Gravity waves: a reader’s take

I’m busy much of today, but have a few contributions from others to show.

I thought I had posted on the discovery of gravity waves from the LIGO Project when it happened, but I can’t seem to find the post. (I did mention the award of this year’s Nobel Prize in physics to its discoverers.) At any rate, you can read about that discovery, which detected the almost-undetectable but predicted waves coming from the collision of two black holes, at the website of Official Website Physicist™ Sean Carroll. The detection of those waves, and the apparatus required to do it, is to my mind one of the great intellectual achievements of our species.

This came to mind when I got an email yesterday from reader Tim Anderson, who regularly sends us photos of animals and stars. Here’s what he said (the emphasis is mine):

I don’t know if you read the story about the detection of the radiation from the collapse of two neutron stars. Seventy observatories around the world collected data from all wavelengths between gamma and infrared after LIGO observed the gravitational waves coming out of the event. We can see the event happening in real time.
But here is the most astonishing measurement. LIGO measures gravitational waves via a metric called “peak strain”. Imagine an object that is one metre long and that is aligned along the wave path from the neutron star-pair collapse. The “peak strain” measures how much spacetime distorts the object from end to end as the wave passes through.
LIGO measured the peak strain to be 1 X 10 ^ – 22 m. That is less than one quarter of the diameter of a proton. And we measured it!
And here is another astonishing thing. The lead paper covering the discovery has 4500 listed authors (approximately one-third of the professional astrophysicists on our planet). They are listed in alphabetical order, so this paper will be forever known as Abbott et al.
Wikipedia has a nice article about the LIGO project, which has now detected gravity waves five times, and using two independent stations 1865 miles apart:
Each detector has two arms, each 4 km long. Here’s a photo of the one at Hanford, and you can read more about this apparatus and the experiment at the LIGO site.
The paper, which does indeed have 4500 authors, can be seen here (pdf here), and if you want the full list of names, click on this icon after the title:
Here’s just part of it. It’s so long that there’s even a Coyne in the list (no relation):

33 Comments

  1. Posted November 5, 2017 at 9:34 am | Permalink

    Oh goodie, a chance for me to be the first pendant. LIGO detects gravitational waves not gravity waves. They are different.

    • Posted November 5, 2017 at 9:43 am | Permalink

      Pedant, to be pedantic.

      • MKray
        Posted November 5, 2017 at 9:47 am | Permalink

        I have known people who study gravity waves, and for them the difference is not pedantry. For the record, they are waves in the upper atmosphere a bit like waves on the sea.

        • Posted November 5, 2017 at 10:17 am | Permalink

          “.. they are waves in the upper atmosphere”

          You’re specifically talking about ‘atmospheric waves’, but the term ‘gravity waves’ applies to much more: In fact ‘waves in the sea’ are not just ‘like’ it, they too ARE gravity waves.

          And yes, gravitational waves are something else entirely. Unlike what some news outlets reported, NO one got the Nobel Prize this year for the discovery of gravity waves (which only would have taken a trip to the seashore).

          https://en.wikipedia.org/wiki/Gravity_wave

      • Posted November 5, 2017 at 10:11 am | Permalink

        Actually I thought that was deliberate. I often call pedants ‘pendants’ because they can’t resist ‘correcting’ me and probing my point.

        • Posted November 5, 2017 at 10:12 am | Permalink

          Proving my point. If they start probing my point I usually make a swift exit.

    • Craw
      Posted November 5, 2017 at 10:37 am | Permalink

      The hanged man speaks!

      • Posted November 5, 2017 at 10:15 pm | Permalink

        😀 you mean as he dangles like a pendant?

    • Posted November 6, 2017 at 9:14 pm | Permalink

      Anecdote time: I was learning electrostatics back in high school and my teacher pointed out the similarities with gravitation, so knowing that electromagnetic waves exist (as light), I googled “gravity waves”. I was extremely disappointed. And then a few years later we found gravitational waves and I realized how I f**ked up.

