Hunting Ghosts Across the Cosmos

By Corey S. Powell | February 29, 2016 11:56 pm
Credit: LIGO, NSF, Aurore Simonnet (SSU).

What we see versus what we believe: The bottom signal represents the vibration signal at the two LIGO gravitational wave facilities. The illustration above indicates the astrophysical interpretation of the signal–two black holes merging into one. It has taken a century to come up with the concept and technology to track down invisible gravitational waves (Credit: LIGO, NSF, Aurore Simonnet)

The recent discovery of gravitational waves by the twin LIGO detectors drove home the gaping chasm between the popular image of how astronomers explore the cosmos and the way it actually happens. In the layperson’s view — which, to be fair, aligns well with daily experience of how we find out new things — exploration is a matter of looking, seeing, and understanding. In reality, most of what astronomers do involves looking without seeing, or seeing without understanding. It involves not just working at the edge of perception, but trying to deduce what lies beyond perception.

At the risk of sounding unscientific, I’d call it cosmic ghost hunting.

Look at the specifics of the first-ever confirmed gravitational wave signal (known as GW150914, in the businesslike style customary to people who are used to sifting through a lot of data). It was created by the merger of a pair of black holes, 29 and 36 times as massive as the sun. When the two collided and combined, the event briefly emitted 50 times as much energy as all the light from all the stars in the entire visible universe. The event literally shook the foundations of space and time. And we could barely see it, or more accurately, we could not see it at all. There is, as yet, no confirmed radiation signal of any kind associated with the black hole merger; it began in blackness and ended in blackness, shining only in gravity.

The actual signal from GW150914 took the form of a subtle squeezing and stretching of the two LIGO facilities in Louisiana and Washington state. The amount of squeezing: about 1/10,000th the diameter of a proton. The effect is so subtle that it’s taken scientists more than four decades to come up with a workable device that can pick it up. The effect is so obscure that the physicists working on LIGO disagreed passionately about whether the “O” in the name could be justified. The “O” stands for “Observatory”–but is that the right term for an experiments that picks up things that fundamentally cannot be observed?

This is how you actually "observe" gravitational waves. (Illustration from the discovery paper by Abbott et al)

This is how astronomers actually “observe” gravitational waves. (Illustration from the discovery paper by Abbott et al)

LIGO is just the latest and most dramatic example of cosmic ghost hunting. Another notable one is the discovery of dark energy, a kind of antigravity effect that is causing the expansion of the universe to accelerate. And how do we know this? Well, the story began with teams of researchers who were trying to measure the deceleration of the universe, on the assumption that the mutual gravitational pull of all the galaxies should be slowing things down. OK, and how do you do that? Ah, here come more ghosts.

You cannot directly observe the expansion of the universe. You have to infer it by the way that the light from extremely distant stars is stretched by the stretching of space, which causes the light to lose energy and become redder. To deduce how the rate of expansion is changing, you have to take on an even more complex problem. The way to solve it is to look at how much the light of a distant supernova (exploding star) has been stretched and reddened, and then compare that to how much the light has been dimmed by distance. Then there’s a whole other calculation needed to figure out the true brightness of the star and to compare it to the light collected by the digital detectors at the observatory. Human eyes are not involved in any stage of the process.

The astrophysicists crunching the numbers uncovered a ghostly effect: The universe was not slowing down as expected, but speeding up. That acceleration is a symptom of dark energy–not that we know what it is, exactly, we just know broadly what it does. It is an energy that pushes things apart. It is everywhere, and it cannot be seen. It haunts the universe.

Even seemingly tangible things like planets around other stars mostly exist not as visible things but as indirect interpretations. The Kepler Observatory, which is responsible for the bulk of the exoplanets discovered so far, finds alien worlds by watching their shadows as they pass in front of their stars. That may seem fairly concrete, but there are a lot of things that can cause a small variation in a star’s brightness other than a transiting planet.

