How can the universe be infinite if expansion started 13.8 billion years ago?

[Meow12]

The universe started off as a point and has been expanding for 13.7 billion years. Since this is a finite amount of time, how can the universe be infinite?

 

[PeroK]

The universe started off as a point

It didn't. This is is a common misconception. It started out in a "hot, dense" state.

and has been expanding for 13.7 billion years. Since this is a finite amount of time, how can the universe be infinite?

There are two possibilities: either the universe is much larger than the observable universe or the universe is infinite. If it's infinite, then it has always been infinite - even when it was initially hot and dense.

 

[Orodruin]

The universe started off as a point and has been expanding for 13.7 billion years.

It did not so any logical inference from that is not going to tell you anything about the actual physical model.

 

[Ibix]

The universe started off as a point and has been expanding for 13.7 billion years.

Some sources are sloppy about the distinction between the universe and the observable universe (which is the part of the universe we can see, more or less), and also which cosmological model they are talking about.The observable universe is finite and was small in the past, although "started as a point" is a bit dubious for various reasons. Depending on which cosmological model you are talking about the universe may be finite and very large, in which case it was small in the past too, or it may be infinite, in which case it always was.

 

[phyzguy]

Just listen to the theme song from "The Big Bang Theory" show. "The whole Universe was in a hot dense state."

 

[phinds]

The universe started off as a point and has been expanding for 13.7 billion years.

As said above, this is a common misconception. Try reading actual physics instead of pop-sci presentations.

 

[DaveC426913]

The universe started off as a point and has been expanding for 13.7 billion years. Since this is a finite amount of time, how can the universe be infinite?

You might be interested in this thread that I started recently.

It does go around in circles a bit (by "it" here, I mean "me") but ultimately it (and by "it" here, I mean the knowledgable PF members that weighed in with nigh-infinite patience) explains how a universe can be infinite in extent - and yet still expand.