Information on the public domain? Why the works before 1923 are in the public domain?

Question

Information on the public domain? Why the works before 1923 are in the public domain?

Answer 1

The original idea is that everything should be in the public domain.  The government gives the copyright / patent holder exclusive rights for a limited time.  The government gives the holder the means to enforce these rights (the court system).  In exchange, the holder has to give up the rights when the time runs out.

For current works, copyright is (in many places) the life of the creator plus 70 years.  But in the United States, all books and other works published before 1923 have expired copyrights and are in the public domain.