Gravitational Waves

[aqua]

2hats thanks for your science posts across the boards, I really appreciate you knowledge and time spent with them all

2hats is my urban crush I have to say. I barely understand some of the things he says. They're words I know but in sentences that make my head hurt!

 

[2hats]

When do you think gravity particles will be detected rather than waves?

Freeman Dyson has suggested that they might never be detectable.

A problem is that gravitons are (at best) most likely extremely weakly interacting so a detector would end up being impractically massive - many hundreds of times the mass of the Earth for any probability of single particle detection over many years of observing (the LIGO mirrors, to detect individual gravitons, would have to be so big that they would collapse under their own gravity and form black holes). At worse gravitons may be hard to tempt out into the open (if at all) in this universe as they may well be intimately wrapped up with higher dimensions.

So they may only ever be observable indirectly, which is in some senses what this experiment has done. A more empirical approach (proposed by Krauss) might be through observing polarisations in the cosmic microwave background, which calculations show would arise from quantum mechanical effects, demonstrating that gravity is quantised and thus inferring the existence of gravitons.

 

[HAL9000]

Freeman Dyson has suggested that they might never be detectable.

A problem is that gravitons are (at best) most likely extremely weakly interacting so a detector would end up being impractically massive - many hundreds of times the mass of the Earth for any probability of single particle detection over many years of observing (the LIGO mirrors, to detect individual gravitons, would have to be so big that they would collapse under their own gravity and form black holes). At worse gravitons may be hard to tempt out into the open (if at all) in this universe as they may well be intimately wrapped up with higher dimensions.

So they may only ever be observable indirectly, which is in some senses what this experiment has done. A more empirical approach (proposed by Krauss) might be through observing polarisations in the cosmic microwave background, which calculations show would arise from quantum mechanical effects, demonstrating that gravity is quantised and thus inferring the existence of gravitons.

wasn't the answer i was expecting, but very interesting. thanks

 

[spitfire]

I don't know how you manage to explain this stuff to mortals but you do it very well. Thanks 2hats

 

[Mumbles274]

2hats are you Brian cox in disguise?

 

[spitfire]

Don't scare him off!

 

[spitfire]

just in case like.....

 

[twentythreedom]

Freeman Dyson has suggested that they might never be detectable.

A problem is that gravitons are (at best) most likely extremely weakly interacting so a detector would end up being impractically massive - many hundreds of times the mass of the Earth for any probability of single particle detection over many years of observing (the LIGO mirrors, to detect individual gravitons, would have to be so big that they would collapse under their own gravity and form black holes). At worse gravitons may be hard to tempt out into the open (if at all) in this universe as they may well be intimately wrapped up with higher dimensions.

So they may only ever be observable indirectly, which is in some senses what this experiment has done. A more empirical approach (proposed by Krauss) might be through observing polarisations in the cosmic microwave background, which calculations show would arise from quantum mechanical effects, demonstrating that gravity is quantised and thus inferring the existence of gravitons.

This ^^

 

[2hats]

2hats are you Brian cox in disguise?

I take offence at the suggestion that I might in some way be responsible for the output of D:Ream.

 

[Johnny Vodka]

So does this mean there are aliens or not?

 

[spitfire]

I take offence at the suggestion that I might in some way be responsible for the output of D:Ream.

Double bluff.

 

[eoin_k]

I now have this image of 2hat's avatar reading out his posts in an annoyingly smug tone, while trying to look dishy yet deep.

 

[HAL9000]

Brian Cox was on the radio talking about the speed of the black holes just before they collided.

• Two black holes were traveling towards each other at 33 percent of the speed of light
• 1/10 of a second later and just before they collided, speed had jumped to 66 percent of light speed.

To put that in perspective, the voyager probe is leaving the solar system at 0.0057 percent of light speed (17.46 km/s). So its a huge acceleration. Picture from the physics paper

Phys. Rev. Lett. 116, 061102 (2016) - Observation of Gravitational Waves from a Binary Black Hole Merger

Looking at the picture it appears the acceleration was a bit longer than a 1/10 of a second. Even so, the speed and acceleration is enormous (Brian Cox is a bit cleverer than I.)

