Bigelow, who has a long-standing interest in the paranormal and has invested extensively in UFO research, has a counterpart in the late James Randi, a magician and hard-line sceptic who set up a US$1million award for anyone who could offer definitive proof of the paranormal. It remained unclaimed for two decades and was terminated in 2015. But in this instance, Bigelow was not looking for sensational phenomena.

The Institute sought applicants who would take an evidentiary approach. There were to be no quotations from scripture, no faith-based outpourings: adjudication would be according to legal and scientific standards of verification.

The six judges brought impressive credentials. They were Jessica Utts, emeritus professor of statistics from Irvine; theoretical physicist Harold Puthoff; Jeffrey Kripal, chair of philosophy and religious thought at Rice University; journalist Leslie Kean, who had written front-page stories on UFO evidence for The New York Times; and distinguished forensic neurologist Christopher C. Green.

When the list of winners was announced in November, the prize haul had grown to well over US$1.5 million with an additional endowment to reward those on a short list of 29 submissions, all now published on the Institute website. Clearly this bid to promote life after death as the $1.5 million question was something more than gimmickry and wacky extravagance, so what does it all amount to, now that the evidence is out there?

Eight out of the 10 authors who each won US$50,000 for highly commended essays, and nine of the 15 on an extended shortlist, hold postgraduate qualifications in the "hard" sciences. They include a pharmacologist, a computer engineer, an evolutionary biologist, a clinical oncologist, a bioengineer, and a postdoctoral research fellow in biomedical engineering.

Third prize (US$150,000) was awarded to Leo Ruickbie, Fellow of the Royal Historical Society in Britain and author of several books on the history and sociology of paranormal beliefs. Runner-up (US$300,000) Pim van Lommel is a clinical cardiologist whose previous honours include winning the Scientific and Medical Network book prize in 2010. First prize, a unanimous choice, was an essay by Jeffrey Mishlove, who holds the only doctorate yet awarded in parapsychology.

Central to many of the essays is a concern with how evidence for the survival of consciousness beyond biological life presents a fundamental challenge to prevailing models of human perception and cognition. As Bigelow put it in an interview on the announcement of the prize, if the mind does not cease functioning with the death of the brain, "Where the hell is your mind?"

Mishlove's essay pursues this speculation, drawing on extended discussions he has hosted since the mid 1980s with researchers in diverse fields for his You Tube channel, New Thinking Allowed. Mishlove is a skilled interviewer, meticulously attentive to argument and data, but he knows how to focus on key points and steer the dialogue at a pace that allows a general audience to follow.

An early guest was pioneering biologist Francis Crick, co-winner of the Nobel Prize for his breakthrough work on the structure of DNA. "It's very rash to say that these things are beyond the scope of science," Crick says, in response to Mishlove's challenge about how consciousness can be understood purely in terms of neurons, "though we can't see how to do it at the moment."

A generation later, Mishlove persuades philosopher Ruth Kastner, who belongs to a research group on the foundations of physics at the University of Maryland, to address the question again. Kastner professes herself "paranormally challenged", but interested in how witness accounts of near-death experience may be understood in terms of quantum theories of space-time. She insists, though, on avoiding slippage between modelling possibility and claiming actuality.

This points to an essential problem with the brief for the competition. Bigelow does not seek to invest in speculation. He wants evidence, and evidence that will at least point in the direction of proof. But legal and scientific approaches to proof, assumed to be almost interchangeable in the competition brief, are divergent in essential ways.

The law counts evidence by "weight", so multiple indicators from multiple sources may add up to proof beyond reasonable doubt. Proof in science depends on identifying causality and being able to replicate apparently causal relationships in predictable ways. Witness testimony, often central to a court case, has no place in scientific understanding.

Our senses deceive us, so interpretations we regard as common sense may be no more than consensual delusion. But to what extent should we disbelieve our senses? Ruickbie's essay presents this challenge as what he terms "the Scrooge paradox", a reference to the withered old sceptic in Charles Dickens's A Christmas Carol.

Scrooge, who sees a ghost and assumes it's a symptom of indigestion, is an emblem of how human intelligence withers under the constraints of hard rationalism and rational self-interest. It may take a supernatural apparition to burst the locks on embargoed dimensions of the mind.

Van Lommel argues that mounting evidence surrounding the phenomenon of near-death experience (NDE) is testing the viability of prevailing scientific assumptions about the relationship between consciousness and the physical brain. There are now over 20 million documented cases of NDE in Europe. "Some scientists do not believe in questions that cannot be answered," but it may be a matter of adjusting the formulation of the question. Not "What is the biological basis of consciousness?" but "Is there a biological basis of consciousness?"

Whatever the evidence of the survival of consciousness after physical death, scientific proof is surely a chimera. "It's not our system," as Officer Ripley puts it in Ridley Scott's Alien. Only through consciousness can we contemplate the mysteries of consciousness, and if we are doing so in ways that are restricted through certain kinds of framing, we're pretty much stuck. All that can be proved is the limits of science.