e-den physics

Introduction

Although some artificial life projects (such as Conway's Life) have an underlying set of laws that allow replicators to emerge spontaneously, current limitations of computer speed and memory usually prevent such replicators from displaying complex neurological behaviours. Accordingly, e-den grafts biological rules onto a simplified physics that could not, in itself, support that biology; there has been no attempt to demonstrate that biology and neurology can emerge from physics. Because the digital world of e-den runs on a physical computer according to defined rules, the program demonstrates that Life can ride on a deterministic, reductionistic substrate but ironically, within the context of its own physics, Life is an inexplicable, vitalistic addition.

At the physical level, all Bugs share the same 2-dimensional grid. It is within this Grid that they move, feed and interact; this is the only world that they see. The internal characteristics of each organism, however, exist in a separate biological domain. Although a few private internal parameters can be sensed by an individual organism, and acted upon, the process that adjusts their internal sensors to match those parameters is not derivable from the physics of the Grid nor accessible to the organisms themselves. Their brains, their metabolism and their genes are not made of the same physical stuff as the Grid and are not even located within the Grid itself.

Not only is Bug biology not derivable from Bug physics, but causality in the Grid often flows the "wrong way", from biology to physics. Entities that we would normally consider high-level and emergent, like Life, produce elementary forces in the Grid, controlling the charges and the movements of atoms. Whereas Earth physics is the same for both living and dead matter (some quantum physicists might disagree), the physical laws of the Grid draw a fundamental distinction between the two.

The Physics of Inanimate Matter.

In the absence of Life, the physics of the Grid are very simple. The universe is a two-dimensional array of digits which may range from 0 to 9. Zeros are equivalent to empty spaces; other digits are equivalent to atoms. Only one atom at a time may occupy a single space and if one atom is pushed onto another, the second is usually pushed away. If this is not possible, because there is no vacant space nearby, the smaller of the two atoms (the lower digit) is destroyed.

Atoms can be considered to have mass-energy, charge and colour. Their mass-energy is proportional to the digit used to represent them. In tdvantage he original version of e-den, the energy of an atom was equal to its mass but was expressed in energy units that were each one-tenth of a mass unit (for example, a 4 atom had a mass-energy of 4 mass units or 40 energy units.

THIS HAS RECENTLY CHANGED. The energy e of an atom of mass m is now given by the equation: e = 10 x 2^m

(This relationship was changed to make corpses more energetically attractive for a carnivore. Although a carnivore recives most of a victim's enregy stores in the event of a conflict it previously received little reward if the victim died before the encounter... For instance, when the carnivore chased the victim into an obstacle. Also, victims running along with low energy stores were hardly worth catching. This meant that there was an evolutionary trend for carnivores to devolve into omnivores or herbivores. Now, at least, the corpses themselves are worth consuming, with one 6 atom being equivalent to 32 1-atoms. If the current batch of beta-testers feel a different ratio would be better, let me know.

The colour of an atom is determined by the digit and therefore directly reflects its mass : there are nine basic colours (colour 1 to colour 9), with zeroes being invisible. (It would be just as valid to say that atoms were colourless but their mass was visibly apparent in some other way - on the basis of size, for instance). In graphical representations of the Grid, the following colour associations have been adopted : 1s are white, 2s dark blue, 3s light blue, 4s red, 5s green, 6s yellow, 7s light grey, 8s dark grey and 9s black.

The charge of an atom is always 'neutral' for inanimate matter. This is represented within the software as a negative digit but this can become confusing because positive digits repel negative digits and negative digits exert no force at all; thus, this document refers to charged (*1-*9) and uncharged atoms (1-9). Like an atom's mass, the charge of an atom is visible but, because of the default wiring of the Bug retina, the visual distinction between the charged and uncharged states is not usually as great as that between colours. *3 and 3 are hence like two different shades of the same colour

There are 18 potential combinations of mass/colour and charge/shade, as well as the invisible zero, giving 19 possible physical states for each space in the Grid.

Theoretically, all mass-energy in the Grid comes from radiant energy that continuously bathes every square. This radiant energy is capable of lifting the energy state of a square by one mass unit: from 0 to 1, from 2 to 3 and so on, but this becomes progressively less likely for higher energy states. Usually it is only the first energy transition, from 0 to 1, that occurs with appreciable frequency. The observer readily observes that, as time proceeds, 1 atoms appear spontaneously in vacant spaces. Such atoms are the ultimate source of all organic energy and hence function as the base of the food chain, much like grass or plankton. This precipitation of matter from the background radiation is more likely in the spaces adjacent to existing 1s, so that 'grass' usually grows along an advancing edge, like a crystal emerging from a supersaturated solution. For the less common energy transitions, from 1 to 2 and from 2 to 3 and so on, a similar prerequisite exists - an adjacent atom that is already in the higher state must be present to guide thee transition. Thus, new 2s usually appear where a 1 atom is adjacent to an existing 2; new 3s where a 2 is next to an existing 3, and so on.

The amount of energy bathing the world during each moment - and hence the probability that a vacant space may turn into a 1 atom - is expressed as a parameter called 'climate'. Favourable climates (high values) produce greater quantities of grass at the base of the food chain and hence support greater populations of organisms.

