New 'time travel' study reveals future impact of climate change on coastal marshes

A new Tulane University study published in Nature Communications offers a glimpse into the possible impact of climate change on coastal wetlands 50 years or longer into the future.

Scientists are usually forced to rely on computer models to project the long-term effects of rising seas.

But an unexpected set of circumstances enabled a real-world experiment along the Gulf Coast.

An extensive network of nearly 400 monitoring sites was established along the Louisiana coast after hurricanes Katrina and Rita.

Then the rate of sea-level rise in the region surged to more than 10 millimeters (half an inch) per year -- at least three times the global average.

That exposed the region to the kind of ocean rise not expected until around 2070.

The accelerated rise created a unique opportunity to determine whether the marshes can survive that pace of coastal flooding.

"It is the dream of every field researcher who does experiments -- we can basically travel 50 years into the future to get a peek at what's in store," said Torbjörn Törnqvist, Vokes Geology Professor in the Tulane Department of Earth and Environmental Sciences.

The researchers used new techniques developed by European scientists to measure sea-level rise right off the coast with satellite data, something that was previously not available.

The team then compared the rate of water-level rise at each monitoring site with the rate of wetland elevation change determined by other instruments and found that almost 90% of the sites were in deficit.

"To our knowledge, this is the first time that a climate impact experiment has been carried out over a region this large, based on hundreds of monitoring stations that have collected data for about 15 years," said Guandong Li, a PhD candidate in Earth and Environmental Sciences at Tulane who led the study.

"This has also allowed us to study the climate impact on a heavily human-influenced landscape, rather than a more resilient pristine ecosystem."

Li was investigating the role of land subsidence in coastal Louisiana when a team led by Sönke Dangendorf, the David and Jane Flowerree Professor in Tulane's Department of River-Coastal Science and Engineering, demonstrated the unprecedented rates of sea-level rise along the Gulf and Southeast U.S. coasts since 2010.

"Guandong immediately dropped everything he was working on to take advantage of this unique opportunity," Törnqvist said.

"He set out to answer the key question of whether coastal marshes can keep up with this rate of sea-level rise, as some earlier modeling studies had suggested they can."

If the current climate scenario persists, the rate of sea-level rise by 2070 is expected to be about 7 millimeters (one quarter inch) per year.

The study projects that approximately 75% of wetland sites will be in deficit by that time, potentially resulting in a rate of wetland loss much higher than what has already occurred in the past century.

However, the researchers emphasize that there is hope for a more favorable outcome if immediate action is taken.

By meeting the targets set by the Paris Agreement and reducing carbon emissions, it is possible to shift to a more sustainable climate trajectory that would reduce the rate of wetland loss.

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Simulating quantum 'time travel' disproves butterfly effect in quantum realm

Using a quantum computer to simulate time travel, researchers have demonstrated that, in the quantum realm, there is no "butterfly effect." In the research, information -- qubits, or quantum bits -- "time travel" into the simulated past. One of them is then strongly damaged, like stepping on a butterfly, metaphorically speaking. Surprisingly, when all qubits return to the "present," they appear largely unaltered, as if reality is self-healing.

"On a quantum computer, there is no problem simulating opposite-in-time evolution, or simulating running a process backwards into the past," said Nikolai Sinitsyn, a theoretical physicist at Los Alamos National Laboratory and coauthor of the paper with Bin Yan, a post doc in the Center for Nonlinear Studies, also at Los Alamos. "So we can actually see what happens with a complex quantum world if we travel back in time, add small damage, and return. We found that our world survives, which means there's no butterfly effect in quantum mechanics."

In Ray Bradbury's 1952 science fiction story, "A Sound of Thunder," a character used a time machine to travel to the deep past, where he stepped on a butterfly. Upon returning to the present time, he found a different world. This story is often credited with coining the term "butterfly effect," which refers to the extremely high sensitivity of a complex, dynamic system to its initial conditions. In such a system, early, small factors go on to strongly influence the evolution of the entire system.

Instead, Yan and Sinitsyn found that simulating a return to the past to cause small local damage in a quantum system leads to only small, insignificant local damage in the present.

This effect has potential applications in information-hiding hardware and testing quantum information devices. Information can be hidden by a computer by converting the initial state into a strongly entangled one.

