# Tag Info

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Summary There's a 1 in 500 billion chance you're standing under a star outside the Milky Way, a 1 in 3.3 billion chance you're standing under a Milky Way star, and a 1 in 184 thousand chance you're standing under the Sun right now. Big, fat, stinking, Warning! I did my best to keep my math straight, but this is all stuff I just came up with. I make no ...

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Does the Milky Way move through space? Yes it does. I'm very fascinated with space, although I don't have a degree or any formal education, I'm still very in love with everything about it and want to learn constantly. Good man Mike. One thing I ask myself is if our galaxy moves through space? It does. When we look at the Cosmic Microwave ...

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The Universe is space and time. If there are other universes they can't be "next to" ours, as "next to" is a statement about the relationship between things in space, and the Universe is not in space. It is space. You can't have two universes colliding at a particular time, because time is a property of the universe. Your mental image of ...

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We don't know in general but to the extent we can measure, the laws seem to be the same, even if conditions are not. For example radioactive decay: We know how fast various elements decay, and we can observe the results of radioactive decay in distant supernovae. The conclusion is that, for at least some elements, the rate of radioactive decay is the same ...

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I think your question is on topic, but @RhysW has linked a very helpful post in understanding why your question is a common misconception about the Big Bang. No Center There is no 'center' to the universe. At any point, a local observer will claim that they are at the center of the universe by the way galaxies move away from them. How can we possibly know ...

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Galaxies move through space with velocities of the order of a several 100 km per second; small velocities for small groups (~100 km/s; e.g Carlberg et al. 2000) and large velocities for rich clusters (~1000 km/s; e.g Girardi et al. 1993). In addition to this so-called "peculiar velocity", galaxies also also carried away from each other due to the expansion ...

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There are three main space weathering processes that will affect the surface of the marble. Cosmic rays, high energy particle from the sun and beyond, will hit the surface. This can change the chemistry of the surface. Solar wind particles, hydrogen and helium, can become implanted in the surface Micrometeoroids will impact the surface, causing small ...

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The answer to this is surprising: We are. And many (if not all) other galaxies. And they move faster than light. See, the universe is expanding, at an accelerating rate. The fabric of spacetime itself stretches out, so that galaxies seem to move away from each other. The interesting thing is that relativity does not forbid these from moving away faster ...

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A quick google gave me these (approximate) figures: 7.5 x 1018 grains of sand in all the beaches and deserts of the world 7 x 1022 stars in the observable universe If these are reasonable estimates, then there are approximately nine thousand stars in the observable universe for each grain of sand on Earth. (By observable universe, I mean in all the ...

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This is a reasonable estimate for the number of atoms in the observable universe. It might seem like a small number, compared with the number of atoms in a human only as a result of our brain's inability to have an intuition about very large numbers and exponential scales. There is a very very big difference between $10^{27}$ and $10^{83}$. How big is the ...

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Dark matter galaxies are possible but very speculative. On a theoretical level, they are hard to form because dark matter interacts only gravitationally (see Anders Sandberg's answer), which makes it hard to lose energy and become bound structures. On an observational level, they would be hard to detect. Gravitational lensing can do something, but since one ...

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Probably not. Dark matter should really be called "transparent matter" since it does not interact with light. This has an important consequence: it is hard for dark matter - whatever it is - to lose energy by radiating. This is why normal matter can form clouds that accrete into dense regions that in turn become galaxies and stars: energy is ...

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All Conselice et al. (2016) appear to suggest is that when you look at something like the Hubble deep field, there are many faint (and presumably low mass) galaxies that are not seen. This has absolutely no effect on the need for dark matter. The main results are: (i) as you look back in time, the overall (co-moving) density of galaxies (more massive than a ...

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Olber's Paradox was created at a time before the idea of a finite universe was accepted. (It was thought of in the 1600's). In order to resolve Olber's Paradox, you have to introduce the idea that either the universe had a beginning or it is of finite size. (Note: the solution does not require an expanding universe). So, at the time, it was a paradox. ...

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The easiest explanation for why the maximum distance one can see is not simply the product of the speed of light with the age of the universe is because the universe is non-static. Different things (i.e. matter vs. dark energy) have different effects on the coordinates of the universe, and their influence can change with time. A good starting point in ...

