Sunday, 20 March 2016

Are We Real? Dreaming, Reality, Consciousness & Perception

This is the first article that I have written about dreaming, the nature of reality, perception and consciousness. This article was researched using online sources and covers some of the basic ideas and theories related to the philosophy of the mind and nature of reality. Although lengthy and varied in terms of content and themes, this is only really an introduction to a very complex, multi-disciplinary topic and should be regarded as a starting point for a more extensive exploration into this subject.

'The Dream Argument'
The dream argument is the theory that the act of dreaming provides preliminary evidence that the senses we rely upon (to distinguish reality from illusion) should not be fully trusted. Therefore, any state of consciousness which is dependent on our senses should be carefully examined and rigorously tested to determine whether it is in fact reality.

Typically, when we dream we are unaware that we are doing so, unless we are lucid dreaming. This has led to philosophers pondering the notion that we could be dreaming constantly, instead of being in waking reality. We cannot be 100% certain that we are not dreaming at any given time.

In the West, this philosophical conundrum was referred to by Plato (Theaetetus) and Aristotle (Metaphysics). Having received significant consideration in René Descartes' Meditations on First Philosophy (1641), the dream argument has become one of the most prominent sceptical hypotheses which clearly has an archetype in elements of Plato's Allegory of the Cave also.

This type of argument is well known as ‘Zhuangzi dreamed he was a butterfly’ (莊周夢蝶 - Zhuāngzhōu mèng dié): One night, Zhuangzi (369 BC) dreamed that he was a carefree butterfly, flying happily. After he woke up, he wondered how he could determine whether he was Zhuangzi who had just finished dreaming he was a butterfly, or a butterfly who had just started dreaming he was Zhuangzi. This was a metaphor for what he referred to as a ‘great dream’, stating:

‘He who dreams of drinking wine may weep when morning comes; he who dreams of weeping may in the morning go off to hunt. While he is dreaming he does not know it is a dream, and in his dream he may even try to interpret a dream. Only after he wakes does he know it was a dream. And someday there will be a great awakening when we know that this is all a great dream. Yet the stupid believe they are awake, busily and brightly assuming they understand things, calling this man ruler, that one herdsman ‑ how dense! Confucius and you are both dreaming! And when I say you are dreaming, I am dreaming, too. Words like these will be labeled the Supreme Swindle. Yet, after 10,000 generations, a great sage may appear who will know their meaning, and it will still be as though he appeared with astonishing speed.’

Some schools of Buddhist thought (i.e. Dzogchen), consider perceived reality literally unreal. One prominent contemporary teacher, Chögyal Namkhai Norbu, claims: ‘In a real sense, all the visions that we see in our lifetime are like a big dream…’ In this context, the term 'visions' denotes not only visual perceptions, but appearances perceived through all senses, including sounds, smells, tastes and tactile sensations, as well as other mental processes and operations.

Dreaming provides a framework for those who question whether our own reality may indeed be no more than an illusion. The ability of the mind to be tricked into believing a mentally generated world is the ‘real world’ means at least one variety of simulated reality is a common, even nightly event.

Those who argue that the world is not simulated must concede that the mind - at least the sleeping mind - is not itself an entirely reliable mechanism for attempting to differentiate reality from illusion.

Descartes stated: ‘Whatever I have accepted until now as most true has come to me through my senses. But occasionally I have found that they have deceived me, and it is unwise to trust completely those who have deceived us even once.’

Cartestian Philosophy
‘Cartesian Doubt’ is a form of methodological scepticism associated with the writings and methodology of Descartes (1596 - 1650). Cartesian Doubt is also known as Cartesian scepticism; methodic doubt; methodological scepticism; Universal Doubt; or hyperbolic doubt. Cartesian Doubt is a systematic process of being sceptical about (or doubting) the truth of one's beliefs and this has become a characteristic method in philosophy. This method of doubt was largely popularized in Western philosophy by Descartes, who sought to doubt the truth of all his beliefs in order to determine which beliefs he could be certain were true. Methodological scepticism is distinguished from philosophical skepticism in that methodological scepticism is an approach that subjects all knowledge claims to scrutiny with the goal of sorting out true from false claims, whereas philosophical scepticism is an approach that questions the possibility of pure knowledge.

In the past, philosophers John Locke (1632 – 1704) and Thomas Hobbes (1588 – 1679) have separately attempted to refute Descartes's account of the dream argument. Locke claimed that pain in dreams is not of the same intensity as pain in reality. Various scientific studies conducted in the late 20th century provided evidence against Locke's claim by concluding that pain in dreams can accurately mirror pain in waking life. Hobbes's refuted the dream argument by claiming that dreams are susceptible to absurdity while the waking life is not. 

Many contemporary philosophers have attempted to refute dream scepticism in detail (i.e. Stone (1984) & Sosa (2007) being 2 notable examples). Sosa presents a new theory of dreaming and argues that his theory raises a new argument for scepticism, which he attempts to refute. In A Virtue Epistemology: Apt Belief and Reflective Knowledge, he states: "In dreaming we do not really believe; we only make-believe’. Jonathan Ichikawa (2008) and Nathan Ballantyne & Ian Evans (2010) have offered critiques of Sosa's proposed solution. Ichikawa argued that as we cannot tell whether our beliefs in waking life are truly beliefs and not imaginings, like in a dream, we are still not able to tell whether we are awake or dreaming.