"We found that even if an intruder performs state-damaging measurements on the strongly entangled state, we still can easily recover the useful information because this damage is not magnified by a decoding process," Yan said. "This justifies talks about creating quantum hardware that will be used to hide information."

This new finding could also be used to test whether a quantum processor is, in fact, working by quantum principles. Since the newfound no-butterfly effect is purely quantum, if a processor runs Yan and Sinitsyn's system and shows this effect, then it must be a quantum processor.

To test the butterfly effect in quantum systems, Yan and Sinitsyn used theory and simulations with the IBM-Q quantum processor to show how a circuit could evolve a complex system by applying quantum gates, with forwards and backwards cause and effect.

Presto, a quantum time-machine simulator.

In the team's experiment, Alice, a favorite stand-in agent used for quantum thought experiments, prepares one of her qubits in the present time and runs it backwards through the quantum computer. In the deep past, an intruder -- Bob, another favorite stand-in -- meaures Alice's qubit. This action disturbs the qubit and destroys all its quantum correlations with the rest of the world. Next, the system is run forward to the present time.

According to Ray Bradbury, Bob's small damage to the state and all those correlations in the past should be quickly magnified during the complex forward-in-time evolution. Hence, Alice should be unable to recover her information at the end.

But that's not what happened. Yan and Sinitsyn found that most of the presently local information was hidden in the deep past in the form of essentially quantum correlations that could not be damaged by minor tampering. They showed that the information returns to Alice's qubit without much damage despite Bob's interference. Counterintuitively, for deeper travels to the past and for bigger "worlds," Alice's final information returns to her even less damaged.

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Time-traveling illusion tricks the brain

The Rabbit Illusion (see video: https://youtu.be/yCpsQ8LZOco).

We experience the world through our senses, a constant torrent of sights, sounds, smells, and more. Our brains take these signals and process them, giving rise to our individual perceptions of the world. But sometimes our senses play tricks on us, notably in the case of perceptual illusions.

Now, Caltech researchers have developed two new illusions that reveal how the senses can influence each other -- in particular, how sound can give rise to visual illusions. These illusions occur so quickly that they illustrate a phenomenon called postdiction (as opposed to prediction) in which a stimulus that occurs later can retroactively affect our perceptions of an earlier event.

The Caltech work is among the first to show this kind of time-traveling illusion across multiple senses.

The work was done in the laboratory of Shinsuke Shimojo, Gertrude Baltimore Professor of Experimental Psychology and affiliated faculty member of the Tianqiao and Chrissy Chen Institute for Neuroscience at Caltech. A paper describing the research appears in the October 3 issue of the journal PLOS ONE.

"Illusions are a really interesting window into the brain," says first author Noelle Stiles (PhD '15), a visitor in biology and biological engineering and a postdoctoral scholar-research associate at USC. "By investigating illusions, we can study the brain's decision-making process. For example, how does the brain determine reality with information from multiple senses that is at times noisy and conflicting? The brain uses assumptions about the environment to solve this problem. When these assumptions happen to be wrong, illusions can occur as the brain tries to make the best sense of a confusing situation. We can use these illusions to unveil the underlying inferences that the brain makes."

The two illusions in this study were developed to illustrate how stimuli that occur later can affect the perception of stimuli that have already occurred. Postdictive processing has been demonstrated within individual senses, but this work focuses on how the phenomenon can bridge multiple senses. The key to both of the new illusions is that the audio and visual stimuli occur rapidly, in under 200 milliseconds (one-fifth of a second). The brain, trying to make sense of this barrage of information, synthesizes the stimuli from both senses to determine the experience, using postdiction to do so.

The first illusion is called the Illusory Rabbit. To produce the illusion, first a short beep and a quick flash are played nearly simultaneously on a computer, with the flash appearing at the left side of the screen. Next, 58 milliseconds after the first beep, a lone beep is played. Finally, 58 milliseconds after the second beep, a second nearly simultaneous beep-flash pair occurs, but with the flash appearing on the right side of the screen. The beep location is always central and does not move. Though only two flashes are played, most people viewing the illusion perceive three flashes, with an illusory flash coinciding with the second beep and appearing to be located in the center of the screen.

