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The Earth As a Gravitational Wave Detector

Soulskill posted about 8 months ago | from the we'll-never-get-funding-to-build-it dept.

Earth 70

b30w0lf writes "Gravitational wave detection — i.e. the detection of propagating ripples in spacetime — is a hot subject these days, with ground-based interferometer experiments like LIGO active, and hopes for a space interferometer like LISA. However, physicist Freeman Dyson proposed back in 1969 that the earth itself could be used as a gravitational wave detector. The idea is behind the approach is that gravitational waves impact the earth's crust, causing potentially detectable seismic waves. Using Dyson's approach, Physicists at Harvard and NINP, Florence were able to put an upper limit on the intensity of gravitational background radiation based on a year of observational seismic data (abstract, full pre-print). The upper limit they found improved currently laboratory upper limits by 9 orders of magnitude."

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orders of magnitude? (-1)

Anonymous Coward | about 8 months ago | (#46485679)

Is that all you people can say to attempt to look intelligent? Good god.

Re:orders of magnitude? (-1)

Anonymous Coward | about 8 months ago | (#46485733)

Opligotory XKCD http://i.imgur.com/LE7UflB.png [imgur.com]

Re:orders of magnitude? (1)

i kan reed (749298) | about 8 months ago | (#46485773)

Orders of magnitude are an important part of understanding the significance of sample data, versus error. That's like, high school chemistry stuff. It seems relevant to the fact that they're trying sample incredibly small variations.

Re:orders of magnitude? (1)

angel'o'sphere (80593) | about 8 months ago | (#46487629)

Order of magnitude does not mean what you think it means if we are talking about wavelength.

Re:orders of magnitude? (1)

i kan reed (749298) | about 8 months ago | (#46490013)

We aren't though, the reflexive reference would have to be to the noun "intensity" in the summary.

Re:orders of magnitude? (1)

angel'o'sphere (80593) | about 8 months ago | (#46491887)

Well, the summary said intenisty, but some posters argued it was not intensity but wavelength / frequency.

Perhaps I (we?) should read the article itself :)

Re:orders of magnitude? (0)

Anonymous Coward | about 8 months ago | (#46492213)

Or maybe there is more than one thing that is relevant than a single number? The summary makes it quite clear they are talking about orders of magnitude in intensity, but like other gravity wave projects, this is specific to a particular frequency band. Posters pointing out that what frequency you look at too aren't contradicting the summary or what orders of magnitude is referring to in this case.

Re:orders of magnitude? (2)

K. S. Kyosuke (729550) | about 8 months ago | (#46486167)

You know, "orders of magnitude" are not that thing when you ask for extra large dishes in a restaurant.

Not just noise (1)

i kan reed (749298) | about 8 months ago | (#46485721)

Noise is "easy" enough to account for, but what about other things that could generate similar signals. like constant gas expansion in the mantle, or whatever? I'd be fascinated to know if they have some tools to help with that.

Re:Not just noise (4, Informative)

geoskd (321194) | about 8 months ago | (#46486119)

Thay're not saying that gravity waves are creating the signals. What they are saying is that if gravity waves are creating any signals at all, the size of the signals being measured limits the possible size of the gravity waves to smaller than a certain size. It is putting an upper bound on the possible size of gravity waves. This is important, because the previously determined upper bound on gravity wave size was 9 orders of magnitude bigger than it is now that we have these experimental results.

Re:Not just noise (3, Informative)

K. S. Kyosuke (729550) | about 8 months ago | (#46486235)

but what about other things that could generate similar signals

What "other things"? Electromagnetism is the only thing that has comparable speed to gravity waves, and unlike gravity waves, it only penetrates Earth-sized solid matter with exponential falloff at short distances. Forget possible seismic causes for the kind of measurements they must be looking for. Just recalling my high school physics 101, you know...

Also, from TFA:

Gravitational waves are the last untested prediction of Albert Einstein's General Theory of Relativity.

I'd argue that this is debatable, seeing that we've already measured the decay of at least one binary pulsar that wonderfully corresponds to the predicted gravity-wave-mediated energy loss.

