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Physics Discussion Thread

The Technology & Economic Forum is a venue to discuss issues pertaining to Technological and Economic developments in India. We request members to kindly stay within the mandate of this forum and keep their exchanges of views, on a civilised level, however vehemently any disagreement may be felt. All feedback regarding forum usage may be sent to the moderators using the Feedback Form or by clicking the Report Post Icon in any objectionable post for proper action. Please note that the views expressed by the Members and Moderators on these discussion boards are that of the individuals only and do not reflect the official policy or view of the Bharat-Rakshak.com Website. Copyright Violation is strictly prohibited and may result in revocation of your posting rights - please read the FAQ for full details. Users must also abide by the Forum Guidelines at all times.
Amber G.
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Re: Physics Discussion Thread

Postby Amber G. » 25 Oct 2017 21:33

JayS wrote:
Amber G. wrote:^^^ Next step LISA (or eLISA) is to be built in space. Better vacuum, much less thermal noise, seismic activity - much much better isolation.

And the tubes, instead of 4 Km, could be millions of Km long. (You don't need tubes, just multiple sats)
(All of this will be in about 20 years).

Meanwhile, in about 5-7 years - addition of LIGO-India, and Japan - the sensitivity is going to be 10x, resulting 1000x times detecting of GW. Probably one event of so every day -- we may start mapping the universe using GW.


Wasn't there a proposal to build 3 sat system to detect GW..? I remember to have read about quite a few years ago. And as you already mentioned, the system will be ultra sensitive.

OK, googled for it- It LISA which was joint venture between NASA and ESA. Never really took off.

Nice gif showing proposed orbit.

https://en.wikipedia.org/wiki/File:LISA_motion.gif

LISA, specially after recent success of GW detection, has lot of enthusiasm and serious work/planning is in process. It is scheduled to be launched around early 2030, but get a push ahead.

LISA's size and precision are really amazing..

LISA consists of three spacecraft that are separated by millions of Kms (and trailing tens of millions of Kms) -- more than 100 x the distance to the Moon - behind the Earth as we orbit the Sun. These three spacecraft relay laser beams back and forth between the different spacecraft and the signals are combined to search for gravitational wave signatures that come from distortions of spacetime.
Giant detector (bigger than the size of Earth) are needed to catch gravitational waves in lower frequency. LISA operates in the low frequency range, between 0.1 mHz and 1 Hz (compared to LIGO's frequency of 10 Hz to 1000 Hz).

LISA stands for "Laser Interferometer Space Antenna"
eLISA is "evolved Laser Interferometer Space Antenna"

Image
(Image - courtesy lisa.nasa.gov)

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Re: Physics Discussion Thread

Postby Bade » 25 Oct 2017 23:07

This one is good read for the layman...

Colliding neutron stars apply kiss of death to theories of gravity
https://arstechnica.com/science/2017/10 ... f-gravity/

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Re: Physics Discussion Thread

Postby Amber G. » 29 Oct 2017 03:33

^^^ This is also noted in
The Best of the Physics arXiv (week ending October 28, 2017):

GW170817 Falsifies Dark Matter Emulators
On August 17, 2017 the LIGO interferometers detected the gravitational wave (GW) signal (GW170817) from the coalescence of binary neutron stars. This signal was also simultaneously seen throughout the electromagnetic (EM) spectrum from radio waves to gamma-rays. We point out that this simultaneous detection of GW and EM signals rules out a class of modified gravity theories, which dispense with the need for dark matter. This simultaneous observation also provides the first ever test of Einstein's Weak Equivalence Principle (WEP) between gravitons and photons. We calculate the Shapiro time delay due to the gravitational potential of the total dark matter distribution along the line of sight (complementary to the calculation in arXiv:1710.05834) to be about 1000 days. Using this estimate for the Shapiro delay and from the time difference of 1.7 seconds between the GW signal and gamma-rays, we can constrain violations of WEP using the parameterized post-Newtonian (PPN) parameter γ, and is given by |γGW−γEM|<3.9×10−8.

