The seven-day week is almost universal, across diverse cultures. It has no basis in astronomy (or anything else) that anyone can identify.
Different cultures vary on almost everything. What people eat (and how), standards of dress, etiquette, hospitality, all of these things can differ. But somehow, a week of seven days is found across the world, and has been for as long as anyone knows.
Atheism has no explanation. Even Wikipedia has no explanation. (Those two statements, unfortunately, are virtually identical.) Some have speculated that the Babylonians first came up with it based on lunar phases, but since a week based on lunar phases would often require extra days, it would hardly provide a compelling case for others to adopt, unless a week of approximately seven days had some other appeal to it. Somehow, the ancient Hebrew practice of a seven day week managed to become the standard everywhere. Atheism can’t explain it.
There’s another group that has no real explanation, either — those who say they believe the Bible but claim that the first chapter of Genesis is talking about geological ages, rather than an actual seven-day week. They may think they’ve made an accommodation for modern theories, but they’ve left a big gap — whence, then, the seven-day week? Why should the whole world adopt such a thing? What would influence them to do so?
There have been attempts to do away with the seven-day week. In France, after the revolution, they used a ten-day week for a time. Soviet Russia attempted to use a five-day week, with workers getting the fifth day off, though everyone was on a different schedule. (Yes, in the “worker’s paradise” they had to work eight days to get two days off, and your wife probably got a different day off than you. Brilliant.) They also attempted a six day week, with every sixth day off work — thus, the Soviet calendar below, with the day off marked in blue.
It didn’t work. It didn’t even work at the time: the calendar shows the six-day week marked out on a calendar that is based on a seven-day week. Even in atheist Russia, the first day of the week on that calendar is labeled with the Russian word for “Resurrection,” the seventh day with “Sabbath.” The French experiment faded quickly. Both France and Russia use a seven-day week, just like everyone else.
So far, no one has come up with a non-Genesis explanation that has any credibility. For those who believe that Genesis 1-2 is history and actually means what it says, there’s no difficulty. God instituted a seven-day week. He could have spoken the world into existence and completed the task in seven seconds, or less. He used seven days for a reason. He placed an awareness of it within the humans He had made.
God also placed within us an awareness that it isn’t right for people to work every day, they need a break every week. Everyone knows that: even if people could gain more money, and more power, and more influence by working more — it’s not sustainable. The seven-day week, and a period of rest from work every week, has been placed within us by the Creator. Atheism may try to find another explanation for many of the things God has done but they have nothing on this one. It would be better if they just accepted this:
1 Thus the heavens and the earth were finished, and all the host of them.
2 And on the seventh day God ended his work which he had made; and he rested on the seventh day from all his work which he had made.
3 And God blessed the seventh day, and sanctified it: because that in it he had rested from all his work which God created and made.