The fact that the illusory flash is perceived in between the left and right flashes is the key evidence that the brain is using postdictive processing.

"When the final beep-flash pair is later presented, the brain assumes that it must have missed the flash associated with the unpaired beep and quite literally makes up the fact that there must have been a second flash that it missed," explains Stiles. "This already implies a postdictive mechanism at work. But even more importantly, the only way that you could perceive the shifted illusory flash would be if the information that comes later in time -- the final beep-flash combination -- is being used to reconstruct the most likely location of the illusory flash as well."

The second illusion is called the Invisible Rabbit. In this related illusion, three flashes are shown on the screen, the first on the left, the second in the middle, and finally the third on the right, with only the first and third flashes coinciding with beeps. In this case, most people do not see the second flash -- the one without a corresponding sound -- at all. The absence of the second beep leads the brain to decide after the fact that there actually was no flash, even though it was in fact present.

By showing that a sound can excite a visual illusion, the researchers have uncovered new clues as to how the brain combines the senses over space and time to generate an integrated sense of perception.

"The significance of this study is twofold," says Shimojo. "First, it generalizes postdiction as a key process in perceptual processing for both a single sense and multiple senses. Postdiction may sound mysterious, but it is not -- one must consider how long it takes the brain to process earlier visual stimuli, during which time subsequent stimuli from a different sense can affect or modulate the first. The second significance is that these illusions are among the very rare cases where sound affects vision, not vice versa, indicating dynamic aspects of neural processing that occur across space and time. These new illusions will enable researchers to identify optimal parameters for multisensory integration, which is necessary for both the design of ideal sensory aids and optimal training for low-vision individuals."

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Using math to investigate possibility of time travel

Ben Tippett, a mathematics and physics instructor at UBC, recently published a study about the feasibility of time travel.

After some serious number crunching, a UBC researcher has come up with a mathematical model for a viable time machine.

Ben Tippett, a mathematics and physics instructor at UBC's Okanagan campus, recently published a study about the feasibility of time travel. Tippett, whose field of expertise is Einstein's theory of general relativity, studies black holes and science fiction when he's not teaching. Using math and physics, he has created a formula that describes a method for time travel.

"People think of time travel as something as fiction," says Tippett. "And we tend to think it's not possible because we don't actually do it. But, mathematically, it is possible."

Ever since HG Wells published his book Time Machine in 1885, people have been curious about time travel--and scientists have worked to solve or disprove the theory, he says. In 1915 Albert Einstein announced his theory of general relativity, stating that gravitational fields are caused by distortions in the fabric of space and time. More than 100 years later, the LIGO Scientific Collaboration--an international team of physics institutes and research groups--announced the detection of gravitational waves generated by colliding black holes billions of lightyears away, confirming Einstein's theory.

The division of space into three dimensions, with time in a separate dimension by itself, is incorrect, says Tippett. The four dimensions should be imagined simultaneously, where different directions are connected, as a space-time continuum. Using Einstein's theory, Tippett says that the curvature of space-time accounts for the curved orbits of the planets.

In "flat" -- or uncurved -- space-time, planets and stars would move in straight lines. In the vicinity of a massive star, space-time geometry becomes curved and the straight trajectories of nearby planets will follow the curvature and bend around star.

"The time direction of the space-time surface also shows curvature. There is evidence showing the closer to a black hole we get, time moves slower," says Tippett. "My model of a time machine uses the curved space-time -- to bend time into a circle for the passengers, not in a straight line. That circle takes us back in time."

While it is possible to describe this type of time travel using a mathematical equation, Tippett doubts that anyone will ever build a machine to make it work.

"HG Wells popularized the term 'time machine' and he left people with the thought that an explorer would need a 'machine or special box' to actually accomplish time travel," Tippett says. "While is it mathematically feasible, it is not yet possible to build a space-time machine because we need materials--which we call exotic matter--to bend space-time in these impossible ways, but they have yet to be discovered."

For his research, Tippett created a mathematical model of a Traversable Acausal Retrograde Domain in Space-time (TARDIS). He describes it as a bubble of space-time geometry which carries its contents backward and forwards through space and time as it tours a large circular path. The bubble moves through space-time at speeds greater than the speed of light at times, allowing it to move backward in time.

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