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current status of the horizon problem in cosmology
The horizon problem is the question why different areas on the sky
(think: temperature of the CMB) are similar even though they were not causally connected (if one calculates the growth of the "sphere of influence" with time according to classical cosmology). One solution is inflation (exponential expansion in the very early universe), since in this picture the regions WERE causally connected but have been moved apart by inflation. In the article below, noted cosmologist and famous writer John D. Barrow claims that there is no horizon problem in cosmology (and hence that at least this motivation for inflation is not necessary, though of course that does not prove that inflation didn't happen). Nevertheless, in the more than 15 years since its publication, the horizon problem is regularly mentioned. Has there been a refutation of Barrow's claim in the refereed literature? @ARTICLE {JBarrow95a, AUTHOR = "John D. Barrow", TITLE = "Why the Universe is not Anisotropic", JOURNAL = PhysRevD, YEAR = "1995", VOLUME = "51", NUMBER = "6", PAGES = "3113", MONTH = "15" # mar # "1995" } |
#2
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current status of the horizon problem in cosmology
On May 2, 5:04*am, (Phillip Helbig---
undress to reply) wrote: The horizon problem is the question why different areas on the sky (think: temperature of the CMB) are similar even though they were not causally connected (if one calculates the growth of the "sphere of influence" with time according to classical cosmology). *One solution is inflation (exponential expansion in the very early universe), since in this picture the regions WERE causally connected but have been moved apart by inflation. In the article below, noted cosmologist and famous writer John D. Barrow claims that there is no horizon problem in cosmology (and hence that at least this motivation for inflation is not necessary, though of course that does not prove that inflation didn't happen). *Nevertheless, in the more than 15 years since its publication, the horizon problem is regularly mentioned. Has there been a refutation of Barrow's claim in the refereed literature? @ARTICLE * * *{JBarrow95a, * * * * * * * *AUTHOR * * * = "John D. Barrow", * * * * * * * *TITLE * * * *= "Why the Universe is not Anisotropic", * * * * * * * *JOURNAL * * *= PhysRevD, * * * * * * * *YEAR * * * * = "1995", * * * * * * * * *VOLUME * * * = "51", * * * * * * * * *NUMBER * * * = "6", * * * * * * * * *PAGES * * * *= "3113", * * * * * * * * *MONTH * * * *= "15" # mar # "1995" * * * * * * * } If the universe has infinite size and it has redshift due to local expansion, isotropy is expected. The horizon after 15 billion light years distance in uniformly unobservable. The expansion may be due to a spinning universe. |
#3
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current status of the horizon problem in cosmology
In sci.astro.research Globemaker wrote:
The expansion [[of the universe]] may be due to a spinning universe. There are *very* tight observational limits on any overall rotation of the universe. Notably, Collins & Hawking Monthly Notices of the Royal Astronomical Society, Vol. 162, p. 307 (1973) http://adsabs.harvard.edu/abs/1973MNRAS.162..307C showed that the universe can't have rotated any more than a few microarcseconds (i.e., about 1e-11 revolutions) in a Hubble time. More recently Bunn, Ferreira, & Silk Physical Review Letters 77, 2883 (1996) http://link.aps.org/doi/10.1103/PhysRevLett.77.2883 used a very different analysis to limit the overall rotation of the universe per Hubble time to no more than around 1e-6 radians, i.e., around 1e-7 revolutions. -- -- "Jonathan Thornburg [remove -animal to reply]" Dept of Astronomy & IUCSS, Indiana University, Bloomington, Indiana, USA "Washing one's hands of the conflict between the powerful and the powerless means to side with the powerful, not to be neutral." -- quote by Freire / poster by Oxfam |
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current status of the horizon problem in cosmology
On May 2, 10:04*am, (Phillip Helbig---
undress to reply) wrote: The horizon problem is the question why different areas on the sky (think: temperature of the CMB) are similar even though they were not causally connected (if one calculates the growth of the "sphere of influence" with time according to classical cosmology). *One solution is inflation (exponential expansion in the very early universe), since in this picture the regions WERE causally connected but have been moved apart by inflation. In the article below, noted cosmologist and famous writer John D. Barrow claims that there is no horizon problem in cosmology (and hence that at least this motivation for inflation is not necessary, though of course that does not prove that inflation didn't happen). *Nevertheless, in the more than 15 years since its publication, the horizon problem is regularly mentioned. Has there been a refutation of Barrow's claim in the refereed literature? I don't know any refutation of Barrow's claim in the refereed literature, but I do know that the horizon problem arises from thinking of the universe within a classical framework, that is to say, not taking into account an understanding of quantum mechanics. In quantum theory it is not possible to talk of a distance between particles unless there is some way to measure, at least in principle, that distance. I find it obvious that in the early universe, that is to say early on the timescale of inflation, i.e. ~10^-33 sec no such measurements are possible, even in principle. It is equally obvious, from Einstein's argument in the 1905 paper, that the inflation means that the universe was expanding faster than itself. I.e. that inflation has always been nonsensical to anyone with a grasp of what Einstein was actually saying. Oh, I know there are lots of modern physicists who think they have a better understanding than Einstein, but quite frankly, they don't, and that is why inflation has found its way into the text books. |
