The entire space is the infinitesimally thin surface which is the balloon surface, yet it is still expanding. Dots on that surface that used to be X distance apart are now > X distance apart in the future. That is all you would know and be able to measure.
That doesn’t mean there can’t be a higher spatial dimension that our observable universe is part of; we just haven’t observed it or can’t observe it.
I guess we’re sort of like ants crawling on the surface of an opaque, seemingly-indestructible balloon. We’re pretty clever ants, but we probably aren’t gonna peer inside the balloon anytime soon.
> That doesn’t mean there can’t be a higher spatial dimension
> that our observable universe is part of; we just haven’t
> observed it or can’t observe it.
Light intensity, gravity, and electromagnetism decay at 1/r^2, which is the same rate at which the area of the surface of an expanding 3D bubble grows. So each unit of light / gravity / electromagnetism could be seen as taking up a specific "patch" of expanding area.
However, the strong nuclear force decays much faster than 1/r^2. In fact, at some distance it goes negative and then decays back to zero. This could be (wild speculation) a force that propagates in many more dimensions. And it's not the only force that does this, the weak nuclear force also decays much more rapidly than 1/r^2 with distance.
I'm not a physicist and I would love nothing more than to hear what holes could be punched into this hypothesis.
I'm not a physicist either but believe that this is a well-known idea.
I say that partly pejoratively, with a Sabine Hossenfelder sort of jocular but judgmental tone.
I’m personally excited to see how astrophysicists will take dark matter out of its darkness and cast it into intuitive lights, like some have with the rising dough analogy for cosmic expansion.
Is it new space?
If I have a long ass string, is the string gradually getting longer, or will it break apart?
In our universe, however, the space that's created is the same as the space that was just there. It'd be like if the rubber band stretched, but didn't lose any density while it did so.
Insane, I know.
How much is the space inside me growing on a daily basis?
Unfortunately, it doesn't answer your more fundamental question of "if I make 2 marks in space, and then those expand apart, what is in the new space, and how do I know they really are farther apart?"
I have never heard a good description of this on human scales, only at stellar and galactic scales.
in these analogies, the balloon surface is made of rubber, or the stretchy thing is made of whatever stretchy things are made of
is space something tangible? what is it made of? what is its physical property? how can it stretch?
The most obvious interpretation of general relativity is in terms of B-theory of time: Spacetime is some 'pre-existing', 'eternal' thing over mich matter is distributed. This also fixes the geometry (things like lengths and angles) via Einstein's equations, which more or less state that energy-momentum ∝ Ricci curvature.
In our universe, that distribution comes in layers, ie there's a spatial slicing where the matter distribution appears homogeneous. In that sense, there is a priviledged slicing, which has the unfortunate side effect of making people forget the lessons of special relativity.
Now, the average density of matter changes from layer to layer, and, if our universe were described by the 'closed' Friedmann model, so would the (finite!) volume of the slice. That change is not arbitrary: The layers can be labelled by cosmological time, and with its increase, the average proper distance between galaxies increases as well. That's called the metric expansion of space, because in our idealized model, the metric (a thing defining distances and angles) within a given slice is just a scaled version of the one in a different slice.