At low levels of climate, these processes reverse so that all atoms have a tendency to fall back into lower energy states and, in particular, grass is replaced by empty space. This process of 'die-back' becomes increasingly likely in any one space as the climate falls below 20. Thus, in the long term, life is only sustainable at climates above 20. Climates lower than this are primarily useful for reducing excessive populations.

In the absence of life, with climates greater than 20, the Grid eventually fills with neutral atoms and initially the vast majority of these are 1s. Eventually deposits of more massive atoms accumulate and grow very slowly. Apart from this, no atoms move and the universe is static.

The Physics of Animated Matter

When Life is added, however, new forces are created. Atoms that are part of a living organism are charged; they exert a repulsive force on neutral atoms and, sometimes, on other charged atoms. They form chains of linked atoms and move together, more like molecules than lone atoms. These 'molecules', the organisms bodies, not only contain the mass-energy of their individual atoms but also a variable amount of surplus energy that powers the organisms actions, keeping it alive and maintaining its charge. When the organism dies, its atoms break their bonds and become neutrally charged.

The fact that the charged body of an organism repels neutral atoms means that organisms are usually surrounded by a clear zone, or force field, which is one space thick. Since organisms may only move one space at a time, they usually move into spaces that are vacant. There are two exceptions to this.

Firstly, the repulsive force exerted by a charged atom depends upon its overall mass or charge, and is much greater for a *9 than a *1. A charged atom can only repel a neutral atom that is lighter than itself, is the same mass, or is at most one unit more massive: a *6 may repel a 7 or anything lighter, a *5 may repel a 6 or anything lighter, and so on. If a neutral atom is too massive to be repelled, it stays in the organism's force field, a situation that may be injurious or even fatal to the organism.

Secondly, by mutual consent, two organisms may allow their force fields to overlap, so that their charged atoms lie next to each other, or with only a single shared space between them. The force field of each organism then impedes the movement of its neighbour, so that the two consenting organisms cannot push against each other any further and cannot disrupt each other's structural integrity. In this situation, they are selectively paralysed and only movements away from the other organism succeed. If, at any stage, either organism withdraws its consent for the overlap, the two force fields come into conflict and the situation can only be resolved with the death of one of the organisms. The corpse of the loser becomes neutral, is pushed out of the victor's force field like any other dead matter and the victor is free once more to move in any direction.

An organism's force field is thus, to some extent, adjustable: although it always repels neutral atoms, the degree to which it repels other organisms is under each organism's control. The tolerance of a force field to neighbouring organisms is referred to as its 'friendliness', which can range in value from -10 to +10. Unfriendly force fields, with negative values for friendliness, cannot remain in contact for more than a moment. As soon as they touch, one organism dies. The loser's energy flows through the point of contact into the victor; its atoms lose their charge and are either consumed or repelled. Which of the two organisms dies depends on many factors, including the friendliness of each organism, their metabolic well-being and the particular atoms coming into contact.

Apart from introducing positive charge and repulsive forces, the presence of Life has other physical effects on the Grid: it encourages more frequent interconversion of mass and energy. Four processes in the Bugs' Grid involve such a conversion. The first, already discussed, is the spontaneous growth of 'grass' from the radiant energy bathing the Grid; this occurs even in the absence of Life (so 'grass' is not actually alive). The second process occurs during the growth of organisms, when they convert their energy stores into new charged atoms as they increase in size. The third process involves the voluntary conversion of stored energy into neutral matter, allowing an organism to deposit new atoms in the Grid. The fourth, analogous to eating, occurs when an organism annihilates a neutral atom and consumes its energy. This process can only occur within the field of a three-atom, which thus functions something like a digestive cell or like the chlorophyll of plants. The most massive neutral atoms (7, 8 and 9) are not susceptible to this process and are thus 'inedible' or 'inorganic'.

Unlike inanimate matter, living matter can move spontaneously. No atom bears momentum so that, in the absence of a new force being applied, an atom falls still again immediately after being moved. Most often, an organism moves into a space already cleared by its force field. If the movement results in two atoms competing for the same space, however, the neutral atom must be displaced or the organism dies. Whether the organism is able to push the obstruction away depends on the relative masses of the two atoms involved. The velocity of all motion in the Grid is the same: one square per moment. Organisms can only move more slowly than this by moving intermittently. Because the organisms pay an energy penalty based on the number of recent moves, such slow, intermittent movement is energetically favourable.

The Grid supports entities equivalent to light and sound, so that Bugs can potentially 'see' and 'hear'. Light is radiated (or reflected) from all atoms; its colour and shade is determined by their mass and charge. Light is radiated only in the four cardinal directions, however, north, south, east and west. It is visible up to 50 squares away but only along uninterrupted lines; any atom other than a 1 obscures the view of atoms further along the line. Atoms of grass (1s) do not obstruct the line of sight but emit their own signal, so that, in any one direction, an organism can see the nearest grass atom (if it is not itself obscured) as well as the first large atom behind it. Sound is produced whenever an organism moves; the sound is louder for larger organisms, is detectable up to 50 squares away, and fades away over 5 moments if the organism is still.

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