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(*CHART FROM “OBSERVABLE UNIVERSE” WIKI-ENTRY*)
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-the observable universe is a spherical region of the ‘universe’ comprising all matter that may be observed from ‘earth’ at the present time, because ‘light’ and other signals from these objects have had time to reach ‘earth’ since the beginning of the ‘cosmological expansion’-
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(there are at least ‘2 trillion’ galaxies in the ‘observable universe’, containing more ‘stars’ than all the ‘grains’ of ‘sand’ on ‘planet earth’)
(that’s quite a strange phrase, isn’t it?)
(what constitutes a ‘grain’?)
(and what exactly is ‘sand’?)
(‘solid matter’ broken down by ‘liquids’ to ‘fundamental particles’)
(“castles made of sand”)
(a ‘planet’ is composed of ‘sand’)
(assuming the universe is ‘isotropic’, the distance to the edge of the ‘observable universe’ is roughly the same in every direction)
(that is, the ‘observable universe’ is a ‘spherical volume’ (a ‘ball’) centered on the ‘observer’)
(every location in the ‘universe’ has its own ‘observable universe’, which may or may not overlap with the one centered on ‘earth’)
(the word observable used in this sense does not depend on whether modern technology actually permits detection of ‘radiation’ from an object in this region (or indeed on whether there is any ‘radiation’ to detect))
(it simply indicates that it is possible in principle for ‘light’ or other signals from the object to reach an observer on ‘earth’)
(in practice, we can see light only from as far back as the time of ‘photon decoupling’ in the ‘recombination epoch’)
(that is when ‘particles’ were first able to emit ‘photons’ that were not quickly re-absorbed by other ‘particles’)
(before then, the ‘universe’ was filled with a ‘plasma’ that was opaque to ‘photons’)
(the detection of ‘gravitational waves’ indicates there is now a possibility of detecting ‘non-light signals’ from before the ‘recombination epoch’)
(the surface of ‘last scattering’ is the collection of points in ‘space’ at the exact distance that ‘photons’ from the time of ‘photon decoupling’ just reach us today)
(these are the ‘photons’ we detect today as ‘cosmic microwave background radiation’ (CMBR))
(however, with future technology, it may be possible to observe the still older ‘relic neutrino background’, or even more distant events via ‘gravitational waves’ (which also should move at the ‘speed of light’))
(sometimes ‘astrophysicists’ distinguish between the visible universe, which includes only ‘signals’ emitted since ‘recombination’ – and the observable universe, which includes ‘signals’ since the beginning of the ‘cosmological expansion’ (the ‘big bang’ in traditional ‘physical cosmology’, the end of the ‘inflationary epoch’ in ‘modern cosmology’))
(according to calculations, the comoving distance (‘current proper distance’) to particles from which the CMBR was emitted, which represent the ‘radius’ of the ‘visible universe’, is about ‘14.0 billion parsecs’ (or about ‘45.7 billion light years’), while the ‘comoving distance’ to the edge of the ‘observable universe’ is about ‘14.3 billion parsecs’ (or about ‘46.6 billion light years’), about 2% larger))
(the best estimate of the ‘age of the universe’ as of ‘2015’ is ‘13.799±0.021 billion years’ but due to the ‘expansion’ of ‘space’ humans are observing ‘objects’ that were originally much ‘closer’ but are now considerably ‘farther away’ (as defined in terms of ‘cosmological proper distance’, which is equal to the ‘comoving distance’ at the ‘present time’) than a static ‘13.8 billion light-years’ distance)
(it is estimated that the ‘diameter’ of the ‘observable universe’ is about ‘28.5 gigaparsecs’ (or ’93 billion light-years’ / ‘8.8×1023 kilometers’ / ‘5.5×1023 miles’), putting the ‘edge’ of the ‘observable universe’ at about ‘46.5 billion light-years away’)
(the total ‘mass’ of ‘ordinary matter’ in the ‘universe’ can be calculated using the “critical density” + the ‘diameter’ of the ‘observable universe’ to be about “1.5×1053 kg”)
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💕💝💖💓🖤💙🖤💙🖤💙🖤❤️💚💛🧡❣️💞💔💘❣️🧡💛💚❤️🖤💜🖤💙🖤💙🖤💗💖💝💘
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*🌈✨ *TABLE OF CONTENTS* ✨🌷*
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