expanding universe question

[BrianSoddingBoru4]

It's not "empty space" that's expanding, it's just space.

And the space isn't coming from anywhere, it's more like it's stretching.
Kaku likes to use a balloon as an example. When you blow up a balloon even though it's getting bigger, there isn't more rubber being added to it, just the rubber that is already there is stretching.

That seems unreasonable, a deflated balloon has some air in it and to make the balloon expand more air, other gas or liquid must be added to expand the balloon and if to much of these properties are added the balloon burst. I've not seen anyone claiming that the space of the universe will burst.

GC

Kaku was using an analogy to explain a rather esoteric concept to laymen. As all analogies are necessarily flawed (otherwise, there would BE no analogies), it is important to remember that the balloon thing was a simple attempt to paint a mental picture. Obviously, the expansion of the universe isn't exactly like the expansion of a toy balloon.

Boru