Does anybody have any references where Einstein speaks about Time Machines? From collected sources I found, he strongly rejected the idea of Time Machine but through his theory implied that time travel may be possible if wormholes existed. Something needs to be infinitely fast to do this? Have their own gravitational field? Answers to these also please. If something goes at infinite velocity doesn't wave nature becomes superior than their particle nature? So that means even if time travel is possible only wave packets of existing particles will reach the future or past? Any definite sources such as books/journals/research papers etc.?