Erik Verlinde's New Theory Of Gravity Tries To Explain Dark Matter

Collage of six cluster collisions with dark matter maps. The clusters were observed in a study of how dark matter in clusters of galaxies behaves when the clusters collide Photo: wikipedia.org

Although gravity is the most familiar force of the universe, it is a thorny problem for theoretical physicists as it has long defied its inclusion in quantum mechanics. Another problem is dark matter only interacts with gravity and also defies the standard model of particle physics.

Professor Erik Verlinde, a researcher from the Delta Institute for Theoretical Physics in Amsterdam, believes that gravity is not an actual force of the universe but an effect due to the increasing entropy of the universe. In his latest paper, which is available on arXiv but is yet to be peer-reviewed, the scientist claimed that this “emergent” (and not real) force of gravity has a dark component that behaves like dark matter.

Mysterious Universe: Super Force Mysterious Universe

Photo: quantumdiaries.org

"We have evidence that this new view of gravity actually agrees with the observations," said Verlinde in a statement. "At large scales, it seems, gravity just doesn't behave the way Einstein's theory predicts."

Erik Verlinde, Theoretical Physicist at Amsterdam

Quite the bold statement from the researcher, especially since it has been shown that Einstein’s general relativity agrees quite well with large-scale observations. In the paper, Verlinde admits that the idea of this dark gravitational component needs to answer several questions before it is able to be as successful at explaining the early universe and large scale cosmology as the current theory of gravity.

The theory of entropic gravity was first proposed by Verlinde in a paper in 2010 and published in the Journal of High Energy Physics in 2011. The proposed idea was welcomed by some as a novel approach to the problem of gravity in quantum mechanics.

Verlinde's new theory of gravity passes first test Phys.org

Others were more skeptical and devised ways to see if gravity could really be an emergent phenomenon. In 2011, Archil Kobakhidze of the University of Melbourne looked at how gravity affects fundamental particles. His findings strongly support the idea that gravity is a real force.

Entropic gravity is appealing because it is able to reproduce the laws of Newtonian gravitation and Einstein field equations from the first thermodynamics and quantum mechanical principles, but the theory itself doesn’t make predictions so it can’t be falsified.

Einstein’s general relativity is constantly being tested, and discoveries like gravitational waves have only strengthened its role as the best theory of gravity we currently possess.


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The above post is reprinted from materials provided by IFL Science . Note: Materials may be edited for content and length.

Dark Energy vs. Dark Matter: What The Universe is Made Of

Dark Energy vs. Dark Matter

While dark energy repels, dark matter attracts. And dark matter’s influence shows up even in individual galaxies, while dark energy acts only on the scale of the entire universe

Our universe may contain 100 billion galaxies, each with billions of stars, great clouds of gas and dust, and perhaps scads of planets and moons and other little bits of cosmic flotsam. The stars produce an abundance of energy, from radio waves to X-rays, which streak across the universe at the speed of light.

Yet everything that we can see is like the tip of the cosmic iceberg — it accounts for only about four percent of the total mass and energy in the universe.

About one-quarter of the universe consists of dark matter, which releases no detectable energy, but which exerts a gravitational pull on all the visible matter in the universe.

Because of the names, it’s easy to confuse dark matter and dark energy. And while they may be related, their effects are quite different. In brief, dark matter attracts, dark energy repels. While dark matter pulls matter inward, dark energy pushes it outward. Also, while dark energy shows itself only on the largest cosmic scale, dark matter exerts its influence on individual galaxies as well as the universe at large.

In fact, astronomers discovered dark matter while studying the outer regions of our galaxy, the Milky Way.


A ring of possible dark matter highlights this Hubble Space Telescope image of a distant galaxy cluster. [NASA/ESA/M.J. Jee/H. Ford (Johns Hopkins)]

The Milky Way is shaped like a disk that is about 100,000 light-years across. The stars in this disk all orbit the center of the galaxy. The laws of gravity say that the stars that are closest to the center of the galaxy — which is also its center of mass — should move faster than those out on the galaxy’s edge.

Yet when astronomers measured stars all across the galaxy, they found that they all orbit the center of the galaxy at about the same speed. This suggests that something outside the galaxy’s disk is tugging at the stars: dark matter.

Calculations show that a vast "halo" of dark matter surrounds the Milky Way. The halo may be 10 times as massive as the bright disk, so it exerts a strong gravitational pull.

The same effect is seen in many other galaxies. And clusters of galaxies show exactly the same thing — their gravity is far stronger than the combined pull of all their visible stars and gas clouds.

Scientists shed light on mystery of dark matter HeritageDaily

Are dark matter and dark energy related? No one knows. The leading theory says that dark matter consists of a type of subatomic particle that has not yet been detected, although upcoming experiments with the world’s most powerful particle accelerator may reveal its presence. Dark energy may have its own particle, although there is little evidence of one.

