EXCUSE ME, BUT IS THIS NOT THE FABRIC OF EMPEROR’S CLOTHES THAT IS WAVING ?!
In my opinion, the only empirical evidence for the physical existence of gravitational waves is the 2017 Nobel Prize in Physics —
The three distinguished physicists of international renown were awarded over a million dollars, along with the highest and the most prestigious prize in world science for their
decisive contributions to the LIGO detector and the observation of gravitational waves.
Therefore, no doubt, gravitational waves must exist, and be experimentally detectable. If spacetime, as a fabric, a real physical entity, can be bent and curved by mass of planets and stars, then surely there could also be physical ripples, or waves, in this fabric. After all, Albert Einstein is the greatest scientific genius of all time. He must have been right. Trust me.
Well, then why would Prof. George F. R. Ellis, or some other respectable mainstream physicists, have any doubts pertaining to the degree to which our representations of the nature of spacetime are an adequate representation of its true ontological nature?
The hidden issue underlying all this discussion is the question of the ontological nature of spacetime: Does spacetime indeed exist as a real physical entity, or is it just a convenient way of describing relationships among physical objects? Is it absolute or relational? I will not pursue this contentious point here. I emphasize that the discussion in this paper is about models, or representations, of spacetime, rather than making any ontological claims about the nature of spacetime itself. However, I do believe that the kind of proposal made here could provide a useful starting point for a fresh look at the ontological issue, and from there a renewed discussion of the degree to which our representations of the nature of spacetime are an adequate representation of its true ontological nature.
If you want to know what spacetime is, ask an expert:
Does spacetime exist as a real physical entity, or is it just a convenient way of describing gravitational interactions among physical objects?
In my opinion, spacetime does not exist as a real physical entity, and is merely a mathematical construct, which neither can be physically bent, curved, warped, nor can wave.
The reason for my opinion is that if spacetime were to be a real physical entity, then it would follow that it must be composed of something physical, like matter, or energy. If so, then spacetime could not only be easily experimentally detectable, like air of our atmosphere, but also it could be quantized. However, one of the reasons that we do not yet have a theory of quantum gravity, is that it was simply impossible to quantize spacetime:
Well, how would you expect to realistically quantize something that does not exist as a real physical entity that is made of matter, or energy?
And, by the way, spacetime is not made of quantum vacuum, either. Then maybe spacetime is made of very, very tiny, special, invisible and undetectable “spacetime atoms” ?
Unfortunately, if spacetime were to be made of matter, like “spacetime atoms”, then wouldn’t we effectively have the same old Luminiferous Aether that had already been consigned to the Museum of Scientific Blunders?
The most important and fundamental issue is this:
As a real physical entity, what exactly is spacetime made of? Is it possible to detect not just the physical existence of how this “fabric” allegedly bends, curves, or waves, but simply to detect the physical existence of this “fabric”, apart from it bending, curving, or waving? Is it possible to detect the physical existence of anything (large-scale) that is not bending, curving, or waving?
That is the reason why, according to Frank Wilczek, a Nobel Prize-winning physicist at the Massachusetts Institute of Technology, the most disturbing question in physics is:
Why doesn’t empty space weigh anything ?!
WHAT IF THE COSMOS HAD NO FABRIC ?!
Nobody really knew what gravity was and how it worked, other than Newton mathematically quantifying its observable effects. So, the clever trick that Einstein pulled off, called GTR, was conveniently replacing one unexplained mystery (Newtonian gravity) with another unexplained mystery, i.e. his experimentally undetectable spacetime that curves due to object’s mass, while itself not being made of anything physical, akin to Cheshire cat’s grin that is hanging there, without the actual cat being present:
My answer to the question: What exactly is spacetime made of?, is that spacetime is, obviously, made of space and time.
To quantify “time”, we use physical devices called “clocks”, and to quantify “space”, we use various linear, or other devices. But why there isn’t any device that we could use to quantify spacetime ?!
Now, the question is: Does a clock go around, because time physically flows through it, like flowing water that is powering a water-wheel?
And, when the clock stops, does it mean that it is because time stopped, and is not “flowing” anymore?
It is quite clear that a clock is not a device that could, even in principle, detect the physical existence of time passing, or not passing (static time).
