The Expanding Universe
The universe is expanding, so objects are moving farther away from each other over time. Moreover, this expansion is accelerating. This means that the speed at which a galaxy recedes from Earth increases with time. Therefore, galaxies are moving away from Earth faster and faster as time progresses.Definition: \( a \) is the distance between points in the universe, also known as the comoving distance or scale factor.
To understand the history of the universe, we must understand how the scale factor \( a \) evolves with time \( t \), i.e., \( a(t) \). The variation of the scale factor over time is determined by the energy density of the universe.
When the universe was very young, radiation was the dominant component, and \( a \) was proportional to \( t^{1/2} \). Later, as non-relativistic matter became the most abundant form of energy density, \( a \) became proportional to \( t^{2/3} \).
After enough time goes by, the acceleration will leave every galaxy completely isolated in the Universe, as all the other structures accelerate irrevocably away. So, there will be a point where our galaxy will be the only astrological thing we will be able to observe in the space.Every time galaxies are being further away from the earth so our chances to find them are inevitablement worst each time in the future. I lose sleep wondering if there was a moment of our past where we were able to reach some amazing discovery but now is too late to find it.