Andre Lefebvre Posted June 24, 2015 Posted June 24, 2015 I read quite a few of the preceding posts regarding black hole but I couldn't find any clear description of a black hole. From what I know, a Black hole is the maximal déformation of the geometry of a certain volume of space-time. That déformation of the volume of space-time extends way down to its center of gravity. Which seems to mean that the deformation in question is the result of something acting on the center of gravity itself. And that means that de déformation is not, at all, caused by the presence of a ball of matter floating in space, like a bowling ball placed on a mattress. If you look, for example, at the M31 galaxy (Andromeda) where there is a black hole in its center, the galaxy doesn't have the form of a funnel. You can get in the Black hole from either side of the galaxy. And you certainly whon't get trough and emerge on the other side. The first consideration we must do is accept that; if its not the quantity of matter that deforms space-time it has to be the next best bet: the mass energy of that quantity of matter. And we can had that, the "mass energy" directs itself toward the center of gravity of that quantity of matter. To support this view, just think that the mass of a proton consist of its three internal quarks for 1% and its inner energy for 99%. So what kind of space-time deformation are we talking about? The only possibility is that the deformation is in the fabric of space-time itself and not at all in the fabric of matter. First of all, the déformation of space-time is not in a downward direction; so the name Black "hole" is physically inappropriate. It is not a "hole". Instead, we should talk about a "Black ball"; because the circular event horizon of a Black hole doesn't represent a pancake; it represents a volume of space-time: a"ball". So, again, what can we say about the fabric of space-time? We can only say that it has a metric. And, it's easy to understand that the expansion of the universe is exactly the progressive growth of that metric. But what does that mean? What does it looks like? To find out, lets say we choose a metric (a lenght) of one foot. The continuous growth of that metric will result in the fact that our foot will gradually become a foot that mesures 13 inches-> 14 inches -> 15 inches and so on, but will still be "a foot". That is the expansion of the metric of the universe. The whole thing started when the universe had a diameter of 10^-35 meter; and the date was: 10^-43 sec after time = zero. And the universe of that epoch is still de same universe today. So what happens if we choose one precise point of the frabic of the universe and we block the growth "movement" at that point? I'd say that the expansion of space-time will stop for that point and a deformation will occur around it because the surroundings of the point will continue to expand. Lets say that we stopped the expansion of our chosen point at the moment where our metric had grown to the size of two feet. In stopping its growht, we have obtained a metric of space-time that is now "stable". That part of space-time doesn't change its metric anymore; even though the rest of the universe still expands. That is exactly the situation in which we observe our space-time from the level of the galaxies down to the level of the atoms. We live in a volume of space-time where its metric is stabilized. That volume of stable space-time is our galaxy. Now; lets choose a déformation of space that is occupied by a great big star. The point "center of gravity" of that deformation is blocked like the rest of the galaxy where this star is located and the "mass energy" of the star is what stabilises its volume, gives its form etc.. What we now are going to do is add "mass energy" to that star. To do so, all we have to do is accumulate matter particles, containing mass energy, on the surface of the star so that the energy of those particles joins the mass energy of the star. Adding mass énergy increases the action on the centre of gravity of the deformation of its space-time so gradually, or point "center of gravity" start to "back up" in its metric. This is called "collapsing". When we will have added enought mass energy to our star, its metric will collapse with all the matter it contains (passing trough opposite reactions encountered) back to the size of the original metric it started from : The one wich has (or had) the size of 10^-35 meter. We have now obtained a "Black hole" with its singularity that everybody cannot describe. We can even make a parallel between the photon liberation at 380,000 years after Big bang and the horizon of a Black hole where we find the limit of "free" photons near a Black hole. With these informations, we can now start again breaking our brain on problems created by Black holes. Our actual finding, above, is that the production of a Black hole is exactly the reverse process of the production or the evolution of the universe. So whatever mathematics says that doesn't correspond to the evolution of the universe since 13,7 billion years has great chances to be wrong..
Strange Posted June 27, 2015 Posted June 27, 2015 I read quite a few of the preceding posts regarding black hole but I couldn't find any clear description of a black hole. https://en.wikipedia.org/?title=Black_hole From what I know, a Black hole is the maximal déformation of the geometry of a certain volume of space-time. Not quite. The maximum spacetime curvature happens at the singularity, nit the event horizon, and it is the event horizon that defines a black hole. (And the singularity probably doesn't exist.) Which seems to mean that the deformation in question is the result of something acting on the center of gravity itself. It is the result of the mass of the black hole which is, as you say, concentrated at the center of the black hole (for a non-rotating balck hole, anyway - for a rotating black hole it is slightly more complex). And that means that de déformation is not, at all, caused by the presence of a ball of matter floating in space, like a bowling ball placed on a mattress. If you look, for example, at the M31 galaxy (Andromeda) where there is a black hole in its center, the galaxy doesn't have the form of a funnel. You seem to be confused by some (rather poor) attempts to visualize the curvature of spacetime. This is a slightly more accurate image: http://www.quora.com/If-gravity-is-because-of-curvature-of-space-time-what-results-in-the-earths-own-gravitation-force But note that trying to show what four dimensions looks like is impossible, even when it isn't curved. That is why the maths is more important than pictures. The first consideration we must do is accept that; if its not the quantity of matter that deforms space-time it has to be the next best bet: the mass energy of that quantity of matter. Both mass and energy (and other things, such as momentum and pressure) contribute to the gravity of an object. And we can had that, the "mass energy" directs itself toward the center of gravity of that quantity of matter. To support this view, just think that the mass of a proton consist of its three internal quarks for 1% and its inner energy for 99%. quarks are bound by the strong nuclear force - nothing to do with gravity. So what kind of space-time deformation are we talking about? The type defined by the Einstein Field Equations. And for non-rotating black holes, the Schwarzschild solution to those equations. For a rotating black hole, it is the Kerr metric. The only possibility is that the deformation is in the fabric of space-time itself and not at all in the fabric of matter. Correct. The Einstein Field Equations describe the curvature of space-time. First of all, the déformation of space-time is not in a downward direction; so the name Black "hole" is physically inappropriate. As "down" is defined to mean "towards the center of gravity" then it is reasonable to describe the curvature as downward. This is espeically apparent