There is no such device that could , even in principle, detect the physical existence of time (passing, or not) nor the velocity of its possible “flow”, and there is no such device that could detect the physical existence of space, nor the actual number of dimensions that space might have.
I know, at the first glance it looks like space must have 3 dimensions (at least). At the first glance it also looks like the Earth is flat and motionless, and it looks like color is a property of physical objects. Because appearances can be deceiving, scientific method prefers objective experimental results.
When a cosmonaut’s spaceship comes back to Earth after traveling long time at near-the-speed-of-Light velocity, and his clock is late, relative to clocks on Earth, then what does it mean? Well, maybe cosmonaut’s clock electric battery is running low?
Wait a minute! For a Nobel Prize to be awarded, something physically real must have been detected!
No doubt. But whatever that was, it was not the fabric of the Cosmos waving that was detected. Maybe it was just noise that was being misinterpreted? Impossible? “If the correlation properties of signal and the noise are similar, how is one to know precisely what is signal and what is noise?” So, gravitational wave discovery faces scrutiny.
For the fabric to wave, the Emperor’s clothes would have to be made of something physically real.
Yes, it is that simple.
The Emperor has no clothes.
“ Ptolemy made a universe which has lasted 1400 years. Newton made a universe which has lasted 300 years. Einstein also made a universe, but I can’t tell you how long it will last.” — George Bernard Shaw, from the speech in Albert Einstein’s honor at the Savoy Hotel in London, October 28, 1930
Einstein’s general relativity and the theory of quantum mechanics are fundamentally incompatible, which has prompted over 30 years of work in string theory and quantum gravity. Not only Einstein’s theory does not work on the quantum scale; it does not work on the scale of galactic clusters either.
It was a speech that changed the way we think of space and time. The year was 1908, and the German mathematician Hermann Minkowski had been trying to make sense of Albert Einstein’s hot new idea – what we now know as special relativity – describing how things shrink as they move faster and time becomes distorted. “Henceforth space by itself and time by itself are doomed to fade into the mere shadows,” Minkowski proclaimed, “and only a union of the two will preserve an independent reality.” And so spacetime – the malleable fabric whose geometry can be changed by the mass of stars, planets and matter – was born. It is a concept that has served us well, but if physicist Petr Horava is right,
spacetime may be no more than a mirage.
Horava, who is at the University of California, Berkeley, wants to rip this fabric apart and set time and space free from one another in order to come up with a unified theory that reconciles the disparate worlds of quantum mechanics and gravity – the most pressing challenge to modern physics.
“ Today, the big-bang theory has become the orthodox cosmology. It nevertheless faces a major hurdle in providing a convincing account of how the universe can come to exist from nothing as a result of a physical process. No greater obstacle lies in the path of explanation than the mystery of how time itself can originate naturally. Can science ever encompass the beginning of time within its scope? […] Despite its popularity, the big-bang theory has not been without its detractors. Right from the start, attempts by astronomers to date the age of the Universe ran into trouble. The age kept coming out wrong. There wasn’t enough time for the stars and planets to come into existence. Worse still, there were astronomical objects that seemed to be older than the Universe – an obvious absurdity. Could it be that Einstein’s time and cosmic time are not the same? Is Einstein’s flexible time simply not flexible enough to stretch all the way back to the moment of Universe’s creation? […] Important though Einstein’s time turned out to be, it still did not solve the riddle of time. The time that enters into physical theory, even Einstein’s time, bears only the vaguest resemblance to the subjective time of personal experience, the time that we know, but cannot explain. For a start, Einstein’s time has no arrow. It is blind to the distinction between past and future. Certainly, it doesn’t flow like the time of Shakespeare or James Joyce, or for that matter of Newton. It is easy to conclude that something vital remains missing, some extra quality of time is left out of the equations, or that there is more than one sort of time. The revolution begun by Einstein remains frustratingly unfinished. […] The broad conclusion I reach, however, is that we are far from having a good grasp of the concept of time. Einstein’s work triggered a revolution in our understanding of the subject, but the consequences have yet to be fully worked out. There are major problems which hint at deep-seated limitations of the theory; discrepancies concerning the age of the Universe and obstacles to unifying Einstein’s time with quantum physics are two of the more persistent difficulties. Perhaps more worryingly, Einstein’s time is seriously at odds with time as we humans experience it. All this leads me to believe that we must embrace Einstein’s ideas, but move on.”
