Theological Implications of Relativity

“A thousand years in your sight are like a day that has just gone by, or like a watch in the night.” (Psalm 90:4, NIV)

“But you must not forget this one thing, dear friends: A day is like a thousand years to the Lord, and a thousand years is like a day. The Lord isn’t really being slow about his promise, as some people think. No, he is being patient for your sake. He does not want anyone to be destroyed, but wants everyone to repent.” (2nd Peter 3:8-9, NLT)

Numerous scripture passages imply that God’s relation to time is different from ours. Given that we don’t see time the way God does, it isn’t surprising to learn that our intuitive understanding of time is flawed. Moreover, some Christian theologians have argued that time itself was created by God,An early example is Clement of Alexandria, whose view we’ll discuss in Chapter 10 (along with numerous other views). and there are indications in scripture that time had a beginning. In 1st Corinthians 2:7, for example, the apostle Paul speaks of “God’s wisdom, a mystery that has been hidden and that God destined for our glory before time began.” (NIV, emphasis mine) The Greek phrase here is προ των αιωνων, which can also be translated “before the ages.” The word αιωνων (aionon) is the genitive plural form of the word αιων (aion), which means an age or long period of time. The idea that time itself had a beginning makes good sense in the context of general relativity, as we’ll see in chapter 8. For these reasons, personally, I think Einstein’s theories accord beautifully with Christianity.

However, some Christians are uncomfortable with Einstein’s theories.For an example, see chapter 18 of the book Philosophical Foundations for a Christian Worldview, by Christian philosophers J.P. Moreland and William Lane Craig (Downer’s Grove: InterVarsity Press, 2003), pp. 368-389. They argue that Christians should not embrace Einstein’s theories, and recommend Lorentzian relativity instead. Although I disagree with their views on relativity, I highly recommend the book. It’s an excellent resource for thoughtful Christians, especially those interested in philosophy. Perhaps some of this discomfort results from confusing the theory of relativity with forms of philosophical relativism that are incompatible with Christianity. That’s just a silly mistake. As I emphasized at the beginning of this chapter, scientific theories of relativity have nothing to do with relativism.

A more pressing worry is that Einstein’s theories may not leave room for a robust conception of human free will. If your past and future coexist together in a four-dimensional physical thing called spacetime, it’s not easy to see how your choices and actions could make any difference to the future, which—in some sense—already exists as part of that four-dimensional entity. I have several responses to this worry. First, it is far from obvious exactly what “free will” amounts to, or what the biblical view of free will is supposed to be. This is a complex issue, and Christians don’t all agree on the relevant scriptural points. Some traditional views about God’s providence and foreknowledge fit nicely with the idea that the future is fully predetermined. But if you don’t like those theological views (I confess, I don’t particularly care for them either), there are other things to say about the matter. For one, the idea that spacetime is a physical thing doesn’t imply that events in your future light cone (the events you could potentially influence by your choices and actions) have already happened. They certainly haven’t happened yet in your frame of reference. Nor have they happened in the reference frame of any space alien who might be flying past you just now, since her future light cone coincides with yours at the moment when she passes by.

On the other hand, if the alien is living in a galaxy far, far away (recall this example about the hypothetical planet in Andromeda), she might think that some event in your future is simultaneous with an event that she is experiencing now. Suppose the alien is eating a cheeseburger right now, as you read this sentence—that is, she’s having lunch “now” according to your frame of reference. But in her reference frame, as she enjoys the first bite of that delicious beef and dairy product (this was her motive for abducting those cows, I presume), she regards her lunchtime as simultaneous with the event of you brushing your teeth tomorrow evening. In a sense, your “tomorrow” has already occurred in her frame of reference! Does this show that the course of your future has already been determined, and there’s nothing you can do to change it?

