What is the Universe expanding into?

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Discussion Overview

The discussion revolves around the concept of the universe's expansion and what it might be expanding into. Participants explore theoretical implications of the universe being everything that exists, including matter and energy, and question the nature of space and time in relation to this expansion.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants assert that if the universe encompasses everything, it cannot be expanding into anything, as there is no "outside" to the universe.
  • One participant mentions that general relativity describes the universe in terms of 4D spacetime, suggesting that "space is expanding" means galaxies are becoming further apart in successive slices of spacetime.
  • Another participant raises the question of whether the expansion from the Big Bang created the time/space continuum, indicating that this is currently not known.
  • There are concerns about common misconceptions regarding the nature of the universe's expansion and black holes, highlighting the challenges in explaining these concepts to others.
  • Some participants argue against the idea that spacetime is "created," suggesting it is a pre-existing 4-dimensional geometry that contains all information about time.

Areas of Agreement / Disagreement

Participants express differing views on the nature of the universe's expansion and the creation of spacetime, with no consensus reached on these complex topics.

Contextual Notes

There are unresolved questions regarding the implications of the universe's expansion and the nature of spacetime, as well as the definitions of key concepts involved in the discussion.

Akshaya dhakal
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TL;DR
If it is everything then what is it expanding into?
As we know universe is everything having every matter and energy. From the observation using Hubble's law it was said that the galaxies are moving away from the Earth which means the universe is expanding. If it is everything then what is it expanding into. Is there some outer edge that it can expand into or any center it is expanding from? Is it infinite?
 
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Our current best model of the universe is infinite, yes. But even finite and closed models don't expand into anything. As far as we are aware there is nothing outside the universe for it to expand into.

The thing to remember is that general relativity describes 4d spacetime, and space at any given time is a 3d slice through that. So what we mean when we say that "space is expanding" is that there is a particular way to slice spacetime so that everything looks more or less the same everywhere in a slice, and when we do that, in each successive slice galaxies are slightly further apart. Nothing is expanding into anything because nothing is really expanding - things are just further apart in different slices of spacetime.
 
Akshaya dhakal said:
Summary:: If it is everything then what is it expanding into?

As we know universe is everything having every matter and energy. From the observation using Hubble's law it was said that the galaxies are moving away from the Earth which means the universe is expanding. If it is everything then what is it expanding into. Is there some outer edge that it can expand into or any center it is expanding from? Is it infinite?
Doesn't he expansion which basically started at the big bang been create the fime/space continuum in the process? Ex nihilo so to say. It's pretty difficult wrapping ones head around...

Explaining this to someone is pretty steeply up-hill. There are many misconceptions surfacing again and again. Some of the more annoying are people thinking that an explosion in vacuum looks exactly like a fireball in an atmosphere. Also that black holes basically works like a giant vacuum cleaner, gobbling up everything within it's gravitational sphere of influence. I'm sure there are tons of others.

Regards.
 
sbrothy said:
Doesn't he expansion which basically started at the big bang been create the fime/space continuum in the process?
This is currently not known.
 
DennisN said:
This is currently not known.

What would it even mean to "create time/space continuum"?
 
sbrothy said:
Doesn't he expansion which basically started at the big bang been create the fime/space continuum in the process?
No. Spacetime doesn't get "created"; it just is. It is a 4-dimensional geometry that already contains all of the information about "time".

DennisN said:
This is currently not known.
Yes, it is; the answer is no. See above.
 
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