Scientists know that dark matter exists because although we can’t see it, we can see the effects of what it does in the world, sort of like a ghost bumping around a haunted house. And we’re not sure what it is, but some think it may just be a WIMP.
Those are some of the insights that emerged from a Harvard Science Book Talk on Monday that featured an online conversation between Peter Fisher, the Thomas A. Frank Professor of Physics at MIT, who just wrote a book titled “What Is Dark Matter?,” and Melissa Franklin, Mallinckrodt Professor of Physics at Harvard.
Fisher opened the event, sponsored by the Harvard Division of Science, Harvard Library, and Harvard Book Store, with a short response to the question the title poses: “The answer is we don’t know.” He offered several possibilities, explaining that his subject could be a particle, a heavy particle, “tiny black holes from the beginning of the universe, or it could be something we haven’t even thought of.”
To shed some light on the topic, Fisher recounted the history of particle physics, from the invention of quantum mechanics in the 1930s to the development of the standard model theory in the 1990s, which explains three out of four known fundamental forces (electromagnetic, weak and strong interactions, but not gravity).
Parallel to the development of this science, astronomers studying the universe were making discoveries about the movement of the stars away from the Earth — proof the universe is expanding. That movement, astronomers realized, was happening faster than forces such as the gravity of the component stars could explain. “They studied the way galaxies moved with respect to each other, and the way stars moved within galaxies. And the only way they could come up with explaining how everything was moving in the biggest scales of the universe was the introduction of matter that we couldn’t see,” he said.
The answer, requiring all these disciplines, was that there “were actually two kinds of matter that we couldn’t see.” These were dark energy and dark matter. “Dark matter makes particles or stars within galaxies move more quickly than you’d expect from the mass in those galaxies,” he said.
To illustrate, Fisher shared a slide of the Andromeda galaxy, with its lush swirl of stars emanating out in a flat disc. “It looks very similar to the Milky Way in the middle,” he said, pointing out the “glowing region in the very middle of that: a big black hole about a million times the mass of our sun. There’s a lot of matter being pulled into the dense central region, and you can see there’s this beautiful pancake shape with spiral arms,” containing roughly a trillion stars.
“What’s particularly interesting is you can see that there’s a sharp end to the disc part. And that edge is really only explainable if you hypothesize that there is some substance called dark matter that is making a gravitational pull that makes that shape.”
Andromeda is not unique. In fact, Fisher explained, images of deep space provided by the Hubble Space Telescope reveal a striking consistency. “There have been very detailed measurements of literally thousands of galaxies, and they all share the same features,” he said. “A careful study of all these different kinds of galaxies always comes up with the same conclusion, which is the stars are moving too fast to be explainable by the amount of light coming from that galaxy,” he said. “This must denote the presence of dark matter around the galaxy.”
Franklin, paraphrasing Fisher’s book, likened the search to a ghost hunt. “If you have ghosts in your house moving things around, you can’t see them or hear them or feel them. So what you want to do is figure out from the movements what exactly is going on.”
What dark matter is, however, is much less clear. One theory is that it is a new kind of particle, a weakly interacting massive particle (or WIMP). If that theory is correct, said Fisher, dark matter is likely all around — but “here on Earth, it’s hard to find dark matter because there’s so much normal matter around. You have to look and think about galaxies as a whole” in order to get a large enough scale to study dark matter.
Another theory is that dark matter is primordial black holes, dating back to the origins of the universe. If that’s the case, Fisher noted, these “tiny” bits of matter “could just go straight through the Earth. They don’t pick up much matter. They can go straight through pretty much anything and nobody really notices it.”
The ongoing search, Fisher cautioned, will require continuing advancements in technology but also caution and a careful understanding of how our tools work. To illustrate what can go wrong, he described the nation’s Distant Early Warning Line, a system of radar stations along the Arctic Circle created as a defense against a possible Soviet missile attack during the Cold War. “These radar operators saw all kinds of stuff that it took years to explain,” he said, resulting in theories about UFOs that are still around. “Anytime you build a new device, you see things you don’t expect.”
