# Tag Info

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If there are infinitely many possibilities shaping up our universe, then mathematically the probability that a specific outcome happens (say an a monkey reproducing Shakespear's work) is exactly ZERO! In physics, there are only probabilities and no certainties. Implications: the idea that an exact replicas of "me", and such, rests on a zero-probability event ...

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How about space? I understand a standard assumption in cosmology is that the universe is spatially infinite in extent. Of course whether it actually is - is an entirely separate question. For how can you measure something to be infinite? It maybe that some parameter is inversely related to that something. And you could measure that value to be zero. In ...

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If I'm understanding the question correctly, it's referring to a universe that (1) has a spatial topology that wraps around, and (2) has cosmological conditions such that a timelike curve can circumnavigate the universe (in the sense of reuniting with a geodesic that has been at rest relative to the CMB). I assume that "looped" doesn't refer to closed ...

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This is a philosophical question so here is a philosophical answer. The scientific method in based on repeated observations and experiment. The whole science is just a collectivist instrument of acquiring knowledge. Being an instrument, it has its own limitations. Among them are: The tools employed by science are built by humans. As such, all tools use ...

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No (understandable/explainable) physical quantity could be infinite. "Infinity" is is physically very vague. When we say something is "infinite", it almost means we're throwing our hands up in despair that we can't explain something, or that quantity doesn't make sense in some particular framework. The whole point of physical quantities (observables) is to ...

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Here is a list of actual infinities in physics, mentioning Real Numbers. For instance, a set of all possible distances, this is a set with infinite cardinality, and thus actually infinite. Even the same distance, from infinitude of possible observers, is infinitely large or distance between relatively moving objects has infinity of values, taken at ...

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First of all, galaxies don't shrink. If our own galaxy were shrinking, then we would be moving towards our galactic centre, and we would observe a blueshift in that direction. Second, the accelerated expansion can be determined from the relation between redshift and brightness of distant supernovae. Neither redshift nor brightness would be affected by ...

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I don't see any logical connection to accelerating expansion. If shrinking of galaxies could explain away the acceleration of the expansion, then it could also explain away the expansion itself. Regardless of whether we're talking about expansion or acceleration of expansion, the effect isn't measured by watching the apparent sizes of galaxies get smaller ...

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Not sure if all "dynamical physical processes in the universe [are] actually chaotic," but some of them are for sure. I'm sure you know of the n-body problem, see here: http://en.wikipedia.org/wiki/N-body_problem Another example is that of turbulence in fluid flow: http://www.wolframscience.com/reference/notes/997b Here's something to think about. Let's ...

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There are quite a few common misconceptions about the expansion of the universe, even among professional physicists. I will try to clarify a few of these issues; for more information, I highly recommend the article "Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe" from Tamara M. Davis and ...

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You didn't really state what do you imagine when asking your question... Depending on which level do you want our things to change their size. Here are a few options: The atoms could increase distance between themseves We'd notice this for sure, because things would became larger, but they'd keep their original weight All particles (proton, neutron, ...

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Depends. If you simple assume matter growing we would see the distance between the surfaces of celestial bodies diminishing. Given that we regularly monitor the distance between the surfaces of the Earth and Moon by laser ranging to accuracies of less than one cm (which means less than one part in $10^8$ over the time the project has been running). This is ...

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On space-time, the useful notion of points are events. Only events that are separated by time-like curves are causally connected. Causal connectedness implies that fields happening at one of the events can influence fields happening at the other. Events that are separated by space-like curves are not causally connected, they might be still connected ...

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All points in the observable universe are "connected" in the sense that they can be acted upon by forces that have an infinite range (gravity and electromagnetism). However, points that are outside of our cosmological horizon (due to the expansion of the universe) are no longer causally connected with points in our local vicinity, since they are receding ...

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The only thing that prevents us defining a total conserved energy for the entire universe is that if the universe is infinite then the total energy could be infinite or indeterminate. The statements that say energy is not conserved in general relativity are wrong, irrespective of who says them. You can define energy over any finite volume of space and you ...