A roundup of the most interesting papers from the arXiv: (see links above)

This Doctor Diagnosed His Own Cancer with an iPhone Ultrasound
How to Root Out Hidden Biases in AI
Yahama’s Robo-motorcyclist Tears Around a Racetrack at 124 MPH
CRISPR 2.0 Is Here, and It’s Way More Precise
This Is the Reason Ethereum Exists
Individuals, Institutions, and Innovation in the Debates of the French Revolution

Generative Adversarial Networks: An Overview

Towards Automatic Abdominal Multi-Organ Segmentation in Dual Energy CT using Cascaded 3D Fully Convolutional Network

Light Storage for 150 Milliseconds at Room Temperature

GW170817 Falsifies Dark Matter Emulators

The Nature of the Giant Exomoon Candidate Kepler-1625 b-i

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Re: Physics Discussion Thread

Postby ArjunPandit » 29 Oct 2017 05:28

For those who like to compare things
Image

Image


Image

very noob pooch, I want to combine these images and show in a single chart, how can i upload images created by myself over here?

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Re: Physics Discussion Thread

Postby ArjunPandit » 29 Oct 2017 05:54

https://www.newscientist.com/article/mg23631482-800-hiding-in-plain-sight-the-mystery-of-the-suns-missing-matter/

A mass equivalent to 1500 Earths has vanished from the sun. Tracking it down could transform how we see the stars

THERE is a hole in the sun. Right in the middle, a mass the size of 1500 Earths has simply disappeared. Much of what we know about the sun’s behaviour says it should be there – but when we interpret the data encoded in sunlight, that chunk of stuff is nowhere to be seen.

That has shaken up our understanding of how the sun works, and physicists are struggling to figure out what fills that hole. It could be a thing, like dark matter. It could be a concept, with elements such as carbon and nitrogen simply behaving in a way we didn’t expect under crushing pressure. Or perhaps we’re looking at the sun in the wrong way.

It’s a very hot problem, says Sunny Vagnozzi, a physicist at Stockholm University in Sweden. That’s no joke. The sun is important not just because it supplies the heat and light that sustain us. It is also our key to the wider universe, the reference against which we measure stars: their brightness, their age, how likely their solar systems are to support life. Start messing with the sun, and the consequences stretch as far as our telescopes can see. “If we get the sun wrong, we get everything wrong,” says Sarbani Basu at Yale University.

It’s not easy to figure out what’s inside the sun. “We can’t go and take a sample,” says Basu. There are two main ways to investigate. Helioseismologists such as Basu look at sound vibrations on the sun’s surface, which give outward evidence of the vast quantities of energy being unleashed within. That energy depends on the sun’s internal structure, as well as its ingredients, which Basu can identify by working backwards from observations beamed from her space-based probes.

Then there are spectroscopists, who look at the light from the sun. They pass it through high-tech prisms, decomposing it into stripes that serve as unique barcodes for its constituent elements.

For years, these two methods painted the same picture of the sun: a vast and dense ball of matter, mostly hydrogen and helium, that clumped together some 4.6 billion years ago and formed our solar system. Included in the mixture was a sprinkling of other elements carried by the explosions of larger, dying stars. For simplicity, astronomers refer to all these heavier elements, which include carbon, oxygen, nitrogen, magnesium, iron and sulphur, as metals. They can be found scattered throughout the interior of the sun, making up a little less than 2 per cent of its total mass. Despite their minority status, these heavy elements play a crucial role, shuttling energy from the core out to the boiling layer on the surface.

In the late 1990s, Martin Asplund was a young researcher in Copenhagen when he first realised this picture was not quite right. He was studying the motions of the outer layers of boiling stars, a requisite step towards performing more accurate spectroscopic calculations to unlock the light’s secrets.

At the time, the mathematical imaginings of star surfaces used by spectroscopists were simplistic. In fact, they were literally one-dimensional, concerned only with the behaviour of an idealised solar surface possessing zero width. But the surface of the sun is decidedly three-dimensional. With a departmental supercomputer at his disposal, Asplund built a model that took height and width into account.

“It could have been that it made no difference at all,” says Asplund, now at the Australian National University in Canberra. Over the years, there had been many little upgrades to these solar models, and all of them had left the heavy elements relatively untouched. But Asplund’s update was different. By 2009, he had startling results: a quarter of the metals we had counted on being there could no longer be found. They had simply vanished.

Staring at the sun
His measurements flew in the face of what researchers like Basu had observed. If you assumed that Asplund’s figures held up, helioseismology could no longer explain the behaviour of the sun. The quantities of helium on the solar surface didn’t tally; the outer layer became too thin; sound travelled through it at the wrong speed. It was clear that someone somewhere was doing something wrong. “A lot of people doubted it,” says Asplund. “I was not very popular.”

