05/17/2012 08:16 am ET Updated Jul 17, 2012

Science and the Ups and Downs of Christ's Ascension

May 17 is known as Ascension Thursday (the 40th day of Easter). It is the day many Christians observe Christ's ascension into heaven, though some will do it on the following Sunday. The day means many things to Christians, including the idea that Christ will also one day descend from heaven in his return.

What intrigues me about the ascension of Christ is not only what it tells me about the ancient world and its "scientific" knowledge of the universe, but also what it tells me about many Christians today.

As to the former, while ancient "science" is not really science, one may call it that loosely in that it is an ancient perspective on the structure of the universe. This comes out clearly in many places, but especially in Acts 1:9-11, which records the ascension of Christ in these words:

When he had said this, as they were watching, he [Jesus] was lifted up, and a cloud took him out of their sight. While he was going and they were gazing up toward heaven, suddenly two men in white robes stood by them. They said, "Men of Galilee, why do you stand looking up toward heaven? This Jesus, who has been taken up from you into heaven, will come in the same way as you saw him go into heaven."

The ancient world at this time understood the relationship of earth to heaven as one of moving up and down. This is not only directional, as if one is on an escalator -- though the Old Testament patriarch Jacob did have a vision of a ladder that went up to heaven (Genesis 28:10-19) and some tried to build a ziggurat to heaven, known popularly as the Tower of Babel (Genesis 11:5-8) -- but also an act of moving from imperfection below toward perfection above.

This perception of the universe lasted for millennia.

Earth is below and most likely understood to be a disc by many of the ancients. Above it is the firmament (Genesis 1:6-7), a solid dome that holds back the waters of heaven, the same waters that are said to flood the earth in Noah's day (Genesis 7:11). The firmament provides a structure for the universe, a barrier to heaven (which is above it), and the planets move across it.

Imagine "The Truman Show."

The ancient Christian theologian Augustine, for example, affirmed that this firmament was a solid dome in response to philosophers arguing that there is no way for water to stay in the sky since it is too heavy. Augustine was convinced, however, that even without a firm dome God could keep water in the sky if he wanted to since he could do anything. "If God ever wished oil to remain under water," argued Augustine, "it would do so" ("The Literal Meaning of Genesis" 2.2). Likewise, I'm sure the same could be said about Jesus standing on a cloud at his ascension.

This idea of heaven above was easily incorporated into the later Ptolemaic system of the universe, named after Claudius Ptolemy (c. C.E. 90-168). According to this revised view, the universe was a set of nested spheres along which the planets rotated around the earth (geocentered). This system stuck around for a long time.

Medievals understood this view of the universe to have a theological message. The earth is not so much the center of the universe in the Ptolemaic system as much as it is the bottom. Like earlier ancient models, to move up in the spheres is to leave earth and move toward perfection in heaven. Christ leaving his throne in heaven for earth is not a journey to the center of the universe, but a condescension of Christ to live in the margins at the bottom of the universe.

This was a sign of his love for humans.

Christ's ascension and return mentioned in Acts made sense in this up-and-down universe; it was not like anyone had ever been to space. This was eventually challenged, however, when the astronomer Nicolaus Copernicus (1473-1543) introduced the heliocentric view, namely that the earth and the planets move around the sun (helio).

There were many implications for Copernicus' position. To reject the idea of heaven as above runs counter to the record of Acts and it could put Jesus' return into question, particularly since Acts says his return will happen the same way as he left.

Copernicus' discovery took a long time to be accepted, especially because of the theological significance of the earlier views. In fact, a 1999 Gallup poll showed that 18 percent of Americans were still geocentric at the turn of the millennium.

So where did Christ go when he ascended? Did he really move into the sky on a cloud? Did he hide up there and wait for the disciples to leave before disappearing another way? When he returns will he come from space? Does he wave to the International Space Station on his way back? As one of my students responded: "You're right, I do imagine heaven above like that, as if Wile E. Coyote's spirit ascends into the clouds."

You get the point.

How should Christians understand the ascension of Christ? Those who are aware of the difficulties of the ascension in the known universe allegorize it and treat it as a metaphor. Others stick to the script. "The Jesus Film" project, for example, has Jesus ascending into the sky at the end of the movie and that is actually closer to the biblical story, which does not indicate any sense of implied allegory.

This means that many modern Christians who read the accounts of the ascension and predictions of Christ's return in literal terms are actually thinking about the universe like ancient peoples. Perhaps there is an unacknowledged disconnect. Maybe contemporary Christians do not imagine a firmament above since they are aware of space and galaxies, but when it comes to how they describe Christ's ascension and return, they are absolutely ancient.

They may play with their iPads, but they are thinking like a generation writing on clay tablets. They may read the news about future trips to other planets, but imagine our planet in such foreign terms that it might as well be an alien world.

As an historian, I'm curious as to how different Christian beliefs will be in the next century. Many already know how young earth creationism is challenged by discoveries in the last 200 years and some are becoming aware of the challenges of neuroscience to long-standing theological conclusions about human nature. Yet I think that many professional or avid lay theologians miss the discussions that have to occur in lesser-challenged ideas, like the ascension and return of Christ.

These are simply the ups and downs of doing Christian theology.