Descartes did not just use dreaming as a means of questioning reality. He also postulated the idea of ‘the evil demon’, a concept which is also known as the ‘evil genius’, and occasionally as ‘malicious demon’ or ‘genius malignus’. In Meditations on First Philosophy, Descartes hypothesized the existence of an evil demon, a personification who is ‘as clever and deceitful as he is powerful, who has directed his entire effort to misleading me’. 

The evil demon presents a complete illusion of an external world, including other minds, to Descartes' senses, when in fact there is no such external world in existence. The evil genius also presents to Descartes' senses a complete illusion of his own body, including all bodily sensations. 

Some Cartesian scholars opine that the demon is also omnipotent, and thus capable of altering mathematics and the fundamentals of logic, though omnipotence of the evil demon would be contrary to Descartes' hypothesis, as he rebuked accusations of the evil demon having omnipotence. It is one of several methods of systematic doubt that Descartes employs in the Meditations

Another such method of Cartesian systematic doubt is the deus deceptor (French: dieu trompeur), the ‘deceptive god’. Cartesian scholars differ in their opinions as to whether the deus deceptor and the evil demon are the same ‘being’ for the purposes of Descartes’ argument. Among the accusations of blasphemy made against Descartes by Protestants was that he was positing an omnipotent malevolent God. While methodic doubt has a nature, one need not hold that knowledge is impossible in order to apply the method of doubt. 

Indeed, Descartes' attempt to apply the method of doubt to the existence of himself spawned the proof of his famous saying, ‘Cogito ergo sum’ (‘I think, therefore I am’ or ‘je pense, donc je suis’ in French). Descartes tried to doubt his own existence, but found that even his doubting showed that he existed, since he could not doubt if he did not exist. If he did not exist, he could not think: thinking was proof of existence. A fuller version of Descartes’ maxim is: ‘dubito, ergo cogito, ergo sum’ (‘I doubt, therefore I think, therefore I am’).

Auguste Rodin, 'The Thinker' (Le Penseur) (1904)

Solipsism is often introduced in the context of relating it to pathological psychological conditions. Solipsism Syndrome is a disassociative mental state, where the patient rejects or detaches from reality. Some psychiatrists and psychologists believe that children – who are ego-centric in early childhood – are solipsistic, but later, as a result of cognitive development, learn to infer that other minds do in fact exist. However, in this article, solipsism is considered within the context of the philosophy of the mind and questions as to the nature of reality, rather than psychology or psychiatry. 

Solipsism (Listeni/ˈsɒlᵻpsɪzəm/; from Latin ‘solus’ meaning ‘alone’ and ‘ipse’ meaning ‘self’) is the philosophical idea that only one's own mind is sure to exist. As an epistemological position, solipsism holds that knowledge of anything outside one's own mind is unsure - the external world and other minds cannot be known and might not exist outside of the mind. As a metaphysical position, solipsism goes further to the conclusion that the world and other minds do not exist. A controversial feature of the metaphysical solipsistic worldview is the denial of the existence of other minds. Since personal experiences are private and ineffable, another being's experience can be known only by analogy.

Sigmund Freud (1856 – 1939) stated that other minds are not known, but only inferred to exist. He stated: ‘consciousness makes each of us aware only of his own states of mind, that other people, too, possess a consciousness is an inference which we draw by analogy from their observable utterances and actions, in order to make this behaviour of theirs intelligible to us. (It would no doubt be psychologically more correct to put it in this way: that without any special reflection we attribute to everyone else our own constitution and therefore our consciousness as well, and that this identification is a sine qua non of understanding)’.

Philosophers try to build knowledge on more than an inference or analogy. The failure of Descartes' epistemological enterprise popularized the idea that all certain knowledge may go no further than ‘I think; therefore I exist’, without providing any real details about the nature of the ‘I’ that has been proven to exist. The theory of solipsism also merits close examination because it relates to three widely held philosophical presuppositions, each itself fundamental and wide-ranging in importance:
  • My most certain knowledge is the content of my own mind - my thoughts, experiences, affects etc
  • There is no conceptual or logically necessary link between mental and physical - between, say, the occurrence of certain conscious experience or mental states and the 'possession' and behavioural dispositions of a 'body' of a particular kind (i.e. brain in a vat, see below)
  • The experience of a given person is necessarily private to that person

Solipsism was first recorded by the Greek presocratic sophist, Gorgias (c. 483 - 375 BC) who is quoted by the Roman skeptic Sextus Empiricus as having stated:
  • Nothing exists
  • Even if something exists, nothing can be known about it
  • Even if something could be known about it, knowledge about it can't be communicated to others

Much of the point of the Sophists was to show that ‘objective’ knowledge was a literal impossibility. The foundations of solipsism are in turn the foundations of the view that the individual's understanding of any and all psychological concepts (i.e. thinking, willing, perceiving etc) is accomplished by making analogy with his or her own mental states – i.e. by abstraction from inner experience. 

And this view, or some variant of it, has been influential in philosophy since Descartes elevated the search for incontrovertible certainty to the status of the primary goal of epistemology, whilst also elevating epistemology to ‘first philosophy’. George Berkeley's arguments against materialism in favour of idealism provide the solipsist with a number of arguments not found in the theories of Descartes. While Descartes defends ontological dualism, thus accepting the existence of a material world (‘res extensa’) as well as immaterial minds (‘res cogitans’) and God, Berkeley (1968 – 1753) denies the existence of matter but not minds, of which God is one.

