4 ms·

When the universe expands...what does it expand _into_?

zach_garwood 4y ago
It doesn't expand into anything. Spacetime is all there is. As it expands, there's just more of it. Astrophysics, like quantum physics, isn't intuitive in the same way that classical, human-scale physics is to us.
- Maursault 4y ago
  > It doesn't expand into anything. Spacetime is all there is. As it expands, there's just more of it. But what if it isn't, and everything except for space is actually shrinking, galaxies, nebula, stars, planets, are actually getting smaller at a fantastic rate? I'm not serious.
kadoban 4y ago
The best analogy I've seen is imagine our universe as the surface of a balloon. Only the surface, we can't see or touch anything else. If you inflate the balloon, our universe expands. Points get farther away from each other, proportionally to how far away they started. In this analogy, we're not expanding into anything we can see or feel or know anything about, the only real difference is that points are a bit farther apart.
- Bradley_A_Pliam 4y ago
  This explains why there is no "epicenter to speak of", but why is that expansion faster than the speed of light? How could it be? And is the evidence for that expansion really that solid?
  - kadoban 4y ago
    > why is that expansion faster than the speed of light Because it's space expanding, not something moving inside of space. It doesn't follow the same rules.
    - Bradley_A_Pliam 4y ago
      I find this to be the crux of the issue. To be exempt from the rules that material things must follow, you simply need to designate it as space. If space is what fills an area between object A and object B and that space grows or expands. This is no different than object A moving away from object B. What's the difference? There seems to be none.
_8j50 4y ago
Spacetime is a thing, they are intertwined. That's like asking where does time flow to, infinity just like space. I think of reality as a superset of spacetime, matter,energy,etc... could there be other things or universes in reality? I don't know but put simply I understand it to mean the distance relative to a refernce frame expands. My question to people who actually know this subject: has 'c' been proven to be constant, resisting expansion? The speed of light/causality might be affected if time also expanded along with space? Or how can space expand without time expanding given its relationship with time?
- richardfey 4y ago
  Some day we might create the necessary mathematics to explore the answer space of these questions (and related ones). We don't yet have the technology, so to speak, to "think" of this.

It doesn't expand into anything. Spacetime is all there is. As it expands, there's just more of it. Astrophysics, like quantum physics, isn't intuitive in the same way that classical, human-scale physics is to us.

Maursault 4y ago
> It doesn't expand into anything. Spacetime is all there is. As it expands, there's just more of it. But what if it isn't, and everything except for space is actually shrinking, galaxies, nebula, stars, planets, are actually getting smaller at a fantastic rate? I'm not serious.

kadoban 4y ago

The best analogy I've seen is imagine our universe as the surface of a balloon. Only the surface, we can't see or touch anything else. If you inflate the balloon, our universe expands. Points get farther away from each other, proportionally to how far away they started. In this analogy, we're not expanding into anything we can see or feel or know anything about, the only real difference is that points are a bit farther apart.

Bradley_A_Pliam 4y ago
This explains why there is no "epicenter to speak of", but why is that expansion faster than the speed of light? How could it be? And is the evidence for that expansion really that solid?
- kadoban 4y ago
  > why is that expansion faster than the speed of light Because it's space expanding, not something moving inside of space. It doesn't follow the same rules.
  - Bradley_A_Pliam 4y ago
    I find this to be the crux of the issue. To be exempt from the rules that material things must follow, you simply need to designate it as space. If space is what fills an area between object A and object B and that space grows or expands. This is no different than object A moving away from object B. What's the difference? There seems to be none.

_8j50 4y ago

Spacetime is a thing, they are intertwined. That's like asking where does time flow to, infinity just like space. I think of reality as a superset of spacetime, matter,energy,etc... could there be other things or universes in reality? I don't know but put simply I understand it to mean the distance relative to a refernce frame expands. My question to people who actually know this subject: has 'c' been proven to be constant, resisting expansion? The speed of light/causality might be affected if time also expanded along with space? Or how can space expand without time expanding given its relationship with time?

richardfey 4y ago
Some day we might create the necessary mathematics to explore the answer space of these questions (and related ones). We don't yet have the technology, so to speak, to "think" of this.