The universe's age is hidden in a single expansion number
In short: How long has the universe existed? By taking the reciprocal of one specific constant, astronomers can estimate our cosmic history. This value, known as the Hubble constant, measures how fast galaxies are receding from Earth, providing a fundamental yardstick for the scale and age of everything we see.
In 1929, Edwin Hubble first identified a straight-line correlation linking how far galaxies are from us to their speed. Such findings confirmed that our universe is currently growing larger. The proportionality constant in this relationship is the Hubble constant (H0). By calculating the reciprocal of this constant, scientists can derive an approximate age for the universe, which currently sits between 13 and 14 billion years.
However, pinning down the exact number is one of modern astronomy's greatest challenges. A significant discrepancy exists known as the "Hubble tension." While fundamental physics suggests a value around 68 km/s/Mpc, observational data varies wildly. For instance, a landmark 2001 measurement by Wendy Freedman found a value of 72, while more recent observations of exploding stars suggest 69.8 km/s/Mpc, with other reports reaching as high as 74 km/s/Mpc.
These small differences—as little as 2 km/s/Mpc—are profound. They imply that our current understanding of physics might be missing something major, such as new particles or a previously unknown form of dark energy. This tension highlights the gap between what our theories predict and what we actually observe in the cosmos.
The Hubble Space Telescope has been instrumental in this journey. Since its launch, it has revolutionized our understanding of cosmic age and celestial bodies. It even facilitated the first observation of two astronomical objects colliding when it captured fragments of comet Shoemaker-Levy 9 hitting Jupiter.
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Sources
- Summary by Intellect · source: Hubble Time
- Also: Hubble time | astronomy | Britannica
- Also: What is the Hubble constant? | University of Chicago News
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