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A warm welcome to the new NetWeather Astronomy & Cosmology thread. This thread has been designed to encompass all aspects of astronomy for all levels of expertise, from a casual interest to the 'would-be Stephen Hawkins'! So please feel free to browse and ask any questions you might have, and I'm sure there will be plenty of members ready to discuss the answers. There are a whole raft of resources available on the internet so I'll post a few links below, and feel free to add your own links in what is a diverse and fascinating field of study. http://www.eso.org/public/ http://www.nasa.gov/ http://www.space.com/ http://www.sciencedaily.com/news/space_time/ http://en.wikipedia.org/wiki/Astronomy I'll kick off the discussion with a question that was posed by Snowlady36 'How fast is the universe currently expanding?' An interesting question!. The best I can come up with is from well known TV astronomer Phil Plait, host of Discovery Channel's 'Bad Astronomy'.....According to his interpretation, the universe expands at a rate of 74 Kilometers per second per every 3 million light years of distance.....here's the link http://blogs.discovermagazine.com/badastronomy/2009/05/07/the-universe-is-expanding-at-742-kmsecmpc/#.U06z71e59tA Can anyone else come up with a different answer?
The universe began with the big bang (Some may think others way of the beginning of the universe). But the universe has to end one day? Or will just go on forever? There are some predictions about the fate of the universe. 1.Big freeze This scenario is generally considered to be the most likely,as it occurs if the universe continues expanding as it has been. Over a time scale on the order of 1014 years or less, existing stars burn out, stars cease to be created, and the universe goes dark.Over a much longer time scale in the eras following this, the galaxy evaporates as the stellar remnants comprising it escape into space, and black holes evaporate via Hawking radiation.In some grand unified theories, proton decay after at least 1034 years will convert the remaining interstellar gas and stellar remnants into leptons (such as positrons and electrons) and photons. Some positrons and electrons will then recombine into photons.In this case, the universe has reached a high-entropy state consisting of a bath of particles and low-energy radiation. It is not known however whether it eventually achieves thermodynamic equilibrium. 2.Big Crunch If the energy density of dark energy were negative or the universe were closed, then it would be possible that the expansion of the universe would reverse and the universe would contract towards a hot, dense state. This is a required element of oscillatory universe scenarios, such as the cyclic model, although a Big Crunch does not necessarily imply an oscillatory Universe. Current observations suggest that this model of the universe is unlikely to be correct, and the expansion will continue or even accelerate. 3.Big Rip This scenario is possible only if the energy density of dark energy actually increases without limit over time. Such dark energy is called phantom energy and is unlike any known kind of energy. In this case, the expansion rate of the universe will increase without limit. Gravitationally bound systems, such as clusters of galaxies, galaxies, and ultimately the Solar System will be torn apart. Eventually the expansion will be so rapid as to overcome the electromagnetic forces holding molecules and atoms together. Finally even atomic nuclei will be torn apart and the universe as we know it will end in an unusual kind of gravitational singularity. At the time of this singularity, the expansion rate of the universe will reach infinity, so that any and all forces (no matter how strong) that hold composite objects together (no matter how closely) will be overcome by this expansion, literally tearing everything apart. 4.Vacuum metastability event If our universe is in a very long-lived false vacuum, it is possible that a small region of the universe will tunnel into a lower energy state. If this happens, all structures within will be destroyed instantaneously and the region will expand at near light speed, bringing destruction without any forewarning. 5.Heat death The heat death is a possible final state of the universe, estimated at after 10150 years, in which it has "run down" to a state of no thermodynamic free energy to sustain motion or life. In physical terms, it has reached maximum entropy (because of this, the term "entropy" has often been confused with Heat Death, to the point of entropy being labelled as the "force killing the universe"). The hypothesis of a universal heat death stems from the 1850s ideas of William Thomson (Lord Kelvin) who extrapolated the theory of heat views of mechanical energy loss in nature, as embodied in the first two laws of thermodynamics, to universal operation. But its all a very long time away. So what do you think?