npts2020 Posted March 1 Share Posted March 1 On 2/28/2024 at 4:51 PM, Sensei said: ..then who made up the Universe.. ? What makes you think the universe was "made up" and hasn't always existed? Just because you have a linear existence with a fairly definable beginning and end because of time, doesn't mean the universe must behave in a similar manner. Personally, I have a lot more faith in the laws of conservation of matter and energy than I do in the relevance of time in relation to the universe as a whole. Link to comment Share on other sites More sharing options...
John Cuthber Posted March 1 Share Posted March 1 4 hours ago, npts2020 said: What makes you think the universe was "made up" and hasn't always existed? Among other things... https://en.wikipedia.org/wiki/Olbers's_paradox Link to comment Share on other sites More sharing options...
MigL Posted March 1 Share Posted March 1 (edited) Would Olber's paradox work in a universe where light from extremely distant sources, is red-shifted, due to expansion, to undetectable levels ? Only if you also consider the "other things", John. ( I know, I know, off topic ... sorry ) Edited March 1 by MigL Link to comment Share on other sites More sharing options...
npts2020 Posted March 2 Author Share Posted March 2 20 hours ago, John Cuthber said: Among other things... https://en.wikipedia.org/wiki/Olbers's_paradox This could be an interesting discussion on its own but if you believe modern cosmologists, there is a point where the universe (possibly the majority of it) is expanding away from us faster than the speed of light. It seems to me, that would explain why the entire sky isn't bright and does little to show whether the universe is infinite or not. 1 Link to comment Share on other sites More sharing options...
dimreepr Posted March 2 Share Posted March 2 23 minutes ago, npts2020 said: This could be an interesting discussion on its own but if you believe modern cosmologists, there is a point where the universe (possibly the majority of it) is expanding away from us faster than the speed of light. It seems to me, that would explain why the entire sky isn't bright and does little to show whether the universe is infinite or not. Indeed, since it's not even a tangent of the topic at hand. Link to comment Share on other sites More sharing options...
MigL Posted March 3 Share Posted March 3 On 3/2/2024 at 6:41 AM, npts2020 said: the universe (possibly the majority of it) is expanding away from us faster than the speed of light. It seems to me, that would explain why the entire sky isn't bright and does little to show whether the universe is infinite or not. No. That implies that, if you wind the expansion backwards in time, you come to an 'origin' point, IOW, expansion of the universe contradicts a universe that has existed forever. Based on the expansion constant, also known as Hubble's constant, we can say our observable universe started expanding about 13.8 Billion years ago. ( If you're going to discuss with scientists, like John, who actually know their sh*t, you really should 'brush up' on yours ) PS My apologies, Dim, for continuing along the tangent; never pass up an opportunity to educate. Link to comment Share on other sites More sharing options...
John Cuthber Posted March 4 Share Posted March 4 On 3/2/2024 at 11:41 AM, npts2020 said: This could be an interesting discussion on its own but if you believe modern cosmologists, there is a point where the universe (possibly the majority of it) is expanding away from us faster than the speed of light. It seems to me, that would explain why the entire sky isn't bright and does little to show whether the universe is infinite or not. And, if the universe is accelerating away from me, and has been doing so eternally, why is (any of) it still here? The question was "What makes you think the universe was "made up" and hasn't always existed?" Link to comment Share on other sites More sharing options...
npts2020 Posted March 5 Author Share Posted March 5 18 hours ago, John Cuthber said: And, if the universe is accelerating away from me, and has been doing so eternally, why is (any of) it still here? I'm pretty sure I never said expansion was eternal, only possibly the universe. If you can't distinguish between the two propositions, I will be happy to elucidate. On 3/3/2024 at 3:20 PM, MigL said: No. That implies that, if you wind the expansion backwards in time, you come to an 'origin' point, IOW, expansion of the universe contradicts a universe that has existed forever. Based on the expansion constant, also known as Hubble's constant, we can say our observable universe started expanding about 13.8 Billion years ago. ( If you're going to discuss with scientists, like John, who actually know their sh*t, you really should 'brush up' on yours ) PS My apologies, Dim, for continuing along the tangent; never pass up an opportunity to educate. And that assumes we can see and measure the limits of our universe, a demonstrably untrue notion as shown by your use of the word "observable". In order to have an "origin" point, one needs to explain how all of the laws of physics had been broken by making something from nothing at 13.8 billion years ago or any other time. When the choice is something from nothing or a timeless universe, I tend towards the latter. If there is a third choice, I would like to know about it but all of the origin explanations (besides supernatural ones) I have seen lead back to one or the other. Link to comment Share on other sites More sharing options...