This dire-sounding debate has spawned a profusion of papers, blog posts and workshops over the last year. At stake is not Einstein’s reputation, which is after all secure, or even the efficacy of our iPhones, but perhaps the basis of his general theory of relativity, the theory of gravity, on which our understanding of the universe is based. Or some other fundamental long-established principle of nature might have to be abandoned, but physicists don’t agree on which one, and they have been flip-flopping and changing positions almost weekly, with no resolution in sight. […] You might wonder who cares, especially if encountering a black hole is not on your calendar. But some of the basic tenets of modern science and of Einstein’s theory are at stake in the “firewall paradox,” as it is known. […] an odious solution because it contravenes the basic principle of general relativity. He pointed out, however, that in a sense physicists had already thrown Einstein under the bus. In Dr. Maldacena’s holographic universe, considered to be the last word on quantum gravity, the dimensions of space-time do not seem to matter. “We’ve known for years that space-time is not fundamental, general relativity is not fundamental.”, Dr. Polchinski said.
Doom of spacetime (PSW2384)
Nima Arkani-Hamed thinks time may be ripe for another revolution and that revolution could depend on the doom of spacetime.
Arkani-Hamed sketched some of the important lore showing that the spacetime must become approximate. When you try to probe ever shorter distances, you increase the energies (like at the colliders – the inverse relationship holds because the de Broglie wavelength gets shorter when the momentum is higher due to the uncertainty principle) but that strategy fails once the energy is too high and you produce black holes. By adding energy, instead of probing ever shorter distances, you produce a larger black hole. The resolution just doesn’t get better than a Planck length.
Also, you can’t measure things too precisely in quantum gravity, even when things are big, so the limitations of the spacetime affect long-distance physics, too. When you want an accurate measurement, you need large gadgets and very fat experimenters to reduce the risk of fluctuations and random evaporation of finite objects, but such gadgets and fat men may collapse into a black hole as well when they’re too fat, so the experiment breaks down.
So the spacetime must be approximate, it must emerge. He showed the AdS holography as an example of physics in a tin can. After healthy doses of a useful review of these gems of contemporary research, he asked a question: How could an old physicist usefully exploit the information from a traveler in the future that determinism is dead? Well, such a general surprising thesis doesn’t immediately lead to a new theory, quantum mechanics.
A good strategy would be to reformulate things he knew in a way that doesn’t depend on the old dogma that is known to be wrong – determinism in this case – too much. He could figure out that the principle of least action is a good starting point and rediscover Feynman’s path integrals in this way. That’s the strategy that Nima wants to use with the information he got from a time traveler from the future – that the spacetime is doomed (I tried to watch the Hitchhiker’s Guide to the Galaxy last night but I failed to complete it again – it just seems like too many seemingly unrelated silly would-be jokes).
The application of this strategy means to find a way to calculate the known amplitudes in a way in which the spacetime and perhaps quantum mechanics don’t look central. So he outlined the amplituhedron program, the picture that the amplitudes have so many complicated terms because the amplitudes are really volumes of a polytope in an auxiliary space and the polytope is cut to many complicated pieces in some ad hoc ways. This program interprets a scattering process as a generalization of the process where just numerical labels scatter – and their scattering means a permutation.
At the end, there were questions. Most of the questions ended with the answer “no, I don’t think that there’s a known direct relationship between the amplituhedron and a god ABC in the religious sect XYZ”, if I exaggerate just a little bit. Over the years, I’ve been getting so many questions of this kind – questions that are insanely far from the topic I talked about and that indicated that I was mostly wasting my time – that I grew disillusioned about the usefulness of popular talks in general.
One question led Nima to an important and cool answer saying that from the old-fashioned perspective, the scalars’ j=0j=0 scattering is the simplest one, gluons with j=1j=1 are harder but doable, but j=2j=2 graviton scattering is ludicrously hard even at the basic level. But from the novel emerging viewpoint, it’s the other way around. Gravity sees the new simplifying structure most clearly and things get messier as you lower the spin.
Is Einstein’s Greatest Work All Wrong, Because He Didn’t Go Far Enough?