Re:Not just noise (0)

Anonymous Coward | about 8 months ago | (#46490767)

I'd argue that this is debatable, seeing that we've already measured the decay of at least one binary pulsar that wonderfully corresponds to the predicted gravity-wave-mediated energy loss.

Still doesn't hurt to test it again. Science has to work all the time, not just once.

Are they finding the waves, or ruling them out? (1)

timeOday (582209) | about 8 months ago | (#46485753)

The Guardian link is reporting on a likely confirmation of gravitational waves. But the seismograph study seems to be ruling them out, at least near the frequency of 1 hz. They made a new, more sensitive detection mechanism and found nothing, thus ruling out the existence of any wave above a very low energy level. Am I missing the point?

Re:Are they finding the waves, or ruling them out? (0, Interesting)

Anonymous Coward | about 8 months ago | (#46485897)

GW's can't be detected directly by the current crop of apparatus because the doppler shift caused by GW's is cancelled out by the DS of the compressed light stream by GR. It's been a fiasco. The announcement coming Monday is for indirect measurements of GW's from a telescope analyzing the CBR light polarity.

Neither. (5, Informative)

tlambert (566799) | about 8 months ago | (#46486529)

Neither.

What they did is say is basically "We now have a detector 10^9 times more sensitive, which is capable of detecting gravitational waves up to 10^9 times smaller than previous detectors, if there are waves. We didn't see any waves with this detector. Therefore if they exist, they are smaller than what our new detector can detect".

In other words, if there are gravitational waves, they are smaller magnitude than they are able to detect with the new detection system. This doesn't rule them out, it just blacks out a potential energy/amplitude range in which they might have existed before nothing was seen in that search band.

They've more or less reduced the probability set, and pissed in a number of esoteric theories cheerios, but not done a lot else to prove or disprove gravity waves.

It's the difference between having to look for a lost item in an entire warehouse, or having to look for it in a crackerjack bix sized area of the warehouse - albeit it'll take a lot more expensive and redesigned equipment to even look in part of the crackerjack box.

Frankly, if we threw 4 ten ton spheres into relatively deep space (e.g. solar orbit), arranged them at the vertices of a tetrahedron, and then used laser interferometry between the spheres, and then threw another ten ton sphere across the solar system at a non-trivial speed, and through the tetrahedron, not intersecting a face or the body center, we could pretty much say once and for all if there were gravity waves or not, based on delay (or non-delay) of the effect of the moving sphere being "not there, then suddenly there, then suddenly not there", at least to about 1/2 the wavelength used by the interferometers (hence the need for a "non-trivial speed" for what is, in effect, a gravitational probe inserted into the system, to do the experiment).

Doing the more or less definitive experiment would be expensive (as in "on the order of the cost of the LHC").

Re:Neither. (2)

hubie (108345) | about 8 months ago | (#46487495)

and pissed in a number of esoteric theories cheerios

I'm not inclined to think this is the case. I think their result was many orders of magnitude over the previous measurement because there was only one other measurement made in this frequency range. The previous experiment [aps.org] was a torsion bar experiment done in a modest-sized lab. According to the LISA folks [nasa.gov] :

In general, a ground-based interferometer is limited to frequencies above about 10 Hz because of seismic noise

I didn't read the torsion bar paper to see what they did to eliminate noise sources.

It doesn't rule them out, but holy cow... (1)

GPS Pilot (3683) | about 8 months ago | (#46488463)

It doesn't rule them out, but holy cow, a nine-order-of-magnitude sensitivity leap is huge. This must be a devastating wake-up call to the theorists who were predicting amplitudes that LIGO-style detectors have a snowball's chance of finding.

The extreme sensitivity of this approach means that nobody will invest in another LIGO-style detector, correct?

Re:It doesn't rule them out, but holy cow... (0)

Anonymous Coward | about 8 months ago | (#46489931)

The extreme sensitivity of this approach means that nobody will invest in another LIGO-style detector, correct?

