# Tag Info

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According to our current scientific knowledge we know that we don't know what the 70% of the energy of the Universe is. Also, a comprehensive description of the thermodynamics of the Universe is impossible with the current standard Cosmological model and Einstein's General Relativity. In particular it's very complicated, and incomplete, as I said, to ...

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Light itself has temperature. If you let it fall upon a cold black body long enough, the body would warm up to that temperature and emit light of that temperature itself. What's the temperature of sunlight on the earth? About 5000K. It's the temperature that the surface of the sun had about 8 minutes ago. The sun could have extinguished 8 minutes ago, but ...

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The temperature 2.73 K is not calculated, it is measured. The cosmic microwave background (CMB) has the properties of a blackbody radiation at the temperature 2.73 K. It is based just on the measurement of CMB, no calculation of dark matter or dark energy is involved. Temperature does not simply depend on mass or gravity. Temperature is a quantity which in ...

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Mass in and of itself will not generate heat. Heat comes about when two objects interact with each other i.e. when they change from one state with a given energy to another. More specifically, if an object has more energy after an event than it did before, the net gain in heat would be negative for the surroundings (the environment becomes colder), and vice ...

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From the Friedmann equations, you can derive that $$\dot{R}^2 - \frac{8\pi}{3}G\rho R^2 = -k c^2,$$ where $\rho$ is the total density of the universe and $k$ is a constant that determines the shape of the universe: $k=-1,0,1$ for an open, flat and closed universe, respectively. If the universe is a hypersphere ($k=1$), then $R$ can be thought of as its ...

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There's a very common misconception that the Big Bang happened at a point like a bomb going off. It doesn't help that almost ever TV documentary on the subject represents the Big Bang in this way. Explaining what actually happened is hard without going into the Maths, but here's an explanation I gave taken from (of all places) the Science Fiction Stack ...

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The question you are asking yourself is ill defined. The universe has no center, thus you cannot ask what is there. The important thing to realize is that a singularity (presented in the Big Bang Theory) is not a physical thing, you can't say "oh look at that singularity over there"(from that point the universe started). In fact a singularity is merely a ...

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Although the general theoretical description of the Universe is given by Friedmann–Lemaître–Robertson–Walker metric, and although it allows the Universe to be both finite (closed) and infinite (opened), scientific observation has shown that the universe began a finite period ago (approximately 13.798 Billion years ago). There was a big-bang, inflation of ...

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It depends what you mean by 'cannot happen'. Go back to a period before you saw that documentary, but not so far back time didn't exist, in ancient Greece there began a raging debate between Plato and his student Aristotle, about the nature of knowledge. Ultimately Aristotle's views gave us theories such as causation, and centred around observed ...

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The simple answer to your question is that if there are other universes by virtue of the expansion we see in the universe around us, there is no way we can know anything about them directly (since the distance between them is increasing, and light can only go at light speed, so no information exchange). Now, with that said, Velenkin thought about Alan ...

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You are right that we do not know if the universe is finite or infinite in space. Cosmologists do now think that it has an infinite future because of the accelerated expansion rate due to dark energy but this does not tell us anything about the question of infinite space. To answer the question for space we first have to assume spacial homogeniety, i.e. ...

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The uncertainty principle is a mathematical consequence of wave behaviour. It is true for sound waves, electrical signals, radio waves, etc. Anywhere you might want to work with Fourier transforms. Let's say you want to send a pulse via a radio wave. Furthermore, lets say you make the amplitude of the pulse a Gaussian function with time: \$f(t) \sim ...

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The answer depends on the interpretation of quantum mechanics you like the most. As they are mathematically equivalent, the question is metaphysical rather than scientific. Some of the ways to explain: There is no uncertainty in the system. The uncertainty is in the observer. By making the measurement the observer introduces the uncertainty because he ...

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This reply probably would be more suitable as comment, but i'm unable to comment yet, so: First of all we can't really describe universe as a system that even close to entropy which actually would be a lowest energy and most stable state for universe. So, following from that: universe is unstable, and as it's unstable there is no really a problem for ...

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Usually when someone asks about why a system is the way it is we answer it by saying that it is the most stable lowest energy state. That's a lousy explanation. A system doesn't have to be in the lowest energy state (in that case the Universe would be very boring). In fact, some systems don't even have a definite energy. To visualize what I've ...

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Physics isn't entitled in answering the question "why" but rather "how". The question "why" is always diverted to philosophy, and some liars use it to make religions.

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I disagree with most answers here. Pretty much all branches of Physics and Laws of Physics does not depend on whether the universe is old or whether the earth is old. What would be different would be the Assumptions, Models, and currently accepted Initial Conditions if they are not so. For instance, before the discovery of the expansion of the universe the ...

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There is just a caveat in expressing the age of the universe in terms of earth years. This is implicitly assuming that the clock being used to measure is at rest with respect to earth or at least has the same astronomical conditions as the earth. Furthermore, you would be implicitly assuming that this clock holds this same condition throughout the time ...

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