Science and miracles

Science and miracles

Negative image of Shroud of Turin (Public Domain)

Originally published 6 March 1989

By now every­one has heard the result of the car­bon-14 dat­ing tests on the Shroud of Turin, the linen cloth pre­served in the cathe­dral at Turin, Italy, bear­ing the like­ness of a man and pur­port­ed to be the wind­ing sheet of Christ.

The offi­cial report of the inves­ti­gat­ing sci­en­tists has appeared (Nature, Feb. 16, 1989). The report is itself in many ways more inter­est­ing than the result. It is a clas­sic illus­tra­tion of the sci­en­tif­ic way of know­ing and deserves a wider circulation.

Ques­tion: How old is a cer­tain piece of cloth? For­get for the moment what makes this par­tic­u­lar piece of cloth his­tor­i­cal­ly inter­est­ing; can we deter­mine its age? The answer: Yes, by a method known as car­bon-14 dating.

Car­bon dat­ing exploits the pre­cise­ly mea­sur­able radioac­tive decay of car­bon-14 atoms. The details of how the method works are not — in this con­text — impor­tant. The point is that there are peo­ple who claim they can find out how old some­thing is by count­ing atoms. Can we believe them? Can we trust their results?

Let’s put them to the test. Take wood from the heart of a 1,000 year-old sequoia tree whose age can be deter­mined by count­ing rings. Or bone from the tomb of an Egypt­ian king. Or a threads from your great-great-grand­moth­er’s wed­ding dress. Send the sam­ple to a car­bon-dat­ing lab and ask them to deter­mine the age. Don’t tell them you already know the answer. See if they get it right.

Now, take my word for it, this has been done, over and over again. Car­bon dat­ing has been thor­ough­ly test­ed and cal­i­brat­ed with objects of known age. The method is com­pli­cat­ed — it is based on some high-pow­er chem­istry and physics and expen­sive equip­ment — but it works. Any skep­tic who can afford the fee can put it to the test.

Shroud put to the test

Three car­bon-dat­ing labs, in Zurich, Oxford, and Ari­zona, par­tic­i­pat­ed in the test on the Shroud of Turin. Along with sam­ples from the shroud, each group was giv­en three con­trol sam­ples of cloth — linen from a 900 year-old Nubian tomb, linen from a 2nd-cen­tu­ry AD mum­my of Cleopa­tra, and threads from an 800 year-old gar­ment of St. Louis d’An­jou. None of the sam­ples were iden­ti­fied. None of the labs com­mu­ni­cat­ed with each oth­er until the results were in.

The final report of the inves­ti­ga­tion describes in detail the meth­ods by which sam­ples were tak­en from the shroud, then cleaned and pre­pared for analy­sis by lab­o­ra­to­ry staffs. Also described is a sta­tis­ti­cal analy­sis of the results. All three labs agree on the ages of all four sam­ples with­in exper­i­men­tal error, and cor­rect­ly dat­ed the con­trol sam­ples. Con­clu­sion: The Shroud of Turin is medieval.

Is that con­clu­sion absolute? Of course not. No sci­en­tif­ic test can prove any­thing with absolute cer­tain­ty. As one of the Oxford inves­ti­ga­tors wrote (in a let­ter to Nature), “If we accept a sci­en­tif­ic result, we must exer­cise a crit­i­cal notion of the prob­a­bil­i­ties involved. If we demand absolute cer­tain­ty, we shall have to rely on faith.”

Sci­ence is not faith. Sci­ence is com­mon sense. There is always a remote pos­si­bil­i­ty that some unknown agency act­ed on the shroud in such a way as to cause the car­bon dat­ing exper­i­ments to give a false result.

For exam­ple, a Har­vard Uni­ver­si­ty physi­cist has pro­posed (whether seri­ous­ly or not I do not know) that neu­tron emis­sion from the radi­ant body of the res­ur­rect­ed Christ might have trans­formed some non­ra­dioac­tive car­bon into car­bon-14 by neu­tron cap­ture, thus inval­i­dat­ing an impor­tant assump­tion upon which the age mea­sure­ment is based.

The three lab­o­ra­to­ries appar­ent­ly con­sid­ered this bizarre pos­si­bil­i­ty, and their reply (artic­u­lat­ed by R. E. M. Hedges of Oxford) goes some­thing like this: 1. No known phys­i­cal process could pro­duce a neu­tron flux of the required mag­ni­tude, and if a super­nat­ur­al expla­na­tion is pro­posed, then there is hard­ly any point in doing the exper­i­ments. 2. It would be an amaz­ing coin­ci­dence if the pro­posed neu­tron emis­sion was such as to make the appar­ent age of the cloth coin­cide with the very time — mid-14th cen­tu­ry — when the shroud is first men­tioned in history.

Confirming explanations

Sci­ence can­not dis­prove sup­posed mir­a­cles. What sci­ence can do is con­firm a per­fect­ly nat­ur­al expla­na­tion for this remark­able object which is con­sis­tent with every­thing else we know about the world. Name­ly, the shroud is a medieval icon or forgery.

It is to the cred­it of Church offi­cials in Italy that they autho­rized the tests and accept the results. Their actions are con­sis­tent with a recent dec­la­ra­tion of Pope John Paul II on the prop­er rela­tion­ship of sci­ence and the­ol­o­gy. “Sci­ence can puri­fy reli­gion from error and super­sti­tion,” wrote the Pope, and “reli­gion can puri­fy sci­ence from idol­a­try and false absolutes.”

He con­tin­ued: “The unprece­dent­ed oppor­tu­ni­ty we have today is for a com­mon inter­ac­tive rela­tion­ship in which each dis­ci­pline retains its integri­ty and yet is rad­i­cal­ly open to the dis­cov­er­ies and insights of the other.”

Some peo­ple will still want to believe that the Shroud of Turin is the wind­ing sheet of Christ, and that is their right; no car­bon-14 test, or any oth­er test, will dis­suade them. They pre­fer the appar­ent cer­tain­ties of mir­a­cles to the con­sid­ered prob­a­bil­i­ties of nat­ur­al science.

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