 

[alcopop]

Indeed, Rainer Weiss (MIT) has been explaining just a few of the engineering challenges in dealing with the noise environment in order to measure at 10^-21. Not just local geological, man made vibrations. Not just thermal noise. But quantum noise too. The measurement they have made is equivalent to measuring the distance from the Earth to the nearest star within an accuracy of the width of a human hair.

This black hole collision was observed on September 14th last year, but it occurred about 1.3 billion years ago. The event was brief but for a moment equivalent to fifty times the power output of the entire observable universe.

How brief is brief?

Many thanks

 

[BandWagon]

What next?

Gravitational waves: what breakthroughs can we expect next?

Quote:

The telescope could ultimately be used to answer questions about dark energy. This is a mysterious force in space itself, which is sometimes called antigravity, and which is causing the distant universe to accelerate. Identified only in 1998, it accounts for more than two thirds of the mass of the cosmos.

“We really don’t know what dark energy is,” said Prof Sathyaprakash. “But what we can do is map the geometry of the universe by using black holes and neutron stars as distance markers. They can give us very precise distance. If we do this, we should be able to get a precise geometry of the universe and in the long run – it is not going to be easy - but in 10 or 15 years we will be able to figure out what is the characteristic of this dark energy.”


Or maybe it's the cosmological constant.....

 

[2hats]

How brief is brief?

Something like 0.2 seconds, I think it was.

 

[HAL9000]

How brief is brief?

Many thanks

This graph shows the collision, as Mr Hat said its about 0.2 seconds.

 

[HAL9000]

This was on the bbc page, Animation of the black holes colliding

 

[Supine]

I now have this image of 2hat's avatar reading out his posts in an annoyingly smug tone, while trying to look dishy yet deep.

His posts are great. I like to read them using the voice of kenneth williams

 

[MikeMcc]

I take offence at the suggestion that I might in some way be responsible for the output of D:Ream.

well it can only get better...

 

[2hats]

The LIGO team have reported a second observation of gravitational waves - seen in data taken last December (LIGO is offline at the moment undergoing upgrades to improve coverage and sensitivity). This event involved two black holes colliding, each smaller than those involved in the first observed event, some 1.4 billion light years away.

DOI:10.1103/PhysRevLett.116.241103

e2a: worth noting that this analysis was a joint effort with the European Virgo gravitational wave team. Once their detector, in Italy, comes up to speed (later this year), data from that will be combined with the LIGO detectors in the US and then researchers should be able to pinpoint the location of sources of gravitational waves (at the moment with two detectors they can only narrow down the source to a large area on the sky).

 

[2hats]

Amazing achievement - these experiments are very *very* hard to do. Einstein's work continues to hold up incredibly well

Now further analysis of the LIGO signals received thus far may be hinting that there might be evidence of echoes in the waves, contrary to predictions arising from general relativity (which essentially would not allow for such information leakage from a black hole's event horizon).

Note that the paper is a preprint and not yet peer reviewed - the possibility is being floated for further consideration. If, after further data and more analysis, the echoes prove to be noise and not a genuine signal (they are under 3σ and not at 5+σ) then general relativity would be upheld but quantum ideas will need to be re-evaluated (quantum interpretations point to structure at the event horizon which could leave wiggle room for signals to leak out; Hawking radiation being an example of such). If not, and general relativity is observed to be breaking down at the event horizon, let alone at the centre of a black hole, then we could be on the verge of a new exotic physics.

Discussion in this Nature article.

 

[2hats]

Press conference with further announcements on subsequent research findings from the LIGO/VIRGO collaboration due at 1500BST this afternoon. Live webcast.

