Male Hubble teams getting more telescope time

Researchers at the Space Telescope Science Institute (STScI) which runs the Hubble Space Telescope program, have found that there continues to be a gap between the number of projects given the go-ahead by male principle investigators (PIs) versus those headed by females.

Principle Investigators (PIs) are typically listed as the lead on proposals and when they are male, the researchers report, the chances are greater that their project will be approved.

In their paper uploaded to the preprint server arXiv (soon to be published in Publications of the Astronomical Society of the Pacific) the researchers note that efforts have been made to get rid of gender bias, but there still appears to be room for improvement.

It's not easy getting time on Hubble, researchers must form teams and then come up with something relevant and interesting to study.

After that, they have to write a proposal and submit it to STScI, after review the proposal is accepted or rejected, only a quarter of those submitted wind up getting telescope time.

Unfortunately, it seems that the odds are diminished even further if the PI is female. Not by much, the researchers report, just by four or five projects each proposal cycle, but that's enough to cause concern, especially in light of the fact that program officials have been trying to eliminate such perceived bias.

They've tried giving talks to reviewers, to explain the problem in the hopes it will cause them to be less biased, they've tried moving team members name to the back page, and even using just an initial for the first name of the PI. None of its worked, and the researchers don't know why.

They acknowledge that it's possible that female led proposals are simply not as interesting or as well thought out or written, in some cases, but also point out that very few if any proposals are written by only female teams, they're all filled with both men and women. Gender appears to only play a role for the PI.

The researchers have been studying the problem for two years, and are still mystified by the lack of change, they note that the problem is more pronounced when the PI is more senior, the difference is smaller for recent graduates, suggesting that the problem may solve itself given time.

They also note that Hubble isn't the only program with the problem, some small studies have suggested that female led proposals meet with less success on other observatories as well.

More information: Full paper: arxiv.org/abs/1409.3528

Time Warped - YouTube

A fascinating look at the mysteries of time perception by BBC’s Claudia Hammond, author of Time Warped – a fine addition to these 7 essential books on time.

The Corpus Clock and Chronophage

Known as the Corpus Clock, the machine has been invented by and designed by Dr John Taylor for Corpus Christi College Cambridge for the exterior of the college's new library building.

The Clock was unveiled on 19th September by Stephen Hawking, cosmologist and author of the global bestseller, A Brief History of Time.

Dr Taylor, an inventor and horologist, has put 500,000 pounds of his own money and seven years into developing the clock, which has been inspired from a design by a clock made by the legendary John Harrison, the pioneer of longitude.

Of John Harrison's many innovations, he came up with the 'grasshopper escapement, explained Dr Taylor, referring to the device used by Harrison to turn rotational motion into a pendulum motion for timekeeping.

No one knows how a grasshopper escapement works, so I decided to turn the clock inside out and, instead of making the escapement 35 mm across, it is 1.5 m across, he said.

He calls the new version of the escapement a Chronophage (time-eater) a fearsome beast which drives the clock, literally eating away time.

The Chronophage is currently installed and on public view in Edinburgh, at the National Museum of Scotland.
For more information please log on to http://www.corpusclock.co.uk

Time machine will study the early universe

With MOSFIRE, it will now become much easier to identify faint galaxies, "families of galaxies" and merging galaxies. The instrument also will enable detailed observations of planets orbiting nearby stars, star formation within our own galaxy, the distribution of dark matter in the universe and much more.

A new scientific instrument, a "time machine" of sorts, built by UCLA astronomers and colleagues, will allow scientists to study the earliest galaxies in the universe, which could never be studied before.

The five-ton instrument, the most advanced and sophisticated of its kind in the world, goes by the name MOSFIRE (Multi-Object Spectrometer for Infra-Red Exploration) and has been installed in the Keck I Telescope at the W.M. Keck Observatory atop Mauna Kea in Hawaii.

MOSFIRE gathers light in infrared wavelengths - invisible to the human eye - allowing it to penetrate cosmic dust and see distant objects whose light has been stretched or "redshifted" to the infrared by the expansion of the universe.

