This is in response to a post by 9mm, found here: http://www.livejournal.com/users/9mm/809368.html
I go back in time to 1980 (when I was born) and do absolutely nothing and interact with absolute nothing except I carve my name into a tree deep in the woods behind my house. I come back to now, and i go see said tree, and it's got my name on it. volia.
so maybe I changed some air patterns, but nothing significant will come of it. maybe it rained in seattle for an extra day in 1992.
#1, if time travel is ever invented, it will exist in all times at once, simply due to the fact that if it exists, people will use it. Everyone will want to go see the pyramids being built, but that only exists at one point in time, and so they'd all pile up on eachother and there'd be some evidence. thus the fact that we have not found any evidence of time travel in the present or the past or the distant past means that either it will never exist in our universe, or they're really good at cleaning up after themselves. (not bloody likely)
#2, what if the future IS set in stone?
Ok, seems unlikely, but consider it this way.
Hypothesis: the interaction of all bits of matter and energy are governed by certain laws. Those laws can be mathematically defined.
The so called "free choice" of conscious beings is really influenced by all of their input over the course of their lifetime (aka, your past experiences determine what you will do in certain circumstances, even sitting there consciously deciding to do something contrary is predicted because everything in your life has lead up to that point). Given that, the entire universe could be run as a simulated model on a sufficently powerful computer (impossible, but this is theory remember) and therefore everything that has ever happened or will happen is already set in stone, simply because all of the interactions of all bits of matter and energy are known, including those interactions inside the human brain. Free will is an illusion, but that doesn't make it any less real. You CAN choose what you will do, it's just that a sufficiently advanced model of the universe would know what you would choose before you chose it.
Everything was set at the big bang.