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The problem with this question is that gravitational potential energy between massive objects is a Newtonian concept but the question of energy conservation in cosmology can only be discussed properly in terms in general relativity. The general answer is that energy is always conserved if you take into account the energy in the gravitational field as well ...

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Really, the question does boil down to metaphysics if taken out of the mathematical construct. It's a matter of simple metaphysical logical consistency. Time cannot have a beginning because time cannot, by definition, be a function of NO time. But it cannot be eternal (without beginning or end) either because any value of time given to an object on the ...

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Entropy isn't a force that causes things to happen. But anyway, the answer is no. Not all matter in the universe is expected to eventually collapse into black holes. See Adams and Laughlin, http://arxiv.org/abs/astro-ph/9701131 , section VD. Note also that black holes eventually evaporate, so when matter collapses into black holes, the result is that it ...

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If there were a matter-antimatter boundary, we would observe gamma radiation from the annihilation events on the boundaries. We do not observe such radiation events.

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As I mentioned in the comments, your first two questions are based on an assumption about repeats that isn't justified. see Multiverse theory and infinite individuals for more details. Re the last question: the grandfather paradox is based on the existance of closed time-like curves, and the existance or otherwise of these is unrelated to the concept of a ...

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So first of all, there are several multiverse theories. As a cosmologist, I personally don't know anyone that subscribes to the one you've written here. The standard multiverse theory comes from quantum mechanics. In it, we say that every time an action is taken that (more or less) collapses a wavefunction in our universe, it simply means that other ...

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The expansion of the universe is (approximately) described by the FLRW metric. The Wikipedia article I've linked gives lots of gory details, but the key result we need is the dependance on the acceleration on the density and pressure: $$\frac{\ddot{a}}{a} = -\frac{4\pi G}{3}\left( \rho + \frac{3p}{c^2} \right) + \frac{\Delta c^2}{3}$$ If there is no dark ...

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I guess that you are imagining an expansive force accelerating the Universe versus gravity pulling the Universe together, and that if somehow gravity were weaker, the expansive force would win. That is not the correct picture. In popular models, the accelerating Universe is caused by gravity, because of a vacuum energy with negative pressure (see dark ...

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I think the term acceleration implies a change in direction of the net forces acting on galaxies on the large scale. Gravity (regardless of magnitude) acts to collect the galaxies, while the acceleration acts in the opposite direction.

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The dark matter is known (from galactic rotation curves and microlensing) to clump around galaxies and to mass considerably more than the visible matter. This contradicts your hypothesis, so no.

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It's both effects combined. They are not in competition. You get a Lorentz time dilation (i.e. frequencies are slowed) from the relative motion and also the `stretching' of the wavelength (i.e. an additional decrease in frequency) due to the expansion of the Universe. They are separate effects and they combine together.

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Yes, indeed. "cosmological redshift CAN be interpreted as atomic frequencies increasing by the scale factor as the Universe" evolves (NOT expanding). Your statement correspond the interpretation that the 'space is not expanding' but instead the ruler (always made of atoms) shrink as time goes by, giving an apparent increase of the space. Space expansion ...

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"Metric expansion only occurs with proper distances (between events at the same cosmological time)" Why would this effect disappear when you integrate over paths in space-time (e.g. photon trajectories)? The redshifting of light by spacetime geometry is an observational fact, not an ad hoc conjecture. "Can the cosmological redshift be interpreted ...

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The primordial ball could not have had space in it unless the ball itself was "in space". That is part of the universe which cannot be seen, and thus cannot be theorized about. Wherever and whenever the primordial ball was is beyond the scope of physics I think.

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I remember being confused by this, and thanks to help from this site I think I understand the problem (though I probably don't! :-). If you take the FLRW metric and extrapolate to zero density you get the Milne metric, which is hyperbolic and maximally curved. However the Milne metric is equivalent to the Minkowski metric with a co-ordinate transformation, ...

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