Sandro Posted October 13, 2016 Share Posted October 13, 2016 Let's consider that the big bang did not happen everywhere, but at a precise point in the universe and the big bang is not an event in the past but is a continuous event of energy creation. Keeping in view this as we see the universe? In particular, the Hubble law would function in a similar manner? And the WMAP image would occur just as it is? Thanks for the answers Link to comment Share on other sites More sharing options...
Mordred Posted October 13, 2016 Share Posted October 13, 2016 No the two cases would not be identical. A universe with a centre and expanding outward is inhomogeneous and anistropic. Has a preferred location and direction. Expansion data shows the expansion as homogeneous and isotropic. Geometrically the two are dinstict in preserving angles. Ordinarily I would refer you to the balloon or raisin bread analogy but your post indicates your already familiar with them 1 Link to comment Share on other sites More sharing options...
Strange Posted October 13, 2016 Share Posted October 13, 2016 Let's consider that the big bang did not happen everywhere, but at a precise point in the universe and the big bang is not an event in the past but is a continuous event of energy creation. This is one of the models that Hoyle tried when he was trying create a (quasi-) steady state theory. The thing that killed of this and hsi other attempts was the CMB. There is no other model that predicts exactly what we observe. 1 Link to comment Share on other sites More sharing options...
Sandro Posted October 14, 2016 Author Share Posted October 14, 2016 The thing that killed of this and hsi other attempts was the CMB. If the expansion happen from a precise point (center of the universe) we do not however observe the CMB? How it should be different? (Excuse the insistence but I want to try to understand) Geometrically the two are dinstict in preserving angles. Please could you explain better this concept. It refers to the Hubble's law? Link to comment Share on other sites More sharing options...
Airbrush Posted October 14, 2016 Share Posted October 14, 2016 (edited) If the universe was finite in size then would that not mean there was a central point of origin? This would be in a multiverse of big bangs occurring in a larger structure. An infinite number of big bang occurring separated by incredibly vast distances. Edited October 14, 2016 by Airbrush Link to comment Share on other sites More sharing options...
Strange Posted October 14, 2016 Share Posted October 14, 2016 If the expansion happen from a precise point (center of the universe) we do not however observe the CMB? How it should be different? (Excuse the insistence but I want to try to understand) Please could you explain better this concept. It refers to the Hubble's law? The main thing I was commenting on there was the "continuous creation" aspect. In that case (at least in Hoyle's model) the universe has always been (roughly) the same as it is now and it is the continuous creation of matter that allows it to expand. In that case, there is no explanation for the CMB. As to the "from a central point" bit, that is addressed by Mordred's comment about isotropy. The expansion is the same in all directions - in other words, everything is moving away from everything else. This is not consistent with expansion from a point. If the universe was finite in size then would that not mean there was a central point of origin? Not really. The model is based around expansion caused by the scaling of space. So if you consider any number of points in space (where you are, the location of Mars, the centre of the Andromeda galaxy, the most distant galaxy we can see) and run the clock backwards then, as universe shrinks these points in space all get closer to one another. Eventually they are all adjacent. And that is the location of the big bang: everywhere. 1 Link to comment Share on other sites More sharing options...
geordief Posted October 14, 2016 Share Posted October 14, 2016 The main thing I was commenting on there was the "continuous creation" aspect. In that case (at least in Hoyle's model) the universe has always been (roughly) the same as it is now and it is the continuous creation of matter that allows it to expand. In that case, there is no explanation for the CMB. As to the "from a central point" bit, that is addressed by Mordred's comment about isotropy. The expansion is the same in all directions - in other words, everything is moving away from everything else. This is not consistent with expansion from a point. Could everything have started from the same region and thereafter have started retreating from themselves in a uniform way ? If we go back in time to what is loosely called the Big Bang might we find a circumstance where there was (at that time ) a centre but which is no longer apparent because it is so hard to discern? I am not saying that could be likely but is it possible.? I think there are supposed to be "inflation" and "expansion" as two distinct phenomena .I am not suggesting necessarily that "inflation" might have had a centre but could it have ?. Link to comment Share on other sites More sharing options...
Mordred Posted October 14, 2016 Share Posted October 14, 2016 (edited) no both inflation and expansion are homogeneous and isotropic in terms of expansion. An easy way to understand the difference. Draw a right angle triangle. Now in the homogeneous and isotropic case increase the distance on each leg equally. All angles are preserved. In the isotropic case apply expansion only to 1 leg. All angles are not preserved. this results in angle changes Edited October 14, 2016 by Mordred 1 Link to comment Share on other sites More sharing options...
Airbrush Posted October 15, 2016 Share Posted October 15, 2016 The model is based around expansion caused by the scaling of space. So if you consider any number of points in space (where you are, the location of Mars, the centre of the Andromeda galaxy, the most distant galaxy we can see) and run the clock backwards then, as universe shrinks these points in space all get closer to one another. Eventually they are all adjacent. And that is the location of the big bang: everywhere. That is hard to visualize. If the universe had a finite size, for example about twice the size of the observable universe, imagine the finite universe is an irregular blob, roughly spherical in shape about 180 Billion LY across. The distance between opposite edges of the universe can be divided in half to find a center point. Even an irregularly shaped asteroid has a true center of gravity. So why not with the finite universe? Link to comment Share on other sites More sharing options...
