The classic solipsistic argument. You are right in that there is no "objective" truth, nor "objective" reality that is accessible to us.
However, the rocks are convergently available to us through vision, somatosensation, hearing (if clanked together), smell (yes!), and even taste. Other people will agree with you 100% about the existence of the rocks and most of the properties of the rocks.
Further, the rocks can be measured and examined by way of apparatus such as weights, imaging through magnetism and radiation, etc. Finally, the rocks can be manipulated in different ways and the way the rocks behave can be described formally through chemistry, physics, mechanics etc.
The point is, the rocks behave as predicted, formally described, and do so in ways that intersubjectively is consistent.
Most modern scientist describe themselves as "moderate realists". By this they agree with you that the world is not accessible by other means than our sensory and cognitive systems, but that we can describe the world in ways that reliably capture some of its properties, tranceding our subjective opinions.
This is quite different from religion. In religion the question is not whether there are 4 rocks. There are hundreds of religions. The don't agree whether there IS a god, what the properties of "god" is, how many gods there are, what gods rules are (if there are rules). Basically, religion is chaos, social manipulation of the stupid and needy, and opinion where there are no facts. Religion is fantasy.
NN
Interesting post. Science and religion are not different in the way you describe, though. Modern day religions are just outdated sciences, though ones concerned mostly with morals and not physics, biology and the like. The fact that Christianity is most commonly attacked on these grounds (ie the natural sciences) is a joke... as if this were what is really important. What's really important is the way Christianity has set the rules of right and wrong in our world for over a millennium.
In a thousand years, people will probably look back at some of our most fervently defended scientific theories and laugh. During Aristotle's lifetime, I'm sure plenty of people laughed at the simple minded religious nuts while, in all seriousness, proclaiming the heart was "scientifically proven" to be the center of the "soul." They saw that blood vessels flowed from the heart to every part of the body, and concluded that these vessels transmitted "animal spirits" which governed one's behavior. Because the brain didn't react to touch, Aristotle concluded it was a lump of earth and water, used for cooling the body. Neither he, nor anyone else at the time, could see nerves, so this is what they believed. Who's to say our observations aren't similarly hampered and incomplete?
Then again, maybe the theories won't be much different even ten thousand years from now. Even so, there's no guarantee the rules of the game won't change suddenly, without warning, for no apparent reason at any time and require a total re-evaluation of all our scientific knowledge. Imagine if tomorrow we woke up and the sun didn't rise, people floated through the air, and we suddenly had a sixth sense unlike anything we'd previously known... sure it's not likely, but
for all we know, it's not impossible (since our conception of what is possible is based on inductive reasoning), and an event like this would make even our most cherished scientific "truths" appear as no more than religious babble to a future audience entertaining anyone stupid enough to repeat them.
Also, religion isn't "social manipulation of the stupid and needy," it's social manipulation
BY the stupid and needy. This is a huge misconception. Religions like Christianity are gangs of likeminded people who wage war against the rest of the world, a war of values, of right and wrong. They aren't being manipulated like little sheep, they are manipulating THE REST OF US, by setting the rules of right and wrong, and enforcing them through sheer numbers. Even people who claim they are atheists on account of history, biology, or physics quibbles still behave like Christians for the most part, because they have the same values.
