Enya - Oíche Chiúin - Silent Night

It seems that going back in time, traveling to the past is possible in our Universe. It is also proven that the shape of our universe is flat, that it is practically infinite, will expand forever and will exist forever. All this is also mentioned in the announcement of NASA (WMAP - Fate of the Universe - NASA), where the following is written: “The geometry of the universe is flat and it will expand forever“. The nature of dark energy is simply not clear, so it is difficult to accurately determine and know what the changes in the expansion rate of the universe will be in the future. The worst thing that can happen to our Universe, is the so-called “Heat Death“, which could occur in trillions upon trillions of years. When this “heat death“ occurs, space-time and energy will still exist - in this sense, our universe will continue to exist forever, but boringly. I say “boring“, because at that time, when “heat death“ occurs, all the useful energy will be distributed evenly in the time-space continuum, and no new processes will occur, since all atoms will be broken into subatomic particles, and then they will also disintegrate, black holes will also evaporate. Therefore, nothing interesting will happen. In other words, space and time will exist, but nothing will happen inside it that would add meaning to its existence. However, it should be noted here, that the past does not disappear anywhere, but always exists, as long as time and space exist. And our time-space, it seems, will always exist. Thus, our past will always exist. Therefore, if time travel to the past is truly, practically possible in the future for our (or for any other) civilization, then such a civilization will always exist. how? Imagine that after 100 trillion years, when our universe will be old, where no new stars will be born, and everything already existing and formed at that time will only go to aging and slowly disintegrating... if a highly developed civilization reaches that period and exists, which will have the technology to travel to the past, then this civilization will not have to continue to exist in such a dying Universe and wait for its end (Heat Death). Such a civilization will simply go back in time of the youth and prosperity of our Universe and continue to exist, develop and advance forever, since it will be able to pass into the past multiple times, when Universe will become old, again and again and will be developed to a higher and higher level with each transition. This is an optimistic view, although we can be extremely pessimistic and assume the worst case scenario, such as that our universe is not one where time travel is physically possible at all, not only practically, and not only for our civilization, but in general, we can assume that our universe’s physical arrangement, its fundamental laws, simply do not provide for and do not allow it to be possible to “move against the flow of the river of time“. We can also assume the second extremely pessimistic view that our Universe is not going to exist forever and will not happen so called “Heat Death“, but there will be another process - the tearing apart of time-space and the fundamental destruction of our universe, complete vaporization, known as the “Big Rip“. However, we can say with almost 100% certainty that this will not happen. Before the geometry of our universe was known with great precision, it was assumed that the “Big Rip“ would occur more than 20 billion years from now. However, after, as we mentioned above, the geometry of our universe became clear and also that its time-space continuum will always exist and will always expand, we no longer have a reason for this pessimistic view. Even if the “Big Rip“ theory turns out to be true, it should be noted that, this does not mean the destruction of everything - the complete annihilation of existence. The total destruction of our universe would not be the same as the destruction of existence in general, since there seem to be many other universes besides us - multiverses, which differ from each other in physical properties, geometries, ways of formation, expansion rates, end scenarios, and so on. Among the infinitely large variety of such Universes, there are those, whose physical properties would allow a high-tech civilization (or civilizations) developed within it, to move in the past of its own Universe and thus exist forever. In the time-spaces of such Universe, incredibly highly developed civilizations will constantly exist, travel and develop more and more. Let’s briefly list the 4 levels of Max Tegmarkian classification of Multiverses: 1. The first level - our own Universe, which extends beyond our observable Universe (perhaps infinitely) and gives rise to an infinitely large number of other observable Universes similar to our observable Universe, although they all have the same physical laws. 2. The second level - other Universes beyond our Universe, with different physical laws. The second level may i