I'm not sure what you mean by "BBT", but you aren't adequately representing the family of cosmological models that make up the standard cosmological model. Infinitely large models begin with singularities. The singularities at the beginning of these models has no influence on the size of these models, finite or not. In these models, it is true that any finite volume of space approaches zero as one approaches the singularity, but infinite volumes remain infinite.
At Rest with our Hubble view
- Thread starter quantum_wave
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I mean Big Bang Theory with Inflation, and that is the consensus model of the standard cosmology, to my understanding. It is often simply referred to as BBT. BBT includes several theories; General Relativity, Inflationary Theory, and the cosmological principle. At least those are what I have seen called the standard hot big bang cosmology.
Here is an old link, out of date in some respects, but still a good place to get the standard hot big bang model.
http://www.damtp.cam.ac.uk/research/gr/public/bb_history.html
The consensus standard cosmology called BBT features potentially infinite expansion, but the size of the universe at any point in time is finite.
The infinite models are not part of the group of theories that make up the consensus standard cosmology.
Well, we don't seem to be looking at the same reputable sources. In the standard cosmology, the consensus is that there was a beginning to the universe. I don't know of any reputable source that says the standard cosmology denies that there was a beginning. The implied beginning is often characterized as a singularity. The nature of the implied beginning singularity is characterized as an infinitely dense zero volume point.
The size of the universe that has expanded from that point is always finite and still expanding. It may expand infinitely, but it will never be infinite if you are describing BBT with inflation.
That is my take on it anyway.
Not my theory, it is what I find to be the characterization of BBT.
It is referred to as the surface of last scattering. http://universeadventure.org/eras/era2-synthesis.htm
We agree on that, but still I don't think we are on the same page where it comes to the finite universe. There are a finite number of galaxies that formed after transparency, there was a finite amount of energy, the expansion has been taking place for a finite period of time. The BB universe is finite. I'm always open to reputable links that say otherwise.
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I assure you that you are imagining this. The visible universe will always be finite in the standard cosmological model, but whether the space is infinite is up for grabs.
This is not exactly true. If you are interested, you might want to check out John Earman, "Bangs, Crunches, Whimpers and Shrieks." It does get a little technical, though.
Again, good luck with your theory.
Please, just get a basic astronomy textbook. Anything of first year university.
Have it your way. I've already checked enough sources to know that the current consensus is BBT, the standard cosmology. It has a beginning singularity, meaning that space and time had a beginning. The spacetime universe is expanding but finite. In that consensus model, space is not infinite. We don't all agree with the consensus, but that doesn't change it.
If you care about being informed you should do a little research or give us a link to show that I am wrong about this.
Sigh. I did my graduate work on cosmology.
Try this: http://www.astro.ucla.edu/~wright/cosmology_faq.html#RB. Or better yet, read the entire tutorial.
Try this: http://www.astro.ucla.edu/~wright/cosmology_faq.html#RB. Or better yet, read the entire tutorial.
Look closely at it. Shear stress is something you associate with an elastic solid.
Fair enough.quantum_wave said:
It is.quantum_wave said:
Stop right there. Spacetime is curved relative to the energy density of space. Spacetime isn't space. You can move through space. But spacetime includes time. You can draw worldlines in it, but you can't move through it. This one point is just about the most important point to appreciate.quantum_wave said:
It would be better to say "motion through any volume of space can be modelled via curved spacetime where curvature is relative to the gradient in energy density in that particular volume". It might sound like nitpicking, but it's important to get this sort of thing right.quantum_wave said:
The important point is that if the energy density is absolutely uniform, light travels in straight lines. Regardless of the density. And when light travels in straight lines, things don't fall down.quantum_wave said:
I've visited that site many times. Your appeal to authority works with me though, lol. You should know what you are talking about.
But to be clear, I do not see you saying that the consensus cosmology is BBT with Inflation, which is what I am saying. I do not see you saying that there was a singularity and spacetime began with the Big Bang, which I think is generally accepted. I am saying that BBT is primarily General Realtivity, Inflationary Theory, and the Cosmological Principle. Are you saying that is wrong?
Your link is a fine tutorial, but where does it say there is a consensus in the scientific community, and what it is? Am I wrong to think that the consensus is BBT? I'm sure you don't think I mean that the consensus makes BBT fact, it is just the generally accepted view by the scientific community as represented in the popular media. Do you have a problem with that and can you explain why?
I've just looked at that site. The opening paragraph does not auger well:
"We have observations that say that the radius of curvature of the Universe is bigger than 70 billion light years. But the observations allow for either a positive or negative curvature, and this range includes the flat Universe with infinite radius of curvature. The negatively curved space is also infinite in volume even though it is curved. So we know empirically that the volume of the Universe is more than 20 times bigger than volume of the observable Universe. Since we can only look at small piece of an object that has a large radius of curvature, it looks flat. The simplest mathematical model for computing the observed properties of the Universe is then flat Euclidean space. This model is infinite, but what we know about the Universe is that it is really big".
