dimreepr Posted February 5, 2020 Posted February 5, 2020 8 minutes ago, michel123456 said: The observer knows that galaxy g1 he sees today is in fact the image of the ancient galaxy g when it was at g1. Today, galaxy g is at g1'. which today, g, g1 or... my now or my now1? 14 minutes ago, michel123456 said: So the concept of universal now, where the universe has ~13 BY of age, does not make full sense. you only see the light that has caught up with your now.
Bufofrog Posted February 6, 2020 Posted February 6, 2020 20 minutes ago, michel123456 said: Am I a lunatic? Well, having to ask that question is not a good sign... On 2/5/2020 at 10:52 AM, michel123456 said: So the concept of universal now, where the universe has ~13 BY of age, does not make full sense. You seem to be over thinking this and confusing yourself. Everything you see happened in the past. Images from your television happened a tiny fraction of a second ago. The image of the moon you see happened about 1 second ago. The image of the sun that you see happened about 8 minutes ago. The image of Alpha Centauri happened about 4.5 years ago. So lets look at this idea of a 'universal now'. In the universal now lets say that the Death Star destroys Alpha Centauri. Well obviously I won't be able to see that rather spectacular explosion from earth because the image of the exploding star will not reach me for another 4.5 years. So I will see that explosion 4.5 years into my future. Here is a simplified scenario just to get the concept: So if we are looking at a galaxy that is say 10 billion light years away, then we are looking at the galaxy as it was 10 billion years ago. That means its brightness, location and shape are all the way it was 10 billion years ago. In the universal now the galaxy is much farther away and probably much different in appearance. The galaxy might be 40 billion light years away in our universal now. So in the universal now, the light leaving that galaxy will not be something I could see until 40 billion years in the future on earth. This next paragraph is an unnecessary complication of the basic concept but is added for completeness. In reality a galaxy that is said 10 billion light years away means that the light from galaxy has been traveling for 10 billion years not that it was actually emitted from the galaxy when it was 10 billion light years away. The light was actually emitted from the galaxy when it was closer than 10 billion light years, lets say 8 billion light years (forgive me but I don't feel like getting the actual number) but since the universe is expanding as the light moves it must travel farther than 8 billion light years. PS don't get confused by years and light years. 10 billion years - time, 10 billion light years - distance. Hope that helps some...
michel123456 Posted February 6, 2020 Author Posted February 6, 2020 (edited) 1 hour ago, Bufofrog said: Well, having to ask that question is not a good sign... You seem to be over thinking this and confusing yourself. Everything you see happened in the past. Images from your television happened a tiny fraction of a second ago. The image of the moon you see happened about 1 second ago. The image of the sun that you see happened about 8 minutes ago. The image of Alpha Centauri happened about 4.5 years ago. So lets look at this idea of a 'universal now'. In the universal now lets say that the Death Star destroys Alpha Centauri. Well obviously I won't be able to see that rather spectacular explosion from earth because the image of the exploding star will not reach me for another 4.5 years. So I will see that explosion 4.5 years into my future. Here is a simplified scenario just to get the concept: So if we are looking at a galaxy that is say 10 billion light years away, then we are looking at the galaxy as it was 10 billion years ago. That means its brightness, location and shape are all the way it was 10 billion years ago. In the universal now the galaxy is much farther away and probably much different in appearance. The galaxy might be 40 billion light years away in our universal now. So in the universal now, the light leaving that galaxy will not be something I could see until 40 billion years in the future on earth. This next paragraph is an unnecessary complication of the basic concept but is added for completeness. In reality a galaxy that is said 10 billion light years away means that the light from galaxy has been traveling for 10 billion years not that it was actually emitted from the galaxy when it was 10 billion light years away. The light was actually emitted from the galaxy when it was closer than 10 billion light years, lets say 8 billion light years (forgive me but I don't feel like getting the actual number) but since the universe is expanding as the light moves it must travel farther than 8 billion light years. PS don't get confused by years and light years. 10 billion years - time, 10 billion light years - distance. Hope that helps some... Thank you for your input. it was not so much necessary but thanks anyway. Question: since the BB was a single event (that happened everywhere says the Theory), since it is an event that happened ~13BY ago, when all the universe was in an extremely dense situation, doesn't that mean that all the basic elements of the universe have the same age? aka ~13BY. Edited February 6, 2020 by michel123456 basic
Bufofrog Posted February 6, 2020 Posted February 6, 2020 24 minutes ago, michel123456 said: doesn't that mean that all the basic elements of the universe have the same age? aka ~13BY. No. Only H, He and Li were formed after the big bang. The heavier elements were formed in stars, the heaviest elements were formed in super novas.
swansont Posted February 6, 2020 Posted February 6, 2020 40 minutes ago, Bufofrog said: No. Only H, He and Li were formed after the big bang. The heavier elements were formed in stars, the heaviest elements were formed in super novas. And those elements could not form until the universe cooled sufficiently. About 3 minutes to form nuclei. But elements did not form (electrons combining with nuclei; I think the date is specific to hydrogen) until about 380,000 years after the BB.
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