If you assume the best about another species and you're right... Great but if they turn out to be killers. Your species is wiped out. If you assume the worse about another species then the logical thing to do is wipe them out before they can harm you. If you're wrong about them, at least you're still alive. Even if not competing for resources, the logical thing to do is wipe them out before they can wipe you out. If going by logic not emotion, other intelligent species will always be a risk.
Pets: Dogs are able to detect speech and distinguish between different languages, study finds | Daily Mail Online
I think the argument is moot, tbh. As the original article points out, the chances of there being another civilisation in exactly the right place at exactly the right time are minuscule. Plus the fact that FTL travel breaks the laws of physics as we know them. Ok, there could be something we haven't discovered yet, but the idea that it's possible to flit around the galaxy like it was a shopping expedition seems to me highly unlikely, given the vastness of spacetime as we know it. It would be like a microbe on a grain of sand in Crosby setting out to find its cousin in Sydney, without even knowing which direction to go in. Or that Sydney exists. Imo, routine interstellar travel is the stuff of science-fiction - sadly (it would be really exciting if it were possible). The only thing that seems within the realms of possibility would be a multi-generational space ark, but that would still have the same issue of being in the right place at the right time. Far more chance of being wiped out by a comet than by aliens, I think.
Or, indeed, like cicadas do on earth. Or those alien eggs in, er, Alien. Or Bagpuss at the end of each episode. And the little mice.
We could play fantasy whatiffery forever - where would sci-fi be without imagination? - but I doubt we'll ever know. I know that there are proposals such as the Alcubierre Drive, but they are highly speculative, requiring exotic types of energy which aren't even known to exist. My 50p would be on the universe being full of life forms, in various stages of development - all, like us, tied to their own star system because of the vast unnavigable gulf of interstellar space. I'd be happy to be proven wrong, of course. But just imagine the new heights of burbling our Boris would get up to if faced with an alien visitation. We could send the rambling halfwit up to meet them... please log in to view this image ...they'd leave utterly baffled.
The Large Hadron Collider blips that could herald a new era of physics Hints of a new particle carrying a fifth force of nature have been multiplying at the LHC – and many physicists are convinced this could finally be the big one PHYSICS 12 January 2022 By Harry Cliff please log in to view this image Marcus Marritt At half past six on the evening of 20 January 2021, amid the gloom of a long winter lockdown, a small team met on Zoom to share a moment they knew might change physics forever. “I was literally shaking,” says Mitesh Patel at Imperial College London. He and his team were about to “unblind” a long-awaited measurement from the LHCb experiment at the CERN particle physics laboratory near Geneva, Switzerland – one that might, at long last, break the standard model, our current best picture of nature’s fundamental workings. The measurement concerns subatomic particles known as “beauty” or “bottom” quarks. Over the past few years, their behaviour has hinted at forces beyond our established understanding. Now, with the hints continuing to firm up, and more results imminent, it’s crunch time. If these quarks are acting as they appear to be, then we are not only seeing the influence of an unknown force of nature, but perhaps also the outline of a new, unified theory of particles and forces. That is a big if – but many particle physicists are on tenterhooks, myself included.”I’ve never seen something like this,” says Gino Isidori, a theorist at the University of Zurich, Switzerland. “I’ve never been so excited in my life.” For all its dazzling success in describing the basic ingredients of our universe, the standard model of particle physics has many shortcomings. It can’t explain dark matter, the invisible stuff that keeps galaxies from flying apart, or dark energy, which seems to be driving the accelerating expansion of the universe. Nor can it tell us how matter survived the big bang, rather than being annihilated by an equal amount of antimatter. What’s more, it has several apparently arbitrary features that beg deeper explanations. Clearly, the standard model isn’t the whole picture. To complete it, we need to break it. CERN and Mont Blanc: Explore particle physics and glaciers in Switzerland on a New Scientist Discovery Tour The saga of the beauty quarks began in the mid-2000s when Gudrun Hiller, a theoretical physicist then at the University of Munich, Germany, was panning for insights in a flood of data from the Belle experiment in Japan and the BaBar experiment in California. These “B-factories” produced beauty quarks by colliding electrons with their antiparticles, positrons. The beauty quarks would live for an instant – around 1.5 trillionths of a second, on average – before decaying into other particles. A strange beauty Hiller was particularly interested in an extremely rare decay where a beauty quark transforms into a