#5
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current status of the horizon problem in cosmology
In article
, Oh No writes: On May 2, 10:04*am, (Phillip Helbig--- undress to reply) wrote: The horizon problem is the question why different areas on the sky (think: temperature of the CMB) are similar even though they were not causally connected (if one calculates the growth of the "sphere of influence" with time according to classical cosmology). *One solution is inflation (exponential expansion in the very early universe), since in this picture the regions WERE causally connected but have been moved apart by inflation. In the article below, noted cosmologist and famous writer John D. Barrow claims that there is no horizon problem in cosmology (and hence that at least this motivation for inflation is not necessary, though of course that does not prove that inflation didn't happen). *Nevertheless, in the more than 15 years since its publication, the horizon problem is regularly mentioned. Has there been a refutation of Barrow's claim in the refereed literature? I don't know any refutation of Barrow's claim in the refereed literature, but I do know that the horizon problem arises from thinking of the universe within a classical framework, that is to say, not taking into account an understanding of quantum mechanics. Right. The general wisdom is that some aspect of quantum mechanics, or something else in the early universe outside the scope of classical cosmology, solves the problem. That might be the case. However, Barrow's point was that such a solution is not NECESSARY. It doesn't rule out inflation, or anything else outside the scope of classical cosmology which occurs when classical cosmology is not an appropriate approximation, but the claim is that the horizon problem actually doesn't exist in classical cosmology. |
#6
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current status of the horizon problem in cosmology
"Phillip Helbig---undress to reply"
schreef in bericht ... The horizon problem is the question why different areas on the sky (think: temperature of the CMB) are similar even though they were not causally connected (if one calculates the growth of the "sphere of influence" with time according to classical cosmology). One solution is inflation (exponential expansion in the very early universe), since in this picture the regions WERE causally connected but have been moved apart by inflation. In the article below, noted cosmologist and famous writer John D. Barrow claims that there is no horizon problem in cosmology (and hence that at least this motivation for inflation is not necessary, though of course that does not prove that inflation didn't happen). Nevertheless, in the more than 15 years since its publication, the horizon problem is regularly mentioned. Has there been a refutation of Barrow's claim in the refereed literature? @ARTICLE {JBarrow95a, AUTHOR = "John D. Barrow", TITLE = "Why the Universe is not Anisotropic", JOURNAL = PhysRevD, YEAR = "1995", VOLUME = "51", NUMBER = "6", PAGES = "3113", MONTH = "15" # mar # "1995" } For a copy of the article (?) this link: http://www.gravityresearchfoundation...994/barrow.pdf For a link to a url discussing the issues involved go he http://www.astronomynotes.com/cosmolgy/s12.htm Inflation is the explanation to solve the horizon problem. In wikipedia we can read: http://en.wikipedia.org/wiki/Horizon_problem "Inflation then expanded it rapidly, freezing in these properties all over the sky; at this point the universe would be forced to be almost perfectly homogeneous," We are speaking here about a time period less than 1 second. I assume 1 second "my" clock/watch time. This is extremely short. I do not understand how you can use this to explain that the Universe is so homogenous, i.e. that there are roughly speaking galaxies everywhere. [[Mod. note -- Is 1 second an "extremely short" time? That depends on the standard of comparison. For example, 1 second is a very *long* time compared to processes that operated in a nanosecond. Inflation is usually understood as taking (*much*) less than a nanosecond. The following quote from http://en.wikipedia.org/wiki/Inflation_%28cosmology%29 is a nice brief synopsis of how inflation ensures that the observable universe is isotropic: For cosmology in the global point of view, the observable universe is one causal patch of a much larger unobservable universe; there are parts of the universe which cannot communicate with us yet. These parts of the universe are outside our current cosmological horizon. In the standard hot big bang model, without inflation, the cosmological horizon moves out, bringing new regions into view. As we see these regions for the first time, they look no different from any other region of space we have already seen: they have a background radiation which is at nearly exactly the same temperature as the background radiation of other regions, and their space-time curvature is evolving lock-step with ours. This presents a mystery: how did these new regions know what temperature and curvature they were supposed to have? They couldn't have learned it by getting signals, because they were not in communication with our past light cone before.