Innholdsfortegnelse for EG24 i New Scientist - The Essential Guides

EXOPLANETS LET’S start close to home – conceptually speaking. Given the vastness of the universe and the number of stars it contains, it would take a peculiarly blinkered view to believe that our solar system, with its ordered retinue of eight planets, is the only such collection of worlds in our galaxy. Only in the past three decades, however, have our telescopes been able to see planets orbiting other stars, known as exoplanets. We have now discovered more than 5000 of them, and most don’t look anything like Earth. HOT JUPITERS The surprises with exoplanets started in 1995 with 51 Pegasi b, the first planet to be discovered orbiting a main sequence star, the most common type of star in the galaxy, other than the sun. At about half the…

THE first hints that something dark permeates the universe came in the 1930s, when astronomers spotted something odd. Clusters of galaxies were rotating far faster than they should have been. At such rotational speeds, from our understanding of gravity and dynamics, some of their constituent parts should have been flung off into the depths of space, but they were holding together. Maybe, suggested Swiss astronomer Fritz Zwicky, there was some matter that we couldn’t see holding everything in place. The hunt for Zwicky’s “dark material” never really took off, partly because there were lots of questionable assumptions behind his assertion. Things changed in 1970, though, when Vera Rubin and Kent Ford at the Carnegie Institution of Science in Washington DC made a surprising discovery about the Andromeda galaxy. They noticed…

ASCEPTIC might view complications such as dark matter and dark energy as today’s equivalent of the Ptolemaic epicycles, the convoluted tweaks made to the model of the planets’ motions to maintain the fiction that they were all revolving around Earth. I have more skin in this game than most: I introduced the mystery elements of dark matter and dark energy into our standard cosmology. So, is the model I helped construct right; is our cosmology a true reflection of reality? Dark energy is the current incarnation of the cosmological constant. Albert Einstein introduced this in 1917 with the intention of maintaining a static universe that was neither expanding nor contracting, a situation he seemed to have taken for granted. He came to dislike it when observations in the following decade…

FOR almost a century, physicists attempting to understand the most fundamental layers of reality have been inadvertently describing systems without knowing what is going on inside them. In the 1930s, when Enrico Fermi worked out how a neutron decays into a proton and spits out an electron – known as beta decay – he did so only by considering the electrons, protons and neutrons involved. Only decades later, when physicists discovered an intermediary particle called the W boson, did they realise there was a deeper layer of interactions playing out at tinier scales. From today’s perspective, Fermi’s description is the prime example of an effective field theory (EFT), a mathematical framework that allows us to divide reality into different size scales and analyse them separately. In this way, physics behaves…

TO HUMAN eyes, the night sky is serene, save for the moon and a few wandering planets. Peer into space with a telescope that can scan the entire sky in days, however, and it appears as a great cosmic fireworks display – a riot of bangs and flashes radiating across the electromagnetic spectrum, from radio waves to gamma rays. Let’s start with something relatively familiar: a stellar flare such as our sun’s solar flares – the source of the spectacular northern lights. A stellar flare is an explosion in the atmosphere of a star that results in an intense flash of radiation across the electromagnetic spectrum. When our sun flares, we see a sudden burst of brightness before it quickly returns to quiescence. Something similar goes on in stars of…

THROUGHOUT all of human history, people have looked up at the night sky and wondered about the universe and how it came to be. In one respect, however, we’re very different from our ancestors: we more or less understand what we’re looking at. Take an image from the Hubble Ultra Deep Field (right), for example. We know the blotches of light on it aren’t stars, but entire galaxies similar to our Milky Way. And because it takes time for light to travel through space, we aren’t seeing what these galaxies look like today, but rather what they were like over 13 billion years ago, a few hundred million years after the big bang. Just over a century ago, scientists didn’t have the faintest understanding of our universe’s distant past, and…

AN INSTANT after the big bang, a vast shower of particles was released into the cosmos. Ever since, they have been flooding through space, carrying with them secrets from the dawn of time. These ghostly things are neutrinos, elementary particles that we know exist but that are exceedingly difficult to detect. They pass clean through matter: 100 trillion of them are streaming through your body every second and you never notice. A fabulous prize awaits if we could spot them, though. The big bang theory predicts that neutrinos created in the first second of the universe would still be flowing through the cosmos today. We call this the CNB, or the cosmic neutrino background. If we could detect it, it would paint us an unprecedented picture of the universe in…

NEARLY 50 years ago, physicist Frank Wilczek took a walk that would change the course of particle physics forever. On that walk, he had the germs of two profound ideas. The first was how a theoretical particle, later dubbed the Higgs boson, might interact with other particles. This would be how the Higgs was found decades later. The second idea has taken a little longer to catch on. Wilczek, who is based at the Massachusetts Institute of Technology, had imagined a way that very light – essentially massless – particles could be made. He talked to his colleague, the late Steven Weinberg, who had been thinking along the same lines. Together, they predicted a class of particles we now call axions. Axions, if they exist, would abide by the strange…

