Do you ever wonder how far along we are in our understanding of science?

Additionally, in your example of travel you're limiting yourself to our current understanding of time and space.

Time and space are completely relative things and can be viewed differently depending on the observer. If I were going the speed of light and you saw me, my time would be different then yours. If I was going the speed of light for just 6 months my time and came back to earth, you would be dead, your kids would be dead, and their kids would be dead because of Einstein's theory of special relativity.