Shape of the Universe

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Just like to get an idea of what people currently think what the shape of the universe is.

Since the curvature is likely zero, does this mean that the universe is infinite.

Also, I get the idea that the size of the universe, if has one, extends beyond the light cone. How is this possible?
Hi. Fascinating discussion. I'm new to this forum and I picked this post because you say that space is likely flat or 'Euclidean'. I would agree, but what leads you to believe it is if I may ask?
 
  • #27
bapowell
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Hi. Fascinating discussion. I'm new to this forum and I picked this post because you say that space is likely flat or 'Euclidean'. I would agree, but what leads you to believe it is if I may ask?
Welcome to PF! We are able to measure the curvature of the observable universe using data from the cosmic microwave background. These data show that the observable universe is close to being flat, but we can't tell if it's exactly flat or slightly curved. I believe the latest measurements show that the universe is flat to within a percent or so.
 
  • #28
Chronos
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Our best evidence to date for the flatness of space [i.e. Eucldean geometry] comes mainly from CMB data via Planck and WMAP, which as bapowell noted, gives us highly accurate measurements of curvature. These measurements are further affirmed by independent surveys from other studies [e.g., BOSS and SDSS]. These enable us to approximate the mass contained within very large volumes of the universe and which directly affects the curvature, or flatness, of space.
 
  • #29
bapowell
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Thanks for your reply. On the microwave background radiation; Aside from it being used to estimate the curvature, and being a pillar of the 'Big Bang' theory; doesn't the measured uniformity in the radiation seem counter-intuitive to the observed existence of galactic clusters and super clusters?
Great question! The answer is "no" -- while the CMB is indeed very uniform, it's not perfect. There are tiny fluctuations in the temperature at 1 part in 100,000 that are understood to be the primordial "seeds" of the galaxies and galaxy clusters that we observe today. Though tiny at the time the CMB was formed, these inhomogeneities eventually grew as gravitational instabilities into bound structures. Regarding even larger structures, like super clusters, there are some hints that the CMB lacks statistical isotropy on the largest length scales: there are some curious "anomalies" regarding the size of fluctuations on the largest scales and the alignment of the multipole vectors that describe these fluctuations.
 
  • #30
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Thanks for your reply. On the microwave background radiation; Aside from it being used to estimate the curvature, and being a pillar of the 'Big Bang' theory; doesn't the measured uniformity in the radiation seem counter-intuitive to the observed existence of galactic clusters and super clusters? In other words the universe seems too clumpy in its distribution of matter. Just a thought.
Although the CMB is nearly uniform it isn't absolutely completely uniform, there are hotter and colder spots.
It can be argued that these tiny initial variations correspond to areas of very slightly different density, and that these were the seeds of the large scale structures which we observe.
 
  • #31
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Although the CMB is nearly uniform it isn't absolutely completely uniform, there are hotter and colder spots.
It can be argued that these tiny initial variations correspond to areas of very slightly different density, and that these were the seeds of the large scale structures which we observe.
Thanks for your reply. I understand it is what is the current explanation. But I've always wondered how such structures could have formed from such a nearly if not virtually uniform explosion.
 
  • #32
bapowell
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Thanks for your reply. I understand it is what is the current explanation. But I've always wondered how such structures could have formed from such a nearly if not virtually uniform explosion.
Inflation provides a mechanism by which quantum vacuum fluctuations are converted into classical perturbations. These are widely believed to be the source of the temperature anisotropies observed in the CMB.
 
  • #33
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Inflation provides a mechanism by which quantum vacuum fluctuations are converted into classical perturbations. These are widely believed to be the source of the temperature anisotropies observed in the CMB.
Thanks again. But doesn't Guth's Inflation Theory have some problems? Among them he predicts that protons will have a finite lifetime of Ten to the 30th years. Haven't experimental results failed thus far to confirm this? Beyond this the Big Bang itself seems to wildly violate the first law of thermodynamics particularly since there is no recognized source for the explosion. These are just some of the problems I've kind of always had with that theory.
 
