I have heard this analogy before, but I guess I just can’t grasp it-- how is our third dimension represented in this case?
Screw the balloon, I think of the universe as a sponge. The balloon illustrates relative expansion between 2 points well enough, but I’m afraid the universe is a bit more complex.
“like taking air out of a balloon!”
As described in the seminal paper by Basie, Calloway, Ellington, and Miller?
The reason why we can’t factually measure the size of the universe, is because our largest tape measure keeps collapsing once it gets approx. 11 feet out. We once got it out to 14 feet, but that was just a fluke.
It don’t mean a thing if it ain’t got that string.
I see that units of frequency are incommensurable with units of speed. But suppose at some point in time the Hubble constant had been 1/2 light years/s/Mpc. Then two objects three Mpc awy from each other would have been receding from each other at 1.5 times the speed of light. Arriving at this conclusion does not involve comparing units of frequency with units of speed, it just involves noting an implication of what it would mean, in terms of the speeds of objects, for the Hubble constant to have some particular value.
But why isn’t it a problem that you could have things receding from each other at faster than light speed given particular distances and particular values for the Hubble constant?
-FrL-
It isn’t. The balloon’s surface is meant to be a two-dimensional representation of our three-dimensional space.
To add the missing dimension you need to be able to think four-dimensionally (or five-dimensionally if you want to count time) and have a four-dimensional balloon with a three-dimensional “skin”.
shrug Uhh-dun-oh. Trying to measure or indeed even talk about “space” is like trying to discern the meaning of “Jabberwocky”. You can give it a mathematical treatment which describes it in terms of curvature and corresponding energy, but the underlying physicality of it is still a mystery. We can only cope with the concepts of things being made of stuff, and Minkowski space and pseudo-Riemannian manifolds aren’t “stuff”; they’re just (fiendishly complex) equations.
The only reason I say that it is assumed that the expansion of space is isentropic (i.e. the rate is the same regardless of whatever direction you are measuring in) is because a lack of symmetry would be problematic in terms of causality, i.e. you could go in one direction and go faster for the same amount of energy expected as opposed to going a different direction, a violation of the (assumed) equivalence principle. Of course in a local frame where a concentration of mass-energy was warped space-time, you will have a bias, hence why planets and galaxies and celestial superstructures aren’t being flung apart at accelerating rates (and in fact everything in and around the Local Group is streaming toward a mass concentration obliquely known as The Great Attractor). On a cosmological scale, however, the distribution of energy is pretty evenly distributed.
Stranger
IIRC the Period of Rapid Expansion enabled the universe to expand at a rate faster than c because, although mass cannot be accelerated to or beyond c, spacetime itself has no velocity limit.
This leads me to believe that, if the effect can be recreated artificially at the local level, warp drive is possible. 
I fail to see the practical applications of a device which allows us to move faster than light away from everything 
Except as a weapon, of course
Quoth kniz:
Inflation is not yet a theory, if that’s what you’re complaining about. Any cosmologist will admit that the evidence for the inflationary model is thin, and we’re very eager to find some more concrete evidence for (or against) it. It’s currently our best bet for the early behaviour of the Universe, but as you correctly point out, the scientific method isn’t satisfied with “best bet”.
I thought spacetime was shaped like a cone.
By now the skin would be billions of light years thick. We are on a massive scale here.
Ok, now that’s funny.
You know, I think that it may be a fundamental characteristic of something that Kari Byron has the smartest fanboys in the universe.
Tris
It’s been a while since I read anything about this, but I ( vaguely ) recall that the expansion of space supposedly provides the energy for the creation of more space, as expansion releases energy, just as a fireball cools as it expands.
noted didn’t read everyone response
But watching what I asumeing is the same show as you. I remember them mentioning that the universe in its firsts billionths of a billionths of a second was travel much faster. Maybe in that time it made up that extra space.
What do tampons and the universe have in common? 
