From the perspective of many atheists (though not all), there is no external supernatural meaning-giver that provides the yardstick by which all is measured. And yet, we nonetheless have a direct experience of things or activities being meaningful to us. Where does this meaning come from? Is it “real” in any meaningful sense? Let’s explore that question from the perspective of an atheist for the moment. While not all atheists go through this particular line of reasoning, I, personally, find it quite compelling.
Let’s suppose, for the sake of simplicity, that humans are the only truly sentient, conscious entities in the entire universe. This may very well be false, but it doesn’t change the argument. If there is something else truly sentient and conscious in the universe, simply substitute the first thing of that type that came into existence into the following argument in place of humans.
Now imagine the universe before humans. There are galaxies, stars, planets, even life, but nothing truly sentient. Nothing self-reflective. Nothing whose minds have developed to the point of being able to really think abstract thoughts. In such a universe, devoid of anything that can think, is there any “meaning”? I would say no, there isn’t any.
But now, gradually, perhaps with no clear “ah-hah” moment that distinguishes before and after since it is all really a question of degree, there comes to be some life-form, some being, some human or proto-human that decides that something else matters… that something has meaning. In a very real sense, “meaning” has started to exist. Maybe it only exists in the mind of that proto-human, but nonetheless the universe is now different. Before, there was clearly no meaning anywhere in the universe. After, there is something within the universe that can think well enough, deeply enough, reflectively enough, that it can ascribe meaning to things… even to the universe itself.
In that transition, the universe itself, in a sense, has become self-aware. The universe now contains beings that can think about the universe. Consider how profound that is! Meaning now exists! It may not be an absolute meaning in any real sense, but it is meaning nonetheless.
Now, imagine what a loss to the universe it would be if the last such self-aware being were to perish. Meaning itself would cease to be. Whatever the content of the “meaning” that the meaning-attributing-beings themselves gave to the universe, a higher-order meaning would be lost. A meta-meaning, as it were. It seems that there is an absolute good that comes from there being meaning-attributing-beings in the universe, because without them, there is no meaning.
Now, it’s a long way from that very simple, but very profound, observation to the development of a system of meaning applicable to day-to-day life. But long as that way is, we have to realize that what we have already done is something that theists have said for a long time is impossible. We have derived a basis for a moral absolute in the absence of God. There is good in the world, and it comes from interacting with, thinking about, and trying to understand the universe itself. The better we can do those things, the more meaning the universe itself has, because we are part of the universe. In a very real sense we are the most important part, because we are the beings that attribute meaning, the beings that determine what is important. There is no value without beings that can attribute value, and we are those beings.
As I said, not all atheists follow this line of thought. But it is the line of thought that I find most compelling, and thus is the approach that I can most readily explain and defend.