At the end of Infinity War, we saw Thanos, after all was said and done, just sit back on his farm and take in everything that happened. However, there may have been more to that farm that we initially realized. We could assume back when the film came out that the farm was on Titan, since that was Thanos’s home world but if that was the case, how did Thanos build a farm on a dead world?
A minor theory about the end of the film is that while Thanos did return to Titan, he used the Infinity Gauntlet to return to Titan in the past. This seems like a stretch, but recently released concept art may have given this theory more credit. On his website, concept artist Pete Thompson was given the go ahead to post high quality images of his work on the film. One was a long shot of Thanos’s farm which is confirmed to be on Titan based on the name of the image, Titan Thanos farm.
But looking at the image, things seems much less dead there than we saw earlier in the film on Titan. It’s entirely possible that there are just places on the planet that aren’t as decimated as the area they fought on earlier but considering that earlier that day Thanos had dropped the moon from the sky, it probably wouldn’t look this nice. You could also argue that Thanos just used the Infinity Gauntlet to restore the planet but considering the state the Gauntlet was in that may not be possible.
So, the theory goes that Thanos used just the Time Stone to return to Titan in the past. The reason for this is unknown, maybe he wanted to lay low and recover in a place no one could follow him. Thor did almost kill him after all. He could have also gone back because he had nothing left in the present as he told the manifestation of Gamora, so he returned to a time where he had everything ahead of him on Titan. Whatever the reason, if this theory is true and Thanos is in the past, this may even more confirm that time travel is an element in Avengers 4.
What this could mean is that the heroes could be tracking Thanos in the past as part of the plot of the film or it could at the very least show a hint at Thanos’s full ability to travel through time to set up to him chasing the heroes through it in Avengers 4.