[5][6] Inflation answers this question by postulating that all the regions come from an earlier era with a big vacuum energy, or cosmological constant. A space with a cosmological constant is qualitatively different: instead of moving outward, the cosmological horizon stays put. For any one observer, the distance to the cosmological horizon is constant. With exponentially expanding space, two nearby observers are separated very quickly; so much so, that the distance between them quickly exceeds the limits of communications. In the global point of view, the spatial slices are expanding very fast to cover huge volumes. In the local point of view, things are constantly moving beyond the cosmological horizon, which is a fixed distance away, and everything becomes homogeneous very quickly. -- jt]] 1. IMO the inside of the Sun (Interior of the Earth) is rather homogeneous. It is a boiling pot. The reason is communication ("lava flows") at very low speeds over very long periods of time. [[Mod. note -- The author is mistaken in thinking that the interior of either the Sun or the Earth is homogeneous. See http://en.wikipedia.org/wiki/Sun http://en.wikipedia.org/wiki/Structure_of_the_Earth for brief introductions to their actual (inhomogeneous) internal structure. -- jt]] 2. When you look to pictures of old super novae you see something that is very inhomogeneous. http://en.wikipedia.org/wiki/Supernova This tells me: 1. Slow processes - homogenous results. 2. Fast processes - inhomogenous results. What is the solution ? Nicolaas Vroom http://users.telenet.be/nicvroom/ |
#7
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current status of the horizon problem in cosmology
On May 5, 5:29*pm, (Phillip Helbig---
undress to reply) wrote: In article , Oh No writes: On May 2, 10:04*am, (Phillip Helbig--- undress to reply) wrote: The horizon problem is the question why different areas on the sky (think: temperature of the CMB) are similar even though they were not causally connected (if one calculates the growth of the "sphere of influence" with time according to classical cosmology). *One solution is inflation (exponential expansion in the very early universe), since in this picture the regions WERE causally connected but have been moved apart by inflation. In the article below, noted cosmologist and famous writer John D. Barrow claims that there is no horizon problem in cosmology (and hence that at least this motivation for inflation is not necessary, though of course that does not prove that inflation didn't happen). *Nevertheless, in the more than 15 years since its publication, the horizon problem is regularly mentioned. Has there been a refutation of Barrow's claim in the refereed literature? I don't know any refutation of Barrow's claim in the refereed literature, but I do know that the horizon problem arises from thinking of the universe within a classical framework, that is to say, not taking into account an understanding of quantum mechanics. Right. *The general wisdom is that some aspect of quantum mechanics, or something else in the early universe outside the scope of classical cosmology, solves the problem. *That might be the case. *However, Barrow's point was that such a solution is not NECESSARY. *It doesn't rule out inflation, or anything else outside the scope of classical cosmology which occurs when classical cosmology is not an appropriate approximation, but the claim is that the horizon problem actually doesn't exist in classical cosmology. To be honest, the only way I can understand this claim is to think that Barrow has not understood the problem. The horizon problem results from a very straightforward argument concerning causality and the light cone in the early universe. Since it is straightforward I would think that many people have understood it, and would see straight away that Barrow's claim does not stand up. It does not follow that a refutation would have been published, because a) such a refutation would be fairly trivial and obvious to those who do understand the problem, and b) it is not necessarily the case that journals like it when attention is drawn to the publication of claims which should never have been published in the first place. |
#8
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current status of the horizon problem in cosmology
"Nicolaas Vroom" schreef in bericht
... The following quote from http://en.wikipedia.org/wiki/Inflation_%28cosmology%29 is a nice brief synopsis of how inflation ensures that the observable universe is isotropic: For cosmology in the global point of view, the observable universe is one causal patch of a much larger unobservable universe; there are parts of the universe which cannot communicate with us yet. These parts of the universe are outside our current cosmological horizon. In the standard hot big bang model, without inflation, the cosmological horizon moves out, bringing new regions into view. As we see these regions for the first time, they look no different from any other region of space we have already seen: they have a background radiation which is at nearly exactly the same temperature as the background radiation of other regions, and their space-time curvature is evolving lock-step with ours. This presents a mystery: how did these new regions know what temperature and curvature they were supposed to have? They couldn't have learned it by getting signals, because they were not in communication with our past light cone before.