That's pretty modern in historical terms. Also not really on the same scale but probably is around as difficult. Have a proper look at Puma Punku - it's really weird. Particularly when it was supposed to be a lot older than the less intricate cities nearby from much later. There really are not convincing explanations currently. The architecture and scale are just not in line with anything else. When I hear the origin stories from local legends, they're honestly more convincing than our explanations - and they are truly out of this world. I'm none the wiser on it though - quite simply more questions and answers. The other one is Gobeckli Tepe - which autocorrect hates but has stuff that honestly gets you in the mind of Noah's Ark. Carvings of things these people should have never been able to see or even have heard of. To put it into context - thousands of years before the pyramids or Stonehenge.

Red and Blue Army!

That is completely illogical.

If time travel were possible, then that would mean that an advanced alien culture would likely have discovered it before us. That would strongly suggest that they could also achieve interstellar travel.

The multitude of possibilities makes any theory guess work, so it is not really possible to calculate plausibility.

I like the time travel idea but it begs a whole lot of questions about how it would work in the real world. The paradox question for one.
It is doubtful that one could travel in time to one's own timeline because your very existence in the past would alter it. If that is not possible, then what would be the value of creating a new timeline where you never existed in the future?

A bit tricky to get around.

The universe is quite big and law of coincidence/averages etc says there are enough planets with enough stars for there to be at least one more earth like planet. If life can only evolve in our format then that type of atmosphere is needed. If life can evolve a different way then the planets with life count would increase greatly.

I dont dissmiss interstella travel I dissmiss aliens .In fact we will invent interstella travel and traveling at many times the speed of light .This will lead to being able to achieve time travel .

Well at this moment in time the evidence is with me .You are just guessing . I think my time travel theory holds more water than little green men travelling billions of miles for wiz around our planet . If they had come that far its a bit rude not to say hello

Interstellar travel would be possible if the occupants of the ship were AI. In that case time matters not provided that maintenance could be performed on them and the ship. Or they could self procreate.

More interesting is the information coming to light around black holes. It appears that there is a black hole at the centre of each galaxy. Some galaxies collide (not physically as the distance between stars means the likely hood of an actual collision is remote), but black holes do merge, creating larger black holes with a subsequent increase in gravity.

They thus suck more of the surrounding stars and planets into themselves.

Some theorise that the universe will continue expanding and that other galaxies will disappear from our vision completely.

More likely is that the expansion will slow as a black hole gets large enough for its gravity to slow galaxies and reverse their direction.

We may never know, as a race, because we will be long gone by then unless we can conquer interstellar travel.

Aliens. Mathematically, life will exist on other planets the question is whether it has reach a high intelligence and without destroying itself. As we seem to be heading towards doing.

Time travel. As has been said there is a paradox that cannot be accounted for. Treading on a butterfly will alter the timeline.