Physics Discussion Thread

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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.


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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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Re: Physics Discussion Thread

Postby Amber G. » 12 May 2018 02:16

Today is Richard Feynman's 100th Birthday. And centenary celebrations are taking place.

Richard Feynman – iconic physicist, Nobel laureate and a great teacher – was born on this day 100 years ago in 1918!

I fondly remember many seminars and lectures given by him and discussions with this great teacher as he loved to teach/discuss. Like many I have used videos of his lectures in my classes.

I got my copy of Feynman lectures on Physics in 1966. The online version is available at (http://www.feynmanlectures.caltech.edu/ A true gem.

More on celebrations see stories like : Richard Feynman’s centenary celebrations
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Re: Physics Discussion Thread

Postby Amber G. » 12 May 2018 02:25

For those brfites who are seriously interested in physics -- Enjoy this awesome plenary session. There is in-depth review from APS News and also a video of all the key note speeches. Video is about 2 hours so set up some quality time to watch in full.

The theme of "Quarks to Cosmos" with three plenary sessions: 1) Kavli Foundation Keynote Plenary Session: A Feynman Century. 2) A range of topics "From Nuclear Security to Neutron Star Mergers" and 3) APS Medal winner Eugene Parker and Nobel Prize winners Rainer Weiss and Barry Barish. (Gravitational wave's etc - I, Badeji and few others discussed this very important discovery here in brf)

Talk on the life of Richard Feynman was given by an expert: his younger sister, Joan. Her talk, titled "Being Feynman’s Curious Sister" spanned her childhood spent learning from her brother, to her experiences as a female scientist and state of modern environment (an example of her climate research)

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Re: Physics Discussion Thread

Postby Amber G. » 15 May 2018 07:36

Sharing sad news - Eminent Physicist George Sudarshan (1931-2018) passed away. He will be fondly remembered as a guru to many of us. He was also a family friend.

I and few others discussed his contributions many times in Brf.

He was nominate 9 times for the Nobel Prize and at least twice it was unjustly denied to him. One of the most infamous case was Noble prize for quantum representation of light - known as Sudarshan-Glauber representation was given to Glauber only. Worse aspect of this was that the the work that the Noble committee cited for awarding was demonstrably Sudarshan's work. As many eminent scientists said at that time the Noble committee can choose it's recipient but it does not have the right to award a person for the work done by another. Shame on the Noble committee and the recipient for remaining quiet even after the facts became public.
(Around that time, I have posted many posts regarding that)

Apart from contributions to quantum optics, He discovered (with Marshak,the V-A theory of the weak interaction. This was independent of Feynman and Gell-Mann, and actually slightly before them. Feynman who got lot of credit for that actually gave credit to Sudarshan. (Again this has been discussed in BRF physics thread).


http://www.thehindu.com/news/national/kerala/eminent-physicist-sudarshan-dead/article23884743.ece
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Re: Physics Discussion Thread

Postby Amber G. » 15 May 2018 08:47

^^^Apart from contributions to quantum optics, He discovered (with Marshak,the V-A theory of the weak interaction. This was independent of Feynman and Gell-Mann, and actually slightly before them. Feynman who got lot of credit for that actually gave credit to Sudarshan. (Again this has been discussed in BRF physics thread).

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Re: Physics Discussion Thread

Postby Amber G. » 02 Jun 2018 03:53

On Oct 13, 2017 I posted about a major discovery here in brf

If what is said in rumor is true, all news papers will carry the story, so stay tuned.


All newspapers, TV's etc, had the story in front pages the next day confirming what many knew for some time but were waiting for official press conference.

The LIGO's Gravitational wave discovery of merging neutron stars in 2017 was remarkable and with the discovery of merging black holes (also discovered within year or so) is , IMO,the most exciting/major discovery of last 50 years. It also produced many other discoveries and new frontiers in other branches in of physics (both theoretical and experimental) and engineering.

..
This is why I was saying it is a BIG deal!

I said it here



Brf devoted a lot of posts (dozens !!) on this subject. (see posts around oct 17 -- a few pages). I reviewed a lot of them and if I may say so, the quality of posts is good. So, if you are not familiar with LIGO, those pages are excellent for background information.

LIGO's related discovery is in news again!..and I found it amazing that it is some thing we discussed in BRF an year ago.