Not really. Remember, there’s no absolute fact of the matter what time it is “now” on that distant alien planet. The notion of simultaneity at a distance is merely a convention, a simple way of thinking about events that have no absolute relation in time at all. In reality, there’s no fact of the matter which day on the alien planet is simultaneous with today or tomorrow on Earth. Moreover, the alien won’t actually see what you do tomorrow until light from Earth reaches her. You’ll get to see your own future long before she sees it! By the time the alien sees your “tomorrow,” tomorrow will have passed. Both you and she will be inside your future light cone, and everyone will agree that the alien saw what you did after you did it. No one—no physical creature, anyway—can “now” see your future. Here’s the upshot: there’s no clear sense in which your future already exists now. The future is part of spacetime, which does exist as a real physical thing. But it doesn’t make sense to say that all of spacetime exists “now.” Spacetime as a whole doesn’t exist at any particular time.

Still, since spacetime is a real physical thing, many physicists have concluded that the entire history of the universe—past, present, and future—must simply exist, timelessly. On this view, all of the events that have ever occurred or will ever occur are just there, frozen inside the unchanging, four-dimensional object called spacetime. In the words of Hermann Weyl, a contemporary of Einstein’s:

The objective world simply is, it does not happen. Only to the gaze of my consciousness, crawling upward along the life line [i.e. worldline] of my body, does a section of this world come to life as a fleeting image in space which continuously changes in time.Hermann Weyl, Philosophy of Mathematics and Natural Science, trans. Olaf Helmer (Princeton: Princeton University Press, 1949), 116.

In my opinion, however, that way of thinking is confused. Spacetime is a real physical thing, but that doesn’t mean we have to regard it as a physical object. We can instead think of spacetime as a physical process. Consider the following analogy. A few years ago, Hurricane Sandy blasted across the entire eastern seaboard, all the way from Florida to Maine. Severe flooding occurred in downtown Manhattan where I teach, and our campus had to close for a few days. Was the flooding a real physical thing? You bet it was. Yet the flooding wasn’t an object, and it didn’t simply exist. It was a physical process that happened over a period of time. Similarly, we can think of spacetime as something like a process, a thing that happens. Granted, different observers may disagree about which events happen simultaneously. But that certainly doesn’t prove events don’t happen at all!

Here’s another analogy that may be helpful. Suppose there is more than one universe. (Many cosmologists believe this is true, as mentioned in chapter 3, and we’ll revisit this hypothesis in chapter 8.) Furthermore, suppose time in other universes has no relation to time here in our universe. (Many cosmologists believe this too.) In other words, there is no fact of the matter whether an event that occurs in some other universe happens before or after an event that occurs here in our universe. Would the fact that there is no time relation between those two events imply that events don’t really happen, or that time is just an illusion? Hardly. There could still be a very real distinction between past, present, and future here in our universe, even if there is no fact of the matter which events here are simultaneous with events there.

It’s easy to think of spacetime as an object when visualizing worldlines, light cones, planes of simultaneity, gravitational curvature, and so on. When thinking about the nature of time itself, however, those visualizations may be misleading. It is more natural to think of the passage of time as a process. Although Einstein’s theories do show that our ordinary intuitions about time are mistaken in some ways, his theories give us no reason to reject the notion of time altogether. Nor do they give us reason to believe that future events are just “there,” frozen inside a timeless four-dimensional object.

But what if God sees the entirety of spacetime “all at once,” so to speak? Traditionally, most Christian thinkers have affirmed that God knows the future, and there is strong biblical support for this claim. Some have suggested that God knows the future simply by seeing it, perhaps from a perspective beyond space and time. If the future is already finished from God’s perspective, does this eliminate the possibility of human free will? I have no idea. The relation between God’s foreknowledge and human freedom has been debated for centuries, and I won’t even try to summarize the arguments here. In any case, it is unclear whether Einstein’s theories bear on those issues at all, except to the extent that relativity lends support to the traditional Christian claims that God isn’t confined within space and time, and that space and time themselves are part of the created physical world.