"I'm not convinced this explanation-by-analogy style is really all that helpful, particularly with regards to "the big bang is an expanding balloon". What makes it such a confusing analogy is that most people were already picturing something like an expanding sphere anyway, just one filled uniformly with matter moving away from a central point as it expands. And it doesn't reinforce that the Universe has no center, since most people can easily imagine what the center of a balloon is."
The key to the balloon analogy is that it only applies to the surface. The interior of the balloon is to be ignored. You say you can easily find the center of the balloon, so I think you don't get this, because I suspect your "center" is the 3D center of the balloon. But that doesn't exist. Only the surface does. What's the central surface point of a sphere? There isn't one. That's the universe, only the surface is 3D, not 2D.
I'm fairly sure that even a large number of people using the "expanding ballon" metaphor don't get that, let alone the poor readers. I tend to be surprised when I see it explained correctly.
Also, in the classic picture of the wormhole, like you might find here: http://casa.colorado.edu/~ajsh/schwm.html , the wormhole is not the tunnel itself. If you see someone drawing an arrow that goes down the middle of the tunnel as the path of travel, they don't know what they are talking about. (That's the best picture I could find quickly, they're actually showing something else with that arrow, so I do not accuse them.) The wormhole is the sides; the image is two 2D chunks of space being connected through a 3rd dimension. (Incidentally you can tell Hollywood doesn't know either, because they always actually "draw" the wormhole.) The curvature of the 2D planes corresponds to gravity in these displays.
This is also true of the classic "rubber sheet" gravity analogy; the rubber sheet applies only to 2D, and the 3D "things" usually drawn should be understood to be merely labels explaining where the curvature comes from. You really shouldn't see a "rolling ball" on the surface, you should see it in the surface. Again, this is done incorrectly far more often than it is done correctly.
I get the intention behind the analogy, but I know from experience that nobody ever comes away from it understanding what they're meant to. I don't think I've ever mentioned to a friend without them pointing out that balloons do have centers, or asking what's outside of the balloon. I've had much better luck just telling people why what they think is happening can't possibly be right, so they stop defending it or trying to reconcile it with reality, and then building up.
But, I'm not a physics professor. Your mileage may vary.
Ah, you do get it, I apologize for suggesting otherwise. Statistically, my odds were good, because you're right, and virtually nobody does it right. (I claim a Bayesian defense!)
Unfortunately, I don't know how to do any better. There's a leap to even abstractly understanding 4+ dimensions and a lot of people simply won't make it. Without that you've "already lost" regardless of how clever your metaphor is.
The key to the balloon analogy is that it only applies to the surface. The interior of the balloon is to be ignored. You say you can easily find the center of the balloon, so I think you don't get this, because I suspect your "center" is the 3D center of the balloon. But that doesn't exist. Only the surface does. What's the central surface point of a sphere? There isn't one. That's the universe, only the surface is 3D, not 2D.
I'm fairly sure that even a large number of people using the "expanding ballon" metaphor don't get that, let alone the poor readers. I tend to be surprised when I see it explained correctly.
Also, in the classic picture of the wormhole, like you might find here: http://casa.colorado.edu/~ajsh/schwm.html , the wormhole is not the tunnel itself. If you see someone drawing an arrow that goes down the middle of the tunnel as the path of travel, they don't know what they are talking about. (That's the best picture I could find quickly, they're actually showing something else with that arrow, so I do not accuse them.) The wormhole is the sides; the image is two 2D chunks of space being connected through a 3rd dimension. (Incidentally you can tell Hollywood doesn't know either, because they always actually "draw" the wormhole.) The curvature of the 2D planes corresponds to gravity in these displays.
This is also true of the classic "rubber sheet" gravity analogy; the rubber sheet applies only to 2D, and the 3D "things" usually drawn should be understood to be merely labels explaining where the curvature comes from. You really shouldn't see a "rolling ball" on the surface, you should see it in the surface. Again, this is done incorrectly far more often than it is done correctly.