8) Cosmologists are of the opinion that there is no center and no edge to the universe and that the term "Big Bang" is misleading and confusing to lay people. It gives people an impression that the universe came into existence in an explosion, hence there should be a center of the explosion. I am having a hard time trying to visualize how the universe could come into existence without a center. The best I can come up with is a sheet of infinite size that suddenly popped into existence and expanded outward, but this would still give the universe two edges.brianclark wrote:Maybe we have just located the Center of the Universe ?
I have always imagined that if Big Bang occurred, then all matter would depart the center in a spherical shape and thus leave a void behind so that in fact the Universe would be a hollow sphere ! ..................and that we are located in some part of the shell ,,,,,,or were there some secondary Bangs also ?
Brian in Fife
That is mainly based on the Cosmological Principle: "On large spatial scales, the Universe is homogeneous and isotropic".starnut wrote:Cosmologists are of the opinion that there is no center and no edge to the universe
Cosmologists don't say that the Universe has no center. What they say is that the Universe has no three-dimensional center. I find that the famous balloon analogy is a big help. It considers the view of 3D universe as seen by 2D creatures. From our viewpoint, the balloon is a 3D object with a center. Its surface expands outward from that center. But for 2D creatures living on the balloon, there is no center. "Up" and "down" are not directions they can perceive. To them, they are living on an infinite surface. If they travel far enough in one direction, they come back to where they started. They can even do clever experiments, such as measuring the summed angles of triangles, and figure out that their universe is spherical in 3D. But they can still never see its center.starnut wrote:Cosmologists are of the opinion that there is no center and no edge to the universe and that the term "Big Bang" is misleading and confusing to lay people. It gives people an impression that the universe came into existence in an explosion, hence there should be a center of the explosion. I am having a hard time trying to visualize how the universe could come into existence without a center. The best I can come up with is a sheet of infinite size that suddenly popped into existence and expanded outward, but this would still give the universe two edges.
Oh, my aching head...anyone got a better idea?
I guess it depends on what you mean by "observable". By your definition, perhaps you don't believe in electrons, quarks, or even other galaxies. These are all observed indirectly. Likewise for the geometry of the Universe. It is described by General Relativity, a theory that accurately predicts many, many things (all observed in one manner or another).SmartAZ wrote:I guess I understand the 4D universe concept as well as anybody, which is to say zero equals zero. I am very suspicious of any concept not based on observation, and this one is by definition not observable.
That observation proves nothing of the kind. It is possible that the Universe itself is smaller than the visible Universe, in which case what we see in one direction would be similar to what we would see in the opposite direction (i.e. space curved back on itself). CMB measurements have mostly, but not 100% ruled out this possibility. And the fact that we don't see a uniform white background doesn't mean the Universe doesn't go on forever, nor that there can't be an infinite number of stars. Regardless of the size of the Universe, we don't see every star because the finite age of the Universe limits the number we can possibly see. The fact that the sky is mostly dark is observational evidence in support of the Big Bang, and therefore also in support of a four-dimensional Universe.SmartAZ wrote:Here is one example of an observation that disproves a common notion.
Many people speak of space "curving back on itself" somehow. If there were any such effect we would see every star in the universe in every direction we look. In other words, space would be uniformly white. We observe that space is uniformly black beyond the stars we can see. So space does not curve back on itself. (It also does not go on forever. Or at least there is a limit to the number of stars out there.)
Space "curving back on itself" is a 3D analogy for a non-3D solution. Regardless which direction is traveled in a straight line, the "termination point" will be at the end of the universe - a single point where space/time no longer exists. Quite like an inverted singularity. Because I don't believe in infinity, the "end of the universe" would be one Planck Length (1.6 ^ 10−35 meters) that would take a photon 46B years to cross.SmartAZ wrote:Here is one example of an observation that disproves a common notion.
Many people speak of space "curving back on itself" somehow. If there were any such effect we would see every star in the universe in every direction we look. In other words, space would be uniformly white. We observe that space is uniformly black beyond the stars we can see. So space does not curve back on itself. (It also does not go on forever. Or at least there is a limit to the number of stars out there.)
It was supposed to say just what it did. The actual Universe can be smaller than the observable Universe. Sounds odd, but nothing in theory precludes it. If, in fact, it's true, then we should see photons from some distant objects mirrored on opposite sides of the sky. That's because if the Universe is smaller than the observable Universe, there will have been enough time for some light to have made it across and to wrap around and reach us.SmartAZ wrote:Say what? That didn't come out right. What was that supposed to say?It is possible that the Universe itself is smaller than the visible Universe,
At least some cosmologists are also of the opinion the universe is expanding. That would imply to me that everywhere in the universe is receding from ??? the center of the universe ???starnut wrote:Cosmologists are of the opinion that there is no center and no edge to the universe
I understand that the classical concepts of gravity and space time cease to exist at distances this small, but Planck Time (the time reqired for one photon to cross a Planck Length) is defined as 5.3912×10-44 seconds not 46B years.Dr. Skeptic wrote:Because I don't believe in infinity, the "end of the universe" would be one Planck Length (1.6 ^ 10−35 meters) that would take a photon 46B years to cross.
That's true. But the center is a point in spacetime, not a three dimensional point that we can observe. There is no center or edge to the three dimensional universe, anymore than there is a center or edge to the circumference of a circle that is expanding in diameter. If your universe is that circumference, you can figure out that it is expanding even though you can never see from where (except mathematically).bystander wrote:At least some cosmologists are also of the opinion the universe is expanding. That would imply to me that everywhere in the universe is receding from ??? the center of the universe ???
Relativity! If the photon has eyes, it would take 5^-44s to "cross" (quantum mechanics makes it more of a jump) the Planck Length. As an observer relative to the Earth, it would take the entire distance of the expanding universe (46 billion light years) for that photon to make the quantum jump.bystander wrote:I understand that the classical concepts of gravity and space time cease to exist at distances this small, but Planck Time (the time reqired for one photon to cross a Planck Length) is defined as 5.3912×10-44 seconds not 46B years.Dr. Skeptic wrote:Because I don't believe in infinity, the "end of the universe" would be one Planck Length (1.6 ^ 10−35 meters) that would take a photon 46B years to cross.
Precisely. We have observed the structure of the Universe, and developed a theory that explains what we see. GR fits the bill beautifully, and has held up to many independent tests.SmartAZ wrote:That is where the disconnect occurs. I took a science class once and they taught me that step #1 of the method was, "Observe a phenomenon."But the center is a point in spacetime, not a three dimensional point that we can observe.
Correct. The problem arises when we start to think those inferences are basic principles, forgetting that someone made them up. For example, curved space is only needed to explain an expanding universe, which is based on the hypothesis that red shift directly relates to distance, which is based on some assumptions about brightness and sizes of observed stars. If those assumptions were wrong then the hypothesis is wrong, the universe is not expanding, and space is just the way it looks. But the red shift/distance thing is now regarded as a basic principle so the underlying assumptions and hypotheses are not examined much any more.Chris Peterson wrote:Good science doesn't depend on directly observing everything. There are lots of things we have never observed, such as the electron shell structure of atoms. But, like the geometry of the Universe, we observe other things that let us make inferences about things we can't see directly.