strange quark, the third heaviest of six types of quark. In doing so, it emits two oppositely charged muons, heavier versions of electrons. Rare decays such as these are very valuable, as they could be strongly influenced by unknown forces of nature, should they exist. The idea is to make the most precise measurement possible of such decays and compare them with the most precise predictions theorists can muster using the standard model. If the two disagree, you have evidence for a new force. The trouble was, theoretical predictions of how often a beauty quark should transform into a strange quark and two muons were plagued by uncertainties from quantum chromodynamics (QCD), the theory of the strong force that governs how quarks interact with one another within the standard model. This made it very hard to make any meaningful comparison with experimental measurements – any discrepancy could be down to the imprecision of the predictions. “We realised that we hit a wall,” says Hiller. Undeterred, she and her collaborator Frank Krüger realised that if you look at how often this decay occurred compared with a similar decay that spits out electrons instead, the nasty uncertainties from QCD cancelled out. The ratio of the two decays could be predicted very precisely – but would be sensitive only to forces pulling on the electrons and muons with differing strength. That was a long shot. All known forces pull on the two particles equally, and the assumption was that any undiscovered forces would do so too, meaning Hiller and Krüger’s ratio wouldn’t reveal anything new. A decade later, collisions at CERN’s Large Hadron Collider (LHC) began producing a torrent of beauty quarks, which were recorded and analysed by the LHCb experiment, one of four large particle detectors on the 27-kilometre accelerator ring beneath the French-Swiss border. Now, physicists could really start to put these rarest decays under the microscope. As they did so, intriguing anomalies began to emerge. The first came when early measurements suggested that decays producing a strange quark and two muons happened less often than the standard model predicted. Then, in 2013, the LHCb experiment released a new measurement that analysed the angles that the particles produced in these decays went flying out at. This time, there were even stronger hints of deviations from the standard model. And yet there were still sufficient theoretical uncertainties to leave room to quibble. Could Hiller and Krüger’s ratio help? In 2014, LHCb released the first measurement comparing how often beauty quarks decayed into muons and electrons. To almost everyone’s surprise, the data once more disagreed with the standard model. Beauty quarks appeared to be decaying to muons less often than to electrons. Analysis concluded there was less than a 1 per cent chance the deviation was purely down to some random statistical wobble in the data. This was still a long way short of the gold-standard statistical significance required to declare a discovery in particle physics, which corresponds to a 1 in 3.5 million chance of the result being a fluke. Strong deviations Still, when you combined the measurements of the muon-to-electron ratio, the angles and how often the decays happened, a coherent picture did seem to be emerging. Since then, almost every time a measurement has been updated with yet more beauty quark data, the deviations from theory have become stronger. Almost, because there was one notable exception. When the Hiller-Krüger ratio was updated with more data in 2019, the measured value moved towards the standard model value. “We really thought we had it,” says Patel, who led the work. “We ended up feeling gutted.” So, when Patel and his colleagues met on Zoom in January 2021 to unveil a new measurement, emotions were running high. “These anomalies could be the real deal” University of Cambridge experimental physicist Paula Alvarez Cartelle pushed the button to reveal the result. The measured value of the ratio had stayed almost exactly the same, but the error on it had shrunk, creating an unmistakable tension with the standard model prediction. There was now less than a 1 in 1000 chance the discrepancy was a statistical fluke. Everyone on the call erupted. “There was an awful lot of swearing,” says Patel. However, the team also felt the weight of responsibility; they knew the result would create huge excitement. As Alvarez Cartelle puts it: “You don’t want to think, ‘I just broke the standard model’, but at the same time you’re a bit, ‘Oh ****!’.” please log in to view this image Anomalies come and go in particle physics, and no measurement of the muon-electron ratio on its own has yet crossed the threshold of statistical certainty for it to be regarded as a definitive discovery. But there is a coherency to what have become known as the “B anomalies” that has led a growing number of physicists to regard this as the real deal. “I’ve turned into a believer,” says Ben Allanach, a theorist at the University of Cambridge. “There’s always healthy scepticism, but the fact that it’s coming from lots of different angles and saying the same thing is pretty convincing.” In which case, what could be causing these anomalies? Allanach has spent the past few years trying to figure that out. For him, the most promising candidate is a force carried by a hypothetical particle known as a Z