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goodoldrebel
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If the universe is finite then what is beyond? If infinite then how can humanity conceive the 'big picture'?
cepheid said:We have an FAQ page for this: https://www.physicsforums.com/showthread.php?t=506986
Farahday said:May we presume the cosmological model is using the first definition and not the second?
cepheid said:Yes, the theoretical models are for all of spacetime, not just the portion of it that we can see.
To elaborate on the OPs question about boundaries and what exists beyond them. The answer is that nothing exists beyond the boundaries, because there are no boundaries. In the standard models, if the universe is finite, then it is unbounded, meaning that it has no edges. This is made possible by spatial curvature. An analogy is a two-dimensional being living on the surface of a sphere. This surface has a finite area, and yet it has no edges for the being to reach. If the being travels far enough in any direction, it will end up back where it started.
Farahday said:I see. Then does there exist some point in the "whole of the universe" at which some object within a finite distance that was moving away from me is now moving toward me or does the rate of expansion preclude that from happening? And if that is the case, then wouldn't the rate of expansion have to exceed 'C' in order to preclude neutrinos from doubling back - thus invalidating Einstein (if neutrinos haven't already done that)?
cepheid said:Yes, the theoretical models are for all of spacetime, not just the portion of it that we can see.
To elaborate on the OPs question about boundaries and what exists beyond them. The answer is that nothing exists beyond the boundaries, because there are no boundaries. In the standard models, if the universe is finite, then it is unbounded, meaning that it has no edges. This is made possible by spatial curvature. An analogy is a two-dimensional being living on the surface of a sphere. This surface has a finite area, and yet it has no edges for the being to reach. If the being travels far enough in any direction, it will end up back where it started.
Hmmmmm. So there is no limit to the expansion. Could it therefore be or have been infinite (no limit)? Certainly if the cosmos is only 13+billion light years in size, there must be some calclation as to the rate of expansion from t=1...or is it possible we can only detect 13+B light years of data...which would render the age approximation of the cosmos moot?Mark M said:When talking about the expansion of the universe, you must specify two points, so a sufficiently far object will be receding much faster than light. But remember, general relativity puts no limit the expansion of the universe, just the observers within it. Also, neutrinos do NOT move faster than light. That is impossible, though they move very close.
goodoldrebel said:Yet, a two-dimensional theory does not directly address the question. Pinning 'no beginning and no ending' on "Spatial curvature" does not solve the three dimensionality dilemma of the infinite universe
Farahday said:Hmmmmm. So there is no limit to the expansion. Could it therefore be or have been infinite (no limit)? Certainly if the cosmos is only 13+billion light years in size, there must be some calclation as to the rate of expansion from t=1...or is it possible we can only detect 13+B light years of data...which would render the age approximation of the cosmos moot?
Also in some speculative models, Neutrinos have a tachyonic nature and travel faster than 'C'. Those Lorentz violating variants of quantum gravity are part of the Standard-Model Extension.
Also mass is just a condition - readily exchangeable with energy. Only those things with the property of mass are subject to the speed limit.
cepheid said:The theory itself is not two-dimensional. It is a full description of the four dimensions of spacetime that employs the idea of curvature and non-Euclidean geometry. In other words, saying that you live in a closed universe is saying that, in this universe, geometry doesn't behave like the way you learned in school. In a closed universe, parallel lines eventually meet. The sum of the three angles of a triangle is greater than 180 degrees. If you travel far enough in any given direction, you'll end up back where you started. So the geometry in this curved 3D space is analogous to the geometry on a curved 2D surface. I was using a direct lower-dimensional analogy to give you a way to visualize the implications of this curvature in the higher-dimensional case.
Farahday said:Hmmmmm. So there is no limit to the expansion. Could it therefore be or have been infinite (no limit)?
Farahday said:Certainly if the cosmos is only 13+billion light years in size,
Farahday said:Also in some speculative models, Neutrinos have a tachyonic nature and travel faster than 'C'. Those Lorentz violating variants of quantum gravity are part of the Standard-Model Extension.
Farahday said:Also mass is just a condition - readily exchangeable with energy. Only those things with the property of mass are subject to the speed limit.
Farahday said:possible we can only detect 13+B light years of data...which would render the age approximation of the cosmos moot?
