"does the universe have a center-of-mass—basically, a “center of gravity” applied to the universe as a whole?
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Some philosophical questions about cosmology ( I didn't know another more suitable place to post this at LT)
I'm inviting you to help me think this through——
"does the universe have a center-of-mass—basically, the idea of a “center of gravity” applied to the universe as a whole?"
(Note: This is a question that numerous people have thought of and asked. Thus, there are brief "explanations" here and there on pages around the internet of science-topics in which there's a simple and brief, "No," given in answer.
If all you're interested in is posting one of the many such pages, please don't bother. I've seen several and I already know these exit--and that this is the standard answer from cosmologists.
If, however, after reading the following, you know of a site which develops an answer in its details of why not--and a lay person / non-specialist might read and understand some of the explanation, then please do post it. Thanks.)
_____________
Scientists are trying to account for what they estimate to be about 95 to 96 percent of the matter and energy which, according to their calculations, ought to exist but have not been detected so far. This is divided roughly into about 73 percent of what is called “dark energy” and 23 percent “dark matter”--”dark” because it has not been observed as far as is known.
Meanwhile, some amateur cosmologists wonder: does the universe have a center-of-mass—basically, the idea of a “center of gravity” applied to the universe as a whole?; it should be noted that the question means the whole universe rather than the “visible universe” since this may be related to the mass that is so far undetected. I wonder about this, too.
Taking the “big bang” as a conceptual model, we're to understand that, at the origin of the universe there was effectively an ultimate state of maximum density in which was concentrated the entire mass of the universe—a minimally-tiny point. This point, at the “big bang” errupted in a gargantuan explosion-like expansion. But we're told (see Sean Carroll work) not to think of it as really like an immense explosion conceptually such as, on a vastly smaller scale, those to which we are accustomed from earth's experience. This explosion was supposedly both quantitatively and qualitatively different. Exactly how and why it was is—or was—is, to me, still not at all clear.
At the same time, we're also offered ( see Sean Carroll's work) as an example of limited application the model of an expanding balloon. If you take an uninflated balloon and, using a marking-pen, mark its surface randomly all over with small ink-dots and then you inflate the balloon slowly, what you'll notice is that the all the dots seem to grow more distant from each other—each one moves away from all the others in a rate that matches the rate of the balloon's expansion. In a roughly similar manner, all the widely-separated objects in the universe—galaxies and entities larger that galaxies—are growing more distant from each other while, internally, they each roughly maintain the integrity of their individual structural proportions—the galaxies themselves are not expanding, the distances between them are increasing . So, from any vantage point, all the other large entities appear to be moving further way rather than drawing closer.
But, we're cautioned that the analogy of the balloon is only approximate and must not be taken too far. We're not supposed to imagine that the universe's expansion is—or was, from the original big bang—quite like a giant explosion which quickly inflates a big balloon.
We're told (see Sean Carroll) that the answer to the question—“Is there a center of mass to the universe as a whole?”—“No, there is not.” and the reason we're given is that, from any vantage point, the large-scale objects are all moving away from each other and this is supposed to indicate that there is no center of mass.
The logic of that “explanation” escapes me since, like the universe's large-scale objects, the marks on the surface of the balloon also all appear to move farther away from each other as the balloon expands. And, yet, for all that, no one would assert that the balloon has no center of mass and that this center is to be found not on the balloon's surface area—where all the “dots” are located—but within the interior of the balloon's surface—at what would be the mid-point of its diameter if it were a true sphere.
Specifically, what I wonder about are the following questions:
Is the current general expansion of the universe supposed to “account for,” to be, in some positive manner, related to the “original” big bang? In other words, are things such as galaxies moving farther and farther from each other by the residual “force”, so to speak, of the universe-forming big bang?
If it is not, then to what are we to attribute the universe's expansion?
Let's return to the model of the balloon's expanding surface as a working analogy for the visible part of the universe in which we find our planet, solar system and galaxy and all the other detectable entities near and far in the universe from the earth's moon to the most distant observable star or galaxy.
As we know or assume, gravity is at work everywhere throughout this superficial extent and it constantly affects all the motions of all the objects—matter and (all? Or most?) of the radiant (?) energy—in this “spherical” space. Thus, gases, dust, and denser or more massive objects, and what we call visible light are all subject to this gravity. If so, then, like everything else, gases and more solid ( i.e. heavier) matter, light moves along the surface of the expanding spherical universe which means that, over its entirety, it follows the curve of the expanding “edge” of the visible universe and never other than under exceptional circumstances, does it leave the approximate surface region for anything “below” or “beneath” it—and, we are assuming here, there is no meaning to there being anything “beyond” (outside) its limits.