prime. This would be very heavy, electrically neutral and, crucially, would interact with electrons and muons with different strengths. This could explain why beauty quarks decay into muons less often than to electrons – the Z prime is stopping them. This could also explain one of the most mysterious, seemingly arbitrary features of the standard model: the fact that matter particles come in three “generations”. The first comprises the familiar particles that make up most ordinary matter: the electron, the electron neutrino and the up and down quarks. The second contains heavier copies of these particles: the muon, muon neutrino, charm and strange quarks. And the third generation is heavier still: the tau, tau neutrino, top (or “truth”) and beauty quarks. The existence of these generations has long been a puzzle, as has the peculiar fact that the masses of the matter particles vary so wildly, with the top quark being around 350,000 times heavier than the electron. The different generations could be explained if the beauty quark anomalies are revealing the presence of a new force that acts almost exclusively on the third generation of particles. “The model I’m working on contains a symmetry which means that if you squint a bit, only the third generation is allowed to have a mass,” says Allanach – which would explain why these particles are so heavy. The implications of this new force wouldn’t end there. In the second half of the 20th century, physicists discovered that the three forces of nature described by the standard model – the strong and weak forces and electromagnetism – could each be described using a mathematical symmetry. In the 1970s, there was a big push to bring all three forces together under a single bigger symmetry, to create a so-called grand unified theory, which promised to unify these forces and the matter particles into one elegant structure. The problem was that the various grand unified theories predicted that protons should decay, while every experiment performed failed to see any sign of that. What’s more, the energies required to probe these theories are over a trillion times higher than even the LHC can achieve, meaning that the new particles they predict are well out of experimental reach. As a result, the quest to unify the forces and the matter particles has been stalled for decades. The B anomalies appear to be resurrecting aspects of the old grand unified theories, but at far lower energies than anyone had expected. “What we’re doing is putting in a tiny bit of symmetry – it’s an element of a grand unified theory, but it’s only a little one,” says Allanach. He believes that the hints of a new force we are seeing at the moment could be a low-energy remnant of a much grander symmetry that only becomes apparent at very high energies. In other words, we might be catching a glimpse of the edge of a grand unified theory. Hiller pioneered an alternative explanation for the B anomalies that goes further still – a particle known as a leptoquark. Again, a leptoquark would be the carrier of a new force. This force would transform quarks directly into electrons, muons and taus, collectively known as leptons – hence the particle’s name. Unlike Z prime models, leptoquark models also aim to explain a second set of anomalies that have appeared in another type of beauty quark decay, this time to charm quarks, while pointing to a unified theory that’s much closer at hand in terms of energy scales. The colour violet Isidori is a proponent of leptoquarks. He says the models represent a “change of paradigm” compared with the old grand unified theories. While the old ones looked for symmetries that unified all three forces, the modern leptoquark models instead unify leptons with quarks. They do this by differing from the standard model in a crucial way. In the standard model, the equivalent of electric charge for the strong force, which acts on quarks, is known as “colour”. It comes in three varieties, red, green and blue. Leptons don’t carry colour, so they don’t feel the strong force. In leptoquark models, however, there is a fourth colour, sometimes labelled violet, which arises from an enlarged version of the symmetry that describes the strong force. This larger symmetry then breaks down into the usual three-colour strong force with red, green and blue quarks, while the leftover fourth colour is carried by the leptons. Leptons are really just differently coloured quarks. please log in to view this image Painstaking analysis of particle decays in the LHCb detector is uncovering unexpected anomalies CERN, LHCb This is heady stuff – but the challenge now is to prove that these anomalies are the real deal. Isidori, for one, is convinced. “For me, the evidence is already very solid,” he says. But not everyone agrees. Although a series of unfortunate statistical flukes now seems like a very unlikely explanation given the range of different anomalies, the looming spectre is the chance of a conspiracy of missed biases, either in the theoretical predictions or the experimental measurements, or perhaps both. New measurements are already under way at LHCb to confirm the picture and test for hidden experimental effects. In October 2021, my University of Cambridge colleague John Smeaton and I performed a new measurement of the Hiller-Krüger ratio using an unexplored part of the LHCb data sample. It revealed very