There is a high probability it is a simulation. Nature scientists speculate about this, because there are some mistakes in our world, for example light speed isn`t infinetely. So in a real world synchronisity would be really synchron, but in our world it isn`t, it`s just fake synchronisity. I read this in an article in a science magacine and there were more examples like this for mistakes in our world and they have all in common to save lots of computing-power when simulating a world, like cheap tricks in game-programming.
Also our world is made of information. If you go deeper and deeper, matter doesn`t really exist, the only thing you will find is a possibility-field with the information that there should be matter. Just information.
And if we will have the computing-power to simulate a world, we will do it. AI-creatures in that world will not know that it is a simulation and if they evolve, they also will create a simulation of their world.
How high is the probability that we are the first ones who do this? It`s very very small.