Biggest Detector To Look For Gravitational Waves

Hugh Pickens sends in coverage in the Telegraph of a joint NASA-ESA experimental mission, to launch around 2020. It involves three spacecraft orbiting the Sun, separated by 3 million miles, each with a payload of two lasers and a 4.6-cm cube of gold-platinum alloy. The point of it all is to look for gravitational waves. The mission is called LISA, a reasonably non-strained acronym for Laser Interferometer Space Antenna. The Telegraph makes a point of LISA being the largest experiment ever constructed (in terms of its dimensions). Neither that newspaper nor the project page at NASA mentions how much the experiment will cost, but it's almost certainly an order of magnitude or more above the $66 million estimated for a gravitational wave detector the size of the galaxy, which we discussed last fall.

Comments

Dimensional challenges

[SimonInOz]

I read that as a 4.6m cube of gold/platinum alloy and was thinking that was just the sort of thing Lex Luthor would want to steal.

Now come on, it'd make a great show ...

Lousy Democrats

[BitHive]

Shooting all our remaining gold into space so they can shine lasers at it. Typical.

Re:Lousy Democrats

[jandoedel]

it's only the thin coating surrounding the mass that is made of a gold/platinum alloy, not the entire cube. So it is NOT 2kg of gold...
actually gold coatings are used quite a lot for these things.

They have a mass floating freely in space, and surrounding it is this gold/platinum coat, that never touches it, it just flies around it and has microthrusters to keep it away from the central mass. This gold/platinum coat is shielding the mass from some external influences, like the solar magnetic field, so that the central mass only feels the influence of the gravitational waves.

Unlike the "Galaxy sized detector"

[TwineLogic]

This detector would be 3,000,000 miles across when measured from one man-made component to another. The article linked to as a 'galaxy sized detector' is actually about a proposal to observe pulsars looking for the effect of gravitational waves.

When observing pulsars, I assume it is not possible to be 100% of what one is seeing, considering that pulsar observations continue to accumulate and scientists have not had the chance to see a pulsar close-up.

In comparison, using man-made scientific instruments, which are much more under the control of the investigating scientists, to perform the measurement is more trustworthy than observing pulsars. In this regard, the huge scale of the equipment (3 Million Miles) is very significant -- the instruments will be able to make a fine measurement across this distance -- and comparing it with the size of the galaxy is not really a valid comparison.

On the other hand, the snark-value of the comparison was high, and providing the link without these details only raised the snark-tasticness.

Re:Unlike the "Galaxy sized detector"

[Anonymous Coward]

...the huge scale of the equipment (3 Million Miles) is very significant -- the instruments will be able to make a fine measurement across this distance -- and comparing it with the size of the galaxy is not really a valid comparison.

It's a valid comparison because, when you're using pulsars to detect gravitational waves, the effective size of your detector is the distance from one pulsar to another, which is (some large fraction of) the size of the galaxy. Okay, pulsars aren't man-made - but if we deliberately set out to make the transmitter component of a galaxy-sized gravitational-wave detector, we wouldn't be able to produce anything nearly as suited for the task as they are. They keep time as well as our best clocks, and are trillions of times as powerful as any radio transmitter we could build (and they need to be, if we want to see them at these distances).

The snarkiness is entirely justified, I think, as a response to the Telegraph's claim that LISA is the largest gravitational wave detector, when it's not. This doesn't mean that it isn't useful, though. LISA and pulsar observations are sensitive to gravitational waves of different frequencies - about 10^-1 and 10^-9 Hz respectively - so they're complementary techniques in the same way that (say) optical and radio astronomy are.

Re:Unlike the "Galaxy sized detector"

[JakartaDean]

It's a valid comparison because, when you're using pulsars to detect gravitational waves, the effective size of your detector is the distance from one pulsar to another, which is (some large fraction of) the size of the galaxy. Okay, pulsars aren't man-made - but if we deliberately set out to make the transmitter component of a galaxy-sized gravitational-wave detector, we wouldn't be able to produce anything nearly as suited for the task as they are. They keep time as well as our best clocks, and are trillions of times as powerful as any radio transmitter we could build (and they need to be, if we want to see them at these distances).

The snarkiness is entirely justified, I think, as a response to the Telegraph's claim that LISA is the largest gravitational wave detector, when it's not. This doesn't mean that it isn't useful, though. LISA and pulsar observations are sensitive to gravitational waves of different frequencies - about 10^-1 and 10^-9 Hz respectively - so they're complementary techniques in the same way that (say) optical and radio astronomy are.

Wikipedia http://en.wikipedia.org/wiki/Gravitational_wave does a pretty good job of describing these things, with the bonus that it doesn't say anything about "proving" Einstein's theory of general relativity. The take-home point is how tiny these waves are. The predicted energy is enough to distort space by 10 ^-20. From the stupid wording in the Telegraph article, the satellites will be 5 million kilometres apart, and will be able to detect displacements of "40 millionths of a millionth of a metre." So, they can detect displacement of 40*10^-12 / 5*10^9 which I get as 8*10^-22, so good enough I guess. The scales are unimaginable to me, at both ends.