LIGO is primarily for looking at higher frequencies, especially above 100 Hz, as at lower frequencies you run into more and more noise that is difficult to isolate to the levels necessary for useful detection of gravity waves in that setup. This will have more impact on proposed space based measurement schemes meant to target those frequencies that are difficult to noise sources on Earth.

Re:Neither. (1)

phantomfive (622387) | about 8 months ago | (#46490205)

Frankly, if we threw 4 ten ton spheres into relatively deep space (e.g. solar orbit), arranged them at the vertices of a tetrahedron, and then used laser interferometry between the spheres, and then threw another ten ton sphere across the solar system at a non-trivial speed, and through the tetrahedron, not intersecting a face or the body center, we could pretty much say once and for all if there were gravity waves or not, based on delay (or non-delay) of the effect of the moving sphere being "not there, then suddenly there, then suddenly not there", at least to about 1/2 the wavelength used by the interferometers (hence the need for a "non-trivial speed" for what is, in effect, a gravitational probe inserted into the system, to do the experiment).

That doesn't sound easy to get right, even with a ton of money. That's a tough engineering problem there.

Resonant Detector (4, Informative)

mbone (558574) | about 8 months ago | (#46485757)

The crucial thing is that they improved the limits in the narrow frequency band where the Earth is a resonant detector :

in the frequency range 0.05 Hz – 1 Hz

This is very cool, but note that it is at a frequency where there are not a lot of expected sources (stellar-mass binary black hole coalescence is up in the kHz range).

The announcement on Monday [theguardian.com] about inflationary gravitational waves is likely to get a good deal more scientific attention.

Re:Resonant Detector (3, Informative)

mbone (558574) | about 8 months ago | (#46485901)

Actually, scratch the above. Reading their paper and the Dyson paper [harvard.edu] , the frequency limit is set by the seismometers, not by the normal modes of the Earth.

Re:Resonant Detector (2)

bware (148533) | about 8 months ago | (#46485969)

[...] note that it is at a frequency where there are not a lot of expected sources

There are sources [nasa.gov] in that range, thus LISA [nasa.gov] . Galactic black holes merging, inspirals of stellar mass objects by galactic black holes.

LISA was a high pick in the DOA Astro2010 Decadal, now sacrificed on the altar of HSF and JWST.

Re:Resonant Detector (1)

photonic (584757) | about 8 months ago | (#46487033)

The LISA project has a long history, with several iterations of down-sizing its costs, and at some point the Americans pulled out of the project completely. The latest version of the project is called ELISA [elisascience.org] , which was recently approved as ESA's L3 mission in 2034. A bit late, but better than nothing ...

Re:Resonant Detector (2)

bware (148533) | about 8 months ago | (#46487427)

'95-ish? That's the first meeting I remember where there was a realistic attempt to propose something to NASA. I don't think there wasn't much research funding before that. Not that long a history.

Mostly the cost estimates have gone up, especially after the scrutiny brought by JWST overruns brought more honest costing. It was always going to be a flagship mission. We could debate whether eLISA is actually going to save that much money over the combined US/ESA LISA proposed in Astro2010, which we cast as the sweet spot of science per dollar.

And as far as eLISA and 2034, well, I ain't holding my breath for funding profiles that far in the future. Actuarially, it's unlikely that it'll fly in my lifetime (scientifically, and otherwise). So for me, not better than nothing.

Re:Resonant Detector (1)

Saija (1114681) | about 8 months ago | (#46486887)

My god the words "resonant" and "Freeman" on the same subject... something it's not going to end well to us

What is this supposed to mean? (0)

Anonymous Coward | about 8 months ago | (#46485867)

"The upper limit they found improved currently laboratory upper limits by 9 orders of magnitude."

Requesting clarification for term: "currently laboratory upper limits".

45 year old story (0)

T.E.D. (34228) | about 8 months ago | (#46485873)

I know Slashdot takes a lot of heat for reposting old stories, but this one is truly impressive. Its 45 years old! Most Slashdot readers weren't even born yet. The Beatles were still together. I was 2.

Its like the editors went, oh old stories huh? You think these are old stories? I'll show you old stories, mofo!

