How can the observable universe be over 90 billion light-years across when the universe is only 14 billion years old?
In: Physics
Based on the measured light spectrum of the star, scientists will know the distance from the earth to the star.
However, some aspects need to be clarified:
First: The age of the universe according to the Big Bang theory is 14 billion years, but there are galaxies more than 14 billion years away. Why? Because the Universe is expanding. This was given by Edwin Hubble and has been recognized by the academy. See details: [https://en.wikipedia.org/wiki/Edwin_Hubble](https://en.wikipedia.org/wiki/Edwin_Hubble)
An example: an ant crawls on a rubber sheet at a speed of 10m / h. If the rubber expands at 80m / h, the ant’s position will be at 90m. The same applies to objects that are moving in space, and even light with constant speed applies.
Second, how to know an object in the universe 90 billion light-years from Earth?
Traditional measurement: Use “trigonometric in triangle” geometry to measure distances. Specifically: take the earth and another fixed planet (possibly the sun) that we already know the distance. Then measure the angle and use trigonometry to calculate the distance.
However, this way cannot measure stars at a distance = 90 billion light-years away.
Alternatively: use modern technical means to determine the spectrum of light emitted by the star. The light from each star will have a different spectrum depending on the intensity and distance. Based on color, experts can determine the actual brightness of the object, then compare with the light of the star as a standard to calculate the distance to the earth.
In this way, two factors need to be based:
* Edwin Hubble’s Law: the speed of a galaxy’s distance away is proportional to the distance from it to the Earth.
* [Doppler effect](https://en.wikipedia.org/wiki/Doppler_effect)
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