"The instrument was designed to study the most distant, faintest galaxies," said UCLA physics and astronomy professor Ian S. McLean, project leader on MOSFIRE and director of UCLA's Infrared Laboratory for Astrophysics.

"When we look at the most distant galaxies, we see them not as they are now but as they were when the light left them that is just now arriving here. Some of the galaxies that we are studying were formed some 10 billion years ago - only a few billion years after the Big Bang. We are looking back in time to the era of the formation of some of the very first galaxies, which are small and very faint. That is an era that we need to study if we are going to understand the large-scale structure of the universe."

With MOSFIRE, it will now become much easier to identify faint galaxies, "families of galaxies" and merging galaxies. The instrument also will enable detailed observations of planets orbiting nearby stars, star formation within our own galaxy, the distribution of dark matter in the universe and much more.

"We would like to study the environment of those early galaxies," said McLean, who built the instrument with colleagues from UCLA, the California Institute of Technology and UC Santa Cruz, along with industrial sub-contractors. "Sometimes there are large clusters with thousands of galaxies, sometimes small clusters. Often, black holes formed in the centers of galaxies."

Light collected by the Keck I Telescope was fed into MOSFIRE for the first time on April 4, producing an astronomical image. Astronomers are expected to start using MOSFIRE by September, following testing and evaluation in May and June.

MOSFIRE allows astronomers to take an infrared image of a field and to study 46 galaxies simultaneously, providing the infrared spectrum for each galaxy. Currently, it can take three hours or longer to obtain a good spectrum of just one galaxy, McLean noted.

McLean built the world's first infrared camera for wide use by astronomers in 1986 and since then has built eight increasingly sophisticated infrared cameras and spectrometers - which split light into its component colors - as well as helping on a few others.

McLean and Charles Steidel, the Lee A. DuBridge Professor of Astronomy at the California Institute of Technology, led the project to build MOSFIRE from scratch over seven years. Harland Epps, a UC Santa Cruz professor of astronomy and astrophysics, designed the optics for the instrument.

A team of nearly two dozen people helped, including Kristin Kulas and Gregory Mace, UCLA graduate students in physics and astronomy who work in McLean's laboratory; Keith Matthews, an instrument designer from Caltech; and Sean Adkins, an engineer who is the instrument program manager for the Keck Observatory in Hawaii.

Most of the mechanical parts for MOSFIRE were built at UCLA and Caltech. The slit unit that enables 46 objects to be isolated was manufactured in Switzerland. The computer programming was led by UCLA.

"My father, who was an engineer, called me an astronomer by inclination, a physicist by training and an engineer by default," McLean said. "I'm an applied physicist and an astronomer."

MOSFIRE cost $14 million and likely would have cost at least twice as much if the scientists had not built it themselves, McLean estimates.

MOSFIRE was federally funded by the National Science Foundation (through the Telescope System Instrumentation program), and by Gordon and Betty Moore. Gordon Moore is co-founder, former chairman and chief executive officer, and chairman emeritus of Intel Corp.

"He is a wonderful man with a penetrating intellect," McLean said of Moore. "We are deeply indebted to him and hope to be able to show him MOSFIRE this summer."

"We had an outstanding team," he added, "with four institutions involved and many industrial partners. It was a fantastic team effort."

In the late 1990s, McLean delivered an infrared spectrometer called NIRSPEC to the Keck Observatory in Hawaii, which housed the world's largest optical and infrared telescope at the time and which contains what had been the most powerful infrared spectrometer in the world. NIRSPEC is still on the Keck II Telescope.

While NIRSPEC's camera has one megapixel, MOSFIRE has four megapixels. MOSFIRE's detectors are approximately five times more sensitive than those on NIRSPEC and about 100 times more sensitive than those from McLean's 1986 infrared camera. In addition, the digital imaging devices available today are far superior to those of 15 years ago. The result is that MOSFIRE is much more sensitive to faint objects.

Discoveries made with NIRSPEC include the detection of water on comets, insights into the stars orbiting the enormous black hole at the center of the Milky Way galaxy, and the discovery of the chemical composition of brown dwarfs.

