system
Given the following post, respond as if you're commenting on Reddit:
human
Is there a 'fantastic planet' out there? Could there be a terrestrial planet thousands of times the size of Earth, orbiting a Sun thousands of times as big as ours, inhabited by giant humanoids?

Theoretically, could there be a terrestrial planet thousands of times the size of Earth, orbiting a Sun thousands of times as big as ours, inhabited by giant humanoids? I was reading about geometric scaling of animal life on Earth due to the increased difficulty of absorbing oxygen with bigger organism size. I'm curious if the size of oxygen atoms would limit such massive life from occurring somewhere out there. 

EDIT Well to open up the question...What about a smaller planet with less gravity? I guess I'm ultimately interested in what science can tell us about the potential range and scope of alien life - intelligent life.
gpt
There are other scaling problems than just oxygen absorption. Strength is approximately related to the cross-sectional area of a muscle, but mass is proportional to volume. If you double in height your muscle cross section, and thus strength, go up by a factor of 4 but your weight goes up by a factor of 8. If you scale things up too much, you become too heavy to move. This is one reason why terrestrial animals are limited in size and why aquatic life can be bigger. A large planet would have higher gravity and would only make this problem worse.