This contains an assumption that the universe must be curved, but because we can't see any curvature, then the curvature must be very slight and thus the universe must be very large. That's a non-sequitur. And the infinite model is plain wrong - an infinite universe simply cannot expand because the pressure is counter-balanced everywhere.
"We have observations that say that the radius of curvature of the Universe is bigger than 70 billion light years. But the observations allow for either a positive or negative curvature, and this range includes the flat Universe with infinite radius of curvature. The negatively curved space is also infinite in volume even though it is curved. So we know empirically that the volume of the Universe is more than 20 times bigger than volume of the observable Universe. Since we can only look at small piece of an object that has a large radius of curvature, it looks flat. The simplest mathematical model for computing the observed properties of the Universe is then flat Euclidean space. This model is infinite, but what we know about the Universe is that it is really big".
This contains an assumption that the universe must be curved, but because we can't see any curvature, then the curvature must be very slight and thus the universe must be very large. That's a non-sequitur. And the infinite model is plain wrong - an infinite universe simply cannot expand because the pressure is counter-balanced everywhere.
I don't know where PhysBang is coming from, but I'm sure we will either find out, or not, lol.
What people call the Big Bang Theory is the consensus, but sometimes this means different things to different people.
According to the authors of the WMAP papers the consensus model is GR, the use of the Robertson-Walker metric (which assumes a degree of isotropy and homogeneity which we call the cosmological principle), the Friedmann-Lemaitre equation that couples energy density to what we would roughly call the expansion of space, the hot and dense state of the very early universe, and inflation. Not all cosmologists are so gung-ho about inflation, but at least WMAP is able to give some pretty decent measurements of features of the CMB that we expect to be there from inflation.
Many cosmologists don't even think about inflation, because they are working on much later problems, like galaxy formation or supercluster formation. I've never really liked inflation, because I think it was introduced for a bad reason. However, I think that it is getting some evidence regardless of its origins.
Every spacetime that can be represented by a FRLW model has a radius of curvature by definition. That's just the mathematical facts.
You are free to defend this crackpot claim with a mathematical demonstration that everyone, including Einstein, who has ever worked with GR to do cosmology is wrong.
PhysBang
Whatever the current radius, we can see all of the Universe(at least in principle)all the way back to the beginning of time and space 13.7 billion years ago. We see it as it was then(IE the further away the further back in time)it is actually much bigger today than it appears to be. The Universe is FINITE but UNBOUNDED. It has a finite size it could have reached since the expansion began, but there are no edges and every point is observationally dead center(give or take a few light years)to the whole thing. We see the CMBR at 13.7 billion years in all directions, as will ever point in spacetime. Einstein thought the Universe was static, he even put a fudge factor in his equation because without it the Universe he thought existed would have collapsed by now. He called it the Cosmological Constant at the time, but after Hubble demonstrated an expanding Universe he called it his biggest mistake. Dark Energy, strangely enough, is today pretty close to the value of the CC he came up with, but is different in origin and effects over time. Einstein thought his CC would hold the Universe at it's present size, but Dark Energy was weak in the beginning(as compared to gravity in the dense soup of the early Universe) but as gravity loses it's effectiveness because matter is thinner and thinner, DE is accelerating the expansion. The expansion rate was slowing for the ~first 5 billion years, becoming neutral in the ~next 5 billion and has started to accelerate in the last few billion. Plotted on a graph it makes a sine curve. In the beginning ours was a gravity dominated Universe, today it is dominated by DE and that will only get worse in the future.
Grumpy
Whatever the current radius, we can see all of the Universe(at least in principle)all the way back to the beginning of time and space 13.7 billion years ago. We see it as it was then(IE the further away the further back in time)it is actually much bigger today than it appears to be. The Universe is FINITE but UNBOUNDED. It has a finite size it could have reached since the expansion began, but there are no edges and every point is observationally dead center(give or take a few light years)to the whole thing. We see the CMBR at 13.7 billion years in all directions, as will ever point in spacetime. Einstein thought the Universe was static, he even put a fudge factor in his equation because without it the Universe he thought existed would have collapsed by now. He called it the Cosmological Constant at the time, but after Hubble demonstrated an expanding Universe he called it his biggest mistake. Dark Energy, strangely enough, is today pretty close to the value of the CC he came up with, but is different in origin and effects over time. Einstein thought his CC would hold the Universe at it's present size, but Dark Energy was weak in the beginning(as compared to gravity in the dense soup of the early Universe) but as gravity loses it's effectiveness because matter is thinner and thinner, DE is accelerating the expansion. The expansion rate was slowing for the ~first 5 billion years, becoming neutral in the ~next 5 billion and has started to accelerate in the last few billion. Plotted on a graph it makes a sine curve. In the beginning ours was a gravity dominated Universe, today it is dominated by DE and that will only get worse in the future.
