How can you claim we objectively know that someone is guilty or even that a crime was committed at all? Even the lawyer hearing the confession cannot possibly assert beyond a reasonable doubt that it is true with no other evidence.
So what's the scientific way? Maybe present evidence to an unaligned third decider that the crime happened and that the most likely explanation is that the accused committed the crime?
I'm sorry, are you to claim in the second paragraph that the way our system works in front of a jury is a scientific way of determining guilt beyond a reasonable doubt?
If so, I invite you to visit the court room more.
As for the first, you can objectively know if the person is guilty in a number of ways. For example, maybe they admit it, plus there is authenticated video + eyewitness + whatever you like evidence that they did it. It happens plenty of times.
If your answer is "nothing is enough to objectively know", then we'll just have to agree to disagree.
Also, note that "reasonable doubt" is a very modern standard. It's not clear why you seem to be holding it up as the "only" or "right" standard.
> For example, maybe they admit it, plus there is authenticated video + eyewitness + whatever you like evidence that they did it.
Then that would be good enough to convince a jury the accused is guilty. You can't allow the defence to just claim "well, he did it", as you appear to desire, because that's ripe for abuse.
So what's the scientific way? Maybe present evidence to an unaligned third decider that the crime happened and that the most likely explanation is that the accused committed the crime?