标题： 五维时空中的时间机器可能存在 显示英文标题

标题： Possible existence of time machines in a five-dimensional spacetime

摘要： 构造时间机器的想法并不新鲜，甚至由于意识到可穿越的虫洞可以转化为时间机器而得到了推动。 这也意味着无法回到时间机器创建之前的时间。 本文通过从一个物理上可接受的模型开始来解决这些问题，以及随之而来的因果性破坏，这个时空由于额外的时间维而成为反德西特时空，从而允许闭合类时曲线的存在。 通过假设额外维度与径向坐标无关，虫洞无论位于何处都能保持其基本几何特性，因此可以作为任何闭合类时曲线的捷径，而这些曲线可以无限延伸到过去。 同样的径向坐标独立性表明，虫洞可以连接现在的一个区域到一个局部区域，该区域（1）位于过去，（2）不包含任何闭合类时曲线。 以前的研究表明，如果这样的区域足够局域化，就有可能避免因果性破坏。 显示英文摘要

摘要： The idea of constructing a time machine is not new and even received a boost thanks to the realization that a traversable wormhole could be converted to a time machine. This also implied that it would be impossible to travel back in time beyond the creation of the time machine. This paper addresses these issues, as well as the concomitant causality violations, by starting with a physically acceptable model, a spacetime that is anti-de Sitter due to an extra time-like dimension, thereby allowing the existence of closed time-like curves. By assuming that the extra dimension is independent of the radial coordinate, the wormhole retains its basic geometric properties regardless of its location and can therefore serve as a shortcut for any closed time-like curve, which, in turn, can extend indefinitely into the past. The same independence of the radial coordinate suggests that the wormhole could connect a region in the present to a local region that (1) lies in the past and (2) does not contain any closed time-like curves. Previous studies have suggested that if such a region is sufficiently localized, it may be possible to avoid a causality violation.