Tomorrow: Jules Verne in 1877 suggested it might be possible to bootstrap space navigation by hitching a ride on a passing comet [wikipedia.org] (tagged: screwyouwhiners)

Re:45 year old story (3, Insightful)

Netdoctor (95217) | about 8 months ago | (#46485957)

Upper Limit on a Stochastic Background of Gravitational Waves from Seismic Measurements in the Range 0.05–1 Hz

Michael Coughlin and Jan Harms
Phys. Rev. Lett. 112, 101102 (2014)
Published March 13, 2014

Good luck with that. (0)

Anonymous Coward | about 8 months ago | (#46485879)

No, seriously, good luck.

There is an absolutely stupid amount of background noise they'll need to account for and rule out.
Hell, these waves themselves WILL be background noise, quite literally.
It't need to be very specific, in a small range as well. Very small range.

It is like trying to find an area of space with no neutrinos. We've barely even left the solar system. That is how hard a problem that sounds.

Re:Good luck with that. (0)

Anonymous Coward | about 8 months ago | (#46486341)

I wonder why all those scientists with PhDs in physics from really good schools didn't think of that...

Use the Moon instead (4, Interesting)

avandesande (143899) | about 8 months ago | (#46486101)

Since the moon is much more stable than the Earth, would it be a better detector? Have seismic readings been taken on the Moon?

Re:Use the Moon instead (0)

Anonymous Coward | about 8 months ago | (#46486433)

Small potatoes. [nanograv.org]
 
And yes, Apollo 11 left instruments for reading activity.

Re:Use the Moon instead (1)

dmgxmichael (1219692) | about 8 months ago | (#46486837)

Yes, during the Apollo missions.

Re:Use the Moon instead (1)

Jim Sadler (3430529) | about 8 months ago | (#46489979)

If gravity waves have actually been detected then we should get data on frequency and variations in intensity if any exist. I think they are simply using geek speak to say that they now have a capacity to detect even less energetic events or isolate specific events of small intensity. They have not detected any actual wave. Isn't it a stretch to think that gravity travels in waves or exists in standing waves? Maybe it simply exists and is all about us and has no movement at all. Gravity may simply be a displacement of space according to the density of the object that causes the displacement. How much gravity can be stuffed into a singularity?

Re:Use the Moon instead (0)

Anonymous Coward | about 8 months ago | (#46490189)

Or you could study GR instead of assuming "geek speak" is the important part.

Re:Use the Moon instead (0)

Anonymous Coward | about 8 months ago | (#46493741)

I would think the moon is a great transmitter of gravity waves, and that all you have to do to detect them is measure the tides.

LIGO is a money pit (3, Insightful)

fluffy99 (870997) | about 8 months ago | (#46486547)

They've sunk over a billion into the Hanford and Livingston observatories. The LIGO observatories from 2002 to 2010 were only operational for a very small fraction of the time, plagued by equipment problems, never acheived the design sensitivity, and NEVER detected anything useful. Most of their data was contaminated by local noise, including the highway a few miles away. They blindly collected terabytes of raw data that has never been fully analyzed and they have minimal local data analysis capability.

Now NSF is pouring even more money into it in the hopes they can improve the sensitivity and actually detect something? At best they might record a perturbance that is correlated between multiple sites (they also partner with an Australian site I believe), of which the value of that data is still debatable.

I wish the NSF would pull the plug on this waste of resources and invest in something more useful like cleaner nuclear power.

Re:LIGO is a money pit (1)

iggymanz (596061) | about 8 months ago | (#46487149)

cleaner nuclear power is solved problem, we already know how to make reactors that can burn "spent fuel" and leave waste that decays in decades rather than millenia. smarter countries are pursuing that, but the USA just extended life on its 2nd gen reactors that were designed in the late 1950s, can melt down if not externally cooled, and make waste that will last longer than any civilization has.

Re:LIGO is a money pit (0)

angel'o'sphere (80593) | about 8 months ago | (#46487619)

Reactors can not "burn spend fuel".
The resulting products of fissioned Uran etc. can not be made to fission another time.
And reactors have nothing to do with gravity wave detection anyway, so what is your point?