THE “cosmological principle” says that the universe is the same everywhere in all directions. It grew out of an essential tenet of cosmology: Nicolaus Copernicus’s argument, made in the 16th century, that Earth doesn’t occupy a special place in the universe, also known as the Copernican principle. But the cosmological principle didn’t earn its current exalted status until the 1920s, when it made it possible to extract a workable model of the universe from Albert Einstein‘s new theory of gravity – general relativity. For more on general relativity, turn back to Sean Carroll’s introduction in Chapter 1 Unfortunately, general relativity is as complex as it is beautiful. Ten intertwined equations balance matter and energy on one side and the warping of space-time on the other. The only way to solve…

We tend to think of space-time as the underlying structure of the universe. But whether it really is fundamental or emerges from something deeper is a question that keeps physicists up at night. “It’s not just a philosophical question that you discuss over a beer,” says Marika Taylor at the University of Birmingham in the UK. “It is actually something that comes into the calculations that people do.” The best place to start is quantum mechanics, which describes the behaviour of subatomic particles. Famously counterintuitive, one of the theory’s core tenets is that connections between particles can transcend our usual notions of space and time. This happens via a phenomenon called entanglement, in which particles can affect each other’s properties even when they are half a universe apart. Cosmologists now…

YOU will no doubt have heard of space‑time. It is, after all, a staple of science fiction, and part of the everyday language of science. It is also part of life, when you stop to think about it. If you want to meet a friend for coffee, you have to tell them where you are going to be – your location in space – but you also need to let them know when you will be there. Both bits of information are necessary because we live in a four-dimensional continuum: three-dimensional space and everything within it, from steaming coffee machines to stars exploding in faraway galaxies, all happening at different moments of one-dimensional time. “Space-time” is simply the physical universe inside which we and everything else exist. And yet, even…

IN A sense, we are at the centre of the universe – but only because we can see the same distance in every direction, giving us a perfectly spherical observable universe. The speed limit of light combined with the inexorable expansion of the cosmos means that we can see about 46 billion light years in every direction. What lies beyond this horizon? That is a mystery we may never solve. But there are clues. Two competing effects govern the overall size of the universe: gravity and dark energy. All matter has mass, which causes gravitational forces that pull everything towards everything else. To their surprise, however, cosmologists in the early 20th century found that distant galaxies seem to be hurtling away from us. The mysterious force causing this strange expansion…

Astronomical observations and cosmological considerations suggest that there is a lot of stuff missing from our inventory of the universe. According to cosmologists’ best estimates – based on data that has been tested for decades now – around 85 per cent of the universe’s matter is exotic stuff that doesn’t reflect, emit or absorb light. It’s known as “dark matter”. The only force that this hypothetical stuff definitely deigns to interact with, as far as we know, is gravity. This makes it incredibly difficult to detect. A slew of ingenious experimenters have attempted to find traces of dark matter in situations as varied as detectors placed at the bottom of mineshafts and in the data from CERN’s Large Hadron Collider. So far, everyone has come away empty-handed. But no one…

THE James Webb Space Telescope was, prior to its launch, perhaps the most hotly anticipated scientific instrument ever. It is a time machine that helps us see back to the enigmatic era of the universe’s first stars, which we know precious little about. Unreal, too, because it can reveal the atmospheres of potentially habitable planets orbiting other stars more clearly than ever before. It is no exaggeration to say that this telescope, with its gigantic gold-plated mirror, is transforming our view of the universe and our place in it. The JWST’s story begins around Christmas 1995. That year, the world was gripped by O. J. Simpson’s murder trial, Bridget Jones first appeared in print and Forrest Gump won big at the Oscars. For 10 December days, the Hubble Space Telescope…

A black hole is a region of space so dense that nothing, not even light, can move quickly enough to escape. At least that was the thinking until the 1970s, when Stephen Hawking calculated that black holes aren’t completely black after all. Instead, Hawking argued, they slowly give off radiation – now known as Hawking radiation – that eventually means the black hole will evaporate. Hawking’s calculations created a problem. Quantum theory says information can never vanish, so what happens to the information that has fallen into the black hole? Where does it go? This is the black hole information paradox. It has troubled physicists for decades because it highlights the profound disconnect between general relativity, Albert Einstein’s theory of gravity from which black holes were summoned, and the laws…

WHEN I started my career, more than 50 years ago, no one was sure that black holes existed. Today, there is no longer any doubt. We know they form from collapsing stars and that supermassive ones sit at the centres of galaxies. We have even taken a picture of two of them. But an important open question remains: could smaller black holes have formed in the early universe, shortly after the big bang? The question matters more than you might think. Back in the 1970s, I was working on this idea under the supervision of Stephen Hawking, who had started to think about the possibility of these “primordial black holes” just a few years before. Our work together set the trajectory of my career. We still don’t know if they…