Innholdsfortegnelse for EG19 i New Scientist - The Essential Guides

THERE is nothing quite so remarkable and yet completely mundane as time. In our daily lives, we are swept along by its steady, unrelenting current, but our emotions can make it seem to slow down or speed up. When we study it, we find it isn’t the steady tick of a universal clock, but something woven into the fabric of the universe. It can squeeze and stretch and its perceived direction, which we take as a given, isn’t easily explained. This latest New Scientist Essential Guide aims to capture the mysterious essence of time in all its guises. These range from the malleable time in Albert Einstein’s relativity through to the strange treatment of time in quantum mechanics. On the way, we grapple with what time really is, how we…

The roots of thermodynamics lie in efforts to understand the steam engines that powered the industrial revolution of 18th and 19th-century Europe. During that time, the French engineer Sadi Carnot realised that their heat always tends to dissipate, moving to cooler regions. Anything that goes against this grain requires additional energy to power it. This movement from hotter to cooler is an expression of a more fundamental drive in the universe: disorder, as measured by entropy, always increases. The specifics don’t matter – heat always flows, flipped coins always jumble, burning logs always turn to ash. Entropy increase is so universal that many physicists propose it is why we see time flowing. It is certainly why our hearts must constantly pump blood, supplying our cells with energy as a temporary…

TIME dilation effects have been demonstrated in many experiments. One, in 1971, sent some of the most accurate clocks we have made yet, atomic clocks – which work using lasers to bounce the electrons in an atom at a given frequency – flying on aeroplanes. The clocks on planes fell behind clocks that stayed put on the ground, due to the difference in velocity. Another, in 1980, showed that an atomic clock sped up when launched on a rocket 10,000 kilometres above Earth’s surface, where the planet’s gravitational field is weaker. In recent decades, time dilation has been tested to further extremes using atomic clocks. In 2018, Christian Lisdat at the National Metrology Institute of Germany and his colleagues put one of the most accurate atomic clocks, a strontium atomic…

PART of what turned me into a theoretical cosmology enthusiast as a child was watching the documentary A Brief History of Time and hearing about the mystery around the big bang. It showed how the equations that we use to describe space-time broke down into a singularity when we ran time all the way back to the beginning. When the film came out in 1991, popular science books and magazines used the term big bang to refer to the moment when our universe came to be. It was the beginning of time and the beginning of space, and thus the beginning of space-time. In a very basic way, this wasn’t super hard to relate to. For example, in my family’s own Jewish tradition, our origin story for the universe begins…

IT ALL started during the industrial revolution, when Victorian engineers were desperately trying to figure out why their coal-powered steam engines were so inefficient and improve the design and efficiency of existing labour-saving “engines”, like the waterwheel and windmill. This new industrial world represented an exciting playground for natural philosophers, where they could start to dissect the mystery of energy and the rules governing how it is transformed into useful work. Entropy was essentially a mathematical way to quantify heat that wasn’t available for doing useful mechanical work, such as driving a piston. In the 1840s, French engineer Sadi Carnot discovered that heat always tends to dissipate, moving to cooler regions. Anything that goes against this grain requires additional energy to power it. That too is because the jostling molecules…

Can you first explain how the idea of inflation became dogma? Inflation was based on an “aha!” moment around 1980. People were building grand unified models of particle physics, which encompass all the known fundamental forces and particles, except for gravity. To make the models work, they had to introduce fields with potential energy. When you couple these fields to gravity, their potential energy behaves a bit like an explosive: it causes the universe to blow up in size. The explosive expansion can turn a small, lumpy universe into a huge, smooth, flat universe like the one we see around us. The second insight, which persuaded many people, is that inflationary expansion isn’t perfectly smooth and uniform. The field that drives inflation fluctuates quantum mechanically, so that inflation lasts longer…