similar effects to those seen in March, strengthening the case for a new force. Meanwhile, the growing excitement around the anomalies has awoken the two big beasts of the LHC, the ATLAS and CMS experiments. In 2012, they discovered the Higgs boson, the long-predicted standard-model particle that gives all other fundamental particles their mass, and are now beginning to think about ways they might spy the predicted Z primes or leptoquarks. In Japan, the Belle II experiment is gradually accumulating data that will allow it to independently check several of LHCb’s results. Later this year, an upgraded LHCb will begin collecting data at a far higher rate than before, allowing us to seek out even rarer decays where the anomalies could be even stronger. If the emerging picture is confirmed, we are in for a revolution in our understanding of the constituents of nature that could reveal a deeper structure beneath the standard model, while perhaps even giving us a handle on the nature of dark matter or the strange properties of the Higgs boson. If that happens, it will be the greatest discovery in fundamental physics since the standard model was put together. The stakes are high and the game is on. New Scientist audio You can now listen to many articles – look for the headphones icon in our app newscientist.com/app More on these topics: ELECTROMAGNETISM PHYSICS HADRON COLLIDER
Ancient Mars may have had a liquid ocean despite freezing temperatures A model based on Earth’s oceans and atmosphere explains how Mars could have been cold and wet 3 billion years ago SPACE 17 January 2022 By Alex Wilkins please log in to view this image Artist’s view of ancient Mars, with frozen ice sheets and glaciers flowing into the northern ocean NASA / USGS / ESA / DLR / FU Berlin (G. Neukum). Mars may have had a liquid water ocean 3 billion years ago, even if the temperature at the surface was below freezing. There is strong geological evidence that Mars once had an ocean, such as ancient shorelines, but it is unclear what conditions could have made possible all the features seen on the planet today. If it was warm enough for a liquid ocean, there should be valleys scarred by rivers, but these haven’t been observed. If the climate was too cold, there would have been land ice, which doesn’t fit with our observations of rock deposits from historical tsunamis. Now, Frédéric Schmidt at the University of Paris-Saclay in France and his colleagues have found that a liquid ocean could have existed with an above water temperature of just below freezing. In this scenario, the ocean is kept warm enough to remain liquid by water circulation that could give it a temperature of around 4.5°C . Schmidt and his team used a model that simulates how Earth’s oceans and atmosphere interact, but changed the parameters to match Mars’s ancient environment, such as its atmospheric gas makeup and a lower sun power. As well as a liquid ocean, the model also suggests there may have been moderate rainfall along the ocean shores and a largely frozen southern region. Read more: Ancient Mars lake had fast-moving floods that carried huge boulders The ancient climate features that the model produced were similar to Earth’s billions of years ago, and would have contained some of the key ingredients for microbial life. “If we could travel in time to 3 billion years ago, we could live on this ancient Mars with just a spacesuit for oxygen,” says Schmidt. “Pressure, clouds, liquid water, ocean, rain, snow and glaciers: all of them were very similar to Earth today. Only oxygen was missing.” The study shows that an ocean at this stage in Mars’s past is plausible, says Sanjeev Gupta at Imperial College London, but it is only a simulation. “The authors pull together observations from other studies with evidence for an ocean to tie into their results, but proof of an ocean does not come from the modelling. We would need stronger geological evidence for an ocean,” he says. Journal reference: PNAS, DOI: 10.1073/pnas.2112930119 Sign up to our free Launchpad newsletter for a voyage across the galaxy and beyond, every Friday More on these topics: MARS
Do we create space-time? A new perspective on the fabric of reality For the first time, it is possible to see the quantum world from multiple points of view at once. This hints at something very strange – that reality only takes shape when we interact with each other PHYSICS 2 February 2022 By Amanda Gefter please log in to view this image Mary Iverson IMAGINE approaching a Renaissance sculpture in a gallery. Even from a distance, it looks impressive. But it is only as you get close and walk around it that you begin to truly appreciate its quality: the angle of the jaw, the aquiline nose, the softness of the hair rendered in marble. In physics, as in life, it is important to view things from more than one perspective. As we have done that over the past century, we have had plenty of surprises. It started with Albert Einstein’s theory of special relativity, which showed us that lengths of space and durations of time vary depending on who is looking. It also painted a wholly unexpected picture of the shared reality underneath – one in which space and time were melded together in a four-dimensional union known as space-time. When quantum theory arrived a few years later, things got even weirder. It seemed to show that by measuring things, we