A recent study speculated that if an alien civilisation grew to the point where it needed whole galaxies as energy sources, it might have to leave its own galaxy and "mine" other galaxies for stars, reconfiguring the cosmos itself , before it all expands out of reach. If you're advanced enough to worry about the stars going out, perhaps it's just contingency planning at its finest.
Aliens and dark energy aside, there sure is a lot of space — we know the universe is at least 30 billion light years across, and might even be infinite. Hydrogen is the lightest element — it is simply a single electron and a single proton, orbiting each other. Hydrogen can be found everywhere, from hot, dense stellar nurseries where new stars form, to the cold and tenuous voids between galaxies.
It's the most abundant element in the universe , making up 75 per cent of all its atoms. But most hydrogen atoms floating in space are so spread out, they're essentially invisible to astronomers. So how can we tell if they're there? Ionic hydrogen is formed when a nearby hot, bright star splits or ionises a hydrogen atom into protons and electrons.
Atomic hydrogen is created in parts of the universe that are cold enough to allow protons and electrons to recombine. Molecular hydrogen H2 , which is the same form we find here on Earth, is formed in giant clouds where the hydrogen becomes dense enough that two pairs of atoms stick together. We also sometimes find other molecules in these clouds ranging from simple carbon monoxide CO to more complicated like ethanol C2H6O — that's right, astronomers are searching for beer in space.
Atomic and molecular hydrogen are relatively easy to find because they absorb and emit particular wavelengths of light, giving each a unique telltale signature that astronomers can measure. Ionised hydrogen is almost totally invisible, except for one amazing feature: it makes things twinkle. When you look up at the night sky, you might see stars, and also perhaps a few planets. The planets are distinctive because they don't twinkle, while all the stars do.
This is because the stars are so far away that all their light travels along a single, very thin beam toward us. The thin beam is distorted as it travels through our constantly moving atmosphere, making the light look a little brighter or a little darker moment to moment. Planets are close enough to Earth that their beam of light is too large to be "scintillated" like stars. Indigenous Australians have used the twinkling of stars to forecast the weather for tens of thousands of years. The same thing happens with galaxies, which produce radio waves.
These waves are scattered by the electrons of the ionised hydrogen in exactly the same way as our own atmosphere scatters light from stars. Distant galaxies appear to twinkle, and that twinkling tells astronomers that space isn't empty, but filled with incredibly diffuse ionised hydrogen. What about the space between hydrogen atoms?
What is a vacuum made of? Is there a smallest possible scale? Is space fundamentally smooth, with infinite resolution, or is it made up of some very, very, very, tiny pixels? Protons and neutrons started to form within the first second; within minutes these protons and neutrons could fuse and form hydrogen and helium nuclei. After , years, nuclei could finally capture electrons to form atoms, filling the Universe with clouds of hydrogen and helium gas.
After around , years it left behind a bath of photons — the Cosmic Microwave Background that Penzias and Wilson accidentally detected. Within this were tiny ripples of matter that were stretched to enormous sizes during inflation, and in turn these became the seeds for the galaxies and galactic clusters we see today.
If this is how we think the Universe began, then how will it end? Big Bang: How the Universe was created. Share using Email. What created all the planets, stars and galaxies? Around the BBC. Because space itself is intimately connected with matter in the universe, as matter was created in the big bang, so was space. There is no 'empty space' that the universe is expanding into.
Newsletter Get smart. Sign up for our email newsletter. Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue. See Subscription Options. Discover World-Changing Science. Joel R. Primack, a cosmologist at the University of California at Santa Cruz , notes that the big bang involves physical processes quite unlike those of everyday experience.
For that reason, people often find it quite difficult to grasp what astronomers mean when they refer to an Rexpanding universe.
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