Read more:<\/strong><\/em><\/p>\n But where things get tricky are the more abstract questions relating to space and time.<\/p>\n When did time begin? What came before that? Does the Universe go on forever? If so, how can this be possible?<\/p>\n Faced with some of these astrophysical uncertainties and cosmological conundrums, we asked radio astronomer Dr Alastair Gunn to share some of his knowledge and expertise, to help us get a better grasp on some of the biggest unanswered questions about the space and Universe. \u00a0<\/p>\n Astronomers have found that the Universe is 13.8 billion years old.<\/p>\n That\u2019s quite old, but some very distant parts of the Universe may simply be too far away for light to have travelled to us during that time.<\/p>\n This defines what astronomers call the \u2018observable Universe\u2019, that is, the parts of the Universe we can actually see. We can never observe anything beyond this finite limit.<\/p>\n However, the question whether the wider Universe is finite or infinite depends on its geometry.<\/p>\n Einstein\u2019s General Theory of Relativity allows three shapes, or geometries, for the Universe: \u2018flat\u2019, \u2018closed\u2019 or \u2018open\u2019.<\/p>\n It is difficult to envisage these but they can be compared to a sheet of paper (flat), a sphere (closed) or a saddle (open). Which one it is depends on its total density and its rate of expansion.<\/p>\n Over the past few decades astronomers have measured these quantities and found that the Universe is almost certainly \u2018flat\u2019.<\/p>\n This may<\/em> mean the Universe is infinite, but it may also mean its geometry is just very complex, though still finite.<\/p>\n Other studies have recently suggested the Universe is \u2018closed\u2019, and therefore finite. So, frustratingly, astronomers are currently unable to say whether the Universe is infinite or not. \u00a0<\/p>\n The Universe has been expanding for the last 13.8 billion years. So, the regions of space that lie at the edge of the observable Universe are now much further away than when their light was emitted.<\/p>\n This means the edge of the observable Universe lies about 46 billion lightyears away in every direction.<\/p>\n The observable<\/em> Universe is thus a sphere with a diameter of about 92 billion lightyears and a volume of about 410 nonillion (410 thousand billion billion billion) cubic light-years!<\/p>\n However, there is no reason to suspect this limit is an actual edge<\/em> to the Universe or that what lies beyond this, if it exists, has an edge at all.<\/p>\n Even if the Universe is finite, it does not have to have an edge, in the same way that the surface of the Earth is finite but unbounded.<\/p>\n It all depends on the actual geometry of the wider Universe, and this we currently don\u2019t know for sure.\u00a0<\/u> \u00a0<\/p>\n If the Universe is infinite then it can simply keep expanding without getting any bigger (since you can\u2019t get bigger than infinity).<\/p>\n That might seem a facetious answer. But, when astronomers refer to the \u2018expansion\u2019 of the Universe they are referring to the abstract concept of \u2018empty space\u2019.<\/p>\n As the Universe expands<\/a>, space itself inflates, creating extra distance between objects.<\/p>\n There is no conundrum in this, whether or not the Universe is infinite. \u00a0<\/p>\n Observations have shown that ordinary matter in the Universe accounts for only 4.9% of its content.<\/p>\n 26.8% of it is due to dark matter<\/em><\/a>, a form of matter not directly visible.<\/p>\n The remaining 68.3% is due to dark energy<\/em><\/a>, a mysterious energy field causing the expansion of the Universe to accelerate.<\/p>\n The exact nature of dark matter and dark energy are currently not fully understood.<\/p>\n Of the 4.9% we do<\/em> understand, about 74% is hydrogen, 24% helium and the rest is heavier elements. \u00a0<\/p>\n One of the fundamental axioms of physics is that the laws that govern the Universe are the same everywhere and have remained so throughout time.<\/p>\n However, there is no convincing physical reason why this should be the case.<\/p>\n To test this, scientists have attempted to measure small differences in the constants that govern the forces of nature.<\/p>\n Most have demonstrated, with a high degree of accuracy, that the laws of nature are the same everywhere.<\/p>\n However, some studies have hinted that one constant, the \u2018fine structure constant\u2019 \u2014 the constant which determines how electric charges interact \u2014 might have been different in the past.<\/p>\n The result, which may not be statistically significant, is controversial, and most scientists would agree is currently unproven. \u00a0<\/p>\n Physicists believe there are various ways that \u2018alternative\u2019 or \u2018parallel\u2019 universes could be created.<\/p>\n Some involve the splitting of space due to unequal inflation just before the Big Bang.<\/p>\n Others are based on the \u2018many-worlds\u2019 interpretation of quantum physics, on the string theory of elementary particles, the fact that the constants of nature are so finely balanced, or simply on the assumption that the Universe is infinite.<\/p>\n![\""Spiral\"](\""https:\/\/images.immediate.co.uk\/production\/volatile\/sites\/25\/2022\/01\/09_hubble_mrk1337_esapotw2145a-0bc14f8.jpg?quality=90&resize=620%2C465"\" "\\"\"Spiral\\"\/")
<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>Is the Universe infinite?<\/h3>\n<\/div>
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<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>Could there be an edge of the Universe?<\/h3>\n<\/div>
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<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>If the Universe is infinite, how can it be expanding?<\/h3>\n<\/div>
![\""Illustration\"](\""https:\/\/images.immediate.co.uk\/production\/volatile\/sites\/25\/2020\/07\/GettyImages-1015900082-b33ac06-e1594827120351.jpg?quality=90&resize=620%2C424"\" "\\"\"Illustration\\"\/")
<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>What is the Universe made of?<\/h3>\n<\/div>
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<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>Are the laws of physics the same everywhere?<\/h3>\n<\/div>
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<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>Do parallel universes exist?<\/h3>\n<\/div>
![\""Do\"](\""https:\/\/images.immediate.co.uk\/production\/volatile\/sites\/25\/2022\/02\/GettyImages-679649206-3298d2c.jpg?quality=90&resize=620%2C349"\" "\\"\"Do\\"\/")
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<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>![\""3D\"](\""https:\/\/images.immediate.co.uk\/production\/volatile\/sites\/25\/2020\/04\/GettyImages_954315786-39d4c88-scaled-e1587559656873.jpg?quality=90&resize=620%2C414"\" "\\"\"3D\\"\/")
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