Electric Boogaloo

D and I have already learned in our two short weeks of home ownership that nothing is as easy as it looks. I bought a beautiful hanging lamp for the dining room to replace the one that is there now. It seemed like it would be an easy one for one replacement. Not so...

The new one on the left (with glass sconces on all the sockets) is supposed to replace the old one on the right (note the lovely white paint--wonder how that happened?).

The problem is that the new lamp has completely different hardware, which doesn't appear compatible with what is actually in the ceiling. The old chandelier (which D kindly put back in place after admitting defeat, so we wouldn't have to look at a hole with wires sticking out) is completely oriented vertically. It has an adapter piece with threads on it to screw into both the lamp and the electrical box. I can't find a picture online and forgot to take one when the hardware was exposed. The new one has what all the online how-to guides show as normal:

Except that the hole in our ceiling is too small to even fit this horizontal bar inside. We are stumped. We think maybe this would require cutting into the drywall and replacing the electrical box. And we're not sure if the ceiling can even support the weight of the new lamp if we did try to install it ourselves (the old one was about 4 lbs., the new one about 8 lbs.). The old hardware in the ceiling is obviously outdated, since I can't even find a picture online in the how-to guides.

So I suppose we have to admit defeat completely and call an electrician. Except that it seemed so easy and I don't want to throw money away for something we can do ourselves. This was going to be the first step to replacing all the ceiling fixtures in our house, mostly with ceiling fans. I think that after this failure, we are probably not capable of more advanced lighting installation. If you have any ideas (besides "call an electrician"), I would love to hear them.

But hey, at least we remembered to turn off the right circuits!

Edited to add: My friend and her handyman husband informed me that, indeed, my wiring is out of date. Apparently a box that would fit the horizontal bar inside is the smallest kind installed today. So we need an electrician to reoutfit us...