Delta1212 Posted October 15, 2016 Share Posted October 15, 2016 That is hard to visualize. If the universe had a finite size, for example about twice the size of the observable universe, imagine the finite universe is an irregular blob, roughly spherical in shape about 180 Billion LY across. The distance between opposite edges of the universe can be divided in half to find a center point. Even an irregularly shaped asteroid has a true center of gravity. So why not with the finite universe? Well sure, it could. But there could be an actual Santa Claus outside of the observable universe as well. There's presently no evidence for either. Link to comment Share on other sites More sharing options...
StringJunky Posted October 15, 2016 Share Posted October 15, 2016 That is hard to visualize. If the universe had a finite size, for example about twice the size of the observable universe, imagine the finite universe is an irregular blob, roughly spherical in shape about 180 Billion LY across. The distance between opposite edges of the universe can be divided in half to find a center point. Even an irregularly shaped asteroid has a true center of gravity. So why not with the finite universe? Only the observable universe is spherical and a discrete space with a centre. The geometry or shape of the wider universe could be one of a few candidates, like a torus, for example; there is no centre. Visualise the surface of a sphere and you will see there is no centre and as it expands each adjacent point on that surface moves further apart Link to comment Share on other sites More sharing options...
Mordred Posted October 15, 2016 Share Posted October 15, 2016 (edited) That is hard to visualize. If the universe had a finite size, for example about twice the size of the observable universe, imagine the finite universe is an irregular blob, roughly spherical in shape about 180 Billion LY across. The distance between opposite edges of the universe can be divided in half to find a center point. Even an irregularly shaped asteroid has a true center of gravity. So why not with the finite universe? Its easier to visualize without being finite or infinite if you treat it as a fluid or gas. We use the ideal gas laws to model expansion. As the volume increases, density decreases. There doesn't need to be any outside for this to work. Nor is there any requirement for a finite universe. This works in both cases. As the temperature reduces roughly the same everywhere expansion maintains a homogeneous and isotropic adiabatic expansion. Edited October 15, 2016 by Mordred Link to comment Share on other sites More sharing options...
Airbrush Posted October 16, 2016 Share Posted October 16, 2016 ....run the clock backwards, as the universe shrinks these [widely separated] points in space all get closer to one another. Eventually they are all adjacent. And that is the location of the big bang: everywhere. No that is the center of a finite big bang. It does not matter what shape a finite universe takes, there is always a center of gravity, assuming a finite-sized universe. I don't know if the center of gravity would be the same location as where the finite big bang originated. Link to comment Share on other sites More sharing options...
StringJunky Posted October 16, 2016 Share Posted October 16, 2016 ....would be the same location as where the finite big bang originated. This is where you have got it wrong; The universe isn't in anywhere, so it can't have an origin; it is everything that exists. Link to comment Share on other sites More sharing options...
Sandro Posted October 17, 2016 Author Share Posted October 17, 2016 The main thing I was commenting on there was the "continuous creation" aspect. In that case (at least in Hoyle's model) the universe has always been (roughly) the same as it is now and it is the continuous creation of matter that allows it to expand. In that case, there is no explanation for the CMB. The CMB radiation represents the birth of the first photons in the universe. If hypotetically we consider the big bang as a continuous event of energy creation, we can also assume that it evolves in a manner similar to the ΛCDM model and therefore present a CMB? Draw a right angle triangle. Now in the homogeneous and isotropic case increase the distance on each leg equally. All angles are preserved. In the isotropic case apply expansion only to 1 leg. All angles are not preserved. this results in angle changes This concept of the angles preserved refers to measurements of the redshift of galaxies or is it just to explain the theoretical differences? Observational data from the redshift could be reconciled with an expansion model similar to a bomb (with an expansion center)? Link to comment Share on other sites More sharing options...
Strange Posted October 17, 2016 Share Posted October 17, 2016 No that is the center of a finite big bang. It does not matter what shape a finite universe takes, there is always a center of gravity, assuming a finite-sized universe. I don't know if the center of gravity would be the same location as where the finite big bang originated. It makes no difference if it is finite or infinite. And, no, a finite universe does not need to have a centre. Take for example, the 2D surface of the Earth as a simpler analogy. Where is the centre of the Earth's surface? There isn't one. If the Earth were expanding, then all cities and towns would move apart from one another equally. And, from simple arithmetic, the speed at which they move apart would be proportional to their distance. The CMB radiation represents the birth of the first photons in the universe. If hypotetically we consider the big bang as a continuous event of energy creation, we can also assume that it evolves in a manner similar to the ΛCDM model and therefore present a CMB? Not quite. It represents the point at which the universe had cooled enough to allow them to travel freely.. If you are going to propose an alternative mechanism, then you must explain (1) why it has a (perfect) black body spectrum and (2) why it is the temperature it is. This concept of the angles preserved refers to measurements of the redshift of galaxies or is it just to explain the theoretical differences? Observational data from the redshift could be reconciled with an expansion model similar to a bomb (with an expansion center)? If there were an explosion some distance away then some stuff would be moving away, some would be moving towards us, some would be going left, right, up down. So we would see a range of different red/blue shifts depending where you look. This is the opposite of isotropic. 1 Link to comment Share on other sites More sharing options...