The easiest conclusion was that Asplund was wrong. In the hope of performing an independent cross-check, earlier this year a team examined the contents of the solar wind – streams of particles that continuously fly off the sun. The group found nothing to indicate that any matter was missing. Instead, they found indications of a total metallicity more or less on a par with what Basu’s work predicts.

“You might naively think this solves the problem,” says Vagnozzi, who participated in this study. “But it doesn’t.” The hole is filled, but the filling makes no sense. The proportions of various elements are all wrong – different from anything anyone else has found – offering no definitive resolution. “You essentially screw up the sun,” says Vagnozzi.

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Re: Physics Discussion Thread

Postby ArjunPandit » 29 Oct 2017 05:56

^^The above article also briefly talks about how neutrino detection can help solve this problem too

The easiest way to resolve the controversy would be to produce an independent measurement of the sun’s insides – one more conclusive than earlier attempts to test the solar wind. That knockout punch could come from neutrinos, lightweight particles produced as shrapnel in the fusion reactions taking place inside the sun.

Every second, some 65 billion of those solar neutrinos are passing through any given square centimetre on Earth, travelling at nearly light speed. The vast majority are created when hydrogen nuclei collide in the outer reaches of the sun. But one in a hundred, or thereabouts, are born during heavier fusion processes involving atoms of carbon, nitrogen and oxygen. By measuring the amount of these CNO neutrinos that reach a given spot on Earth, you can work out the exact number spilling out of the sun – and from that, how many of these heavy elements are there creating them.

Such a direct probe would allow us to bypass all the theory that underpins the work of Asplund and Basu. “We would be able to really solve this,” says Michael Wurm, a neutrino hunter working on the Borexino detector underneath the mountains of central Italy.

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Re: Physics Discussion Thread

Postby Amber G. » 30 Oct 2017 11:17

Speaking about Neutrinos, perhaps many people may have wondered if there were any neutrino's observed in the recent Neutron Start collision event. I was curious. I have not seen this mentioned in any mainstream media but this is interesting.
When LIGO and Virgo collaborations have announced the detection of a new gravitational wave even (GW170817) -- first time that a binary neutron star merger has been detected with the LIGO observatory.

As mentioned this unique observation is even more compelling since the same collision was seen by the Fermi and INTEGRAL satellites as a result of a short gamma-ray burst (GRB) and, subsequently, across the electromagnetic spectrum, with radio, optical, and X-ray detections. These observations made it possible for the first time to pinpoint the source location of a gravitational wave event. The source was found to be in a galaxy 130 million light years away, known as NGC 4993.

For Neutrinos -- In a joint effort by the ANTARES, IceCube, Pierre Auger, LIGO, and Virgo collaborations scientists have searched for neutrino emission from this merger. The search looked for neutrinos in the GeV to EeV energy range and did not find any neutrino in directional coincidence with the host galaxy.

(But this nondetection agrees well with expectation from short GRB models of observations at a large off-axis angle, which is most likely the case for the GRB detected. (More in the scientific paper published around the same time).. some cut and paste from there..
The search for neutrino emission from this collision of two neutron stars has been conducted in collaboration with both the ANTARES and Pierre Auger observatories, which bring improved sensitivities at different energies. At the exact time of the merger, the source could fortuitously be seen from an ideal viewing angle by the Pierre Auger observatory. For IceCube and ANTARES, the direction to the source was in a part of the sky where the detectors are less sensitive, but still capable of making significant observations.
The first study concentrated on a time window within 500 seconds around the detection of GW170817, and yielded no associated neutrino events. Later, scientists expanded the search to include possible emission of high-energy neutrinos up to 14 days after the merger, suggested by theoretical predictions, and also searched for lower energy neutrinos associated with the merger remnant and ejected material. These follow-up studies did not find any significant emission either.


So no neutrinos this time, hopefully we will see it next time.,

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Re: Physics Discussion Thread

Postby Prem » 31 Oct 2017 05:24

https://soundcloud.com/nasa/sets/spookyspacesounds

NASA compilation of elusive "sounds" of howling planets and whistling helium.

