Massei — Bamidbar-Numbers 35
Whoever kills a person, based on the testimony of witnesses, he shall slay the murderer. A single witness may not testify against a person so that he should die.
In this verse, the Torah states that a murderer can only be convicted based on testimony of live witnesses. Contrary to common law jurisprudence in the US and the UK, and civil law jurisprudence of most other western countries, circumstantial evidence cannot be used alone to convict according to the Torah law. (It may, however, be used to interrogate witnesses in order to ascertain their truthfulness or to acquit the accused.) The only basis for a Torah conviction is eye-witness testimony. This seems strange, though. Why, for example, may fingerprints or DNA evidence, which is, surely, incontrovertible, not be used to convict a criminal?
When a person is accused of committing a crime, before he is either proven guilty or acquitted, he is in a state of superposition of two states – innocence and guilt. In other words, from our perspective, his state is in doubt. He might be said to be 50% innocent and 50% guilty. Sounds familiar? Does it sound like a Schrödinger Cat? Of course it does! (If you wish to revisit Schrödinger’s cat, see for example my post On the Age of the Universe in the Many-Worlds Interpretation of Quantum Mechanics.) Until the wavefunction of the accused is collapsed, he is in a blurred state. To be precise, he is neither innocent, nor guilty, nor both, nor neither; rather he is in a unique quantum-mechanical state of linear superposition of two states: innocent and guilty.
As I discussed at length in my essay, Towards Reconciliation of Biblical and Cosmological Ages of the Universe, according to the Copenhagen interpretation of quantum mechanics as it was understood by such physicists as John Von Neumann, a Nobel Laureate, Eugene Wigner and John Wheeler; only a human being can collapse the wavefunction. Perhaps this is why the Torah requires eye-witnesses to convict an accused criminal. Only a live witness can collapse the wavefunction of the accused by testifying about his crime.
An interesting question is, why does the Torah requires at least two witnesses to convict a criminal? Wouldn’t one person be enough to collapse the wavefunction? It seems as if it would, at least from a quantum-mechanical point of view. One observer is enough to collapse the wavefunction of the Schrödinger Cat! What makes our situation different from the gedanken experiment with the cat?
The problem here is that we don’t necessarily know who is the “cat” and who is the observer. If a single witness comes and testifies in court that he saw ploni ben ploni (so and so) committing a crime, what stops the accused from turning the tables on the witness and testifying that the so-called witness was the one who actually committed the crime and now is trying to pin it on him, but he – an innocent bystander – is actually the witness to the crime and can testify to this fact? As we see, this situation is untenable. Therefore, the Torah requiresthat at least two witnesses, who are unrelated to each other, who both saw the crime (and each other), testify about the event in precise detail and not contradict each other in any of the minute details.
To further support this proposition, let us recall that when the point in question doesn’t involve a human being, one witness is enough. For example, if one witness testifies that that the piece of meat on the table was treif (not kosher) and two witnesses testify that they saw the man eating this piece of meat, it is enough to convict him for a violation of the Biblical prohibition to eat treif, which makes him liable to receive malkot – lashes. (See Rambam Laws of Sanhedrin Chapter 16.) Why is it enough for one witness to testify that the meat was not kosher but we require no less than two to testify to the person eating it? Because the situation is not symmetric – the meat cannot turn around and claim that it is really the witness who is “not kosher”. The person accused of eating this meat, however, can easily turn the tables on the witness and claim that it was the witness who actually ate the meat and is now trying to pin this sin on him. We wouldn’t know who the “cat” is and who is the “observer.” Therefore, in situations which are not symmetric the Torah requires only one witness, but in symmetric situations where the roles can be swapped, it requires two.