when you consider the Gullstrand-Painlevé metric instead of the Schwarzschild: http://jila.colorado.edu/~ajsh/insidebh/waterfall.html It is not a "hole". Instead, we should talk about a "Black ball"; because the circular event horizon of a Black hole doesn't represent a pancake; it represents a volume of space-time: a"ball". Correct. A black hole is spherical (at least, in the case of a Schwarzschild black hole). They are not holes, but the name is not going to change: you will have to learn to live with it. We can even make a parallel between the photon liberation at 380,000 years after Big bang and the horizon of a Black hole where we find the limit of "free" photons near a Black hole. No, there are completely different. In the case of the early universe, the problem was simply that the average path before the photon would be absorbed again was very short. Nothing to do with the curvature of spacetime at an even horizon. Our actual finding, above, is that the production of a Black hole is exactly the reverse process of the production or the evolution of the universe. Wrong. So whatever mathematics says that doesn't correspond to the evolution of the universe since 13,7 billion years has great chances to be wrong. I don't think anyone is going to throw out the theory of General Relativity because your guesses/intuition don't agree with it. 1
md65536 Posted June 27, 2015 Posted June 27, 2015 (edited) And that means that de déformation is not, at all, caused by the presence of a ball of matter floating in space, like a bowling ball placed on a mattress. If you look, for example, at the M31 galaxy (Andromeda) where there is a black hole in its center, the galaxy doesn't have the form of a funnel. The "funnel" shape does not represent 3 spatial dimensions, it's only a 3d representation of 4d spacetime. The funnel is 2 spatial dimensions, and... ??? Does anyone know what the z-axis (down) represents in these diagrams? It doesn't represent time, right? In the rubber sheet analogy it represents energy or something??? Or is it just a representation of the intrinsic curvature of spacetime, drawn extrinsically with an extra spatial dimension that isn't real? From https://www.physicsforums.com/threads/what-is-the-path-of-light-through-strong-gravity.749087/page-2, by Drakkith: Note that a 2d plane can exist, and be curved, and yet still be only 2-dimensional. The curvature is not part of another spatial dimension. The curvature we talk about in regards to spacetime is known as intrinsic curvature, not extrinsic curvature. Extrinsic curvature is like the curvature of the surface of the Earth. It is a 2d plane that is embedded in 3 dimensions. Intrinsic curvature is more complicated. Here's what wiki has to say on it: ...a space of three or more dimensions can be intrinsically curved. The curvature is intrinsic in the sense that it is a property defined at every point in the space, rather than a property defined with respect to a larger space that contains it. In general, a curved space may or may not be conceived as being embedded in a higher-dimensional ambient space; if not then its curvature can only be defined intrinsically. It's important to understand that we live in 3-dimensional space and therefor cannot tell if our universe is embedded in another spatial dimension or not. Because of this, the curvature of spacetime is necessarily intrinsic and cannot be drawn accurately. It also means that drawing 1 or 2 dimensional curved surfaces is possible, but only if they are drawn as extrinsically curved. If you take a black hole, and consider 2 spatial dimensions of it, you get a plane. In spacetime this plane has extreme intrinsic curvature. If you embed this intrinsically curved plane in 3 dimensions, it looks like a funnel. So I think the funnel shape is not representative of any geometrical shape, but merely the intrinsic curvature of spacetime illustrated along an extra dimension in the diagram (ie. the intrinsically curved 2d plane embedded in a in a higher (3) dimensional space). Edited June 27, 2015 by md65536
ajb Posted June 27, 2015 Posted June 27, 2015 (edited) Does anyone know what the z-axis (down) represents in these diagrams? It doesn't represent time, right? In the rubber sheet analogy it represents energy or something??? Or is it just a representation of the intrinsic curvature of spacetime, drawn extrinsically with an extra spatial dimension that isn't real? You mean Flamm's paraboloid? It is used to visualise the spacial curvature of the Schwarzschild metric. You take a constant time slice and (usually) set theta= pi/2. The remaining coordinate are r and phi. The z-axis is not physical in any way, it is added so that we can use Flamm's paraboloid to visualise the curvature in terms of r and phi.. Edited June 27, 2015 by ajb
md65536 Posted June 27, 2015 Posted June 27, 2015 (edited) You mean Flamm's paraboloid? It is used to visualise the spacial curvature of the Schwarzschild metric. You take a constant time slice and (usually) set theta= pi/2. The remaining coordinate are r and phi. The z-axis is not physical in any way, it is added so that we can use Flamm's paraboloid to visualise the curvature in terms of r and phi.. (after some websearching) Yes that's what I was describing. The Flamm paraboloid is an embedding diagram, and the z-axis provides an extrinsic representation of the intrinsic curvature. I didn't realize until now that the "funnel" diagrams can actually be very different things. An apparently more-common "funnel" diagram is a plot of gravitational potential (a gravity well diagram), which is approximated by the rubber sheet model. The z-axis of this does not represent curvature. It sounds like it is fairly common to mix up the different diagrams: https://en.wikipedia.org/wiki/Gravity_well#Gravity_wells_and_general_relativity So different "funnel" shapes can arise from plotting different things on the z-axis, none of which correspond to the spatial shape of a black hole in 4d spacetime. Edited June 27, 2015 by md65536
Andre Lefebvre Posted June 27, 2015 Author Posted June 27, 2015 (edited) Which seems to mean that the deformation in question is the result of something acting on the center of gravity itself. It is the result of the mass of the black hole which is, as you say, concentrated at the center of the black hole. Exactly; but “mass” is not a quantity of matter in physics; it's energy And that means that de deformation is not, at all, caused by the presence of a ball of matter floating in space, like a bowling ball placed on a mattress. If you look, for example, at the M31 galaxy (Andromeda) where there is a black hole in its center, the galaxy doesn't have the form of a funnel. You seem to be confused by some (rather poor) attempts to visualize the curvature of spacetime. Sorry; but I’m not confuse at all since I don’t think that deformation of space-time is not in the shape of a funnel. The one confused are those who think that it is in a shape of a funnel. I visualise it more in a collapsing of its metric, actually. The first consideration we must do is accept that; if it’s not the quantity of matter that deforms space-time it has to be the next best bet: the mass energy of that quantity of matter. Both mass and energy (and other things, such as momentum and pressure) contribute to the gravity of an object. Like I said “mass” is not a quantity of matter. Energy involved in gravity has to be “mass energy”. Pressure comes from the “mass energy” and momentum has to be defined so we understand your meaning. And we can add that, the "mass energy" directs itself toward the center of gravity of that quantity of matter. To support this view, just think that the mass of a proton consist of its three internal quarks for 1% and its inner energy for 99%. quarks are bound by the strong nuclear force - nothing to do with gravity. Which remains to be seen. We have no explanations on the “origin” of strong nuclear force. All we know is that it has a “vector”: the gluon