play a part in determining their properties. But in the quantum world, unlike with relativity, there has never been a way to reconcile different perspectives and glimpse the objective reality beneath. A century later, many physicists question whether a single objective reality, shared by all observers, exists at all. Now, two emerging sets of ideas are changing this story. For the first time, we can jump from one quantum perspective to another. This is already helping us solve tricky practical problems with high-speed communications. It also sheds light on whether any shared reality exists at the quantum level. Intriguingly, the answer seems to be no – until we start talking to each other. When Einstein developed his theory of relativity in the early 20th century, he worked from one fundamental assumption: the laws of physics should be the same for everyone. The trouble was, the laws of electromagnetism demand that light always travels at 299,792 kilometres per second and Einstein realised this creates a problem. If you were to race alongside a light beam in a spaceship, you would expect to see the beam moving far slower than usual – just as neighbouring cars don’t look to be going so fast when you are zipping along the motorway. Yet if that was the case, the laws of physics in that perspective would be violated. “In the quantum world, there has never been a way to reconcile different perspectives and glimpse the shared reality beneath” Einstein was convinced that couldn’t happen, so he was forced to propose that the speed of light is constant for everyone, regardless of how fast they are moving. To compensate, space and time themselves had to change from one perspective to the next. The equations of relativity allowed him to translate from one observer’s perspective, or reference frame, to another, and in doing so build a picture of the shared world that remains the same from all perspectives. He went on to develop these ideas into general relativity, which remains our best theory of gravity. But it isn’t the whole story. In Einstein’s writings, reference frames are always defined by “rods and clocks”, physical objects against which space and time are measured. These objects are, however, governed by a different theory altogether. Quantum theory deals with matter and energy and is even more successful than relativity. But it paints a deeply unfamiliar picture of reality, one in which particles don’t have definite properties before we measure them, but exist in a superposition of multiple states. It also shows that particles can become entangled, their properties intimately linked even over vast distances. All this puts the definition of a reference frame on shaky ground. How do you measure time with a clock that is entangled, or distance with a ruler that is in multiple places at once? “How do you measure time with a clock that is entangled, or distance with a ruler that is in multiple places at once?” Quantum physicists usually avoid this question by treating measuring instruments as if they obey the classical laws of mechanics developed by Isaac Newton. The particle being measured is quantum; the reference frame isn’t. The dividing line between the two is known as the Heisenberg cut. It is arbitrary and it is moveable, but it has to be there so that the measuring device can record a definite result. Consider Schrödinger’s cat, the thought experiment in which an unfortunate feline is in a box with a radioactive particle. If the particle decays, it triggers a hammer that breaks a vial that releases a poison that kills the cat. If it doesn’t, the cat lives. You are outside the box. From your perspective, the contents are entangled and in a superposition. The particle both has and hasn’t decayed; the cat is both dead and alive. But, as in relativity, shouldn’t it be possible to describe the situation from the perspective of the cat? This conundrum has long bothered Časlav Brukner at the Institute for Quantum Optics and Quantum Information in Vienna, Austria. He wanted to understand how to see things from multiple points of view in quantum theory. Following Einstein’s lead, he started from the assumption that the laws of physics must be the same for everyone, and then developed a way to mathematically switch between quantum reference frames. If we could describe a situation from either side of the Heisenberg cut, Brukner suspected that some truth about a shared quantum world might emerge. Think inside the box What Brukner and his colleagues found in 2019 was a surprise. When you jump into the cat’s point of view, it turns out that – just as in relativity – things have to warp to preserve the laws of physics. The quantumness previously attributed to the cat gets shuffled across the Heisenberg cut. From this perspective, the cat is in a definite state – it is the observer outside the box who is in a superposition, entangled with the lab outside. Entanglement was long thought to be an absolute property of reality. But in this new picture, it is all a matter of perspective. “What is quantum and what is classical depends on the choice of quantum reference frames,” says Brukner. Jacques Pienaar at the University of Massachusetts says all this allows us to rigorously pose some fascinating questions. Take the well-known double-slit experiment, which showed that a quantum particle can travel through two slits in a