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Re: Physics Discussion Thread

Postby Amber G. » 06 Nov 2017 11:38

Some may be interested, if near Ahmadbad .Prof. Bala Iyer is one of the leaders for LIGOIndia..And there is a public lecture by him.
Details in the following image.
<details>

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Re: Physics Discussion Thread

Postby Amber G. » 07 Nov 2017 01:11

xpost -
India's Astrosat and its CZTI (Cadmium Zinc Telluride Imager) was in limelight in its role about the recent big LIGO/Neutron Start inspiral discovery. (see many posts here or in Physics dhaga around October 20). Kilonova which was detected here on earth by LIGO and 70+ observatories around the world in many EM spectrum as well as Gravitational waves .

There is another significant achievement by Astorsat and CZTI - which ought to be a major news item.

It's sensitive CZTI has measured X-ray polarization of Neutron star - Famous pulsar in Crab Nebula remnant of super-nova (SN 1054). For those, not familiar with this event which happened in 1054 AD was recorded by astronomers, and people, all over the world. One can not miss it as this was the most bright event (apart from moon) in night sky -- one can see this even in daylight.

Anyway for such a short time ( year or so) of operation," CZTI has recorded several gamma-ray bursts, measured the phase resolved hard X-ray polarization of the Crab pulsar, and the hard X-ray spectra of many bright Galactic X-ray binaries. The excellent timing capability of the instrument has been demonstrated with simultaneous observation of the Crab pulsar with radio telescopes like GMRT and Ooty radio telescope." VERY IMPRESSIVE!

Here is the Arxiv paper:
Cadmium Zinc Telluride Imager onboard AstroSat : a multi-faceted hard X-ray instrument

A. R. Rao, D. Bhattacharya, V. B. Bhalerao, S.V. Vadawale, S. Sreekumar

The AstroSat satellite is designed to make multi-waveband observations of astronomical sources and the Cadmium Zinc Telluride Imager (CZTI) instrument of AstroSat covers the hard X-ray band. CZTI has a large area position sensitive hard X-ray detector equipped with a Coded Aperture Mask, thus enabling simultaneous background measurement. Ability to record simultaneous detection of ionizing interactions in multiple detector elements is a special feature of the instrument and this is exploited to provide polarization information in the 100 - 380 keV region. CZTI provides sensitive spectroscopic measurements in the 20 - 100 keV region, and acts as an all sky hard X-ray monitor and polarimeter above 100 keV. During the first year of operation, CZTI has recorded several gamma-ray bursts, measured the phase resolved hard X-ray polarization of the Crab pulsar, and the hard X-ray spectra of many bright Galactic X-ray binaries. The excellent timing capability of the instrument has been demonstrated with simultaneous observation of the Crab pulsar with radio telescopes like GMRT and Ooty radio telescope.


There are a few regular papers mentioning this (more may follow) but as someone said "Indian astronomers obtain the most precise hard X-ray polarization measurements of the Crab pulsar so far" -- which will help understand Neutron (this pulsar).

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Re: Physics Discussion Thread

Postby Amber G. » 08 Nov 2017 11:16

^^^^
Amber G. wrote:India's Astrosat and its CZTI (Cadmium Zinc Telluride Imager) was in limelight in its role about the recent big LIGO/Neutron Start inspiral discovery. (see many posts here or in Physics dhaga around October 20). Kilonova which was detected here on earth by LIGO and 70+ observatories around the world in many EM spectrum as well as Gravitational waves .

There is another significant achievement by Astorsat and CZTI - which ought to be a major news item.
<snip>
.

Here is one newspaper article from today:
Isro’s multi-wavelength space telescope AstroSats’ breakthrough discovery
AstroSat measurement of polarisation of X-ray emission from the Crab Pulsar
Image
CHENNAI: Isro’s multi-wavelength space telescope AstroSat has made a breakthrough discovery in X-ray emission while helping the Indian scientists to solve one of the puzzles in astronomy that is to measure the elusive properties of high energy X-rays. These properties of high energy X-rays can throw more light on their sources which include neutron stars (pulsars) and black holes. In a paper published in ‘Nature Astronomy’, a team of scientists has documented the results of their study of the Crab pulsar in the Taurus constellation.

Using data from the CZT Imager instrument of the AstroSat, the scientists have performed the most sensitive measurement of X-ray polarisation of the Crab pulsar, the rotating pulsar which is the main energy source of the nebula. The measurements have for the first time enabled the study of polarization at different rotation phases of the pulsar. It has revealed the strange polarisation of Crab Pulsar which challenges the prevailing theories of high energy X-ray emission from pulsars. “This new paradigm can throw new light on our understanding of pulsars. This is fully an Indian discovery involving Indian scientists and telescopes,” said Professor Santosh Vadawale of Physics Research Laboratory, Ahmedabad and the lead author of this paper.