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Here is an overview of different scales we may look at the universe. On scales beyond it's almost homogeneous, and we get at the border of the visible universe. Many detailed images are available, e.g. from the Hubble Space Telescope. If you need a three-dimensional description of the universe, your program will probably need to read portions of star, cloud,...

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Your are misunderstanding the expansion of the Universe. The Big-Bang is not an explosion: this is the moment in time when the Universe had an (near) infinite density. So there is no center in the Universe as there is no center of the SURFACE of the earth (this is the most popular 2-dimensional analog). Since this primordial ultra-high density state, the ...

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Dark Matter Your understanding of dark matter isn't bad, but here's a few clarifying details. Orbits: The speed of an object's orbit is related to 2 things: the radius of its orbit and the mass inside of it. In the solar system, over 99% of the mass is concentrated at the centre, so radius is the dominant effect on orbital speed. As we look at planets ...

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Let us define this as the largest observable density of a stable object, in order to exclude black holes which may have a very large (infinite) density at their centers or objects collapsing towards a black hole status. If we restrict the definition in this way, then the answer should be the core of the most massive neutron star that we know about. At ...

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The answer is yes time dilation does affect how much time an observer experiences since the big bang until the present (cosmological) time. However there is a certain set of special observers called comoving observers, these are the observers to which the Universe appears isotropic to. For example we can tell the Earth is moving at about 350 km/s relative ...

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There is also another mediator particle which moves at the speed of light other than the photon. This is the gluon, which is the exchange particle for the strong force. The odd thing about the gluon is that it's never seen by itself (that is, outside of collections of other gluons). Also, though neutrinos do in fact have mass, they are neutral particles. ...

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Yes there are. They are mainly based on what dominates the energy density of the universe at the time and they are known as epochs. Thus we have the inflationary epoch in the first tiny fraction ($\sim 10^{-32}$) of a second, when the energy density was dominated by an inflationary field. Then we are in the electroweak epoch, when the weak nuclear and ...

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Without checking the numbers in detail, according to Wikipedia, the volume of the observable universe is about $3.5\cdot 10^{80} \mbox{ m}^3$, and the volume of Earth is about $1.08321\cdot 10^{21} \mbox{ m}^3$. By dividing the two volumes we get a factor of $3.2\cdot 10^{59}$, or written as decimal number: The observable comoving volume of the universe is ...

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This question begs the question, does everything need a practical use? The answer is a resounding no. What's the practical use of the Louvre, or of your local neighborhood public park where you enjoy weekend barbecues? There are some things that are very worthwhile that have little or no economical gain. Your local neighborhood public park in fact has ...

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Later estimates shows that the star could be as old as 14.5 billion years (± 0.8 billion years), which is still it older than the universe's calculated age of about 13.8 billion years, an obvious dilemma. There is no dilemma. That ± 0.8 billion years is important. Subtract 0.8 billion years from that 14.5 billion year figure (later revised to 14.27 billion ...

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It is a common misconception that galaxies receding faster than light cannot be observed. There are two versions of this misconception: Galaxies that are now receding faster than light cannot be seen. If we observe a galaxy today, it may recede faster than light now, but when it emitted the light we see now, it did not. Both are incorrect. Intuitive ...

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Under General Relativity (GR) alone, a Black Hole's (BH's) event horizon is a point of no return -- anything that passes through the event horizon is lost and gone forever, and nothing comes out. Hence, under GR alone, BHs are utterly black and don't have a temperature at all. This is why the absorption of radiation (or anything else) by a BH doesn't raise ...

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This is a question that concerns the initial mass function (IMF) - an empirical (that is, defined by observations rather than theory) function that describes the statistical distribution of stellar masses. Edwin Salpeter (1955) was the first to describe the IMF, though if you read Chabrier (2003) there are some reasonably comprehensive explanations of the ...

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Information cannot "leave" the black hole. There is no way (by our current framework of physics) that an entity inside the event horizon can send a signal out. However, entropy can leave. The black hole has entropy proportional to its surface area, and this roughly corresponds to "the number of ways that black hole could have been created". The surface area ...

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