grating at once. “We see that, relative to the electron, it is the slits themselves that are in a superposition,” says Pienaar. “To me, that’s just wonderful.” While that might all sound like mere theorising, one thing that gives Brukner’s ideas credence is that they have already helped solve an intractable problem relating to quantum communication (see “Flying qubits”). Quantum reference frames do have an Achilles’ heel though, albeit one that might ultimately point us to a deeper appreciation of reality. It comes in the form of “Wigner’s friend”, a thought experiment dreamed up in the 1950s by physicist Eugene Wigner. It adds a mind-bending twist to Schrödinger’s puzzle. Faced with the usual set-up, Wigner’s friend opens the box and finds, say, that the cat is alive. But what if Wigner himself stands outside the lab door? In his reference frame, the cat is still in a superposition of alive and dead, only now it is entangled with the friend, who is in a superposition of having-seen-an-alive-cat and having-seen-a-dead-cat. Wigner’s description of the cat and the friend’s description of it are mutually exclusive, but according to quantum theory they are both right. It is a deep paradox that seems to reveal a splintered reality. Brukner’s rules are no help here. We can’t hop from one side of the Heisenberg cut to the other because the two people are using different cuts. The friend has the cut between herself and the box; Wigner has it between himself and the lab. They aren’t staring at each other from across the classical-quantum divide. They aren’t looking at one another at all. “My colleagues and I were hoping that the Wigner’s friend situation could be rephrased in quantum reference frames,” says Brukner. But so far, that hasn’t been possible. “I don’t know,” he sighs. “There’s a missing element.” please log in to view this image Suhaimi Abdullah/Getty Images Hints as to what that might be are coming from work by Flavio Mercati at the University of Burgos in Spain and Giovanni Amelino-Camelia at the University of Naples Federico II in Italy. Their research seems to suggest that by exchanging quantum information, observers can create a shared reality, even if it isn’t there from the start. The duo were inspired by research carried out in 2016 by Markus Müller and Philipp Höhn, both then at the Perimeter Institute in Waterloo, Canada, who imagined a scenario in which two people, Alice and Bob, send each other quantum particles in a particular state of “spin”. Spin is a quantum property that can be likened to an arrow that can point up or down along each of the three spatial axes. Alice sends Bob a particle and Bob has to figure out its spin; then Bob prepares a new particle with the same spin and sends it back to Alice, who confirms that he got it right. The twist is that Alice and Bob don’t know the relative orientation of their reference frames: one’s x-axis could be the other’s y-axis. “Alice and Bob’s communication may forge the structure of space-time” If Alice sends Bob just one particle, he will never be able to decode the spin. Sometimes in physics, two variables are connected in such a way that if you measure one precisely, the other no longer exists in a definite state. This tricky problem, known as the Heisenberg uncertainty principle, applies to particles’ spin along different axes. So if Bob wants to measure spin along what he thinks is Alice’s x-axis, he has to take a wild guess as to which axis that really is – if he is wrong, he erases all the information. The pair can get around this, however, if they exchange lots of particles. Alice can tell Bob, “I’m sending you 100 particles that are all spin ‘up’ along the x-axis.” As Bob measures more and more of them, he can begin to work out the relative orientation of their reference frames. Here is where it gets interesting. Müller and Höhn realised that, in doing all this, Alice and Bob automatically derive the equations that enable you to translate the view from one perspective to another in Einstein’s special relativity. We tend to think of space-time as the pre-existing structure through which observers communicate. But Müller and Höhn flipped the story. Start with observers sending messages, and you can derive space-time. For Mercati and Amelino-Camelia, who first came across the work a few years ago, that flip was a light-bulb moment. It raised a key question that turns out to have a crucial bearing on Brukner’s work: are Alice and Bob learning about a pre-existing space-time or is the space-time emerging as they communicate? Make some space There are two ways in which the latter could play out. The first has to do with the trade-off in quantum mechanics between information and energy. “To gain information about a quantum system you have to pay energy,” says Mercati. Every time Bob chooses the correct axis, he loses a bit of energy; when he chooses wrong and erases Alice’s information, he gains some. Because the curvature of space-time depends on the energy present, when Bob measures his relative orientation he also ends up changing the orientation a tiny bit. There could be a more profound sense in which quantum communication creates space-time. This comes into play if space is what’s called “non-commutative”. If you want to arrive at a point on a normal map, it doesn’t matter in which order you specify the coordinates. You can go over five and