There was a question:
Zynda wrote:AmberG, what would be the outcome of two neutron stars colliding/merging? I've heard cosmologists say that result probably might be formation of a new black hole but is it possible due to the energy released from collision, the stars disintegrate and individual neutrons spread around


To which I responded: and gave some theoretical limits on when the merger is results in a black hole or sNS. Since the total mass was very much between these two limits so no one was sure..
In fact we did ask the LIGO team and at that time...
BTW - Per LIGO team, we still don't know if the recently detected merger resulted into black hole or not. It requires further study.


Well now the article about the "further study" has appeared! The author is Pawan Kumar and the data is from Chandra ..
Link:
>>> ]Using NASA’s Chandra X-ray Observatory, researchers from the University of Texas at Austin and the University of California, Berkeley, sought to understand what happened during and after the merger. LIGO data suggested the new object, dubbed GW170817, had a mass about 2.7 times that of our Sun. That’s a rather curious finding, because it doesn’t quite fit into what we know of neutron stars or black holes. If it’s a neutron star, GW170817 would be the most massive object of its kind known to science; the largest known neutron stars are between 2.3 to 2.4 solar masses—{{ BTW these values - 2.3, 2.4, 2.7 are exactly same as I posted in BRF !!} these objects are already testing the limits of how much material can be packed into a small space before collapsing into a black hole. But if it’s a black hole, it would be the least massive black hole ever detected, as the tiniest black holes are between four and five solar masses.>>>

Link:https://arxiv.org/pdf/1712.03240.pdf

They are not 100 % sure but they think it is a lightest known black hole!




Image
After two stars underwent supernova explosions, two neutron stars were left behind. New research suggests gravitational wave radiation pulled them together until they merged and collapsed into a black hole.
Image: CXC/M. Weiss; X-ray: NASA/CXC/Trinity University

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Re: Physics Discussion Thread

Postby Zynda » 02 Jun 2018 19:52

^^Thanks AmberG for the following up with Ligo Team and posting here the findings. Surely interesting...

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Re: Physics Discussion Thread

Postby Amber G. » 03 Jun 2018 23:27

^^^ Thanks. It has been very exciting last year.

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Re: Physics Discussion Thread

Postby Amber G. » 06 Jun 2018 10:38

Nice article in Scientific American which covers the news I posted on June 1. It covers recent paper (https://arxiv.org/abs/1805.11581 ). What can #GW170817 tell us about the structure of neutron stars? -
Image
Gravitational Waves Reveal the Heart of Neutron Stars
>>>Scientists are mapping the extreme interiors of exotic stars with unprecedented clarity, and setting new boundaries on the births of black holes
Inside a neutron star—the city-size, hyperdense cinder left after a supernova—modern physics plunges off the edge of the map. There, gravity squeezes matter to densities several times greater than those found in the nucleus of an atom, creating what theorists suspect could be a breeding ground for never-before-seen exotic particles and interactions. But densities this high cannot be probed by laboratory experiments, and remain too challenging for even today’s most powerful computers to tackle.

So when the universe deigned to help out, astronomers jumped at the chance. Last August the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO), along with a European detector named VIRGO picked up gravitational waves reverberating through spacetime from the merger of two neutron stars some 130 million light-years from Earth. Those waves, now reanalyzed in a new paper by the LIGO–VIRGO team, provide some of the best hints yet about the nature of the merger’s progenitors—and what neutron star stuff actually is.

As the two stars circled toward mutual doom, shedding orbital energy into gravitational waves, they also began raising tides on each other’s surfaces. Those tidal interactions sucked away even more orbital energy, tightening the neutron stars’ orbit and hastening their collision. The strength of those tides, baked into the gravitational waves detected by LIGO–VIRGO, depended on each neutron star’s internal structure, which physicists model using an “equation of state.” For a neutron star an equation of state mathematically describes how the star’s innards react to changes in density, pressure and temperature.


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The new study follows up on an initial calculation released last October by the same team, which had failed to detect these tides in the gravitational wave signal at all. “Our first analyses were fairly ‘eyes wide open’—we made few assumptions,” says Jocelyn Read at California State University, Fullerton, who leads LIGO’s “Extreme Matter” team.

On the second go-round, though, the team looked at more orbits of the two objects and added in some additional constraints. Namely, they assigned both objects identical equations of state—a reasonable assumption, given that all available data about the merger makes it all but certain that the collision’s source was a pair of neutron stars.

Next, they tested possible equations of state that could explain the data, adding other sensible, real-world requirements. For instance, pressure and density changes could not create sound waves moving faster than the speed of light inside a neutron star (or any other object, for that matter). And the equation of state had to also fit the heaviest confirmed neutron star, which weighs in at roughly 1.97 solar masses. If neutron star material could not sustain sufficiently high pressures, such an object would not be a neutron star at all—it would have long ago collapsed into a black hole.