  • #34
bapowell
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Thanks again. But doesn't Guth's Inflation Theory have some problems? Among them he predicts that protons will have a finite lifetime of Ten to the 30th years. Haven't experimental results failed thus far to confirm this? Beyond this the Big Bang itself seems to wildly violate the first law of thermodynamics particularly since there is no recognized source for the explosion. These are just some of the problems I've kind of always had with that theory.
Inflation as a general theory has nothing specific to say about proton lifetimes. Protons are thought to decay via certain GUT reactions, and the early models of inflation were sought within these GUTs; however, most of these early models have since been abandoned because they don't match cosmological observations. The generic predictions of inflation: flatness, superhorizon correlations of the temperature and polarization anisotropies, and adiabatic Gaussian perturbations, are all well-supported by current data. Finding a specific mechanism for the inflationary expansion within beyond-the-Standard Model physics is an ongoing effort, though there are several proposals that seem to work within supergravity, string theory, and more modest extensions of the SM.

The big bang was not an explosion. Cosmologists don't know "where it all came from", but any process that alleges to explain the origin should not violate any physical principles.
 
  • #35
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Inflation as a general theory has nothing specific to say about proton lifetimes. Protons are thought to decay via certain GUT reactions, and the early models of inflation were sought within these GUTs; however, most of these early models have since been abandoned because they don't match cosmological observations. The generic predictions of inflation: flatness, superhorizon correlations of the temperature and polarization anisotropies, and adiabatic Gaussian perturbations, are all well-supported by current data. Finding a specific mechanism for the inflationary expansion within beyond-the-Standard Model physics is an ongoing effort, though there are several proposals that seem to work within supergravity, string theory, and more modest extensions of the SM.

The big bang was not an explosion. Cosmologists don't know "where it all came from", but any process that alleges to explain the origin should not violate any physical principles.
Thank you for that summary and your politeness. I have more recently read that a proposed 'GUT' ('Subquantum Kinetics' 1994 - Paul A. LaViolette PhD.) does better than the SM 'expanding universe' theory on multiple cosmological tests when compared with the 'tired-light' hypothesis. Have you read this anywhere?
 
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  • #36
bapowell
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Thank you for that summary and your politeness. I have more recently read that a proposed 'GUT' ('Subquantum Kinetics' 1994 - Paul A. LaViolette PhD.) does better than the SM 'expanding universe' theory on multiple cosmological tests when compared with the 'tired-light' hypothesis. Have you read this anywhere?
No. Which tests?
 
  • #37
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No. Which tests?
No. Which tests?
The Galaxy Number Count - Totani, "Near-infrared faint galaxies in the Subaru Deep Field".
The Tolman Galaxy Surface Brightness Test. Paper IV.
The "Galaxy Angular Separation vs Galaxy Cluster Redshift Graph" data taken from Hickson and Adams "evidence for cluster evolution".
The Hubble Diagram Test. data from Kristian, Sandage and Westphal.
 
  • #38
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Thank you for that summary and your politeness. I have more recently read that a proposed 'GUT' ('Subquantum Kinetics' 1994 - Paul A. LaViolette PhD.) does better than the SM 'expanding universe' theory on multiple cosmological tests when compared with the 'tired-light' hypothesis. Have you read this anywhere?
The 'Tired light' hypothesis is generally no longer considered as a reasonable explanation for cosmological red shift.
http://www.astro.ucla.edu/~wright/tiredlit.htm
The currently most accepted model is that there is a 'Dark energy', causing the (accelerating) expansion.
https://en.wikipedia.org/wiki/Lambda-CDM_model
We don't know what the energy is, but this model fits the observations, tired light does not.
 
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  • #39
bapowell
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The Galaxy Number Count - Totani, "Near-infrared faint galaxies in the Subaru Deep Field".
The Tolman Galaxy Surface Brightness Test. Paper IV.
The "Galaxy Angular Separation vs Galaxy Cluster Redshift Graph" data taken from Hickson and Adams "evidence for cluster evolution".
The Hubble Diagram Test. data from Kristian, Sandage and Westphal.
Links would be helpful, but I was able to find a few of these papers. None of them mention tired light or LaViolette's work. Can you provide references in which either of these two theories are shown to provide better fits to the data than the concordance LCDM model?
 
  • #40
Chronos
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TROU, your references appear to be an unvetted collection of popular press and journal publications of unqualified merit or relevance. Publication does not confer any measure of validity without peer review - i.e., concurrence by recognized experts in the field.
 

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