How We Came to Know the Cosmos: Light & Matter

Discover How We Came to Know the Cosmos

Chapter 27. Empiricism and Epistemology

27.1 John Locke and empiricism

The English philosopher John Locke rejected Rene Descartes’ rationalism (discussed in Chapter 26) and, in 1690, he popularised the concept of the ‘tabula rasa’. Locke argued that the mind does not have innate ideas, and so sensory knowledge is the only knowledge we can have. This view is known as empiricism.

Locke claimed that if we had innate ideas - knowledge that does not come from experience - then all beings that possess a mind should be aware of them. Yet people don't appear to understand mathematics until they are taught and some people are never able to learn.

Locke argued that if a human mind can exist without being conscious of an idea, then it can’t be innate. Even if we could find some rational knowledge that everyone is aware of possessing, then Locke claimed this would still not show that we have come to know these ideas innately and not through shared experiences.

Locke argued that we have two types of experiences: sensations and reflections. We gain some knowledge from reflection, some from sensation, and some from both. In An Essay Concerning Human Understanding, Locke described reflection as “that notice which the mind takes of its own operations, and the manner of them”. Reflection allows us to be conscious of our mental processes, and so tells us about how our minds operate. Examples of reflection include “thinking, doubting, believing, reasoning, knowing”, and “willing”. These experiences all invoke qualia (discussed in Chapter 26) that do not correspond to external objects, and so Locke referred to reflection as an “internal sense”.[1]

Sensations arise from external stimulus and tell us about the external world. Locke described two types of sensations, those corresponding to primary and secondary qualities. Primary qualities are similar to the properties Descartes equated with rational introspection, such as size, shape, and quantity. Secondary qualities correspond to qualia, like colour, sound, and emotion. Locke highlighted the problem of secondary qualities with his example of the inverted spectrum.

Like Descartes, Locke claimed that it’s impossible to know if different people experience the same qualia,

if the idea that a violet produced in one [person’s] mind by [their] eyes were what a marigold produced in another [person’s], and vice versa. This could never be known, because one [person’s] mind couldn’t pass into another [person’s] body to perceive what appearances were produced.[1]

This assumes that different people could experience different colours despite exhibiting the same behaviour and brain activity.

A photograph of yellow and blue plants, and their inverse, which look blue and yellow, respectively.

Figure 27.1
Image credit

Locke claimed that it’s impossible to know if different people experience the same colours when they look at the same object.

Locke accepted that we don’t observe the external world directly, but did not see qualia as proof that the mind is composed of a non-physical substance, or that the external world does not exist. Instead, Locke advocated causal realism, the view that we can at least derive the existence of external objects from the qualia they invoke in us. Specifically, Locke believed that an object’s primary qualities are representative of its true nature and that they are responsible for inducing the secondary qualities we experience in their presence. We cannot know if these objects really resemble the qualia they invoke.

Like Thomas Hobbes (discussed in Chapter 26), Locke didn’t think we’re capable of understanding how external objects give rise to qualia. He stated that,

experience...convinces us, that we have an intuitive knowledge of our own existence and an internal infallible perception that we are. In every act of sensation, reasoning, or thinking, we are conscious to ourselves of our own being, and in this matter we don’t fall short of the highest degree of certainty.[2]

But this tells us nothing of the substance the mind is made of, and so Locke did not accept Descartes’ dualism. He suggested it’s equally possible that the mind and body could be made of the same substance, leading to the idea that physical matter could be capable of thought.

27.2 George Berkeley and idealism

In 1710, twenty years after Locke first published his theory of knowledge, the Irish philosopher George Berkeley criticised Locke’s belief in causal realism, the view that we can determine the existence of the external world.

Berkeley argued that causal realism is inconsistent with empiricism. This is because it assumes there’s a chain of causes, starting with the external object and ending with the secondary qualities we experience as qualia. Yet the brain only has access to the final stage, the qualia.

In A Treatise Concerning the Principles of Human Knowledge, Berkeley stated that,

extension, figure, and motion are only ideas existing in the mind, idea can be like nothing but another idea.[3]

The qualia we perceive when we’re awake can be indistinguishable from the qualia we experience when we dream or hallucinate. This shows that qualia can be invoked without the existence of a causal link and, because there’s no way to know when a causal link does or does not exist, Berkeley concluded that we have no reason to believe it exists at all.

