Our observable universe is not 30 to 38 billion light years in distance.
 Dusty_Matter Posted: Fri, Jun 26 2009 10:17 PM | Reply |
While perusing the August 2009 issue of Astronomy magazine, I came across a one page article who’s topic was on the edges of our universe. In it, was the idea that the limit of our observable universe is roughly to about 38 billion light years in radius from us. This is wrong. In the article the author mentions a galaxy named A1689-zD1, who’s light took 13 billion years to reach us. In other words, we can glimpse a galaxy as it was 13 billion years ago. Now, 13 billion years ago A1689... was only 3.35 billion light years away from us, however because of the expansion of the universe it now lies about 30 billion light years away. This is true.
If it took 13 billion years for the light to now reach us, from a galaxy that was only 3.35 billion light years away from us in distance, that would mean that that light is extremely stretched. (red-shifted)
If the universe is 13.7 billion years old, and now A1689... Is 30 billion light years away from us, if we subtract 3.35 billion light years from that distance and average out that galaxies speed of recession from us, how fast is that galaxy’s average speed of recession from us? The answer is almost twice the speed of light. 30 - 3.35 = 26.65
26.65/13.7 = 1.945
How can we observe something that’s average speed is almost twice the speed of light? And as an object gets farther and farther away from us their speed of recession increases due to the expansion of the universe. In other words A1689... Is really traveling at more than twice the speed of light from us, now. How can they say then, that our observable universe is roughly 30 to 38 billion light years in distance? It’s not. Looking out in distance is also looking back in time, and we can only see so far back into time. About 13 billion years or so.
It’s like taking a photo of a bird in flight. And then six months from that time, you pull out the photo show it to a friend, and say. “That bird is now thousands of mile away, and so because of this photo, I can now see over a thousand miles in the direction that that bird flew in.” The Hubble Ultra Deep Field shows lots of little baby galaxies. These galaxies are now well over 20 billion light years away. Do you think they stayed little baby galaxies? They never merged, or collided, shrank in numbers, and grew in size? Is the photo of A1689... From 13 billion years ago still a current photo? Because that galaxy (which has certainly changed in over 13 billion years time) is now 30 billion light years away, is it justifiable to say that we can now observe things 30 billion light years away? Can we see objects that are receding from us at twice the speed of light or greater? The answer is no.
While distances can be confusing, we can only see as far back in time as about 13 billion years ago. That severely limits our observational horizons. We cannot see those ancient distant objects where they reside today, and their light will now never reach us. Our observable universe is limited by time, and speed of recession, and nothing is going to change that.
The author then said something about the “great attractor” being beyond our visible universe. He says “many astronomers think this…” As far as the “great attractor” is concerned, it is not located outside of our observable universe, especially if you are saying that the horizon to our observable universe is at least 30 billion light years away. In fact it lies much closer than even 13 billion light years away. It is thought to be in the region of the Shapely Supercluster. All less than even a billion light years away. I can’t help but wonder, just how “many astronomers” think it’s beyond our visible universe?
I am also beginning to wonder if the writer of these articles is really doing his own writing.
I am also beginning to wonder if the writer of these articles is really doing his own writing.
“You cannot choose what reality is. It is what it is” ---- Me.
