How Big Is The Known Universe?

By Antonia Čirjak on June 2 2020 in Answer

Understanding how big is the universe, which is home to trillions of galaxies except our own, is a mind-boggling thing to do, as we are talking about areas so vast that we question the idea of infinity itself. 
Understanding how big is the universe, which is home to trillions of galaxies except our own, is a mind-boggling thing to do, as we are talking about areas so vast that we question the idea of infinity itself. 
  • The observable universe is, by today’s knowledge, spreading in a diameter of 93 billion light-years from Earth.
  • The things we have the chance to observe are not there when we actually have visual confirmation, because again - it took billions of years for light to travel from a distant point in space to Earth.
  • Two trillions of galaxies are estimated to exist in the current observable universe.

If you ever tried to grasp your mind around the notion of the universe, and you got a little bit lost and dizzy, do not worry. Understanding how big is the universe, which is home to trillions of galaxies aside from our own, is a mind-boggling thing to do, as we are talking about areas so vast that we question the idea of infinity itself. 

More Than One Answer

As far as NASA is concerned, there is no true answer to this, or better to say there is more than one way you could explain the size of the universe we live in. One problem that goes against providing a very specific number lies in the fact the size of the universe is constantly changing. Also, we need to think of space in space-time terms, as we can not talk about these two notions separately.  

Just our own galaxy, the Milky Way is so big that it would take you 100,000 years to reach its borders if you were traveling as fast as the light is, of course. 

Observable Universe

The crucial thing to understand is that when we discuss the size of the universe, we are only talking about the part of it that is observable. It would be scientifically unfair to talk about the things you can not even see, and provide numbers without worrying that you could be way off in your calculation.

However, what we can talk about are the limits we have reached with the type of technology we have. By today’s calculations, with using either telescopes based on Earth or the ones we deployed in space, the radius we can see is about 46.5 billion light-years. That means that, if you take Earth as a central point for your measurement, the diameter we can observe is 93 billion light-years. 

The perception of size has changed as technology changed. Back in the day, people used to think that Earth is the center of the universe, or that the Sun is the one spinning around us, not the other way around. 

Measuring The Isotropic Shape

One thing we are also assuming here is that the universe has an isotropic shape, which would mean that the distance to the farthest borders is the same in every direction you look at. This means that, by today’s assumptions, the universe is shaped like a sphere, and that all the calculations that happen come from the fact that we take Earth as a starting point of measurement. Now, imagine if we could set-up telescopes on another planet, that would be billions of light-years away. Now that planet would become the center, and the observable space from that planet would be different than our experience here on Earth. 

One thing that is certain is that, even if we can not exactly know the size of the space, we can talk about the time of space. The cosmological expansion will have to stop eventually unless we learn something more in the future, and the space of possible infinite space would be stopped by its finite time. 

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