Hello. I have three questions that I would like to ask. 1. Could someone provide me with a resource containing examples of arbitrary parameters in theoretical physics. E.g. a modern example, yet to be varified, is dark energy. A historical example, one which has since been discredited, is the luminiferous ether. 2. What is your opinion on the relatively frequent invoking of arbitrary parameters within theoretical physics? Naturally they will be necessary when theories are first being developed, but what about when a theory has been around for many years, or even decades, and yet still contains arbitrary parameters that have not been observed in nature or experimentally verified. Any personal opinions on this? 3. In your opinion, is it justifiable that many scientific theories, with their arbitrary parameters, can be used as support for related theories that are developed further down the line. What becomes of these related theories if and when said arbitrary parameters are discredited? Do foundations crumble? Or is it merely a case of patching things up with more arbitrary parameters? I apologise if I come across as a little cynical here, that is not my intention. On the contrary, I myself am hoping to work my way through the formal scientific education system in the coming years, with the intention of one day being a scientist. So for me, this is more of an area of concern for which I would like some clarification, rather than an attempt to sneer at the scientific community. Thank you.