One of the things which would follow from the view just described is that, unlike the current view of things, the most “distant” light reaching Earth is not properly thought of as being potentially either significantly “older” / “earlier” or “younger” / “later” in the evolution of the universe; that is, we can not, even figuratively, say that, in examining such light, we are “looking back” at light from an earlier age in the universe and, least of all can we say that we're observing light from some of the (relatively) early stages of the universe's existence since, by the view being offered for consideration here, all this light is travelling a spherical circuit and there is no way to meaningfully say that some of the light is, since “farther away”, “more distant” in the age of the universe. True, stars form and burn for a time and eventually burn out. In that sense, some light is “younger” or “older” as a function of the star's age. But, on the scale of universal existence-time, none of this light is vastly younger or older, relatively speaking since all of it is found somewhere on the “surface”—to use the balloon analogy—of the expanding universe.
Is there any meaningful difference between conceptualizing the gravity which is granted as being at work between and among all the universe's matter and energy and supposing that it might have, alternatively, somewhere at a “core,” an “interior” center of mass, something “beneath” (in space-like sense) and prior (in a time-like sense) an expanding outer “shell” of objects of mass and energy?
We might speculate about the phenomenon of black holes in this scenario.
Suppose that we take our balloon analogy and adapt it slightly so that the surface of the balloon is very hot, very large and, for the sake of visualization, covered with pancake-batter. If you've ever cooked pancakes, you know that more or less soon after the batter is poured on the cooking surface and starts to cook, bubbles appear on the surface, they often burst, and they leave a little hole on the surface of the batter--prior, that is, to turning over the pancake and cooking its second-surface.
Imagine for a moment that, beneath, within, under, the superficial area of what we see as the visible universe, there's a region of matter and energy which is opaque to light and which is far more dense than any of the superficial region in which our cosmos is found. Suppose that this interior region constitutes, as a whole, the place at the core of which is the universe's center of mass and that, at its outer-most region, where it is nearest our cosmos, “weak-spots” can form in the usually-uniform outward-pushing-energy which is (as hypothesized here) the ultimate big-bang sourced residual force (primal, primary momentum) driving all expansion, all rotation, all gravitational attraction over the space-time of our cosmos. Suppose that, as a consequence of a combination of greatly massive objects on our cosmic surface's “side”, and a corresponding abnormal or non-uniform “weakness” in the outward momentum, a hole forms as a depression which, like the pancake-batter, seeps down from the rest of the uniform surface of the batter?
An observer, from the inside, would, if he could see great stretches of the entire cosmic spherical space-time, see scatered about at great expanses of space-time, more or less lengthy lava-like “danglings” where the upper cosmos is hanging (down inside) from an otherwise higher, spherical vault while, on “our side”, an observer sees this same “drooping” thing as a hole, a depression, into which nearby energy and matter is dragged if it is within the event-horizon.
These are not meant to be conceptualized as two separate or distinct “universes” any more than you have two pancakes cooking on the surface of the griddle when you've only poured one out onto it. There's one pancake with a “upside”, which has “holes” on its upturned surface, and another, a “downside,” which, since the griddle is hard and flat, does not admit anything to dangle down from the underside but which, if it were simply a weaker area of outward-pushing momentum, might allow cosmic density to fall in and hang down like so many (mobile?) icicles.
Why not this partial-hypothesis somewhere in the mix of speculations?
_______________
See also :
Scientific American | Cosmology: The Inflation Debate: Is the theory at the heart of modern
cosmology deeply flawed? By Paul J. Steinhardt (2011) (link to a .pdf download file)
Scientific American | Cosmology : POP! goes the
universe : THE LATEST ASTROPHYSICAL MEASUREMENTS,
COMBINED WITH THEORETICAL PROBLEMS, CAST DOUBT
ON THE LONG-CHERISHED INFLATIONARY THEORY
OF THE EARLY COSMOS AND SUGGEST WE NEED NEW IDEAS
By Anna Ijjas, Paul J. Steinhardt and Abraham Loeb | January 2017 (link to a .pdf download file)
Paul J. Steinhardt's Princeton University homepage
and his pages on: Inflationary Cosmology, Dark Matter , Dark Energy
"What is dark energy?" : https://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy
(Scientific American) "What are dark matter and dark energy, and how are they affecting the universe?" https://www.scientificamerican.com/article/what-are-dark-matter-and/
Can we identify the centre of the Universe? at https://www.physicsforums.com/
Inflationary Paradigm after Planck 2013
by Alan H. Guth, David I. Kaiser, and Yasunori Nomura (Replies to A. Ijjas, P. J. Steinhardt and A. Loeb, “Inflationary paradigm in trouble after Planck2013,” Phys. Lett. B 723, 261 (2013) (arXiv:1304.2785 (astro-ph.CO)). )
Links related to the physicist and popular science-writer Sean Carroll:
https://www.preposterousuniverse.com/
https://www.preposterousuniverse.com/self.html
See his author page at Library Thing.