Taking all that into account, the new analysis finds the two neutron stars involved in the merger, each weighing perhaps 1.4 solar masses, were rather small for that weight: about 12 kilometers in radius. That would match previous controversial x-ray measurements of neutron star radii. And it hints midsize neutron stars possess relatively low interior pressures compared with the 1.97–solar mass heavyweight, which must have higher pressures to provide a stiff backbone against such crushing gravity.

Compared with lab measurements of matter at much lower densities, the new data show tentative hints of an upward bend in how pressure increases in denser and denser matter. Such a bend would not be expected if neutron stars are made solely of neutrons and protons—in that case, pressure should just increase smoothly. “There could be some interesting structure in the equation of state emerging,” Read says, adding the caveat that the data are also still consistent with a steady growth of pressure, corresponding to a “boring” neutron star made of only protons and neutrons. If physicists can confirm a bend like this in the equation of state, though, it might be a clue matter changes phase at very high densities, much like water changing from liquid to solid at sufficiently low temperatures. In neutron stars such a phase transition could arise from neutrons breaking apart into a soup of their constituent particles, quarks.



The new study echoes the findings of a previous analysis of the same event published in April by a team led by graduate student Soumi De at Syracuse University, but with twice the precision. “That’s encouraging, that this one event is not yet fully exploited,” says James Lattimer, an astrophysicist at Stony Brook University and a co-author on the earlier paper.

Both Lattimer and Read’s teams plan to keep reanalyzing last August’s signal. “We haven’t wrung everything we can out of this,” Read says. Soon, signals of additional neutron star mergers are likely to emerge from gravitational-wave detectors, providing even more data for astrophysicists hoping to pin down these exotic objects’ equation of state.

In the meantime there’s another helpful result, published in The Astrophysical Journal Letters last week. In the aftermath of last August’s neutron star merger, other astronomers scoured its wreckage with the Chandra X-Ray Observatory, hoping to glimpse its ultimate outcome: a single, heavier neutron star or a black hole.

A single giant neutron star weighing roughly 2.7 solar masses would have far outweighed the previous record holder, forcing the neutron star equation of state to accommodate an even tougher constraint. But it was not to be; the Chandra data revealed relatively few x-rays streaming from the merger’s wreckage, an observation consistent with the formation of a black hole. According to Lattimer, that’s interesting as its own limit—astronomers now know neutron star matter cannot possibly support so much weight. “I don’t think I thought imaginatively enough about all the things that mergers are going to be able to tell us,” he says.


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Re: Physics Discussion Thread

Postby Amber G. » 06 Jun 2018 10:42

Some time ago there was a discussion about India and Nobel Prize.. Some may find it interesting -- thoughts by a well known physicist.
Why is India not producing Nobel Laureates?
By: Rajesh Gopakumar

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Re: Physics Discussion Thread

Postby Neshant » 07 Jun 2018 12:33

I've been watching this snippet from a documentary on space-time.

I've not been able to understand something :

When the alien on the bicycle cycles away or towards Earth, why does his distance from earth have an increasing impact on his "now slice"?

He's only biking at a very slow rate so WHY does distance magnify that time dilation?

Before anyone dives into explaining that speed has an effect on time or gravity has an effect on time, i already understand that.
But I don't understand the above question in bold and the quote below from the video at 6:44.



Even at a relatively slow speed, you can have tremendous disagreements on our labeling of now (what happens at the same time) if we are spread out far enough in space

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Re: Physics Discussion Thread

Postby Amber G. » 30 Jun 2018 00:13

https://twitter.com/cardiffPHYSX/status ... 4251535362
>>Listen to @chrisenorth and @JeniMillard (also @AwesomeAstroPod presenter) in conversation with @LIGO Nobel Prize Winner Prof Barry Barish. They discuss the beginnings of LIGO, technological challenges, and how winning the Nobel has changed things for Barry.

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Re: Physics Discussion Thread

Postby Amber G. » 10 Jul 2018 20:18

And Don't make other plans for Thursday, July 12, at 11 am (U.S. ET.) -- Listen to press conference/announcement.. Rumor is that there is an exciting news is about another Multi-messenger Astronomy - Neutron stars colliding and getting detected by LIGO as well as other telescopes? Neutrinos?