From a farmhouse in the English countryside, gentleman scientist Julian Barbour plots to take relativity to its logical extreme and redefine the very nature of gravity, space, and time.
By Zeeya Merali
Julian Barbour ( Platonia.com ) cuts an unlikely figure for a radical. We sip afternoon tea at his farmhouse in the sleepy English village of South Newington, and he playfully quotes Faust: That I may understand whatever binds the world’s innermost core together, see all its workings, and its seeds. His love of Goethe’s classic poem, about a scholar who sells his soul to the devil in exchange for unlimited knowledge, is apropos. Forty years ago, Barbour’s desire to uncover the innermost workings of the universe led him to make a seemingly reckless gamble. He sacrificed a secure and potentially prestigious career as an academic to strike out on independent research of his own. His starry-eyed quest: upending Albert Einstein’s theory of relativity, and with it our understanding of gravity, space, and time. It was less than a century ago that Einstein was the most radical physics thinker around. With his general theory of relativity, he discarded the traditional notion of space and time as fixed and redefined them as flexible dimensions woven together to create a four-dimensional fabric that pervades the universe. In Einstein’s vision, this stretchy version of space-time is the source of gravity. The fabric bends and warps severely around massive objects such as the sun, drawing smaller objects such as planets toward them. The force that we perceive as gravity is the result. Yet Einstein’s fabric left a few loose threads that cosmologists have struggled to tie up ever since. For one,
general relativity alone cannot explain the observed motions of galaxies or the way the universe seems to expand. If Einstein’s model of gravity is correct, around 96 percent of the cosmos appears to be missing.
To make up the difference, cosmologists have posited two mysterious, invisible, and as yet unidentified ingredients: dark matter and dark energy, a double budget deficit that makes many scientists uncomfortable. Einstein also failed to deliver an all-encompassing theory of “quantum gravity”—one that reconciled the laws of gravity observed on the scale of stars and galaxies with the laws of quantum mechanics, the branch of physics that explains the behavior of particles in the subatomic realm.
While other scientists tread softly around the edges of Einstein’s theory, hoping to tweak it into compliance, Barbour and a growing cadre of collaborators see a need for a bold march forward. They aim to demolish the space-time fabric that stands as Einstein’s legacy and remap the universe without it. This new cosmic code could eliminate the need to invoke dark matter and dark energy. Even more exciting, it could also open the door to the theory of quantum gravity that Einstein was never able to derive. If Barbour is right, some of the most fundamental things cosmologists think they know about the origin and evolution of the universe would have to be revised.
“We have radically reformulated Einstein in a different light that might be valuable for understanding cosmology and quantum gravity,” Barbour says. “It is a very ambitious hope that it could play such a role.”
Barbour’s penchant for mapping space and time is apparent even before we meet. His home, College Farm, is hidden away some 20 miles from the nearest city of note, Oxford. Knowing that visitors often struggle to find the 17th-century farmhouse, he has sent two sets of directions. The first includes detailed instructions for navigating through the village’s rolling hills along sunken roads, passing thatched cottages, the local Duck on the Pond pub, and the ancient church near his home. Those directions might have served equally well for locating Barbour’s house at the time it was built in 1659, a few decades before another English physicist, Isaac Newton, wrote his Principia, setting down the ideas about motion and gravity that dominated physics for almost three centuries.
In one respect Barbour has spent 40 years faithfully preserving Newton’s universe, meticulously restoring the farmhouse’s period features. He proudly shows me that each window frame is adorned with a small metal animal figure—a lion, a stag, a cockerel, and the flying horse Pegasus. The lion is Barbour’s favorite because it is original; the rest he had specially made based on designs seen in other buildings of the same era in the village. He taps the sturdy stone wall surrounding the window. “These were here 350 years before us and our modern conceptions of physics,” he tells me, “and chances are they’ll still be standing 350 years after we’ve gone.”
By contrast, the second set of directions for finding Barbour’s farmhouse—GPS coordinates—work only in the modern, post-Einstein reality. The satellite navigation system pinpoints positions on Earth to within 10 meters (30 feet) in a matter of seconds by comparing the timing of signals received from a number of satellites at known locations above the globe. The system works with such stunning accuracy because it compensates for the fact that clocks on fast-orbiting satellites run at different rates from those on the ground. The fact that gravity and motion affect the flow of time was discovered by Einstein as a core element of his theory of relativity.
