The paper that explains how the grandfather paradox, in which supposedly going back in time and killing your grandfather would prevent you from being born, is solved. According to the paper, the closed time-like curve (CTC) that the killer follows to the other time fails, supposedly preventing an experience of a murder in the universe and dematerialing the would-be killer. The would-be killer would still experience murdering, and live a supposedly normal life until they died. However, unlike a murder that is not part of a time travel journey, the murder is not experienced in our universe. This doesn't mean that the whole multiverse ends with the first murder in it, but the conditions above apply. At any rate, a time travel company must protect itself given this natural phenomenon, by doing all it can to screen would-be killers with a disclaimer. The two-level multiverse is given experience by time travelling non-murderers and stopped from being given experiences by time travelling murderers. If the murderer time travels again they will continue not to cause experience in the first multiverse. It is better to prevent murder by searching for a criminal record and searching forward in time for a crime using the quantum box. If the first and only two people in the multiverse time travelled and killed each other then the experienced universe would stop because all its inhabitants had become time travelling killers and the universe is only projected to people, of whom there would be none of. If the murderer goes on to help, e.g. discovers a needed technology in the universe then it is unclear what will happen. This definition of time travel may apply to times outside the person's timeline. In conclusion, time travellers shouldn't murder (it doesn't matter if they slightly improve the timeline, although changing their future technology or science is discouraged) shown by them leaving the experiencing universe. Meditation and related technologies can be used to prevent potential criminals from offending, and time travel should be security-cleared, pre-planned and short. Law should be followed, not what the natural phenomenon is.