Delta1212 Posted October 17, 2016 Share Posted October 17, 2016 No that is the center of a finite big bang. It does not matter what shape a finite universe takes, there is always a center of gravity, assuming a finite-sized universe. I don't know if the center of gravity would be the same location as where the finite big bang originated. You are confusing "finite" with "bounded." It is possible for a space to be finite but unbounded, in which case there is no center. Link to comment Share on other sites More sharing options...
Airbrush Posted October 17, 2016 Share Posted October 17, 2016 (edited) .... like a torus, for example; there is no centre. A finite torus does have a center of gravity. No matter how irregular the shape of the finite torus, it would definitely have a center of gravity. You are confusing "finite" with "bounded." It is possible for a space to be finite but unbounded, in which case there is no center. Could be. What I mean is a universe that has a finite-size. Then let's suppose the universe was finite and bounded, for example. That universe would definitely have a center of gravity. This is where you have got it wrong; The universe isn't in anywhere, so it can't have an origin; it is everything that exists. Not in a finite, bounded universe. A finite, bounded universe would exist within something else, within the next higher structure, within a "bulk" in multiverse theory. The bulk outside our tiny, finite universe could be empty, or there could simultaneously exist a finite, or infinite, number of other big bangs. The other big bangs could be giant, but not infinite. "The brane multiverse follows from M-theory and states that our universe is a 3-dimensional brane that exists with many others on a higher-dimensional brane or "bulk". Particles are bound to their respective branes except for gravity." "...Proponents of one of the multiverse hypotheses include Stephen Hawking,[16]Brian Greene,[17][18]Max Tegmark,[19]Alan Guth,[20]Andrei Linde,[21]Michio Kaku,[22]David Deutsch,[23]Leonard Susskind,[24]Alexander Vilenkin,[25]Yasunori Nomura,[26]Raj Pathria,[27]Laura Mersini-Houghton,[28][29]Neil deGrasse Tyson,[30] and Sean Carroll.[31] https://en.wikipedia.org/wiki/Multiverse Edited October 17, 2016 by Airbrush Link to comment Share on other sites More sharing options...
Strange Posted October 18, 2016 Share Posted October 18, 2016 A finite torus does have a center of gravity. No matter how irregular the shape of the finite torus, it would definitely have a center of gravity. I believe he was referring to the surface of a torus (as a 2D analogy). Could be. What I mean is a universe that has a finite-size. Then let's suppose the universe was finite and bounded, for example. That universe would definitely have a center of gravity. As far as I know, there are no modern cosmological models that describe the universe with a boundary. 1 Link to comment Share on other sites More sharing options...
StringJunky Posted October 18, 2016 Share Posted October 18, 2016 I believe he was referring to the surface of a torus (as a 2D analogy). Yes, I should have mentioned that. Link to comment Share on other sites More sharing options...
Sandro Posted October 18, 2016 Author Share Posted October 18, 2016 If there were an explosion some distance away then some stuff would be moving away, some would be moving towards us, some would be going left, right, up down. So we would see a range of different red/blue shifts depending where you look. This is the opposite of isotropic. In an explosion everything moves in a centrifugal direction, so we should not look blue shift... we should not only observe redshift with slight differences in the proportion distance / redshift based on the direction in which you observe? Link to comment Share on other sites More sharing options...
Strange Posted October 18, 2016 Share Posted October 18, 2016 (edited) In an explosion everything moves in a centrifugal direction, so we should not look blue shift... we should not only observe redshift with slight differences in the proportion distance / redshift based on the direction in which you observe? If the explosion is throwing things towards you then that will be blue-shifted. we should not only observe redshift with slight differences in the proportion distance / redshift based on the direction in which you observe? We do not see that. Edited October 18, 2016 by Strange 1 Link to comment Share on other sites More sharing options...
Airbrush Posted October 18, 2016 Share Posted October 18, 2016 The only way the balloon analogy would make sense is if the thickness of the skin of the balloon is greater than the diameter of the observable universe. It's time to think up a better analogy. Link to comment Share on other sites More sharing options...
Strange Posted October 18, 2016 Share Posted October 18, 2016 The only way the balloon analogy would make sense is if the thickness of the skin of the balloon is greater than the diameter of the observable universe. It's time to think up a better analogy. The only way the balloon analogy makes sense is if: 1) You remember that it is a 2D analogy for 3D space (so there is no thickness) 2) The only things it illustrates are: 2.1) There is no centre of the surface 2.2) All dots on the surface move away from each other and the speed of separation is proportional to how far apart they are. Link to comment Share on other sites More sharing options...
Mordred Posted October 18, 2016 Share Posted October 18, 2016 (edited) 2.3 the angles between dots is preserved. Which is only possible in the isotropic case. Edited October 18, 2016 by Mordred Link to comment Share on other sites More sharing options...
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