For all practical purposes, such credences don’t matter. Such scenarios certainly can and do happen, but in almost all cases there’s nothing you can do about them without exceeding your own bounded rationality and agency.
If the stakes are very high then it may make sense to consider the probability of some sort of trick, and attempt to get further evidence of the physical existence of the coin and that its current state matches what you are seeing.
There is essentially no point in assigning probabilities to hypotheses of failures of your mind itself. You can’t reason your way out of serious mind malfunction using arithmetic. At best you could hope to recognize that it is malfunctioning, and try not to do anything that will make things worse. In the case of mental impairment severe enough to have false memories or sensations this blatant, a rational person should expect that a person so affected wouldn’t be capable of correctly carrying out quantified Bayesian reasoning.
My own background credences are generally not insignificant for something like this or even stranger, but they play essentially zero role in my life and definitely not in any probability calculations. Such hypotheses are essentially untestable and unactionable.
For all practical purposes, such credences don’t matter. Such scenarios certainly can and do happen, but in almost all cases there’s nothing you can do about them without exceeding your own bounded rationality and agency.
If the stakes are very high then it may make sense to consider the probability of some sort of trick, and attempt to get further evidence of the physical existence of the coin and that its current state matches what you are seeing.
There is essentially no point in assigning probabilities to hypotheses of failures of your mind itself. You can’t reason your way out of serious mind malfunction using arithmetic. At best you could hope to recognize that it is malfunctioning, and try not to do anything that will make things worse. In the case of mental impairment severe enough to have false memories or sensations this blatant, a rational person should expect that a person so affected wouldn’t be capable of correctly carrying out quantified Bayesian reasoning.
My own background credences are generally not insignificant for something like this or even stranger, but they play essentially zero role in my life and definitely not in any probability calculations. Such hypotheses are essentially untestable and unactionable.