An old philosophical dilemma: how can individuality exist if everything in the universe is connected? Or the other way round: where does connectedness come from if every object is unique? It is usually staged as a paradox. At the technical level it is simply two characteristics of one system.
Here is how it breaks down.
Integrated information theory: two numbers
Back in 1998 Giulio Tononi and Gerald Edelman described consciousness through two properties, integration and differentiation. Tononi later folded them into a single measure, Φ (phi), integrated information, but for our question it helps to pull them apart again.
The first number is integration, which I will write as Φ. It shows how much a system behaves as a single whole.
The second is the diversity of states the system can take. Call it D. It shows how many distinguishable configurations the system can sustain.
These are different quantities, and both are needed.
High Φ with low D gives a monolith like a crystal: unified but monotonous, the same state repeated throughout.
High D with low Φ gives a heap of sand: many parts, each sitting in its own state with no link to its neighbours; varied, but formless.
Consciousness lives where both numbers are high: there are many states, and all of them are bound into one experience.
What this means for unity and multiplicity
The two characteristics complement each other: unity is measured through Φ, multiplicity through D.
A human being is a system with fairly high Φ (the world is experienced as a whole) and very high D (thousands of distinguishable thoughts, feelings and perceptions a day).
A beehive, if you follow the theory's logic, is more integrated than a single bee and less integrated than a human brain, while the diversity of its states is enormous: thousands of bees, each in its own state. Nobody can measure this yet.
The Earth as a living biosphere may sit higher still on both axes. We have no precise figures: measuring Φ for such systems would take instruments that do not exist yet.
Where this gets tested
In small systems Φ can be estimated approximately; Tononi, Boly, Massimini and Koch review these attempts (Nature Reviews Neuroscience, 2016). A derived measure, the perturbational complexity index (PCI), is already used in clinics to assess the level of consciousness in unresponsive patients (Casali et al., Science Translational Medicine, 2013). PCI tells wakefulness apart from sleep, anaesthesia and the vegetative state.
So the quantity can be estimated in practice, if only approximately. Exact computation is impossible; the approximation works.
In this model the philosophical dilemma of "unity or multiplicity" becomes an engineering question: what are this system's Φ and D? Each system occupies its own place on the (Φ, D) plane, and the argument ends there.
What remains open
Why is integration accompanied by experience from the inside? That is David Chalmers's hard problem of consciousness. The theory records the link between Φ and consciousness, but it does not explain why high integration feels like anything.
Chalmers does not say there is no answer. He says that no amount of data about Φ will answer the question of why high Φ is like something from the inside. The question stays open, and that is where the edge of our knowledge runs.
Practical takeaway
When someone tells you "everything is one, everything is connected", ask them to be specific: in what sense, and with what Φ? High Φ means a unified system in which every part carries information about the whole. Low Φ with high D means a collection whose connections are more imagined than real.
This is graph theory applied to connectivity, and it needs no mysticism.
Unity and multiplicity are two coordinates. The only question is where on that plane we happen to be.