While some science fiction technologies are already here or very close (C3PO, Longevity, AGI, etc) some are very far away or not possible at all. I will try to explain why FDVR is one of these and why it is so hard. Let’s start with the definition of FDVR as portrayed in popular science fiction works like “Matrix” or “3 Body Problem” is the idea of directly sending and receiving signals from the brain to simulate a realistic virtual reality for the brain.

Let’s look at the simplest problem first. If we want to get signals from the brain and use them in virtual reality we have to intercept them and cut off the connection to the real body. There is currently no known way to do this without damaging the body permanently and even if we could, a body without signals is not really functioning. laying in your own piss would be your smallest problem. You wouldn’t even be able to breathe. But even if we manage to do this we would only have solved the easiest part. Now that we have the output, we also need input.

Simulating feelings from every nerve end of your body requires the system to not only simulate the entire virtual reality which would have to be accurate on a molecular level (smell, taste) but also would need to be rendered quite far and needs full simulation of realistic physics (eyes, touch). And not only would the world need to be simulated to such a degree, but your body would also need to be a 1 to 1 simulation. every nerve end and visual receptor needs to be simulated to achieve a realistic experience that would fool your brain. This leads to the next problem: To get all these signals back into the brain we would need to understand the encoding and position of every input signal to the brain. This requires such an in-depth understanding of the brain that FDVR would be the most boring thing we could do with it at this point.

If we had the computing power to simulate all this and the deep understanding of the brain required to do it, It would be easier to simply make a digital copy of your brain and run it as a simulation. And if there is enough computing power to simulate a world to this degree, then we are most likely already living in one. The computing power to do this even for a few people could exceed what is possible with the energy in our solar system, following the law of computational irreducibility.

So in conclusion, if a future ASI would have access to such a deep understanding of biology and so much energy and computing power, using it for FDVR would be a total waste. But who knows maybe we get a fast takeoff soon and ASI will find some ways and we archive FSVR with some compromises in a few decades. I personally would bet that FDVR will never play a huge part in our society.