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Introduction to Virtual Worlds

What is a virtual world? In this article, we discuss the virtual world with reference to Milgram's Continuum and real examples.

What is a virtual world?

A virtual world is a three-dimensional virtual space that can be populated by people, objects and locations.

It can be distinct or seamlessly integrated with the real world, and responds to actions and interactions by users who experience it.

A virtual world possesses certain features like:

  • It is three-dimensional
  • It is populated with entities that serve a purpose determined by the creator of the world
  • It responds to user’s presence and actions by transforming in some way
  • It is mediated through a computing system

There are alternative definitions of virtual worlds. These focus on user-avatars, persistence and networked systems. Our definition of a virtual world does not preclude any of these virtual worlds.

Instead, it focuses on dimensionality as a key feature of the world. Virtual Reality (VR) and Augmented Reality (AR) are the two most well-recognized approaches for experiencing virtual worlds. To understand these, we first need to explore Milgram’s reality-virtuality continuum.

Milgram’s Continuum

The concept of a reality-virtuality continuum was introduced by Paul Milgram and Fumio Kishino in 1994 (see Figure 1).

The continuum classifies a virtual world system based on the interplay between the real environment, the virtual environment and the resulting virtual world.

Towards the left edge of the continuum is the ‘real environment’ with practically no computer-generated content in it. Towards the right edge, we have a ‘virtual environment’ constituted entirely of computer-generated content.

The Milgram's continuum Figure 1: The concept of Milgram’s continuum (proposed by Paul Milgram and Fumio Kishino, 1994)

In the middle region of the continuum, we have augmented reality (AR) and augmented virtuality (AV). The term “augmented” is used to show that real-world objects and virtual content co-exist to create the user’s experience of the virtual world.

The original continuum considered visual elements only. However, if we include input modalities, most modern-day VR systems sit in the AV region of the continuum. Let’s look at some examples and position them on the continuum (see Figure 2).

This will help us understand the continuum better.

RV Continuum sample in virtual world Figure 2: RV Continuum with examples of virtual worlds

Projection AR has virtual content overlaid directly onto real-world objects. This alters the appearance of real-world objects. The overlay can also lead to a change in people’s thinking about how to use the object (see Figure 3).

Projection AR Figure 3: Projection AR transforms the Berliner Dom into a word cloud (Source:

The Microsoft HoloLens (see Figure 4), is an example of “see-through” AR. The user of the HoloLens sees and interacts with the real world as well as with a superimposed layer of computer-generated content.

Hololens in AR and VR Figure 4: Hololens for Augmented and Virtual Reality (Source:

Smartphone or tablet AR (see Figure 5) is called “video AR”. The real world is captured as a video and the virtual content is overlaid onto it. The screen of a smartphone or tablet serves as the window through which the user sees the virtual world.

Augmented reality medical 3D Figure 5: Augmented Reality Medical 3D Science (Source:

The “First Contact” application on the Oculus platform (in Figure 6) and the fully immersive social VR such as VRChat (see Figure 7) can be positioned on the virtual end of the curve.

First Oculus contact Figure 6: ‘First Contact’ applications on Oculus Rift (Source:

The designer of a virtual world decides which part of the continuum is best suited for the experience they wish to deliver. The designer also identifies what virtual content needs to be generated and how it behaves and interacts with the user and the real world.

These design choices are critical for creating compelling VR and AR interactive experiences for the users of the virtual worlds.

VRChat environment Figure 7: VRChat environment

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