"What is accepted as knowledge today is sometimes rejected tomorrow." Let us consider the knowledge problems raised by this statement in two areas of knowledge. Our earth has gone through many phases, while passing through these phases many new knowledge has been introduced, found and developed, known by theory or principle, or in some cases it is known by giving new name simply by modifying an old one name (further development of the theory). While discovering new knowledge in the meantime, it has also dominated or rejected what was believed in the past. The level or degree of knowledge has increased dramatically over the last century. In the past, authorities allowed a lesser degree of critical thinking, either because the question of knowledge on the subject was new or because they had insufficient resources or little education to find more information. Today, the development of science and technology and the surpassing of education have made it possible to search and discover the unanswered questions of the past and thus have made it possible to acquire new knowledge and also to prove what was once accepted as a matter of knowledge. Thus, generally accepted knowledge is sometimes discarded. This essay will examine when knowledge is accepted, when it is rejected, and under whose authority.As a chemistry student, while studying the optical isomer in organic chemistry, I had the opportunity to learn about more about thalidomide (C13H10N2O2) (or widely known as thalidomide children). The thalidomide disaster constitutes one of the darkest episodes in the history of pharmaceutical research. After researching thalidomide, I discovered its mechanism, reason and consequences. Thalidomide was developed as a sedative and sleeping pill in the 1950s. Researchers at the time found it to be a useful anti-nausea medication and was prescribed to patients to get rid of morning sickness . It was produced and promoted by the medical company Chemie Grünenthal as a completely safe medicine for pregnant women, used against morning sickness. The medical company has done research and is investing millions of money into it. This drug was sold by prescription in Europe, Australia and Canada. Some countries even sold it without a prescription, resulting in thousands of children being born without organs; some had hands, some had legs, and some had abnormal internal organs like hearts and kidneys. Likewise, many died at birth due to their malformations. This drug was later found to cause serious birth defects when taken by pregnant women..