IN 1878, James Clerk Maxwell wrote: “The truth of the second law is therefore a statistical not a mathematical truth, for it depends on the fact that the bodies we deal with consist of millions of molecules… Hence the second law of thermodynamics is continually being violated.” What this means is there are rare interactions between atoms and molecules where entropy is lost instead of gained, as if the process were running backwards in time. For natural processes, like a cup of coffee inevitably going cold, violations in the form of a few energy gaining interactions make no difference to the overall trend towards a state with the lowest energy and most disorder. But things are very different in the nanoworld. Back in 2001, Denis Evans at the Australian National…

3000 BC: SOLSTICE MARKER A method used by ancient humans. An artificial hill with a vaulted central chamber can only be reached by a narrow passage. It is aligned so that the rising sun casts a ray into the narrow passage on the winter solstice – this is the only time of the year that the chamber gets any light. 1500 BC: SUNDIAL A sundial measures the passage of time using the motion of the sun across the sky. As the sun moves from east to west, the shadow of a sundial moves from west to east. It takes a full day for the shadow to move back to the same position. 600 BC : WATER CLOCKS One of the oldest instruments used to measure time, water clocks measure time by tapping…

How do you make an atomic clock? People have made atomic clocks for many decades. The traditional way is to shine microwaves onto atoms, such as caesium or rubidium, to make their electrons flip from one quantum state – known as spin – to another at regular intervals. This flipping is the tick of the clock. In the clocks I make, the principle is the same. But we use laser light and shine it on strontium atoms, so electrons undergo energy transitions between two stable orbitals – and that’s the tick. How good is your clock? There are three important performance metrics. First: how precise is your clock, or how well can you measure time? Second: how reproducible is it? This refers to whether you can get the same kind…

EVEN in the absence of clocks, schedules and calendars, our bodies still march to the beat of internal timekeepers called circadian rhythms. This innate evolved connection to the spinning of Earth on its axis ensures that biological processes occur at the right time of day or night, and is vital for our health. Not only will various organs work optimally at certain times, but the way our bodies respond to medicines and our likelihood of developing certain diseases is all tightly connected to whether our bodies are operating in time with the physical world around us. How does the body keep track of this clock? Light hits specialised cells on the retinas in our eyes that send signals about the time of day to a master clock in the brain.…

WITH access to artificial light, many of us are staying awake when our brains and bodies are expecting sleep, throwing the body into uncoordinated chaos. For evidence on why this is bad news, look no further than night-shift workers. This type of working pattern is so bad for our health that more than one report in the past few years has classified night shift work as “probably carcinogenic”. It is also linked to increased risk of type 2 diabetes, heart disease, stroke, sleep problems and depression. Divorce rates are high in this group, too. Today, the average Westerner spends 90 per cent of their life indoors. That means getting less light during the day and being exposed to more light at night. This pattern is increasingly being linked to disrupted…

When we talk about time, we frame it in terms of space. English speakers look “forward” to good times ahead and leave the past “behind”. A day flies by just as a ball does, while a deadline approaches the same way a tiger might. But the spatial metaphors we use vary from language to language, and some people think those differences affect our perception of time. The idea that language shapes thought is controversial. Critics argue that the words we use simply reflect thoughts that have emerged or been constructed through other means. Yet when we compare mental representations of time in speakers of different languages, there are hints that they influence the way people think about it. In Mandarin, earlier events are said to be “up” and later events…

PREDICTING the future is easy, if you are a physicist. Break a glass, and you can boldly assert that it will fall into a number of shards, assuming you know the initial conditions. Knowing the past is more difficult – you need to store much more information to piece a pile of broken glass back together. This “causal asymmetry” makes it easier to determine cause and effect and thus place events in order. But it doesn’t exist in the quantum world. Among its weirdest predictions is the notion of quantum superposition: the idea that an object can be in two different states at the same time. This is often taken to mean that an event can be said to have happened and not happened, or that a cat – to…

