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As the comments to the questions state, this is a question on the research state about the generation of the universe, and the first moment is modeled in the Big Bang model. The real beginning point is not yet known even in this model since gravity has not been consistently quantized within the model, only effective theory is used. Nevertheless existing ...


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OK, I'll give this a shot, cause . . . why not. The article you quoted covers a lot of ground - perhaps too much ground. And I'm not sure the quote of Matt Strassler is fair because he's answering a very specific question and while the source is given, it's not mentioned that it's a specific question that he's answering. but, lets jump to this part: ...


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Let embrace your attitude here. If the atom is 'empty', all that we have is charge and mass. By Newton's third law we have that this 'empty' with charge and mass need to absorb energy and momentum too. Now we have an empty space with charge and mass that absorb momentum and energy. Furthermore, this empty are allowed to move through space, because is ...


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As you correctly point out, the solution follows by integrating the differential equation. The general idea is to expand the left hand side of your differential equation by realizing that $$\text{d}\ln n^c(T) = \frac{1}{n^c(T)} \text{d}n^c(T) = \frac{1}{n^c(T)} \frac{\partial n^c(T)}{\partial T}\text{d}T = \frac{T}{n^c(T)} \frac{\partial n^c(T)}{\partial ...


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Your question really breaks down into two elements. "Missing" antimatter Antimatter galaxies being outside the observable universe. Presumably, by "missing" you are alluding to the question as to why we observe matter and not antimatter, if for some reason we wish discount CP violation (covered by Anna). The thing is, having antimatter outside the ...


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We need to first ask ourselves what is Space? What is Time? Then we can begin to answer your question after we define what these two are and the relationship between them. According to Geometrical Mathematics and based on Numerical Vector Space is nothing more then an empty construct and has no Dimensions until you give it a coordinate. We can define space ...


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The accepted model for the universe is the Big Bang. It is accepted because it fits data and observations up to now very well, using General Relativity and the standard model of particle physics . In this model it is CP ( charge and parity) violation which gives rise to particle antiparticle asymmetry, and since the standard model of particle physics cannot ...


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There are two parts to your question. First, why can we see things "46 billion light years away" if the Universe is only about 13.8 billion years old? Because the Universe is expanding. How far does a photon travel in 13.8 billion years in an expanding Universe? It depends on the rate of expansion. I'll give a simplified example to illustrate the point: ...


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When they say the universe was the size of a baseball about a billion billion billion billionth of a second after the big bang, does that means the observable universe was the size of a baseball, or does it mean the entire universe? In the past, the answer would have been the entire universe. Big bang cosmology is all about the expanding universe starting ...


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A black hole is little more than a spatially closed, gravitationally bound quantity of matter with an escape velocity greater than or equal to the speed of light, but for a black hole to have a validated existence, it must be perceived from OUTSIDE, not inside. In a universe-sized black hole, it would not seem like a black hole from within. The mass inside ...


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There is quite a nice description of this area in the Wikipedia article on the shape of the universe. As well as the torus possible shapes include the Poincaré dodecahedral space and the Picard horn. Googling will find you lots of stuff about the duodecahedral shape, and despite its potential for causing sniggers there is quite a bit on Picard's horn as ...


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Because near matter spacetime isn't expanding, and if it isn't expanding it can't be stretching the matter. The expansion of spacetime is a prediction of general relativity for the special case of a matter distribution that is homogenous and isotropic. If we feed in this condition we find that the geometry of spacetime is described by an equation called the ...


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General relativity deals with equivalence classes of maps. If you take one map of space-time, put it through a continuously differential equation, and alter the metric accordingly, you get an equivalent map. You can't talk about one or the other being right. They're equivalent. Either they're both right or they're both wrong. To be fair, that's just a ...


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Does our universe have an even distribution of matter in every direction In physics we have to define our terms. In this case, universe, matter and the dimensions in which we define direction, and define what we mean by uniformity. If we take universe to be the observable universe, dimension of the order of billions of light years and units of matter ...


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I am refering to large scales I hope and unfortunately I am not schooled in the terms and there defintion's used by physicists and the community I am merely approaching this from a educated layman point of view and with the application of some reason. Within contained heated fluids there can be a movement of flow in a particular direction but the contents 0f ...


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The distribution of matter is highly uneven in the "local" universe. Dark matter appears to be concentrated in and around galaxies and in clusters on scales of tens to thousands of kpc, and probably forms even larger filamentary structures which lead to the large scale structure we see on very big scales (tens of Mpc). All around us we see galaxies in ...