“Current theories say all emissions are coming from inside the light cylinder. But, these results suggest that it cannot come from inside, so it has to come from outside. So, that new theoretical understanding of pulsars has to be developed,” he added. “In X-ray polarisation, we observed the emissions even when the beams are not pointing towards us which also known as off pulse duration,” Professor Dipankar Bhattacharya of IUCAA, Pune, and co-author of this paper told Deccan Chronicle. He gave an example of the lighthouse to explain the discovery. ““Like a lighthouse, it was believed, the rotating pulsars emit radiation when the beams are pointing towards us. But, in our X-ray polarization we have discovered that the Crab Pulsar emit radiation even beams not pointing towards us,” he explained.

This discovery potentially redefines the concept of how pulsars emitting the X-rays. X-ray polarisation measurement is very difficult and so far the only reliable measurement obtained worldwide is for the pulsar in the Crab Nebula – the ghostly remains of a massive stellar explosion known as the supernova, observed in 1054 AD. To get the micro-second accuracy required for combining the data, the AstroSat team sought help from radio telescopes – the Indian Giant Meterwave Radio Telescope (GMRT), at Khodad near Pune and Ooty Radio Telescope. The team monitored radio pulsations from Crab and meticulously corrected for all known anomalies. The scientists after spending several months on the data came up with the best measurements of Crab X-ray polarisation in the world.

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Re: Physics Discussion Thread

Postby Amber G. » 18 Nov 2017 10:27

As I said.. these announcements are going to become even more routine. Here is the SIXTH discovery of Gravitational Waves & the lightest Black Hole collision detected to date!!

LIGO and Virgo announce the detection of a black hole binary merger from June 8, 2017
Image
LIGO and Virgo announce the detection of a black hole binary merger from June 8, 2017
News Release • November 15, 2017

Scientists searching for gravitational waves have confirmed yet another detection from their fruitful observing run earlier this year. Dubbed GW170608, the latest discovery was produced by the merger of two relatively light black holes, 7 and 12 times the mass of the sun, at a distance of about a billion light-years from Earth. The merger left behind a final black hole 18 times the mass of the sun, meaning that energy equivalent to about 1 solar mass was emitted as gravitational waves during the collision.

This event, detected by the two NSF-supported LIGO detectors at 02:01:16 UTC on June 8, 2017 (or 10:01:16 pm on June 7 in US Eastern Daylight time), was actually the second binary black hole merger observed during LIGO’s second observation run since being upgraded in a program called Advanced LIGO. But its announcement was delayed due to the time required to understand two other discoveries: a LIGO-Virgo three-detector observation of gravitational waves from another binary black hole merger (GW170814) on August 14, and the first-ever detection of a binary neutron star merger (GW170817) in light and gravitational waves on August 17.

A paper describing the newly confirmed observation, “GW170608: Observation of a 19-solar-mass binary black hole coalescence,” authored by the LIGO Scientific Collaboration and the Virgo Collaboration has been submitted to The Astrophysical Journal Letters and is available to read on the arXiv. Additional information for the scientific and general public can be found at http://www.ligo.org/detections/GW170608.php.

A fortuitous detection

The fact that researchers were able to detect GW170608 involved some luck.

A month before this detection, LIGO paused its second observation run to open the vacuum systems at both sites and perform maintenance. While researchers at LIGO Livingston, in Louisiana, completed their maintenance and were ready to observe again after about two weeks, LIGO Hanford, in Washington, encountered additional problems that delayed its return to observing.

On the afternoon of June 7 (PDT), LIGO Hanford was finally able to stay online reliably and staff were making final preparations to once again “listen” for incoming gravitational waves. As part of these preparations, the team at Hanford was making routine adjustments to reduce the level of noise in the gravitational-wave data caused by angular motion of the main mirrors. To disentangle how much this angular motion affected the data, scientists shook the mirrors very slightly at specific frequencies. A few minutes into this procedure, GW170608 passed through Hanford’s interferometer, reaching Louisiana about 7 milliseconds later.

