- #1
Maxila
- 80
- 0
I have a question that I have tried to answer by searching the internet, and by writing a few astronomy professors and professors of astrophysics. One replied however in it, he only confirmed what I knew and didn’t address the question.
As I understand the accelerating Universal expansion, the empirical evidence is that more distance supernova have a greater net red-shift, after adjusting for the expected red-shift due to the expansion of space, than was expected if universal expansion was slowing down.
To be clear I have no questions regarding the evidence, it is empirical and has been verified by others since it was discovered. I also understand that uniform expansion produces a red shift that grows with distance, and that this effect is subtracted away and they look at the residual.
It is the interpretation of the positive residual red-shift that I find counter to how I would expect to interpret that empirical evidence. The clearest way I can think of to explain why is to create an example scenario.
I will round the age of the Universe to 13.7 billion years. If I were to compare a supernova red-shift of one 12 billion years distant, to one 6 billion light years distant, I would expect the residual red-shift to be greater in the supernova of 12 billion years distant than the one 6 billion years distant. The reason is due to the different travel times and the age of the universe they represent. Photons emitted from a supernova 12 billion light years distant are showing me velocity information from the supernova when the Universe was 1.7 billion years old. At that age of the Universe, I would expect a supernova, and any galaxy, to be receding at a greater velocity, than a supernova 6 billion light years distant after the universe has aged to 7.7 billion years old when they should have been receding more slowly.
The photons we see from the closer supernova are showing its velocity when the Universe was 7.7 billion years old. The receding velocity of that galaxy should be less than a galaxy that was receding away when the Universe and its expansion was only 1.7 billion years old?
Summing it up, I need help understanding why a residual positive red-shift for more distant galaxies indicates an accelerating expansion, when I would expect to see that greater residual red-shift in the more distant galaxies, because they represent an earlier point the Universal expansion, when it should have been expanding faster than later points in time?
Maxila
As I understand the accelerating Universal expansion, the empirical evidence is that more distance supernova have a greater net red-shift, after adjusting for the expected red-shift due to the expansion of space, than was expected if universal expansion was slowing down.
To be clear I have no questions regarding the evidence, it is empirical and has been verified by others since it was discovered. I also understand that uniform expansion produces a red shift that grows with distance, and that this effect is subtracted away and they look at the residual.
It is the interpretation of the positive residual red-shift that I find counter to how I would expect to interpret that empirical evidence. The clearest way I can think of to explain why is to create an example scenario.
I will round the age of the Universe to 13.7 billion years. If I were to compare a supernova red-shift of one 12 billion years distant, to one 6 billion light years distant, I would expect the residual red-shift to be greater in the supernova of 12 billion years distant than the one 6 billion years distant. The reason is due to the different travel times and the age of the universe they represent. Photons emitted from a supernova 12 billion light years distant are showing me velocity information from the supernova when the Universe was 1.7 billion years old. At that age of the Universe, I would expect a supernova, and any galaxy, to be receding at a greater velocity, than a supernova 6 billion light years distant after the universe has aged to 7.7 billion years old when they should have been receding more slowly.
The photons we see from the closer supernova are showing its velocity when the Universe was 7.7 billion years old. The receding velocity of that galaxy should be less than a galaxy that was receding away when the Universe and its expansion was only 1.7 billion years old?
Summing it up, I need help understanding why a residual positive red-shift for more distant galaxies indicates an accelerating expansion, when I would expect to see that greater residual red-shift in the more distant galaxies, because they represent an earlier point the Universal expansion, when it should have been expanding faster than later points in time?
Maxila