THE idea of time crystals was first speculated by MIT physicist and Nobel laureate Frank Wilczek in 2012, while he was teaching a class on ordinary crystals, such as salt or snowflakes. In a typical crystal, the atoms or molecules are tightly arranged in regularly repeating patterns in three-dimensional space, resembling a lattice. Wilczek thought it might be possible to create a similar crystal-like structure in time, which is treated as a fourth dimension under relativity. Instead of regularly repeating rows of atoms, a time crystal would exhibit regularly repeating motion. Many physicists were sceptical. They argued that a time crystal whose atoms could loop forever, with no need for extra energy, would be tantamount to a perpetual motion machine – forbidden by the laws of physics. Wilczek countered that…

IT IS well established that people have a bias towards the present. We focus on salient attractions in the moment at the expense of the health, well-being and financial stability of our future selves, community or descendants. In business and finance, this bias surfaces as short-sighted corporate decisions. In politics, it is the way governments ignore the lessons of history and the future consequences of their policies. And on slow-burning problems like climate change, it manifests as the unwillingness to make small sacrifices today that could make a major difference tomorrow. Instead, all that matters is next quarter’s profit, winning the election or sating some other near-term desire. These time-blinkered perspectives cannot be blamed on one single cause. It is fair to say, though, that our psychological biases, or “temporal…

As time passes in a closed system – one where nothing can go in or out – entropy will always increase. This is the second law of thermodynamics, and it is perhaps the most profound of the four laws of thermodynamics. Its importance is best expressed by sketching out a situation that violates it. Imagine placing 20 coins, heads up, on a tray, filming it as you give it a shake and then playing the film backwards. The coins start out as a jumbled mess, but all jump and eventually come to rest with the same side up – an unreal, slightly creepy sequence. Similarly, imagine an egg yolk and white reassembling themselves after you’ve cracked it open, or even a world where it’s just as easy to pair up…

WHILE most physicists agree that there is a link between entropy and the arrow of time, how they relate is disputed. Some physicists think increasing entropy gives time its arrow, while some say the arrow is just an illusion. Others think we lack a basic understanding of time and, perhaps, marrying the quantum and classical worlds together will lead us to a new way of thinking about it. Some theories do away with entropy in the picture of time altogether. However, some solutions to the equations of general relativity appear to provide a route to the past. Einstein’s theory predicts that time runs more slowly in strong gravity, so you grow old more slowly living in a bungalow than in a skyscraper: being closer to the ground, you are in…

IN 1967, the second was official redefined using a microwave atomic clock accurate to 1 second every 300 years. These work by driving an electron to bounce between two energy states within an atom, in this case caesium-133, and counting the number of bounces. It is a time standard that persists today, even if the accuracy of microwave atomic clocks has improved to the point that the best caesium clocks now keep time with an accuracy of 1 second in roughly 300 million years. And it is a measure that has served us well. The steady backbeat of the caesium atom’s vibration underpins all manner of modern technologies, from GPS and smartphones to the internet and electricity grids, all of which require exquisitely precise synchronisation. But it is no longer…

WHAT would happen to the human body and mind if we did away with time altogether? In1962, French geologist Michel Siffre set about doing just that, spending 63 days in a deep cave, cut off from all light except his torch. His escapade revealed that the body has its own clock that will shift if not kept in check by exposure to both light and dark. In a follow-up experiment, Siffre extended his cave time to an epic six months, during which his circadian rhythm stretched to 48 hours, his sense of time passing slowed and he also became depressed, much like we see with shift workers. Experiencing a marked contrast between day and night is important. Our light exposure influences the amplitude of our biological rhythms: they become flatter…

A DEEP understanding of time has proved almost superfluous to scientific progress. In physics, for example, Isaac Newton’s laws of motion, Albert Einstein’s general relativity and quantum theory don’t require us to know the nature of time to make them work. Even clock makers needn’t understand time. Clocks, however, give us a clue about where to concentrate our efforts because a clock needs some kind of moving part to gauge the passing of time. This can be the tick-tock of an escapement, an oscillating quartz crystal or the ejection of a particle from a radioactive atom – one way or another, there must be movement. When something moves, it changes. Clocks tell us that time is inextricably linked somehow to change. Yet that only takes us so far. From this…