The theory of Cartesian Duality proposes the belief that both ideals and ‘reality’ exist. Dualists argue that the distinction between the mind (or 'ideas') and matter can be proven by employing Leibniz' principle of the identity of indiscernibles (which states that if 2 things share all exactly the same qualities, then they must be identical, as in indistinguishable from each other and therefore one and the same thing). 

Dualists attempt to identify attributes of mind that are lacked by matter (such as privacy or intentionality) or vice versa (such as having a certain temperature or electrical charge). 

One notable application of the identity of indiscernibles was by Descartes’ famous ‘cogito ergo sum’ argument, referred to above. As he was unable to doubt the (separate) existence of his body, he inferred that the person ‘Descartes’ (i.e. his mind) must not be identical to the Descartes body, since one possessed a characteristic that the other did not - namely, it could think and be known to exist. Solipsism agrees with Descartes in this aspect, and goes further - only things that can be known to exist for sure should be considered to exist. The Descartes body could only exist as an idea in the mind of the person Descartes. Descartes and dualism aim to prove the actual existence of reality as opposed to a phantom existence (as well as the existence of God in Descartes' case), using the realm of ideas merely as a starting point, but solipsism usually finds those further arguments unconvincing. 

The solipsist instead proposes that his/her own unconscious is the author of all seemingly ‘external’ events from ‘reality’. Berkeley, an idealist philosopher, argued that physical objects do not exist independently of the mind that perceives them. An item truly exists only as long as it is observed; otherwise, it is not only meaningless, but simply non-existent. 

The observer and the observed are one and the same. Berkeley does attempt to show things can and do exist apart from the human mind and our perception, but only because there is an all-encompassing Mind in which all ‘ideas’ are perceived – in other words, God, an omniscient being who observes all. Solipsism agrees that nothing exists outside of perception, but would argue that Berkeley falls prey to the egocentric predicament – he can only make his own observations, and thus cannot be truly sure that this God or other people exist to observe ‘reality’. The solipsist would say it is better to disregard the unreliable observations of alleged other people and rely upon the immediate certainty of one's own perceptions.

Solipsism is not a falsifiable hypothesis - there does not seem to be an imaginable disproof. Not even the complete death - i.e. annihilation of the solipsist - could falsify his belief in solipsism because he could not analyze that observation. 

One critical test is nevertheless to consider the induction from experience that the externally observable world does not seem, at first approach, to be directly manipulable purely by mental energies alone. One can indirectly manipulate the world through the medium of the physical body, but it seems impossible to do so through pure thought (i.e. via psychokinesis). 

It might be argued that if the external world were merely a construct of a single consciousness i.e. the self, it could then follow that the external world should be somehow directly manipulable by that consciousness, and if it is not, then solipsism is false. An argument against this states the notion that such manipulation may be possible but barred from the conscious self via the subconscious self, a 'locked' portion of the mind that is still nevertheless the same mind. 

Lucid dreaming might be considered an example of when these locked portions of the subconscious become accessible. An argument against this might be brought up in asking why the subconscious of the mind would be locked, also the access, to the autonomous ('locked') portions of the mind during the lucid dreaming, is obviously much different (for instance: is relatively more transient) than the access to autonomous regions of the perceived nature.

Philosophical Zombies
The theory of solipsism crosses over with the theory of the philosophical zombie in that all other seemingly conscious beings actually lack true consciousness, instead they only display traits of consciousness to the observer, who is the only conscious being there is. A philosophical zombie (or ‘p-zombie’ in the philosophy of mind and perception) is a hypothetical being that is indistinguishable from a normal human being except in that it lacks conscious experience, qualia, or sentience. For example, a philosophical zombie could be poked with a sharp object, and not feel any pain sensation, yet, behave exactly as if it does feel pain (it may say ‘ouch’ and recoil from the stimulus, or say that it is in intense pain). 

The notion of a philosophical zombie is used mainly in thought experiments intended to support arguments (often called ‘zombie arguments’) against forms of physicalism such as materialism, behaviourism and functionalism. 

Physicalism is the idea that all aspects of human nature can be explained by physical means - specifically, all aspects of human nature and perception can be explained from a neurobiological standpoint. Some philosophers, like David Chalmers, argue that since a zombie is defined as physiologically indistinguishable from human beings, even its logical possibility would be a sound refutation of physicalism. 

However, physicalists like Daniel Dennett counter that Chalmers's physiological zombies are logically incoherent and thus impossible. Zombie arguments often support lines of reasoning that aim to show that zombies are metaphysically possible in order to support some form of dualism - in this case the view that the world includes two kinds of substance (or perhaps two kinds of property) - the mental and the physical. According to physicalism, physical facts determine all other facts. Since any fact other than that of consciousness may be held to be the same for a p-zombie and a normal conscious human, it follows that physicalism must hold that p-zombies are either not possible or are the same as normal humans.

The unifying idea of the zombie is of a human that has no conscious experience, but one might distinguish various types of zombie used in different thought experiments as follows:
  • A behavioural zombie that is behaviourally indistinguishable from a human
  • A neurological zombie that has a human brain and is generally physiologically indistinguishable from a human
  • A soulless zombie that lacks a soul
There have been some interesting thought experiments carried out, which illustrate the concept of the philosophical zombie in far greater detail than is possible herein.

