What is time travelling? Yes it is travelling in time, but how exactly it is defined? It’s not necessary to alter time itself to do it. Time travel is travelling to a different position time without experiencing the time passing or experiencing the positive or negative change in time much quicker than real-time.
So if I want to travel one week in future, I could ask doctors to put myself in artificial coma and then wake me up. A week would had passed, but for me it would had been just a quick moment.
The problem in this technique is that your body is getting older and long time in coma will have some other unpleasant side-effects, like muscles becoming shriveled, you get bedsore etc.
In sci-fi movies this is solved by cryogenic sleep or suspended animation. In movies like Alien, Planet of the Apes, 2001: A Space Odyssey, Avatar, Prometheus, Passengers and many others, the astronauts are put in some kind of hypersleep to survive very long-distance space travel.
This is not as far-fetched as one might think. People can survive under ice almost half an hour and still fully recover. What if this could be prolonged? There is a article about the subject here.
Also some terminally ill people have been cryogenically frozen in hopes of one day waking them up again. This is a big business although many doctors say that the tissue damage caused by the freezing can not be reversed even with future technology.
Now we can go to Egypt.. to the Pharaohs and pyramids. We know that the ancient Egyptians believed in afterlife and prepared the Pharaohs for that. Their internal organs were removed and conserved in jars. They were placed inside monumental structures that can last thousands of years. The walls were covered with “spells” and the chambers were filled with gold and other valuables.
What if our interpretation about the religious reasons is too complicated. What if this was their version of the cryogenic sleep. Maybe they understood that when they preserve the body and the organs and they seal it in chamber that can survive thousands of years, maybe one day the science has advanced to the point where we can resurrect them.
Maybe even the hieroglyphs were used as “universal sign language” which could also be read in future despite spoken languages being changed. It did not work out that well, but again it’s plausible. We have sent messages to space on Pioneer and Voyager probes. They were written in “universal language” which alien species could read – but how could they if even we, human, can not.