LIGO Livingston quickly reported the possible detection, but since Hanford’s detector was being worked on, its automated detection system was not engaged. While the procedure being performed affected LIGO Hanford’s ability to automatically analyze incoming data, it did not prevent LIGO Hanford from detecting gravitational waves. The procedure only affected a narrow frequency range, so LIGO researchers, having learned of the detection in Louisiana, were still able to look for and find the waves in the data after excluding those frequencies. For this detection, Virgo was still in a commissioning phase; it started taking data on August 1.



More to learn about black holes

GW170608 is the lightest black hole binary that LIGO and Virgo have observed – and so is one of the first cases where black holes detected through gravitational waves have masses similar to black holes detected indirectly via electromagnetic radiation, such as X-rays.

This discovery will enable astronomers to compare the properties of black holes gleaned from gravitational wave observations with those of similar-mass black holes previously only detected with X-ray studies, and fills in a missing link between the two classes of black hole observations.

Despite their relatively diminutive size, GW170608’s black holes will greatly contribute to the growing field of “multimessenger astronomy," where gravitational wave astronomers and electromagnetic astronomers work together to learn more about these exotic and mysterious objects.



What’s next

The LIGO and Virgo detectors are currently offline for further upgrades to improve sensitivity. Scientists expect to launch a new observing run in fall 2018, though there will be occasional test runs during which detections may occur.

LIGO and Virgo scientists continue to study data from the completed O2 observing run, searching for other events already "in the can," and are preparing for the greater sensitivity expected for the fall O3 observing run.





LIGO is funded by the NSF, and operated by Caltech and MIT, which conceived of LIGO and led the Initial and Advanced LIGO projects. Financial support for the Advanced LIGO project was led by the NSF with Germany (Max Planck Society), the U.K. (Science and Technology Facilities Council) and Australia (Australian Research Council) making significant commitments and contributions to the project. More than 1,200 scientists and some 100 institutions from around the world participate in the effort through the LIGO Scientific Collaboration, which includes the GEO Collaboration and the Australian collaboration OzGrav. Additional partners are listed at http://ligo.org/partners.php

The Virgo collaboration consists of more than 280 physicists and engineers belonging to 20 different European research groups: six from Centre National de la Recherche Scientifique (CNRS) in France; eight from the Istituto Nazionale di Fisica Nucleare (INFN) in Italy; two in the Netherlands with Nikhef; the MTA Wigner RCP in Hungary; the POLGRAW group in Poland; Spain with the University of Valencia; and the European Gravitational Observatory, EGO, the laboratory hosting the Virgo detector near Pisa in Italy, funded by CNRS, INFN, and Nikhef.

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Re: Physics Discussion Thread

Postby ArjunPandit » 20 Nov 2017 08:21

https://www.newscientist.com/article/mg ... star-ever/

behind a paywall but the main article is on arxiv
arxiv.org/abs/1711.01898

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Re: Physics Discussion Thread

Postby ArjunPandit » 20 Nov 2017 08:24

A question that comes to my mind is why not any Indian writing such paper? Didn't astrosat provide more data that the chinese would have?

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Re: Physics Discussion Thread

Postby saip » 28 Nov 2017 22:09

Meet the 11-year old who won a $25,000 science prize

CNN

Five out of nine finalists are of Indian descent.

Image

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Re: Physics Discussion Thread

Postby Prem » 29 Nov 2017 07:49

https://timesofindia.indiatimes.com/cit ... 812320.cms?

IT-Kharagpur research promises a quantum leap in futuristic tech

KOLKATA: A research led by an IIT Kharagpur faculty member, which finds mention in acclaimed science journal 'Nature Physics', promises to increase manifold the speed and the storage capacity at which tomorrow's devices — your laptops and your smartphones — work. The toolbox of the future will be infinitely faster, smaller and much more efficient.Sajal Dhara and his team have proved that next-generation devices like quantum computers can be designed even without the use of electrons. Since the artificially created new particle is lighter than the mass of an electron by 0.0001 times, for a layman this will translate into simple solutions to the most intricate problems and lightning fast applications."Just imagine a caricature version of tiny fireflies being laws of physics but different from our classical world," Dhara explained. "We have discovered new insights on the mass of these intriguing particles. The new understanding is expected to inspire a giant leap towards futuristic technology development. Quantum computation is just one application, there are limitless possibilities," he added.The October issue of 'Nature Physics' gives a lowdown on Sajal Dhara's discovery, which is a collaborative work with the University of Rochester and the International Centre of Theoretical Sciences (ICTS), Bangalore. The other collaborators with Dhara are, C Chakraborty, KM Goodfellow, L Qiu, TA O'Loughlin, GW Wicks and AN Vamivakas, all from University of Rochester and Subhro Bhattacharjee from ICTS, TIFR.A physics graduate from Presidency College, who did his masters from IIT Kharagpur, PhD from TIFR and post-doctoral from Pennsylvania and Rochester universities, Dhara joined as a faculty at IIT Kharagpur in October 2016. Too excited at being able to reach "somewhere" in his "quest for light", Dhara says he will spend the next few years perfecting the polariton for quantum devices."Light is an electromagnetic wave but it also shows particle properties with zero mass. Matter on the other hand are made of atoms that have a certain mass. We have artificially created a combined particle state that is made of half-light and half-matter, or polaritons," Dhara said.