Proposed nuclear clock (ACES) may keep time with the Universe

The exquisite accuracy of atomic clocks is widely used in applications ranging from GPS navigation systems and high-bandwidth data transfer to tests of fundamental physics and system synchronisation in particle accelerators.

A proposed new time-keeping system tied to the orbiting of a neutron around an atomic nucleus could have such unprecedented accuracy that it neither gains nor loses 1/20th of a second in 14 billion years - the age of the Universe.

"This is nearly 100 times more accurate than the best atomic clocks we have now," says one of the researchers, Scientia Professor Victor Flambaum, who is Head of Theoretical Physics in the UNSW School of Physics.

"It would allow scientists to test fundamental physical theories at unprecedented levels of precision and provide an unmatched tool for applied physics research."

In a paper to be published in the journal Physical Review Letters - with US researchers at the Georgia Institute of Technology and the University of Nevada - Flambaum and UNSW colleague Dr Vladimir Dzuba report that their proposed single-ion clock would be accurate to 19 decimal places.

The exquisite accuracy of atomic clocks is widely used in applications ranging from GPS navigation systems and high-bandwidth data transfer to tests of fundamental physics and system synchronization in particle accelerators.

"With these clocks currently pushing up against significant accuracy limitations, a next-generation system is desired to explore the realms of extreme measurement precision and further diversified applications unreachable by atomic clocks," says Professor Flambaum.

"Atomic clocks use the orbiting electrons of an atom as the clock pendulum. But we have shown that by using lasers to orient the electrons in a very specific way, one can use the orbiting neutron of an atomic nucleus as the clock pendulum, making a so-called nuclear clock with unparalleled accuracy."

Because the neutron is held so tightly to the nucleus, its oscillation rate is almost completely unaffected by any external perturbations, unlike those of an atomic clock's electrons, which are much more loosely bound.

Stephen Hawking at 70: A Brief History of Time - Video

A film about the life and work of the cosmologist, Stephen Hawking, who despite his near total paralysis, is one of the great minds of all time.


Brilliant but unmotivated, Stephen Hawking was a 21-year-old PhD student at Cambridge when he first noticed something was wrong. He was falling down a lot, and dropping things.

He went into the hospital for tests, and learned he had amyotrophic lateral sclerosis, or ALS. The doctors told him he would gradually lose control of every muscle in his body.

“My dreams at that time were rather disturbed,” Hawking said. “Before my condition had been diagnosed, I had been very bored with life.

There had not seemed to be anything worth doing. But shortly after I came out of hospital, I dreamt that I was going to be executed. I suddenly realized that there were a lot of worthwhile things I could do if I were reprieved.”

The doctors gave the young man two and a half years to live. That was in early 1963. Over the next half century, Hawking defied all odds and went on to become one of the most celebrated scientists of the era, making major contributions to quantum cosmology and the understanding of black holes.

Along the way, the wheelchair-bound Hawking became a cultural icon, a symbol of disembodied intellect and indomitable spirit.

This coming Sunday, 49 years after his grim diagnosis, Hawking will turn 70. A scientific conference in his honor got underway today at the University of Cambridge’s Centre for Theoretical Cosmology, and will culminate on Sunday with a public symposium, “The State of the Universe,” featuring some of the world’s greatest astronomers and physicists, including Martin Rees, Kip Thorne and Saul Perlmutter.

You can watch live streaming video of the events at the official website.

To help celebrate, we present Errol Morris’s 1992 film of A Brief History of Time (above), Hawking’s bestselling book.

Morris weaves biography in with the science, interviewing members of Hawking’s family–his mother, sister and aunt–along with friends and colleagues, including Roger Penrose, Dennis Sciama and John Archibald Wheeler.

A Brief History of Time was Morris’s first film as a director-for-hire (he was recruited by Steven Spielberg for Amblin Entertainment), which created some difficulties, but Morris was pleased with the outcome.

He later said, “It’s actually one of the most beautiful films I ever shot.” The film won the Grand Jury Prize for Documentary Filmmaking and the Documentary Filmmaker’s Trophy at the Sundance Film Festival.

