How can the universe be 13.7bln years old if time depends on your frame of reference? Could others “think” it’s older or younger?
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Imagine a inflating a balloon with pictures of galaxies drawn on the surface.
It is expanding equally in all directions. We measure that, which means that we can also calculate how fast those galaxies are all moving away from each other. We can reverse than math to see how long ago they were all very close together. We have done several version of this experiment and each time, it brings us back to the answer of 13.7N years ago.
Time is not dependent on how old or young any human thinks the universe is. It’s a measurable, observable phenomenon and is required for the second law of thermodynamics to be true.
>How can the universe be 13.7bln years old if time depends on your frame of reference?
we are not using our time reference, we are using speed of light to measure the expansion, using the factor of the constant speed of it.
It can not be younger nor older. Just the measurements can vary depending on the scale.
For example:
If a coffee costs $1 in USA, and 200$ in Portugal (using our old currency) is it more expensive in Portugal? No, because 200PT are still same as 1 Dollar. More or less.
>In physical cosmology, the age of the universe is the time elapsed since the Big Bang. Astronomers have derived two different measurements of the age of the universe: a measurement based on direct observations of an early state of the universe, which indicate an age of 13.787±0.020 billion years as interpreted with the Lambda-CDM concordance model as of 2021; and a measurement based on the observations of the local, modern universe, which suggest a younger age. The uncertainty of the first kind of measurement has been narrowed down to 20 million years, based on a number of studies that all show similar figures for the age. These studies include researches of the microwave background radiation by the Planck spacecraft, the Wilkinson Microwave Anisotropy Probe and other space probes. Measurements of the cosmic background radiation give the cooling time of the universe since the Big Bang, and measurements of the expansion rate of the universe can be used to calculate its approximate age by extrapolating backwards in time. The range of the estimate is also within the range of the estimate for the oldest observed star in the universe.
We did several studies on stars distance, movements and etc and all studies point to similar results basically
The age of 13.7b years is for a specific reference frame. If you imagine the expanding universe as an expanding grid, it is a reference frame that lies on one of the grid lines. In other words, it moves perfectly with the expansion of the universe, without any other additional velocity. Such a reference frame is called a co-moving frame.
In a reference frame that has an additional velocity, the universe will appear younger. The Earth actually has a small velocity relative to the co-moving frame of around 370 km/s, but the resulting age difference is smaller than the measurement error on the 13.7 b years.
You are right. The 13.7bln years number is in the frame of reference where the cosmic microwave background appears isotopic (same in every direction).
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