Empirical limits in science

Visible light is the range of electromagnetic radiation which can be perceived by the human eye which is usually 380-700 nm.[8] The perception of visible light can be inconsistent between human beings, particularly in those with colour-blindness, where individuals have difficulty differentiating between certain colours.[9] The ability to detect contrast is also variable between human beings and this limits the consistency in qualitative findings made by scientists.[10] Visual acuity, colour discrimination and contrast sensitivity decrease with age in human beings.[11] Electromagnetic radiation beyond visible light is not usually detectable by the human eye and this limits scientific discovery using the human eye alone. Scientific devices such as the microscope,[12] infrared spectroscope[13] and Ultraviolet-visible spectrophotometer,[14] have enabled increases in visual acuity and increased the range of electromagnetic radiation detectable.[13][14] This enables scientists to make observations beyond those possible with the human eye alone.

The audible spectrum in humans is between 20 Hz and 20000 Hz; sounds outside of this range are not usually detected by the human ear.[7] The frequencies of sound which can be heard also depend on the amplitude of sound produced and adequate functioning of the human ear.[15] The upper limit of audible frequency detectable decreases with age.[7] Some sounds may be perceived initially but can initiate progressive degradation of the human ear causing them not to be perceived in later tests.[16] Devices such as the cochlear implant have enabled the preservation and restoration of hearing in some individuals.[17] This preservation of hearing enables individuals with hearing difficulties make observations and contribute to scientific discovery.

The ability to feel the precise nature of touch on the body is known as tactile acuity.[18] Tactile acuity differs between parts of the body and amongst individuals. The threshold of tactile acuity is dependent on the site of the body being used (to touch) and the number and size of receptive fields in that region of the body.[19] With aging comes a decrease in human tactile acuity.[20]

As with the other senses, olfaction differs amongst human beings.[21] The threshold of olfaction is the smallest amount of odorant which can be smelt by the human nose.[21] A common stance from the 19th century is that human beings have poor olfaction compared to other mammals. This idea was based on the hypothesis that evolution of humans caused a reduction in the brain’s olfactory bulb.[22] The olfactory bulb is relatively large when compared to other mammals and it is predicted that humans can detect over one trillion odours.[23]

The way to describe different smells is shown to be limited through tests in the English language. This is not necessarily the case in other language which may even incorporate odour into the grammar of the language.[24]

The sense of taste is not used in all scientific investigations, generally due to its irrelevance to the aims of the experiment being conducted or as a safety precaution.[25] Taste is a sense which has been investigated to a lesser extent compared to the other senses.[26] Differences in taste sensitivity in human beings could be because of variation in number of taste buds present on the human tongue.[27]

Until the late 16th Century it was believed, amongst western astronomers such as Ptolemy, that the sun and moon orbited the earth.[30] The main observations which lead to this geocentric model were the perception of an unmoving earth and the observance of both sun and moon once a day.[30] Before the 16th century, there were other astronomers such as Aristarchus of Samos who believed in a heliocentric model in which the earth orbits the sun.[31] From the late 16th century onwards, with advancements in technology and observations such as the orbit of Mars, the predominant position was changed and a heliocentric model was widely accepted.[28]