Our universe being a simulation in some other universe seems to be a popular topic these days. I'm not sure that there is way for us to determine if this is the case or not, but I thought of something that might be a good argument for it being true.
One thing I want to address is most people seem to think of our universe being a simulation which is an exact replica of the one rendering it. There isn't any reason to believe this. It could be the case, but one alternative would be that the universe above is is completely different in physics, reality, even logic. What if 1 + 2 = 3 only makes sense in this universe and the true reality has completely different logic and math? Think about playing pong. That universe is not much like ours. Of course Pong is so simplistic no one would say it's the simulation of a universe. But you can imagine someone simulating a reality which has nothing to do with their universe, but has beings with sentience in it.
Another thing is the idea that someone is trying to simulate a universe at all. Many times we'll see a fractal rendered on a computer. Imagine some computer running a fractal like algarithm, or just solving an equation, which just happens to be the laws of physics for our universe. The entirety of our uiniverse might not be something graphic to whatever it's being rendered in, it may be just a calculation running in the background of some super powerful computer. Imagine of the big bang was just the first part of a continuing calculation. When you look at the most fundamental laws of physics, there doesn't seem to be anything physical to them, it's point particles, fields, and probabilities. Easier expressed as math than matter. The people running it may not even be aware that their program has created sentient beings.
Or of course this could also be like a super complicated version of The Sims as well, or Grand Theft Auto, some video game where the AI has gotten so complex it has become self aware.
One thing to be taken into consideration is that any simulator has a finite amount of resources. The simulation would necessarily I have to be a finite space. If any system can determine that it is in fact infinite they would be able to conclude that they are not part of a simulation. If you were running a simulation however and wanted to give the impression that they have infinite resources there are several ways to go about this.
When you're playing a first-person shooter things in the distance don't have as much detail and aren't taking as much processor power to render as things in the foreground and things behind walls aren't being processed at all. There are certain aspects to our universe like the fact that we can't tell which hole a particle of light went through until we observe it. Before we look at it it could have gone through any holes. Perhaps this is a way to save processing power by not having to do calculations on all the particles in the universe that nobody is paying attention to.
There is another trick there is another trick they could use to make the universe appear infinite when it is in fact not. Our universe is expanding every foot of space is gaining a small amount. I wrote another blog on this subject but the conclusion is that the farther away from where you are the faster the universe is moving away from you. At a certain distance the universe is expanding faster than the speed of light. This means that anything beyond this sphere is completely inaccessible to you or any part of this section of the universe.
Imagine if the expansion of the universe is just a method to make the universe appear infinite but when rendering it you would only need to calculate all the atoms in the visible universe not the infinite universe. It still sounds crazy to think of a computer that could process all the atoms even only in the visible Universe however keep in mind the nature of the universe and complexity and size of the one running the simulation are unknown to us and perhaps the number of atoms in this universe is not even a difficult strain on the processing power available there.