Thank you.goodoldrebel said:Two excellent points. I presume the calculated age reflects 'detectable' data.
Farahday said:years in size, there must be some calclation as to the rate of expansion from t=1.
goodoldrebel said:Can you detail a bit more about three-dimensional universe curvature as it relates to infinitely? Many thanks.
Farahday said:Thank you.
I must; however, admit I am somewhat skeptical about the validity of expansion related red shift. Would it not seem reasonable to assume if a body is moving away at high velocity that its signature - width of its apparent diameter and strength of signal or luminocity - should also evidence a correspoding dimunition? I know of no such corroborating data or evidence.
Any links you might provide would be appreciated.
Yes CMB not light. 13+B light years of it may be calculable, but that is the limit of our ability to detect, not necessarily the limit of the phenomenon. Any observations we might make are limited by our technology, not the nature of the cosmos.cepheid said:The age of the universe is NOT estimated based on the size of the observable portion of it. It is determined independently through other observational means.
Farahday said:Hmmmmm. So there is no limit to the expansion. Could it therefore be or have been infinite (no limit)? Certainly if the cosmos is only 13+billion light years in size, there must be some calclation as to the rate of expansion from t=1...or is it possible we can only detect 13+B light years of data...which would render the age approximation of the cosmos moot?
Farahday said:Yes CMB not light. 13+B light years of it may be calculable, but that is the limit of our ability to detect, not necessarily the limit of the phenomenon. Any observations we might make are limited by our technology, not the nature of the cosmos.
cepheid said:*Sigh*
I have no idea what you mean by the part in bold, so I cannot address your specific objection. However, we have an FAQ page for this as well. This is the third cosmology FAQ article that I have linked to this thread:
https://www.physicsforums.com/showthread.php?t=506994
Maybe you just check out all of them first, and then come back with questions:
https://www.physicsforums.com/forumdisplay.php?f=206
Farahday said:Thank you.
I must; however, admit I am somewhat skeptical about the validity of expansion related red shift. Would it not seem reasonable to assume if a body is moving away at high velocity that its signature - width of its apparent diameter and strength of signal or luminocity - should also evidence a correspoding dimunition? I know of no such corroborating data or evidence.
Any links you might provide would be appreciated.
Farahday said:Thanx for the link, but I saw no references that might tell me where to find observational data that receding galaxies are dimming at a rate appropriate to their predicted velocities relative to us. I would consider such observations to be crucial in support of expansion redshift theory. Do you have a specific link you might suggest that covers this?
cepheid said:I can supply such a link, but first I need to explain some background. Luminiosity is the term in astronomy for the rate at which an object outputs energy (in the form of light or EM radiation). So luminosity is measured in watts (or, more typically, in units of "sun luminosities"). Luminosity distance is a distance measure in cosmology that is made by assuming that the inverse square law for the dimming of light is true. In other words, if you compare the apparent brightness of an object (how much light you receive from it per unit area and per unit time) to the intrinsic brightness of that object (its luminosity), and you assume the inverse square law is true, then you can infer a distance to that object. The distance you infer is called the "luminosity distance." The luminosity distance is a distance measure that is based on how bright an object appears.
Now, any given cosmological model predicts a definite relationship between the luminosity distance to an object and the redshift of that object. This relationship is basically the one that you are asking about above. Different models (i.e. with different parameters) predict different curves for this relationship. If you have something that is of a known intrinsic luminosity (a so called "standard candle"), then you can figure out its luminosity distance. You can also figure out its redshift through spectroscopy. This gives a way of determining the actual measured relationship between luminosity distance and redshift. You can then go and fit a theoretical curve to the data (i.e. you can see which model best matches the observations).
For reasons I won't get into here, Type Ia supernovae are thought to be such a standard candle. In other words, they are all thought to have the same luminosity. (It is actually slightly more complicated than this, but that is the basic idea). There is a paper by Perlmutter et al. 1999
http://iopscience.iop.org/0004-637X/517/2/565/pdf/39148.web.pdf
that shows (figure 2) essentially apparent brightness (which equivalent to luminosity distance) vs. redishift for a large number of supernovae from a couple of different supernova surveys. The data strongly favour a particular cosmological model in which the density of "dark energy" is non-zero. This is some of the first observational evidence for accelerated expansion. This, of course, is just one (very notable) example of a measurement of apparent brightness vs. redshift and comparison to theory.
