Take light's speed (versus Tachyons, particles supposedly having higher velocity than light, defying the theory of relativity) or absolute temperature (maybe in some day scientists will go below 0 degree Kelvin).
Light speed does not actually describe how fast light travels. It only describes how fast it could travel in a vacuum. In our Universe, there is no such thing as a perfect vacuum (across physically quantifiable units of space), but in many places it gets close enough to accurately estimate. It gives us a "pressure spectrum" through which to measure the speed of light. This is a theory based on facts that have been tested by people who, at first, doubted it... but they also tested it and did so rigorously. This is why Relativity is so widely accepted in the scientific community. It has yet to be debunked.
I don't think light actually moves at all. I don't think anything really "moves," because to me, everything already exists within the same place. I don't think light actually moves, because the matter in between two other particles share an electromagnetic relationship. Without particles of matter, you can't have light. Light exists AS the relationship between particles of matter. The further any two particles are apart from each other, the faster the relationship is realized. This is called conjecture. It's an idea that has no basis in experimentation (that I know of.) but it's something I've come to believe (however poorly refined such thoughts/beliefs may be.)
I'm an amateur and an enthusiast, but it doesn't take much more than an open state of mind to understand what the pursuit of science is all about. It's not about finding answers to your questions. Science is about finding better questions and being satisfied in the pursuit of better answers while never being satisfied with the answers. It's about being satisfied with never being fully satisfied. There are no complete answers. There is no end in sight nor a hope for one. That is science. It's about admitting that you might not know what you're talking about.
Personally, I believe that in a perfect vacuum, not even light can travel. There just is no such thing as a "perfect vacuum." I believe that if there was, it would destroy itself, possibly creating what we see now and it would occur at every moment. The destruction of the vacuum is what composes everything. It's hard to describe physically (or philosophically), but I believe that light would somehow travel through this reverberation as well as electrons and the nuclear components. This is also conjecture.
Tachyons are part of a hypothesis. They're not yet theory, because facts which prove the hypothesis of tachyons have not yet been discovered. If the prediction is someday proved by experiment, we will acquire a theory on tachyons. They're more than conjecture because of the mathematical and hypothetical background that they have been derived from. My level of mathematics is practically inept, but I understand the idea of tachyons intuitively. I have a feeling that the unseen parts of our Universe are much more complex than particles that move faster than light. I think that they don't really move at all, but there's hardly a point to get into anything more. I've already spouted more than I can back up with any type of evidence, but at least I know the difference between a scientific theory and a personal opinion.
For my first post, I'm almost glad I exposed this much of my... self. Call it what you will, but I'm glad I stumbled across this forum and I hope to learn more than there is to know in the moments past. After reading a few other threads, my expectations sunk but my hopes hang high. I'll end my rant by saying that I think some of you seem genuinely enlightened and I pray such knowledge is contagious.