More details soon.
Added later:
The press conference will be streamed live on https://www.youtube.com/c/VideosatNSF/live
Also: SF press conference on breakthrough in multimessenger astrophysics
Media are invited to attend a U.S. National Science Foundation (NSF) press conference announcing recent multi-messenger astrophysics findings led by NSF's IceCube Neutrino Observatory.

Representatives from nearly two dozen observatories on Earth and in space that participated in the research will be in the room during the event and will be available to the media after the press conference concludes. Reporters watching the event remotely can send questions to symposium@nsf.gov.

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Re: Physics Discussion Thread

Postby Amber G. » 13 Jul 2018 00:34

Listened to the NSF press conference... Now this will be a major news in all the news papers..
A Nice article in Science:
http://science.sciencemag.org/content/361/6398/eaat1378

or this:
Here's Why Today's Neutrino Discovery Is a Big Deal

***
So now we have multi-messenger astronomy events for EM as well as Gravitational waves, and now between EM and Neutrinos..

I hope we will see a event pretty soon (5-10 years) - merger of neutron star, may be, which can be observed in EM. GW and neutrinos..

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Re: Physics Discussion Thread

Postby Mort Walker » 13 Jul 2018 19:01

AmberGji,

A single neutrino at 290 TeV or several? So correlated with gamma rays consistent to TXS 0506+056?

Also. Multi wavelength observations are detection with different sensors at specific EM frequencies when neutrino interacts with other atoms when passing through?

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Re: Physics Discussion Thread

Postby Amber G. » 14 Jul 2018 23:33

^^^ Yes, one event was the main news, but there are others (may be as many as dozen or so) where the evidence may become stronger.

One should note that telescopes like Fermi have data archived for years and so they will be able to confirm if other observations which IceCube recorded earlier, too has high degree of confidence of multi-messenger confirmation.

In the particular case above, Ice Cube, after determining the direction of the origin, sent an alert, and sure enough other telescopes (Fermi, and Magic) pointed in the required direction and were able to see the gamma ray burst.
Also. Multi wavelength observations are detection with different sensors at specific EM frequencies when neutrino interacts with other atoms when passing through?


Just to be clear, IceCube sensors detected neutrinos (by seeing the muon tracks which were picked up by ice-cube sensors) and were able to find the exact direction, but the exciting news was, other telescopes (gamma ray telescopes), were able to see "blazars" (which produced both neutrinos, and gamma rays) in exactly the same position in the universe. The cosmic rays were produced due to a super massive black-hole sucking up vast amount of matter, billions of light years away.

Hope this is helpful - much more detail/clear explanation, as you know, is in the good readable article in Science - or a few other sources.

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Re: Physics Discussion Thread

Postby Mort Walker » 15 Jul 2018 19:34

Thanks. I'm glad this article in Science is free since I don't have a subscription.

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Re: Physics Discussion Thread

Postby Amber G. » 30 Jul 2018 09:16


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Re: Physics Discussion Thread

Postby Amber G. » 09 Aug 2018 06:36

Subir Sachdev (Harvard) along with Dam Thanh Son (UChicago) , and Xiao-Gang Wen (MIT) share the 2018 Dirac Medal for their work on "novel phases in strongly interacting many-body systems."

Congrats! Subir Sachdev was born in India and I think was at IIT Delhi as a student in late 70's.

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Re: Physics Discussion Thread

Postby Amber G. » 14 Aug 2018 21:46

Exactly one year ago LIGO and ego_virgo detected #gravitationalwaves from #GW170814, the merger of two #BlackHoles over a billion light years away. GW170814 was the first signal observed by the Advanced Virgo detector, helping to pinpoint its location much more precisely.

Justifiably, as I said at that time, the great discovery won Noble prize and every other honor..

I am glad and proud that India has invest a lot in IndlGO - LIGO India which is on track to open in 5 years or so.

One thing makes me happy that his also has increased interest in physics in India (and other places).
Not surprising a question in International Physics Olympiad was on LIGO (Laser Interferometer Gravitational Observatory) detection of gravitational waves. India created history to win 5 gold at the International Physics Olympiad.

(Sadly many informative posts here in this dhaga were deleted due to idiotic and silly trolling by one person which drove many of the serious and knowledgable posters away from brf -- making many of technical dhaga's much less informative)

https://pbs.twimg.com/media/DkhyV3XW0AE2V73.jpg

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Re: Physics Discussion Thread

Postby Neshant » 20 Aug 2018 04:16

Looks like there is no low power way to warp space-time if it takes large colliding black holes to warp it's fabric.

Excluding worm holes, a warp drive is so far the only theoratical means of faster-than-light (FTL) travel.


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