 

[Vintage Paw]

LIGO Detects Fierce Collision of Neutron Stars for the First Time

 

[HAL9000]

"A simultaneous detection of gamma rays and gravitational waves from the same place in the sky is a major milestone in our understanding of the universe," said Davide Lazzati, a theoretical astrophysicist in the OSU College of Science

On July 6, Lazzati's team of theorists had published a paper predicting that, contrary to earlier estimates by the astrophysics community, short gamma-ray bursts associated with the gravitational emission of binary neutron star coalescence could be detected -- whether or not the gamma-ray burst was pointing at Earth

Gamma-ray burst detection just what researchers exclusively predicted

Article claims that theorists predicted a gamma ray burst and gravity emission happening at the same time. Then....

IGO, and the European Gravitational Observatory's Virgo team on Aug. 17, 2017, detected gravitational waves -- ripples in the fabric of space-time -- produced by the coalescence of two neutron stars.

 

[bubblesmcgrath]

"Neutron stars are the leftover, dense cores of larger stars that ended their lives in supernova explosions. When two neutron stars merge, they can explode as a kilonova, as shown in this artist's impression. While kilonovas are believed to be rare, the observations confirm that these objects also produce heavy elements such as gold and platinum, including those found on Earth."

Killonova

First Glimpse of Colliding Neutron Stars Yields Stunning Pics




"The kilonova on Aug. 17 was visible to several instruments on multiple telescopes that are all managed by the European Southern Observatory. Some of those observations are shown here in a composite image. Upper left: Observations from the OmegaCAM (a wide-field imager) on the Very Large Telescope array (VLT) Survey Telescope (VST). Upper right: The VISTA InfraRed CAMera (VIRCAM) on the VISTA (Visible and Infrared Survey Telescope for Astronomy). Lower left: The Gamma-ray Burst Optical/Near-infrared Detector (GROND) on the MPG/ESO 2.2-meter telescope. Lower right: The Visible MultiObject Spectrograph (VIMOS) on the VLT. Center: The Multi Unit Spectroscopic Explorer on the VLT."

An interesting article on how Edo Berger's day went...☺...
Neutron-Star Collision Shakes Space-Time and Lights Up the Sky | Quanta Magazine

 

[ferrelhadley]

LIGO seems to have 4 candidates this week.

 

[2hats]

The all-pervading ultra-low frequency background noise of gravitational waves revealed by the NANOGrav collaboration through analysing 15 years worth of pulsar timing data (a very different approach to that used by LIGO and related gravity wave observatories).

15 Years of Radio Data Reveals Evidence of Space-Time Murmur

Scientists have found evidence of a universal background of gravitational waves, or ripples in the fabric of space-time.

www.jpl.nasa.gov

News conference shortly:

​

Note: This has relied on determining the position of the solar system barycentre (centre of mass) to better than 100 metres (a prerequisite for achieving the degree of accuracy necessary in the underlying pulsar timing). The largest contribution to error in this is Jupiter, though refining it might hint towards additional planets in the solar system. One should also be aware that this result is only good to 4σ (physicists are usually only satisfied at 5+σ).

Scientific commentary with links to published papers.

 

[petee]

The all-pervading ultra-low frequency background noise of gravitational waves revealed by the NANOGrav collaboration through analysing 15 years worth of pulsar timing data (a very different approach to that used by LIGO and related gravity wave observatories).

15 Years of Radio Data Reveals Evidence of Space-Time Murmur

Scientists have found evidence of a universal background of gravitational waves, or ripples in the fabric of space-time.

www.jpl.nasa.gov

News conference shortly:

​

Note: This has relied on determining the position of the solar system barycentre (centre of mass) to better than 100 metres (a prerequisite for achieving the degree of accuracy necessary in the underlying pulsar timing). The largest contribution to error in this is Jupiter, though refining it might hint towards additional planets in the solar system. One should also be aware that this result is only good to 4σ (physicists are usually only satisfied at 5+σ).

Scientific commentary with links to published papers.

that was reported in the NYT this morning, so it's biggish news i imagine.

https://archive.ph/GqDIG

 

[Orang Utan]

Has a dubstep producer sampled it yet?