Berkeley showed that if secondary qualities exist in the mind, then primary qualities must also exist there, as we cannot imagine them devoid of qualia,

extension, figure, and motion, abstracted from all other qualities, are inconceivable. Where therefore the other sensible qualities are, there must these be also, to wit, in the mind and nowhere else.[3]

Berkeley claimed that we can’t conceive of something existing in space without having a position and a velocity (which could be zero), yet it’s evident that these are relative concepts, and so originate in the mind. He went on to suggest that this must also be true of mass and numbers.

Berkeley stated that,

number is so visibly relative, and dependent on [people’s] understanding, that it is strange to think how any one should give it an absolute existence without the mind. We say one book, one page, one line, etc.; all these are equally units, though some contain several of the others. And in each instance, it is plain, the unit relates to some particular combination of ideas arbitrarily put together by the mind.[3]

Berkeley rejected Descartes’ dualism and Locke’s agnosticism. Because everything that we experience originates in the mind, Berkeley claimed that the only theory available to empiricists is idealism, the view that physical objects do not exist.

Berkeley described the mind as “one simple, undivided, active being”, and because nothing can exist without a mind to perceive it, he concluded that the external world must exist within the mind of God.[3] A modern version of this idea could include other types of perceivers, such as that provided by an advanced computer simulation.

Quantum computers and artificial realities

Quantum computers

All computers can be described as Turing machines, a concept devised by the British mathematician Alan Turing in 1936.[4] Moore’s Law, devised by the Intel co-founder Gordon Moore in 1965, states that the number of transistors on a microprocessor doubles every 18 months.[5] If this process continues, then by 2030, the circuits on a microprocessor will be measured on an atomic scale.

The physicist Paul Benioff first considered a quantum Turing machine in 1981,[6] and in 1985, David Deutsch showed how this could be done.[7] Quantum computers are faster than classical computers because classical computers store information in definite states, in terms of 1s or 0s. A quantum computer can store information in a superpositional state and hence perform more than one calculation at once.

In 1999, physicists at IBM developed a 3-qubit quantum computer (where a qubit, or quantum bit, is a unit of quantum information) and by 2001, they had developed a 7-qubit computer that could be used to calculate prime factors.[8]

In 2007, Canadian company D-Wave Systems developed a 16-qubit quantum computer, which could solve Sudoku puzzles.[9] They developed a 1000-qubit quantum computer in 2015.[10]

Artificial realities

It’s thought that quantum computers will be used to design others, and there’s no known physical law preventing them from reaching the state where they can simulate conscious experiences. This leads back to the philosophical question of whether we could be living inside a simulation.

In 2003, the Swedish philosopher Nick Bostrom suggested that if it’s possible to simulate entire universes, then most advanced civilisations will probably come to build simulation machines.[11] Bostrom predicted that one day everyone alive will exist inside of a simulation, making it almost certain that we are in one now.

Human consciousness is predicted to require about 1016 - 1017 (10-100 million, billion) operations per second and Bostrom predicted that it would take about 1033 - 1036 (1-1000 million, billion, billion, billion) operations per second to simulate our current experience of the universe.

In 1992, the American engineer Kim Eric Drexler showed that a system the size of a sugar cube could perform 1021 (1000 billion, billion) operations per second,[12] and, in 2001, the computer scientist Robert Bradbury showed that a computer with a mass similar to that of a large planet could perform 1042 (a million, billion, billion, billion, billion) operations per second.[13]

One problem with Bostrom’s idea is that it relies on the fact that we know what advanced civilisations are likely to do. If we could ask any of our ancestors what the 21st century is like, it’s doubtful that many of their predictions would be correct. The further back you go, the more likely it is that they would be wrong.

Bostrom’s idea also suggests that the laws of physics would be similar on both sides of the simulation. This may be the case, but it’s also possible that if we’re in a simulation, then our knowledge of any external laws is severely limited.

27.3 David Hume and epistemology

The British philosopher David Hume agreed with Berkeley’s claim that we do not directly experience any properties of the external world, but this did not lead him to accept idealism, the view that physical objects do not exist. Instead, he remained just as sceptical about the existence of the mind.

In 1748, Hume combined Descartes’ rationalism with Locke’s empiricism and argued that we gain knowledge from both impressions, which arise from external stimulus, and ideas, which are innate.

In An Enquiry Concerning Human Understanding Hume argued that innate ideas, like those found in mathematics, do not tell us anything useful about the external world. All useful knowledge comes from the qualia we experience, but these do not tell us anything that is necessarily true.

Hume stated that qualia make little sense to us until our minds have learned to interpret them and that interpretations occur by custom, instinct, and habit; if we experience two events in succession enough times, then we will come to expect one event after witnessing the other.

