Is the age of the Universe really 13.8 billion years? Ok, I know this has been asked by a lot of people, but my reason for asking this question is a bit different. Please read further.
I was watching a video by Fermilab (Start at 6:30, at 8:30 he mentions how we cannot ever see light emitted from objects &gt; 14bn light years away). In it, the presenter Dr. Don Lincoln talks about the speed of light and how some things are faster than that. Expansion of the Universe can be faster than the speed of light, because galaxies 1 megaparsec away appear to be moving at the rate of 68km/s, galaxies 2 megaparsecs away at 136km/s, and so on. So the velocity of the galaxies doubles every megaparsec. If we do the math, the speed of the galaxies moving away surpasses the speed of light at 14 billion light years away.
14 billion is just 200 million give or take more than the current measurement of the age of the Universe.
My question is, at 14 bn light years away the galaxies are moving faster than the speed of light and we can never see anything beyond that ever. Does this mean that even after say 5 billion years (assuming we still exist), if somebody uses the same technique to measure the age of the Universe, they will end up with the same number that is lesser than 14 billion?
The age of the universe is not calculated based on the size of the visible universe. The age of the universe is being calculated based on the fact that the laws of nature have no direction. This means that you can use the laws of nature to predict future behavior, but also assume previous behavior. Based on calculating backwards with the laws of nature, for instance, general relativity, physicists can to a pretty certain degree calculate backwards how the universe started.
The fact that the universe is expanding and the size of the universe is what it is, has no relation to the age of the universe. Please, look at another video from Don Lincoln about the size of the universe and its age. Here it is explained that the universe already had an extra large expansion making it bigger than the age.
What will happen, though, is that the visible universe, which is smaller as the actual size of the universe, will be more empty over the course of time. In the 5 billion years you mentioned, there will be more galaxies outside the visible boundaries of the universe, because they are moving away from us faster than the speed of light. The expansion of the universe, hypothesized due to dark energy, makes the universe bigger, not older.
If the laws of nature don't drastically change, and we use these laws in 5 billion years to calculate the age of the universe, we should end up with the right number, 14 billion plus 5 billion years.