Consensus Reality
Consensus reality is the idea that we generally agree what is and is not reality, based on a consensus view. The appeal to consensus arises from the fact that humans do not fully understand or agree upon the nature of knowledge or ontology, often making it uncertain what is real, given the vast inconsistencies between individual subjectivities. 

We can, however, seek to obtain some form of consensus with others as to what is real and then use this consensus as a pragmatic guide, either on the assumption that it seems to approximate some kind of valid reality, or simply because it is more ‘practical’ than perceived alternatives. 

Consensus reality therefore refers to the agreed-upon concepts of reality which people in the world, or a culture or society, believe are real (or treat as real), usually based upon their common experiences as they believe them to be. Those who do not share the same ideas as to what constitutes reality, would therefore be deemed ‘living in another world’. Throughout history this has also raised a social question as to the effects of a society in which all individuals do not agree upon the same reality. Children have sometimes been described or viewed as ‘inexperience[d] with consensus reality’, although it is generally assumed that their perspective will progressively form closer to the consensus reality of their society as they age.

In considering the nature of reality, 2 broad approaches exist: the Realist approach (there is a single, objective, overall reality believed to exist irrespective of the perceptions of any given individual); and the Idealistic approach (an individual can verify nothing except their own experience of the world, and can never directly know the truth of the world independent of that). 

There are sub-categories of approach as well, for example, Objectivists (who reject the notion of subjective reality; and hold that while each individual may indeed have their own perception of reality, that perception has no effect on what reality actually is - in fact, if the perception of reality differs significantly from the actual reality, serious negative consequences are bound to follow); and Materialists (who do not accept the idea of there being different possible realities for different people, rather than different beliefs about one reality. A person who believed in a different reality, when proof of one objective reality is provided, would be considered delusional).

Consensus reality may be understood by studying socially constructed reality, a theme within the sociology of knowledge. One example which demonstrates these ideas well is religious belief/worldview: reality for people who follow a particular theocentric religion is different from reality for those who follow another theocentric religion, or from those that eschew theocentric religions in favour of science alone, for explaining life and the universe. 

In societies where theocentric religions are dominant, the religious understanding of existence would be the consensus reality, while in a predominantly secular or humanist society where consensus is grounded in science, not faith or belief, the religious worldview would remain the non-consensus (or alternative) reality. Thus, different individuals and communities have fundamentally different world views with completely different comprehensions of the world around them, and of the constructs within which they live. Thus, a society that is, for example, completely secular and one which believes every eventuality to be subject to metaphysical influence will have very different consensus realities. Many of their beliefs on broad issues such may differ in direct consequence because of the differences in the perceived nature of the world they live in.

Reality in Eastern Philosophies
There are many theories which propose varied conceptualisations of the nature of reality and illusion. For example, Maya (Sanskrit: माया māyā) literally ‘illusion’ or ‘magic’, has multiple meanings in Indian philosophies depending on the context. 

In ancient Vedic literature, Māyā literally implies extraordinary power and wisdom, whilst in later Vedic texts and modern literature dedicated to Indian traditions, Māyā connotes a ‘magic show, an illusion where things appear to be present but are not what they seem’. Māyā is also a spiritual concept connoting ‘that which exists, but is constantly changing and thus is spiritually unreal’, and the ‘power or the principle that conceals the true character of spiritual reality’. The concept implies the role of imagination in the creation of the world. In early Vedic usage the term was used to refer to ‘the wondrous and mysterious and wondrous power to turn an idea into a physical reality’.

Reality in Buddhism is called ‘dharma’ (Sanskrit) or ‘dhamma’ (Pali). This word is foundational to the conceptual frameworks of the Indian religions and refers in Buddhism to the system of natural laws which constitute the natural order of things. Dharma is therefore reality as-it-is (‘yatha-bhuta’). The teaching of Gautama Buddha - the method by which people can come out of their condition of suffering (‘dukkha’), involves developing an awareness of reality (‘mindfulness’). 

Buddhism thus seeks to address any disparity between a person's view of reality and the actual state of things. This is called developing Right or Correct View (Pali: ‘samma ditthi’). Seeing reality as-it-is is thus an essential prerequisite to mental health and well-being. Buddhism addresses deeply philosophical questions regarding the nature of reality. One of the fundamental teachings is that all the constituent forms (‘sankharas’) that make up the universe are temporary (Pali: ‘anicca’), arising and passing away, and therefore without concrete identity (‘atta’). This lack of enduring identity (‘anatta’) of phenomena has important consequences for the possibility of liberation from the conditions which give rise to suffering. 

This is explained in the doctrine of interdependent origination. One of the most discussed themes in Buddhism is that of the emptiness (‘sunyata’) of form (matter), an important corollary of the transient and conditioned nature of phenomena. Reality is seen as a form of 'projection', resulting from the fruition (‘vipaka’) of karmic seeds (‘sankharas’). The precise nature of this 'illusion' that is the phenomenal universe is debated among different schools.

Some consider that the concept of the unreality of ‘reality’ is confusing. They propose that, in Buddhism, the perceived reality is considered illusory not in the sense that reality is a fantasy or unreal, but that our perceptions and preconditions mislead us to believe that we are separate from the elements that we are made of. Reality would be described as the manifestation of karma. 

Other schools of thought in Buddhism (i.e. Dzogchen) consider perceived reality as literally unreal and that all the ‘visions’ that we experience in a lifetime are one big dream (for example, according to Chögyal Namkhai Norbu Rinpoche) - this idea has already been touched upon above, in the section on 'The Dream Argument'. 

