In science, objective proof demands verification and repeatability
by other people, usually called peers.

     The the existence of peers beyond being mere hallucinations, can
not itself be objectively proven without a peer to verify it.  But if no
peers have been yet verified, who will then act as a verified peer to
peer review the verification of the first peer?

     Therefore there can be no objective proof that other people exist,
otherwise one would be assuming the existance of what one was trying to
prove.  Even scientists are smart enough to avoid circular logic.

     Thus 'objective' science rests at best on whimsy and what people
choose to believe based on subjective experiences of the existence of
others, and emotional needs to not be alone.