[shadedragon]

If we changed the past it would already be changed, would it not be? We wouldn't know otherwise, because once the past is changed, so to, is the products given by the reality passed through, and thus we would not be them. Thus we would become an alternate reality while the reality that occurs becomes another reality- an alternate reality- and would live on in our reality.
So while the past is changeable, we are not who our past selves were and thus do not receive the direct benefits of what we spent our energy on to alter, but instead we create a parallel reality that coexists with our own that influences ours, and ours, theirs. Sometimes that can produce effects of dejavu and intuition, while other times those things come of other things.
We can exist in other moments through the time travel we already do with our own mind's in what we refer to as memory. We can also time jump using energy currents. Time both exists and does not exist- it is a truth but for only those who still need it to find more truth, like a crutch. There's nothing wrong with these things- after all we make up our own rules as we go and we have eternity to do all that we do.
Future time jumping is the same thing. We are simply jumping to an alternate reality and experiencing it as it is most near our own. But the farther from the truth it is, the more we can suffer due to the gap in between reality and non. When we suffer, our heart contracts to protect us from the pain, but if we never let go of the handle, we fail to continue to expand, and only contract as a result.
Our heart also contracts to tell us the largeness of the truth we are experiencing In that moment.