount (percentage) of radioactive atoms in the initial sample, the possible causes of contamination and their relative influence, and the final percentage to expect after a given time. On this basis, the result of measurements (number of radioactive atoms in the sample) is compared with what the theory predicts for each time period, and thus the age is inferred. But it is not easy to accurately establish the history of an object and its environment to eliminate causes of error.

An example may clarify the above. If I deliver to a laboratory a piece of tree branch, still green, I expect the C14 result to indicate an age of zero with respect to the current date, because the branch was still alive when it was cut from the tree. If I am told that the C14 content corresponds to an age thousands of years ago, I will have to find a reason for what is clearly the wrong date, but I will not deny that the branch was alive a few days ago. In this example we can suggest an answer: if the tree was growing in an environment loaded with CO2 from fossil fuels (carbon oil), its C14 percentage will be so minimal that an obvious interpretation will lead to prehistoric ages. The opposite could occur if the sample, even if really very old, were contaminated with modern carbonaceous material.

In the case of the Turin canvas it has been noted that the small samples analyzed were taken from the edge of the cloth, in an area where relatively recent repairs have been made (within the last few centuries), and where it is very likely that the threads are not exclusively part of the original weave. To what extent this is so, cannot be decided a posteriori: threads are destroyed in the measuring process, and other threads that are still preserved may suggest that there was a mixture, but neither prove nor deny it. It really would be highly desirable to obtain samples from an area totally free of other fabric or thread foreign to the canvas, possibly from a near-central part, but away from the patches covering the 1532 burns, as well as the other clearly visible burns.

Contamination by contact with other materials can also introduce modern C14 into the samples. One of the most important requirements of the experimental dating method is the most thorough cleanliness possible, using organic and inorganic solvents that do not affect the cellulose, but do affect any adhesion. We assume that this care was given in the case of the Shroud, and that there was no foreign matter in the combustion chamber when burning the threads to produce the CO2 which then passes through the mass spectrometer.

But such complete cleanliness cannot be automatically assumed without testing, even microscopic. There still remains the possibility of some kind of external contamination resistant to all normal washing, or of some chemical reaction that incorporates modern C14 into the cellulose structure, permanently and indistinguishably from its original composition. Both types of contamination of the Shroud have been asserted by credible authors, although -without having access to their data- I do not believe it is possible to correctly evaluate the importance of such effects.

Dr. Garza-Valdés claims to have found in samples of the Shroud a layer of organic matter produced by microorganisms still living and multiplying in the threads. According to his experiments, this kind of plastic adhered to the fibers is resistant to all normal cleaning methods, and may constitute an important percentage of carbonaceous matter. The same has been affirmed by Dr. Kouznetsov. Without a series of well-controlled samples, and quantitative measurements, it is not possible to judge the importance that this material would have in altering the dating of the canvas2. But it is surprising that the same C14 content is claimed (in the original "Nature" article) in samples that were subjected to very thorough cleaning and in others that were measured without any cleaning, despite the obvious dirty state of the canvas after centuries of handling and exposure to smoke, water, and other contaminants.

Dr. Kouznetsov and co-workers in Russia have noted two new factors, one of a general nature and one specifically applicable to the Turin canvas. First, they claim that in the flax plant there is a process of isotopic fractionation, which concentrates C14 preferentially in the cellulose fibers that then form the threads of the fabric. If so, all dates obtained for similar fabrics will be in error: even fabrics made today must give a date in the future. I have not seen any scientific publication showing such a result, and without access to the original data and work, I cannot give a more accurate and reliable critique. Nor have I seen any studies indicating whether the various varieties of flax behave identically, or whether the chemical environment of the soil and other environmental variables may influence the claimed enrichment, to establish more precisely whether or not this factor is important in the case at hand. Such laboratory checks should be made without question. To my knowledge, other similar ancient canvases have been dated without problems.

The fire of 1532, according to Dr. Kouznetsov, did have an important impact on the composition of the threads under study. Under oxygen-deprived conditions and at temperatures of several hundred degrees, the coffer wood undergoes chemical reactions and produces active compounds that act on the linen cellulose. This molecularly binds modern wood vapors to the original fibers, contaminating the fabric with C14-rich material, which is then examined for dating. Descriptions of work done in Russia contain claims of a quantitative relationship leading to a date of 2000 years ago when the C14 abundance is corrected to account for the effects of fire. Again, I do not have at my disposal the detailed set of measurements and calculations; the theory is plausible, but its exact value can only be judged with a series of controlled measurements, if possible made by several researchers in independent laboratories, and with results published under the scrutiny of the scientific community. The environment of such a fire is not difficult to duplicate, and experimentation is the ultimate criterion for establishing the validity of the hypothesis.