  2. Posted November 5, 2017 at 9:40 am | Permalink

    Hmm… Three Abbots and not a single Costello.

  3. alexandra Moffat
    Posted November 5, 2017 at 9:47 am | Permalink

    Wish that Feynman was still alive to be part of this…..

  4. Posted November 5, 2017 at 9:52 am | Permalink

    <They are listed in alphabetical order, so this paper will be forever known as Abbott et al.

    Budding scientists are advised to change their name to Aaron A. Aardvark.

    • Posted November 5, 2017 at 10:19 am | Permalink

      Not a good idea if Judge Cal ever becomes Chief Judge.

    • Ken Kukec
      Posted November 5, 2017 at 10:22 am | Permalink

      Works for bail bondsmen.

      • yazikus
        Posted November 5, 2017 at 10:24 am | Permalink

        You need a symbol/numeral first, #1 Aaron A. Aardvark. (And yes, I knew a bondsman when he was setting up his business and this very much was a topic of discussion).

  5. yazikus
    Posted November 5, 2017 at 9:58 am | Permalink

    A neat tidbit, the calculations have to take wolf activity on the reservation into account. If anyone ever has a chance, a tour of Hanford is well worth the time!

  6. Craw
    Posted November 5, 2017 at 10:35 am | Permalink

    Instruments of such sensitivity would detect the chi, or the power of prayer. I hope they corrected for that.

    😉

  7. Posted November 5, 2017 at 10:38 am | Permalink

    “It’s so long that there’s even a Coyne in the list…”

    There are two Coynes on the list. There’s a D. C. Coyne and an R. Coyne.

  8. Emerson
    Posted November 5, 2017 at 10:38 am | Permalink

    4500 authors? It’s GUINESS time, people! (As a curiosity, one could count the letters to see how many would have each author written individually if that were possible…)

    • Posted November 7, 2017 at 3:47 pm | Permalink

      I would love for some sensible sociologist of science (Yves Gingras? Stephen Cole?) to figure out what happened here – physics seems to have gone from underreporting contributions to perhaps the other way.

  9. ThyroidPlanet
    Posted November 5, 2017 at 10:51 am | Permalink

    THAnk you Tim for the FFR (fun fast read)!

    So fast I can’t be bothered to properly use capital or lowercase letters1!!!1!1

  10. Charles Sawicki
    Posted November 5, 2017 at 11:20 am | Permalink

    “LIGO measured the peak strain to be 1 X 10 ^ – 22 m. That is less than one quarter of the diameter of a proton. And we measured it!”

    Post is off by 7 orders of magnitude:
    Diameter of proton is about 1fm so a peak strain of 10-(exp22)is 10-(exp 7) or 1 ten millionth the proton diameter.

  11. Mark R.
    Posted November 5, 2017 at 11:56 am | Permalink

    Only science could produce a consensual paper written by 4,500 independent humans. That in itself is a remarkable achievement. Go science! Can you imagine 4,500 theologians agreeing on the precise nature of god?

    • Steve Bracker
      Posted November 5, 2017 at 12:28 pm | Permalink

      “Can you imagine…” Easily, if one of the theologians has somehow acquired the ability to burn dissenters at the stake. Probably the big difference between science and theology is not the size of consensual groups but the methods considered legitimate to achieve consensus.

      I’ve been on the inside of several large scientific collaborations, and have seen the struggles that go into achieving a consensus wording for a paper. On one hand, the result being reported may be so clearcut that the only issues center on clarity and brevity. On the other, reporting a complicated or marginal result may begin with the same sectarian divisions for which theology is famous, but only very rarely do you end up with two papers interpreting the same observations differently (schism), and burnings at the stake are rarer still. In the end, reason and evidence usually carry the day.

