……it’s a matter of time
Often, in metropolitan areas, it is common to describe how far one is from a given spot by saying how long it would take to get there. For example, “..the City Center is about 30 minutes from the lake.” Everyone pretty much knows what that means….at a typical driving speed it will take 30 minutes to get to the lake from the City Center. So, we are describing distance in terms of time, given that everyone knows what the typical driving speed is. It is exactly the same for describing distances in space. Except here we use the term light year, as opposed to “minute”, meaning that 1 “light year” is the distance light will travel in a year. The word light clarifies that the “typical” speed is the speed of light, as opposed to, say, the speed of the family car. And, of course, the word year refers to the time the light travels…..a year. For us earth bound mortals a light year turns out to be a little under 6,000 million miles (5,866,000,000,000 miles to be sure). For example, “The distance across the Milky Way galaxy is 100,000 light years.” So, at the speed of light, it would take about 0.100 million years to travel across our galaxy…..586,600,000,000,000,000,000 miles! A fair distance indeed!
However, looking further out into space, we can see objects that are 2,000 million light-years away and more. In fact, there are objects in deep galactic space that are 12,000 million light-years distant….it takes light 12,000 million years to get here for us to see it. It is here that an impossible situation occurs. For a variety of reasons it is theorized that the universe is about 13,700 million years old. That being the case, when we observe something that can be measured at 13,700 million light years distant, then we are looking at the limit of what we could ever see! There may well be structures beyond 14,000 million light years from us but we cannot see them today simply because time has not existed in this universe long enough for the light or radiation to reach us. We have reached a time barrier. There’s a couple of interesting concepts that emerge:
- At the very minimum, an object just beyond the time barrier, say 1 light year beyond, will not be visible until next year….provided however, that the universe is not expanding. But the Universe is expanding, therefore the light from the object will have that additional distance to travel and so will not be seen until sometime later than next year!
- Let’s suppose we wait the extra 1-plus years and the light from that object 13,700 million plus light years away actually arrives. What do we see? We will see the object as it appeared when it first begin emitting light….when it first formed! In fact, the object may have lived it’s life and died eons ago. However, the entire life history of that object is currently traveling through space….waiting for us to sequentially detect it and see it’s origin, it’s development, and finally, it’s destruction! We can see it…but it is not interactive!
- Bear in mind that while we can see the object by detecting the energy it emitted way back then, we cannot travel to it….this is not a time machine waiting for us to hop on. The object is as surely gone as is a jet plane flying high overhead, although we may still hear it’s engines.