EDIT: Figures 7 and 9 from that paper are really neat too. They make great summaries of how where you are (in parameter space) affects various things (like curvature, expansion history/future, and acceleration).
goodoldrebel said:Are you referring to more than just time dilation?
Farahday said:Things change slower in the presence of mass (gravity). Kind of gives a mystical property to time, but then all kinds of things effect rates of change.
When two masses approach each other, the space between them shrinks...ever thought about the possibility it might be just that simple. Not the masses acting on each other, but on space itself - lessening the density/volume? Things can only directly alter the condition of other things with which they are in contact...further change is called propagation.
Farahday said:I thank you for the link. It certainly identifies all the problems involved in trying to calculate the effect of vast distances of ambient matter on fragile light waves - and the vagarities of dealing with somewhat unknown quantities - high and low redshift supernovas which, themselves, redden over time.
Farahday said:As an observer of ardent perspective (infinite and eternal cosoms) it has reminded me modern cosmology deals with statistical probability rather than iron-clad
Farahday said:fact and the multiple interpretations therefrom are not so much dogma as they are data based.
Farahday said:They link those probabilities to a large number of variables - known variables. I would suggest the number of unknown variables is vastly larger.
Farahday said:Cite: "the data are strongly inconsistent with the flat universe model that has been the theoretically favored cosmology. If the simplest inflationary theories are correct and the universe is spatially flat, then the supernova data imply that there is a significant, positive cosmological constant. Thus the universe may be flat or there may be little or no cosmological constant, but the data are not consistent with both possibilities simultaneously. This is the most unambiguous result of the current data set."
While I remain unconvinced, at least I can see where the interpretation comes from.
Farahday said:Things change slower in the presence of mass (gravity). Kind of gives a mystical property to time, but then all kinds of things effect rates of change.
When two masses approach each other, the space between them shrinks...ever thought about the possibility it might be just that simple.
Not the masses acting on each other, but on space itself - lessening the density/volume?
Things can only directly alter the condition of other things with which they are in contact...further change is called propagation.
Farahday said:Thanx for the link, but I saw no references that might tell me where to find observational data that receding galaxies are dimming at a rate appropriate to their predicted velocities relative to us. I would consider such observations to be crucial in support of expansion redshift theory. Do you have a specific link you might suggest that covers this?
lostprophets said:if infinite means growing quicker than you can measure then yes infinite is possible.
if it is growing then i see (without fact) that its a spiral growth
if its finite that would mean an overlap which kinda makes it infinite..
or an finite inward spiral..
i kinda feel that there's at least 3.or 3 parts to 1
all guess work and my thoughts on the question.
lostprophets said:if infinite means growing quicker than you can measure then yes infinite is possible.
if it is growing then i see (without fact) that its a spiral growth
if its finite that would mean an overlap which kinda makes it infinite..
The answer to this question is currently unknown and is a topic of ongoing scientific research and debate. Some theories suggest that the universe is infinite, while others propose that it is finite but unbounded. More evidence and research are needed to determine the true nature of the universe.
Scientists use various methods to study the size of the universe, such as measuring the cosmic microwave background radiation, observing the redshift of distant galaxies, and studying the curvature of space-time. These methods help scientists estimate the size and shape of the universe.
According to current theories, the universe is expanding at an accelerating rate due to dark energy. This suggests that the expansion of the universe may continue indefinitely. However, there are also theories that propose the expansion may eventually slow down or even reverse. Further research is needed to determine the fate of the universe.
The concept of an edge to the universe is often misunderstood. The universe does not have a physical edge like a boundary or a wall. Instead, the edge of the observable universe is the furthest distance we can see due to the limitation of the speed of light. Beyond this point, the universe may continue, but we cannot observe it.
The size of the universe has significant implications for our understanding of reality. It challenges our perceptions of time, space, and our place in the universe. It also raises philosophical questions about the meaning of existence and our role in the grand scheme of things. The study of the size of the universe continues to push the boundaries of our understanding and perspective.