We know that matter is discrete, and energy is quantized, (and more quantized things I don't know about.) There is also Planck length? and Planck time? Is spacetime continuous? If we don't know yet, I sure hope it is, because I much prefer to imagine discrete matter and energy interacting in a continuous "environment." What implications would there be if spacetime was not continuous? I, for some reason, really hope that spacetime is continuous. Then again, I also think that whatever is the real case, perhaps it would be possible to model spacetime to be continuous and not care about what it really is, as long as it explains phenomenon and can be used to engineer things. Oh, one more thing: What is the deal with string theory? Why has it been a candidate for a theory of everything for so long? What are string theorists working on at the moment? What does string theory have to say about spacetime, (other than it's dimensions, for example, it's continuity.)?