Did our universe (or multiverse) have to exist? Is it possible that our universe didn’t exist?
Prima facie, it certainly seems like it is metaphysically possible that our universe didn’t exist. Also, there doesn’t seem to be any good reason to think that our universe exists metaphysically necessary.
Notice that something being eternal is not the same thing as it existing metaphysically necessary. Obvious examples of things that exist metaphysically necessary, if they exist, are things like abstract objects (e.g. the number 7, sets, etc.) or God. If there were an eternally existing computer, for example, we could easily ask why is just happened to exist rather than nothing. Perhaps the eternal computer is casually dependent on an eternal being like a computer maker. Another example would be one book sitting on another from eternity. Yes, the book sitting on top has always existed, but it is causally dependent on the book that’s on the bottom.
Nothing in the universe seems to exist necessarily. Think about trees, chairs, phones, humans, animals, plants, planets, starts, galaxies, etc. These things obviously could have failed to exist, and these things pass out of existence. Now the immediate objection might be that matter is what exists necessarily. But why think matter exists necessarily? Isn’t there a states of affairs (i.e. possible world) where matter doesn’t exist? Matter is composed of quarks such that if there are no collection of quarks then matter doesn’t exist at all. Obviously, it seems like there could have been a different set of quarks in our universe; it seems implausible to think that each and every quark exist metaphysically necessary.
Also, it seems like our universe could have been composed of different laws of nature; it’s possible.
If everything in the universe is contingent, then wouldn’t the universe itself be contingent? The immediate charge will be that I am committing the fallacy of composition. The fallacy of composition isn’t always a fallacy. For instance, if every brick in the wall is red, then the wall is red. If I came across a lamp in my living room, we’d say that it exists contingently. Now suppose we increase the size of the lamp to be the size of the state of a planet, same problem. Now increase the lamp to be the size of a universe, same problem.
Since it’s possible that our universe (or our multiverse) could have been different, it follows that the universe isn’t itself necessary. Ask yourself if the leather chair in your living room could have been made of ice. Well if the chair is made of ice it isn’t the same chair as the leather chair. Obviously, chairs can be made of leather or ice. However, the leather chair I’m in isn’t the same chair as a chair of ice. If the universe contained one more rock or tree, which is possible, it wouldn’t be the same universe. Think about a flock of sheep. Flock A is different from Flock B in the sense that they have different types of sheep. Hence, this is true whether or not you think of a Flock or the universe as objects in themselves or as collections of objects.
It should also be noted, as far as I’ve investigated, that no contemporary Philosopher defends the notion that the universe exists metaphysically necessarily. The philosopher, and seemingly the only one, who might have defended the idea that the universe is metaphysically necessary was Spinoza. The only time I ever come across the objection is by people on the internet who haven’t studied the argument and/or haven’t studied metaphysics.