Timelike

The boundary of the conformal compactification contains components which correspond to singularities, and components which correspond to spacelike infinity, timelike infinity, (and null infinity). ❋ Gordon McCabe (2009)

The far future of our universe is therefore representable by de Sitter space-time, and in this type of space-time the future timelike boundary is a spacelike hypersurface. ❋ Gordon McCabe (2009)

Now, in an open or flat Friedmann-Robertson-Walker cosmological model with no cosmological constant, whilst the past 'Big-Bang' singularity corresponds to a spacelike hypersurface in the boundary of the conformal compactification, the future timelike infinity corresponds to a single point. ❋ Gordon McCabe (2009)

And Frank Tipler, in his youth, did some pioneering research on closed timelike curves in general relativity, so he has credentials as an honest physicist. ❋ James F. McGrath (2010)

The result is a nonzero interval, spacelike for two photons emitted simultaneously from a source and timelike between different points on the worldline of a photon bouncing between mirrors. ❋ Unknown (2008)

The interval is zero between two points within a single lap, but it is nonzero (and timelike) when you take points on two different laps. ❋ Unknown (2008)

But there are soulutions that allow 'closed timelike curves' - travel backwards in time, at least back to a defined origin. ❋ Unknown (2008)

The math is almost identical to my example, except that you get a timelike interval instead of a spacelike one. ❋ Unknown (2008)

They pass through the interior, but the singularity is timelike, and therefore avoidable, and the spacetime has a white hole horizon as well, so there is, in principle, an exit route. ❋ Sean (2009)

Would we lose sight of it as it makes its timelike loop? ❋ Sean (2009)

Somewhat contrary comment regarding item 3, and closed timelike curves. ❋ Sean (2009)

The Kerr spacetime, as you know, contains closed timelike curves. ❋ Sean (2009)

The problem arises, again, if things moving along the closed timelike curve start interacting with the rest of the universe. ❋ Sean (2009)

At least, there would only be flashing lights if you brought along some strobes, and decided to start them flashing as you traveled along your closed timelike curve. ❋ Sean (2009)

So: if there were a closed timelike curve, we would age along it, and feel older when we finished our journey than when we started it, just as for any other journey. ❋ Sean (2009)

And that situation will never change — no matter what clever engineers may do in the future, if they create closed timelike curves they cannot pass through events in spacetime through which closed timelike curves did not pass (corollary of Rule 6). ❋ Sean (2009)

Or possibly a DeLorean, in the unlikely event that your closed timelike curve started right here on Earth and never left the road. ❋ Sean (2009)

But the large-scale curvature of spacetime caused by gravity could, conceivably, cause timelike curves to loop back on themselves — that is to say, become closed timelike curves — such that anyone traveling on such a path would meet themselves in the past. ❋ Sean (2009)