Disclaimer: The following WU is not very relevant to real life. But then, we're on E2. So who cares? Enjoy.
Consider the following:
Personal reality (not necessarily the same as real reality) is created by, and limited to, perception. Everything we understand to be real or to be not real is a result of our brains processing perceptions. For those who argue that information about reality can also come from God or other supernatural beings ... such divine communication would also be classed as a form of perception.
Perception is flawed.
Putting these two facts together leads to the unpleasant conclusion that we can't put a reasonable level of faith in our personal reality. "So what?" I hear you say. "I've seen the matrix, I know that perceived reality might be so much horseshit. It's been done - why have you noded this?" I hear you continue. I've noded, dear audience, because I'd like to drop yet another lead brick of doubt on the delicate spiderweb of reality. I was just getting you in the mood, so to speak.
Perception does not occur in real-time
Of course we all recognise the phenomenon of lightning occuring before thunder. Not to mention the interesting fact that our observation of celestial bodies can be out of date by aeons. But ponder the significance! The sensory input device that we depend upon most heavily is sight. The data which this device collects is stored in light, as electromagnetic radiation wave specifics; frequency, amplitude, etc. But light needs to time to travel from the observed object to the observer, and then the observer's brain needs time to send the data through the optic nerve, process the data through the visual cortex, and then to run the perception through reasonability filters (to make sure that the perception fits within an acceptable range of the observer's personal reality). The perception processing lag time can be assumed to be moderately constant, so to calculate the time taken just to see an object "x":
Perception Lag = Processing Time + (distance to x / speed of light)
As you can see, this leaves us with the conclusion that any sensory perception is guaranteed to be out of date, and therefore not accurate or trustworthy. Should you be making everyday decisions based on such irredeemably limited info? Of course not! The most rapid sense we have is touch (perception lag is only neural travel time + psychological processing time), but it has no long-range capability.
When you look at the moon, you're not seeing what the moon actually looks like. You're seeing what it looked like two seconds ago. The sun is eight minutes out. Alpha Centauri looked like that at some point in 1997. As a matter of fact, every single star in the night sky could have vanished last Thursday and we won't find out about it for quite some time to come. Astronomy is largely a study of ancient history.
The reason I titled this node "Reality Perception Sphere" is that the accuracy and reliability of reality perception exists like a sphere, centred on each person's head. The greater the radius, the less helpful the information is.
I realise that the amounts of time I'm talking about here are almost too small to bother with, here on earth where things are fairly quick, but any delay in the fundamental building blocks of our reality is pretty serious.
This rant is now complete.