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The universe is as far as we know, generally uniform. That is, if we "zoom out" it all looks more or less the same.


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I would make an argument using Killing Vector Fields. Since the metric is not dependent on $\phi$, the vector $\left(\frac{\partial}{\partial \phi} \right)^a$ is a KVF. That is, the quantity $L = u_a \left(\frac{\partial}{\partial \phi} \right)^a = g_{ab} u^b \left(\frac{\partial}{\partial \phi} \right)^a = g_{\phi \phi} u^{\phi} = r^2 \sin^2{\theta} ...


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I'm going to first address some misconceptions you seem to have and then I will get to answering your question. Now, as stated in the comments, @Pulsar did a very thorough job of answering this question in another post. But I read through that answer and it's a bit technical. I already knew the stuff, so it made sense to me, but I can see how someone ...


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The discrepancy between the predicted big bang nucleosynthetic abundance of Lithium 7 and the measured value can be summarised as follows. If we take what we know about the the baryonic mass density of the universe and the Hubble constant, we get a self-consistent picture between the cosmic microwave background, observations of galaxy recession etc. and the ...


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There are two ways I can answer this question. I'm pretty sure one of the ways is, while technically correct, mostly worthless to you because it ignore the question you're trying to ask and focuses on the question you did ask. So let's start with that one. The redshift used by Hubble comes from expansion only and from gravity only. In general relativity, ...


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From expansion of the universe, the expansion of the universe is a repulsive force. Why it is a force? Because just like gravity, it is from spacetime, eventually it pushes atoms apart


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The reason it's thought of as expansion of space rather than just things moving farther apart through space is that the math of general relativity describes it that way, and GR has been well-supported by experiments so far. GR is all about curvature of spacetime, and curvature of anything can be determined by how we measure distances. A lot of the math in ...


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The balloon analogy imagines the universe as a 2D surface expanding around a central point as it moves through a 3rd dimension of time. This may be the origin of confusion as in reality there is no 2D surface of expansion, like a wave front, but rather an expansion of 3D spacetime, wherein every point in space quite literally is its own central point from ...


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Your question may presuppose that the Universe had a beginning in its own past. If we apply the logic of our experience and perception that we live with in space/time, this may seem like a reasonable inference. But just as complex systems may need more than knowledge of the sum of their constituents to be understandable, broader knowledge of the Universe ...


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I'll answer your question with an analogy. Imagine a really small balloon, so small that it occupies a point. Now, imagine that the balloon is expanding uniformly outward from that point. Note that that central point is not part of the balloon. It's the same idea as to what happened with the BB. In this analogy, the universe is the surface of the balloon. ...


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it must have started from a single point This is a common misconception popularized buy the media. Imagine this grid: Imagine each square getting larger. If you think about it, you will see that each point on the grid is expanding. The grid is the universe. Each point on the universe is its own "singularity".


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No, the argument is not correct. The spatial "conformal" coordinate $R$ in which, together with the conformal time $\tau$, the angle of the light rays is 45 degrees is not $\rho$ but nothing else than $r$: $$ ds^2 = -dt^2 + a(t)^2 dr^2 = a(t)^2 (-d\tau^2 + dr^2) $$ If you want a diagram with $\tau$ on the vertical axis where the light rays are drawn at 45 ...


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The reason dark energy, and matter does not become diluted is because it is a "data backup" of all the possibilities that did not manifest into "known matter" AS more and more decisions are made (split universes) a larger probability tree grows which leads invariably to having (to) store more information in the backup. This effect is what we term "gravity" ...


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Surely therefore our locally measured time is not the cosmological time t but rather the conformal time T? I don't think so. Our locally measured time is our locally measured time. If you had a clock that started ticking when the big bang occurred, the clock reading would be 13.8 billion years. If it displayed the conformal time, the clock reading would be ...


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No. It is perfectly possible to have a flat universe that expands forever and is accelerating. Dark energy is what makes this possible. Whilst the curvature of the universe is defined by the sum of all the energy densities in it, the effects of matter (baryonic or dark) and dark energy are quite different on its dynamics. It is in fact quite possible to ...


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As somebody said in the comments, physics has no "proofs". It has measurements/data and mathematical models that attempt to fit the data with specific assumptions. At most models are validated, not proven, if all known observations are consistent with the mathematical model. In the case of dark matter the first indications of its necessity in a ...


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Well, yes. "Expansion" of time as you call it is the cosmological age. The "direction" of progression of the time defines cosmological arrow of time.


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This is a commonly considered idea, of which one variant is the "Hubble bubble". Anything that happens outside of the visible universe, is, after all, in principle unknowable to us.