which is not an explanation at all. But let’s imagine that a gluon has an "intern" “topology” (flow of direction) that sends everything to its center (which would explain the "gluing" effect) then we would have a natural explanation of the strong nuclear force. I prefer this idea of topology instead of “strong nuclear force” which comes from nowhere for the glue. Mainly because it’s natural and it’s simple. Furthermore, we have a lot more informations now, than what was known in 1935, when Yakawa and others suggested a strong nuclear force, to keep stable ordinary matter. I agree that this idea eliminates one of the four fondamental forces but gravitation isn’t a force either; it’s a consequence of space deformation. So the superforce, instead of being, four at the beginning but brought down to only three, by Einstein, are now left to two. So what? Specially since the two remaining forces where joined in the "electroweak" force. Some day we will be able to eliminate those last two somewhat “magical” forces by an observed natural and simple "consequence". The only possibility is that the deformation is in the fabric of space-time itself and not at all in the fabric of matter. Correct. The Einstein Field Equations describe the curvature of space-time. You should add: “locally”. Einstein field equation describes local space-time not universal space-time. As a matter of fact, universal space-time is "flat". Let’s note that a “flow of direction” imprinted in the gluon would be imprinted in the space-time fabric itself. As you can see I’m not trying to teach what we know; I’m trying to understand what we don’t know. It is not a "hole". Instead, we should talk about a "Black ball"; because the circular event horizon of a Black hole doesn't represent a pancake; it represents a volume of space-time: a «ball". Correct. A black hole is spherical (at least, in the case of a Schwarzschild black hole). They are not holes, but the name is not going to change: you will have to learn to live with it. I didn't mention "spherical"; I mentioned "volume". I don’t have to live with it since I understand that it’s not a “hole”. It’s people that are told it is a “hole” that have that problem. We can even make a parallel between the photon liberation at 380,000 years after Big bang and the horizon of a Black hole where we find the limit of "free" photons near a Black hole. No, there are completely different. In the case of the early universe, the problem was simply that the average path before the photon would be absorbed again was very short. Nothing to do with the curvature of spacetime at an even horizon. The causes "might" be completely different; but I’m not explaining the causes of the liberation or the capture of photons; I’m just making a parallel of both situations. The causes are not exactly known since we don’t exactly know what happens at the horizon of a black hole. What we have are mostly speculations. On the other hand, if collapsing of a black hole is the collapsing of the volume of its metric that had been expanding, chances are that my visualisation of the event is pretty close to reality; I would say. Our actual finding, above, is that the production of a Black hole is exactly the reverse process of the production or the evolution of the universe. Wrong. Why? Saying “wrong” is not enough; I’m sorry. When I talk about “our finding”, I’m talking about the reflection above, not of the speculations in vogue. So whatever mathematics says that doesn't correspond to the evolution of the universe since 13,7 billion years has great chances to be wrong. I don't think anyone is going to throw out the theory of General Relativity because your guesses/intuition don't agree with it. Nobody is talking about throwing out the theory of General Relativity since it is exact. We might just have to get rid of the intuitive influence of the notion that “masses are attracted to each other” and start considering “attraction” as being “tidal effects” between space-time deformations. Hope this will reduce the bad perception my first message made. I don't want to aggress anything and nobody. All I try to do is find answers where information seems to be turning in a circle. Edited June 27, 2015 by Andre Lefebvre
Strange Posted June 27, 2015 Posted June 27, 2015 Exactly; but “mass” is not a quantity of matter in physics; it's energy While mass and energy are equivalent, they are not the saem. You can't really say that energy is a quantity of matter. Would you go to the market and ask for 5 joules of apples? No, you would use kg. Sorry; but I’m not confuse at all since I don’t think that deformation of space-time is not in the shape of a funnel. No one says it is. That is why I think you are confused. Like I said “mass” is not a quantity of matter. Simply repeating that doesn't make it any less wrong. Energy involved in gravity has to be “mass energy”. Correct. Pressure comes from the “mass energy” and momentum has to be defined so we understand your meaning. Pressure and momentum (which is already defined) have to be included in the EFE. Which remains to be seen. We have no explanations on the “origin” of strong nuclear force. All we know is that it has a “vector”: the gluon which is not an explanation at all. But let’s imagine that a gluon has an "intern" “topology” (flow of direction) that sends everything to its center (which would explain the "gluing" effect) then we would have a natural explanation of the strong nuclear force. We don't have an explanation for the "origin" of anything (in physics; that is the domain of philosophy and religion). You should add: “locally”. Einstein field equation describes local space-time not universal space-time. It seems to work pretty well in cosmology. So, again, you seem to be wrong. As you can see I’m not trying to teach what we know; I’m trying to understand what we don’t know. I think you need to start by learning some physics first before inventing stuff that appears to have no basis. I didn't mention "spherical"; I mentioned "volume". What is the difference? A sphere has volume. I don’t have to live with it since I understand that it’s not a “hole”. It’s people that are told it is a “hole” that have that problem. I don't think many people have a problem with the name or the analogy. Anyway, no one is going to change the name just because you find it confusing. The causes "might" be completely different There is no might about it. They are completely different. The causes are not exactly known since we don’t exactly know what happens at the horizon of a black hole. GR describes exactly what happens at the event horizon. The only uncertainties are when people attempt to combine this with quantum theory. What we have are mostly speculations. No, what we have are precise mathematical models. my visualisation of the event is pretty close to reality; I would say. Perhaps you could show the evidence or maths that supports that belief? Nobody is talking about throwing out the theory of General Relativity since it is exact. Then why do you keep making statements that appear to be inconsistent with GR.
Andre Lefebvre Posted June 28, 2015 Author Posted June 28, 2015 I really have noting else to add since only the afirmation part is reproduced without the explanation part. Then why do you keep making statements that appear to be inconsistent with GR. It would be nice to point out where my statements "appear" to be inconsistent with GR. Maybe where you say that GR is universal; but everybody knows that it describes local space-time. Furthermore I took notice that you skipped the part of my argument saying that "universe is falt" which doesn't give it a lot of gravity. But I don't think that this conversation will continue from my part. I like discussions to be honestly for understanding not confronting. Anyway, what I think doesn't change anything in the world of people around me; only the world i, myself, understands it. Have a nice confrontation with somebody else. I wih you a very nice day.