In 1992 Morris told the New York Times Magazine that A Brief History of Time was “less cerebral and more moving” than anything he had worked on before.

“This feeling of time, of aging, of mortality combined with this search for the most basic and deep questions about the world around us and ourselves,” Morris said, “is pretty persuasive stuff.”

Time Warp: Event-hiding 'temporal cloak' demonstrated

Last year researchers at Imperial College London proposed that along with being used to cloak physical objects metamaterials could also be used to cloak a singular event in time.

A year later, researchers from Cornell University have demonstrated a working "temporal cloak" that is able to conceal a burst of light as if it had never occurred.

In a research paper published in the Journal of Optics last year, Prof. Martin McCall and his team at Imperial College London said it should be theoretically possible to create a "Spacetime Cloak" by using metamaterials - a class of artificial materials engineered to have properties not be found in nature - to speed up the leading edge of light waves, while slowing down the trailing half.

This would create a "corridor" between the two halves, at which point their source wouldn't be observable.

To demonstrate the theory, a Cornell research team led by Moti Fridman sent a beam of light down an optical fiber and passed it through a split-time lens - a silicon device originally designed to speed up data transfer.

As the beam passes through the first lens it is compressed, leaving a dead zone or gap in the flow of light.

A similar lens further along the path reverses the velocity adjustments, decompressing the light wave so it appears that the light coming through the second lens is uninterrupted as if no distortion had occurred.

To test the temporal cloak's performance the researchers created pulses of light directly between the two lenses that repeated like clockwork at a rate of 41 kHz.

When the cloak was off, the researchers were able to detect a steady beat, but after switching on the cloak, which was synchronized with the light pulses, it appeared as if the pulses were erased from the data stream.

Rather than relying on the properties of metamaterials as was initially proposed by McCall, the temporal cloak demonstrated by the Cornell research team relies on the fundamental properties of light and how it behaves under highly constrained space and time conditions.

The length of the cloaked area is a mere six millimeters (0.2 in) long and the effect can only lasts for 110 nanoseconds.

The team says the best it can achieve will be 120 microseconds because longer durations would create turbulence in the system that would hint that an event had occurred.

To achieve any measurable macroscopic effects would require an experiment on planetary or even interplanetary scales, the researchers say.

The Cornell team will present their findings in a presentation "Demonstration of Temporal Cloaking" at the Optical Society's Annual Meeting, Frontiers in Optics (FiO) 2011, being held in San Jose, California, next week.

Space–time invisibility cloak could 'edit history' - physicsworld.com

Physicists in the UK have proposed a "space–time" invisibility cloak that, if built, could be used to prevent signal interference or give the illusion of a Star Trek teleportation device.

The idea comes after four years of research by different groups that are creating devices to make objects invisible.

In 2006 researchers at Duke University in the US created the first device that could cloak a small object in two dimensions in the microwave region of the electromagnetic spectrum. Last year groups at Cornell University and the University of California at Berkeley, US, independently created 2D cloaks that operated at optical wavelengths.

Then, earlier this year, a team at the Karlsruhe Institute of Technology in Germany went one step further to produce a 3D optical cloak.

The latest development, by Martin McCall and colleagues of Imperial College, London, and the University of Salford, might see cloaks add yet another dimension to their capability: time. The idea is to create a tunnel through which an object could perform an action – move or change shape, for example – while appearing as though it is doing nothing at all.

Space–time invisibility cloak could 'edit history' - physicsworld.com

Atomic Fountain reveals 'Gravitational Red Shift'

Atomic fountain reveals 'gravitational red shift' - New Scientist

YOUR watch runs a tiny bit faster at the top of Everest, where Earth's gravity is slightly weaker, than it does at sea level.

This difference is dubbed the "gravitational red shift" (GRS) and is one of the trickiest predictions of general relativity to measure because the effect is so small.

Now the accuracy of measurement has been improved by a factor of 10,000. Holger Müller at the University of California, Berkeley, decided to reanalyse a decade-old experiment.

In the 1990s, a team led by Nobel laureate Steven Chu made an "atomic fountain" of caesium atoms, launching them 30 centimetres into the air.

