This was discovered when the first experiments to verify the Einstein-Rosen-Podolsky effect were done. You need the results of measurements on the opposite end to decrypt the information at the end you are at.
I guess I'm over my head in such matters. From my, admitedly, shallow understanding of wave function collapse, etc., I was under the apparent misimpression that once collapsed (e.g., by Alice entangling a 'modulation' photon M (of a known polarization) with one member (photon A) of an entangled pair, one of which was sent to Alice and the other (photon B) which was sent to Bob, photon B's polarization state was determined and could not subsequently be altered by Bob's measurement with his receiver. Could you recommend a good article which explain this paradox to a non-quantum mechanic? --Steve