Could a Distant, Dark Body End Life on Earth?

An unseen threat might come from deep space in the future. 

#space #earth #asteroid #supernova


DANGER ZONE. Many dark objects lie too far from the Sun to be observed. An unseen threat might come from deep space in the future. 

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Although we live in relative quiet within the cosmos, going about our lives and seeing the stars as a distant backdrop, we are very much part of the universe that surrounds us. Dangers lurk in space, as any glance at the Moon’s cratered surface confirms.

Not only must our planet avoid collisions with Earth-crossing asteroids, but more remote threats exist. If a nearby star went supernova, a gamma-ray burst erupted nearby, or a black hole or stream of antimatter somehow wandered into our neighborhood, it could spell disaster. While astronomers say those events are unlikely, another dark, distant interloper could create havoc on Earth by its mere presence. 

Where could such trouble come from? The Sun hasn’t always been a solitary star. It was born in a group of suns, as all stars are, and its native companions have been scattered by the gravitational tug created by orbiting the galaxy’s center. 

Yet some 5 billion years after the Sun’s birth, a few of its associates still linger near the old neighborhood. Among them are the Sun-like star Alpha (α) Centauri, the yellowish dwarf Tau (τ) Ceti, and the cool red dwarf Wolf 359. Is the Sun truly single, or could a cool, dark companion loom in the background, periodically nudging comets toward Earth? 

The discovery of Sedna, a trans-Neptunian object found in 2003, and the subsequent discovery of Eris, fueled the idea that large, dark bodies float in the solar system’s distant reaches. Those bodies exist apart from the numerous comets that populate the Oort Cloud. Close passages of well-known stars will occur far on down the line: For example, in less than a million and a half years, Gliese 710, a red dwarf now 60 light-years away, will slide within a light-year of the Sun. This will unleash a torrent of comets from the Oort Cloud into orbits that could intersect Earth’s, and they will arrive near our planet within a liberal span of about 2 million years. 

But bombings from comet nuclei could result from other sources, too. A number of astronomers suggest the Sun may have a hidden, dark companion that periodically sends comets sunward, raining them down on the inner solar system.


UNSEEN COMPANION. A small dim object called a brown dwarf could orbit the Sun in our solar system’s distant regions. Brown dwarfs fall somewhere between the smallest star and the largest planet. This artist’s conception shows a pair of brown dwarfs.NASA/ESA/A. Feild (STScI)

In 1984, University of Chicago paleontologists David Raup and J. John Sepkoski revealed their finding that Earth’s extinction events were periodic. At the time, they suggested the Sun’s orbit about the Milky Way’s center was responsible, unleashing comets at regular intervals of about 26 million years. 

In the same year, University of California, Berkeley, physicist Richard Muller proposed the responsible mechanism was “Nemesis,” an unseen, distant stellar companion to the Sun. Muller thought an M dwarf — a small, cool star — could lurk unnoticed in the distance yet have a huge effect on the Oort Cloud.  about:blank


With the advent of the Two Micron All-Sky Survey (2MASS), however, astronomers scoured the whole sky at near-infrared wavelengths, producing 2 million images that would have uncovered Nemesis, had it existed. So the mystery of what lurks out in the darkness beyond the Oort Cloud, if anything, continues.  

Not all scientists are unconcerned about the idea of a dark threat. Michael Rampino, a geologist at New York University, searches for an astronomical object he believes may be responsible for recurring extinction events every 25 to 35 million years. 

As suggestive evidence, Rampino employs the large-impact events that produced craters under the Chesapeake Bay between Virginia and Maryland and in Popigai, Siberia, about 35 million years ago and the K-T impact in the Yucatán Peninsula, the “dinosaur-killer” that occurred 65 million years ago. Rampino believes several smaller lines of evidence suggest another catastrophic impact 95 million years ago. 

If a dark monster is out there, it could be a small brown dwarf. If such a starlet exists, it might weigh less than 40 Jupiter masses, making it slip under the radar of the 2MASS survey. It would have a highly elliptical orbit that would make it hard to spot because most of its time would be spent far from us. Still, most astronomers remain skeptical. Only time will tell.

The Quantum Experiment that Broke Reality

Do atoms going through a double slit ‘know’ if they are being observed?

