There is actually a whole sequence of such limits: the visibility limit (where light emitted in the distant past reaches us now) is furthest out, then comes the

There is actually a whole sequence of such limits: the visibility limit (where light emitted in the distant past reaches us now) is furthest out, then comes the reachability limit (where light emitted by us now can still be observed), then the round trip limit where we can send a message now and recieve an answer (before we are beyond their reachability limit), then the limit where we can send a message, recieve an answer and then send a final goodbye, then the limit for two full exchanges, and so on... But at least one could do the respective trips to slightly closer galaxies within a lifetime: http://arxiv.org/pdf/astro-ph/0509268.pdf http://arxiv.org/pdf/astro-ph/0509268.pdf (published in Phys.Rev. D, http://journals.aps.org/prd/abstract/10.1103/PhysRevD.72.107302 http://journals.aps.org/prd/abstract/10.1103/PhysRevD.72.107... )