The brain-in-a-vat -concept points to the question, how do you know that you are not really living in a awfully sophisticated virtual reality? You have no direct access to the universe itself, you have to experience it through your sense and those can be fooled. This is an ancient old question debated in Philosophy in many forms since at least Descartes. Matrix has made this idea ‘pop’ in recent years.

If you are a brain-in-a-vat how could I find something like that out? Of course, without direct access to the outside world, you can’t know anything about it, but there are ways to suggest that the reality you think is real is not. Of course these ways come in different degrees of certainty and you can never be absolutely sure, but absolute certainty is rarely an requirement outside philosophers, others are usually content with bloody damn sure.

1. You could try and find discrepancies in the world and sources that allegedly are of the world. E.g. let’s say a number of reputable books in biology claims that a certain species is abundant in some part of the world. You examine the said part of the world and notice that there really aren’t any examples of said species around.

Problems are that people make mistakes and people copy those mistakes, an error in a reputable source can easily propagate to others. Other problem is that it depends on the people who created the virtual reality, or your actual reality, people of obviously huge capabilities to make a silly mistake or mistakes like that.

But it’s possible and would probably make an interesting movie.

2.  A sophisticated virtual reality probably requires huge amounts of computational resources and those kind of resources are probably finite in any kind of universe we can imagine. One universe can’t contain a real-time simulation of another universe in 1:1 scale with equal complexity and detail. You could try and make this reality as complex as possible, requiring more computational resources that is practical for running such a sophisticated virtual reality. This could happen by creating, yes, you guessed it, another sophisticated virtual reality.

Problems: We don’t know how much computational resources are needed, it could be well beyond our capabilities even if we could utilize huge amounts of computational resources despite of practical, social, economic and so on problems.  More to the point we wouldn’t know when our virtual reality would be sophisticated enough. What if everything is scripted for another 1000 years from now?

This way seems awfully unwieldy but if it led to us having a sophisticated virtual reality that would be way cool!

3. You could sit back and wait for some kind of authoritative message from the people running reality.

Problems: How would I know I’m not really crazy? Why would the message me (or us) in the first place? I might not even be the reason why this simulation exists, even if it feels like that.

This way seems very uncertain and is kind of boring as well.

4. You could do the Matrix and try and learn to “bend the rules”.

Very uncertain a way, potentially even dangerous and results would be ambigous anyway.

5. You could try and map the extense of the reality.

We assume that the universe continues as it is quite the same in all directions. You hop in your FTL-spaceship and check that it really does so and that all the (somehow) visible objects are really there. If, again, this reality is a limited simulation, we should run in to its limits sooner or later.

Problems: Where to begin? First of all, our reality creating overlords might cheat or change the rules or add content to the universe when needed. Not to mention my FTL-spaceship still hasn’t arrived.

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Do you have any other ones?