Thus, perceived reality is deemed to be relatively ‘unreal’. It is claimed that, on careful examination, the dream of life and regular nightly dreams are not very different, and that in their essential nature there is no difference between them. The non-essential difference between the dreaming state and ordinary waking experience is that the latter is more concrete and linked to attachment; the dreaming experience while sleeping is slightly detached. Also according to this theory, there is a correspondence between the states of sleep and dream and our experiences when we die. After experiencing the intermediate state of ‘bardo’, an individual comes out of it, a new karmic illusion is created and another existence begins. This is how transmigration happens. 

According to Dzogchen teachings, the energy of an individual is essentially without form and free from duality. However, karmic traces contained in the individual's mindstream give rise to two kinds of forms: (a) forms that the individual experiences as his or her body, voice and mind: and (b) forms that the individual experiences as an external environment. What appears as a world of permanent external phenomena, is the energy of the individual. There is nothing completely external or separate from the individual. Everything that manifests in the individual's field of experience is a continuum. This is the 'Great Perfection' that is discovered in Dzogchen practice. 

It is possible to do yogic practice such as Dream Yoga and Yoga Nidra whilst dreaming, sleeping and in other bardo states of trance. In this way the yogi can have a very strong experience and with this comes understanding of the dream-like nature of daily life. This is also very relevant to diminishing attachments, because they are based on strong beliefs that life's perceptions such as objects are real and as a consequence: important. If one really understands what Buddha Shakyamuni meant when he said that everything is (relatively) unreal, then one can diminish attachments and tensions. The teacher advises that the realization that life is only a big dream can help us finally liberate ourselves from the chains of various emotions, different kinds of attachment and the chains of ego. Then we have the possibility of ultimately becoming enlightened. Different schools and traditions in other strains of Tibetan Buddhism give different explanations of what is called ‘reality’.

Arthur Bowen Davies, 'Maya, the Mirror of Illusion' (1910)

Multiverse Theories & Reality
The American philosopher and psychologist William James (1842 – 1910) coined the term ‘multiverse’ in 1895, but in a different context to that in which is it used today. The multiverse (or ‘meta-universe’) is the hypothetical set of finite and infinite possible universes, including the universe in which we live. Together, these universes comprise everything that exists: the entirety of space, time, matter, energy, and the physical laws and constants that describe them. 

The various universes within the multiverse are called ‘parallel universes’, ‘other universes’ or ‘alternate universes’. The structure and form of the multiverse depends largely on the specific multiverse theory or hypotheses under consideration. The issue of whether multiverse theory can be scientifically validated remains under intense debate, with prominent scientists both supporting and rejecting the notion.

Cosmologist Max Tegmark has provided a taxonomy of 4 different levels of universes beyond the familiar observable universe. The 4 levels of Tegmark's classification are arranged such that subsequent levels can be understood to encompass and expand upon previous levels:
  • Level I: Beyond our cosmological horizon
A prediction of chaotic inflation is the existence of an infinite ergodic universe, which, being infinite, must contain Hubble volumes realizing all initial conditions. Accordingly, an infinite universe will contain an infinite number of Hubble volumes, all having the same physical laws and physical constants. In regard to configurations such as the distribution of matter, almost all will differ from our Hubble volume. However, because there are infinitely many, far beyond the cosmological horizon, there will eventually be Hubble volumes with similar, and even identical, configurations. Given infinite space, there would, in fact, be an infinite number of Hubble volumes identical to ours in the universe. This follows directly from the cosmological principle, wherein it is assumed that our Hubble volume is not special or unique.
  • Level II: Universes with different physical constants
Bubble universes - every disk represents a bubble universe. Our universe is represented by one of the disks. Universe 1 to Universe 6 represent bubble universes. Five of them have different physical constants than our universe has. In the chaotic inflation theory, a variant of the cosmic inflation theory, the multiverse as a whole is stretching and will continue doing so forever, but some regions of space stop stretching and form distinct bubbles (like gas pockets in a loaf of rising bread). Such bubbles are embryonic level I multiverses. Different bubbles may experience different spontaneous symmetry breaking, which results in different properties, such as different physical constants. Level II also includes John Archibald Wheeler's oscillatory universe theory and Lee Smolin's fecund universes theory.
  • Level III: Many-worlds interpretation of quantum mechanics
Hugh Everett's many-worlds interpretation (MWI) is one of several mainstream interpretations of quantum mechanics. In brief, one aspect of quantum mechanics is that certain observations cannot be predicted absolutely. Instead, there is a range of possible observations, each with a different probability. According to the MWI, each of these possible observations corresponds to a different universe. Suppose a 6-sided die is thrown and that the result of the throw corresponds to a quantum mechanics observable. All 6 possible ways the die can fall correspond to 6 different universes. Tegmark argues that a Level III multiverse does not contain more possibilities in the Hubble volume than a Level I or Level II multiverse. In effect, all the different ‘worlds’ created by ‘splits’ in a Level III multiverse with the same physical constants can be found in some Hubble volume in a Level I multiverse. Tegmark states: ‘The only difference between Level I and Level III is where your doppelgängers reside. In Level I they live elsewhere in good old 3-dimensional space. In Level III they live on another quantum branch in infinite-dimensional Hilbert space’. Similarly, all Level II bubble universes with different physical constants can, in effect, be found as ‘worlds’ created by ‘splits’ at the moment of spontaneous symmetry breaking in a Level III multiverse. According to Yasunori Nomura, Raphael Bousso & Leonard Susskind this is because global spacetime appearing in the (eternally) inflating multiverse is a redundant concept. This implies that the multiverses of Levels I, II, and III are, in fact, the same thing. This hypothesis is referred to as ‘Multiverse = Quantum Many Worlds’.Related to the many-worlds idea are Richard Feynman's multiple histories interpretation and H. Dieter Zeh's many-minds interpretation.
  • Level IV: Ultimate ensemble
The ultimate mathematical universe hypothesis is Tegmark's own hypothesis. This level considers all universes to be equally real which can be described by different mathematical structures. Tegmark writes that: ‘Abstract mathematics is so general that any Theory Of Everything (TOE) which is definable in purely formal terms (independent of vague human terminology) is also a mathematical structure. For instance, a TOE involving a set of different types of entities (denoted by words, say) and relations between them (denoted by additional words) is nothing but what mathematicians call a set-theoretical model, and one can generally find a formal system that it is a model of… [this] implies that any conceivable parallel universe theory can be described at Level IV [and] subsumes all other ensembles, therefore brings closure to the hierarchy of multiverses, and there cannot be, say, a Level V’. Jürgen Schmidhuber, however, says that the set of mathematical structures is not even well-defined and that it admits only universe representations describable by constructive mathematics - that is, computer programs. Schmidhuber explicitly includes universe representations describable by non-halting programs whose output bits converge after finite time, although the convergence time itself may not be predictable by a halting program, due to Kurt Gödel's limitations. He also explicitly discusses the more restricted ensemble of quickly computable universes.