As the search for dark matter continues, such meticulous discipline is vital. However, despite the many questions that remain, we can be confident that dark matter exists because “all of the measurements are made repeatedly using very different kinds of telescopes,” he said. The movement of stars, for example, has been observed with large optical telescopes and also radio telescopes. “It’s not a guarantee, but it gives one confidence that the same overall effect is observed in two very different ways.”
Physicists Create ‘the Smallest, Crummiest Wormhole You Can Imagine’ – The New York Times
In an experiment that ticks most of the mystery boxes in modern physics, a group of researchers announced on Wednesday that they had simulated a pair of black holes in a quantum computer and sent a message between them through a shortcut in space-time called a wormhole.
Physicists described the achievement as another small step in the effort to understand the relation between gravity, which shapes the universe, and quantum mechanics, which governs the subatomic realm of particles.
“This is important because what we have here in its construct and structure is a baby wormhole,” said Maria Spiropulu, a physicist at the California Institute of Technology and the leader of a consortium called Quantum Communication Channels for Fundamental Physics, which conducted the research. “And we hope that we can make adult wormholes and toddler wormholes step-by-step.”
In their report, published Wednesday in Nature, the researchers described the result in measured words: “This work is a successful attempt at observing traversable wormhole dynamics in an experimental setting.”
The wormhole that Dr. Spiropulu and her colleagues created and exploited is not a tunnel through real physical space but rather through an “emergent” two-dimensional space. The “black holes” were not real ones that could swallow the computer but lines of code in a quantum computer. Strictly speaking, the results apply only to a simplified “toy model” of a universe — in particular, one that is akin to a hologram, with quantum fields on the edge of space-time determining what happens within, sort of in the way that the label on a soup can describes the contents.
To be clear: The results of this experiment do not offer the prospect anytime soon, if ever, of a cosmic subway through which to roam the galaxy like Jodie Foster in the movie “Contact” or Matthew McConaughey in “Interstellar.”
“I guess the key question, which is perhaps hard to answer, is: Do we say from the simulation it’s a real black hole?” Daniel Jafferis, a physics professor at Harvard, said. “I kind of like the term ‘emergent black hole.’”
He added: “We are just using the quantum computer to find out what it would look and feel like if you were in this gravitational situation.” He and Alexander Zlokapa, a doctoral student at the Massachusetts Institute of Technology, are the lead authors of the paper.
Physicists reacted to the paper with interest and caution, expressing concern that the public and media would mistakenly think that actual physical wormholes had been created.
“The most important thing I’d want New York Times readers to understand is this,” Scott Aaronson, a quantum computing expert at the University of Texas in Austin, wrote in an email. “If this experiment has brought a wormhole into actual physical existence, then a strong case could be made that you, too, bring a wormhole into actual physical existence every time you sketch one with pen and paper.”
Daniel Harlow, a physicist at M.I.T. who was not involved in the experiment, noted that the experiment was based on a model of quantum gravity that was so simple, and unrealistic, that it could just as well have been studied using a pencil and paper.
“So I’d say that this doesn’t teach us anything about quantum gravity that we didn’t already know,” Dr. Harlow wrote in an email. “On the other hand, I think it is exciting as a technical achievement, because if we can’t even do this (and until now we couldn’t), then simulating more interesting quantum gravity theories would CERTAINLY be off the table.” Developing computers big enough to do so might take 10 or 15 years, he added.
Leonard Susskind, a physicist at Stanford University who was not part of the team, agreed. “They’re learning that they could do this experiment,” he said, adding: “The really interesting thing here is the possibility of analyzing purely quantum phenomena using general relativity, and who knows where that’s going to go.”
The two faces of Einstein
Wormholes entered the physics lexicon in 1935 as one of the weirder predictions of Albert Einstein’s general theory of relativity, which describes how matter and energy warp space to create what we call gravity. That year Einstein and his colleague, Nathan Rosen, showed in a paper that shortcuts through space-time, connecting pairs of black holes, could exist. The physicist John Wheeler later called these connectors “wormholes.”
