Increase of separations between objects as the UniverseĮxpands. Speed of light times the light travel time due to the In anĮxpanding Universe this distance NOW is larger than the Mean the spatial separation NOW, with the positions ofīoth objects specified at the current time. When talking about the distance of a moving object, we Of distances which go to infinity in the empty Universe model since Part 2 of the cosmology tutorial for a discussion of the other kinds The speed of light times one half the age of the Universe. Of distance does agree with the assumptions in this question: theĪngular size distance, and it does reach a maximum value of In the empty Universe, one of the many possible definitions We must ignore gravity, so this would only happen in a nearly empty The Universe at almost the speed of light, and then emitted light whichĬame back to us at the speed of light. One assumes that all the galaxies left from a single point at the Bigīang, and the most distant one traveled away from us for half the age of ![]() This question makes some hidden assumptions about space and time whichĪre not consistent with all definitions of distance and time. Why isn't the most distant object we can see 7 billion light years If the Universe is only 14 billion years old, Particular model for the vacuum energy which causes the acceleratingĪ search of astro-ph on the LANL preprint serverīack to top. Steinhardt and colleagues have adopted quintessence as the name for a Quintessence, or the fifth essence, is a fifth element beyond the standardĮarth, air, fire and water of ancient chemistry. Z close to 0.1 is compared to a distant supernova with z Note that these distances are all proportional to the age of theīut this dependence cancels out when the brightness of a nearby supernova at Supernovae at high redshifts will appear to be fainter than they wouldįor a decelerating expansion because their Is longer, and the distance NOW is larger.īut if the expansion is decelerating, it was faster in the pastĪnd the distance NOW is smaller. Then the expansion was slower in the past,Īnd thus the time required to expand by a given factor If the expansion of the Universe is accelerating Of the supernova, we need to know its distance now. This factor is (1+z), where z is the redshift.īut in order to determine the expected brightness Which tells us by what the factor the Universe has expanded since the The evidence for an accelerating expansion comes from observations of the Why do we think that the expansion of the Universe These light isotopes are all well fit byįinally, the angular power spectrum of theĪt the several parts per million level is consistent with a dark matterĭominated Big Bang model that went through the inflationary scenario.īack to top. This is a direct observation of the evolution of the Universe.Ībundances. Steady State model, but many observations support the Big Bang over the The observations listed above are consistent with the Big Bang or with the Time dilation in supernova light curves.Isotropy - very strong data showing that the sky looks the same in all.Homogeneity - fair data showing that our location in the Universe. ![]() Many of these factsĪre consistent with the Big Bang and some other cosmological models,īut taken together these observations show that the Big Bang is theīest current model for the Universe. None of these prove theīig Bang, since scientific theories are not proven. The evidence for the Big Bang comes from many pieces of ![]() The expansion of the Universe is accelerating,īack to top.
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