To remap the cosmos, Barbour has tapped into both Newton’s and Einstein’s conceptions of nature and then discarded key elements of both. Newton imagined that the universe was spanned by absolute space, which served as a rigid invisible backdrop or grid against which the position of all stars and planets (or farmhouses and the Duck on the Pond pub, for that matter) could be definitively located. Remove all objects from the universe and Newton’s grid would remain while time ticked along at a steady universal rate, as if marked by God’s wristwatch.
Einstein saw time and space as altogether more malleable. During his student days, he had studied the work of James Clerk Maxwell, a Scottish physicist who recognized the speed of light—300,000 kilometers or 186,000 miles per second—as a fundamental property of electromagnetic fields. In Maxwell’s time, most physicists thought that light, like sound, needed some kind of medium for transmission; the mysterious, invisible substance they hypothesized, called the luminiferous ether, would presumably be influenced by the motion of Earth around the sun and the movement of the solar system through the galaxy, a dynamic that stood to alter the speed of light depending on the relative direction from which that light came. But numerous experiments failed to discover any evidence of the ether, and Einstein realized the speed of light must stay constant no matter which direction it came from or how an observer moved. That understanding contradicted Newton’s view of space. In his physics, you could catch up to anything, even light, if you moved fast enough. But if the speed of light holds steady no matter where you were or how you were moving, it would always seem to zoom away from you at the same constant 186,000 miles per second. Einstein enshrined that principle in his first theory of relativity (special relativity), which states that you can never catch up to a light beam no matter how hard you might try.
Barbour first heard these ideas as a teenage schoolboy in the early 1950s, a time when Einstein was still alive. As a 3-year-old child Barbour had earned the nickname “Why?” from a friend of his mother’s because of his ever-curious nature. Yet upon learning of relativity, he uncharacteristically did not question it. “I was lost in admiration,” he says. “Everyone thought Einstein was the greatest figure after Newton, and so I took it on trust, almost like someone being indoctrinated into a religion.”
It took another decade for Barbour’s questioning nature to overcome his awe. Twenty-four years old and a recent graduate of the University of Cambridge in 1961, he was planning on graduate school in astronomy. But he took a year off the academic conveyor belt to visit Germany and learn two languages: “Russian, because I adored the writer Pushkin, and German, because the first girl I fell for was a German au pair,” he says with a chuckle. So taken was he with the country that he stayed on to complete an astronomy Ph.D. at the University of Cologne, gaining the mathematical and language skills to read Einstein’s texts in their original German and grapple with their meaning. What struck Barbour most was Einstein’s comment that his intuitive leap about space and time had been inspired by Austrian physicist and philosopher Ernst Mach, whose study of the speed of sound in fluids helped explain the sonic boom heard when objects break the sound barrier. (“Mach numbers” are named in his honor.) Long before Einstein, Mach had advocated a “truly relative” theory, in which objects were positioned only in relation to other tangible objects—Earth relative to sun, pub relative to farmhouse—and not against any abstract background grid. “Mach wanted to obliterate Newton’s absolute space and time, arguing that physics should not be at the mercy of an invisible grid that nobody can verify exists,” Barbour says. “This informed Einstein’s thinking at the time.”
That Machian ideal seized young Barbour, too. “It was something in my psyche,” he says. “The insight resonated very deeply with me.” The more he read, the more Barbour became convinced that Einstein had failed to take Mach’s ideas seriously enough. “I have certain knowledge from my readings in German,” he says, “that Einstein didn’t implement Mach’s ideas in the most direct way because he thought that way was too hard.”
Barbour felt that Einstein had taken a circuitous route to reframing the cosmos. Einstein’s 1905 publication on special relativity seemed to bring him closer to Mach’s camp, dismantling part of Newton’s grid by abolishing the notion that time was absolute. But it did so only by linking time to the three dimensions of space to create a rigid, four-dimensional block of space-time. Then, with the broader, more all-encompassing version of relativity (general relativity) he published in 1916, Einstein reshaped that backdrop into a more malleable four-dimensional space-time. Sure, Einstein’s space could be warped by the presence of massive objects, undulating like the hills of South Newington. But despite the name of his famous concept—the theory of relativity—Einstein’s universe still required a background against which particles and objects could be located in both time and space. Compared to Mach’s ideals, Einstein’s theory was not truly relative.