[5][6] Inflation answers this question by postulating that all the regions come from an earlier era with a big vacuum energy, or cosmological constant. A space with a cosmological constant is qualitatively different: instead of moving outward, the cosmological horizon stays put. For any one observer, the distance to the cosmological horizon is constant. With exponentially expanding space, two nearby observers are separated very quickly; so much so, that the distance between them quickly exceeds the limits of communications. In the global point of view, the spatial slices are expanding very fast to cover huge volumes. In the local point of view, things are constantly moving beyond the cosmological horizon, which is a fixed distance away, and everything becomes homogeneous very quickly. -- jt]] IMO there are two issues: 1. Observations - The visible (human / light cone ) issue 2. The physical issue. The first issue that we see a rather homogenous distribution of galaxies all around us. This picture represents the past and only a small (?) part of the total Universe. Assuming that space expands and using the same telescope with the same accuracy we will see even less. This is because the distance you can see which such a telescope is constant. The second issue is a physical issue: which evolution of physical processes and events happen to "create" what we see. Maybe the state of the Universe was always rather homogeneous. Maybe the state was even more homogeneous in the past (as observed by the Micro Wave Background Radiation) as in the present (galaxy Clusters) IMO you should compare the Big Bang evolution with a Super Super Nova of a black hole. IMO you do not need inflation over a very very small timescale. The problem with inflation (a discontinuous increase and decrease in speed / a small big bang) is: how did it start and how did it stop. 1. IMO the inside of the Sun (Interior of the Earth) is rather homogeneous. It is a boiling pot. The reason is communication ("lava flows") at very low speeds over very long periods of time. [[Mod. note -- The author is mistaken in thinking that the interior of either the Sun or the Earth is homogeneous. See http://en.wikipedia.org/wiki/Sun http://en.wikipedia.org/wiki/Structure_of_the_Earth for brief introductions to their actual (inhomogeneous) internal structure. -- jt]] I wrote on purpose "rather" homogeneous. 2. When you look to pictures of old super novae you see something that is very inhomogeneous. http://en.wikipedia.org/wiki/Supernova This tells me: 1. Slow processes - homogenous results. 2. Fast processes - inhomogenous results. What is the solution ? Nicolaas Vroom http://users.telenet.be/nicvroom/ |
#9
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current status of the horizon problem in cosmology
"Nicolaas Vroom" schreef in bericht
... The following quote from http://en.wikipedia.org/wiki/Inflation_%28cosmology%29 is a nice brief synopsis of how inflation ensures that the observable universe is isotropic: For cosmology in the global point of view, the observable universe is one causal patch of a much larger unobservable universe; there are parts of the universe which cannot communicate with us yet. These parts of the universe are outside our current cosmological horizon. In the standard hot big bang model, without inflation, the cosmological horizon moves out, bringing new regions into view. As we see these regions for the first time, they look no different from any other region of space we have already seen: they have a background radiation which is at nearly exactly the same temperature as the background radiation of other regions, and their space-time curvature is evolving lock-step with ours. This presents a mystery: how did these new regions know what temperature and curvature they were supposed to have? They couldn't have learned it by getting signals, because they were not in communication with our past light cone before.[5][6] Inflation answers this question by postulating that all the regions come from an earlier era with a big vacuum energy, or cosmological constant. A space with a cosmological constant is qualitatively different: instead of moving outward, the cosmological horizon stays put. For any one observer, the distance to the cosmological horizon is constant. With exponentially expanding space, two nearby observers are separated very quickly; so much so, that the distance between them quickly exceeds the limits of communications. In the global point of view, the spatial slices are expanding very fast to cover huge volumes. In the local point of view, things are constantly moving beyond the cosmological horizon, which is a fixed distance away, and everything becomes homogeneous very quickly. -- jt]] IMO there are two issues: 1. Observations - The visible (human / light cone ) issue 2. The physical issue. The first issue that we see a rather homogenous distribution of galaxies all around us. This picture represents the past and only a small (?) part of the total Universe. Assuming that space expands and using the same telescope with the same accuracy we will see even less. This is because the distance you can see which such a telescope is constant. The second issue is a physical issue: which evolution of physical processes and events happen to "create" what we see. Maybe the state of the Universe was always rather homogeneous. Maybe the state was even more homogeneous in the past (as observed by the Micro Wave Background Radiation) as in the present (galaxy Clusters) IMO you should compare the Big Bang evolution with a Super Super Nova of a black hole. IMO you do not need inflation over a very very small timescale. The problem with inflation (a discontinuous increase and decrease in speed / a small big bang) is: how did it start and how did it stop. 1. IMO the inside of the Sun (Interior of the Earth) is rather homogeneous. It is a boiling pot. The reason is communication ("lava flows") at very low speeds over very long periods of time. [[Mod. note -- The author is mistaken in thinking that the interior of either the Sun or the Earth is homogeneous. See http://en.wikipedia.org/wiki/Sun http://en.wikipedia.org/wiki/Structure_of_the_Earth for brief introductions to their actual (inhomogeneous) internal structure. -- jt]] I wrote on purpose "rather" homogeneous. 2. When you look to pictures of old super novae you see something that is very inhomogeneous. http://en.wikipedia.org/wiki/Supernova This tells me: 1. Slow processes - homogenous results. 2. Fast processes - inhomogenous results. What is the solution ? Nicolaas Vroom http://users.telenet.be/nicvroom/ |
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