Theoretical physicist and string theorist, Brian Greene has also proposed a theory of multiverses, identifying 9 types:
  • Quilted
The quilted multiverse works only in an infinite universe. With an infinite amount of space, every possible event will occur an infinite number of times. However, the speed of light prevents us from being aware of these other identical areas
  • Inflationary
The inflationary multiverse is composed of various pockets in which inflation fields collapse and form new universes
  • Brane
The brane multiverse follows from M-theory and states that our universe is a 3-dimensional brane that exists with many others on a higher-dimensional brane or ‘bulk’. Particles are bound to their respective branes except for gravity
  • Cyclic
The cyclic multiverse (via the ekpyrotic scenario) has multiple branes (each a universe) that have collided, causing Big Bangs. The universes bounce back and pass through time until they are pulled back together and again collide, destroying the old contents and creating them anew
  • Landscape
The landscape multiverse relies on string theory's Calabi–Yau spaces. Quantum fluctuations drop the shapes to a lower energy level, creating a pocket with a set of laws different from that of the surrounding space
  • Quantum
The quantum multiverse creates a new universe when a diversion in events occurs, as in the many-worlds interpretation of quantum mechanics
  • Holographic
The holographic multiverse is derived from the theory that the surface area of a space can simulate the volume of the region.
  • Simulated
The simulated multiverse exists on complex computer systems that simulate entire universes
  • Ultimate
The ultimate multiverse contains every mathematically possible universe under different laws of physics

In several theories, there is a series of infinite, self-sustaining cycles (for example, an eternity of Big Bangs, Big Crunches, and/or Big Freezes). 

A different form of multiverse has been envisaged within string theory and its higher-dimensional extension, M-theory. These theories require the presence of 10 or 11 spacetime dimensions respectively. The extra 6 or 7 dimensions may either be compactified on a very small scale, or our universe may simply be localized on a dynamical (3+1)-dimensional object - a D3-brane. This opens up the possibility that there are other branes which could support other universes. This is unlike the universes in the quantum multiverse, but both concepts can operate at the same time. 

Some scenarios postulate that our Big Bang was created, along with our universe, by the collision of two branes.

A black-hole cosmology is a cosmological model in which the observable universe is the interior of a black hole existing as one of possibly many universes inside a larger universe. This includes the theory of white holes, which are on the opposite side of space-time.While a black hole sucks everything in, including light, a white hole releases matter and light. Hence the name ‘white hole’. 

Under the Anthropic principle, the concept of other universes has been proposed to explain how our own universe appears to be fine-tuned for conscious life as we experience it. If there were a large (possibly infinite) number of universes, each with possibly different physical laws (or different fundamental physical constants), then some of these universes (even if very few) would have the combination of laws and fundamental parameters that are suitable for the development of matter, astronomical structures, elemental diversity, stars, and planets that can exist long enough for life to emerge and evolve. The weak anthropic principle could then be applied to conclude that we (as conscious beings) would only exist in one of those few universes that happened to be finely tuned, permitting the existence of life with developed consciousness. Thus, while the probability might be extremely small that any particular universe would have the requisite conditions for life (as we understand life), those conditions do not require intelligent design as an explanation for the conditions in the Universe that promote our existence in it. Possible worlds are a way of explaining probability and hypothetical statements. 

Some philosophers, such as David Lewis, believe that all possible worlds exist and that they are just as real as the world we live in – this is a position known as modal realism). A metaphysical issue which crops up in multiverse theories that posit infinite identical copies of any given universe, is the notion that there can be identical objects in different possible worlds. According to the counterpart theory of David Lewis, the objects should be regarded as similar rather than identical.

Simulated Reality Theory
One theory which has caught the public imagination is that of simulated reality – perhaps because this theme has been explored in Hollywood movies and science fiction literature.

