Different perceptions of reality do not only apply to theoretical life forms other than humans, there are exceptions to even the idea of a mass, human-wide perception of reality. A surprisingly large number of people, known as synesthetes, have “cross-wired” senses. This means that a person with synesthesia may sense what most people would consider solely a taste to also have a shape, or a sound to have a temperature in addition to its “normal” qualities. Synesthesia may cause a person to associate a temporal idea, such as a date or length of time, with a spatial idea such as a shape floating in space. Many people see bursts of color for various stimuli that most would consider aural or tactile (About).

But differences in personal realities are not only restricted to how phenomena are sensed. While one person may sense a phenomenon as the image of a pineapple, another may hear it as a bit of music, and a third smell it, all three can agree that there is something external to themselves at the same moment in time that they can sense and react to. However, when independent observers do not share a frame of reference, even when they are otherwise identical, their idea of what phenomena exist during a moment can vary wildly. Two observers separated by a large distance will observe an event taking place at different times by their personal clocks, due to the time light takes to travel from the event to the observer. Thus two different peoples’ ideas of reality will necessarily always be different from each other due to light lag. This effect is negligible on the scale of terrestrial life, but is still present (Greene 137). Velocity also has an affect, two observers physically close but moving on different vectors will observe events at different speeds due to time dilation.