Strange Posted June 28, 2015 Posted June 28, 2015 Sorry, I didn't mean to appear confrontational. But you are making what seem to be erroneous statements mixed up with your own speculation in the mainstream physics section of the forum. When questioned on them, or asked to provide evidence, you just repeat the same claim. Maybe where you say that GR is universal; but everybody knows that it describes local space-time. I don't know that, and it appears to be contradicted by the fact that GR is used as the basis of cosmology. Special relativity describes local space-time. I would be happy to be shown to be wrong; could you provide a reference that says that GR only describes local space-time? Furthermore I took notice that you skipped the part of my argument saying that "universe is falt" which doesn't give it a lot of gravity. There didn't seem to be much to say: the universe as a whole appears to be flat. Yes.
Andre Lefebvre Posted June 28, 2015 Author Posted June 28, 2015 @ Strange I don't know that, and it appears to be contradicted by the fact that GR is used as the basis of cosmology. Special relativity describes local space-time. I would be happy to be shown to be wrong; could you provide a reference that says that GR only describes local space-time? I've read it a few times in "scientific popularisation"; but I'm sorry. You're right it's special relativity that describes local space-time. But, on the other hand, since most of the universe is flat, gravitation does seems to manifests itself only in spécific places. The last analysis of polarisation B on Planck’s photo of CMB shows that where there is matter (gravity) it focusses polarity; and where there's no matter it disperses it. But it doesn't really change anything because where gravity is weaker than expansion we don't observe gravitational effects. So in regards to facts, gravity is local; in regards to theory it's not. But even if we would eliminate the notion of universality of GR, it wouldn't change anything in observations (and probably not in the theory either). The special relativity eliminated "instantaneity of Newtons gravitation but did not eliminate its universality. Maybe Planck’s photos will. But in facts universality is not a "sine qua non" condition to GR, I don't think so. Correct me if I'm wrong. There didn't seem to be much to say: the universe as a whole appears to be flat. Yes. Since Planck’s results in 2015; it doesn't simply "appear" flat`; it is "flat". For which the importance in regard to the universality of GR. While mass and energy are equivalent, they are not the saem. You can't really say that energy is a quantity of matter. Would you go to the market and ask for 5 joules of apples? No, you would use kg. Funny because that answer of yours was to my statement: « Exactly; but “mass” is not a quantity of matter in physics; it's energy”. So I certainly didn’t say that “quantity of matter” was “energy”. Further down, you say that when I state that “mass” isn’t a “quantity of matter”, you respond by: “Simply repeating that doesn't make it any less wrong.” So give me a final answer: Is “mass” a quantity of matter or is it “energy”? I’m ready to accept that “mass” is a quantity of matter and mass energy is the quantity of energy attribute to that quantity of matter. Would that solve the problem between us? The only reason I was saying that mass is not energy is because of “binding energy” in an atom. We don't have an explanation for the "origin" of anything (in physics; that is the domain of philosophy and religion). (Sorry but I hate hearing about religion and philosophy while talking about science. It looks to much like a "last resort" argument) So no wonder that Higgs boson gives mass to particles; it doesn’t need to be explained how it does so and where that mass is from. The same occurs with fundamental forces; all that as to be done is explain something with it and there’s no problem with the fact that it’s a “free invention” that came from imagination. Like Newton said: “It’s not logical, but it works!”. That clarifies a lot of problems; really. But like I said, I’m not teaching what is known; I’m only trying to understand where things come from and what their interactions to produce what we observe is. I don’t really need anybody to describe me what I can see. Rarely is one interpretation better than another one beside the logic and observations backing it. And since I'm heading toward the unknown, which is the fascinating part about physics, let's say that I will have to rest myself on "facts" observed and logic. That's all I can do.
Strange Posted June 28, 2015 Posted June 28, 2015 (edited) But, on the other hand, since most of the universe is flat, gravitation does seems to manifests itself only in spécific places. Well, gravity depends on the presence of mass-energy, so it will obviously vary in different places. But it doesn't really change anything because where gravity is weaker than expansion we don't observe gravitational effects. I'm not sure what that means. The reverse is certainly true: we don't observe expansion where gravity is strong enough to hold objects together. So in regards to facts, gravity is local; in regards to theory it's not. I have no idea what that means. Gravity is not local. Its effects do not "end" anywhere. The special relativity eliminated "instantaneity of Newtons gravitation but did not eliminate its universality. Special relativity says nothing about gravity. But in facts universality is not a "sine qua non" condition to GR, I don't think so. Correct me if I'm wrong. You are wrong. GR can be used to describe the behaviour of the universe. That is a pretty good definition of "universality". Since Planck’s results in 2015; it doesn't simply "appear" flat`; it is "flat". Sorry. I can't get away from this pesky scientific idea that we can't know anything for certain and further observations can always change what we know. It appears flat. Funny because that answer of yours was to my statement: « Exactly; but “mass” is not a quantity of matter in physics; it's energy”. So I certainly didn’t say that “quantity of matter” was “energy”. I don't understand what you are saying: you say it is energy that is the quantity of matter, not mass and then deny you said that... Further down, you say that when I state that “mass” isn’t a “quantity of matter”, you respond by: “Simply repeating that doesn't make it any less wrong.” So give me a final answer: Is “mass” a quantity of matter or is it “energy”? Mass, not energy, is a "quantity of matter" (as much as that phrase means anything). The only reason I was saying that mass is not energy is because of “binding energy” in an atom. That binding energy is the main source of mass in an atom. So I'm not sure what your point is ... :confused: So no wonder that Higgs boson gives mass to particles; it doesn’t need to be explained how it does so and where that mass is from. I'm not sure why you say it doesn't have to be explained. Why isn't the Higgs mechanism an explanation? :confused: And since I'm heading toward the unknown, which is the fascinating part about physics, let's say that I will have to rest myself on "facts" observed and logic. That's all I can do. I shall suggest the moderators move this to the Speculations part of the forum then. Edited June 28, 2015 by Strange
