Originally Posted by
joypulv
Your questions will take your lifetime to answer, probably. Good luck.
With no knowledge of theoretical physics, I see a 'time machine' as being simply a space ship that goes faster than the speed of light and comes back to earth. Or at least that will be the first step. Maybe rearranging molecules and speeding them around might be next.
As for communicating with and changing the past, those are topics that entertain many a theoretician. There's even some good movies on the subject. My favorite question is how can you change the past without changing the present that allows you to even exist?