The branch of philosophy concerned with what we can know is known as epistemology. Hume applied his reasoning to science and argued that we only assume the future will resemble the past, and that the laws of physics will not suddenly change, because this is how the world has always appeared to us.[14]

The British mathematician Bertrand Russell elaborated on this idea in The Problems of Philosophy, published in 1912. Russell stated,

Experience has shown us that, hitherto, the frequent repetition of some uniform succession or coexistence has been a cause of our expecting the same succession or coexistence on the next occasion.

Domestic animals expect food when they see the person who feeds them. We know that all these rather crude expectations of uniformity are liable to be misleading. The [person] who has fed the chicken every day throughout its life at last wrings its neck instead, showing that more refined views as to the uniformity of nature would have been useful to the chicken.

The mere fact that something has happened a certain number of times causes animals and [people] to expect that it will happen again. Thus our instincts certainly cause us to believe the sun will rise to-morrow, but we may be in no better a position than the chicken which unexpectedly has its neck wrung.[15]

Hume claimed that knowledge of the self is also formed by custom and habit. He could not see any evidence that the mind is made of a non-physical substance, or that it persists through time separately from the body.

Hume described the mind as a ‘bundle’ of qualia and did not think there was any evidence of something that takes ownership of these sensations, a self. Although Hume accepted that there are thoughts, he did not accept Descartes’ claim that this means there must be a thinker. Similarly, Hume did not think that there was any evidence of God. Like Hobbes, he did not think that the mind could conceive of such an entity.[14,16]

27.4 Immanuel Kant and rationalist synthetic knowledge

The German philosopher Immanuel Kant began as a rationalist, but he was inspired by the work of Hume and, in 1781, he also developed a theory that combined rationalism with empiricism.[17] Kant argued that true knowledge can only be acquired by combining rationalist ideas with empirical knowledge because he believed that rationalism becomes flawed when it tries to consider anything beyond our sensory experiences, including the existence of God, souls, and free will.

Before Kant, both empiricists and rationalists had accepted that rationalism could only explain analytic knowledge. Analytic knowledge derives from statements that are true by definition. In Critique of Pure Reason, Kant stated that ‘all bodies are extended’ is an example of an analytic statement because being ‘extended’ in space is part of the definition of being a body. Other examples are ‘all daisies are flowers’ and ‘all triangles have three sides’. This is because being a flower is part of the definition of being a daisy, and having three sides is part of the definition of being a triangle.

These are contrasted with synthetic statements, statements that provide information about the world. Examples of synthetic statements include ‘all daisies are pretty’ and ‘all triangles are green’.

It was believed that synthetic knowledge could only be known from experience; however, Kant argued that this is false. Kant believed that mathematics is a kind of rationalist synthetic knowledge because, despite the fact that 7 + 5 = 12, for example, there is nothing within the plus sign, or the numbers seven or five that give the definition of 12. Kant claimed that this means our knowledge of mathematics comes from an innate knowledge of the external world.

Kant extended this idea to the foundations of physical science and stated that another example of a rationalist synthetic statement is ‘the shortest distance between two points is a straight line’. This is because the concept of a straight line is not part of the definition of ‘the shortest distance between two points’, something that was proven with Albert Einstein’s theory of special relativity[18] (discussed in Book I).

Kant argued that aside from rationalist synthetic knowledge, the only way to gain information is through analytic statements, which are entirely empirical. However, because we can only perceive of qualia, Kant accepted Hume’s conclusion, that our capacity for thought is too limited to conceive of objects as they really are, and purely empirical knowledge is formed only by custom, instinct, and habit.

Kant claimed that the mind is needed to make sense of the continuous stream of qualia that we perceive. He claimed that external objects exist outside of time and space and that the mind is needed to organise qualia into separate spatial and temporal locations. This means that the concepts of space and time are rationalist in nature. They are not learned from experience. The mind is also needed to join associated qualia into the objects we recognise.

In order to do this, Kant agreed with Descartes when he stated that the mind must necessarily be a unified whole. Kant did not accept mind-body dualism, however, because the idea of the soul is also formed by custom, instinct, and habit.

Kant stated that the mind is really just a complex set of abilities, or functions, without a subject,

the permanence of the soul, therefore, as an object of the internal sense, remains undemonstrated, nay, even indemonstrable. [We cannot] affirm, from mere conceptions [the souls] permanence beyond life.[17]

27.5 References

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