Conclusions

A legitimate question is whether the ideas for travelling to destinations in our Galaxy discussed in this chapter may be considered even remotely practicable. In fact, perhaps the main result is that wormholes travel between galactic or even inter-galactic travel does not violate any current physics, including the speed of light limit, and is completely predictable from General Relativity. Furthermore, subject to progress in the physics we already have at our disposal, wormholes may be designed, again using General Relativity. As they depend on the existence of black holes, they look at the moment impracticable to build in an engineering sense of course, but the relative abundance of them in our Sun immediate neighbourhood gives hope appropriate ones may be found. Skepticism concerning these galactic travel concepts is justified, but this was also the case with the learned people that in the 1400s and 1500s were exposed to the sketches and drawings of parachutes and flying machines invented by Leonardo da Vinci. In this age we ''know better'' and admire his farsightedness, perhaps criticizing his naivete; and lack of boldness. In this light, probably, some of the ideas about using gravitation, space-time curvature, and dimensions will become eventually a practical device. Certainly, they are from the only proven physics we can use now and for some time in the future, and allow (with some provisos) solving or neatly bypassing questions connected with the time paradoxes: so the usual criticism of time machines, such as that by H.G. Wells, is that they violate the principle of causality. As a consequence, all the precautions time travellers must take to avoid accidentally or deliberately killing one's ancestors become unnecessary using General Relativity as mentioned. Rather than travelling in space, and then putting up with redressing the many problems caused by time, the theory developed by Einstein and its consequences (black holes and intense gravitational effects) provides new opportunities and ways of reaching stars in our Galaxy and beyond. So the answer to the initial question in this section is, literally, ''Time will tell''.

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