An embarrassing question: what were the boundaries of the universe

[houhou.trad]

I say always that the universe has expanded, from an initially-hot and dense state, until it get its current forme...
But it will be very natural to ask the question: at the first instances of its expansion, what were the boundaries of this universe, and what were the exterior of this boundaries..?
Can someone explain me this?

 

[narrator]

A similar question was asked in the "https://www.physicsforums.com/showthread.php?t=550977"" thread.
As I understand it, the universe has always been infinite, even at the beginning, and has been expanding since it was about 6 billion years old.

 

[cephron]

We're actually not sure if it's infinite or not (according to Marcus, and the FAQ, the current data fits both infinite and finite models, pretty much equally well), but:

-If the universe is infinite, then it was already infinite at the point of the Big Bang; there was never a time that it was finite.

-If the universe is finite, it still does not (and never did) have boundaries. What happens when you reach the edge of the universe? Well, you never reach an edge; try this and you'll only end up back where you started (rather like as if you tried to sail to the edge of the earth).

-In either case, it is expanding. One may wonder: if the infinite universe is true, how would an already infinite space expand further? Well, all the things in it just keep getting further away from each other.

 

[houhou.trad]

Thank you narrator and cephron, I think the idea is now somewhat more clear.

 

[sardar]

I can understand why this question may feel embarrassing to ask. The boundaries of the universe are a complex and ever-evolving topic in the field of cosmology. Our current understanding is that the universe is constantly expanding, and there is no definitive boundary or edge. This expansion began with the Big Bang, which occurred approximately 13.8 billion years ago.

At the first moments of the Big Bang, the universe was in a hot and dense state, and it has been expanding and cooling ever since. However, it is important to note that the universe does not have a physical boundary or edge that we can observe or measure. Instead, the concept of boundaries in the universe is more abstract and based on our understanding of space and time.

To better understand this, imagine the universe as a balloon being inflated. As the balloon expands, there is no defined edge or boundary that we can point to. The same is true for the universe - it is constantly expanding and there is no edge or boundary that marks the end of the universe.

As for the exterior of this boundary, it is difficult to say as our current understanding of the universe is limited to what we can observe and measure. Some theories suggest that there may be other universes beyond our own, but this is still a topic of debate and research in the scientific community.

In summary, the concept of boundaries in the universe is a complex and ongoing area of study in cosmology. While it may feel embarrassing to ask, it is a valid and important question that scientists continue to explore and try to understand.