ACCORDING to Einstein’s special theory of relativity, there is no way to specify events that everyone can agree happen simultaneously. Two events that are both “now” to you will happen at different times for anyone moving at another speed. Other people will see a different now that might contain elements of yours – but equally might not. The consequence of this is a picture known as the block universe: the universe seen from an impossible vantage point outside space and time. You can mark what you think is “now” with a red dot, but there is nothing that distinguishes that place from any other, except that you are there. Past and future are no more physically distinguished than left and right. There are things that are closer to you in…

SEARCHING for time’s arrow in the underlying, microscopic laws of physics certainly draws a blank. They give us no reason to think atoms, molecules and so on can’t move backwards as well as forwards in time, much as they (and we) move freely in three dimensions of space. These laws don’t differentiate between past, present and future, or between cause and effect. We have to zoom out a little to find a physical law that does not work just as well back in time as it does forwards. “That distinction only becomes relevant in the macroscopic world, where our incomplete information about the precise physical configuration of a system leads us to perceive an arrow of time, and to put causes first and effects after,” says physicist Sean Carroll at…

THE first big rule of classical causality is that things have causes. They don’t just happen of their own accord. If a ball moves, the likelihood is someone kicked it; if an apple falls from a tree, it’s because its weight became too great for the branch it was hanging from. Second, effects follow causes in a predictable, linear manner. You swing your leg, make contact with the ball, and off it moves, in that order and no other. Third, big effects grow up from little causes. A piston, for example, starts to move when a lot of individual hot atoms hit against it and push it a certain way. The laws of thermodynamics, which govern the way atoms move, then provide certain rules about what causes can precipitate what…

In most science-fiction scenarios, sending messages back in time requires information to move faster than the speed of light. But in theoretical universes where causal loops are allowed, such law-breaking physics isn’t required. A causal loop is a classic time travel conundrum. If you send information to the past – say, you give Albert Einstein the formula E=mc ² before he theorises it himself, then he publishes it and you go on to find it in a textbook – you would create a situation in which the information has no true origin. In 2022, researchers mathematically modelled a set of theoretical universes where all that is known is that there are people who can discern information and act on it, but who can’t communicate faster than light. They didn’t require…

THE flow of time is an enigma; many physicists even suggest it is just an illusion. But clock time is our own invention. We define it by its basic units – the hours, minutes and seconds that break up the day. Since astronomer Christiaan Huygens invented the first pendulum clock in the 17th century, we have been steadily improving the accuracy of scientific clocks, with phenomenal results. Nowadays, the most impressive machines can measure each second so accurately that they wouldn’t miss a beat in 20 billion years, longer than the age of the universe. But it turns out there may be a price to pay for such accuracy. To produce their ticks, clocks need a source of energy. A grandfather clock must be wound up and a wall clock…

ATOMIC CLOCKS The most accurate clocks we have are atomic clocks. These work by exploiting the fact that an atom of caesium, or some other element, emits visible light or microwaves when one of its electrons drops from a high energy state to a lower one. Tuning a laser to just the right frequency lets researchers bounce an electron between two of these energy levels. It is this frequency that serves as the tick of an atomic clock. Most atomic clocks rely on the frequency of the microwave radiation emitted when electrons in caesium-133 atoms change energy states. Next-generation clocks that use strontium atoms have at least three times the precision, barely gaining or losing a second over 15 billion years. Yet this is not enough for many physicists. MOLECULAR…

OUR brains have a complex assortment of neural machinery tasked with imposing temporal order. Put this way, the brain can seem like a Victorian clock-maker’s workshop, stuffed with all manner of contraptions, each designed to measure a different aspect of time. There is the master circadian clock in the suprachiasmatic nucleus, which relies on pendulum-like oscillations inside proteins to keep us in sync with the rhythms of the sun. Then there are collections of brain cells that govern the sub-second timing for quick-fire physical reactions. Yet neither of these can account for the familiar sense that time passes, or that we pass through events as if being dragged along by a current. “Our experience of the world depends on the ordering of what we interpret as events and causalities, and…