A pulse of laser light struck the atoms as they neared their zenith, which kicked them into a two-state quantum superposition. One of the states was given extra momentum, causing it to rise to a slightly higher altitude than the other state before falling.

Müller realised the atoms and their very rapid oscillations could be treated as tiny "clocks" and so could be used to measure GRS. The team compared the difference between the two states and discovered that the state that climbed slightly higher had oscillated ever-so-slightly faster than the lower state.

With an accuracy of 7 parts in a billion, this measurement is 10,000 times as accurate as the previous one (Nature, DOI: 10.1038/nature08776).

ESA Portal - PHARAO atomic clock agreement signed by ESA and CNES

PHARAO atomic clock agreement signed by ESA and CNES

15 December 2009



ESA Portal - PHARAO atomic clock agreement signed by ESA and CNES

PHARAO atomic clock agreement signed by ESA and CNES

15 December 2009
ESA PR 31-2009 Today at the Paris headquarters of the French space agency (CNES), Simonetta Di Pippo, ESA Director of Human Spaceflight, and Thierry Duquesne, CNES Director for Strategy, Programmes and International Relations, signed an agreement that paves the way for the launch of a high-accuracy atomic clock to be attached to the outside of the European Columbus laboratory onboard the International Space Station (ISS).

The PHARAO (Projet d’Horloge Atomique par Refroidissement d’Atomes en Orbite) atomic clock, which will be combined with another atomic clock, the Space Hydrogen Maser (SHM), to form ESA’s Atomic Clock Ensemble in Space (ACES), will have an accuracy of 1x10^-16, corresponding to a time error of about one second over 300 million years.

This new generation of atomic clocks in space will be instrumental in enabling accurate testing of Einstein’s theory of general relativity. In addition, it will contribute to the accuracy and long-term stability of global timescales, e.g. International Atomic Time (TAI) and Coordinated Universal Time (UTC), and also help in the development of applications in the field of geodesy, and support applications involving remote sensing via the GNSS network.

The Illusion of all Time

IT IS the invisible presence that governs your world. Trailing you like an unshakeable shadow, it ticks and tocks incessantly. You can sense it in your heartbeat, in the rising and setting of the sun, and in your daily rush to make meetings, trains and deadlines. It brings order to our lives through the categories of past, present and future.

Time. There is nothing with which we are so familiar, and yet when you try to pin it down you find only a relentless torrent of questions. Why does time appear to flow? What makes it different from space? What exactly is it? It's enough to make your neurons misfire, then sizzle and smoke.

You are not alone. Physicists have long struggled to understand what time really is. In fact, they are not even sure it exists at all. In their quest for deeper theories of the universe, some researchers increasingly suspect that time is not a fundamental feature of nature, but rather an artefact of our perception. One group has recently found a way to do quantum physics without invoking time, which could help pave a path to a time-free "theory of everything". If correct, the approach suggests that time really is an illusion, and that we may need to rethink how the universe at large works.

For decades, physicists have been searching for a quantum theory of gravity to reconcile Einstein's general relativity, which describes gravity at the largest scales, with quantum mechanics, which describes the behaviour of particles at the tiniest scales. One reason it has been so difficult to merge the two is that they are built on incompatible views of time. "I am more and more convinced that the problem of time is key both to quantum gravity and to issues in cosmology," says Lee Smolin of the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, Canada.

According to general relativity, time is stitched together with space to form four-dimensional space-time. The passage of time is not absolute - no cosmic clock ticks away the hours of the universe. Instead, time differs from one frame of reference to the next, and what one observer experiences as time, another might experience as a mixture of time and space. For Einstein, time is a useful measure of things, but nothing special.

Not so in quantum mechanics. Here time plays a key role, keeping track of the ever-changing probabilities that define the microworld, which are encoded in the "wave function" of a quantum system. The clock by which the wave function evolves records not just the time in one particular frame of reference, but the absolute time that Einstein worked so hard to topple. So while relativity treats space and time as a whole, quantum mechanics splits the universe into two parts: the quantum system being observed and the classical world outside. In this fractured universe, a clock always remains outside the quantum system (see Diagram).