By 1964 Barbour was almost finished with graduate school and knew he wanted to pick up where Mach had left off.
Pursuit of Mach’s concept in defiance of Einstein seemed a path to career suicide.
Einstein’s theories were cornerstones of modern physics, whereas Mach’s ideas were largely considered historical curiosities. So Barbour decided to change the rules: Forgoing the security of an academic career, he set out on his own.
That might have seemed reckless to most graduate students, but Barbour’s father had also been an independent scholar, studying Arabic and traveling through the Middle East. “He was a role model to me,” Barbour says. Besides, he had a backup plan. Using his new mastery of Russian, Barbour realized he could work as a translator to pay the bills.
With his newly minted doctorate, young Barbour pressed on where Einstein had feared to tread, coming closer to Mach by dispensing not just with Newton’s rigid grid but with the very concept of space-time. In general relativity, time is a dimension interwoven with the dimensions of space. In Barbour’s universe, on the other hand, time is emergent: It is a measure of how space changes but not a fundamental component of it.
By 1969 Barbour had purchased College Farm, leaving Cologne and moving back to South Newington with Verena Bastian, his German wife. To support his growing family, including son Boris and daughter Jessica, he set up a business as a translator, drawing on his old love of Pushkin and rendering English versions of Russian scientific texts. But all the while, he tinkered away at his Machian model of the universe. “There was the possibility of a big discovery, and I had the scent of something exciting,” Barbour says. The idea was regarded highly enough to make it into the pages of Nature, banishing any worries he might have had that by shunning academia, he would be dismissed as a crank.
From 1975 on, Barbour joined forces with Bruno Bertotti, a physicist at the University of Pavia in Italy, to take on the juggernaut that is Einstein. They developed a technique known as “best-matching,” in which the motion of an object (for instance, the moon) is tracked solely by its changing distance from other objects (like the sun and the Earth), rather than its changing location against a grid. Similar to playing connect the dots to chart how the moon’s position changes over a fortnight, Barbour imagines a triangle whose corners are formed by the location of the three celestial bodies at one point in time and a second triangle formed by the same bodies a moment later. Using the mismatch in the shapes of the two triangles laid one on top of the other, he can quantify the amount of change that has taken place. He even used his best-matching technique to derive Newton’s laws of motion in a completely new way. He made the effort, he says, just to prove his model worked.
By 1982 Barbour and Bertotti had come up with a new theory of gravity that described the world just as accurately as Einstein’s general relativity but without invoking time as a fundamental dimension.
In a sense, Barbour takes physics a step back. He begins not with Einstein’s four-dimensional space-time but with a three-dimensional space vaguely resembling that of Newtonian dynamics. The space of Barbour’s theory, however, is curved, bearing little resemblance to Newton’s rigid Euclidean grid. And in cases where Einstein’s and Newton’s theories differ, Barbour’s shape-based calculations hew to Einstein’s more sophisticated predictions. They match Einstein’s explanations of everything from the bending of light by distant galaxies to the distortion of time in those gps satellites. The added accuracy in Barbour’s calculations arises from the fact that best-matching requires an accounting of the positions and gravitational influence of distant cosmic objects that Newton’s equations tended to ignore. The reason Einstein’s theory is so much better than Newton’s, Barbour notes, is that Einstein was able to get much closer to the Machian ideal.
The success of Barbour’s theory was gratifying, but it also threw him a curveball. He had set out to use Mach’s ideas to topple Einstein, but his results and Einstein’s seemed essentially the same. Still, Barbour remained convinced that Einstein didn’t go far enough: Because relativity wasn’t truly relative—or Machian—fundamental inconsistencies in Einstein’s model of the universe remained. If he had stuck with the Machian approach, Einstein might have attained the all-encompassing “theory of everything” that consumed the last decades of his life. “He might have produced a version of his theory of gravity that would not conflict so fundamentally with quantum mechanics,” Barbour notes. But Einstein had lost his nerve.
