How do we measure the vastness of space? In billions of light years? How do we quantify it?

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"Because of the connection between distance and the speed of light, this means scientists can look at a region of space that lies 13.8 billion light-years away. Like a ship in the empty ocean, astronomers on Earth can turn their telescopes to peer 13.8 billion light-years in every direction, which puts Earth inside of an observable sphere with a radius of 13.8 billion light-years. The word "observable" is key; the sphere limits what scientists can see but not what is there.

But though the sphere appears almost 28 billion light-years in diameter, it is far larger. Scientists know that the universe is expanding. Thus, while scientists might see a spot that lay 13.8 billion light-years from Earth at the time of the Big Bang, the universe has continued to expand over its lifetime. If inflation [see below] occurred at a constant rate through the life of the universe, that same spot is 46 billion light-years away today, making the diameter of the observable universe a sphere around 92 billion light-years. [VIDEO: Oldest Light in the Universe: How it Traveled to Us: https://www.youtube.com/user/VideoFromSpace 
]

[...]

Even bigger?

Scientists measure the size of the universe in a myriad of different ways. They can measure the waves from the early universe, known as baryonic acoustic oscillations, that fill the cosmic microwave background. They can also use standard candles [see below], such as type 1A supernovae, to measure distances. However, these different methods of measuring distances can provide answers.

How inflation is changing is also a mystery.

["Inflation": "According to the theory of inflation, the early Universe expanded exponentially fast for a fraction of a second after the Big Bang.": 
https://www.ctc.cam.ac.uk/outreach/origins/inflation_zero.php
]

While the estimate of 92 billion light-years comes from the idea of a constant rate of inflation, many scientists think that the rate is slowing down. If the universe expanded at the speed of light during inflation, it should be 10^23, or 100 sextillion.

Instead of taking one measurement method, a team of scientists led by Mihran Vardanyan at the University of Oxford did a statistical analysis of all of the results. By using Bayesian model averaging, which focuses on how likely a model is to be correct given the data, rather than asking how well the model itself fits the data. They found that the universe is at least 250 times larger than the observable universe, or at least 7 trillion light-years across.

"That's big, but actually more tightly constrained that many other models," according to MIT Technology Review, which first reported the 2011 story.

Extract source:
https://www.space.com/24073-how-big-is-the-universe.html

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Map of the Universe based on the cosmic microwave background temperature. Scroll down to the "Summary" heading to see the image label:
Image:
The Cosmic Microwave Background temperature fluctuations from the 7-year Wilkinson Microwave Anisotropy Probe data seen over the full sky.: 
https://en.wikipedia.org/wiki/File:WMAP_2010.png

This post was edited by Robert at August 3, 2021 4:32 PM MDT