I'm inviting you to help me think this through——
"does the universe have a center-of-mass—basically, the idea of a “center of gravity” applied to the universe as a whole?"
(Note: This is a question that numerous people have thought of and asked. Thus, there are brief "explanations" here and there on pages around the internet of science-topics in which there's a simple and brief, "No," given in answer.
If all you're interested in is posting one of the many such pages, please don't bother. I've seen several and I already know these exit--and that this is the standard answer from cosmologists.
If, however, after reading the following, you know of a site which develops an answer in its details of why not--and a lay person / non-specialist might read and understand some of the explanation, then please do post it. Thanks.)
_____________
Scientists are trying to account for what they estimate to be about 95 to 96 percent of the matter and energy which, according to their calculations, ought to exist but have not been detected so far. This is divided roughly into about 73 percent of what is called “dark energy” and 23 percent “dark matter”--”dark” because it has not been observed as far as is known.
Meanwhile, some amateur cosmologists wonder: does the universe have a center-of-mass—basically, the idea of a “center of gravity” applied to the universe as a whole?; it should be noted that the question means the whole universe rather than the “visible universe” since this may be related to the mass that is so far undetected. I wonder about this, too.
Taking the “big bang” as a conceptual model, we're to understand that, at the origin of the universe there was effectively an ultimate state of maximum density in which was concentrated the entire mass of the universe—a minimally-tiny point. This point, at the “big bang” errupted in a gargantuan explosion-like expansion. But we're told (see Sean Carroll work) not to think of it as really like an immense explosion conceptually such as, on a vastly smaller scale, those to which we are accustomed from earth's experience. This explosion was supposedly both quantitatively and qualitatively different. Exactly how and why it was is—or was—is, to me, still not at all clear.
At the same time, we're also offered ( see Sean Carroll's work) as an example of limited application the model of an expanding balloon. If you take an uninflated balloon and, using a marking-pen, mark its surface randomly all over with small ink-dots and then you inflate the balloon slowly, what you'll notice is that the all the dots seem to grow more distant from each other—each one moves away from all the others in a rate that matches the rate of the balloon's expansion. In a roughly similar manner, all the widely-separated objects in the universe—galaxies and entities larger that galaxies—are growing more distant from each other while, internally, they each roughly maintain the integrity of their individual structural proportions—the galaxies themselves are not expanding, the distances between them are increasing . So, from any vantage point, all the other large entities appear to be moving further way rather than drawing closer.
But, we're cautioned that the analogy of the balloon is only approximate and must not be taken too far. We're not supposed to imagine that the universe's expansion is—or was, from the original big bang—quite like a giant explosion which quickly inflates a big balloon.
We're told (see Sean Carroll) that the answer to the question—“Is there a center of mass to the universe as a whole?”—“No, there is not.” and the reason we're given is that, from any vantage point, the large-scale objects are all moving away from each other and this is supposed to indicate that there is no center of mass.
The logic of that “explanation” escapes me since, like the universe's large-scale objects, the marks on the surface of the balloon also all appear to move farther away from each other as the balloon expands. And, yet, for all that, no one would assert that the balloon has no center of mass and that this center is to be found not on the balloon's surface area—where all the “dots” are located—but within the interior of the balloon's surface—at what would be the mid-point of its diameter if it were a true sphere.
Specifically, what I wonder about are the following questions:
Is the current general expansion of the universe supposed to “account for,” to be, in some positive manner, related to the “original” big bang? In other words, are things such as galaxies moving farther and farther from each other by the residual “force”, so to speak, of the universe-forming big bang?
If it is not, then to what are we to attribute the universe's expansion?
Let's return to the model of the balloon's expanding surface as a working analogy for the visible part of the universe in which we find our planet, solar system and galaxy and all the other detectable entities near and far in the universe from the earth's moon to the most distant observable star or galaxy.
As we know or assume, gravity is at work everywhere throughout this superficial extent and it constantly affects all the motions of all the objects—matter and (all? Or most?) of the radiant (?) energy—in this “spherical” space. Thus, gases, dust, and denser or more massive objects, and what we call visible light are all subject to this gravity. If so, then, like everything else, gases and more solid ( i.e. heavier) matter, light moves along the surface of the expanding spherical universe which means that, over its entirety, it follows the curve of the expanding “edge” of the visible universe and never other than under exceptional circumstances, does it leave the approximate surface region for anything “below” or “beneath” it—and, we are assuming here, there is no meaning to there being anything “beyond” (outside) its limits.
