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So I was watching the discovery channel special where they theorized what beings on a potentially livable planet would be like. The planet had a lower gravitational constant and higher atmospheric pressure because the seas had evaporated earlier. All of the animals on it did not have eyes, but rather used sonar to asses their environment.

This is an intriguing possibility, but, if we assume that intelligent beings (much like ourselves) were able to develop on such a planet and that they like all other beings there use sonar as their main sense, then wouldn't they not be aware of the existance of light and in turn would they come up with different physical laws?

I thought about what kind of physics they might come up with. They wouldn't be aware of EM radiation directly, but they would be aware of the heat which is cause by it. Thus they would feel the change in days by noting a period when it's warmer (day) and a period when it's colder (night) and they might come up with all kinds of intriguing heat thories, but would they never come up with special relativity?

And furthermore, if they use sonar to 'see' (so to say) then they wouldn't be aware of the cosmos and the only way they could even perceive there to be an atmosphere is to cast larger and larger sound waves upward (surely they'll have a feeling for up, given gravity) to probe deeper and depper. But since sound waves depend on having a medium, and don't travel in vaccum, would they ever be able to develop space travel?

What else can you come up with?
How would the laws of physics differ considerable if we were adorned with a variety of different senses and epistemological tools? Or maybe, would they be the same?

they talked briefly about that (or I missed the beginning) and I believe the animals were a mixutre. I believe the core matter of most animals was organic but also some functions were using methane gas. For example there were these flying birds that flew like jets in that they had their own pokets of methane gas which they combusted to propel them forwards. So they didn't flap their wings and such. Also the intelligent beings floated in the air much like a helium baloon using packets of methane gas that was stored in these baloons attached to their heads. I don't know if their waste was inorganic.

Let's suppose that there are no solid objects and there are no electromagnetically charged objects, and that everything is stratified by density.
Assuming that life can exist in such an environment, it might be difficult for the creatures to notice either gravity or electromagnetism. In fact, due to a lack of objects with well-defined position, they might not even observe kinematics.
If everything is stratified by density, they might not even have a well-formed concept of up or down.

I think that anything that had solid objects that weren't attached to the planet's main body would eventually figure out the existence of gravity. Depending on the planet, they might or might not have lightning and they might or might not have lodestones, but they'll probably experience static electricity at some point.

I think that once they discover certain basic concepts, such as things falling or electrical charge, the exact epistemology ceases to matter. We don't have a natural sense of the nuclear forces, but we can infer them through their effects just as well.

If they never observe something falling, however, and they don't look out at the stars, then figuring out gravity might be a bit tricky.

I assume g is meant and not G.

differnt amout of mass