Mordred Posted June 28, 2015 Posted June 28, 2015 There's a couple of points here that need clarifying. First gravity occurs anywhere there is an energy density. As far as universe geometry, it's really energy-density to pressure relations. This conforms to either the Einstein field equations, as well as the FLRW metric. A key detail to study is the ideal gas laws and the equations of state of each particle species. [latex]w=\frac{\rho}{p}[/latex] Here are the equations of state relations. https://en.m.wikipedia.org/wiki/Equation_of_state_(cosmology) Here is a simplified article I wrote to help describe geometry. http://cosmology101.wikidot.com/universe-geometry page 2 http://cosmology101.wikidot.com/geometry-flrw-metric/ Here is a couple of non pop media papers on the subject. http://arxiv.org/pdf/hep-ph/0004188v1.pdf:"ASTROPHYSICS AND COSMOLOGY"- A compilation of cosmology by Juan Garcıa-Bellido http://arxiv.org/abs/astro-ph/0409426An overview of Cosmology Julien Lesgourgues In the Einstein field equations the energy density/pressure relations are described via the energy-momentum stress energy tensor. https://en.m.wikipedia.org/wiki/Stress%E2%80%93energy_tensor these articles will help understand particle physics in cosmology. http://arxiv.org/pdf/hep-th/0503203.pdf"Particle Physics and Inflationary Cosmology" by Andrei Linde http://www.wiese.itp.unibe.ch/lectures/universe.pdf:"Particle Physics of the Early universe" by Uwe-Jens Wiese Thermodynamics, Big bang Nucleosynthesis Here is a good book on GR, though heavy on math. http://www.blau.itp.unibe.ch/newlecturesGR.pdf"Lecture Notes on General Relativity" Matthias Blau Here is the stress energy/momentum tensor in Minkowskii metric. (Special relativity) [latex]T^{\mu\nu}=(\rho+p)U^{\mu}U^{\nu}+p\eta^{\mu\nu}[/latex] As far as black holes are concerned here is an excellent article. https://www.google.ca/url?sa=t&source=web&cd=1&ved=0CBsQFjAA&url=http%3A%2F%2Fwww.phys.uu.nl%2F~thooft%2Flectures%2Fblackholes%2FBH_lecturenotes.pdf&rct=j&q=black%20holes%20pdf&ei=QkOQVf6BFIWrNtSRgaAN&usg=AFQjCNERag-FH9DCbw66GsxObohS8wEq9A&sig2=3_JOCHB5wqHkhJ__D5-ATQ This article does a good job describing the metrics with a review of SR,GR section.
Andre Lefebvre Posted June 28, 2015 Author Posted June 28, 2015 I wonder what would be the formulas we would use today if Newton had perceive the recession of galaxies instead of the falling of an apple? He would have certainly deduce that mass was "repulsing" themselves instead of "attracting" themselves. Well, gravity depends on the presence of mass-energy, so it will obviously vary in different places. I agree. All we need to know now is if there are places where there's no "mass energy"? The reverse is certainly true: we don't observe expansion where gravity is strong enough to hold objects together. I agree with that; we don't observe expansion. Which means that where we do observe expansion, we don't observe gravity. I stick to "facts". Gravity is not local. Its effects do not "end" anywhere. Maybe not; but in a galaxy, its "effect" doesn't comply to diminishing at the square of the distance; since a lot of stars starting from a certain distance of the center of the galaxy up to the farthest orbiting stars have practically the same speed. Something's wrong somewhere. You are wrong. GR can be used to describe the behaviour of the universe. That is a pretty good definition of "universality". I didn't say it couldn't be use; I said that its using was not a "sine qua non" condition. I don't understand what you are saying: you say it is energy that is the quantity of matter, not mass and then deny you said that.. I must construct bad phrases in English; I'm a French speaking person. What I said is that "mass" wasn't a quantity of matter; that it rather was "energy". And I also said that my opinion was based on Binding energy. Which you said was the main source of mass in an atom. So we agree (I guess) that mass is energy and not a quantity of matter. But after saying energy is the main source of mass, you come back saying that mass is a quantity of matter. I then can understand that you cannot. Why isn't the Higgs mechanism an explanation? It's not an explanation if mass is energy; it could be if mass is a quantity of matter, so that a Higgs boson would simply give a "form" to a quantity of energy without giving it energy (to that form). I shall suggest the moderators move this to the Speculations part of the forum then That would mean that, to you, theoritical physics is not physics.
md65536 Posted June 29, 2015 Posted June 29, 2015 I agree. All we need to know now is if there are places where there's no "mass energy"?Then the conclusion would be that there are places with nothing, and that gravity has no measurable effect on nothingness? I suspect everyone could agree on that (if little more than that). But, on the other hand, since most of the universe is flat, gravitation does seems to manifests itself only in spécific places. [...] Since Plancks results in 2015; it doesn't simply "appear" flat`; it is "flat". For which the importance in regard to the universality of GR. Measurements are consistent with a flat universe, but only "on the largest size scales." There is a lot in between "local" and "largest scale". It is not flat on scales of stars and galaxies etc. In areas where expansion dominates, measurements are consistent with both expansion and gravity being present. In areas where gravity dominates, measurements are consistent with both expansion and gravity being present. It's not like only one may occur in a single place. So in regards to facts, gravity is local; in regards to theory it's not. [...] That would mean that, to you, theoritical physics is not physics. The facts as we observe them are consistent with accepted theoretical physics, if you're claiming otherwise (without the evidence) then you're talking about speculative theory.
Andre Lefebvre Posted June 29, 2015 Author Posted June 29, 2015 It is not flat on scales of stars and galaxies etc. It's not flat from galaxies to atoms. Everybody agrees on that. In areas where expansion dominates, measurements are consistent with both expansion and gravity being present. Mesurement say one thing but "facts" couls say different. For example the center of gravity of a sphere sums up to zero; but what does the particle at the center of a colapsing neutron star thinks about that zero gravity? It's not like only one may occur in a single place. It's not that way according to measurements employed; bur "facts" shows different. The facts as we observe them are consistent with accepted theoretical physics, if you're claiming otherwise (without the evidence) then you're talking about speculative theory. What about those stars orbiting around a galaxy at practically the same speed? Do this "fact" is an evidence of consistency with accepted theoretical physics?
Mordred Posted June 29, 2015 Posted June 29, 2015 Evidently you didn't read the cosmology papers I posted. Granted though they are lengthy. You need a scale of roughly 100 Mpc to have a homogeneous and isotropic condition. This coincides with when one can start to describe the universe as flat. You also didn't look at how crtical density applies. https://en.m.wikipedia.org/wiki/Critical_density_(cosmology)#Density_parameter Note on this link the influence of radiation, compared to matter. " Here is a relevant quote. Einstein's equations now relate the evolution of this scale factor to the pressure and energy of the matter in the universe. From FLRW metric we compute Christoffel symbols, then the Ricci tensor. With the stressenergy tensor for a perfect fluid, we substitute them into Einstein's field equations and the resulting equations are described below." The universe curvature constant k does not depend only upon gravity. It's gravity and pressure relations. (A universe without radiation, only gravity would be a collapsing universe. Which isn't flat.)
