I think there is a mistake in this dichotomy. Do really big numbers "exist?" Are really big numbers meaningful?

Sometimes I think we conflate those two things, and I don't think they are the same.

My interpretation would be that numbers do not exist on their own. Only your thought (as in physical process) of them does.

How can you be sure is not the same with physical reality? Ie. That only your thought of it exists.

After all, the only thing that we can be certain of is our own (subjective) experience.

There is no reason to assume my thought (as in physical process) is self-sustaining. Rather it seems to be powered by the rest of the stuff.

Not sure what you mean about assuming a self-sustaining thought.

The point is that you can never experience anything outside your own point of view, which means that you can never know if anything outside of your own personal experience is at all separate or independent of it.

Sure, you can “trust” others when they say something to you, but you can never experience anything from someone else’s perspective (unless you could become them, but then you’d stop being you). All experience is subjective. We can all try to agree on what something (a physical process) means, but that is only an agreement, it is not “true reality”. So in that sense, you can never know what “true reality” is, except for whatever you subjectively experience.