I don't think that the multiverse account implies that it's irrational to pursue life goals or irrational to believe that pursuing life goals is meaningful or valuable. For even if the multiverse theory is true, I take it that you yourself are confined to one universe, our universe. The beings very similar to you who inhabit other universes are at best "counterparts" of you, which leaves open the question "What will you do with your life?" It may be well and good if one of your counterparts works hard to achieve wisdom, promote justice, or whatever, in some other universe. But his/her hard work isn't yours and doesn't occur in your universe. We need your shoulder to the wheel here!
I can't resist responding to one thing that Prof. Stairs says in his excellent reply: "If there's no such [necessary] being, then it might be that there's no explanation for why contingent things exist." I used to think that myself. But as I thought more about the question "Why do any contingent things exist?" I concluded that the question has a very simple answer -- indeed, many simple answers -- if it's a well-posed question in the first place, and those answers have nothing to do with any necessary being. I try to explain why in this paper.
It is indeed an interesting question, and in fact it's more than one question.
To begin with, my colleague is correct: in special relativity, length is like velocity in classical mechanics: it's a "frame-dependent" quantity. However, the theory of relativity is also a theory of absolutes; between any two points in space-time there is a quantity called the interval, and it is not frame-dependent. To put it in the jargon of relativity, the space-time of special relativity has a metric -- a generalized "distance function" -- and that metric delivers an unequivocal answer to the question of whether the interval between w and x is equal to the interval between y and z.
But now we have a new question: suppose that relativity says that the interval between w and x is, in fact, the same as the interval between y and z. What kind of fact is that? Suppose that the two intervals have no overlap. Doing business as usual, so to speak, we come up with the answer that the intervals are equal, but we could use a different metric function that gave a different answer, and by making adjustments elsewhere, we could make the physics work out. The physics that made the adjustments might be more unwieldy; it might involve some peculiar "universal forces," for example. However, it's not immediately clear that this shows the usual way of doing things to be ontologically privileged.
The debate we're now describing has to do with the "conventionality of the metric," and some heavyweight thinkers, not least the philosopher of science Hans Reichenbach, have argued that the metric is indeed conventional. That is, it depends on choices we make that could, in principle, have been made in a different way.
This issue has a connection to questions about meters and such. We pick out a meter by reference to the standard meter stick (or at least, that's how we used to do it.) But there's some complexity here. Suppose I take my own meter stick, lay it against the standard meter, and find that they match. While they're in contact, there's no doubt that they have the same length. But what about when they're not? Does my meter stick retain its "real" length when I move it around? (Leave issues of relativity aside for the moment. We could say things in a more complicated way that took them into account, but the issue would not really change.) Or does it contract or expand? Or is there really no absolute metaphysical fact of the matter? The conventionalists would pick this last option. When we consider the whole package of our physics and our measuring devices and our assumptions about forces, we may say that (absent unusual circumstances) the measuring rod has the same length when it's "here" as it does when it's "there." But the conventionalist would insist that saying this ultimately rests on certain stipulations or conventions.
The literature on this topic is complex, as you might imagine. Even though he argues for one side rather than the other, I'd suggest that Reichenbach's Philosophy of Space and Time is a good place to start. It's an engaging book that's more accessible than it might appear at first sight.
In my opinion, it's no harder to reconcile freedom (free choice, responsible action) with determinism than to reconcile it with indeterminism. On the contrary, it may be easier; see, for example, this SEP entry. According to compatibilists, we can act freely even if determinism should turn out to be true and hence even if the indeterministic interpretation of quantum mechanics should turn out to be false. But no one thinks that the truth of indeterminism (whether quantum indeterminism or some other kind) by itself would suffice to give us freedom. The debate is about whether indeterminism is necessary for freedom. In my view, incompatibilists bear the burden of showing that it is and have failed to discharge that burden.
Here is an argument that determinism doesn’t undermine, butenhances, free will.
(1) Our actions are caused by our propositional attitudes,such as desire, hope, acceptance and belief.
(2) The more deterministic the relationship between out attitudesand our actions, the more freedom of will we possess.
(4) The more control we have over our own attitudes the morefreedom of will we possess.
(5) Our control overown attitudes consists in the influence of some of our attitudes over others.E.g. We want to smoke. We also want not to smoke (These are called first-orderdesires) And we want not to want tosmoke and we do not want to want to smoke. (These are called second-orderdesires) We have freedom of the will toextent that our desire not to want to smoke wins out. (From ‘Freedom of theWill and the Concept of a Person’, Harry Frankfurt, The Journal of Philosophy,1971).
(6) The more deterministic the relationship between oursecond-order desires and our first-order desires, the more freedom of will wepossess.
(7) Determinism is irrelevant to freedom of the will in allother respects. It doesn’t matter how our attitudes got there – whether byrandom processes or deterministic ones, they are as they are. And we want themto be in control of our minds and our bodies – for self-management and managementof the external world, as far as possible.
Good self-management – looking after your own desires,emotions and reactions to things is a healthy Stoic philosophy. If you feel yourselfgetting angry and resentful ask yourself why you feel this way – for example: isyour pride affected, or your self-esteem or do you feel threatened in someother way? Ask yourself whether you might have done something to bring aboutthe situation that angers you. Ask whether realistically there is somethingconstructive that can be done to rectify matters. If vengeful thoughts arise,recognize them and banish them. No good can be achieved by vengeance. Harm toyourself would result fro, any attempts at revenge. If there is somethingconstructive to be done, decide whether to do it. If you decide to do it, doit. If you decide not to, let the matter pass and move on. Consider that youyourself would prefer peace of mind than the disturbance of the anger. In thisway you can exert some control over your own mind and attain a more sereneexistence.
Also I have heard tell that quantum laws fix the probabilityof any event’s occurring. No self or soul or will can affect theseprobabilities without violating physical laws.