The Dust Theory, by Greg Egan, states that:

… there is no difference, even in principle, between physics and mathematics, and that all mathematically possible structures exist, among them our physics and therefore our spacetime. These structures are being computed, in the manner of a program on a universal Turing machine, using something referred to as “dust” which is a generic, vague term describing anything which can be interpreted to represent information; and therefore, that the only thing that matters is that a mathematical structure be self-consistent and, as such, computable. As long as a mathematical structure is possibly computable, then it is being computed on some dust, though it does not matter how much, only that there can be a possible interpretation where such a computation is taking place.

## Dust Theory 101

Let’s attempt to clarify the strong hypothesis of the dust theory:

- In order for a system to be observable from the inside, it needs to be sufficiently
*expressive*to represent a conscious observer with its own symbols. - A conscious observer is thus an
*arrangement*of the symbols inside the system he/she/it exists. *Subjective perception*of one own’s consciousness requires a*sequence*of arrangements.*Causality*over the sequence of arrangements may be due to the rules of the system (*e.g.*it is being computed) but it’s not required (*e.g.*may happen by chance).- From the point of view of the
*subjective observer*, the*specific order*of a sequence of arrangements does not matter, as long as a consistent interpretation of*an arbitrary arrangement*is enough to provide a*self-consistent*history.

The last point can be a little confusing (and wildly controversial), so allow me to illustrate with an example; suppose that a sub-structure of one’s consciousness has the following sequence of states:

```
0. Birth
1. {... 1, 2, 3, 4, 5 ...}
2. {... 2, 3, 4, 5, 6 ...}
3. {... 3, 4, 5, 6, 7 ...}
4. {... 4, 5, 6, 7, 8 ...}
5. Death
```

Each state contains all the information relevant to a subjective observer to perceive self-consciousness, including *one’s relevant memories and external stimuli*. At this point I must establish an important premise, which is that *any universe that produces (either by computation or by chance) the above sub-structure would be producing my own consciousness*.

Note there’s no particular time isomorphism (let alone scale invariance) in this depiction, but if it helps, one can imagine the observer was 20 at state 1, 40 at state 2… However, imagine that a computer (or an arbitrary universe) produces the following:

```
0. Birth
0. LONG PAUSE
1. {... 1, 2, 3, 4, 5 ...}
0. LONG PAUSE
2. {... 2, 3, 4, 5, 6 ...}
0. LONG PAUSE
3. {... 3, 4, 5, 6, 7 ...}
0. LONG PAUSE
4. {... 4, 5, 6, 7, 8 ...}
5. Death
```

If every state produces exactly the same sub-structure, then no matter how fast or slow these sub-structures are being produced, one’s consciousness would still be *experiencing* the same as before. Now imagine the following:

```
0. Birth
4. {... 4, 5, 6, 7, 8 ...}
3. {... 3, 4, 5, 6, 7 ...}
2. {... 2, 3, 4, 5, 6 ...}
1. {... 1, 2, 3, 4, 5 ...}
5. Death
```

Despite the reversed order, if my consciousness relies entirely in any particular “state”, at point 2 one would still be 40, with all the memories present in a non-reversed way. In fact, one can even mix these states or produce them out-of-order, but the *subjective observer* would still be experiencing the same, from its own point of view.

Therefore, we have just excluded *time* (and *causality* along with it) as a requirement for an universe that sustains consciousness. We may still require *time* (and *causality*) to explain the *mechanism of computation* for such states to have unfold, but, from the point of view of the *subjective observer*, it really doesn’t matter.

A similar exercise can be applied to space, allowing us to conclude that the locality of events is unneeded. If one extends this argument even further, and think about the exact symbols used to represent the state of the consciousness, then one would also be forced to accept that there might exist an infinite set of possible isomorphisms which could be interpreted to represent the *same state*, with no impact on the perception of the subjective observer. Eventually, one would be able to claim that the universe might as well be a gigantic *cloud of dust*, with no particular arrangement, that every possible subjective observer would always find himself (along with his memories and external stimuli) either in a specific permutation of the dust particles, or in any of its isomorphisms.

## What Now

There’s a similar theory advanced by Max Tegmark in The Mathematical Universe:

All structures that exist mathematically also exist physically. That is, in the sense that “in those [worlds] complex enough to contain self-aware substructures [they] will subjectively perceive themselves as existing in a physically ‘real’ world”.

Most of the arguments against this kind of rationale base themselves on the impossibility of asserting claims in a kind-of-MUH:

… in a true multiverse theory, “the universes are then completely disjoint and nothing that happens in any one of them is causally linked to what happens in any other one. This lack of any causal connection in such multiverses really places them beyond any scientific support”.

Despite epistemological concerns, the most plausible argument against the dust theory is given by Greg himself:

However, I think the universe we live in provides strong empirical evidence against the “pure” Dust Theory, because it is far too orderly and obeys far simpler and more homogeneous physical laws than it would need to, merely in order to contain observers with an enduring sense of their own existence. If every arrangement of the dust that contained such observers was realised, then there would be billions of times more arrangements in which the observers were surrounded by chaotic events, than arrangements in which there were uniform physical laws.

Which is a kind of distorted anthropomorphic principle; since we are observers, it would be much more probable that the laws of physics would be less strict than those we observe, just to support us as conscious observers.