So far this discussion has not considered the possibility of non-physical means of travel. It may be that as humans get more understanding of the cosmos, that such means will displace any physical means as inefficient and time consuming.

It already appears from OBE evidence and the like that a persons consciousness can transfer instantly to remote sites. So in whatever medium the transfer occurs- I have been supposing that the medium is a dark matter condensate of axions- the relativistic speed limitations are circumvented.

EPR experiments have already demonstrated faster than the speed of light communication of some sort- it's not full communication- based on the entanglement of the particles involved in the experiment.

So my hypothesis is that at some point in the future communication will occur over what I would call supernatural channels and physical means will become secondary.

Richard

PS I think that alien spaceships that are physical are unlikely because of the time delays; and that something of that sort in a supernatural medium is more likely.