Simulated reality is the hypothesis that reality could be simulated - for example, by computer simulation - to a degree indistinguishable from ‘true’ reality. It could contain conscious minds which may or may not be fully aware that they are living inside a simulation. This is quite different from the current, technologically achievable concept of virtual reality. 

Virtual reality is easily distinguished from the experience of actuality - participants are never in doubt about the nature of what they experience. Simulated reality, by contrast, would be hard or impossible to separate from ‘true’ reality. There has been much debate over this topic, ranging from philosophical discourse to practical applications in computing.

The simulation theory is explained in a number of different ways. In brain-computer interface simulations, each participant enters from outside, directly connecting their brain to the simulation computer. 

The computer transmits sensory data to the participant, reads and responds to their desires and actions in return; in this manner they interact with the simulated world and receive feedback from it. The participant may be induced by any number of possible means to forget, temporarily or otherwise, that they are inside a virtual realm (i.e. ‘passing through the veil’ - a term borrowed from Christian tradition, which describes the passage of a soul from an earthly body to an afterlife). 

While inside the simulation, the participant's consciousness is represented by an avatar, which can look very different from the participant's actual appearance. In a virtual-people (or artificial consciousness) simulation, every inhabitant is a native of the simulated world. They do not have a ‘real’ body in the external reality of the physical world. Instead, each is a fully simulated entity, possessing an appropriate level of consciousness that is implemented using the simulation's own logic (i.e. using its own physics). As such, they could be downloaded from one simulation to another, or even archived and resurrected at a later time. It is also possible that a simulated entity could be moved out of the simulation entirely by means of mind transfer into a synthetic body.

The simulation hypothesis was first published by Hans Moravec, and later expanded upon by the philosopher Nick Bostrom, who developed an expanded argument examining the probability of our reality being a simulacrum. His argument states that at least one of the following statements is very likely to be true:
  • Human civilization is unlikely to reach a level of technological maturity capable of producing simulated realities, or such simulations are physically impossible to construct
  • A comparable civilization reaching aforementioned technological status will likely not produce a significant number of simulated realities (one that might push the probable existence of digital entities beyond the probable number of "real" entities in a Universe) for any of a number of reasons, such as, diversion of computational processing power for other tasks, ethical considerations of holding entities captive in simulated realities etc
  • Any entities with our general set of experiences are almost certainly living in a simulation

Computationalism is a philosophy of mind theory stating that cognition is a form of computation. It is relevant to the simulation hypothesis in that it illustrates how a simulation could contain conscious subjects, as required by a ‘virtual people’ simulation. For example, it is well known that physical systems can be simulated to some degree of accuracy. If computationalism is correct, and if there is no problem in generating artificial consciousness or cognition, it would establish the theoretical possibility of a simulated reality. 

However, the relationship between cognition and phenomenal qualia of consciousness is disputed. It is possible that consciousness requires a vital substrate that a computer cannot provide, and that simulated people, while behaving appropriately, would be philosophical zombies. This would undermine Nick Bostrom's simulation argument - we cannot be a simulated consciousness, if consciousness, as we know it, cannot be simulated. However, the sceptical hypothesis remains intact, we could still be envatted brains, existing as conscious beings within a simulated environment, even if consciousness cannot be simulated. A decisive refutation of any claim that our reality is computer-simulated would be the discovery of some uncomputable physics, because if reality is doing something that no computer can do, it cannot be a computer simulation.

A dream could be considered a type of simulation capable of fooling someone who is asleep, as stated by Descartes, who claimed ‘there are no certain indications by which we may clearly distinguish wakefulness from sleep"’ and goes on to conclude that ‘It is possible that I am dreaming right now and that all of my perceptions are false’.

Chalmers (2003) discusses the dream hypothesis, and notes that this comes in two distinct forms: (a) that he is currently dreaming, in which case many of his beliefs about the world are incorrect; or (b) that he has always been dreaming, in which case the objects he perceives actually exist, albeit in his imagination. Both the dream argument and the simulation hypothesis can be regarded as sceptical hypotheses; however in raising these doubts, just as Descartes noted that his own thinking led him to be convinced of his own existence, the existence of the argument itself is testament to the possibility of its own truth. Another state of mind in which some argue an individual's perceptions have no physical basis in the real world is called psychosis though psychosis may have a physical basis in the real world and explanations vary.

Nested simulations work on the principle that the existence of simulated reality is unprovable in any concrete sense: any ‘evidence’ that is directly observed could be another simulation itself. In other words, there is an infinite regress problem with the argument. Even if we are a simulated reality, there is no way to be sure the beings running the simulation are not themselves a simulation, and the operators of that simulation are not a simulation. Pooch & Sullivan (2000) state ‘recursive simulation involves a simulation, or an entity in the simulation, creating another instance of the same simulation, running it and using its results’.

As to the question of whether we are living in a simulated reality or a 'real' one, the answer may be 'indistinguishable', in principle. In a commemorative article dedicated to the 'The World Year of Physics 2005', physicist Bin-Guang Ma proposed the theory of 'Relativity of Reality', which works on the same notions which appear in ancient philosophy: Zhuangzi's 'Butterfly Dream', and analytical psychology. Without special knowledge of a reference world, one cannot say with absolute sceptical certainty one is experiencing ‘reality’.

