Epistemology: How We Know What Is True
How we know what is true depends on whether we evolved, whether there is physical reality, whether there is objective reality, whether humans can detect any or all reality, and what is important.
Suppose there were no physical and objective reality that you could detect. In other words, you could be just a brain in a vat being fed what your brain interprets as sensory input. You wouldn't know what you really are, and those others who you think are humans like you could be aliens or artificial intelligence. In fact, you could be an alien or artificial intelligence too.
Maybe there is no objective reality in the simulation. For example, one cannot prove that there isn't a simulation administrator who can change any outcome at any time, or who can change a variable temporarily or permanently, which would invalidate previous scientific knowledge.
Maybe the evidence of objective reality that you experience is a deception played on you. Maybe the purpose of the simulation is to test you. Maybe humans are extinct and you are one of a handful of human brains that aliens plugged into in a simulation to see if they want to revive the human species.
How do you think you're doing?
Maybe the simulation administrator can save the state of the simulation and start another simulation running in parallel so that he can introduce different stimuli into each in order to see what the different outcomes would be. Maybe he could cut you out of one simulation, and place you in another in order to see what happens. Maybe he could copy you and place you in another simulation. Maybe there are trillions of such simulations.
Time may not be what it seems. Maybe the simulation administrator could place a copy of you in an older backup of the simulation, which for you would seem exactly like traveling back in time. Maybe he could take a copy of you from a backup and place it in a current simulation, which for you would seem exactly like traveling forward in time. Maybe he has placed hidden mechanisms in the simulation that you can discover and which will allow you to jump into another simulation yourself, which would seem exactly as if you had the power to travel to another time and/or an alternative reality. Such hidden mechanisms to access reality outside the simulation may violate the rules within a simulation, which from your perspective would seem exactly like magic.
Maybe we humans will create such simulations ourselves one day. Maybe the simulation administrator is also in a simulation. Maybe he knows that he is in a simulation.
Suppose you are in a simulation. Is that important? Your life would be exactly as real as it seems to be. You would simply not know about those parts of reality outside of your ability to experience them. Your would probably have many invalid assumptions, but is that important?
If we evolved, then we have whatever genetically programmed behaviors (and assumptions) got the most genes into future generations. This would not override our ability to think, but it would require more careful thinking to overcome genetically programmed assumptions, which would not matter unless we were making a decision that had the possibility of being influenced by genetically programmed assumptions. It appears that almost all decisions are influenced to some degree by genetically programmed assumptions. Fortunately, such assumptions are what worked well in the past, so there is no reason to be too concerned about them unless one is contemplating an action that harms others.
The evidence for evolution is only contradicted by some ancient stories as far as I know, but even if one does not believe in evolution, one should be aware that we could be the product of evolution because the necessary ingredients are: 1) enough time, 2) a means of replication (reproduction), and 3) a means of mutation. In a simulation, is it still possible that we evolved from atoms, which would thus have been simulated atoms. Also, the simulation administrator and/or aliens could have influenced our evolution.
Careful thinking is what is known as science. Science tests theories in every conceivable way that could falsify them, and thus science cannot prove that a theory is true. Science can only try to falsify theories.
Not all theories, can be falsified. For example, one cannot falsify the theory that everything that happens is the will of God. Theories that cannot be falsified are thus not scientific and although non-scientific theories could still be true, they are highly unlikely to be true unless they yield reproducible results.
When making a decision, it is almost never important that science cannot prove that theories are true, and can only prove that theories are false. The reason why science is so useful without being able to prove theories is because of several processes that maximize the probability that a theory is true: 1) it must be falsifiable, 2) it must have been tested by every conceivable test that could falsify it, 3) tests must be double blind in order to eliminate the potential for human bias, 4) tests must be peer-reviewed, 5) tests must consistently yield reproducible results by others, 6) everyone must be free to propose tests, perform tests, and report their results, 7) everyone must be free to question whether the theory considers all the variables, 8) everyone must be free to question whether any of the necessary processes were violated or reported inaccurately.
Anthropogenic Global Warming is an example of a putative scientific theory that violates all of these scientific processes.
Perhaps the most extreme example of those who place a distorted importance on the fact that we cannot know something is true at all levels of reality, are Marxists. Marxists quibble that because we cannot prove anything absolutely, then all theories are equal, but that some people have more ability to propagate and/or enforce their theories than others. Therefore, Marxism claims to balance that power by killing, reeducating, or otherwise neutralizing anyone who disagrees with Marxism. Marxists are thus murderers who are violating their own putative principles. Note how they do not weigh the probability that a theory is true, and they do not consider the degree to which an individual fairly and honestly has ability. Marxists are thus murderers who are violating their own putative principles—over an erroneous philosophical quibble.
This is why epistemology is important. It enables us to easily show that Marxists are the bad guys, although common sense would have been sufficient. Perhaps more importantly, epistemology reveals that no one could possibly be motivated to commit atrocities over a philosophical quibble, and thus the quibble must be a pretense. Even the obvious jealously that motivates Marxists is not nearly sufficient to explain their enormous success in enforcing their inaccurate theories. Marxists are thus actually useful idiots who are being played in order to further the agenda of some cabal who has enormous ability to propagate and enforce theories.