Re:LIGO is a money pit (0)

Anonymous Coward | about 8 months ago | (#46489965)

Just like you can't burn chemical fuel that has been on fire previously... except when you have leftover carbon monoxide... or you produced charcoal... or you produced coal gas...

Nuclear fuel is far from having all of the possible energy extracted from it. It will still have a portion of usable U-235 and plutonium that can be re-concentrated and re-used in normal reactors. Typically for using natural uranium as a starting fuel, over two thirds of the fissile material is left behind and the fuel becomes unusable because of fission products that absorb too many neutrons and need to be removed before a practical amount of fission can be achieved with the fuel. There are other isotopes in the fuel, both stuff from the start like U238 and byproducts that can absorb a neutron and produce energy, but not release any or enough neutrons to sustain a chain reaction, but certain reactor designs can over come this with other neutron sources to extract a lot more energy from what is waste of current reactors.

Re:LIGO is a money pit (1)

angel'o'sphere (80593) | about 8 months ago | (#46498497)

True, and that stuff you mention is not spend yet.

Re:LIGO is a money pit (1)

angel'o'sphere (80593) | about 8 months ago | (#46498501)

And why did some idiot mod me troll, again?

Re:LIGO is a money pit (1)

iggymanz (596061) | about 8 months ago | (#46499513)

because you stupidly make your own definition of "spent fuel" ignoring what the commercial nuclear power industry calls "spent fuel". The spent fuel in cooling ponds and casks is 96% fissionable and/or breedable fuel that can be used in a properly designed reactor.

Re:LIGO is a money pit (1)

angel'o'sphere (80593) | about 8 months ago | (#46500733)

Breedable yes, fissionable: no.
Americans usually mix up 'waste' with spent fuel, obviously you did not, my appologizes.

Re:LIGO is a money pit (1)

iggymanz (596061) | about 8 months ago | (#46499471)

You are very ignorant.

"Spent fuel" from U.S. commercial reactors contains 94 percent U-238, 0.9 percent U-235 and 0.8 percent pu-239. ALL of that can be "burned" in a properly designed reactor, and moreover long-lived isotopes from those reactions can be converted to short lived ones.

Re:LIGO is a money pit (1)

angel'o'sphere (80593) | about 8 months ago | (#46499585)

That is not spent fuel. It is 'part of the fuel'.
That is the reminder in a fuel rod, after a bit of the real fuel is 'spent'. The spent fuel is what is left over after a U-235 atom is split.

You are also very ignorant. The stuff you mention can not be 'burned' in a 'properly designed reactor'. It only can be 'bread' into a fissionable form.

There are no short half life forms of U or Pu, and if there where, what would be the point of : and moreover long-lived isotopes from those reactions can be converted to short lived ones.???

Re:LIGO is a money pit (0)

Anonymous Coward | about 8 months ago | (#46500021)

The stuff you mention can not be 'burned' in a 'properly designed reactor'. It only can be 'bread' into a fissionable form.

The result is still a net gain in energy with careful neutron economy. The fact that there are a couple steps in the nuclear process doesn't change the big picture that those normally unused isotopes become a fuel that can be used for energy production.

There are no short half life forms of U or Pu, and if there where, what would be the point of :

There are a crap ton of fission products that have long lifetimes and represent storage issues. Whether using a special designed burning reactor or an energy producing breeder reactor, you can convert those isotopes into short lived isotopes that simplify waste storage issues.

The spent fuel is what is left over after a U-235 atom is split.

Even using your own personal definition for "spent fuel," and ignoring the large amount of actinides that are created in the process and unusable by most reactors, you still have direct fission products that can be burned with a release of energy, such as I-129

You claim others are ignorant while flagrantly disregarding standard terminology or putting it in scare quotes. That, and being flat out wrong both here and above posts.

Re:LIGO is a money pit (1)

Anonymous Coward | about 8 months ago | (#46487397)

I have ever quite understood why an interferometer would work for detecting gravity waves. If the wave was a distortion between two space dimensions then OK, but if its between a space dimension and the time dimension it seems to me that the effects would cancel out.

Perhaps someone with a a better grasp of general relativity would care to explain.