Something has to give. The fact that the universe has no outside, by definition, suggests that quantum mechanics will be the one to surrender - and to many, this suggests that time is not fundamental. In the 1990s, for instance, physicist Julian Barbour proposed that time must not exist in a quantum theory of the universe. All the same, physicists are loath to throw out quantum theory, as it has proven capable of extraordinarily accurate predictions. What they need is a way to do quantum mechanics in the absence of time.
Single quantum event

Carlo Rovelli, a physicist at the University of Marseille in France, has found just that. In the past year, he and his colleagues have worked out a method to compress multiple quantum events in time into a single event that can be described without reference to time (Physical Review D, vol 75, p 084033).

It is an intriguing achievement. While Rovelli's approach to dealing with time is one of many, and researchers working on other models of quantum gravity may have different opinions on the matter, nearly every physicist agrees that time is a key obstacle to finding an ultimate theory. Rovelli's approach seems tantalisingly close to surmounting that obstacle. His model builds upon research into generalising quantum mechanics by physicist James Hartle at the University of California, Santa Barbara, as well as Rovelli's earlier work on quantum systems.

The idea is this: suppose we have an electron characterised by its spin, a quantum property that is either "up" or "down" along whatever direction you measure it. Say we want to make two consecutive measurements of its spin, one in the x direction and one in the y direction. The probabilities of the possible outcomes will depend on the order in which we perform the measurements. That's because a measurement "collapses" the indeterminate state of the wave function, forcing it to commit to a given state; the first measurement will change the particle's state, which affects the second measurement.

Say we already know the electron's spin is up in the x direction. If we now measure the spin in the x direction followed by the y direction, we will find the x spin up - no change there - and then there is a 50:50 chance of finding the y spin up or down. But if we begin by measuring the y spin, that disturbs the spin in the x direction, creating a 50-50 probability for both measurements.

If reordering the measurements in time changes the probabilities, how can we calculate the probabilities of sequences of events without reference to time? The trick, says Rovelli, is to adjust the boundary between the quantum system under observation and the classical outside world where measuring devices are considered to reside. By shifting the boundary, we can include the measuring device as part of the quantum system.

In that case we no longer ask, "What is the probability of the electron having spin up and then spin down?" Instead we ask, "What is the probability of finding the measuring devices in a particular state?" The measuring device no longer collapses the wave function; rather, the electron and the measuring device together are described by a single wave function, and a single measurement of the entire set-up causes the collapse.

Where has time gone? Evolution in time is transformed into correlations between things that can be observed in space. "To give an analogy," Rovelli says, "I can tell you that I drove from Boston to Los Angeles but I passed first through Chicago and later through Denver. Here I am specifying things in time. But I could also tell you that I drove from Boston to LA along the road marked in this map. So I can replace the information about which measurement happens first in time with the detailed information about how the observables are correlated."

That Rovelli's approach yields the correct probabilities in quantum mechanics seems to justify his intuition that the dynamics of the universe can be described as a network of correlations, rather than as an evolution in time. "Rovelli's work makes the timeless view more believable and more in line with standard physics," says Dean Rickles, a philosopher of physics at the University of Sydney in Australia.

With quantum mechanics rewritten in time-free form, combining it with general relativity seems less daunting, and a universe in which time is fundamental seems less likely. But if time doesn't exist, why do we experience it so relentlessly? Is it all an illusion?

Yes, says Rovelli, but there is a physical explanation for it. For more than a decade, he has been working with mathematician Alain Connes at the College de France in Paris to understand how a time-free reality could give rise to the appearance of time. Their idea, called the thermal time hypothesis, suggests that time emerges as a statistical effect, in the same way that temperature emerges from averaging the behaviour of large groups of molecules (Classical and Quantum Gravity, vol 11, p 2899).

Imagine gas in a box. In principle we could keep track of the position and momentum of each molecule at every instant and have total knowledge of the microscopic state of our surroundings. In this scenario, no such thing as temperature exists; instead we have an ever-changing arrangement of molecules. Keeping track of all that information is not feasible in practice, but we can average the microscopic behaviour to derive a macroscopic description. We condense all the information about the momenta of the molecules into a single measure, an average that we call temperature.