One hint of trouble came to light in the 1970s, when astronomers realized the outer portions of a significant number of galaxies were rotating inexplicably fast, seemingly pulled by more gravity than general relativity could explain. To account for the extra gravity, they embraced the idea of dark matter. If only they could find the missing mass, then all the accounting would fall into place and the rules of gravity would look sensible again.
But clouds of undetectable dark matter was not an entirely satisfying explanation to Hans Westman, a University of Sydney physicist who has collaborated with Barbour at College Farm. Seeking a better answer, he started analyzing a largely forgotten theory developed by the German mathematician Hermann Weyl. Around 1918 Weyl attempted to modify general relativity so that it would not require absolute measurements of scale or distance—so that it would abide by an entirely relative system, again akin to that of Mach. “Einstein called Weyl’s model a stroke of genius of the first rank,” Westman says. On closer inspection, though, he found the theory mathematically messy, yielding unpredictable results. In the end, both Einstein and Weyl tossed the model out.
Westman now argues that this rejection was a grievous mistake, because abolishing a scale of measurement and making everything completely relative might have enabled a different theory of gravity, possibly one that meshed with quantum mechanics and had no need to invoke the notion of dark matter at all. To determine whether a Weyl-inspired theory of the universe could explain away the need for dark matter, physicists will have to put it to the test and see if it produces a universe that looks like ours. Westman thinks it could. A theory that reproduces reality without dark matter would be much more beautiful than one with dark matter, Westman says, because we cannot make predictions based on the properties of an undetectable particle; we can only infer what dark matter must be like in order to have created the configurations we observe.
Many observational astronomers counter that the evidence for dark matter is now so strong that it will take more than a new theory of gravity to disprove it. Only more research, Westman responds, will enfranchise dark matter or cast it from the fold. The ultimate evidence would be direct confirmation of dark-matter particles by one of the specialized detectors created to seek them out.
Barbour’s Machian approach could also help disprove the reality of the other dark mystery of modern cosmology, dark energy. Despite its name, dark energy is better thought of as a repulsive force that pushes galaxies apart from each other. It was first widely invoked by cosmologists in 1998 to explain why the expansion of the universe seems to be speeding up, a finding that won the Nobel Prize in Physics last year. (See the DiscoverMagazine.com interview with Saul Perlmutter, one of last year’s physics Nobelists.)
David Wiltshire, a physicist at the University of Canterbury in New Zealand and a visitor to Barbour’s College Farm, thinks the reason dark energy is so mysterious is that it is an illusion. Wiltshire’s argument is that most physicists essentially ignore one of the major principles at the heart of general relativity: that clocks in different parts of the universe can run at different rates. Einstein held that there is no such thing as universal time and that matter affects the rate at which clocks tick, such that time slows near massive objects. Accordingly, Wiltshire notes, the flow of time near galaxies could be slower than the flow of time in empty space. “In a truly relativistic view, the age of the universe differs from place to place,” he says. “In empty space, over 18 billion years have elapsed since the Big Bang, but within galaxies only about 15 billion years have passed.” (Because Wiltshire starts from a separate set of physical assumptions, his numbers are different from the now canonical 13.7 billion years for the age of the universe.)
By ignoring those nuances, Wiltshire claims, cosmologists have misinterpreted the positions of the distant supernova explosions used to determine how quickly the universe is expanding. Light from a supernova travels to Earth’s telescopes after passing through both patches of empty space (where the universe expands more rapidly) and through intervening galaxies filled with matter (where the expansion slows). As a result, Wiltshire says, cosmologists expect supernovas to be closer than they appear, creating the illusion that the expansion of the universe is speeding up. Supernova measurements are the key evidence for dark energy. But Wiltshire thinks physicists may have been chasing shadows rather than zeroing in on reality for years.
Perhaps the most far-reaching aspect of Barbour’s view of gravity is that it could reconcile general relativity and quantum mechanics, the physics of the subatomic realm, marking a major step toward the long-sought theory of everything. This incompatibility tortured Einstein in his later years and has flummoxed physicists ever since. The crux of the problem is that the quantum realm of the extremely small is defined by uncertainty. Before observing a subatomic particle, there is fundamentally no way of predicting exactly where you will find it when you measure it. Quantum equations describe only the probability of finding a particle in a certain place. This fuzziness is not due to poor measurement; it is an intrinsic property of particles on the quantum scale. In many, many experiments, quantum particles, when measured, turn up in various locations with the same frequencies as predicted by their probabilistic equations.