One of the things which would follow from the view just described is that, unlike the current view of things, the most “distant” light reaching Earth is not properly thought of as being potentially either significantly “older” / “earlier” or “younger” / “later” in the evolution of the universe; that is, we can not, even figuratively, say that, in examining such light, we are “looking back” at light from an earlier age in the universe and, least of all can we say that we're observing light from some of the (relatively) early stages of the universe's existence since, by the view being offered for consideration here, all this light is travelling a spherical circuit and there is no way to meaningfully say that some of the light is, since “farther away”, “more distant” in the age of the universe. True, stars form and burn for a time and eventually burn out. In that sense, some light is “younger” or “older” as a function of the star's age. But, on the scale of universal existence-time, none of this light is vastly younger or older, relatively speaking since all of it is found somewhere on the “surface”—to use the balloon analogy—of the expanding universe.
Is there any meaningful difference between conceptualizing the gravity which is granted as being at work between and among all the universe's matter and energy and supposing that it might have, alternatively, somewhere at a “core,” an “interior” center of mass, something “beneath” (in space-like sense) and prior (in a time-like sense) an expanding outer “shell” of objects of mass and energy?
We might speculate about the phenomenon of black holes in this scenario.
Suppose that we take our balloon analogy and adapt it slightly so that the surface of the balloon is very hot, very large and, for the sake of visualization, covered with pancake-batter. If you've ever cooked pancakes, you know that more or less soon after the batter is poured on the cooking surface and starts to cook, bubbles appear on the surface, they often burst, and they leave a little hole on the surface of the batter--prior, that is, to turning over the pancake and cooking its second-surface.
Imagine for a moment that, beneath, within, under, the superficial area of what we see as the visible universe, there's a region of matter and energy which is opaque to light and which is far more dense than any of the superficial region in which our cosmos is found. Suppose that this interior region constitutes, as a whole, the place at the core of which is the universe's center of mass and that, at its outer-most region, where it is nearest our cosmos, “weak-spots” can form in the usually-uniform outward-pushing-energy which is (as hypothesized here) the ultimate big-bang sourced residual force (primal, primary momentum) driving all expansion, all rotation, all gravitational attraction over the space-time of our cosmos. Suppose that, as a consequence of a combination of greatly massive objects on our cosmic surface's “side”, and a corresponding abnormal or non-uniform “weakness” in the outward momentum, a hole forms as a depression which, like the pancake-batter, seeps down from the rest of the uniform surface of the batter?
An observer, from the inside, would, if he could see great stretches of the entire cosmic spherical space-time, see scatered about at great expanses of space-time, more or less lengthy lava-like “danglings” where the upper cosmos is hanging (down inside) from an otherwise higher, spherical vault while, on “our side”, an observer sees this same “drooping” thing as a hole, a depression, into which nearby energy and matter is dragged if it is within the event-horizon.
These are not meant to be conceptualized as two separate or distinct “universes” any more than you have two pancakes cooking on the surface of the griddle when you've only poured one out onto it. There's one pancake with a “upside”, which has “holes” on its upturned surface, and another, a “downside,” which, since the griddle is hard and flat, does not admit anything to dangle down from the underside but which, if it were simply a weaker area of outward-pushing momentum, might allow cosmic density to fall in and hang down like so many (mobile?) icicles.
Why not this partial-hypothesis somewhere in the mix of speculations?
_______________
See also :
Scientific American | Cosmology: The Inflation Debate: Is the theory at the heart of modern
cosmology deeply flawed? By Paul J. Steinhardt (2011) (link to a .pdf download file)
Scientific American | Cosmology : POP! goes the
universe : THE LATEST ASTROPHYSICAL MEASUREMENTS,
COMBINED WITH THEORETICAL PROBLEMS, CAST DOUBT
ON THE LONG-CHERISHED INFLATIONARY THEORY
OF THE EARLY COSMOS AND SUGGEST WE NEED NEW IDEAS
By Anna Ijjas, Paul J. Steinhardt and Abraham Loeb | January 2017 (link to a .pdf download file)
Paul J. Steinhardt's Princeton University homepage
and his pages on: Inflationary Cosmology, Dark Matter , Dark Energy
"What is dark energy?" : https://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy
(Scientific American) "What are dark matter and dark energy, and how are they affecting the universe?" https://www.scientificamerican.com/article/what-are-dark-matter-and/
Can we identify the centre of the Universe? at https://www.physicsforums.com/
Inflationary Paradigm after Planck 2013
by Alan H. Guth, David I. Kaiser, and Yasunori Nomura (Replies to A. Ijjas, P. J. Steinhardt and A. Loeb, “Inflationary paradigm in trouble after Planck2013,” Phys. Lett. B 723, 261 (2013) (arXiv:1304.2785 (astro-ph.CO)). )
Links related to the physicist and popular science-writer Sean Carroll:
https://www.preposterousuniverse.com/
https://www.preposterousuniverse.com/self.html
See his author page at Library Thing.
