The Grand Time Machine

Time TunnelOne of the lesser understood concepts in astronomy for lay-people is the notion that we can never see what is happening in the universe right now. Instead, when we point a telescope sky-ward, we are looking back in time. Because light is a property in the physical universe, it moves at a finite speed … it takes time for the light that reflects, or is emanated from, any object to reach our eyes. In the tiny distances we are used to on earth, the time differences are infinitesimal, but space is a different story all together. Even looking at our own moon, the light we see has taken 1.3 seconds to reach our eyes after it reflects from the moon’s surface. That means when we see the moon, we are actually seeing what it looked like 1.3 seconds ago, not a live shot.

The farther away we get, the more pronounced the effect gets. The light from our own sun, which powers practically everything on earth at least indirectly, is already over 8 minutes old when it hits our eyes or telescopes or trees and the light from the closest other “sun” to our own, Alpha Centauri (which is actually part of a “system” of stars, as opposed to our single star) is well over 4 years old when it reaches us. The effect is so pronounced that astronomers use the term “light-year” to represent distance. As a measure of the distance light can travel in one year, it is a measure of distance, and not time, but it is also a reference to time in a very direct sense. Any object that is 1 light year away, will be seen by us as it was one year ago.

As we look deeper and deeper into the universe, we look farther and farther back in time. Scientists who study the origins of our universe, often called cosmologists, use powerful telescopes to collect light that has taken billions of years to reach earth, and in that way they can actually look directly at the early universe. Even a normal Hubble Deep Field shot, or the image above looking at a 12.1 billion year old quasar, span vast time ranges, with closer stars appearing newer, and farther stars appearing older. The farthest, and oldest, object we have yet imaged is a distant galaxy, 13.6 billion light years old, from a mere 750 million years after the universe began.

This all presents something of a paradox as well. Another well known concept of cosmology is the expanding universe … astronomers clearly show other objects in the universe to be “receding” from each other. Cosmologists speculate that the universe was once much smaller than it is, and in fact, the “big bang theory” speculates it began as a singularity of infinitesimal size and expanded to present size from there. And therein lies the paradox … if the distant universe was much smaller than today’s universe, how can we look across vast distances to see what they were truly like at a time when there were no vast distances to look across (or more accurately, far less vast distances). When we look at something 12 billion light years away, we are looking at it as it existed in a universe that wasn’t 12 billion light years in size yet.

To me, this seems to indicate that the expansion of the universe, at the very least, is happening at very close to the speed of light, and in some cases faster than the speed of light, although that phrase starts to lose its meaning somewhat when we talk about this. And excellent example of whats happening is to think of raisin muffins rising as they cook … the dough expands and the raisins get farther apart, and raisins that are farthest apart move apart faster than those closer together. There isn’t really a “true” speed of expansion as a result … instead, the expansion can only really be seen in terms of relative expansion to other objects. Where the muffin analogy falls down is that we can only imagine a “finite” muffin, while current speculation points to an “infinite” universe.

Another fly in the ointment, so to speak, is the fact that scientists see evidence of a rapid, mega-expansion early in the life of the universe. Light from this time seems to be forever beyond our view, at least using current viewing methods, and this indicates there almost certainly periods in the very early universe where the speed of expansion was much faster than the current speed of light. There is further evidence that the speed of expansion is in fact increasing today, indicating that some of the most distant objects may “freeze” in our view as they pass beyond that speed threshold, and then fade into blackness.

All of this is, of course, speculation and theory. Its all based heavily on observations rooted in the physical element of electro-magnetic radiation which travels at a finite speed. The information we receive, and the way we perceive it, is very tightly tied to that finite speed. It can make what we see very hard to interpret, and even harder to understand. Scientists make an excellent effort of sorting through all that, but in many ways, we are still looking “through a glass, darkly.”


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