John Cuthber Posted March 5 Share Posted March 5 54 minutes ago, npts2020 said: I'm pretty sure I never said expansion was eternal, only possibly the universe. If you can't distinguish between the two propositions, I will be happy to elucidate. Does the universe have a calendar? How did/ does it know when to switch the expansion on and off? Link to comment Share on other sites More sharing options...
npts2020 Posted March 5 Author Share Posted March 5 1 minute ago, John Cuthber said: Does the universe have a calendar? How did/ does it know when to switch the expansion on and off? AFAICT the universe is eternal. As to switching expansion on and off (if it even switches on and off), figuring that out would advance our understanding of cosmology as much as learning the heavens don't revolve around the Earth. When I try to visualize your proposition, all I come up with is something similar to tides. Our biggest problem is the entirety of human existence is such a small fraction of even the known age of the universe and our ability to effectively measure and study its change a tiny fraction of that existence (assuming we can do it at all). It seems to me Hubble, Webb and most other space missions have helped us take a giant step in understanding how things work but also have raised as many questions as they have answered. 1 Link to comment Share on other sites More sharing options...
MigL Posted March 5 Share Posted March 5 (edited) 10 hours ago, npts2020 said: I'm pretty sure I never said expansion was eternal, only possibly the universe. If you can't distinguish between the two propositions, I will be happy to elucidate. Expansion cannot be eternal, as John has pointed out, but time only begins to make sense once space-time geometry is evident, and that happened at the Planck time of 10-43 sec., about 13.8 Billion years ago. What was there before that time could have been 'eternal', or could have existed for a 'second'; such labels are meaningless since time, as we know it, did not exist yet. But it certainly was not the universe we know ( and may have been embedded in another universe; see Eternal Inflation ). Is that how you were going to elucidate ? No one has invoked a 'creator' or the 'supernatural'; just you. Edited March 5 by MigL Link to comment Share on other sites More sharing options...
npts2020 Posted March 9 Author Share Posted March 9 On 3/5/2024 at 3:39 PM, MigL said: Expansion cannot be eternal, as John has pointed out, but time only begins to make sense once space-time geometry is evident, and that happened at the Planck time of 10-43 sec., about 13.8 Billion years ago. What was there before that time could have been 'eternal', or could have existed for a 'second'; such labels are meaningless since time, as we know it, did not exist yet. But it certainly was not the universe we know ( and may have been embedded in another universe; see Eternal Inflation ). Is that how you were going to elucidate ? No one has invoked a 'creator' or the 'supernatural'; just you. Which leads to the question of "exactly what is time and how does it apply to the universe?". It seems pretty obvious time applies to humans because, so far, all of them have a pretty definably observed beginning and end but we only have a single universe of which we have seen neither the beginning nor end, or even much of the in between (if there is such a thing). If I have "invoked a creator or the supernatural", please post the quote. My bet is that once we figure out a reliable way of measuring gravitational effects from bodies outside our visible universe on bodies inside our visible universe, its size and age will increase greatly. Link to comment Share on other sites More sharing options...
dimreepr Posted March 9 Share Posted March 9 10 hours ago, npts2020 said: Which leads to the question of "exactly what is time and how does it apply to the universe?". It seems pretty obvious time applies to humans because, so far, all of them have a pretty definably observed beginning and end but we only have a single universe of which we have seen neither the beginning nor end, or even much of the in between (if there is such a thing). If I have "invoked a creator or the supernatural", please post the quote. My bet is that once we figure out a reliable way of measuring gravitational effects from bodies outside our visible universe on bodies inside our visible universe, its size and age will increase greatly. My bet is, you've missed the point... Link to comment Share on other sites More sharing options...
Genady Posted March 9 Share Posted March 9 (edited) 10 hours ago, npts2020 said: once we figure out a reliable way of measuring gravitational effects from bodies outside our visible universe on bodies inside our visible universe As the bodies outside our visible universe make pretty much spherically symmetric shell, their gravitational effect inside the shell is identically zero. Edited March 9 by Genady Link to comment Share on other sites More sharing options...
npts2020 Posted March 10 Author Share Posted March 10 12 hours ago, Genady said: As the bodies outside our visible universe make pretty much spherically symmetric shell, their gravitational effect inside the shell is identically zero. Why should this be true? What makes the visible universe spherical is that the limits on the speed of light are the same in every direction, AFAIK there is no spherical symmetry to the mass in the visible universe, what would make it symmetrical outside of it? Link to comment Share on other sites More sharing options...
Genady Posted March 10 Share Posted March 10 3 minutes ago, npts2020 said: Why should this be true? What makes the visible universe spherical is that the limits on the speed of light are the same in every direction, AFAIK there is no spherical symmetry to the mass in the visible universe, what would make it symmetrical outside of it? On the scale of several hundred megaparsec and more the visible universe is homogeneous and isotropic. It means that on that scale it is the same in all directions. Link to comment Share on other sites More sharing options...
MigL Posted March 10 Share Posted March 10 Please look up the definition of 'observable' universe. It is that part of the larger universe that is causally connected to us. Anything outside the observable universe cannot have a causal effect on us, as information transfer is limited by the speed of light, making information from outside the observable universe inaccessible to us. Link to comment Share on other sites More sharing options...
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