Andre Lefebvre Posted June 29, 2015 Author Posted June 29, 2015 (edited) (A universe without radiation, only gravity would be a collapsing universe. Which isn't flat.) That is an evidence. But a universe when starting in a Big bang could be composed of one thing only: the total energy of actual universe being kinetic energy that provoques expansion. That original kinetic energy would afterward transform itself in other forms of energy depending of events. The temperature at the Big bang would then be only a consequence of the total actual energy contained in a small universe only beginning its expansion. That kinetic energy would produce expansion of a flat universe without the presence of anything that could give it a curvature. And it would still be mainly flat today except where events would have demanded otherwise. Density of the universe doesn't produce "pressure" since the expansion produces space-time. So there's no "pressure" involved in a flat expanding universe. Edited June 29, 2015 by Andre Lefebvre
Mordred Posted June 29, 2015 Posted June 29, 2015 (edited) You seem to be missing a key detail judging from your reply and the title of the post. First off we can't think of the singularity of a BH as being the same as the singularity conditions of the Big Bang. For one thing only our Observable portion originated at a finite point. We do not know the size of the entire universe. Only the observable portion. The entire universe could be infinite or finite. Secondly the BB model starts at 10^-43 seconds. Prior to that our understanding no longer accurately describes the conditions, too many infinities. Now inflation occurs at roughly 10^-36 seconds. However this doesn't mean there wasn't expansion between 10^-43 seconds to 10^-36 seconds. In point of detail there was. This expansion isn't due to gravity. It's due to relativistic radiation. Photons, quarks,gluons and electrons in a quark gluon plasma soup. However temperatures were so high, that all particle are in a thermal equilibrium state. So we can accurately model this period via photons and the ideal gas laws. Temperatures also high enough that one can deploy scalar modelling equations of state. Look on the ideal gas laws wiki link I provided. This will probably be to advanced but let's give it a shot. Take the Einstein field equation. [latex]G_{\mu\nu}=8\pi GT_{\mu\nu}[/latex] In the FLRW metric the non vanishing components are [latex]G_{ii}=(2\frac{\ddot{R}}{R}+\frac{\dot{R}^2}{R^2}+\frac{k}{R^2})g_{ii}[/latex] and [latex]G_{ii}=3\frac{\dot{R^2}}{R^2}+\frac{k}{R^2}[/latex] Consequently the energy momentum tensor of matter transforms to [latex]T_{\mu\nu}=(\rho+p)u_{\mu}U_V=\rho G_{\mu\nu}[/latex] [latex] U_{\mu}[/latex] Is the four velocity field. Now I'm going to jump numerous calculations. The big bang at 10^-43 seconds can be described via the radiation equation of state. (We can safely ignore the curvature constant due to the extremely small size of the observable universe in this time era.). Makes absolutely no difference at these small scales. The equations of state for the FLRW metric becomes [latex]p=\frac{1}{3}\rho[/latex] [latex]\rho R^4=N[/latex] This leads to the FLRW metric in the form of the acceleration equation (radiation dominant) [latex]\frac{1}{2}R^2=\frac{4\pi GN}{R^2}-\frac{k}{2}+\frac{\Lambda}{6}R^2[/latex] Edited June 29, 2015 by Mordred
Andre Lefebvre Posted June 29, 2015 Author Posted June 29, 2015 I think you should look at the result analysis of 2015 of Satellite Planck. Before inflation there wasn't any matter whatsoever. As for the size of the entire universe we know that the observable universe goes back to 10^-43 sec. Imagine that expansion was produced at the speed of light. A year after Big bang the radius of the universe would have been 1 light-year. After 13,8 million years it would be 13,6 billion years and the diameter would be 27,2 billion years. Expansion would not have the time to produce more space-time or, for that matter, unobservable universe more than what stands behind those 10^-43 sec. So we've got a good idea of the size of the universe if we keep being logic. Now inflation occurs at roughly 10^-36 seconds. However this doesn't mean there wasn't expansion between 10^-43 seconds to 10^-36 seconds. There definitely was expansion starting for the Big bang; and it never stopped as for inflation, it is completely independent to expansion. This expansion isn't due to gravity That's for sure since expansion is the contrary of gravitation. I can't understand why you cannot visualise a universe at the beginning with nothing more than kinetic energy manifesting in a movement of expansion where there is no pressure involved because there is no opposition to that expansion. To have pressure you need opposition. Further more at that time there was no gravity involved. The first gravity that appeared in the universe was the deformations of space-time around quarks and antiquarks Top; first massive particles to appear.