IT ALL started back in 1900, when Max Planck assumed, purely to make the maths work, that the electromagnetic radiation emitted by a perfectly absorbing “black body” comes in the form of discrete packets of energy, or quanta. In 1905, Albert Einstein took that idea and ran with it. In his Nobel-prizewinning work on the photoelectric effect, he assumed that quanta were real, and all electromagnetic waves, light included, also act like discrete particle-like entities called photons. Work in the 1920s then reversed the logic. It found that discrete, point-like particles such as electrons also come with a wavelength, and sometimes act like waves. Physicist Richard Feynman called this wave-particle duality the “only mystery” of quantum physics – the one from which all the others flow. You can’t explain it…

IT WAS common knowledge among students at the University of Cambridge that whoever obtained the best marks in the final part of the mathematical tripos exams would be summoned to see Stephen Hawking. I had just got my results and had come top. Sure enough, I was invited for a discussion with him. I made my way to his office deep in the labyrinth of the department of applied mathematics and theoretical physics, which was housed in a creaking Victorian building on the banks of the river Cam. Stephen’s office was just off the main common room, and even though it was noisy there, he liked to keep his door ajar. I knocked, paused and slowly pushed it open. I didn’t quite know what to expect on the other side…

IN PHYSICS today, we have two pictures that don’t match up. First is general relativity, Albert Einstein’s set of equations that describe the way classical objects are affected by gravity. It sets out the three dimensions of space and the fourth dimension of time as part of the same entity, woven together in the fabric of space time. That works extremely well to a point. It is excellent at describing the way space-time bends around large masses, the way time slows down when objects move close to the speed of light, and anything that concerns the dynamics of things larger than an individual particle. But the fundamental force of gravity doesn’t fit into quantum mechanics, our best description of the very small. Atoms and subatomic particles seem to follow a…

OUR explanation of the big bang is an extrapolation based on the equations of general relativity and our observations of a universe that, over billions of years, has been expanding and cooling from something denser and hotter. We cannot see back to the very moment of the big bang. Instead, our observations take us back to some 380,000 years after a putative beginning, when the universe had cooled enough for the first atoms to form, sending radiation pinging through the cosmos. We hear that radiation today as the hiss of the cosmic microwave background. With Albert Einstein’s theories, we can go back further, to the first microsecond, when the entire observable cosmos was about the size of our solar system. Beyond that, we are all at sea, with neither theory…

700 MILLION YEARS AGO: SNOWBALL EARTH These days, if you want to see a glacier near the equator, you must scale the rarefied heights of Mount Kenya or the Ecuadorian Andes. Around 700 million years ago it was a bit less of an effort. In fact, you’d struggle to find somewhere that wasn’t frozen over. The Cryogenian period was so called because the planet was repeatedly sheathed in ice in a series of “snowball Earth” episodes. The greatest of these Cryogenian snowballs, the Sturtian glaciation, began 716.5 million years ago. In the space of a few years, land and sea across the globe were swallowed up by sheets of ice that eventually became kilometres thick. They did not melt for another 55 million years. Earth was literally a snowball, like…

THERE are a couple of ways the universe might end. “The expansion could continue forever, or it could stop and reverse,” says Katie Mack at North Carolina State University, author of The End of Everything (Astrophysically speaking). That second, “big crunch”, scenario has generally been more favoured. On its own, the density of matter in the universe seems to suggest that the pull of gravity will eventually overwhelm space-time’s expansive momentum. The universe will reach a zenith of expansion and then begin contracting towards a kind of big bang in reverse. That doesn’t necessarily mean the end of time. A sub-genre of big-crunch scenarios proposes that the universe bounces back. In such “cyclic” cosmologies, time has no obvious end, but is constantly recreated – a process that presumably accounts for…