Instead, dark matter and dark energy appear to be competing forces in our universe. The only things they seem to have in common is that both were forged in the Big Bang, and both remain mysterious.

Other articles on the same theme:

• New Theory Of Gravity Tries To Explain Dark Matter

• What form does the atomic nucleus? New discovery may explain the mysteries of the Universe.

• A new theory on the Creation of the Universe, disprove the Big Bang

• Vera Rubin, the American astronomer who confirmed the existence of dark matter, died at the age of 88 years.

Source: hetdex

One step closer in understanding and detecting Dark Matter

Updated 04/05/2020

The view from inside the Large Underground Xenon (LUX)  dark matter detector, which is nearly a mile underground below the Black Hills of South Dakota. The upgraded detector just finished its 20-month run without finding dark matter activity.

Credit: Matthew Kapust. Copyright © South Dakota Science and Technology Authority

The incredibly sensitive LUX dark-matter detector, buried under a mile of rock, has come up empty on its 20-month search for dark matter — further narrowing down the possible characteristics of the strange substance.

Researchers presented the results today (July 21) at the 11th Identification of Dark Matter Conference (IDM2016) in Sheffield, U.K., which gathers together researchers seeking to understand dark matter, the mysterious material that appears to make up more than four-fifths of the universe's mass, but which scientists have not observed directly.

"LUX has delivered the world's best search sensitivity since its first run in 2013," Rick Gaitskell, a physicist at Brown University and co-spokesman for LUX, said in a statement. "With this final result from the 2014 to 2016 search, the scientists of the LUX Collaboration have pushed the sensitivity of the instrument to a final performance level that is four times better than the original project goals." [The Search for Dark Matter in Images]

The Davis Cavern in the Sanford Underground Research Facility, which used to be a gold mine, was enlarged and outfitted for the Large Underground Xenon (LUX) experiment. It formerly housed Ray Davis' Nobel Prize-winning solar neutrino experiment.
Credit: Matthew Kapust, Sanford Underground Research Facility, © South Dakota Science and Technology Authority

LUX is short for the Large Underground Xenon dark-matter experiment. It rests a mile deep (1.6 km) underground in a former South Dakota gold mine that is now called the Sanford Underground Research Facility. 

Suspended in a 72,000 gallon (272,500 liter) tank of purified water, a 6-foot-tall (1.8 meter) titanium tank holds one-third of a ton (302 kg) of frigid liquid xenon. The xenon's job is to light up, with a jolt of electrical charge and a faint flash of light caught by surrounding sensors, when a dark-matter particle collides with one of its atoms — and the gallons of water and mile of rock's job is to stop anything else from getting in and disturbing it.

This latest result reveals that nothing with the right properties to excite the xenon made it through.

"It would have been marvelous if the improved sensitivity had also delivered a clear dark-matter signal," Gaitskell said. "However, what we have observed is consistent with background alone."

The quest for WIMPs

Even though scientists have never detected dark matter directly, they know it plays an important part in our universe: The way galaxies rotate and the way light bends as it passes by them reveals a substantial amount of extra matter adding to the systems' gravity.

LUX was designed to search for weakly interacting massive particles (WIMPs) — a leading candidate for dark matter. Those particles are 10 to 100 times the mass of a proton, but interact only very weakly with ordinary matter (which is why scientists cannot easily detect them). Most particles, such as the cosmic rays that constantly stream down onto Earth, would be stopped by the rock and water shielding around the detector, but WIMPs would be able to make it through — sometimes, if researchers are lucky, knocking into one of the densely packed xenon atoms in the detector and releasing a light signal along the way (liquid xenon is transparent to those photons). Other particles that make it in will likely hit multiple xenon atoms and set off a cascade of light, whereas WIMPs would be lucky to hit one.

Researchers examined a huge amount of data collected from the carefully calibrated device over the course of the 20-month experiment, which followed on the heels of a less-sensitive, three-month LUX search that ended in 2013, also with a negative result. Researchers were able to filter out signals in the data created by non-dark-matter particles that managed to get inside the experiment. This gave the researchers the capability to look for interacting dark matter, which would be expected to produce only a few signals per century per kilogram of xenon, researchers said in the statement. [No WIMPS in Space? - NASA Scans For Dark Matter

LUX's lack of detection doesn't mean that dark matter is not made of WIMPs, but it does suggest that dark matter WIMPs cannot have a mass or effect on ordinary matter within a certain range.

"Though a positive signal would have been welcome, nature was not so kind!" Cham Ghag, a physicist at University College London and collaborator on LUX, said in another statement. "Nonetheless, a null result is significant as it changes the landscape of the field by constraining models for what dark matter could be beyond anything that existed previously."

