Scientists behind a theory that the speed of light is variable—and not constant, as Einstein had suggested—have made a prediction that could be tested.
Einstein observed that the speed of light remains the same in any situation, and this meant that space and time could be different in different situations.
The assumption that the speed of light is constant, and always has been, underpins many theories in physics, such as Einstein’s theory of general relativity. In particular, it plays a role in models of what happened in the very early universe, seconds after the Big Bang.
But some researchers have suggested that the speed of light could have been much higher in this early universe. Now, one of this theory’s originators, Professor João Magueijo from Imperial College London, working with Dr. Niayesh Afshordi at the Perimeter Institute in Canada, has made a prediction that could be used to test the theory’s validity. According to professor Magueijo, “The idea that the speed of light could be variable was radical when first proposed, but with a numerical prediction, it becomes something physicists can actually test. If true, it would mean that the laws of nature were not always the same as they are today.” Structures in the universe, for example galaxies, all formed from fluctuations in the early universe—tiny differences in density from one region to another. A record of these early fluctuations is imprinted on the cosmic microwave background—a map of the oldest light in the universe—in the form of a ‘spectral index.’
Working with their theory that the fluctuations were influenced by a varying speed of light in the early universe, Professor Magueijo and Dr. Afshordi have now used a model to put an exact figure on the spectral index. The predicted figure and the model it is based on are published in the journal Physical Review D.
Cosmologists are currently getting ever more precise readings of this figure, so that prediction could soon be tested—either confirming or ruling out the team’s model of the early universe. Their figure is a very precise 0.96478. This is close to the current estimate of readings of the cosmic microwave background, which puts it around 0.968, with some margin of error.
Professor Magueijo said, “The theory, which we first proposed in the late-1990s, has now reached a maturity point—it has produced a testable prediction. If observations in the near future do find this number to be accurate, it could lead to a modification of Einstein’s theory of gravity.
The testability of the varying speed-of-light theory sets it apart from the more mainstream rival theory: inflation. Inflation says that the early universe went through an extremely rapid expansion phase, much faster than the current rate of expansion of the universe.
These theories are necessary to overcome what physicists call the horizon problem. The universe as we see it today appears to be everywhere broadly the same: for example it has a relatively homogenous density.
This could only be true if all regions of the universe were able to influence each other. However, if the speed of light has always been the same, then not enough time has passed for light to have traveled to the edge of the universe and ‘even out’ the energy.
As an analogy, to heat up a room evenly, the warm air from radiators at either end has to travel across the room and mix fully. The problem for the universe is that the ‘room’—the observed size of the universe—appears to be too large for this to have happened in the time since it was formed.
The varying speed-of-light theory suggests that the speed of light was much higher in the early universe, allowing the distant edges to be connected as the universe expanded. The speed of light would have then dropped in a predictable way as the density of the universe changed. This variability led the team to the prediction published in November 2016.
The alternative theory is inflation, which attempts to solve this problem by saying that the very early universe evened out while incredibly small and then suddenly expanded, with the uniformity already imprinted on it. While this means the speed of light and the other laws of physics as we know them are preserved, it requires the invention of an ‘inflation field’ – a set of conditions that only existed at the time.
‘Critical geometry of a thermal big bang’ by Niayesh Afshordi and João Magueijo is published in Physical Review D.
Thinking Your Way to Strength?
Anyone who has worn a cast knows that rebuilding muscle strength once the cast is removed can be difficult. Now researchers at the Ohio Musculoskeletal and Neurological Institute (OMNI) at Ohio University have found that the mind is critical in maintaining muscle strength following a prolonged period of immobilization and that mental imagery may be key in reducing the associated muscle loss.
Strength is controlled by a number of factors—the most studied by far is skeletal muscle. However, the nervous system is also an important, though not fully understood, determinant of strength and weakness. Brian C. Clark and colleagues set out to test how the brain’s cortex plays into strength development. They designed an experiment to measure changes in wrist flexor strength in three groups of healthy adults. Twenty-nine subjects wore a rigid cast that extended from just below the elbow past the fingers, effectively immobilizing the hand and wrist, for four weeks. Fifteen subjects who did not wear casts served as the control group.