Re:LIGO is a money pit (1)

joe_frisch (1366229) | about 8 months ago | (#46487885)

By analogy, a black hole is a distortion in space time, but it can bend light. The curved surface of the earth can be measured entirely by measuring the distance between points along the surface.

I believe you are right that you could construct space=time distortions that would not affect the travel time of light, but you can also construct those that do - and gravity wave distortions do change the travel time.

Re:LIGO is a money pit (1)

mikael (484) | about 8 months ago | (#46488313)

Does a large gravitational object then bend gravity waves? If they are ripples in the space-time continuum then wouldn't they be refracted? Would there be S-type and P-type gravity waves which are like shear and pressure waves?

Re:LIGO is a money pit (2)

joe_frisch (1366229) | about 8 months ago | (#46488345)

A heavy object would bend gravity waves - they propagate the same way light does.

My memory is that there are 2 polarizations of gravity waves (sort of the way there are 2 polarizations of light), but they are carried by spin-2 particles not spin-1 so the polarizations look somewhat different. They look vaguely like sheer waves, I do not believe there is an equivalent of pressure waves in standard general relativity.

Re:LIGO is a money pit (1)

Anonymous Coward | about 8 months ago | (#46488579)

You are essentially correct. The only mode that would not cancel out is the tidal mode, which causes the beam to curve, and no experiment is set up to detect that.

Re:LIGO is a money pit (3, Interesting)

joe_frisch (1366229) | about 8 months ago | (#46487873)

LIGO is enormously more sensitive (~12 orders of magnitude), than this seismic measurement but in a different frequency band (~100Hz), so both are valuable measurements sensitive to different types of GW sources .

LIGO itself is a phenomenally difficult project, but with big payoffs. There is the basic physics of understanding how gravity works, but there are also technology spinoffs. The extremely low loss mirror technology developed for LIGO is not being used for other applications, including telecom. The high Q optical cavities are used in commercial measurement devices for measuring tiny concentrations of materials in gasses . There are likely many other spin-offs from the project.

Re:LIGO is a money pit (1)

fluffy99 (870997) | about 8 months ago | (#46488755)

LIGO is enormously more sensitive (~12 orders of magnitude), than this seismic measurement but in a different frequency band (~100Hz), so both are valuable measurements sensitive to different types of GW sources .

LIGO itself is a phenomenally difficult project, but with big payoffs. There is the basic physics of understanding how gravity works, but there are also technology spinoffs. The extremely low loss mirror technology developed for LIGO is not being used for other applications, including telecom. The high Q optical cavities are used in commercial measurement devices for measuring tiny concentrations of materials in gasses . There are likely many other spin-offs from the project.

Near as I can tell, most of the technology flow (at least recently) is in the other direction, i.e. now that extremely low loss mirrors, etc are available they are upgrading LIGO to use them. Obviously they have a special use case and deserve kudos for developing their own fabrication techniques and applications of the technology.

The "big payoff" hasn't happened yet and isn't clearly defined. What exactly would the payoff be? I can see how correlating an observed perturbance as measured by this large scale interferometer with xray telescope data from an observed cosmic event could lend credence to therories about gravity waves.

Re:LIGO is a money pit (3, Interesting)

joe_frisch (1366229) | about 8 months ago | (#46488851)

I was on a LIGO review committed years ago (and worked on the precursor to the project many years before that). At the time of the review, LIGO had worked with a vendor to produce extremely low loss coatings. Based on that technology that vendor was able to move into the (at that time) rapidly expanding telecom optics business - and actually refused to make the parts LIGO needed) because the technology was more valuable to them for telecom. LIGO really was driving the optics business back then.

I believe there have also been spinoffs from their stabilization and vibration isolation work, and possibly from their ultra- stable frequency laser work (Maybe someone from the project will respond.... Stan???).

The value of basic physics like verifying, or disproving general relativity is of course much more difficult to measure. What is the value of understanding the large scale structure of the universe, or physics at very high energies? I don't know the coin to use to measure that. There was a time when number theory, quantum mechanics and relativity all seemed pretty esoteric and useless. That doesn't mean that all basic science is valuable, but there is no way to know in advance what is.