Onward

LUX is one of several efforts to detect dark matter, and its results will help narrow down the searches conducted by future direct-detection experiments, too. Other experiments, like COUPP-60, the XENON Dark Matter Project in Italy, and the Super Cryogenic Dark Matter Search (SUPERCDMS) have used similar techniques that heavily shield a material and wait for naturally-occurring dark matter to pass through.

An experiment at the Large Hadron Collider, on the other hand, has a chance of creating dark matter, and then detecting its signal.

"We viewed this as a David and Goliath race between ourselves and the much larger Large Hadron Collider (LHC) at CERN in Geneva," Gaitskell said. "LUX was racing over the last three years to get first evidence of a dark-matter signal. We will now have to wait and see if the new run this year at the LHC will show evidence of dark-matter particles, or if the discovery occurs in the next generation of larger direct detectors."

LUX's own next-generation detector, LUX-Zeplin, will have 70 times the sensitivity of LUX, researchers said in the statement — which will take LUX's place underground to continue the search.

Other articles on the same theme:

• New Theory Of Gravity Tries To Explain Dark Matter

• What form does the atomic nucleus? New discovery may explain the mysteries of the Universe.

• A new theory on the Creation of the Universe, disprove the Big Bang

• Vera Rubin, the American astronomer who confirmed the existence of dark matter, died at the age of 88 years.

• Dark Energy vs. Dark Matter: What The Universe is Made Of

The above post is reprinted from materials provided by Space.com . Note: Materials may be edited for content and length.

LARGEST MAP EVER MADE WILL UNLOCK THE HISTORY OF THE UNIVERSE 1.2 MILLION GALAXIES

Updated 02/05/2020

"This is one slice through the map of the large-scale structure of the Universe from the Sloan Digital Sky Survey and its Baryon Oscillation Spectroscopic Survey. Each dot in this picture indicates the position of a galaxy 6 billion years into the past. The image covers about 1/20th of the sky, a slice of the Universe 6 billion light-years wide, 4.5 billion light-years high, and 500 million light-years thick. Color indicates distance from Earth, ranging from yellow on the near side of the slice to purple on the far side.

Map of the observable universe. (Pablo Carlos Budassi/Wikimedia/CC BY 4.0)

Galaxies are highly clustered, revealing superclusters and voids whose presence is seeded in the first fraction of a second after the Big Bang. This image contains 48,741 galaxies, about 3% of the full survey dataset. Grey patches are small regions without survey data."

What you're looking at is a slice of the entire universe, a web of galaxies billions of light years away. You're also looking into the past, since the further into the distance you look, the longer it took that light to reach your eyes. It all seems a lot smaller until you realize that each of those dots is hundreds of thousands of light years across.

A collaboration of hundreds of scientists released the "largest-ever, three-dimensional map of distant galaxies" with over 1.2 million spots as a part of the Baryon Oscillation Spectroscopic Survey (BOSS) program using a telescope in New Mexico, according to a press release from Brookhaven National Lab. The map isn't for wanderers; scientists are trying to understand some of the universe's unexplained properties, like what dark matter and dark energy are. Understanding those things requires a three-dimensional map bigger and looking further out than any map scientists have made prior.

"The problem was, if you take data on the brightest galaxies in the sky, they happen to be nearby galaxies," BOSS' principal investigator David Schlegel from Lawrence Berkeley National Lab told Popular Science.

"For a cosmologist, that’s just a map of the backyard. I don’t want a map of the backyard. I want a map of the universe."

Up until fifty or so years ago, scientists more or less understood the universe, said Schlegel. But the discovery of dark matter and dark energy showed we don't really understand most of it, since they make up around 95 percent of the stuff in the universe. Yeah, we don't understand 95 percent of the stuff in the universe.

That's not to say we can't measure or detect dark matter and dark energy, though. If you look at the map, you'll see a web of galaxies and places where dots clump. Dark matter still feels gravity's pull, so galaxies align themselves along the webs and clumps of dark matter. We can detect dark energy too. When we look into space, really distant things we'd expect to look white actually look red; they've been redshifted. That's because their light rays have stretched out, because the space itself the light travels through expands, like a stretched-out tattoo on someone who's gaining a lot of weight.

By measuring really far away things, we found out that the universe wasn't just expanding, but the rate it expanded was actually speeding up. That discovery won a team of scientists the 2011 Nobel Prize in Physics.

"I don’t want a map of the backyard. I want a map of the universe."

