What is the most fundamental physics that we can observe directly with our senses?
If you mean the smallest phenomenon that can be detected, I would submit that the photochemical effect of light triggering a retinal response would be a good candidate. One could also argue for gravity.
I think you need to define what you mean by "fundamental".
My opinion is that everything we observe directly is the lowest level of what physics is. You can think of it as a logical pyramid; directly observable data is in the lowest level, and we build models that allow us to list fewer and fewer "principles" after each abstraction. The upper "logical levels" may be regarded as "more fundamental", but are also necessarily more distant from the raw data from our senses.
Observe ? Light
There are many optic phenomena that are pretty close to fundamental. The minimum light you can observe with your eyes is on the order of two or three photons. When you see rainbows in oil slicks you are seeing the macroscopic effects of microscopic scale films. The famous drop two objects at the same time experiment is a good illustration of the geodesic nature of gravity -- i.e. that it is independent of mass.
Umm, people didnt actually know what is physics until someone define what is physics.
So i would like to think this way... What kind of phenomena will instantly let u relate it to physics?
By fundamental I mean simply and beautifully expressed by mathematics.
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