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Re: Physics Discussion Thread

Postby ashish raval » 26 Dec 2017 06:59


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Re: Physics Discussion Thread

Postby Amber G. » 28 Dec 2017 03:01

Exciting and Historic moment: LIGO gravitational wave detector to be built in India by 2025.

Historic moment: LIGO gravitational wave detector to be built in India by 2025.

Looks like all things are going well .. in collaboration with universities from across the globeLIGO gravitational wave detector to is set to be built in India by 2025 - and it will add the third LIGO detector to the two already operational in the US.

As posted here many times - The LIGO detectors discovered the first gravitational waves produced by two giant merging blackholes last year. The research won a Nobel Prize in Physics this year. Another big achievement was to discover Kilo nova - the merging of two neutron stars. This event was later confirmed by many other telescopes (radio, optical, gamma ray - full spectrum) through the world.


The location has been selected, and the acquisition has started...

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Re: Physics Discussion Thread

Postby Amber G. » 20 Jan 2018 09:36

Highlights of the Year 2017
Multimessenger Astronomy Makes an Explosive Entrance
2017 was another sensational year for gravitational-wave detection. Days after the Nobel Prize in Physics was awarded to three leaders of the decades-long search for these spacetime ripples, the LIGO and Virgo collaborations announced the detection of a gravitational-wave signal emanating from the merger of two neutron stars (see Viewpoint: Neutron Star Merger Seen and Heard). If this achievement wasn’t enough, multiple telescopes around the world also captured the myriad electromagnetic fireworks accompanying this merger. For the first time, electromagnetic signals and gravitational waves were detected from the same source, heralding a new era of astronomy in which scientists can both watch and “listen” to objects in the cosmos. Virgo coming online and adding one detector to LIGO’s two was essential to achieve this triumph (see Focus: Three-Way Detection of Gravitational Waves). With three detectors running, the scientists were able to more accurately pinpoint the source of the gravitational waves, localizing the event to a patch of sky small enough for telescopes to survey.

Cooking Up a Time Crystal
Time crystals are quirky states of matter whose structure repeats both in time and in space. The idea, theorized five years ago by Frank Wilczek (see Viewpoint: Crystals of Time), was initially discarded because theorists proved that time crystals cannot exist in thermal equilibrium. But this year, a quartet of US-based scientists exploited an open loophole in the argument against time crystals: such states can exist in nonequilibrium systems that are driven periodically by an external force. The researchers presented a recipe for cooking up a time crystal using a string of cold, trapped ions (see Viewpoint: How to Create a Time Crystal). In their scheme, the ions are subjected to periodic spin-aligning pulses. The team predicted that the ions would evolve to form time crystals, whose signatures would be periodic oscillations in the spins’ magnetizations. Within three months of the proposal, time crystals were realized in two different systems: a chain of trapped atoms and spin impurities in diamond.

Quantum Cause and Effect
Red suits and white beards are highly correlated this time of the year, and statistical tools can verify that they share a common cause (or Claus!). However, similar inferences are tricky in quantum physics. For example, two entangled photons are by their very nature strongly correlated, but a common cause (or “hidden variable”) is ruled out by so-called Bell-test experiments. To deal with these quantum peculiarities, researchers from the UK and Canada reworked the definition of causality (see Viewpoint: Causality in the Quantum World). The team based their model of quantum cause and effect on unitarity, which says that quantum information is conserved as a system evolves. Under their new formalism, one can determine whether a quantum system A is the common cause of two correlated quantum systems B and C by relating the probability distributions of quantum variables in the different systems. This quantum causality model could help in predicting the effects of peeking at information in a quantum cryptography system.