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The latest data is from the Planck satellite, and you can find the results in this 15MB PDF. The matter and dark energy densities are; $$\begin{align} \Omega_M &= 0.315 \pm 0.017 \\ \Omega\Lambda &= 0.686 \pm 0.020 \end{align}$$ So we get a total density of $\Omega = 1.001 \pm 0.026$. So within the 2.6% experimental error spacetime is flat.


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Is this really possible? No. Or does Hawking's mechanism protect this system from a causality violation, destroying the CTCs in it? No. Hawking's chronology protection conjecture is redundant because time travel is science fiction, because there is no forward travel through time, and no backward travel through time, because there is no motion through ...


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This is a well known and kenned estimate. The Wikipedia article Observable Universe covers this well; look especially at the sections under headings "Mass of ordinary matter" and "Matter content — number of atoms" for how it is derived. In summary: Cosmological models, especially the Lambda CDM-Model refined from the FLRW Metric, imply a relationship ...


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On the scale of the Solar System the cosmological constant makes a negligable difference, and the Schwarzschild metric remains an excellent description of the geometry. If you want to include the effect of the cosmological constant this can be done by using the Schwarzschild-de Sitter metric instead.


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Yes! The center of the universe is the one place where time is "correct". That is, not influenced by extraneous gravitational fields. So by 'correct' I mean where time is running faster (or no slower) than anywhere else. It is left as an exercise to the reader how this location might be found.


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The problem with this question is in the premise that where dynamical chaos is applicable nothing is predictable or can be extrapolated to the past. This is a wrong premise. Take this demonstration of a chaotic system. Note that it is computer simulation and of course it fits real data. Computer simulations are time symmetric, so the individual points can ...


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You seem to be misunderstanding the depth of the prediction we've made of the past in saying that the Big Bang happened. You do make a very valid point that chaotic systems even with as few elements as the solar system are practically impossible to past-predict (I'm going to start using the word "postdict"1 because it makes me feel better). I'm more than ...


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I'm not sure if that touches your question, but the universe is thought to be non-chaotic in the long term behaviour because of some anisotropy in the initial conditions (at least this is the general opinion). I watched a cool vid about that a couple of days ago. The point for which I agree with you, is that if looking at a certain situation, in general one ...


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First possible point of view: In the Pound–Rebka experiment the redshift / blueshift of photons is measured in small distances. This experiment one explain by the influence of gravitational field on the photon: "When the photon travels through a gravitational field, its frequency and therefore its energy will change due to the gravitational ...


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This is yet another instance of taking the ubiquitous balloon analogy too far. See, while it's a wonderful way to express the expansion of the universe, there are some misconceptions that arise from it: We live in a universe of finite size (we don't know, but we think not) and non-zero curvature (according to WMAP, we don't, or at least we think we don't) ...


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As Ben Goldacre says, "I'm afraid it's a bit more complicated than that." Phil Plait (Bad Astronomy) has occasionally written about this. Astronomers don't have a firm definition for the 'border' of a galaxy, tho' certainly objects classified as belonging should show some sort of contained orbit. But it gets worse, as they also have rough categories of ...


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If you mean by "our universe" the matter in spacetime we are able to reach and observe then you are right. The universe will become more and more finite for us unless someone will invent a "warp drive" or "wormhole" (currently the probability for it is very low). According to research you have ca. 100bn years time before all others galaxies will be gone ...


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As far as cosmology is concerned, the book which I consider to be THE best for a mathematical treatment of cosmology, is AK Raychaudhuri's "General relativity, astrophysics, and cosmology". It is excellently presented, Raychudhuri doesn't shy away from the math, and the old-school style makes it all the more elegant. So, I would STRONGLY recommend it. I ...


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Galaxies are not moving away from us, it is the space between us and the galaxies (and everything, in general) that is continually expanding. This is allowed to happen faster than the speed of light, because no object actually crosses the light speed barrier in the process. So consequentially, the universe has no size constraint like the one you've stated.


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As pointed out in the answer above, the observations that lead to the dark energy theory were not all distant (7-14 billion light years), but less so. Dark Energy expansion is observed throughout much of the observable universe - not just the very distant. Also, consider the basic hubble discovery - galaxies 4 billion light years away were moving way from ...


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The thing is, we don't completely base our understanding of the expansion of space on galaxies 7 to 14 billion light-years away. For evidence that the universe is expanding, look at Edwin Hubble's original paper in which he confirmed what we now call Hubble's law. The galaxies he studied are on the order of millions of parsecs away. Multiply that by 3.26 to ...



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