How can the Universe be infinite?

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Discussion Overview

The discussion centers around the concept of the universe's infinitude in the context of its expansion over 13.7 billion years. Participants explore the implications of a finite time frame on the nature of the universe, including distinctions between the universe and the observable universe, and the validity of common misconceptions regarding its origins.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants assert that the universe started as a point, while others challenge this notion, suggesting it began in a "hot, dense" state.
  • There are claims that the universe could either be much larger than the observable universe or infinite, with the latter implying it has always been infinite.
  • Concerns are raised about the common conflation of the universe with the observable universe, which is finite and was smaller in the past.
  • Some participants argue that logical inferences based on the idea of the universe starting as a point do not accurately reflect the physical models of cosmology.
  • References to popular culture, such as the theme song from "The Big Bang Theory," are made to highlight misconceptions about the universe's origins.
  • One participant mentions a previous thread that discusses how an infinite universe can still expand, indicating ongoing exploration of the topic.

Areas of Agreement / Disagreement

Participants express disagreement on the initial conditions of the universe and the implications of its expansion. Multiple competing views remain regarding the nature of the universe and its finitude or infinitude.

Contextual Notes

Limitations include the potential confusion between the universe and the observable universe, as well as unresolved distinctions between different cosmological models that may affect interpretations of the universe's size and expansion.

Meow12
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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?
 
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Meow12 said:
The universe started off as a point
It didn't. This is is a common misconception. It started out in a "hot, dense" state.
Meow12 said:
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.
 
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Meow12 said:
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.
 
Meow12 said:
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.
 
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Just listen to the theme song from "The Big Bang Theory" show. "The whole Universe was in a hot dense state."
 
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Meow12 said:
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.
 
Meow12 said:
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.
 

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