Map of large universe (Hélène Courtois, Daniel Pomarède, R. Brent Tully, Yehuda Hoffman, and Denis Courtois) smithsonianmag

In one theory of the universe, there's a single number called the "cosmological constant" that says dark energy is a uniform thing permeating the universe and making it expand. Some physicists were hoping that a larger map would show the cosmological constant's value changing in different places, rather than just being a single number everywhere, but the single number stuck throughout the swath of the universe covered by BOSS' results. Schlegel thought theoretical physicists might be a little pigeonholed by the results, since they can do more with varying numbers than a single constant.

Mark Wise, theoretical physicist at California Institute of Technology, hadn't reviewed the BOSS results yet but agreed with Schlegel. "It would be more exciting if it was something else," he told Popular Science.

Map of Universe

The BOSS experiment is about more than just dark energy, though, pointed out Anže Slosar, Brookhaven National Lab and BOSS cosmologist who leads his "futile existence as a scientist and a bureaucrat" (much as a cosmologist would), according to his website. The experiment will also help pinpoint the mass of the neutrino particle. Soon, other experiments like the larger Dark Energy Spectroscopic Instrument (DESI) on a telescope at Kitt Peak in Arizona will pick up where the BOSS experiment leaves off. But Slosar was most excited about how intertwined our physical experiences on Earth are with the rest of the universe.

"The fact that it’s the same fundamental laws that guide GPS satellites all the way down to one second after the big bang is pretty mindblowing," he said.

Other articles on the same theme:

• What form does the atomic nucleus? New discovery may explain the mysteries of the Universe.

• A new theory on the Creation of the Universe, disprove the Big Bang

• The First Stars in the Universe could provide clues about Dark Matter

• NOBEL PHYSICS 2016. Nobel Prize winners are David DJ. Thouless, F. M. Duncan Haldane and J. Michael Kosterlitz

The above post is provided by POPULAR SCIENCE.

Note: Materials may be edited for content and length.

The universe: Reading the future from the distant past

Cosmic Calendar - Wikipedia

Scientists work at SLAC and Stanford are combining experimental data and theory to understand how the universe formed and what its future holds. Here, clumps and filaments of dark matter (black areas) serve as the scaffolding for the formation of cosmic structures made of regular matter (bright areas), including stars, galaxies and galaxy clusters.

The Dark Energy Survey World Scientific

These are the fundamental questions "astrophysical archeologists" like Risa Wechsler want to answer. At the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) of Stanford and the Department of Energy's SLAC National Accelerator Laboratory, her team combines experimental data with theory in computer simulations that dig deeply into cosmic history and trace back how matter particles clumped together to form larger and larger structures in the expanding universe.

"Most of our calculations are done at KIPAC, and computing is a crucial aspect of the collaboration between SLAC and Stanford," says Wechsler, who is an associate professor of physics and of particle physics and astrophysics.

Wechsler's simulated journeys through spacetime use a variety of experimental data, including observations by the Dark Energy Survey (DES), which recently discovered a new set of ultra-faint companion galaxies of our Milky Way that are rich in what is known as dark matter. The gravitational pull from this invisible form of matter affects regular matter, which plays a crucial role in the formation and growth of galaxies.

Dark energy is another key ingredient shaping the universe: It inflates the universe like a balloon at an ever-increasing rate, but researchers don't know much about what causes the acceleration.


Two future projects will give Wechsler and other researchers new clues about the mysterious energy. The Dark Energy Spectroscopic Instrument (DESI), whose science collaboration she is leading, will begin in 2018 to turn two-dimensional images of surveys like DES into a three-dimensional map of the universe. The Large Synoptic Survey Telescope (LSST), whose ultrasensitive 3,200-megapixel digital eye is being assembled at SLAC, will start a few years later to explore space more deeply than any telescope before.

"Looking at faraway galaxies means looking into the past and allows us to measure how the growth and distribution of galaxies were affected by dark energy at different points in time," Wechsler says. "Over the past 10 years, we've made a lot of progress in refining our cosmological model, which describes many of the properties of today's universe very well. Yet, if future data caused this model to break down, it would completely change our view of the universe."

The current model suggests that the universe is fated to expand forever, turning into a darker and darker cosmos faster and faster, with galaxies growing farther and farther apart. But is this acceleration a constant or changing property of spacetime? Or could it possibly be a breakdown of our theory of gravity on the largest scales? More data will help researchers find an answer to these fundamental questions.

Other articles on the same theme:

What form does the atomic nucleus? New discovery may explain the mysteries of the Universe.

A new theory on the Creation of the Universe, disprove the Big Bang

The First Stars in the Universe could provide clues about Dark Matter

NOBEL PHYSICS 2016. Nobel Prize winners are David DJ. Thouless, F. M. Duncan Haldane and J. Michael Kosterlitz

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The above post is reprinted from materials provided by SLAC National Accelerator Laboratory. The original item was written by Manuel Gnida. Note: Materials may be edited for content and length.