Re:LIGO is a money pit (1)

Anonymous Coward | about 8 months ago | (#46488119)

The LIGO observatories from 2002 to 2010 were only operational for a very small fraction of the time, plagued by equipment problems, never acheived the design sensitivity, and NEVER detected anything useful.

Holy shit, theoretical science on the very limits of engineering ability is hard and may not result result in a Hollywood-style monitor going "beep, signal detected, beep, signal detected!" when the bright red ON button is pressed?

It was known in advance that the strain sensitivity of LIGO would probably lie right at the very edge of direct detection. Equivalently, that the volume over which is it capable of detecting inspirals is unlikely to produce more than a few during its lifespan. Much as you don't try to build a supercarrier as your first maritime engineering project, a grounds for proving, testing and gaining experience was needed. Advanced LIGO will improve the response limits by a factor of roughly ten and correspond to a range of over one billion light-years, with a strain sensitivity slightly lower than the anticipated stochastic background. A failure to detect at A-LIGO would be extremely surprising and create a lot of difficult to answer problems.

done already in 1997 by Stanford seismologist (2)

peter303 (12292) | about 8 months ago | (#46486857)

Here [stanford.edu] is the null result. I presume there are new analytical techniques every few years.

Re: done already in 1997 by Stanford seismologist (3, Informative)

hubie (108345) | about 8 months ago | (#46487251)

The two used much different frequency regimes. The Stanford paper [stanford.edu] looked for waves with periods of 30 minutes to 24 hours. The one in the article looked for waves with periods of 1 to 20 seconds.

Background on Gravitational Wave Detection (1)

Anonymous Coward | about 8 months ago | (#46487481)

Gravitational Waves [tikalon.com] .

Please explain (1)

Pro923 (1447307) | about 8 months ago | (#46487945)

Where does a gravity wave theoretically come from? All I can imagine is that they would come from a mass increasing or decreasing in magnitude, and I don't know of any way that happens.

Re:Please explain (2)

joe_frisch (1366229) | about 8 months ago | (#46488355)

You can't increase and decrease mass - so no monopole gravity waves.

You can't move the center of mass (conservation of momentum) so no vector gravity waves.

You can change the distribution (imagine two masses moving closer and further apart), and this generate tensor (spin 2) gravity waves.

The coupling is VERY small - so the energy radiated is tiny unless you are dealing with near black-hole conditions.

Re:Please explain (2)

SeanDS (1039000) | about 8 months ago | (#46489091)

Where does a gravity wave theoretically come from? All I can imagine is that they would come from a mass increasing or decreasing in magnitude, and I don't know of any way that happens.

The Guardian article refers to a detector which might have made an indirect detection of gravitational waves.

If two massive bodies such as neutron stars or black holes collide, the energy they lose in the form of gravitational energy is propagated away in waves. These waves are ripples in spacetime, and they are quadropolar in nature. This means that they stretch spacetime in one direction while squeezing it in the other.

Gravitational waves form part of the predictions of Einstein's Theory of General Relativity. They are the last piece of the theory yet to receive a direct detection. A notable indirect detection of gravitational waves is the measurements of the orbital decay of the PSR B1913+16 binary pulsar, for which Hulse and Taylor received the Nobel Prize in 1993.

For the purposes of direct detection of these waves, on Earth we've set up a network of laser interferometers (the major players are Advanced LIGO, Advanced Virgo, GEO-HF and KAGRA, though all but GEO are currently in the process of being commissioned). If we arrange our detectors on Earth at right angles, we become optimally sensitive to the majority of gravitational wave sources. If the masses of the bodies involved in the collision are big enough, the ripples in spacetime will be strong enough to change the time in which it takes light to travel along each arm of the interferometer - in one arm the light will take longer time to travel, and in the other it will take shorter time. If we recombine the light in each arm, we can sense via the interference pattern of the light whether a gravitational wave has passed through the detector. In practice there are loads of other signal sources present in the interferometer, and quantifying and eliminating these sources of noise are the major tasks facing these detectors. With these noise sources accounted for, the first direct detection of gravitational waves might be made in the next few years.

