When you hear the word “probability,” you might think of coin flips, weather forecasts, or casino games. But in scientific reasoning, probability—especially Bayesian probability—is much more than a matter of chance. It is a method for evaluating how likely something is to be true based on prior knowledge and new data.

As physicist E.T. Jaynes famously put it, “Bayes’ theorem is not optional. It is the unique consistent rule for updating probabilities in the light of new evidence.”¹ Whether you’re trying to determine the location of a subatomic particle or the identity of a crucified man wrapped in linen, Bayesian logic is essential.

Stephen Senn, an Oxford statistician, adds: “Bayesian probability reflects how humans actually reason under uncertainty. It is not just a tool of statistics—it is the grammar of belief.”² In other words, it’s how we make rational decisions every day. We gather facts, we recall prior experience, and we adjust our beliefs accordingly.

Let’s say nine out of ten of your trusted friends recommend a new movie. That’s a consensus. Then you remember the director—he’s made other films you liked. That’s weighing the odds. Finally, you watch the trailer and it moves you—now you’re updating your belief based on new evidence. That’s Bayesian reasoning.

And that brings us to the Shroud of Turin.

The Shroud, a linen cloth bearing the faint image of a scourged and crucified man, is perhaps the most analyzed artifact in religious history. But can belief in its authenticity be more than devotional sentiment? Yes. Through scientific consensus, statistical odds, and Bayesian probability, a compelling cumulative case emerges—one that rational minds should not ignore.

As Oxford mathematician and Christian apologist John Lennox notes, “Bayes’ Theorem teaches us that improbability must be weighed against explanatory power and background evidence.”³ That’s exactly what this blog will do.

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Scientific Consensus: What the Experts Agree On

Consensus doesn’t mean certainty, but it tells us where qualified minds converge. When it comes to the Shroud, there are at least five widely acknowledged facts with high levels of agreement across multiple scientific disciplines:

1. The image is not created by pigment or paint. STURP’s 1978 investigation found no traces of paint, dye, or brush strokes.⁴
2. The blood is real human blood. Multiple independent tests revealed hemoglobin and serum albumin consistent with trauma-induced bleeding.⁵
3. The cloth contains a photographic negative image. Discovered in 1898, this negative quality has been confirmed by image scientists and digital analysts.⁶
4. The man matches crucifixion wounds described in the Gospels. These include scourging marks, nail wounds in the wrists and feet, and a pierced side.⁷
5. Botanical and textile analysis place it in the Middle East. Pollen found on the cloth corresponds to flowers from Jerusalem, and the weave—while rare—is consistent with high-quality first-century linen.⁸

This consensus is not religious bias—it includes researchers of all faiths and none. While some scholars still argue for a medieval origin based on flawed carbon dating (more on that later), many others acknowledge that the Shroud continues to defy forgery theories.

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Odds: Weighing the Probability of Individual Features

Let’s now assign basic odds to these five core facts based on peer-reviewed research:

• The image not being a painting: 99:1
• The blood matching crucifixion patterns: 19:1
• Iconographic consistency with early Christian art: 9:1
• The photographic negative quality: 99:1
• Middle Eastern botanical evidence: 9:1

Multiplying these odds together yields a conservative estimate that the Shroud is authentic at odds of 3.08 to 1, or roughly a 75.9% likelihood.⁹ That’s already impressive. But this is where Bayesian reasoning takes us further.

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Bayesian Probability: Dynamically Updating Our Confidence

Bayesian logic doesn’t just ask “how likely is this evidence?” It asks, “given this evidence, how likely is the hypothesis now?”

In Sacred Threads, the Bayesian analysis begins with a 50/50 neutral prior: the Shroud is either authentic or not. But each piece of new evidence raises the probability. Using standard likelihood ratios:

• No pigment (LR = 99)
• Crucifixion blood evidence (LR = 19)
• Iconographic alignment (LR = 9)
• Photographic negative (LR = 99)
• Textile/pollen fit (LR = 9)

The cumulative likelihood ratio becomes over 15 million to 1, yielding a posterior probability of 99.99999% for authenticity.¹⁰

This isn’t hand-waving; it’s statistical modeling. Even if we lower the ratios to be conservative, the odds remain overwhelmingly in favor of the Shroud’s authenticity when analyzed cumulatively.

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The Forger Hypothesis: A Statistical Collapse

Let’s reverse the question. What are the odds that a 13th-century forger:

• Understood 30+ precise elements of first-century Jewish burial practices
• Replicated the exact wounds of Roman crucifixion
• Embedded a superficial, photographic negative image with 3D qualities
• Avoided painting or dye altogether
• Incorporated pollen from Jerusalem flora
• Matched Roman-era textile features…

…all without modern forensics, science, or photography?

According to Sacred Threads, the probability of a single person in the Middle Ages achieving this by chance is less than 1 in 10⁶⁰. That’s a 1 followed by 60 zeroes—far less likely than winning the lottery 10 times in a row.¹¹ Bayesian modeling reduces the forgery hypothesis to statistical absurdity.

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The Science is Not Silent—It’s Surprising

Far from being unscientific, belief in the Shroud’s authenticity reflects how science actually works when confronted with complex, interdisciplinary evidence. As Cambridge physicist David MacKay noted, “The Bayesian framework allows us to calculate the probability of hypotheses given evidence… not just the evidence given a hypothesis.”¹²

The Shroud invites this kind of analysis—and rewards it with a near-certainty.

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Beyond Probability: The Image as Witness

Ultimately, numbers alone don’t move hearts. But they can remove intellectual barriers.

What we see on the Shroud is not vague or artistic. It is anatomically accurate. It bears evidence of scourging, crowning with thorns, crucifixion, and burial—wrapped in haste, but with honor. There is no sign of decomposition. The image is only on the surface fibers. The blood is real. The image formation remains unexplained.

No wonder even agnostic and atheist researchers on the STURP team admitted: “The answer to the question of how the image was produced remains, now as it has in the past… a mystery.”¹³

But perhaps it is more than a mystery.

It is a sign.

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Footnotes:

¹ E.T. Jaynes, Probability Theory: The Logic of Science (Cambridge: Cambridge University Press, 2003).
² Stephen Senn, Dicing with Death (Cambridge: Cambridge University Press, 2003).
³ John Lennox, Gunning for God (Oxford: Lion Books, 2011).
⁴ John P. Jackson, “STURP Final Report,” 1981; summarized in Sacred Threads.
⁵ Pierluigi Baima Bollone, “Identification of Blood on the Shroud,” Shroud Spectrum International, no. 2 (1981).
⁶ Dallis, Sacred Threads, Ibid.
⁷ Ibid., 90.
⁸ Ibid., 92.
⁹ Ibid., 95.
¹⁰ Ibid., 98–99.
¹¹ Ibid., 104–105.
¹² David J.C. MacKay, Information Theory, Inference, and Learning Algorithms (Cambridge: Cambridge University Press, 2003).
¹³ John P. Jackson et al., STURP Final Report, 1981.

Postscript: I’m not typically accustomed to quoting myself, as I’ve done in this blog. However, since Sacred Threads is a downloadable research paper with documented references and page numbers, it serves as a helpful resource for those who wish to explore the evidence further in greater depth.

Tom Dallis, Sacred Threads: The Shroud of Turin in Scriptural and Jewish Context (Cincinnati: Tom’s Theology, 2025).