The Nature of Evidence

In my daily professional life I am an experimental particle physicist. I currently analyze data taken with the ATLAS detector on the Large Hadron Collider at CERN laboratory near Geneva, Switzerland. I probe data that includes collisions of billions of protons to look for patterns that indicate the existence of some unknown phenomena or that measure the properties of a particular physical process. I am currently studying the Higgs Boson that was discovered in 2012 and measuring certain aspects of its character to try to understand if it exactly fits our expectations or whether there may be deviations from our standard model. 

In my personal life I have twice been a member of a jury in both criminal and civil cases. As a juror, I was asked to analyze data presented by witnesses and experts to determine the probability that an event in the past occurred in a certain way. Both my profession as a scientist and my civil duty as a juror required me to examine evidence and draw the most logical and reasonable conclusions based on the evidence. However, the type of evidence available in the different circumstances have very different natures. 

There are some people I talk with, primarily religious skeptics, who don't seem to understand the difference between scientific data and legal/historical evidence; the data from a scientific experiment that allows the investigator to draw reasonable conclusions, and the evidence presented in a courtroom that also leads to reasonable conclusions about what occurred in the past. These data are of a very different type but both lead to reasonably certain conclusions. Scientific data cannot directly tell us what occurred in the past, for direct scientific inquiry requires reproducible experimental results. Past events are not reproducible. Legal historical evidence that is used in a courtroom consists of direct evidence and circumstantial, or indirect, evidence. 

Extraordinary Claims and Extraordinary Evidence

"Extraordinary claims require extraordinary evidence" is a phrase that was popularized by Carl Sagan but has its roots from at least the 18th century Enlightenment when the miracles of Christianity were being questioned by certain intellectual thinkers of the day. The most famous Enlightenment critic of Christianity was probably David Hume who wrote an essay called Of Miracles in 1748 where he states, "Suppose, for instance, that the fact, which the testimony endeavours to establish, partakes of the extraordinary and the marvellous; in that case, the evidence, resulting from the testimony, admits of a diminution, greater or less, in proportion as the fact is more or less unusual."

At first this statement may sound reasonable. For instance, I am more likely to believe you if you tell me you had breakfast this morning than I would believe you if you told me that you levitated off the ground this morning without anything holding you up. But does the fact that I believe you if you say you did something ordinary and I don't believe you if you say you did something extraordinary support the statement that "Extraordinary claims require extraordinary evidence?" Actually, it doesn't. Although I may believe that you ate breakfast this morning, I must obtain supporting evidence if I want to actually determine whether or not that fact is true. If you have cleaned up your kitchen, such evidence may be hard to find. I might have to pump out the contents of your stomach, for instance to see what you ate and when you ate it. It is one thing to say that I believe you ate breakfast because it is an "ordinary" event, but it is quite another to actually find enough evidence to validate your claim. My point is that actual validation of any event requires sufficient evidence.

The Significance of the BGV Theorem

Let's continue to explore the question of whether or not our universe had an actual beginning.  In two previous posts I have said that (1) if our universe had a beginning, then the cause of the universe must be transcendent, a characteristic of the Christian God, and (2) we may never have any observational or theoretical evidence about what happened in the first 10^-35 seconds of the universe.

However, there have still been a lot of ideas from theoretical physicists about what may have happened to bring the universe into being and what we can surmise from the equations and laws that we know describe our universe.  One of the most often discussed papers dealing with our past was published by Arvind Borde, Alan H. Guth, and Alexander Vilenkin in 2003¹ and called the BGV theorem after the three authors.  In this paper, the authors show that any universe which is on average expanding has a timeline that cannot be infinite into the past, it must have had a beginning when it started to expand.  Since our universe is known to be expanding this theorem seems to require that it had a beginning.  (There are some technicalities to this conclusion like, for instance, the difference between "expanding" and "on average expanding" but, in general, what is known about our universe corresponds with the requirements of the BGV theorem.)

Proof, Evidence, Science, and Christianity

In my previous post I said that the Big Bang was evidence for the existence of God, though not proof.  This raises the question of whether or not there is proof for God, or for that matter, whether or not there is proof for anything, even within the scientific realm.   

If by proof, we mean absolute certainty of truth without any doubt or possibility of exception, then proof is not possible within a scientific framework.  Proofs are only possible in logic and in mathematics where there are well defined rules within the discipline.  In those two fields, once a proposition has been proven, that proof is complete and will remain valid.  In contrast, scientific knowledge is the best explanation for the results of current experimental observations among all the available options.  As additional evidence and observations are made, the facts may require modifications and adjustments to the theory.  If an experiment is done that contradicts the current scientific paradigm, then that theory is not wholly true and must be refined or discarded.  Therefore, scientific ideas can be disproved, but never absolutely proven.