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What is a universe, that is what is a universe in its general definition?

First, a stock universe is comprised of things like galaxies that undergo formation and changes across vast spans of time, so an observer (similar to us) basically cannot directly determine the formation, the evolution, the changes that occur in a universe. Direct knowledge that we are so accustomed to in our daily existence cannot be obtained about a universe. We cannot reach out and measure it, take a picture that captures its wholeness, put it on a scale, or gather a sampling of all its facets. Everything a sentient observer may know is based on estimation and extrapolation of facts gathered during a small portion of a fraction of a blink in the cosmic timeline.

*NOTE: **many vCalc equations are embedded throughout vCalc descriptive pages like this page. Even though they may not stand out in the text, if you hover over the name of an equation it will likely be linked to an actual, pop-up executable equation. For example: [Equation Not Found]*

A universe is fundamentally characterized by time and matter and the closely related energy. Einstein's relativity theories bound these two basic elements of a universe together as the conceptual spacetime and so they remain today in our present science understanding.

Remember, this is being written in the Spring of 2017 as science continues to advance. New revolutions, new paradigm shifts will bring us a different picture than we have today and, at the same time, that picture will be based on what we know in the Spring of 2017, just as our knowledge today is based on the gathered knowledge of Copernicus and Galileo and Newton and Einstein and Faraday and Planck and Boltzmann and Euler and Hertz and Michelson and Hawking and ...

One way to describe a Universe is to describes it's basic metrics. We measure it in estimations and extrapolations.

A universe has dimension, although some theories hold that many of a universe's dimensions are infinite. Nonetheless, we estimate. We estimate the dimensions of the "observable universe." We estimate its mass, we estimate its widths. We estimate its age.

Note that I said "observable universe" because many theories characterize the extent of the universe as infinite and always expanding. And if the universe has infinite size, within that infinite space is infinite mass and infinite energy and infinite beauty.

There are many characteristic attributes of a universe but we'll start with the obvious ones that help us first visualize and define a universe:

- Age of the Universe - [Constant Not Found]
- Diameter of the Universe - 8.8E26 m
- Mass of the Universe - 6.0E51 kg
- Density of the Universe - 3.0E-28 kg/m³
- Temperature of the Universe - 2.72548 K
- Rate of expansion of the Universe - 67 km/sfor every ,illion parsecs of distance from the observer

Since in many theories things, like the universe itself, exist because we perceive them. I find it interesting to ponder just exactly what we are seeing.

We perceive things with our senses, and beyond our senses we are able to perceive many spectrums within the electromagnetic spectrum using sensor devices tuned to specific ranges of that spectrum. In the figure below, and thanks to NASA, we see our own Milky Way illuminated in 10 different parts of the electromagnetic spectrum.

Our human senses cannot see the infrared range but seeing the Milky Way in infrared emanations paints the background "in a different light."

The image above shows several ways we can view the universe -- literally -- as NASA has so kindly provided a set of comparative images of our own Milky Way galaxy.