Energy is a good example. Energy is simply the result of various different mathematical equations that we have observed to be invariant with respect to time in closed physical systems. For example, in classical mechanics we observe that for any object moving in a uniform gravitational field the sum of this equation:
mgh
and this equation:
1/2mv2
is constant. So we call the first equation "potential energy" and the second one "kinetic energy" and declare that the sum of the two - the energy - is a "thing" a bit like matter. This is because we are intuitively used to the idea that a "thing" (matter) cannot just appear or disappear. It is conserved. These kinds of conservation laws are central to our particular type of physics.
But it's important to remember that we invented those equations and that therefore there is a sense in which we invented the concept of energy.
Questions:
If we started the process of developing our physics again, might we create a set of models that are just as useful in describing and predicting observations but which use concepts that are completely different from those such as energy that we use now? Might an alien race of physicists do this very thing?
Is there anything at all about our version of physics - perhaps the general idea of conservation laws for example - that we can confidently predict would be universal?
Would the type of physics developed by an alien race depend on their physical circumstances? We are air-breathing creatures who move across the solid surface of our planet. We detect our environment using a particular set of wavelengths of EM waves, vibrations in that air that we breath, chemical traces in that air and in other substances and the electrostatic repulsion of other objects (i.e sight, sound, smell, taste and touch). At night we can see the stars. During the day we can see the Sun. Do these kinds of things dictate our physics?
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Note: mgh = mass X acceleration due to gravity X height
1/2mv2 = half X mass X speed X speed