# What is Animated Physics

The words of Erwin Schrödinger (ca. 1887–1961):

The world extended in space and time is but our representation.

Animated physics is about programming computer animations based on the laws of physics. Gravity is probably one of the easiest and most fun computer animations to work on. Set a bunch of objects in motion and see what happens. Maybe add in a size for the objects and get some crashes, or add some walls and see these things bounce around.

In his Autobiographical Notes in 1949, Einstein wrote of the special theory:

It is striking that the theory introduces two kinds of physical things, i.e., (1) measuring rods and clocks, and (2) all other things, e.g., the electromagnetic field, the material point, etc.

Animated physics uses fixed grids and fixed time steps, similar to frames in a movie. For any number of objects, we display the objects where they are, calculate where they will get to based on their properties and display a new frame. For each object, we assign a name, a location, and location in the prior frame. From there we add in what is needed. Perhaps a mass, perhaps a charge, maybe both or more. Animate this based on the laws of physics and watch what happens.

## Time, Motion and a Deterministic World

Conventional modern physics has a basis in equations of motion to model the particles and forces of matter and energy. These equations tell you where a particle is (or in the case of Quantum Mechanics, the probability of a particle being somewhere) at a particular time. For example, The equation of an ellipse is used to show the orbit of a planet. Plug in the time and out comes the exact location of the planet.

The difficulty with using equations to describe motion was first laid out in a paradox by Greek philosopher Zeno of Elea (ca. 490–430 BC) as Aristotle (ca. 384–322 BC) recounts:

In a race, the quickest runner can never overtake the slowest, since the pursuer must first reach the point whence the pursued started, so that the slower must always hold a lead.

You can never get anywhere because in half the time you will only be half way there. The paradox highlights the notion that the concepts of time and motion are never properly and completely defined.

In addition to the time and motion paradox, is the problem of a deterministic world. Is everything that happens in the future, pre-determined by what has happened in the past? The exact nature of mathematical equations leads to the conclusion that either the world is deterministic, or probabilities must be introduced (as in quantum physics). “Does God play dice?”

## Animated Physics is Different

Animated physics offers an alternative to the understanding of conventional modern quantum physics. Here we use a fixed grid and fixed time steps, similar to frames in a movie, to model the particles and forces of matter and energy. You must run the animation for a period of time find out where a particle is at that time. You are not allowed to change the time frame or grid spacing while an animation is running. The grid provides the standard rulers and clocks to measure the world. Distorted grids can be displayed within the grid, but the grid itself does not change. The animations are used to calculate behavior over time to better understand the world around you.

In animated physics you will never know exactly where things are. Your ability to determine the motion of particles is limited by the time and grid spacing you decided on before the animation is started. The world becomes increasingly “fuzzy” in an animated world as calculation errors caused by the selection of time and grid spacing start to accumulate. The world of animated physics is not deterministic. There is always a time and grid spacing smaller then the one you choose that could contain additional hidden variables.

## The Scientific Method

In conventional modern physics, mathematical equations are deemed to be correct if they correctly predict what happens in experiments. New discoveries are made by correctly predicting the behavior of a system. In animated physics, the same scientific method of hypothesis, prediction, testing and analysis is used. Computer animations are deemed to be correct if they correctly predict the behavior of a system over time.