Sometimes agnostics will note it is possible that there are forces in the universe we cannot understand, and they are absolutely right. The observable universe is 92-94 billion light years in diameter, and we have no way of knowing, and will probably never know what lies beyond this cosmic light horizon. The thought of what exists on these unimaginable orders of magnitude inspires feelings of genuine wonder and reverence, but this is not a reason to remain agnostic about the origin and meaning of life on Earth.
At each observable order of magnitude, we see complicated orderings of matter and energy. There are layers of complexity and beauty, from quarks to superclusters. If we only had enough information we might be able to zoom out further and observe the large scale structure of the universe and the structure of whatever might exist at greater distance scales. There is no reason to assume that complex organization ceases at the largest order of magnitude that we currently have the ability to observe. Of course, we can have no information about what exists that is larger than the universe, but there is good reason to suspect there is something, and that it is ordered in some incredible and unimaginable way.
Some scientists have proposed an alternative to the big bang theory called the ekpyrotic theory of the origin of the universe. This theory imagines that our universe, which has three spacial dimensions, is a “brane” moving within a higher dimensional space, and that the expanding universe as we observe it is the result of a collision between branes. The ekpyrotic theory relies on certain assumptions of string theory, a controversial idea in theoretical physics.
The ekpyrotic theory of the origin of the universe is very speculative. Most likely, we will never be able to test the underlying assumption of string theory — that higher dimensions exist — but the existence of the ekpyrotic theory shows that scientists are willing and able to imagine that structure exists at scales larger than that of the observable universe.
The uncertainties about the origin of the universe are legitimate sources of wonder and doubt. It is entirely possible that intelligence exists at these scales, and it is even possible that such intelligence interacts with our universe in some way, but it has very little to do with the origin or meaning of our lives here on Earth.
Human scientists have an incomplete picture of evolution and very little information about its very beginnings, but the broad outline of the evolutionary process that produced human intelligence is known. We understand how we got to be here, roughly, and we have enough information about the nature of our purpose to have no need to plead agnosticism.
Homo sapiens evolved because the features that humans possess are the ones that were necessary for our DNA to survive and out-compete other DNA variations. Our purpose is therefore clear: to survive and continue to evolve. Finding the answers to the questions that are scientifically unknown, or scientifically unknowable, will tell us nothing further about our purpose in life.
We may discover that evolution started from a cosmic seed, or we may discover some mechanism by which evolution began locally. Either way, we evolved from primordial organisms, and our purpose would remain the same: to be organisms that fight for continued survival and for the survival of our progeny.
Whether or not some higher intelligence exists at distance scales greater than 92 billion light years is irrelevant to any humanly purpose because we can never know, measure, or interact with any entity so big. The idea that an entity on that order of magnitude could have any preferences about what we do with our lives or whether we survive is ludicrous. We would not appear to it as ants appear to us, we would appear as pico-creatures. It is impossible to even imagine the motivations or desires of such an entity, let alone construct an ethical theory based on it.
It is true that agnosticism is the default position of all scientific thinkers (why take a position when there is no information?), but there is ample information about the nature of our universe, and every bit of information tells us that there is no possibility of intelligent design.