up two; or up two and over five – either way you will land on the same spot. But if the laws of quantum mechanics apply to space-time itself, this might not be true. In the same way that knowing a particle’s position prevents you from measuring its momentum, going over five might prevent you from going up two. Mercati and Amelino-Camelia say that if space-time does work in this way, Alice and Bob’s attempts to find out their relative orientation wouldn’t merely uncover the structure of space-time, they would actively forge it. The choices they make as to which axes to measure would alter the very thing their communication was meant to reveal. The pair have also devised a way to test whether this is really the case (see “Does space-time commute?”). All this work points towards a startling conclusion: that as people exchange quantum information, they are collaborating to construct their mutual reality. It means that if we simply look at space and time from one perspective, not only do we miss its full beauty, but there might not be any deeper shared reality. For Mercati and Amelino-Camelia, one observer does not a space-time make. That leads us back to the Wigner’s friend paradox that flummoxed Brukner. In his work, observers can be treated as having perspectives on the same reality only when they are gazing at one another from across the Heisenberg cut. Or, put another way, only when it is possible for them to communicate, which is precisely what Wigner and his friend can’t do. Perhaps this is telling us that until two people interact, they don’t share the same reality – because it is communication itself that creates it. quantum internet. These networks transport information in the form of qubits, or quantum bits, which can be encoded in the properties of particles – typically in a quantum property called spin. One person sends a stream of particles to another, who then measures their spin to decode the message. Except, not so fast. To be a useful means of communication, these particles must travel at close to the speed of light. At such speeds, a particle’s spin gets “quantum entangled” with its momentum in such a way that if the receiver only measures the spin, information will be lost. “This is serious,” says Flaminia Giacomini at the Perimeter Institute in Canada. “The qubit is the basis for quantum information, but for a particle moving at very high velocities, we can no longer identify a qubit.” As if that weren’t enough of a problem, each qubit doesn’t move at one definite speed: thanks to quantum mechanics, it is in what is known as a superposition of velocities. The rules of quantum reference frames developed by Časlav Brukner (see main story) could be the answer. Giacomini has shown how the rules can be used to jump into the particle’s reference frame, even when the particle is in a superposition. From that perspective, it is the rest of reality that is whizzing past in a blurred superposition. Armed with knowledge of how the qubit sees the world, you can then determine the mathematical transformation to perform on the particle to recover the information in the original qubit. Does space-time commute? In ordinary space, it isn’t the journey that matters so much as the destination. If you’re trying to arrive at a given place, it makes no difference whether you head 5 kilometres south and then 3 kilometres west, or vice-versa. That is because the coordinates “commute”; they get you to the same spot regardless of the order. At very small scales to which quantum theory applies, this might not be true. In quantum theory, measuring a particle’s position erases information about its momentum. Similarly, it could be that the order in which movements are made could affect the structure of space. If this is so, it makes no sense to talk about space-time as a fixed arena. Physicists Flavio Mercati and Giovanni Amelino-Camelia think they have a way to find out whether space-time commutes. They were inspired by research that imagined two people exchanging quantum particles and measuring their properties to deduce their relative orientation (see main story). What would happen, Mercati and Amelino-Camelia asked, if this game were played for real? As the people exchange more and more particles, their uncertainty about their orientation should decrease. But will it ever get to zero? In ordinary space-time, it will. But if space-time is non-commutative, some uncertainty will always remain, since their orientation is ever so slightly rewritten with each measurement. The pair might have to exchange trillions of particles before we will have an answer – but Mercati thinks it is worth a try.
Well obviously, the ancient aliens running the simulation that is our reality want to save disk space by only creating data when we look at it.
Reminds me of Lennon's house in that Imagine video (yeas, the song when he talks about imagining no possessions as he walks around his multi-million-pound mansion) that has a sign above the door that says 'This is not really here'. Links up with that Wheeler/Anthropic Theory/Penrose stuff, maybe?
Dolphins get horny after playing with a snake. https://www.sciencealert.com/scient...h-anacondas-in-their-mouths-and-what-the-heck "Afterwards, we were able to observe on the photographs that the adult males were sexually aroused while engaging in object play with the anaconda," write the researchers.
