New Kind of Gravitational Wave Source Detected? (nature.com) 81
"Scientists possibly detected an entirely different type of gravitational wave [source]," writes schwit1. "Gossip over potential detection of colliding neutron stars has astronomers in a tizzy," reports Nature:
Astrophysicists may have detected gravitational waves last week from the collision of two neutron stars in a distant galaxy -- and telescopes trained on the same region might also have spotted the event. Rumours to that effect are spreading fast online, much to researchers' excitement. Such a detection could mark a new era of astronomy: one in which phenomena are both seen by conventional telescopes and 'heard' as vibrations in the fabric of space-time. "It would be an incredible advance in our understanding," says Stuart Shapiro, an astrophysicist at the University of Illinois at Urbana-Champaign...
The Laser Interferometer Gravitational-Wave Observatory (LIGO) in Louisiana and Washington state has three times detected gravitational waves -- ripples in the fabric of space-time -- emerging from colliding black holes. But scientists have been hoping to detect ripples from another cosmic cataclysm, such as the merger of neutron stars, remnants of large stars that exploded but were not massive enough to collapse into a black hole.
One astronomer tweeted last week that "merging neutron-neutron star is the initial call," while Nature adds that the same rumor had already been circulating privately, according to "some astronomers who do not want to be identified."
Friday Ligo announced cautiously that "We are working hard to assure that the candidates are valid gravitational-wave events, and it will require time to establish the level of confidence needed to bring any results to the scientific community and the greater public. We will let you know as soon we have information ready to share."
The Laser Interferometer Gravitational-Wave Observatory (LIGO) in Louisiana and Washington state has three times detected gravitational waves -- ripples in the fabric of space-time -- emerging from colliding black holes. But scientists have been hoping to detect ripples from another cosmic cataclysm, such as the merger of neutron stars, remnants of large stars that exploded but were not massive enough to collapse into a black hole.
One astronomer tweeted last week that "merging neutron-neutron star is the initial call," while Nature adds that the same rumor had already been circulating privately, according to "some astronomers who do not want to be identified."
Friday Ligo announced cautiously that "We are working hard to assure that the candidates are valid gravitational-wave events, and it will require time to establish the level of confidence needed to bring any results to the scientific community and the greater public. We will let you know as soon we have information ready to share."
Not a new kind (Score:5, Insightful)
But a new reason for them being formed.
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That's why it says new kind of graviational wave source.
Or at least it does now.
New kind of gravitational wave detected (Score:5, Informative)
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I agree. Some of those scammers deserve jail time. It's not nice to rob the people.
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Your eye can measure the energy of an individual photon. It doesn't get much smaller than that.
The crudeness of the observing equipment doesn't make measurements impossible.
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Nope. I remember reading that the human eye needs at least 6 photons per second in order to trigger depolarization of nerves.
The latest study from 2016 [nature.com] seems to show that a single photon can, indeed,be enough.
Of course, many photons hit the layers before the receptors (in part due to the eye being suboptimal in that the receptors are at the wrong side or the retina - so much for 'intelligent design"), or miss. But when lucky, we appear to be able to detect single photons.
Luck multiplied with a high number of repetitions approaches certainty, which is also how most of our scientific equipment works.
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The light detecting cells indeed get triggered by a single photon.
But there are two obstacles: the photon could be absorbed by the lense or protective skin over the eye lense. Or it simplybdoes not hit cell, but fluids around it.
And: usually single photon events are filtered out by the nerve system.
Re:The Scam Continues (Score:5, Interesting)
I'm not a gravitational wave astronomer (or any other kind) but I know some physics and I am interested in the details of highly precise astronomical instruments. LIGO can, and does, measure variations in the length of the arms of the interferometer of the order of 10^-18 meters. There are many techniques needed to achieve this accuracy -- extremely stable laser sources where neither the power level nor the phase varies by much more than the inevitable statistical variation due to the beam being made up of photons; very powerful lasers so that that statistical noise is as small as possible in comparison with the total signal; the path is between very solid quartz mirrors VERY carefully suspended in a vacuum, with active damping of some vibration frequencies and active control of the mirror temperature; the beam bounces up and down the tunnels many times, so that the effective path length is longer; etc. etc.. In normal operation the paths are adjusted until the signals from the two arms precisely cancel one another out (destructive interference) and then any change in path lengths, even if only a very tiny fraction of a wavelength, shows up as a small fraction of the very powerful beams not interfering destructively, but instead being detected by a very sensitive detector, etc. etc,
It's a triumph of laser engineering and should be celebrated.
Well said! (Score:2)
Mod this up.
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It's a triumph of laser engineering and should be celebrated.
With alcoholic beverages? I can drink to that!