Of the group with wrist-hand immobilization, half (14) were asked to regularly perform an imagery exercise, imagining they were intensely contracting their wrist for five seconds and then resting for five seconds. They were verbally guided through the imagery exercise with the following instructions: “Begin imagining that you are pushing in as hard as you can with your left wrist, push, push, push… and stop. (Five-second rest.) Start imagining that you are pushing in again as hard as you can, keep pushing, keep pushing… and stop. (Five-second rest.)” This was repeated four times in a row followed by a one-minute break for a total of 13 rounds per session and five sessions per week. The second group performed no imagery exercises.
At the end of the four-week experiment, both groups who wore casts had lost strength in their immobilized limbs when compared to the control group. But the group that performed mental imagery exercises lost 50% less strength than the non-imaginative group (24% vs. 45%, respectively). The nervous system’s ability to fully activate the muscle (called “voluntary activation” or VA) also rebounded more quickly in the imagery group compared to the non-imagery group.
“These findings suggest neurological mechanisms, most likely at the cortical level, contribute significantly to disuse-induced weakness and that regular activation of the cortical regions via imagery attenuates weakness and VA by maintaining normal levels of inhibition,” the research team wrote. “Thus our findings that imagery attenuated the loss of muscle strength provide proof-of-concept for it as a therapeutic intervention for muscle weakness and voluntary neural activation.”
The article, “The power of the mind: the cortex as a critical determinant of muscle strength/ weakness” is published in the Journal of Neurophysiology.
Mystery Bison Hidden in Cave Art
Ancient DNA research has revealed that Ice Age cave artists recorded a previously unknown hybrid species of bison and cattle in great detail on cave walls more than 15,000 years ago.
The mystery species, known affectionately by the researchers as the Higgs Bison* because of its elusive nature, originated over 120,000 years ago through the hybridization of the extinct Aurochs (the ancestor of modern cattle) and the Ice Age Steppe Bison, which ranged across the cold grasslands from Europe to Mexico.
Research led by the Australian Center for Ancient DNA (ACAD) at the University of Adelaide, published in October 2016 in Nature Communications, has revealed that the mystery hybrid species eventually became the ancestor of the modern European bison, or wisent, which survives in protected reserves, such as the Białowieza Forest between Poland and Belarus.
“Finding that a hybridization event led to a completely new species was a real surprise—as this isn’t really meant to happen in mammals,” says study leader, Professor Alan Cooper, ACAD Director, “The genetic signals from the ancient bison bones were very odd, but we weren’t quite sure a species really existed—so we referred to it as the Higgs Bison.”
The international team of researchers also included the University of California, Santa Cruz (UCSC), Polish bison conservation researchers, and paleontologists across Europe and Russia. They studied ancient DNA extracted from radiocarbon-dated bones and teeth found in caves across Europe, the Urals, and the Caucasus to trace the genetic history of the populations.
They found a distinctive genetic signal from many fossil bison bones, which was quite different from the European bison or any other known species.
Radiocarbon dating showed that the mystery species dominated the European record for thousands of years at several points but alternated over time with the Steppe bison, which had previously been considered the only bison species present in Late Ice Age Europe.
“The dated bones revealed that our new species and the Steppe Bison swapped dominance in Europe several times, in concert with major environmental changes caused by climate change,” says lead author Dr. Julien Soubrier, from the University of Adelaide. “When we asked, French cave researchers told us that there were indeed two distinct forms of bison art in Ice Age caves, and it turns out their ages match those of the different species. We’d never have guessed the cave artists had helpfully painted pictures of both species for us.”
The cave paintings depict bison with either long horns and large forequarters (more like the American bison, which is descended from the Steppe bison), or with shorter horns and small humps, more similar to modern European bison.
“Once formed, the new hybrid species seems to have successfully carved out a niche on the landscape, and kept to itself genetically,” says Professor Cooper. “It dominated during colder tundra-like periods, without warm summers, and was the largest European species to survive the megafaunal extinctions. However, the modern European bison looks genetically quite different as it went through a genetic bottleneck of only 12 individuals in the 1920s, when it almost became extinct. That’s why the ancient form looked so much like a new species.”
Professor Beth Shapiro, UCSC, first detected the mystery bison as part of her Ph.D. research with Professor Cooper at the University of Oxford in 2001. “Fifteen years later it’s great to finally get to the full story out. It’s certainly been a long road, with a surprising number of twists,” Professor Shapiro says.
*The Higgs Boson is a subatomic particle suspected to exist since the 1960s and only confirmed in 2012; although some question even that confirmation.