According to Connes and Rovelli, the same applies to the universe at large. There are many more constituents to keep track of: not only do we have particles of matter to deal with, we also have space itself and therefore gravity. When we average over this vast microscopic arrangement, the macroscopic feature that emerges is not temperature, but time. "It is not reality that has a time flow, it is our very approximate knowledge of reality that has a time flow," says Rovelli. "Time is the effect of our ignorance."

It is not reality that has a time flow, but our very approximate knowledge of reality. Time is the effect of our ignorance

Cosmic time
It all sounds good on paper, but is there any evidence that the idea might be correct? Rovelli and Connes have tested their hypothesis with simple models. They started by looking at the cosmic microwave background (CMB) radiation that pervades the sky - relic heat from the big bang. The CMB is an example of a statistical state: averaging over the finer details, we can say that the radiation is practically uniform and has a temperature of just under 3 kelvin. Rovelli and Connes used this as a model for the statistical state of the universe, tossing in other information such as the radius of the observable universe, and looked to see what apparent time flow that would generate.

What they got was a sequence of states describing a small universe expanding in exactly the manner described by standard cosmological equations - matching what physicists refer to as cosmic time. "I was amazed," says Rovelli. "Connes was as well. He had independently thought about the same idea, and was very surprised to see it worked in a simple calculation."

To truly apply the thermal time hypothesis to the universe, however, physicists need a theory of quantum gravity. All the same, the fact that a simple model like that of the CMB produced realistic results is promising. "One of the traditional difficulties of quantum gravity was how to make sense of a theory in which the time variable had disappeared," Rovelli says. "Here we begin to see that a theory without a time variable can not only still make sense, but can in fact describe a world like the one we see around us."

What's more, the thermal time hypothesis gives another interesting result. If time is an artefact of our statistical description of the world, then a different description should lead to a different flow of time. There is a clear case in which this happens: in the presence of an event horizon.

When an observer accelerates, he creates an event horizon, a boundary that partitions off a region of the universe from which light can never reach him so long as he continues to accelerate. This observer will describe a different statistical state of the universe from an observer who doesn't have a horizon, since he is missing information that lies beyond his event horizon. The flow of time he perceives should therefore be different.

Using general relativity, however, there is another way to describe his experience of time. The geometry of the space-time he inhabits, as defined by his horizon, determines a so-called proper time - the time flow he would register if he were carrying a clock. The thermal time hypothesis predicts that the ratio of the observer's proper time to his statistical time - the time flow that emerges from Connes and Rovelli's ideas - is the temperature he measures around him.

It so happens that every event horizon has an associated temperature. The best known case is that of a black hole event horizon, whose temperature is that of the "Hawking radiation" it emits. Likewise, an accelerating observer measures a temperature associated with something known as Unruh radiation. The temperature Rovelli and Connes derived matches the Unruh temperature and the Hawking temperature for a black hole, further boosting their hypothesis.

"The thermal time hypothesis is a very beautiful idea," says Pierre Martinetti, a physicist at the University of Rome in Italy. "But I believe its implementation is still limited. For the moment one has just checked that this hypothesis was not contradictory when a notion of time was already available. But it has not been used in quantum gravity."

Others also urge caution in interpreting what it all means for the nature of time. "It is wrong to say that time is an illusion," says Rickles. "It is just reducible or non-fundamental, in the same way that consciousness emerges from brain activity but is not illusory."

So if time really does prove to be non-fundamental, what are we to make of it? "For us, time exists and flows," says Rovelli. "The point is that this nice flow becomes something much more complicated at the small scale."

At reality's deepest level, then, it remains unknown whether time will hold strong or melt away like a Salvador Dali clock. Perhaps, as Rovelli and others suggest, time is all a matter of perspective, not a feature of reality but a result of your missing information about reality. So if your brain hurts when you try to understand time, relax. If you really knew, time might simply disappear.

Earth Time Timeline