What Lies “Beyond a Reasonable Doubt?”

Sitting in the jury box; watching the DA offer up another set of evidence as "People's Exhibit #24" I remember the judge's admonition that our job will be to determine if the prosecution has proven his case beyond a reasonable doubt. Hearing the word ‘beyond’ makes me want to make this is physical space - as I might for a baseball game say ‘beyond’ second base is the outfield. What lies beyond a reasonable doubt then, is it an unreasonable doubt or a reasonable certainty? I can see myself trading in reasonable for unreasonable - but not for doubt to certainty. 68 years on this planet has taught me that certainty is an illusion.