The problem comes when theorists try to combine relativity with quantum physics. Quantum mechanics still relies on the absolute measurements of time that Einstein discarded. String theorists have tried to reconcile the differences but keep running into roadblocks: For instance, the ripples caused by uncertainty might cause such frenzied gyrations of Einstein’s space-time that every location would be riddled with black holes, an impossible outcome. In other words, relativity and quantum mechanics seem to be hopelessly at odds.
“Most physicists are trained to get on with calculating things and not worry too much about these contradictions,” Barbour says, but to him, they were key. In his true Machian theory, there is no space-time fabric that could be torn apart by quantum fluctuations. In fact, there is no fundamental dimension of time to create conflict between general relativity and quantum mechanics, removing any obstacle to coming up with a complete theory of gravity that works in both cosmic and quantum realms.
Today physicist Sean Gryb, who recently left College Farm for a postdoc position at Utrecht University in the Netherlands, is embarking on that Machian path to the theory of everything. Gryb first learned about Barbour’s gridless universe while a graduate student at the Perimeter Institute in Waterloo, Ontario, in 2008. At the time, Gryb was skeptical, to say the least: He concluded that Barbour must have made a mistake and decided to find it. So in August 2010 he joined a group of friends, including postdoc researchers Tim Koslowski, also at Perimeter, and Henrique Gomes at Imperial College London, to pick apart Barbour’s writings just as the young Barbour had once scrutinized Einstein’s. The students thought that their background in quantum gravity would allow them to find Barbour’s misstep.
That never occurred. Instead, the work withstood their ongoing scrutiny, and last year Gryb, Koslowski, and Gomes took their first tentative steps toward developing a theory of quantum gravity. They hope to show that Barbour’s model, unlike Einstein’s, does not cause gravity to flare up to infinite levels in tiny regions. Without those infinities, there should be no fundamental obstacle to uniting Barbour’s theory with quantum mechanics. Such a marriage could lead to astonishing new insights, like an explanation of what happens inside black holes and what conditions were like at the moment of the Big Bang, when the whole universe was born. “That’s the dream we are working toward now, although the math is tough,” Gryb says with a touch of understatement.
Gryb credits not just Barbour but also the idyllic surroundings of College Farm, which serves as a kind of private research campus, for inspiring the work. “The house evokes a simpler time and just opens your mind to new ideas when you visit,” he says. “Some of our biggest breakthroughs come from talking while walking across the rolling fields or when cooking dinner.” Indeed, Barbour continues to work from College Farm even though he is now, in a startling turn, a visiting professor at Oxford. In 2008 he won his first-ever official research grant and used the money to travel to conferences, as well as fund collaborators like Gryb and Gomes, the first two scientists to complete Ph.D.s on Barbour’s shape dynamics, work that had its origin right there on the farm.
At the end of Goethe’s Faust, the scholar’s sincerity redeems him, and God saves him from the devil’s clutches. Barbour is finding similar redemption in many of his colleagues’ eyes. “He stands out as the soft-voiced English gentleman who makes deep points about gravity that nobody else has considered,” says Olaf Dreyer, an expert on quantum gravity at the Sapienza University of Rome. “Barbour’s insight could be leading to exactly the breakthrough physics needs.” Even a sympathetic character like Dreyer adds a skeptical rejoinder, though: “It could just as easily be leading to a dead end.”
Is Barbour, now 75, waiting to be officially vindicated? Is he amazed that so many physicists embrace what to him are clearly illusions about space and time?
A gentleman to the end, he refuses to answer such pugilistic questions. Instead he comments that it could take many more years to persuade the physics community that his framework will bear fruit, but he is willing to do the work.
“Why do some people get caught by an idea that takes over your life? I don’t know, but I do know that as long as it doesn’t drive you crazy, it is a blessing,” Barbour says gently. “When I started out on this 40 years ago, I said to my family that I know what I want to do and it will take me the rest of my life to do it—and that is the way it has worked out.”
Zeeya Merali is a freelance science writer, author, and blogger for FQXi Community. She covers cosmology for the Discover Magazine, the Nature Journal, the Scientific American, and other science publications.