Originally it seemed that wormholes were effectively useless; theory held that they would slam shut the instant anything entered them. They have never been observed outside of science fiction.
A month earlier that same year, in 1935, Einstein, Rosen and Boris Podolsky made another breakthrough, one they thought would discredit the chancy nature of quantum mechanics. They pointed out that quantum rules permitted what Einstein called “spooky action at a distance.” Measuring one of a pair of particles would determine the results of measuring the other particle, even if the two were light-years apart. Einstein thought this prediction was absurd, but physicists now call it “entanglement” and use it every day in the lab.
Until a few years ago, such quantum tricks weren’t thought to have anything to do with gravity. As a result, physicists were left with no theory of “quantum gravity” to explain what happened when the realms of inner space and outer space collided, as in the Big Bang or inside black holes.
But in 2013 Juan Maldacena, a theoretical physicist at the Institute for Advanced Study in Princeton, and Dr. Susskind proposed that these two phenomena — spooky action and wormholes — were actually two sides of the same coin, each described in a different but complementary mathematical language.
Those spooky, entangled particles, by this logic, were connected by equally mysterious wormholes. Quantum mechanics could be enlisted to study gravity, and vice versa. The equations that describe quantum phenomena turned out to have analogues in the Einsteinian equations for gravity.
“It’s mostly a matter of taste which description you use because they give exactly the same answer,” Dr. Jafferis said. “And that was an incredible discovery.”
The recent wormhole experiment sought to employ the mathematics of general relativity to examine an aspect of quantum magic, known as quantum teleportation, to see if some new aspect of physics or gravity might be revealed.
In quantum teleportation, physicists use a set of quantum manipulations to send information between two particles — inches or miles apart — that are entangled in a pair, without the physicists knowing what the message is. The technology is expected to be the heart of a next-generation, unhackable “quantum internet.”
Physicists like to compare the teleportation process to two cups of tea. Drop a cube of sugar into one teacup, and it promptly dissolves — then, after a tick of the quantum clock, the cube reappears intact in the other teacup.
The experiment became conceivable after a pair of papers by Dr. Susskind and, independently, by Dr. Jafferis, Ping Gao of M.I.T., and Aron Wall, a theoretical physicist at the University of Cambridge. They suggested a way that wormholes could be made traversable, after all. What was needed, Dr. Gao and his collaborators said, was a small dose of negative energy at the exit end of the wormhole to prop open the hatch long enough for information to escape.
In classical physics, there is no such thing as negative energy. But in quantum theory, energy can be negative, generating an antigravitational effect. For example, so-called virtual particles, which flit in and out of existence using energy borrowed from empty space, can fall into a black hole, carrying a debt to nature in the form of energy that the black hole must then pay back. This slow leak, Stephen Hawking calculated in 1974, causes the black hole to lose energy and shrink.
When Dr. Spiropulu proposed trying to recreate this wormhole magic on a quantum computer, her colleagues and sponsors at the Department of Energy “thought I was completely nuts,” she recalled. “But Jafferis said, Let’s do it.”
In ordinary computers, including the phone in your pocket, the currency of calculation is bits, which can be ones or zeros. Quantum computers run on qubits, which can be 0 or 1 or anywhere in between until they are measured or observed. This makes quantum computers super powerful for certain kinds of tasks, like factoring large numbers and (maybe one day) cracking cryptographic codes. In essence, a quantum computer runs all the possible variations of the program simultaneously to arrive at a solution.
“We make uncertainty an ally and embrace it,” Dr. Spiropulu said.
To reach their full potential, quantum computers will need thousands of working qubits and a million more “error correction” qubits. Google hopes to reach such a goal by the end of the decade, according to Hartmut Neven, head of the company’s Quantum Artificial Intelligence lab in Venice, Calif., who is also on Dr. Spiropulu’s team.
