George Jones

This is off-topic for the thread, but I am really curious: For visual observing, how much of a difference is there between the C8 and the C11?

More seriously, I got the only scope that I have ever owned, a C8, ten years ago. When I got my scope, I lived in a third-floor apartment, and I had to carry my equipment down the stairs and outside (and the reverse at the end of a session!). I now have a house, and I keep my C8 on its tripod in the back garden shed. An easy grab and go. Now, that I have a house, I am thinking about getting a larger second scope, but, if this doesn't happen, my C8 will keep me happily occupied (I am strictly visual) for the rest of my life.

It's possible to have more than scope??? Tell my wife.

When you say "mostly formulas and mathematics", do you mean including calculus, or no calculus?

For a person on the Earth, the trip would take at least 4 years, but, due to time dilation/length contraction, a person on the ship can experience an arbitrarily small duration of time for the trip.

I think that in order for the universe to have collapsed long ago, the universe would have to have been substantially less flat. Without dark energy, all closed (homogeneous and isotropic) universes eventually collapse. When there is non-zero dark energy, this is no longer the case., i.e., when there is non-zero dark energy, closed universes can expand forever.

Even after renormalization in a renormalizable quantum field theory, most calculations of {what should be) physical quantities still yield infinity.

But, its finite extent notwithstanding, a 3-sphere has the same cardinality as the real line, and thus has same "fault" as a model of positions in space as (any segment of) the real line ...

In the city in which I used to live, I attended very lively astronomy club meetings. Unfortunately, I moved away from this city eight years ago, and, as I now am an astronomy "lone wolf", I can only a somewhat off-topic comment. I work as an instructor, and I prefer to look at it as follows (which I call Jones's theory of relativity): every year the first-year students get a year younger.

I can remember four episodes in (the original) Star Trek that involved travel into the past, three into Earth's past, and one into the past of another planet.

General relativity does not seem to prohibit time-loops (called closed timelike curves by physicists), but quantum theory might prohibit these, This is what Stephen Hawking thought. Stephen Hawking: "It seems that there is a Chronology Protection Agency which prevents the appearance of closed timelike curves and so makes the universe safe for historians." This roughly states that near the boundary in spacetime where time-loops form, the energy for quantum fields blow up (e.g., infinite blueshift), thus preventing (by wall-of-fire barriers) physical objects from crossing into the region where there are time-loops. There seems to be some semi-classical (part classical, part quantum) evidence for this conjecture, but a more refined analysis by Kay, Radzikowski, and Wald muddies the picture a bit. Their analysis shows that the energy is ill-defined, but not necessarily infinite, at such a boundary. This may be just an indication that the semi-classical theory breaks down at chronology horizons, and that full quantum gravity is needed for definitive predictions.