Time travel to the past means completed reversal of all events that happened in the entire Universe since that period to the current one. While it sounds impossible to accomplish, the second postulate states that there is no energy or other resources required to do this. You can assume for simplicity that anyone can just wish for it and time immediately (absolutely wrong term – there is no any time constraints) will be reversed to the point requested, even when you or any human did not exist. This also assumes that all events in Universe are predetermined in the sense that absolutely the same sequence will be repeated to the your birth, which in some ways most important event – at least for you and then by you until current time. In reality ‘repeated’ is the bad word – it was the same sequence. Paradox that you may see right away is what happens to the next second? If time reversed again – which is true, how the next second comes? The answer is easy – so what? Current Physic deals with multiple paradoxes precisely like that – it just register it – giving them status ‘Law of Nature.” To make you fill better please try to understand that reversal of time does not happened after this moment, it happened before, so next second is still valid.
If you still think that you learning anything, there is more info to come.
Travel to the future together with Universe is easy. You’re doing it right now. But going faster does required a lot of energy, because according to Einstein is equivalent to traveling with speed close to speed of light. Meanwhile speed of light in vacuum itself considers a constant related to structure and configuration of Universe. It is some possibility that while constant it is related to current status – I believe, to the place of measurement too- of Universe and may change insignificantly in few million years. Now we have to say that all time travel and even more – time itself are limited to existence of Universe from it’s beginning Big Bang to the future collapse. But our Universe is not unique. Just consider many other Big Bangs. And, sorry for repeating it, because time makes sense and limits inside of each of Universes only, one can say that all of those Universes exist both consecutively and simultaneously. And both are incorrect, because indirectly using same time frame. Interestingly enough each of them has their own speed of light, which may be differ significantly. And you can travel – sorry, this is not advertising – from one of them to another using, for example, black wholes. Than we have all Universes time mapping. The postulate say that all times between all Universes mapped – linked the way that you cannot create any closed travel sequence that returned you to the past. But you can theoretically travel from one Universe to another one, spend few days, return to original and see the world few centuries later. Vise versa you may return home after few decades and see your young friends still reading this site. It still to be determined if this time travel or its equivalent should follow Albert Einstein rules. It may not follow, because Einstein described our Universe only – only one which has Milky Way, Sun, Earth and as said, most important – you, my reader.