Wi-Fi: The Radar That’s Everywhere
A Wi-Fi router connects you to the world, but its microwave radiation can also be used to produce images of its surroundings, according to researchers at the Technical University of Munich (see Focus: Imaging with Your Wi-Fi Hotspot). This imaging is difficult because the router blasts radiation in all directions, which leads to multiple reflected images. The team solved this problem by processing Wi-Fi radiation data as though they were decoding a hologram—a 2D encoding of a 3D image. They placed a meter-sized cross between a router and a detector and scanned the detector across a 6- m2m2 area, demonstrating that they could reconstruct an image of the cross. The team also simulated the imaging of a small building’s interior, suggesting that the technique could be used to locate objects in a warehouse. Since the radiation penetrates walls, Wi-Fi imaging might eventually be used for law-enforcement purposes.

Cuprate Superconductors Not So Unconventional?
Copper oxide superconductors, or cuprates, hold the record for the highest critical temperature, but their behavior still defies theoretical explanation. It is generally believed that the standard theory of superconductivity, known as the Bardeen-Cooper-Schrieffer (BCS) theory, cannot adequately describe cuprate superconductors because it predicts certain signatures that have not been observed in these materials. Using a scanning tunneling microscope, a team of researchers in Switzerland and Germany found a hallmark of BCS superconductivity in a cuprate compound: twirls of supercurrents containing pockets of nonsuperconducting electrons (see Viewpoint: Cuprate Superconductors May Be Conventional After All). While the results don’t yet clarify the mechanisms that make cuprates supercounduct at high temperature, they suggest that a BCS-based description may hold the key to solving this grand puzzle of condensed-matter physics.

Gluons Provide Half of the Proton’s Spin
The gluons that bind quarks together in nucleons provide a considerable chunk of the proton’s total spin. That was the conclusion reached by Yi-Bo Yang from the University of Kentucky, Lexington, and colleagues (see Viewpoint: Spinning Gluons in the Proton). By running state-of-the-art computer simulations of quark-gluon dynamics on a so-called spacetime lattice, the researchers found that 50% of the proton’s spin comes from its gluons. The result is in agreement with recent experiments and shows how such lattice simulations can now accurately predict an increasing number of particle properties. The simulations also indicate that, despite being substantial, the gluon spin contribution is too small to play a major part in “screening” the quark spin contribution—which according to experiments is only 30%—through a quantum effect called the axial anomaly. The remaining 20% of the proton spin is thought to come from the orbital angular momentum of quarks and gluons.

WIMPs Are No-Shows, Again
Of the many theories about dark matter, the most popular describes it as composed of weakly interacting massive particles (WIMPs). But this “favored” theory is now looking a little, well, less favored. In the last 16 months, the collaborations behind the world’s three largest dark matter detectors reported that they had observed no WIMPs in the theoretically expected mass range. The experiments all use mammoth vats of liquid xenon, which are scrupulously shielded to avoid false signals from cosmic rays, to spot a WIMP’s interaction with regular matter. Writing in January about the null results from the LUX experiment in the US and PandaX-II in China, Jodi Cooley said that some physicists had started to question the simplest WIMP model (see Viewpoint: Dark Matter Still at Large). By October, when XENON1T in Italy (2000 kg) and PandaX-II reported that their more sensitive WIMP searches had also come up empty, Dan Hooper said that dark matter research was in “a state of major disruption” (see Viewpoint: The Relentless Hunt for Dark Matter).

Topological “Face” Recognition
The term “topological” often conjures up images of donuts and pretzels, but condensed-matter physicists know that recognizing topological phases is harder than sorting pastry items. To help them out, researchers from Cornell University devised a machine-learning-based method for determining if a material is topological or not (see Viewpoint: Neural Networks Identify Topological Phases). The idea of using machine learning in condensed-matter physics is not new. Researchers have trained neural networks to spot local order, such as a magnetic alignment of spins. However, topological materials have nonlocal order that is less easy to pin down. To make the identification easier, the team developed a computing protocol to transform system information, such as the many-body electron wave function, into an image that could be fed into a neural network. They applied such a protocol to different insulators, showing that it could identify which systems hosted a quantum Hall topological phase.


rsingh
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Re: Physics Discussion Thread

Postby rsingh » 15 Mar 2018 18:49

Me think this Hawking guy was overhyped.


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