Leaving aside explanatory proposals that rely on natural and reproducible processes, we are faced with hypotheses of an exceptional type, not susceptible to verification in the laboratory, and which are often linked to supposed modes of image formation by a supernatural event. In one way or another it is suggested that any unknown process capable of affecting the canvas with an energy that caused the image, could also alter the canvas in its atomic structure, increasing the C14 content.

The first reaction to these assertions is one of surprise, because of the coincidence that such a phenomenon leads exactly to a date that coincides with the historical dating, and not to another century before or after.... by chance? If the formation of the image is due to a divine decision to leave a motif of credibility in the resurrection, it seems illogical to give us an object that by its very physical nature induces us to doubt its authenticity, making it useless for that purpose. And if the excessive C14 is produced by a known or plausible physical phenomenon, what is its nature?

As we will see in the second part of this article, it is common to attribute the image to an unspecified "radiation". Current physics does not accept any type of electromagnetic radiation that introduces new neutrons into the nucleus of C12 or C13. Even assuming an unknown (and implausible) process by which the N14 in the air would become C14, there is no reason for it to combine chemically with the cellulose of the canvas; a mere surface adherence would not be sufficient to contaminate the samples, resisting cleaning. Nor is the hypothesis of a "dematerialization "4 of the body at the moment of resurrection any more acceptable, so that the particles of the nucleus are released and the neutrons are introduced into the C12 of the canvas. The C14 in our atmosphere is due to the impact of cosmic rays on the N14 in the air, not on the C12. And the observed effect on the fabric is very unlikely physically, unless the neutron energy is adjusted very precisely.

If we take into account the nature of the forces that hold together the particles of nuclei heavier than H, a very obvious objection can be raised to any "dematerialization" that separates them. From He to Iron, nuclear synthesis releases energy, equivalent to about 1% of the initial mass to arrive at C, N, O, Ca which constitute 34% of the atoms in the typical human body. For a 75 kg body, this means that about 500 grams of mass have been transformed into an enormous amount of energy (calculated by Einstein's well-known formula, E=mc2), and this same amount (about 50,000 trillion joules, the energy of a 10 Megaton atomic bomb), is necessary to destroy the nuclei and transform them back into loose particles. Nothing is said in this hypothesis about the source of such energy, nor about the way of channeling it so that its only effect is to undo the atomic nuclei of the body, without affecting or destroying the objects of its surroundings (What is indicated about this dematerialization can be applied also to the proposals of E. Lindner (who suggests a partial annihilation of protons in atoms of the body) and of J.B. Rinaudo (disintegration of deuterium atoms, liberating neutrons that alter the quantity of C14). There is no physical reason for this to occur, nor for the right amount of particles to be produced to give the medieval date, nor for the particles to have the right energy; nor for them to influence the fabric to give the image).

Attributing the image to low-energy X-rays emitted during weak dematerialization also assumes very physically improbable processes. There is no reason why X-radiation, which involves release of excess energy, should be produced when it is necessary to supply the total energy that should account for dematerialization. No radiation propagating according to known laws can explain the characteristics of the image, as described in the second part of this article. Nor do I know of any experiment that would give any basis for thinking that they would have exactly the right wavelength to penetrate only the surface of the flax fibrils, causing the very slight dehydration that gives the canvas the yellowish color of the image (In addition to the above considerations, from the point of view of physics, it is useful to underline the theological difficulty of accepting this dematerialization. The concept of man, as a "rational animal", demands the existence of the body - necessarily made of matter, of atoms - in order to be a human being in its totality: we are not spirits imprisoned waiting to get rid of the body. The Gospel is categorical in showing the risen Christ insisting on his corporeality, on his flesh and bones, on his wounds, on his capacity to be touched and to eat with the disciples. It makes no sense to speak of resurrection if it is only a spirit, which could never die, that is said to "return" to life. That is why it is illogical to affirm that the resurrection destroys the body at its most basic level).

Summarizing all that has been said: assuming that the radiocarbon dating has been carried out in a professional and fully credible way (although with well-known methodological flaws that I do not have to discuss), it is necessary to find an explanation for the fact that its result is in obvious contradiction with what is deduced from all the other studies of the Shroud. It is possible that contaminations of microorganisms or effects of the fire have introduced some C14 into the cellulose of the linen: such an effect has to be established quantitatively. Other forms of radioactive enrichment are implausible because of their gratuitousness from the point of view of the necessary physical processes and their side effects (in addition to their philosophical or theological difficulties). The problem remains unresolved.

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