Mordred Posted June 29, 2015 Posted June 29, 2015 (edited) Note the energy density to pressure relations. Expansion is not governed by gravity. Gravity leads to contraction. The energy density to pressure influences via radiation pressure is simply put greater that the gravitational force. I think you should look at the result analysis of 2015 of Satellite Planck. Before inflation there wasn't any matter whatsoever. As for the size of the entire universe we know that the observable universe goes back to 10^-43 sec. Imagine that expansion was produced at the speed of light. A year after Big bang the radius of the universe would have been 1 light-year. After 13,8 million years it would be 13,6 billion years and the diameter would be 27,2 billion years. Expansion would not have the time to produce more space-time or, for that matter, unobservable universe more than what stands behind those 10^-43 sec. So we've got a good idea of the size of the universe if we keep being logic. There definitely was expansion starting for the Big bang; and it never stopped as for inflation, it is completely independent to expansion. That's for sure since expansion is the contrary of gravitation. I can't understand why you cannot visualise a universe at the beginning with nothing more than kinetic energy manifesting in a movement of expansion where there is no pressure involved because there is no opposition to that expansion. To have pressure you need opposition. Further more at that time there was no gravity involved. The first gravity that appeared in the universe was the deformations of space-time around quarks and antiquarks Top; first massive particles to appear. I fully understand how the Planck data works. You must understand the Einstein field equations, the FLRW metric and the LCDM model intensely involves the ideal gas laws. Not just gravity As far as matter your right, but there is still radiation. Photons, quarks, gluons. Prior to the CMB there is also neutrinos. I've spent years studying BB nucleosynthesis. I also provided the references so you can study it as well. Expansion requires a force that force is pressure which is force per unit volume. You posted prior to my finishing off the other post. I provided the acceleration equation for the radiation dominant epock (PS kinetic energy doesn't exist on its own.) "In physics, the kinetic energy of an object is the energy that it possesses due to its motion.[1] It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes. The same amount of work is done by the body in decelerating from its current speed to a state of rest." https://en.m.wikipedia.org/wiki/Kinetic_energy Now I imagine your thinking in terms of temperature. There is carrier particlez for transferring heat.Photons,phonons and electrons. https://en.m.wikipedia.org/wiki/Heat_transfer_physics All three have the same equation of state. Expansion due to inflation far exceeds the speed of light. It's roughly 60 e folds in less than one second.( There is no limit to volume change. Your not giving inertia to any objects due to expansion. The volume of space simply increases. It is not creating spacetime as per some mystical material.) Also side note Planck data cannot see the BB. It can only view the CMB. Roughly 380,000 years after the BB. Expansion would not have the time to produce more space-time or, for that matter, unobservable universe more than what stands behind those 10^-43 sec. So we've got a good idea of the size of the universe if we keep being logic. There definitely was expansion starting for the Big bang; and it never stopped as for inflation, it is completely independent to expansion. . Wrong inflation and expansion are pretty much the same, just different rates and possibly cause. (Though in some inflation models they are the same.... We also cannot come close to measuring outside or region of causality. Aka observable universe. Ever.... Google lightcone and worldlines. I can't understand why you cannot visualise a universe at the beginning with nothing more than kinetic energy manifesting in a movement of expansion where there is no pressure involved because there is no opposition to that expansion. To have pressure you need opposition. Further more at that time there was no gravity involved. The first gravity that appeared in the universe was the deformations of space-time around quarks and antiquarks Top; first massive particles to appear. Inaccurate, you have to fully understand the ideal gas laws don't require container walls. In this case it's the pressure influence upon other particles within an adiabatic fluid contained within a region. The Google links and articles I posted should have shown you that pressure is indeed involved. This is textbook material not my own ideas. anytime you have sufficient energy density you have gravity. Enough photons can generate gravity. Gravity waves can also produce gravity. Please take the time to read the materials I provided. I specifically chosen those articles as they match textbooks. If you truly want to learn cosmology and can afford textbooks I recommend starting with "Introductory to Cosmology" by Barbera Ryden. Modern Cosmology by Scott Dodelson. ( Though he covers his own inflation model lol) Another good resource though old, I still like his simple down to Earth writing style is "First three minutes by Stephen Weinberg By the way you can see both energy density and pressure in the acceleration equation (Lambda dominant era, today) in this link. https://en.m.wikipedia.org/wiki/Friedmann_equations Edited June 29, 2015 by Mordred
Strange Posted June 29, 2015 Posted June 29, 2015 I agree with that; we don't observe expansion. Which means that where we do observe expansion, we don't observe gravity. I stick to "facts". At the distances where we see expansion, we still see the effects of gravity: distant galaxies held together by their gravity, the large scale structures, eyc. Maybe not; but in a galaxy, its "effect" doesn't comply to diminishing at the square of the distance; since a lot of stars starting from a certain distance of the center of the galaxy up to the farthest orbiting stars have practically the same speed. Something's wrong somewhere. Dark matter solves that dilemma. I must construct bad phrases in English; I'm a French speaking person. What I said is that "mass" wasn't a quantity of matter; that it rather was "energy". And I also said that my opinion was based on Binding energy. Which you said was the main source of mass in an atom. So we agree (I guess) that mass is energy and not a quantity of matter. But after saying energy is the main source of mass, you come back saying that mass is a quantity of matter. I then can understand that you cannot. Ah, maybe I misunderstood, do you mean: "Mass is not a quantity of matter; mass is energy"? If so, I would say you are twice as wrong, as both parts of that statement are wrong! Mass can be considered a "quantity of matter" (but so could volume or number of atoms - "quantity of matter" is not a well defined term.) Mass is not energy. Mass can be converted to energy and energy can be converted to mass but they are not the same thing. It's not an explanation if mass is energy; it could be if mass is a quantity of matter, so that a Higgs boson would simply give a "form" to a quantity of energy without giving it energy (to that form). As mass is not energy, then this argument is moot. That would mean that, to you, theoritical physics is not physics. No, it means that to me, ideas you make up with no evidence or theoretical basis are not science. I think you should look at the result analysis of 2015 of Satellite Planck. Before inflation there wasn't any matter whatsoever. Please provide a reference to evidence that "before inflation there wasn't any matter whatsoever". Imagine that expansion was produced at the speed of light. Sigh. Expansion is not a speed. You really need to learn a little basic physics. A year after Big bang the radius of the universe would have been 1 light-year. After 13,8 million years it would be 13,6 billion years and the diameter would be 27,2 billion years. This is so wrong, I don't know where to start. I'm sure Mordred can suggest a good introductory text.
