How can the Observable Universe be a closed system?

[Cerenkov]

Unfortunately, the "ant on a rubber rope" analogy is useless in our actual universe, in which the expansion is accelerating (or, more precisely, has been since a few billion years ago).

Furthermore, that analogy is not necessary to explain why new objects are continually entering our observable universe. The latter does not just happen with non-accelerating expansion. It happens with accelerating expansion as well. The only difference with accelerating expansion is that there is an event horizon, which imposes an upper limit on how many objects will ultimately be inside our OU; but that limit is approached asymptotically, so new objects are always entering our OU, just fewer per unit proper time as we move into the future.

Ok, so back to where we were.

I retract what I wrote 54 minutes ago, having misunderstood things.

There is no longer any confusion.

Objects can still enter the light cone of our OU as it's base widens over time.

Therefore, the OU cannot be considered a closed system.

Thank you.

Cerenkov.

 

[Bandersnatch]

the diagrams employ non-accelerating expansion.

The ant on a rubber rope exercise, where the rope is steadily stretched (as on the animation), is what shows non-accelerating expansion.
The lightcone diagrams are for the LCDM model, the best-fit description of our actual universe.

With the ant, if you imagine the end of the rope being stretched at a varying speed, it will change how the ant traverses the rope.
If you gradually slow down the stretching, it's similar to what happens in the matter-dominated expansion phase in our universe: the ant still gets however far it wants, only faster.
If you gradually speed up the stretching, it's similar to the dark energy-dominated phase: the ant still always moves further on the rope, always passing more marks (i.e. the emitted light passes by more comoving galaxies, i.e. particle horizon grows, i.e. the observable universe grows), but now there will be a distance which it can never reach (the cosmological event horizon).

 

[Cerenkov]

The ant on a rubber rope exercise, where the rope is steadily stretched (as on the animation), is what shows non-accelerating expansion.
The lightcone diagrams are for the LCDM model, the best-fit description of our actual universe.

With the ant, if you imagine the end of the rope being stretched at a varying speed, it will change how the ant traverses the rope.
If you gradually slow down the stretching, it's similar to what happens in the matter-dominated expansion phase in our universe: the ant still gets however far it wants, only faster.
If you gradually speed up the stretching, it's similar to the dark energy-dominated phase: the ant still always moves further on the rope, always passing more marks (i.e. the emitted light passes by more comoving galaxies, i.e. particle horizon grows, i.e. the observable universe grows), but now there will be a distance which it can never reach (the cosmological event horizon).

Thank Bandersnatch.

That's useful. Knowing the the light cone diagrams are configured for the LCDM model, I mean.

All the best,

Cerenkov.