Grumpy
No. We can see all the visible universe, but not necessarily all of the universe.
It is true that what we can see was smaller (in at least one sense) when it emitted light towards our position.
Any given finite volume is still finite, but it is unknown what the entire volume is.
The distance to the CMBR is only about 13.4 (think .4) billion years in travel time. You can figure out different ways of measuring cosmological distances here: http://www.astro.ucla.edu/~wright/CosmoCalc.html It's really cool. In theory, every point in space sees the CMB the same way.
Einstein realized it was a mistake before Hubble's discovery. He supposedly called the cosmological constant his biggest blunder, but only one hearsay source has made this claim.
Pretty close in the sense that it is on the same order of magnitude, but very different in its effect over cosmological time...
That seems to be very different to me!
No one knows if the universe is finite and unbounded, and if they did tell you that they know this then the lied to you. Einstein even wrote about this, XXXI. The Possibility of a “Finite” and Yet “Unbounded” Universe. He wouldn't have wrote about the possibility of a finite and yet unbounded universe if he thought it was static. It is not scientifically accepted that this theory proves that it is in fact finite and unbounded. The quotations even seem to imply that he had made up this very idea to begin with. He thought the cosmological constant was a mistake, but it turned out that it wasn't really though. The Cosmological Constant would have only made a static universe at certain distances, but it could not make the entire universe static given the rate of acceleration.
It seems I found Einsteins proof that gravity is caused by curvature and could not be caused by a force carrier like the graviton, that I have mentioned before but came up short in finding this.
XXX. Cosmological Difficulties of Newton’s Theory
"Note 1. Proof.—According to the theory of Newton, the number of “lines of force” which come from infinity and terminate in a mass m is proportional to the mass m. If, on the average, the mass-density P0 is constant throughout the universe, then a sphere of volume V will enclose the average mass P0V. Thus the number of lines of force passing through the surface F of the sphere into its interior is proportional to P0V. For unit area of the surface of the sphere the number of lines of force which enters the sphere is thus proportional to P0 · v/F} or P0R. Hence the intensity of the field at the surface would ultimately become infinite with increasing radius R of the sphere, which is impossible. "
XXX. Cosmological Difficulties of Newton’s Theory
"Note 1. Proof.—According to the theory of Newton, the number of “lines of force” which come from infinity and terminate in a mass m is proportional to the mass m. If, on the average, the mass-density P0 is constant throughout the universe, then a sphere of volume V will enclose the average mass P0V. Thus the number of lines of force passing through the surface F of the sphere into its interior is proportional to P0V. For unit area of the surface of the sphere the number of lines of force which enters the sphere is thus proportional to P0 · v/F} or P0R. Hence the intensity of the field at the surface would ultimately become infinite with increasing radius R of the sphere, which is impossible. "
It has been printed several times that I know, but I don't remember his name ever being mentioned with it. But, in Brian Green's new book it does mention him being one of the people that talked about them searching for the real value of the cosmological constant, and has been known to troll internet forums. I had mentioned in Myspace Forums a while back about Michio Kaku's search for the cosmological constant and how the value was close to being the real value of the expansion of the universe. They sent two teams to find the correct value, and then lead to a discovery in the Nobel Prize. I think a lot of the leading theoretical physicist are starting to think the universe may actually be closed Calabi-Yau shapes, since the curvature of a universe could have a negative curvature if the cosmological constant was strong enough to keep the universe from collapsing according to some of Michio Kaku's theories.
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That kind of analysis is what separates laymen like me from the professional level members who have academic credentials. It is helpful to have that perspective.
I don't wonder about why inflation was added because, after all, in order for the CMB to be causally connected to the Big Bang, something had to explain how all of that energy got to such a huge expanse and at the same time was so homogeneous.
It seems to me that either they had to invoke Inflation, or consider the possibility that the Big Bang happened in a pre-existing environment that had it's own background microwave energy, perhaps from a potentially infinite history of multiple big bangs across potentially infinite space and time.
Its a no-brainer to add inflation because there was no other evidence of a greater universe out there, and the event horizon would prevent any observations beyond our Hubble view.
I think Farsight made a good point. The opening paragraph of the link did seem to be muffed up a little bit.
Grumpy, I would like to see the expansion rate plotted on a graph. Do you have it or have you seen it presented that way?... The expansion rate was slowing for the ~first 5 billion years, becoming neutral in the ~next 5 billion and has started to accelerate in the last few billion. Plotted on a graph it makes a sine curve. In the beginning ours was a gravity dominated Universe, today it is dominated by DE and that will only get worse in the future.
Grumpy