Dreaming & Reality in Popular Culture
In Lewis Carroll's Through the Looking-Glass (1871), Alice finds the Red King asleep in the grass; Tweedledum and Tweedledee tell her that the Red King is dreaming about her, and that if he were to wake up she would ‘Go out - bang! - just like a candle....’ A similar theme is explored in The Legend of Zelda: Link's Awakening (1993), told from the perspective of the dreamer in his own realm of dreams.

In the movie The Matrix (1999), machines imprison the human race and plug them into ‘the Matrix’ which is an enormous machine system, using human bioelectricity and body heat as a biological battery to power the machines. Connected to the Matrix, the humans are kept in a dream-like state, in which they dream of being in the world as it is today; they have no reason to suspect that it is anything other than the real world. Certain people sense the innate artificiality of the illusion and, through various means, ‘wake up’, breaking free of the Matrix. The overall theme of the series is the ‘waking dream’ scenario, and speculations on which reality is preferable. 

This concept is further explored during the first sequel, The Matrix Reloaded (2003), where one of the main characters appears to be able to utilize abilities usually used in the ‘dream’ in what the character currently believes is ‘reality’, leaving the viewer to question if the character is in fact in reality, or if they are still inside the dream.

In the original television series The Twilight Zone, the episode ‘Shadow Play’ (S02E26, written by Charles Beaumont, originally aired 5 May 1961) concerns a man trapped in a recurring nightmare in which he dreams he is a prison inmate sentenced to death and to be executed; he tries to convince the characters in his dream that they are only figments of his imagination and that they will cease to exist if the execution is carried out. 

In the Star Trek: Deep Space Nine episode 'Far Beyond the Stars' (S06E13), after losing a close colleague in the Dominion War, Captain Sisko confides in his father about leaving Starfleet. Sisko suddenly experiences visions that he is an African-American named Benny Russell who lives in 1950's America and writes stories for a science-fiction pulp magazine. Inspired by a drawing of a space station, Benny writes a story about a Captain Sisko, set on Deep Space Nine, in a future where the racial prejudices of the period no longer exist. Benny then faces backlash from the publishers who refuse to run a story about a black Captain resulting in Benny suffering a nervous breakdown. The episode left it ambiguous whether Sisko's life in the 24th century is real or the result of imagination combined with mental illness. 

Richard Linklater's Waking Life (2001) deals mostly with this subject, revolving around a man being aware of having been trapped inside his own dream. In the Buffy the Vampire Slayer episode ‘Normal Again’ (S06E17), Buffy is poisoned by a demon, causing her to flash between her life as usually portrayed on the series and another reality, where she has been in a mental institution for 6 years for believing the original reality. The viewer and Buffy herself are presented with uncertainty as to which reality is the hallucination; Buffy even mentions that she was institutionalized after she saw her first vampire and wonders whether she might have been hallucinating a life with exciting, supernatural elements since then (her psychologist discusses how Buffy had snapped back to ‘reality’ for a few months, corresponding to the period when Buffy the Vampire Slayer was dead in the show's usual narrative). The non-supernatural world has both her parents alive and together. Both realities appear completely plausible, in a paradox of sorts. She opts for the world with no vampires or other supernatural beings, as her life as a Slayer is full of pain and grief. However, when her mother tells her she is strong and capable, she returns to her ‘Slayer’ reality. The last scene shows her sitting in the mental institution, in a vegetative state and hallucinating her life as a Slayer.

Christopher Nolan's movie Inception (2010) deals with the fictional science of shared dreaming. The characters enter others' minds, to steal ideas, or in the rare case of inception itself, plant them while the target is unaware they are dreaming. Once in a dream, the characters can enter other layers or dreams within dreams. In the movie, characters can distinguish a dream by using totems - unique items whose properties and behaviour are different in a dream than in the waking world. In the end, the film leaves open the question of whether the protagonist is himself dreaming. Films such as Total Recall (1990) and Blade Runner (1982), which are both based on stories by Philip K. Dick, also hinge upon the idea that what you remember and perceive is not always real.

Metal Gear Solid 2: Sons of Liberty (2001) greatly explores the protagonist Raiden's (and by extension, the player's) diminished sense of reality, and that what you perceive may not be what is truly reality, whilst in Ted Dekker's Circle Series (2004 onwards), the protagonist wakes up in an alternate reality every time he goes to sleep. 

Doctor Who explores the idea of the dream argument many times. In the ‘Forest of the Dead’ (S04E09) the Doctor's companion Donna is ‘saved’ into the Library's hard-drive and begins to live out an imaginary and fake reality. Unaware that the reality she is living in an illusion until a disfigured woman who had been killed in the ‘real’ world and respectively submitted into the hard-drive convinces her that her life is not real. In ‘Amy's Choice’ (S05E07) the two companions of the Doctor, Amy and Rory Pond, have to decide between two realities - one where they are happily married and the other where they are still travelling with the Doctor, and the only way to escape is to kill yourself in the fake reality. Since they are not sure which one is fake and which is real, they are hesitant to choose. In the 2014 Christmas Special, ‘Last Christmas’ (E253), this concept is once again explored, when an alien species latches onto human brains in order to devour it, but makes the victim dream so that he is unaware while they digest. Similar to Inception, it explores the ideas of shared dreaming and the main characters question whether they're awake or still in a dream. The Doctor points out there are multiple ways to determine the answer, such as asking questions that you do not know the answer to, having different people read the same book and discover that the text is different, or even the appearance of fictional characters, such as Santa Claus.

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