I'm just discovering the podcast, and just listened to episode 5, titled "The Expansion of the Universe and the Microwave Cosmic Background".
At one point, it was mentioned that while space is expanding, our "heads are not"....So, the implication being that the space between objects is expanding, but objects themselves are not expanding. Did I understand that correctly?
To use the raisin bread analogy, when the bread expands, increasing the distance between the raisins, are the raisins themselves not expanding in size?
If massive objects are not expanding, then what happens to the "inner space" that exists within all matter, i.e. most solid matter is empty space, and if this is not expanding how is it different from the space between galaxies, etc.?
On the other hand, if objects are expanding in dimension right along with space, then the relative dimensions of the universe would not be changing. By that I mean, if we say that the size of the orbit of the earth around the sun is 1 astronomical unit, then the value of 1 AU is expanding right along with the universe, but to our perspective, it is remaining constant, relative to the distance between familiar objects, such as the distance between new york and los angeles....But I gather the evidence is contra to the idea that physical dimensions of massive objects are expanding....
One thing that was interesting to me, was that the cosmic background radiation is slowly shifting to longer wavelengths (e.g. lower energy). Does this mean that all transmitted electromagnetic photons lose energy overtime? Is it something we could measure? Could we detect a loss of energy of a lightsource between point A and point B? (I'm guessing it would be a rather difficult experiment, indeed)....