Sure there's a real difference. The first account implies that the box is being compressed vertically because gravity acts on all its parts (molecules) whereas the opposing force is acting on its bottom surface (where it touches the table). The second account implies that there is no such compression, that the box, even if it is somewhat elastic, has the same height when it is sitting on the table as when it is floating in outer space. The first account -- correctly -- implies the opposite: that the (not perfectly rigid) box is slightly less tall when it is sitting on the table than when it is floating in space. The first account is also more elegant in this sense. Suppose the table is forcefully kicked out from under the box so that the box starts falling. The first account can easily explain this by pointing out that, with the table out of the way, the gravitational force now acts unopposed. The second account has to say -- oddly -- that the kicking away of the table somehow brings a gravitational...

Why not? We can conceive a nice large space filled with moving matter, all as in our universe, except that the laws of nature vary randomly in space and time -- which is really to say that there are no laws of nature. You could still use geometry to describe the trajectories of objects, but you could not simplify these descriptions with general formulas that cover, say, the force that objects exert on one another. Nor of course could you project any descriptions into the future (predict what will happen) nor even describe with any accuracy what is happening elsewhere or what was happening in the past (because you would have no firm ground for reasoning backward from the data you have to their origins). So it seems that we can conceive such a world. But whether a cognitive subject could have experience of such a world, could hold it together in one mind, that's another question, one that is very interestingly examined in Kant's Critique of Pure Reason .

According to Kant, causality is among the organizing concepts through which our mind unifies its experience. Like space and time, causality as well is then not objective (i.e. wholly independent of our mind), but still "empirically" objective in the sense that we cannot help but structure and anticipate the world of our experience as causally ordered. This sort of account explains your "firm belief" that an uncaused cause defies commonsense. But it also cautions us against claiming any knowledge of what the world might really be like, apart from how our mental faculties are organizing it for us. The very strength of our conviction that nothing like an uncaused Big Bang could possibly have happened -- the strong feeling that we know this "a priori" -- would suggest to Kant that this belief discloses something about ourselves (about our way of organizing and unifying experience) rather about the world we inhabit. And so physicists could actually appeal to Kant in rejecting your belief as a...

The easiest way to think of this may be in terms of some regular relation between time and the size of the universe. Expressing this regular relation as some mathematical formula, it may turn out that, going back from the present in accordance with this formula, we get to a past point of time at which the size of the universe is zero. We would have reason to postulate such a starting point as the origin of the universe if all we know about the universe supports or is at least consistent with our backward extrapolation. Big bang theorists believe that this is (by and large) the case. The same mathematical formula may be such that, going forward from the present, we get to a future point of time at which the size of the universe is zero once more. We would have reason to postulate such an end point of the universe if all we know about the universe supports or is at least consistent with our forward extrapolation. There are other conceivable end-of-time scenarios. The amount of stuff in the...