Re:Unlike the "Galaxy sized detector"

[L4t3r4lu5]

Well, 5000000km is just under 4 x the diameter of the sun (1.4m km), and "40 millionths of a millionth of a metre" is as close to matter 1/333 the average thickness of a cell membrane (3nm).

Hope this clears things up for you :)

Costing

[kakapo]

From memory, LISA is usually listed as being in the $1.5- $2 billion dollar range, which puts in the same category as Hubble or the forthcoming James Webb telescope.

Worth every penny, too, in my opinion.

Re:Costing

[ganv]

Definitely worth every penny. Gravitation wave detection will bring a completely new window on the universe. Even the first radio telescopes or the first infrared telescopes only opened up a new part of the electromagnetic spectrum, and the space observatories have simply allowed higher resolution. Gravitational observatories will be the first to see an entirely new type of radiated energy. The sensitivity of LISA and the frequency band they can study allows them to detect common gravity wave sources...as opposed to ground based instruments which are only likely to detect rare events like black hole or neutron star mergers. Seems to me that if they can get the system working in space it is essentially certain to see gravity waves.

So I didn't RTFA

[jasno]

What happens if they don't find anything?

Do gravitational waves radiate energy? Have we seen instances, such as during a supernova, where there was missing energy which could be explained by them?

Re:So I didn't RTFA

[jasno]

I guess they do carry energy, and we think we've seen proof of it: http://en.wikipedia.org/wiki/Hulse-Taylor_binary.

Re:So I didn't RTFA

[John Hasler]

A gravitational wave is a "ripple in space-time".

Re:So I didn't RTFA

[MrZilla]

What does gravity has to do with quantum mechanics?

Oh nothing at all. It's just one of the biggest unsolved problems in physics at the moment.

not funded yet

[bcrowell]

I believe the slashdot summary and TFA are misleading, because they make it sound like LISA will definitely be built. According to the WP article, LISA is competing against two other space-based science projects for funding, and the decision won't be made until 2013.

Personally, I would love to see LISA fly. Gravitational waves were first predicted in about 1914. Most aspects of general relativity have been tested pretty thoroughly at this point, but almost a century later we still have no direct confirmation that gravitational waves exist (although there is very strong indirect evidence). And if they can be detected, then it opens up an entirely new way of doing astronomy: not with electromagnetic waves, but with gravitational ones.

Re:not funded yet

[Chris Burke]

The NASA and JPL mission pages don't make it clear that this is unfunded as of yet either, which is annoying since I've been reading up on this experiment for some time and am pretty excited about it!

I, too, would love to see LISA fly. We really do need robust tests of gravity waves, and a whole new world of observations will open up to us if it pans out.

One of the coolest things about the mission itself that I read about is the 'drag free' aspect. To ensure that the test masses are in free-fall around the sun without interference by things like the pesky solar wind, they're housed free-floating in a chamber inside the LISA spacecrafts themselves. The spacecraft absorbs the solar wind or other outside forces while measuring any change in relative position to the test mass and using micro-thrusters to keep itself centered on the mass and thus in the same free-fall drag-less orbit. Effin cool imo, even if I don't think it's first time it's been done. :)

Re:not funded yet

[Chris Burke]

But wouldn't that mean the cube's trajectory lead into the sun?

It'll be orbiting the sun, in an orbit much like earth's.

Re:not funded yet

[HBoar]

I think you need to look up what the word 'orbit' means.....

millions

[thoughtsatthemoment]

Damn, I thought one could just write papers to prove something. Now we have to spend millions.

I was like wtf?

[future assassin]

Won't the Ferengi attack the satellites to steal the gold-pressed latinum?

LISA vs. Pulsar Observations

[stewardwildcat]

Just to let you all know, LISA and the Pulsar observations are not observing the same things. Sure they are fighting to detect the first gravitational waves but they are looking at different regimes. Its like comparing the GBT radio telescope to Hubble, they are fundamentally different even if they are looking for the same type of objects. http://www.physik.hu-berlin.de/qom/research/freqref/lisa explains what frequencies LISA will be sensitive to. The Pulsar array is most sensitive to 10^-4 where as LISA is higher frequencies. LIGO is even higher in frequency. You learn about different objects and new phenomena by studying ALL frequencies available to you. Many astronomy projects are expensive as hell but they develop new technologies that benefit our daily lives. Who knows what laser interferometry in space will generate for the public funding the project.

Why gold and platinum?

[MacroRodent]

Wouldn't a lump of lead work as well and be cheaper?

Re:Why gold and platinum?

[SteveFoerster]

Given how much it will cost to get these things into orbit around the sun, I'm guessing the cost of the actual materials is comparatively trivial.

Dumb question regarding gravity in general

[smooth wombat]

We know the Holy Grail is to have a Grand Unified Theory of the four forces. To date, three have been combined with gravity being the lone holdout.

Is there a reason why gravity can't be a force unto itself but rather, the result of the other three forces? By that I mean, since the Strong and Weak forces hold things together, is there some reason they can't be creating gravity with their forces weakening the further out you go, similar to how radio waves get weaker as they propagate outwards.

Even though this experiment is an attempt to detect gravitational waves, since we haven't found any to date, could the above be a different explanation for why we haven't found any (yet)?