Mengenal Kosmologi Non-Standar

A non-standard cosmology is any physical cosmological model of the universe that has been, or still is, proposed as an alternative to the Big Bang model of standard physical cosmology. 

In the history of cosmology, various scientists and researchers have disputed parts or all of the Big Bang due to a rejection or addition of fundamental assumptions needed to develop a theoretical model of the universe. 

From the 1940s to the 1960s, the astrophysical community was equally divided between supporters of the Big Bang theory and supporters of a rival steady state universe.

It was not until advances in observational cosmology in the late 1960s that the Big Bang would eventually become the dominant theory, and today there are few active researchers who dispute it.

The term non-standard is applied to any cosmological theory that does not conform to the scientific consensus, but is not used in describing alternative models where no consensus has been reached, and is also used to describe theories that accept a "big bang" occurred but differ as to the detailed physics of the origin and evolution of the universe. 

Because the term depends on the prevailing consensus, the meaning of the term changes over time. For example, hot dark matter would not have been considered non-standard in 1990, but would be in 2010. 

Conversely a non-zero cosmological constant resulting in an accelerating universe would have been considered non-standard in 1990, but is part of the standard cosmology in 2010.

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Before observational evidence was gathered, theorists developed frameworks based on what they understood to be the most general features of physics and philosophical assumptions about the universe. 

When Albert Einstein developed his general theory of relativity in 1915, this was used as a mathematical starting point for most cosmological theories including the Big Bang and the Steady State theories.

In order to arrive at a cosmological model, however, theoreticians needed to make assumptions about the nature of the largest scales of the universe. The assumptions that the Big Bang relied upon are:

1. the universality of physical laws – that the laws of physics don't change from one place and time to another,
2. the cosmological principle – that the universe is roughly homogeneous and isotropic in space though not necessarily in time, and
3. the Copernican principle – that we are not observing the universe from a preferred locale.

These assumptions when applied to the Einstein field equations naturally result in a universe which has the following features:

1. an expansion of the universe,
2. the universe emerging from a hot, dense state at a finite time in the past,
3. the lightest elements were created in the first moments that time existed as we know it, and
4. a cosmic microwave background pervading the entire universe should exist, which is a record of a phase transition that occurred when the atoms of the universe first formed.

These features were derived by numerous individuals over a period of years; indeed it was not until the middle of the twentieth century that accurate predictions of the last feature and observations confirming its existence were made. Non-standard theories developed either by starting from different assumptions or by contradicting the features predicted by the Big Bang.

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