  12. John A
    Posted November 5, 2017 at 12:31 pm | Permalink

    Isn’t strain a dimensionless measure? Applying a strain of 10 ^ – 22 to the 4km arm length gives a change in size of 2.5 * 10 ^ – 18m. And (Wikipedia) the light is bounced 280 times down each arm, effectively making the arm length 280 * 4km, and making the change in effective arm length ~10 ^ -15m. That is the change in the effective arm length at peak strain. But presumably the experiment detects below peak strain. Wikipedia states “gravitational waves that originate tens of millions of light years from Earth are expected to distort the 4 kilometer mirror spacing by about 10^−18 m, less than one-thousandth the charge diameter of a proton. “. I’m still unsure of the actual space distortion measured. But supremely impressive, nevertheless.

    • John A
      Posted November 5, 2017 at 12:44 pm | Permalink

      I should have said “better than” peak strain to be clear that the peak strain is [presumably] the biggest size change yet detected. Presumably this is at and near the peak of the gravitational wave. The smaller the strain detected, the more impressive. Strain is the dimensionless indication of change per unit size. The size being 4km. So the actual size change at peak strain is 2.5 * 10 ^ -18 … close to that figure given on Wikipedia for that expected of waves originating tens of millions of light years away.

  13. Curt Nelson
    Posted November 5, 2017 at 2:50 pm | Permalink

    I know astronomers are super happy about this observation because they were able to look at the event all different ways as it evolved, but I’ve also heard that observatories in Chili had to wait until night came before they could look, and some significant amount of time passed before the discovery could be recognized and reported and found in the sky…

    So I’m wondering if they didn’t miss the best part —the beginning— and why there’s no talk of that (in the several accounts I’ve heard). I want it to have been a completely observed event with everyone happy, and maybe it is, but I’m reminded of the “landing” of the Philae lander on the comet, with very limited mention of the fact that it didn’t land, it came to rest in a shadow after the landing mechanisms all failed so, aside from getting a brief sniff of the comet’s atmosphere at impact, it didn’t work.

    There’s nothing at all wrong about missing some of the data, of course that will be the case. I’m interested in the entire story and would love to hear about all of it — the neat things they got, what didn’t work out and why, everything. Reporting on such major science projects is probably geared toward accentuating the positive and eliminating the negative for PR reasons.

  14. Posted November 5, 2017 at 2:59 pm | Permalink

    Am I a bad person for not being able to appreciate this as much as it should be appreciated, just because of the 4,500 author issue?

    That kind of stuff bugs me. There is no way that 4,500 people actually deserve to be called “authors” of a paper, be it in the sense of having conceived the science or of having participated in writing to a significant degree, unless perhaps if it were at least 2,000 pages long, and I strongly assume it isn’t a massive door-stopper book.

    I know the usual argument is that each of these people has contributed something to the work, perhaps a technical modification to the detector, but that is like saying that the engineer at Eppendorf who designed our thermocycler should be coauthor, and a colleague who has kindly carried a box of specimens around, and the bus driver who will bring me to work today. Because without them the publication wouldn’t have happened, right?

    • Posted November 6, 2017 at 5:31 am | Permalink

      I have the same problem with the end credits of a modern movie.

      • Posted November 6, 2017 at 6:03 am | Permalink

        Well, at least those people are not all called ‘director’.

        • gravelinspector-Aidan
          Posted November 14, 2017 at 7:53 pm | Permalink

          Many journals these days require a section where the nature of each author’s contribution. Something like “Bloggs – experimental conception and design ; Smith – materials preparation ; Jones – Spongebob pant-squaring and data analysis ; Zeldovich – teaboy.”

    • Posted November 7, 2017 at 3:48 pm | Permalink

      See above. My guess is that this is an overreaction to the old model where some one famous Professor (in the German sense, maybe) that gets the only credit and that’s the end.

  15. phoffman56
    Posted November 5, 2017 at 7:38 pm | Permalink

    “The lead paper covering the discovery has 4500 listed authors”

    Did they share the page charges equally? Perhaps dividing the charge by 4500 would cause ‘small change’ to change to ‘infinitesimal change’. Perhaps also

    (length of-paper)/(length of author list)

    would not only be less than 1, but would begin to approximate a mathematical infinitesimal, i.e. a non-standard real which is larger than 0 but smaller than any positive real number.


%d bloggers like this: