back to article LISA Pathfinder sniffed out gravitational signals down to micro-Hertz

In other space news today, the boffins in charge of the European Space Agency's LISA Pathfinder mission have wrapped up the final results for the space-based gravitational wave dry run. The Pathfinder carries a pair of 2 kg free-falling cubes, separated by 38 cm and linked with lasers.The masses move relative to each other in …

  1. VerySlowData
    Alert

    too many hertz

    Petahertz?? maybe LISA will look for picohertz signals!!

    1. diodesign (Written by Reg staff) Silver badge

      Re: too many hertz

      Ah yeah, pico, not peta. It's fixed. Don't forget to email corrections@theregister.com if you spot anything wrong.

      C.

      1. Brewster's Angle Grinder Silver badge
        Joke

        Motivating forces.

        But we don't get any upvotes for that.

        1. Gordon 10 Silver badge
          Coat

          Re: Motivating forces.

          Copy/pasta your corrections email before pressing send.

          and don't forget to add some smartarse commentardery to the forum post version.

          1. Ben1892

            Re: Motivating forces.

            What ? like "place" missing an L in the sub heading ?

            "Better-than-expected performance created 'the quietest pace in space'

        2. Anonymous Coward
          Anonymous Coward

          Re: Motivating forces.

          "But we don't get any upvotes for that."

          They sometimes send a nice thank you.

      2. ThaumaTechnician

        Re: too many hertz

        Yeah, email the corrections instead, 'cuz reading about them here, permanently, hurts.

  2. onefang Silver badge

    Trying to wrap my brain around gravity waves really hertz.

  3. John Smith 19 Gold badge
    Thumb Up

    "gas molecules bouncing around inside the satellite were sufficient to register as noise. "

    So "Must improve initial vacuum" gets added to the to do list.

    Which is sort of the point of a "pathfinder" mission.

    These are excellent results for a precursor mission but 2034? That said the US project of testing relativity with perfect glass spherical gyroscopes on orbit took more like 50 to get all the tech developed.

    Well done.

    1. DougS Silver badge

      Re: "gas molecules bouncing around inside the satellite were sufficient to register as noise. "

      Impossible to get a perfect vacuum on Earth, so instead make an imperfect seal so those gas molecules eventually find the gap and escape. Then your only noise would be virtual particle pairs being created and annihilated...

      1. Gordon 10 Silver badge

        Re: "gas molecules bouncing around inside the satellite were sufficient to register as noise. "

        plus the random atoms and other doodads getting back in of course - given that space isn't a perfect vacuum.

        1. Not also known as SC
          Coat

          Re: "gas molecules bouncing around inside the satellite were sufficient to register as noise. "

          Space isn't a vacuum at all. It's full of planets and stars etc. Very far apart admittedly...

          1. SkippyBing Silver badge

            Re: "gas molecules bouncing around inside the satellite were sufficient to register as noise. "

            'Space isn't a vacuum at all. It's full of planets and stars etc. Very far apart admittedly...

            So what is the pressure of the solar system...

            1. Not also known as SC

              Re: "gas molecules bouncing around inside the satellite were sufficient to register as noise. "

              Low.

            2. Brewster's Angle Grinder Silver badge

              Re: "gas molecules bouncing around inside the satellite were sufficient to register as noise. "

              "So what is the pressure of the solar system..."

              Depends when and where you measure it. But Wikipedia says the pressure around Earth is a few nano-pascals. Interstellar space is rarely emptier than 1 particle per cc, and at 2.7K that works out at ~1E-17 pascals.

              1. SkippyBing Silver badge

                Re: "gas molecules bouncing around inside the satellite were sufficient to register as noise. "

                'Interstellar space is rarely emptier than 1 particle per cc, and at 2.7K that works out at ~1E-17 pascals.'

                So it'll be alright to get home on and then pump it up there?

        2. DougS Silver badge

          @Gordon 10

          plus the random atoms and other doodads getting back in of course - given that space isn't a perfect vacuum.

          True, but the odds of something getting IN a tiny gap in an object probably less than a meter across are minuscule versus the odds of something that's bouncing around like crazy inside it getting OUT. Meaning you will eventually attain a perfect vacuum, which appears to have happened here.

          Even if something defies the odds and gets in it'll leave pretty quickly via the same "bouncing around like crazy" process and restore your perfect vacuum. I'll bet the odds of a gas molecule getting in to spoil your perfect vacuum are probably less than the odds of a cosmic ray ripping through and upsetting the computers, or a micrometeorite tearing in one end and out the other and destroying it.

        3. Citizen99
          Coat

          Re: "gas molecules bouncing around inside the satellite were sufficient to register as noise. "

          'plus the random atoms and other doodads getting back in of course - given that space isn't a perfect vacuum.'

          Where's Maxwell's Demon when you need it, eh.

    2. frank ly

      Re: "gas molecules bouncing around inside the satellite were sufficient to register as noise. "

      "... testing relativity with perfect glass spherical gyroscopes ..."

      Is that one called 'Balanced Axis Relativity Tester'?

    3. phuzz Silver badge

      Re: "gas molecules bouncing around inside the satellite were sufficient to register as noise. "

      The full scale version of this will use fully separate satellites (rather than two masses inside an enclosure). In fact, the full sized LISA will be formed of three satellites 5 million km apart, so they're just going to have to deal with space not being as perfect a vacuum as they might like.

  4. ant 2

    PicoHertz?

    Pico-Hertz?

    I'm not sure I've got the patience to measure a signal with a wave period of 30,000 years!

    1. Paul Crawford Silver badge

      Re: PicoHertz?

      Indeed, even 1uHz = 11.6 days, 1nHz = 31.7 years period. Of course you could have 800pHz as around 40 years and still be well within advertising standards...

      Of course it might also be related to the time-derivative of gravity (units anyone?!) where it may be something like 1pico-g per second or similar.

  5. JimmyPage Silver badge
    Boffin

    Michelson-Morley

    Ever since this project was announced, I can't help but think it's a sequel to the M+M experiment to find the ether.

    I think there's a good justification for looking back at some of the ideas previously dismissed as "wrong" to see if they might in fact have had some germ of sense in them ?

    A bit like the current vogue for looking back at old medicines for new applications .....

    1. Chemist

      Re: Michelson-Morley

      "A bit like the current vogue for looking back at old medicines for new applications ....."

      I'm not giving away any company secret but doing that was always in vogue. Difference these days is that lots of start-ups talk * about it.

      * applies to other industries too

    2. tfb Silver badge
      Boffin

      Re: Michelson-Morley

      I think that 113 years of relativity (and 102 of GR) with a number of exquisitely precise tests, all of which its passed, is probably why people don't really feel motivated to look for something which is undetectable even in principle if relativity is correct.

    3. phuzz Silver badge
      Boffin

      Re: Michelson-Morley

      It's interesting that you're comparing it to Michelson-Morley, because the actual apparatus is pretty similar in design, a pair of long 'corridors' with a mirror at the end, down which a laser is shone. The time it takes the laser to go from one end to the mirror and back can be measured precisely by looking at the interference pattern it creates with the out-going light.

      M&M were using a right-angled interferometer to try and detect changes in the speed of light. LIGO are using a pretty similar setup (although more precise), to measure changes in the length of the arms of the experiment caused by passing gravity waves. If M&M had access to the same equipment they might have interpreted the data as being small fluctuations in the speed of light.

      We're pretty sure that what LIGO is detecting are gravity waves because they match up with events that we can detect with other means. For example, the collapse of two neutron stars produced gravity waves detected by LIGO (and VIRGO), gamma rays detected by Fermi and INTEGRAL and lower energy EM rays detected by a whole host of different instruments.

  6. Arthur the cat Silver badge

    Table football

    Did anyone else casually glance at the first image and wonder why there was a table football game between the cubes?

  7. Arthur the cat Silver badge

    Quiet

    The scientists reckon the end result is that the Pathfinder was, for a while, the “quietest place in space”

    And then some flash bugger in a Tesla roadster went past with a Bowie song blaring out at 120 decibels.

    1. John Brown (no body) Silver badge
      Pint

      Re: Quiet

      Pint for you sir!

  8. Pascal Monett Silver badge
    Thumb Up

    "a separation of 2.5 million km"

    Are they going to use lasers to keep things in line with that as well ?

    Humanity is truly a thing of wonder. On the one hand, we have people capable of thinking of, designing and creating wondrous things like LISA, and on the other hand we have . . . let's not go there.

    Thumbs up for boffins, once again !

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