Our conviction that green cheese makes up a negligible fraction of the Moon's interior comes not from direct observation but from the gross incompatibility of that idea with other things we think we know.
If time travel were possible, you still wouldn't be able to change the past - it's already happened!
The simplest way out of the puzzle of time travel is to say that it can't be done. That's very likely the right answer. However, we don't know for sure.
As we get older, we tend to grow quite fond of the planets of belief we have constructed for ourselves. We build elaborate defense mechanisms to ward off attacks from competing ideas or new data. The system makes us comfortable but resistant to change, no matter how much change might be called for.
If our local, observable universe is embedded in a larger structure, a multiverse, then there's other places in this larger structure that have denizens in them that call their local environs the universe. And conditions in those other places could be very different. Or they could be pretty similar to what we have here.
I've loved physics from a young age, but I've also been interested in all sorts of big questions, from philosophy to evolution and neuroscience. And what those fields have in common is that they all aim to capture certain aspects of the same underlying universe.