Mordred Posted June 29, 2015 Posted June 29, 2015 Your welcome as to the last point raised by Strange this set of articles cover how expansion works in terms of distance. The tangentspace link has excellent detail on superluminal expansion misconceptions. It's based on the li eweaver and Davies article. http://www.phinds.com/balloonanalogy/: A thorough write up on the balloon analogy used to describe expansion http://tangentspace.info/docs/horizon.pdf:Inflation and the Cosmological Horizon by Brian Powell http://arxiv.org/abs/1304.4446:"What we have leaned from Observational Cosmology." -A handy write up on observational cosmology in accordance with the LambdaCDM model. http://arxiv.org/abs/astro-ph/0310808:"Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe" Lineweaver and Davies
Andre Lefebvre Posted June 29, 2015 Author Posted June 29, 2015 (edited) At the distances where we see expansion, we still see the effects of gravity: distant galaxies held together by their gravity, the large scale structures, eyc. Distant galaxies held together can be explained by something elses than gravity; and so are the "filament" structures at large scale of the universe. All you have to do is consider the expansion of space-time between the filaments. Maybe not; but in a galaxy, its "effect" doesn't comply to diminishing at the square of the distance; since a lot of stars starting from a certain distance of the center of the galaxy up to the farthest orbiting stars have practically the same speed. Something's wrong somewhere. Dark matter solves that dilemma That's a "gratuitous affirmation". You'll have to explain it to me; because those stars are not suppose to have the same speed according to the gravitation's formula. Mass can be considered a "quantity of matter" (but so could volume or number of atoms - "quantity of matter" is not a well defined term.) I'd say that it's mass that is not a well define term. In fact science doesn't seem to know what mass really is. As mass is not energy, then this argument is moot. So then, let's discuss it. What does Higgs boson do and how does he do it? Please provide a reference to evidence that "before inflation there wasn't any matter whatsoever". I'll try right away. http://public.planck.fr/notre-univers/contenu-univers.pdf It's in French but the first two top circles (with dots) concerns the Big bang when the only matter particle is said to be the "inflaton" which is simply the name given by Hawking to the vector of inflation (so a vector that approaches the idea of movement). But it's evident that whatever other kind of matter did'nt exist before inflation. The only thing present is 100% "radiance". Sigh. Expansion is not a speed. You really need to learn a little basic physics. Geez! I know that expansion is given by the ratio of 68,7 km per second per megaparsec; but the reason is that the space-time involved is too great to put it in miles per hours. So if you add all the megaparsecs of the universe, the total expansion cannot exceed light speed, and it doesn't. Because if you take Hubble's constant and multiply it with the number of megaparsec of the universe, you'l get a universe of a diameter of 27,6 billion light-years. This is so wrong, I don't know where to start. I'm sure Mordred can suggest a good introductory text. It's so wrong but you cannot say where it' wrong. I'll tell you were it's wrong. It's wrong, in your option because, to put it simple, when you look at a photo of CMB, you think that while the photon travelling at 300,000 km/sec during 13,8 billion years, the space-time it was going through was expanding behind it. So that the "place" that the picture represents, today, is much farther away than when its photon started is trip. You would be right if light speed didn't eliminate distance and stop time. So the photon that left that "far away" place, "instantly" got to Planck satellite. Whatever you think of the time that was spent for the trip is irrelevant to the photon that made the picture. The balloon analogy use to represent more than what is explained in the link. At the epoch that everybody was sure that space-time was curved, the surface of the balloon represented this curvature of space that everything had to follow to get from one point to another. So nobody could ever get inside the balloon. Only speed could modify the curvature of space-time. But since space-time his proven flat, everybody (every gravitational deformation of space-time) "lives in the balloon. Expansion is exactly the changing of the metric of space-time. A goog analogy (in fact a reality) of the changing of that metric is when you look at a graphic of the electromagnetic spectrum and the gradual expansion of its wavelength. As for inflation, it's completely separate from expansion; even if it involves the sudden growing of space-time. The best image I can imagine is Archimedes tired of waiting that is bathtub gets full, jumps in it when it's 3/4 full. The volume of water suddenly inflated as much as the volume of the body of Archimedes which was immerge. That's inflation and it manifested itself when gluon jumped in our universe (around 10^-36 sec) and almost instantly started disintegrating in massive particles in succession. Edited June 29, 2015 by Andre Lefebvre
Strange Posted June 29, 2015 Posted June 29, 2015 (edited) That's a "gratuitous affirmation". You'll have to explain it to me; because those stars are not suppose to have the same speed according to the gravitation's formula. The rotation curve is easily explained by the addition of extra matter. And, nicely, there is lots of other evidence consistent with that. Also, simulations of the evolution of galaxies and the large scale structure of the universe require exactly that amount of dark matter to match reality. So then, let's discuss it. What does Higgs boson do and how does he do it? The Higgs mechanism is completely over my head. And I have never seen a non-mathematical explanation that makes sense. So the best I can do is refer you to Wikipedia as a start: https://en.wikipedia.org/wiki/Higgs_mechanism If you can understand that, perhaps you could explain it to me It's in French but the first two top circles (with dots) concerns the Big bang when the only matter particle is said to be the "inflaton" which is simply the name given by Hawking to the vector of inflation (so a vector that approaches the idea of movement). But it's evident that whatever other kind of matter did'nt exist before inflation. The only thing present is 100% "radiance". Inflation and the inflaton are completely hypothetical, with no real evidence for them (yet). But it seems I might have misunderstood you again. Sorry about that. I am happy to agree that in the early universe there may have been no matter (depending how that is defined). I thought you meant that there was nothing, which is a common misconception. Geez! I know that expansion is given by the ratio of 68,7 km per second per megaparsec; but the reason is that the space-time involved is too great to put it in miles per hours. It is not because it is "too great"; it is because expansion by scaling means that the speed of separation between two points is proportional to how far apart they are (this is just basic arithmetic or geometry - nothing to do with physics or cosmology). So if you add all the megaparsecs of the universe, the total expansion cannot exceed light speed, and it doesn't. It can and does exceed light speed. Read some of the articles Mordred suggests (I haven't looked at it but I should think the one based on the Lineweaver and Davis paper is good). Because if you take Hubble's constant and multiply it with the number of megaparsec of the universe, you'l get a universe of a diameter of 27,6 billion light-years. The observable universe currently has a diameter of about 93 billion light years. Can I suggest you study a little before pontificating with such certainty on things that clearly have a very limited knowledge of. The whole universe is very much larger than that and may be infinite. It's so wrong but you cannot say where it' wrong. Life is too short. Read some Mordred's suggestions. I'll tell you were it's wrong. It's wrong, in your option because, to put it simple, when you look at a photo of CMB, you think that while the photon travelling at 300,000 km/sec during 13,8 billion years, the space-time it was going through was expanding behind it. So that the "place" that the picture represents, today, is much farther away than when its photon started is trip. You would be right if light speed didn't eliminate distance and stop time. So the photon that left that "far away" place, "instantly" got to Planck satellite. Apart from the fact that the "zero time" thing is just a pop-sci simplification, we are not measuring the time taken or the distance travelled in the photon's frame of reference (which doesn't exist) but in ours. In our frame of reference, it took the light 13.8 billion years to get here. Whatever you think of the time that was spent for the trip is irrelevant to the photon that made the picture. It may be irrelevant to the photon, but it is highly relevant to us. The balloon analogy use to represent more than what is explained in the link. At the epoch that everybody was sure that space-time was curved, the surface of the balloon represented this curvature of space that everything had to follow to get from one point to another. So nobody could ever get inside the balloon. Only speed could modify the curvature of space-time. But since space-time his proven flat, everybody (every gravitational deformation of space-time) "lives in the balloon. Gibberish. Expansion is exactly the changing of the metric of space-time. A goog analogy (in fact a reality) of the changing of that metric is when you look at a graphic of the electromagnetic spectrum and the gradual expansion of its wavelength. Correct. So you are capable of learning something. So if you study, you can fill those big gaps in your knowledge. As for inflation, it's completely separate from expansion; even if it involves the sudden growing of space-time. Also correct. Well done. Edited June 29, 2015 by Strange
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