Okay, okay, I'm finally going to swallow my pride, and ask the dumb question:
Since all matter in the universe supposedly came from a "protoatom" or whatever, which began expanding at the instant of the "Big Bang" (from which locus I assume the "earliest light in the universe" would also originate); and since all matter has been rushing away from that locus ever since the BBM ("Big Bang Moment"), and further since the speed of travel of that matter--including our own galaxy, containing the solar system, the earth and us--would have been traveling at less than the speed of light, my question is:
How can we then "see" the original light? Wouldn't it have gone "past" us and out into the empty void long, long, long ago? Or does it somehow travel along with us at slower than light speed (because there was no universe to expand into)?
If the latter, doesn't that mean that the light would be traveling at less than "light speed"? Is there then such a thing as "slow light"?
I hope someone can 'splain that to me, because I have always found it a source of confusion.
Alamo Girl has given this an even greater theological twist with the posting of her Origins thread a couple of months ago. Check it out. It contains a lot of allusions to modern physics.
Best to you. Everything Good....
Your question is a good one, and I'm probably not going to help much, but here's my thinking on the "original" light. There are probably a few different concepts involved here, so I'm pinging those who know this far better than I do. The well-known background radiation is as original as it gets, and although it isn't in the visible range of the spectrum we can detect it. Why hasn't "left us behind"? Why is it just now getting to us? If it were invisible, that would mean that it is so far away that it hasn't yet had time to get here, which would imply that the universe expanded faster than light. But by the time the first light was created, the presumed inflationary FTL expansion had ended. So it's within range, thus visible. Does that help? I didn't think so. Someone will pop up and explain it to us both.
How can we then "see" the original light? Wouldn't it have gone "past" us and out into the empty void long, long, long ago?
That is not a dumb question. It is an excellent question.
There are two closely interrelated reasons, both from special relativity: time dilation and the relativity of simultaneity.
Let me preface my comments on relativity by saying that the earliest light we see is not from the instant of the Big Bang, but from a time about 300,000 years after the Big Bang. Before that, the universe was opaque, because it was composed of charged particles. Around that time, atoms began to form and the universe became transparent.
As another preface, let me emphasize the fact that because of the expansion of the universe, the farther away something is, the faster it is moving away from us. This is a very key point. Given the finite speed of light, Galileo would not have been surprised to hear that we can see objects in the early universe. If we're fleeing from a light emitting object at nearly the speed of light, then in the emitter's frame, it will take the light a very long time to catch up with us.
As you realize, however, life isn't so simple, because light is also moving at the same speed relative to us. If the object is close by when it emits its signal, it should reach us in a short time no matter how quickly the emitter is receding. How can these two seemingly conflicting pictures be resolved?
Time dilation: To an observer in an inertial frame, time passes more slowly in any other inertial frame that is moving relative to the observer. The objects that we see at a great distance are moving at relativistic speeds with respect to us, therefore, time is moving more slowly. Not only are we seeing them at an earlier time (owing to the time it has taken for the light to arrive), but time is elapsing at a slower rate there than here.
Relative simultaneity: Events that are simultaneous in one frame are not simultaneous in another frame. Because we are receding from these distant objects, events that occur in those distant locations simultaneously (in our inertial frame) with events here actually occur at a much earlier epoch of the universe than the events here. Our axis of simultaneity reaches into the past of receding frames, and the more distant the events, the farther back it reaches.
[Geek alert: why does distance matter, and not just relative velocity? Because the time of the event in the moving frame is the intercept along that frame's time axis. The relative velocity only determines the slope of our axis of simultaneity (i.e., our space axis). To find the intercept, you have to extrapolate that slope over the intervening distance, and the farther you extrapolate it, the farther back in time the intercept gets pushed.]
These two different aspects of special relativity are really two ways of saying the same thing: that as viewed from our inertial frame, much less time has elapsed over there since the Big Bang than has elapsed here. We are only seeing their relic light now, because we had a big head start. (To them, of course, we are the retarded ones; our neck of the woods is the one that sent off its relic light way late.)
Illbay,
If it was like a flash from a camera, yes it would but stars, galaxies and quasars are 'on' for millions to billions of years. Based on the distance, you're loking back in time. If you see an object 100 million lights years away you're seeing the light that shined from that object when it was towards the end of the Cretaceous period (Age of Dinosaurs) ... it's just been travelling all that time. In the meantime, the star could have gone supernova 50 million years ago. Because it's so far away the light from that explosion wouldn't reach us 50 million years from now.
On a smaller scale, the Sun could explode or go dark and we wouldn't know it for 8 minutes.