see, then the work component should be in question, not the Ph. D. which was done 40 years back as that might be prividing substantial information to fresh guys who venture recent times... ...After doing Ph. D., some body is not working being in that field !!! That hardly anybody does, they still continue to work and explore many things which may not be related to their Ph. D., Then how the question of "expire" comes if it is useful by somebody else after 40 years..