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Er what. Firstly I said I'm NOT a gravitational wave astronomer. Secondly, what do you think I'm trying to prove by assertion? The parent asserted that LIGO couldn't work as described for reasons I wasn't really able to make sense. I mentioned some of the techniques (which are widely described on the LIGO website and in the technical literature which are used to make it work as described.
LIGO is precisely the experiment which could have falsified GR, but didn't. GR (and some other things) together predicted
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and that paper is presumably being peer-reviewed as we speak -- hopefully an interesting debate will ensue among those who have invested the effort to understand the physics and engineering, and we will all learn something.
Regarding falsification, you are right, but also wrong. Real life is never as clearcut as the philosophy of science would like it to be. GR has already had a lot of predictions tested and they have so far not falsified it. Given that, if one experiment appeared to contradict it, the firs
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Some predictions of GR (which differ from those of Newtonian gravity) have been accurately tested -- precession of orbit of Mercury; part of the GPS calculation; decay of binary pulsar orbits, etc. There's a wikipedia page https://en.wikipedia.org/wiki/... [wikipedia.org]
GR may not be perfect (and indeed, we know that either it or QM breaks down at very high energies and very small scales because they contradict, but do know that Newtonian mechanics is not correct and that in a number of experiments where GR poredictions
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Relativists cannot falsify a major claim (gravity propagates at c) and you complain about minor errors in Newtonian physics? Those errors exist only because Newton could not have known about the Michelson-Morley experiments on the speed of light that were conducted centuries later.
Thanks for the exchange.
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Got a cite on that? I don't know much GR, but I've never seen anything like that. It would be a way to transmit information faster than light if it existed.
You also don't get waves when propagation is instantaneous, so that makes no sense. LIGO proves that gravity has finite-speed propagation.
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Not finding gravity waves with LIGO would not have 'falsified' GR theory.
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Continuing to not find them with more sensitive instruments certainly would.
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I have to disagree. The noise to signal ratio makes it impossible to ascertain the results regardless of the sensitivity of the instruments.
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No it would not :D
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Considering that Newton's Universal Gravitational Force equation is ...
Have you read The Electro-Magnetic Radiation Pressure (EMRP) Gravity Theory [blazelabs.com], specifically Speed of Gravity [blazelabs.com]?
--
I give it another quarter of a century before these priests ^H^H^H^H scientists ^H^H^H^H clowns discover the 2 missing forces: #5 strong intergalactic force, and #6 the weak intergalactic force, and the white hole at the center
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Relativity deals nicely and rather beautifully with this problem if you take the time to follow the mathematics. The key conclusion is that if something is moving at the speed of light, it is measured as doing so, relative to themselves, by EVERY inertial observer. This is very counter-intuitive, but it tests out extremely accurately in experiments.
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You can hear the Doppler effect by listening to a siren go past you. That's because the siren is moving relative to you. If you were in the emergency vehicle, the siren would not be moving relative to you, and you wouldn't get any Doppler effect. Relativity in action.
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I had not seen that before.
That was a fascinating read.
Thanks.
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Another very interesting read is the complete clusterfuck of the universal constant G -- except it isn't constant -- it oscillates!
Final Demystification of the gravitational constant variation [blazelabs.com]
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Disclaimer: Spring-And-Loop Theory [just-think-it.com] is also an alternative model of how things work at all scales.
The theory GP linked to has been discredited [wikipedia.org]. In essence it says there is a push everywhere, and that one atom/mass blocks another from this push, and this is what (somehow) attracts the two things together. Even intuitively this sounds bizarre/non-workable.
Spring-And-Loop Theory also thinks gravity is a push, not a pull. But there the similarities end. Perhaps the introduction [just-think-it.com] is the best place to start.
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The theory GP linked to has been discredited [wikipedia.org].
While I did only have time to skim a chunk of the website GP linked to, one clear difference between his EMRP theory and Le Sage's theory was the speed of the propagation of gravity (partly due to variation in 'c', if I read it right). So I'd hardly say his theory has been discredited, even if Le Sage's (and others') was ... although I'm not convinced the author addressed the thermodynamic issues with Le Sage's theory - like I said, I only had time to skim it.
In essence it says there is a push everywhere, and that one atom/mass blocks another from this push, and this is what (somehow) attracts the two things together. Even intuitively this sounds bizarre/non-workable.
Well, it might sound bizarre and unworkable to y
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You are apparently not familiar with the science. Laplace proved a long time ago that the speed of gravity would have to be thousands of times faster than the speed of light in order for the solar system to remain stable. Look it up.