The Caltech physicist and Nobel laureate Richard Feynman once predicted that the ultimate use of this quantum power might be to investigate quantum physics itself, as in the wormhole experiment.
“I’m excited to see that researchers can live out Feynman’s dream,” Dr. Neven said.
The wormhole experiment was carried out on a version of Google’s Sycamore 2 computer, which has 72 qubits. Of these, the team used only nine to limit the amount of interference and noise in the system. Two were reference qubits, which played the roles of input and output in the experiment.
The seven other qubits held the two copies of code describing a “sparsified” version of an already simple model of a holographic universe called SYK, named after its three creators: Subir Sachdev of Harvard, Jinwu Ye of Mississippi State University and Alexei Kitaev of Caltech. Both SYK models were packed into the same seven qubits. In the experiment these SYK systems played the role of two black holes, one by scrambling the message into nonsense — the quantum equivalent of swallowing it — and then the other by popping it back out.
“Into this we throw a qubit,” Dr. Lykken said, referring to the input message — the quantum analog of a series of ones and zeros. This qubit interacted with the first copy of the SYK qubit; its meaning was scrambled into random noise and it disappeared.
Then, in a tick of the quantum clock, the two SYK systems were connected and a shock of negative energy went from the first system to the second one, briefly propping open the latter.
The signal then reappeared in its original unscrambled form — in the ninth and last qubit, attached to the second SYK system, which represented the other end of the wormhole.
One clue that the researchers were actually recording “wormholelike” behavior, Dr. Lykken said, was that signals emerged from the other end of the wormhole in the order that they went in.
In a Nature article accompanying Dr. Jafferis’s paper, Dr. Susskind and Adam Brown, a physicist at Stanford, noted that the results might shed light on some still-mysterious aspects of ordinary quantum mechanics. For instance, after the sugar cube dissolves in the first teacup, why does it reappear in the other cup in its original form?
“The surprise is not that the message made it across in some form, but that it made it across unscrambled,” the two authors wrote.
The easiest explanation, they added, is that the message went through a wormhole, albeit a “really short” one, Dr. Lykken said in an interview. In quantum mechanics, the shortest conceivable length in nature is 10⁻³³ centimeters, the so-called Planck length. Dr. Lykken calculated that their wormhole was maybe only three Planck lengths long.
“It’s the smallest, crummiest wormhole you can imagine making,” he said. “But that’s really cool because now we’re clearly doing quantum gravity.”
Distant black hole is caught in the act of annihilating a star – Edmonton Journal
WASHINGTON — Astronomers have detected an act of extreme violence more than halfway across the known universe as a black hole shreds a star that wandered too close to this celestial savage. But this was no ordinary instance of a ravenous black hole.
It was one of only four examples – and the first since 2011 – of a black hole observed in the act of tearing apart a passing star in what is called a tidal disruption event and then launching luminous jets of high-energy particles in opposite directions into space, researchers said. And it was both the furthest and brightest such event on record.
Astronomers described the event in studies published on Wednesday in the journals Nature and Nature Astronomy.
The culprit appears to be a supermassive black hole believed to be hundreds of millions of times the mass of our sun located roughly 8.5 billion light years away from Earth. A light year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km).
“We think that the star was similar to our sun, perhaps more massive but of a common kind,” said astronomer Igor Andreoni of the University of Maryland and NASA’s Goddard Space Flight Center, lead author of one of the studies.
The event was detected in February through the Zwicky Transient Facility astronomical survey using a camera attached to a telescope at the Palomar Observatory in California. The distance was calculated using the European Southern Observatory’s Very Large Telescope in Chile.
“When a star dangerously approaches a black hole – no worries, this will not happen to the sun – it is violently ripped apart by the black hole’s gravitational tidal forces -similar to how the moon pulls tides on Earth but with greater strength,” said University of Minnesota astronomer and study co-author Michael Coughlin. (See animation of tidal disruption event)
“Then, pieces of the star are captured into a swiftly spinning disk orbiting the black hole. Finally, the black hole consumes what remains of the doomed star in the disk. In some very rare cases, which we estimated to be 100 times rarer, powerful jets of material are launched in opposite directions when the tidal disruption event occurs,” Coughlin added.
