Our Universe is huge. In each and every direction on the sky, powerful telescopes observe galaxies whose light took more than 10 billion years to arrive at Earth. But wait - if we receive such ancient light from two opposite directions, and if the Big Bang happened just' 13.8 billion years ago, does that mean that the Universe is expanding faster than light? And wouldn't that violate Albert Einstein's theory of relativity, which says that the speed of light is an absolute limit? The answer may surprise you. But first, we need to take a closer look at the expansion of the Universe.
As described in the previous instalment of this series, we know that the Universe is expanding because galaxies appear to speed away from each other - their mutual distances are continuously increasing. But we also saw that cosmic expansion shouldn't be pictured as galaxies racing through empty space at incredibly high velocities. Instead, it is empty space itself that expands, pushing the galaxies ever further away from each other.
Denne historien er fra February 2023-utgaven av BBC Sky at Night Magazine.
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Denne historien er fra February 2023-utgaven av BBC Sky at Night Magazine.
Start din 7-dagers gratis prøveperiode på Magzter GOLD for å få tilgang til tusenvis av utvalgte premiumhistorier og 9000+ magasiner og aviser.
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Could We Find Aliens by Looking for Their Solar Panels?- Designed to reflect ultraviolet and infrared, the panels have a unique fingerprint
Researchers searching for life beyond Earth spend a lot of time thinking about what telltale signs might be detectable astronomically. Forms of unambiguous evidence for the presence of life on another world are known as biosignatures. By extension, techno signatures are indicators of activity by intelligent, civilisation-building life.
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Particles and corresponding antiparticles are very much alike, except they have opposite electrical charges. For instance, the antiparticle of the electron - known as the positron - has the same tiny mass, but while electrons carry a negative electrical charge, positrons are positively charged.
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The Big Bang produced a Universe filled almost exclusively with hydrogen and helium; all other elements - what astronomers call metals - were produced by stars, supernovae and everything that happens later. So if you can pick out a pristine star with no metals polluting it from among the billions in the Milky Way, then you are likely to have a star dating from our Galaxy's earliest days.
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