Why do cables need break-in?

I suppose, you are very well aware of the fact, that there is no really convincing scientific explanation for this.
Our ears tell us though, that this phenomenon exists. So if you " believe " in science, you'll say that the ears are wrong and if you believe in what you are hearing, you'll say that science falls short of the fact and cannot explain it. P l e a se lets not start this argument again, because it leads nowhere!

There has to be. It's called MSE, or materials science engineering. Some things have no scientific explanation (that's why I'm Psychicanimal--I saw in a dream the girl I'm in love with the day before flying to her country and met her two days later...wow!) but something like this in the 21st century must have one.

To start, science is not a belief. I am a professional scientist. I do not 'believe' in science. Scientific activities search for truth through a systematic process. That's why it starts with observation (or hearing, in this case). Questions arise, hypotheses are formulated and experiments to sustain or defeat those hypotheses are conducted. An inseparable part of this is a process called validation (Quality Control/Quality Asessment).

Does anyone have any validated data sets/explanations?

I do not wish to create controversy. I bought some silver plated copper speaker wire very cheap and two people I really trust told me there would be a long break in perion for the silver. That the sound would get better. How can this be?

Here's my two cents coupled with a little cable geometry theory. I think it has less to do with the wire and more to do with the insulation. In my experience cables with more di-electric material and higher native electrical impedience generally need more break in time. Pure silver definately sounds different than copper or plated silver but all else being equal it's the cable geometry that determines the break in period and how the cable settles in to your system.

Teflon foam or air tube and teflon dielectric combinations seem to take less time to break in and the less gap between conductors the faster the break in too. It seems to be a matter of the capacitance of the cable as related to AC impedience in the audio spectrum. A small charge builds up in the dielectric. If the cable has a low impedience (like Goertz or Nordost for example) it tends to have a very short break in period. If on the other hand it has a dielectric foam insulation and a relatively higher impedance and gap between conductors then the break in is longer. To my ears Audioquest type cables and others like them seem to have longer break in periods. The end results seem close in sound but cables with polystrene and nitrate foams seem to take 50 to 100 hours before they sound almost as good as a Nordost or Goertz out of the box. This is just my opinion and a little information gleaned from listening and reading specs. I hope that it is somewhat helpful.

I agree it is the dielectric. Capacitors also need break in. Once I replaced my power supply capacitors in my amp. The sound was very bright and thin. After 100 hours everything was back to normal. The dielctric needed to be "formed up," I believe this is true of cables.

Psych, it's not the silver, but the quality of the insulation, as explained by Dmi....