Andreoni and Coughlin said the black hole was likely spinning rapidly, which might help explain how the two powerful jets were launched into space at almost the speed of light.
Massachusetts Institute of Technology astronomer Dheeraj Pasham, lead author of the other study, said the researchers were able to observe the event very early on – within a week of the black hole starting to consume the doomed star.
While researchers detect tidal disruption events about twice per month, ones that produce jets are extremely rare. One of the jets emanating from this black hole seems to be pointing toward Earth, making it appear brighter than if it were heading in another direction – an effect called “Doppler boosting” that is similar to the enhanced sound of a passing police siren.
The supermassive black hole is believed to reside at the center of a galaxy – much as the Milky Way and most galaxies have one of these at their core. But the tidal disruption event was so bright that it obscured the light of the galaxy’s stars.
“At its peak, the source appeared brighter than 1,000 trillion suns,” Pasham said.
(Reporting by Will Dunham, Editing by Rosalba O’Brien)
Mars very visible in night sky as it moves closer to Earth – Ashcroft Cache Creek Journal
Some three billion years ago, Mars is believed to have been a water world just like Earth. It possessed great oceans and was most likely on its way to forming life in one form or another. Water is made up of hydrogen, the most common element in the universe, and oxygen, the third most common element. Water is extremely important to the development and sustaininment of life as we know it.
Because Mars is half the size of the earth, the planet lost its heat faster as its internal core stopped rotating. Similar to Earth’s core, which produces a magnetic field around our planet, Mars’ core ceased producing its protective magnetic field, thus allowing the solar winds to eat away at its atmosphere, and the red planet lost its water.
Early telescopic observations were made by the Italian astronomer Giovanni Schiaparelli in 1877, when Mars was in opposition, residing 56-million-kilometres away, and he is said to have seen canali (channels) on Mars. Seeing these features gave the impression of a possible civilization. Since then, the red planet has been the focus of searching for ancient life, and is also the inspiration for science fiction writers and movie makers.
By the 2030s or 2040s, humans are expected to land on this fascinating world, looking for the possibility of life that might have once existed, even at the microbial level. After all, life is life. But Mars is now in the news for other reasons: it is now a very visible object in the night sky.
Appearing as a bright-orange object rising in the northeast sky about forty-five minutes after the sun sets in the west, Mars is nicely placed amongst the bright winter constellations of Orion the Hunter, Taurus the Bull, etc. If you are still not sure where to look, any smartphone astronomy app will guide you.
So why is it so bright? Earth orbits the Sun in 365 days, whereas Mars does so in 687 days. Just like runners on the inner lap on a race track, Earth catches up with, and overtakes, slower Mars every 26 months. This upcoming opposition will occur on Dec. 8 at a separation of only 82 million kilometres. Over the weeks after opposition, our distance increases and Mars will slowly fade. Every seventh opposition is super close, such as back in 2003 and 2020. The next opposition occurs on Jan. 15, 2025.
Be sure to look at Mars the night before, on Dec. 7, as the Full Cold Moon will cover Mars for a little less than one hour. All of Canada, as well as much of the US except for Alaska and the Southeastern states, will see this amazing sight. Throughout its 29.5-day orbit around the earth, the moon moves its width every hour. Throughout the month, it covers stars as seen through a telescope and, in rare events, bright planets. This should be a fantastic photo opportunity, as the disappearance and later reappearance should be quite evident.
Known as “The Backyard Astronomer”, Gary Boyle is an astronomy educator, guest speaker, and monthly columnist for the Royal Astronomical Society of Canada, as well as a STEM educator. In recognition of his public outreach in astronomy, the International Astronomical Union has honoured him with the naming of Asteroid (22406) Garyboyle. Visit his website at www.wondersofastronomy.com.
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