The LISA project referred to in the main article is dead since NASA pulled out funding. The project lives on in the form of the ELISA project, funded by European organisations. This has tentative approval for launch in the next 20 years. This mission is not intended to directly detect the 'first' gravitational wave, but rather to detect them in abundence. Indeed, the problem with this type of detector is dealing with the huge number of potential detections. ELISA is also designed to detect waves in a completely different spectrum from the ground detectors, and from different astronomical sources. By the time ELISA launches it is likely that the network of detectors as part of the LIGO Scientific Community will have made the first detection, here on Earth.

Is 0.05 Hz to 1 Hz an interesting frequency band? (1)

knapkin (665863) | about 8 months ago | (#46488711)

I don't know the answer to this, but looking at some LIGO charts (http://www.ligo.caltech.edu/advLIGO/images/refdes03.gif) they seem to be looking at 10-100Hz (roughly). Are there interesting or even expected sources in the frequency band investigated in this paper?

Re:Is 0.05 Hz to 1 Hz an interesting frequency ban (1)

SeanDS (1039000) | about 8 months ago | (#46489133)

I don't know the answer to this, but looking at some LIGO charts (http://www.ligo.caltech.edu/advLIGO/images/refdes03.gif) they seem to be looking at 10-100Hz (roughly). Are there interesting or even expected sources in the frequency band investigated in this paper?

Gravitational waves are emitted at a wide spectrum of frequencies by different astronomical bodies. LIGO's frequency range is limited mostly by seismic activity at the low end and radiation pressure noise (essentially the momentum imparted by photons hitting mirrors) at the high end. It's about as well as we can do on Earth, currently. Indirect detections via astronomical techniques can avoid the issue of seismic activity disrupting measurements, and so it is possible to look at much lower frequencies. These frequencies, however, correspond to different sources to the ones LIGO can potentially see, so we can learn new information about different parts of our universe from both detection techniques.

Coincidence? (3, Interesting)

uassholes (1179143) | about 8 months ago | (#46489049)

December 27, 2004 at 21:30:26 UT, a burst of gamma rays from SGR 1806-20 passed through the Solar System. The burst was so powerful that it had effects on Earth's atmosphere, at a range of about 50,000 light years.
At 00:58:53 UTC on Sunday, 26 December 2004, an undersea megathrust earthquake occurred in the Indian Ocean which caused a tsunami which killed 250,000 people.

To The Moon (0)

Anonymous Coward | about 8 months ago | (#46491085)

Look and ye shall find. Unless it runs you over first, of course. Otherwise, the gorilla-in-the-picture effect is quite dominant.
At least they're talking about it. [youtube.com] Who can guess what might come out of that?

Don't Mind The Fool In The Basement (0)

Anonymous Coward | about 8 months ago | (#46491121)

If I may be forgiven an admittedly very very foolish (what else, indeed) question :
If an impact on the Moon can cause a massive gamma (etc.) emission, why can't the impact of a gamma (etc.) flash cause an impact emission?
My apologies to the esteemed gentry very justly offended by such raucous croaking. Good day, then.

HAARP (0)

Anonymous Coward | about 8 months ago | (#46491601)

Now if they could design a simple hand-held device to detect HAARP extremely low radio frequencies and put thaty bunch out of business, they'd have something. HAARP technology is responsible for a plethora of human tragedies, cataclysmic seismic and weather related events in recent modern times. The technology is so much in our faces that they don't even whince at such disdain for their secret weapon use.

Re:HAARP (0)

Anonymous Coward | about 8 months ago | (#46492621)

Now if they could design a simple hand-held device to detect HAARP extremely low radio frequencies and put thaty bunch out of business

HAARP operates in the HF band, which is higher than typical AM radio bands and around CB bands, etc... hand held radio receivers have existed there for decades. Even if they operated at extremely low frequencies, you can build a simple receiver with just a coil of wire.

and don't forget ego-virgo... (0)

Anonymous Coward | about 8 months ago | (#46503527)

http://www.ego-gw.it/

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