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#physics #quantum #reality #atoms

Does a massive quantum particle – such as an atom – in a double-slit experiment behave differently depending on when it is observed? John Wheeler’s famous “delayed choice” Gedankenexperiment asked this question in 1978, and the answer has now been experimentally realized with massive particles for the first time. The result demonstrates that it does not make sense to decide whether a massive particle can be described by its wave or particle behaviour until a measurement has been made. The techniques used could have practical applications for future physics research, and perhaps for information theory.

In the famous double-slit experiment, single particles, such as photons, pass one at a time through a screen containing two slits. If either path is monitored, a photon seemingly passes through one slit or the other, and no interference will be seen. Conversely, if neither is checked, a photon will appear to have passed through both slits simultaneously before interfering with itself, acting like a wave. In 1978 American theoretical physicist John Wheeler proposed a series of thought experiments wherein he wondered whether a particle apparently going through a slit could be considered to have a well-defined trajectory, in which it passes through one slit or both. In the experiments, the decision to observe the photons is made only after they have been emitted, thereby testing the possible effects of the observer.

For example, what happens if the decision to open or close one of the slits is made after the particle has committed to pass through one slit or both? If an interference pattern is still seen when the second slit is opened, this would force us either to conclude that our decision to measure the particle’s path affects its past decision about which path to take, or to abandon the classical concept that a particle’s position is defined independent of our measurement.

Photon first

While Wheeler conceived of this purely as a thought experiment, experimental advances allowed Alain Aspect and colleagues at the Institut d’Optique, Ecole Normale Supérieure de Cachan and the National Centre for Scientific Research, all in France, to actually perform it in 2007 with single photons, using beamsplitters in place of the slits envisage by Wheeler. By inserting or removing a second beamsplitter randomly, the researchers could either recombine the two paths or leave them separate, making it impossible for an observer to know which path a photon had taken. They showed that if the second beamsplitter was inserted, even after the photon would have passed the first, an interference pattern was created.

The wave–particle duality of quantum mechanics dictates that all quantum objects, massive or otherwise, can behave as either waves or particles. Now, Andrew Truscott and colleagues at Australian National University carried out Wheeler’s experiment using atoms deflected by laser pulses in place of photons deflected by mirrors and beamsplitters. The helium atoms, released one by one from an optical dipole trap, fell under gravity until they were hit by a laser pulse, which deflected them into an equal superposition of two momentum states travelling in different directions with an adjustable phase difference. This was the first “beamsplitter”. The researchers then decide whether to apply a second laser pulse to recombine the two states and create mixed states – one formed by adding the two waves and one formed by subtracting them – by using a quantum random-number generator. When applied, this final laser pulse made it impossible to tell which of the two paths the photon had travelled along. The team ran the experiment repeatedly, varying the phase difference between the paths.

Double pulse

Truscott’s team found that when the second laser pulse was not applied, the probability of the atom being detected in each of the momentum states was 0.5, regardless of the phase lag between the two. However, application of the second pulse produced a distinct sine-wave interference pattern. When the waves were perfectly in phase on arrival at the beamsplitter, they interfered constructively, always entering the state formed by adding them. When the waves were in antiphase, however, they interfered destructively and were always found in the state formed by subtracting them. This means that accepting our classical intuition about particles travelling well-defined paths would indeed force us into accepting backward causation. “I can’t prove that isn’t what occurs,” says Truscott, “But 99.999% of physicists would say that the measurement – i.e. whether the beamsplitter is in or out – brings the observable into reality, and at that point the particle decides whether to be a wave or a particle.”

Indeed, the results of both Truscott and Aspect’s experiments shows that a particle’s wave or particle nature is most likely undefined until a measurement is made. The other less likely option would be that of backward causation – that the particle somehow has information from the future – but this involves sending a message faster than light, which is forbidden by the rules of relativity.

Aspect is impressed. “It’s very, very nice work,” he says, “Of course, in this kind of thing there is no more real surprise, but it’s a beautiful achievement.” He adds that, beyond curiosity, the technology developed may have practical applications. “The fact that you can master single atoms with this degree of accuracy may be useful in quantum information,” he says.