Question: I wouldn't call this scientifically accurate, but would like some opinion on sensibility of the idea.

As part of a story about two time travelling engineers, they discover that their own universe actually updates itself whenever a frontier in technology is crossed. So basically, the invention of time travel itself caused certain updates to support this new paradigm by offering system-wide resolutions to various time-travel induced paradoxes.

Now, I was wondering which direction to take when trying to offer an explanation - since this one does drive curiosities. I've got two ideas to branch out:

1. The universe is a living organism with a nucleus, mitochondria and RNA, and it is actually responding in a way that gene mutations occur.
2. The universe is an AI driven program, and is continuously updating a logical universe.

Which one of these would be more likely in case of a reactive universe? I'm trying to figure out a way to *know* this to be true from the character's perspective.

Answer: 
A living vessel re-configuring itself based on the behaviour of it's occupants is something that occurs in fiction all the time. Some examples include Moya from Farscape (the ship), the Wraith Hive ships from Stargate Atlantis, and "The Cloud" from Star Trek Voyager. Expanding these "Ship or Nebula" sized organisms up to "Universe" size is not beyond my ability to suspend my disbelief, but I wouldn't suggest to use RNA / mitochondria / human definitions of life, a living being the size of a universe has issues with speed of light propagation of information, and by handwaving away the internals of how that life works you'll be able to suspend belief better.

My biggest issue with a living universe updating in response to what I've done is "Why do you care about little old me"? People have similar questions with religion topics (why does God care about my actions, I'm insignificant), and perhaps some "The universe loves you and wants the best for you" might help sell why the universe cares about what happens enough to update in response to them building a new thing in their garage.

Could also be a population of very large beings, rather than one singular being.

If the universe is a simulation with AI running the show, then this would explain the updates. You'd need to sell that we're in a simulation - perhaps temporary observed changes in planck distance as the simulation struggles with complex behaviour nearby so lowers the resolution of the simulation?

There's two other approaches Id suggest:

* Multi-verse theory, by the act of travelling back in time they move to a new universe, with different properties. So it appears that the universe is reconfiguring.
* Quantum trickery. I'd summarise Quantum mechanics as the more you examine what's going on, the more bizarre the universe gets.
**Observing changes things**

I'm proposing a 3rd option.

The [double slit](https://en.wikipedia.org/wiki/Double-slit_experiment) experiment shows us that observing things can change the properties. How and why lies in the quantum realm on which I've read a lot, but can't pretend to truly understand. As far as I read it, there is a form of uncertainty everywhere. When observing, this uncertainty collapses and resolves into a certainty. This whole experiment shows that this small difference of just observing has 2 wildly different outcomes. In one outcome it's like an energy wave in a sound wave kind of way. In the other one a particle, like ball thrown at something.

Possibly observing can go much further. The moment you can travel through time, different ways of observing are available. The universe doesn't change, but the act of time travel does change the outcome. Essentially "updating" the universe that happen to support your version of time travel.

As an aside, I once heard a theory that the moment we research and discover more about the universe, it gets more complex. Another way to perceive the observing changing the world around you.