Moreover, the precession of Mercury argument is irrelevant to a discussion about the speed of gravity. In fact, relativists were forced to add complex terms to the equations of GR in order to make it act like Newtonian gravity which assumes that gravity is instantaneous. In othe
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I am afraid that you are wrong, they are real. I have even surfed them, here a picture of myself doing it:
http://cdn3.theinertia.com/wp-... [theinertia.com]
Re:Gravitational waves are pseudoscience (Score:5, Interesting)
Consider that a wave implies that something is oscillating, otherwise you don't have a wave at all. Scientists can't even explain what is oscillating when these supposed gravitational waves occur, which is a huge problem
Um, they can and have. The curvature of spacetime is what's rippling, and the observable effect is changes in distance and/or timeflow. It's a consequence of the general theory of relativity.
Re: Gravitational waves are pseudoscience (Score:1)
Check any standard textbook on general relativity. You derive the gravitational waves by linearizing the Einstein field equations, and what you end up with, is that in the weak-field limit you get a wave solution which makes the metric tensor oscillate. That is interpreted as a ripple in spacetime itself, since the metric tensor describes the curvature of spacetime.
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LOL. Did you know that spacetime is a block universe in which nothing happens?
That your mind is to small to accept that our four normal dimensions are local phenomena that vary, and that there is no universal distance or clock to satisfy your belief in them, well, that's no skin off my back. Just don't run for congress, 'k?
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In a more simplistic way, IMHO, their name is self-explanatory.
Water waves are variations in the height of water. A kind of shock-wave is variations on the air pressure around you, etc.
So, gravitational waves are variations on the gravity field around you and, of course, this has an impact on space time as we understand it nowadays and it can be measured now that we have more precise instruments.
At least, that's how I understand it without much research on the subject. Please elaborate if I am too simplist
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Consider that a wave implies that something is oscillating, otherwise you don't have a wave at all.
Nope, shock waves caused by an explosion or earthquake have nothing oscillating as the source. I assume it must the same for most gravitational waves but I am not well versed on the subject.
Waves caused by something oscillating are just many and they tend to have regular patterns.
We know where this leads... (Score:2)
What is the directional sensitivity of LIGO? (Score:2)
Given a (candidate) detection, what can they say about the direction to the source? To be able to identify a single galaxy you need to be accurate to minutes of arc, which surprises me in a device operating so close to the bounds of detectability. How does this work?
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The measurement of direction depends on having three detectors spaced well apart. They compare the time of arrival of each wave pulse at the detectors and get a direction. It's not nearly accurate enough to be a single galaxy, but if there is a new very bright source of gamma rays/X-rays/... in the right general direction appearing at the right time, it's a reasonable working hypothesis that they are related.
So is this the Force? (Score:2)
Are Jedi born to be able to detect these gravitational waves?
Speed of propagation (Score:2)
If we can observe neuron star collision both with LIGO and conventional telescope, then we can compare the speed of propagation of gravitational and electromagnetic waves.
Both should travel at speed of light, but we already observed from supernovas that photons traveled slower than neutrinos. An explanation was quantum fluctuations: each time a photon fluctuates back and forth into an electron-positron pair, it moves much slower than the neutrino.
Re:Speed of propagation (Score:4, Informative)
The supernova signal is due to the time it takes the photons to get out through the remains of the exploding star. They are reabsorbed and reemitted multiple times in this jouney. The neutrinos come straight from the core and mostly escape directly.
Additional detectors? (Score:2)
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TFA says the Virgo detector in Italy has been working from the beginning of August. It isn't "additional LIGO site" but by another organisation. http://www.virgo-gw.eu/
How does that work? (Score:3)
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You don't have to watch the entire sky continuously. The optical signal will persist long enough to point telescopes at the region after the gravitational wave signal is detected. Even if it has not been analyzed and confirmed, the mere presence of a signal is sufficient cause to point optical telescopes in the right general direction. The data from them can then be compared to the last time someone looked in the same place.
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Of course we can watch all of the sky "all" of the time. It's a simple matter of wide angle lenses and a sufficient number of satellites. That's what fast walker was all about. You can't watch it all at high resolution yet, but you can probably spot any event LIGO can detect.
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Rumour has it that this event was spotted early by one of the gamma-ray observing satellites (Compton, I think). They can watch all directions, although with limited resolution, and one the instruments is designed to detect short-lived high energy events quickly,
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If the source is persistent, and you can determine the direction of the source relative to your array... you don't need multiple detectors. The rotation of the Earth will provide you with a short baseline and a (very) coarse position estimate. The orbit of the Earth around the Sun will provide you with a longer baseline and increasingly fine position estimates.
Though it's a bit more complex as the motion of
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currently the direction of the first two detected events was an oblong shaped slice of sky about 600 to 800 square degrees, over 1.5% of the sky...very crude. When the Advanced Virgo detector in Italy helps, things will be much better