# Tag Info

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Total entropy of the universe is equal to the total area of the space boundary, according to holographic principle. Our universe is expanding, asymptotically approaching de Sitter space. In de Sutter space the radius of the cosmic horizon is constant and equal to the Hubble radius - the distance at which cosmological red shift becomes infinite. For ...

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You are correct that the gravity of everythig in the Unuverse should have contracted the universe from everything we know, but the fact is we don't have all the answers. For example, what caused the big bang? What cause the sudden inflation? what is dark energy? String theory has some potential answers for the initial inflation but string theory has run ...

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Your question assumes that the universe started out as a point at the Big Bang and then expanded outwards, however this is not the case. Have a look at my answer to Did the Big Bang happen at a point? for more on this. However your main point remains, that is shouldn't gravity be slowing the expansion, and indeed it did until a few billion years ago. The ...

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The large circles have exactly the same number of points as the smaller circles, which in turn is the same as the number of points on the real line. All contain $\aleph_1$ points. See the Wikipedia article on aleph numbers for more. Arguments based on comparing infinite (transfinite in this case) numbers are rather subtle and you should steer clear of them ...

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First of all, the universe is not infinite. There is enough reason to disprove an infinite universe model. In such a case, the universe can have a beginning. Reasons to why the universe simply cannot be infinite are as old as the time of Isaac Newton. The problem is gravity. In an infinite universe, the total gravity of the mass it contains would be infinite ...

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you cannot look at the expansion of the universe -- or say the big bang -- as being comparable to an explosion. Every point in space drifts away from every other point in space. This is different to an explosion, where you have a real center. The latter aspect is missing -- or say different -- when you look at the expansion of the universe. Here you don't ...

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The Big Bang is a mathematical model of how the observable universe evolved , based on fitting astrophysical observations. Like all models it has its region of validity. When I read cosmology fifty years ago, the model included a singularity at the origin, because that is what the mathematical functions of the General Relativity solutions showed. The model ...

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Questions like this are complicated because you have to be clear what you mean by time. The simplest definition is that time is what is shown on a clock, so if I was holding some hypothetical clock that had been reset to zero at the Big Bang my clock would currently be showing 13.799 billion years i.e. the age of the universe. The question then becomes what ...

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This is true for galaxies beyond the cosmologic horizon. BTW they are not moving at that speed: their apparent speed seen from our place is such. Quite like the fact that the far galaxies we see close to the horizon seems both very young (which they aren't "in real life"), very red-shifted (while their emitted colors are indeed normal) and living very ...

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have a read through Did the Big Bang happen at a point? as this provides important background. If, as you say, you are considering only a simply connected universe, so it isn't finite due to its topology, then the assumption we make when solving Einstein's equations is that the universe is the same everywhere - the technical terms are isotropic and ...

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However, if the universe is infinite and unbounded and uniformly populated, there is no empty volume for the galaxies to move into. Therefore logic dictates that the space between galaxies must be expanding. Your premise is faulty. Just because something is infinite doesn't mean it can't expand. For example, although it's intuitively obvious that the ...

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Let's do a Back-of-the-Envelope calculation. It is typical for large-scale neutrino calorimeters (I have KamLAND specifically in mind because I worked on the project and know the detector reasonably well) to have an energy-scale uncertainty of a couple of percent at a few MeV energy. That's a systematic, and will effect all results more or less equally. ...

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Neutrinos are notoriously difficult to detect . Have a look at this review paper : A core-collapse supernova will produce an enormous burst of neutrinos of all flavors in the few-tens-of-MeV range. Measurement of the flavor, time and energy structure of a nearby core-collapse neutrino burst will yield answers to many physics and astrophysics questions. ...

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You've kind of got a point with "every object in the universe is either orbiting something or it is falling towards something", but the language you use is going to make physicists twitch uncomfortably ;) More formally, consider the following: 1: The gravitational force (or "bending of spacetime" if you prefer) created by any mass has an infinite range. ...

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