Observable Universe Expansion: Age vs. Current Size Explained
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Observable Universe Expansion: Age vs. Current Size Explained
Clip title: If the universe is only 14 billion years old, how can it be 92 billion light years wide? Author / channel: Fermilab URL: https://www.youtube.com/watch?v=vIJTwYOZrGU
Summary
The video addresses a fascinating paradox in cosmology: how can the observable universe be approximately 92 billion light-years wide when it is only 13.7 billion years old? Dr. Don Lincoln from Fermilab initiates the discussion by explaining that looking into space is akin to looking back in time, as light takes a finite amount of time to travel. He introduces the concept of a “light-year,” which measures both distance and time, representing the distance light travels in one year. Based on the universe’s precisely measured age of 13.7 billion years, a naive calculation might suggest a visible radius of 13.7 billion light-years. However, the video immediately clarifies that this simple assumption is “completely wrong” due to the dynamic nature of the universe.
The discrepancy arises from the universe’s continuous expansion since the Big Bang. While light from the earliest epoch (the Cosmic Microwave Background, emitted when the universe was only about 380,000 years old) has been traveling for 13.7 billion years, the space it traverses has been stretching. Crucially, about 5 billion years ago, a mysterious force known as dark energy became dominant, causing the universe’s expansion to accelerate. Therefore, the region of space that originally emitted the light we now see as the CMB, which was initially only about 42 million light-years away, has since stretched significantly. Due to this ongoing and accelerating expansion, that original point in space is now approximately 46 billion light-years away from us, making the current diameter of the observable universe roughly 92 billion light-years.
This accelerating expansion leads to several mind-bending implications. We see distant objects not as they are now, but as they were in their distant past. Furthermore, objects that are currently more than about 15 billion light-years away are receding from us at speeds such that their light, even if emitted now, will never reach us. This means there’s a cosmic horizon beyond which we can never observe new events. The video emphasizes that we are continuously losing sight of distant galaxies as they accelerate beyond our observable universe – indeed, an estimated 20,000 stars slip from our view every second. Ultimately, in the distant future, the accelerating expansion will ensure that humanity will only be able to see galaxies within our local group, with all other galaxies having expanded out of our observable horizon.
Video Description & Links
Description
The size and age of the universe seem to not agree with one another. Astronomers have determined that the universe is nearly 14 billion years old and yet its diameter is 92 billion light years across. How can both of those numbers possibly be true? In this video, Fermilab’s Dr. Don Lincoln tells you how.
For further information, see http://www.fnal.gov
Tags
Physics, Size of the universe, age of the universe, cosmic microwave background radiation, cmb, expansion of the universe, general relativity, dark energy, mysteries of the universe, Fermilab, Don Lincoln, Ian Krass, cosmic, microwave, background, science, learn, explained, how, why, lightyear, light, year, space, earth, expansion, universe, stars