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dnr
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I asked this question of a friend.
We read certain reports that astronomers have “seen” “light” from 500 million years, only, from the creation of the universe. Here is my query.
1. The universe “started” as an almost infinitely dense singularity.
2. As this thing expanded, all sorts of interesting things happened, which resulting in stars, galaxies, heavy elements, x-ray background, etc.
3. As the universe expanded, except for the brief “expansion faster than light” issues, it was expanding at less than the speed of light.
4. This means than all of the bundles of photons have been expanding at the same rate as the universe.
5. So, all information about what happened over the 14 billion years of the universe has expanding at the same rate.
6. This means that there is no “looking” into the past, because this information has been expanding, along with the universe.
7. The universe then should then be uniform, i.e., the same age, since it has been expanding with “us” since the beginning.
8. No matter what direction we look in, we should see exactly the same thing.
9. We should not see stuff from the beginning or 10 billion years ago, because everything has been expanding at the same rate and therefore all bandwidths of information from that source have always been with us.
10. Stuff expanding in the opposite direction from us, is still moving slower than the speed of light, so we should see it exactly as it is now.
11. There is no reason that when we look at increasingly sensitive instruments, e.g., the updated Hubble, that we should see anything but current information, i.e., the wavelengths from everything has been traveling with us since the big-bang.
12. If something happened 10 million years after the beginning of the expansion, then it would look 10+ million years old, but it couldn’t look to be 9 or 8 or 4 or 1 million years old. Those signals arrived long ago.
13. So, if an event occurred 500 million years after the big-bang, then it got to “us” at 500 million years + plus the travel time at the speed of light after it occurred.
14. This means that nothing we can see occurred more than expansion rate + the speed of light. If something occurred 500 million years after the big-bang, then that information has been with us since that time, plus the speed of light.
15. Once this information goes past us, then it is gone. So if something happened 1 second after the big bang, then that information in gone after 1+ seconds. It has passed us by. It is gone. We can’t look into the past and see what happened.
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His answer didn't help.
I used to wonder about this too. I have only worked the answer out mathematically and have never tried to put it into words. Here is my best effort.
It seems that it must take the galaxy more than 15 billion years to get 15 billion light years away from us. And then it would take another 15 billion years for the light it emits to get back to us. So that would make the universe more than 30 billion years old. But this is not what
happens. The key to what is really going on is the following property of the universe: As the universe expands, the fabric of space stretches.
The light we see from a galaxy 15 billion light years away has traveled 15 billion light years. But the galaxy was not 15 billion light years away when it emitted the light. It was, say, one billion light years away. As the light traveled toward us, space stretched due to the expansion of the universe. It did this continuously as the light traveled toward us. By the time the light got to us the galaxy was 15 billion light years away and the light had traveled 15 billion light years. So the galaxy traveled away from us for a little more than one billion years. It then emitted light toward us that took 15 billion years to get to us because the space it traveled through kept stretching and increasing the distance. So the universe is 1 billion years + 15 billion years = 16 billion years old. (These numbers are skewed slightly - the universe is only 13.7 billion years old.)
According to the standard cosmological model, galaxies formed 400 million years after the big bang. The above galaxy had to form within a billion years of the big bang, so it had plenty of time.
The universe is very big, with the light from its youth spread throughout. Some of the primordial light from the early universe passed us billions of years ago. Today, primordial light from farther away is passing us.
---------------------------------
Anyone understand the question and have an answer?
We read certain reports that astronomers have “seen” “light” from 500 million years, only, from the creation of the universe. Here is my query.
1. The universe “started” as an almost infinitely dense singularity.
2. As this thing expanded, all sorts of interesting things happened, which resulting in stars, galaxies, heavy elements, x-ray background, etc.
3. As the universe expanded, except for the brief “expansion faster than light” issues, it was expanding at less than the speed of light.
4. This means than all of the bundles of photons have been expanding at the same rate as the universe.
5. So, all information about what happened over the 14 billion years of the universe has expanding at the same rate.
6. This means that there is no “looking” into the past, because this information has been expanding, along with the universe.
7. The universe then should then be uniform, i.e., the same age, since it has been expanding with “us” since the beginning.
8. No matter what direction we look in, we should see exactly the same thing.
9. We should not see stuff from the beginning or 10 billion years ago, because everything has been expanding at the same rate and therefore all bandwidths of information from that source have always been with us.
10. Stuff expanding in the opposite direction from us, is still moving slower than the speed of light, so we should see it exactly as it is now.
11. There is no reason that when we look at increasingly sensitive instruments, e.g., the updated Hubble, that we should see anything but current information, i.e., the wavelengths from everything has been traveling with us since the big-bang.
12. If something happened 10 million years after the beginning of the expansion, then it would look 10+ million years old, but it couldn’t look to be 9 or 8 or 4 or 1 million years old. Those signals arrived long ago.
13. So, if an event occurred 500 million years after the big-bang, then it got to “us” at 500 million years + plus the travel time at the speed of light after it occurred.
14. This means that nothing we can see occurred more than expansion rate + the speed of light. If something occurred 500 million years after the big-bang, then that information has been with us since that time, plus the speed of light.
15. Once this information goes past us, then it is gone. So if something happened 1 second after the big bang, then that information in gone after 1+ seconds. It has passed us by. It is gone. We can’t look into the past and see what happened.
---------------------------------------------
His answer didn't help.
I used to wonder about this too. I have only worked the answer out mathematically and have never tried to put it into words. Here is my best effort.
It seems that it must take the galaxy more than 15 billion years to get 15 billion light years away from us. And then it would take another 15 billion years for the light it emits to get back to us. So that would make the universe more than 30 billion years old. But this is not what
happens. The key to what is really going on is the following property of the universe: As the universe expands, the fabric of space stretches.
The light we see from a galaxy 15 billion light years away has traveled 15 billion light years. But the galaxy was not 15 billion light years away when it emitted the light. It was, say, one billion light years away. As the light traveled toward us, space stretched due to the expansion of the universe. It did this continuously as the light traveled toward us. By the time the light got to us the galaxy was 15 billion light years away and the light had traveled 15 billion light years. So the galaxy traveled away from us for a little more than one billion years. It then emitted light toward us that took 15 billion years to get to us because the space it traveled through kept stretching and increasing the distance. So the universe is 1 billion years + 15 billion years = 16 billion years old. (These numbers are skewed slightly - the universe is only 13.7 billion years old.)
According to the standard cosmological model, galaxies formed 400 million years after the big bang. The above galaxy had to form within a billion years of the big bang, so it had plenty of time.
The universe is very big, with the light from its youth spread throughout. Some of the primordial light from the early universe passed us billions of years ago. Today, primordial light from farther away is passing us.
---------------------------------
Anyone understand the question and have an answer?