The Size of the Universe we Can See and the Real Size of the Universe (s)

 

Everyone knows that the universe is huge, but no one could have imagined how staggeringly immense the universe, or multiple universes, may actually be. It stops your breath

The age of the universe is about 13.75 billion years, but due to the expansion of space we are now observing objects that are now considerably farther away (as defined in terms of cosmological proper distance, which is equal to the co-moving distance at the present time) than a static 13.75 billion light-years distance.

I will just let you settle while you digest that.

Ready?

The diameter of the observable universe is estimated to be about 28 billion parsecs (93 billion light-years), putting the edge of the observable universe at about 46–47 billion light-years away.

^{Did you think that was big? Well, it’s not, it's small compared to:}

The universe versus the observable universe

Some parts of the universe may simply be too far away for the light emitted from there at any moment since the Big Bang to have had enough time to reach Earth at present,


So these portions of the universe would currently lie outside the observable universe. In the future the light from distant galaxies will have had more time to travel, so some regions not currently observable will become observable in the future.


However, due to Hubble's law in astronomy, a  statement that the distances between galaxies or clusters of galaxies are continuously increasing and that therefore the Universe is expanding.


Regions sufficiently distant from us are expanding away from us much faster than the speed of light (special relativity prevents nearby objects in the same local region from moving faster than the speed of light with respect to each other, but there is no such constraint for distant objects when the space between them is expanding; see uses of the proper distance for a discussion), and the expansion rate appears to be accelerating due to dark energy.


Assuming dark energy remains constant (an unchanging cosmological constant), so that the expansion rate of the universe continues to accelerate, there is a "future visibility limit" beyond which objects will never enter our observable universe at any time in the infinite future, because light emitted by objects outside that limit can never reach points that are expanding away from us at less than the speed of light.


Eh, I hate to say this, but in the view of many at the cutting edge of Cosmology, the Universe is a 100 billion trillion (inflationary Universe growing exponentially) more than what we see.


What do I get out of such observations?  I don't hear you ask. Well, if I were conventionally religious I would take a long hard look at such counter intuitive facts.  But I am not, so what I get from such observations is a sense of humility and the lifting of a weight off one's shoulders.


It is remarkable how much we know, and remarkable how much we don't know. Our size in comparison to another size does not make us unimportant, our quest for knowledge give our life meaning and it is this quest that gives our life importance. 


Sorry, got to go, the kettle is boiling. More later.