For five years, a team led by Alexandre Santerne from Instituto de Astrofísica e Ciências do Espaço examined the Kepler stars one by one, trying to understand exactly what they were seeing. In the end, they concluded that more than half of the inferred giant planets around other stars were not planets at all. They were the kinds of ghosts that vanish when you turn on the lights.

Kepler scientists are now wrestling with another spectral presence, known as KIC 8462852, or Tabby’s star. You might also know it as the “alien megastructure” star, so called because its strange flickering could be caused — possibly maybe — by an enormous artifact orbiting around it. No obvious natural process can explain the star’s peculiar behavior. Then again, we are operating at the edge of perception here, in the zone where it is easy to mistake unusual or misunderstood effects for things that fit into a neat narrative that attracts a lot of media attention–something like an alien megastructure, for instance.

Anyone who has ever watched the silliness of the television “ghost hunter” shows will know how easy it is to mistake signal for noise when you are operating at the edge of perception, how easy it is to get swept up in hypotheses when you do not have enough data to constrain them.

The LIGO folks are certainly aware of the perils of ghost hunting, which is a big part of the reason why their task has taken so long. By the team’s calculation, a signal like GW150914 could happen by chance just once every 203,000 years. This ghost, at least, seems to be the real deal.

Follow me on Twitter for astronomy news and insights: @coreyspowell


  • OWilson

    An excellent article.

    Most of the money (billions) for physics research these days is spent on trying to “prove a hypothesis”, the “god particle”, wimps and others in the particle zoo. One physicist who has been spending millions on the huge underground detecting lab for 30 years now was asked why he hasn’t found anything yet. He replied that finding nothing is useful to our understanding.

    I can speculate that there are other, heavier particles out there we can detect, if only you would give me more money to build a bigger, more expensive and more powerful particle collider, because with sufficient energy levels, you can create mass, apparently indefinitely, E=Mc2.

    Hey, who could argue with that?

    If you look hard enough for something you “believe” in, chances are you are going to find it, or maybe even think you did :)

  • Uncle Al

    recent discovery of gravitational waves” Observation. PSR B1913+16 confirmed relativity’s orbital decay via gravitational radiation. “Eureka!” is rare; “that’s funny…” is common. Administration enforces rules, counts things, and avoids risk. There is nothing funny about it.

    Administration murders discovery. Aristotle versus Galileo, Euclid vs. Bolyai then Thurston, Newton vs. relativity, quantum mechanics, and statistical mechanics. Otto Stern observed the Dirac equation failed for proton magnetic moment, then quarks. Penzias and Wilson pointed a 6-meter microwave horn into empty sky, then cosmic microwave background. Particle theory was mirror-symmetric, then Yang and Lee. Davis, Bahcall and 100,00 gallons of perchloroethylene observed 2/3 too few neutrinos, then neutrino oscillation. Theory rarely discovers. Look!

    • OWilson

      No problem with “looking”, but at some point another “law” kicks in, The Law Of Diminishing Returns.

      As we move from the knowable into the speculative metaphysical, at least prioritization should be considered.

      We could blow the entire budget on searching for ET or all those “multi universes” out there, and some would say that the search for knowledge is worth it.

      But they are the same folks who constantly attack the big drug and pharma industry, although we always get more bang for the buck from these guys. They have to deliver, it’s their nature.

      It’s not even close, humanity wise :)

      • Mike Richardson

        Moon dust contains helium 3, which could fuel fusion reactors in the near future. The asteroids contain more precious metals than we could ever mine on earth. Colonies off this world would provide an insurance policy in case of a planet-wide catastrophe. And contact with alien intelligence, if it does occur, would change humanity in profound ways and perhaps accelerate the development of our own technology. Nobody’s knocking vaccines, but your posts here against scientific research for which you apparently have little interest are starting to remind me of an old Beavis and Butthead T-shirt I saw in college, with the intentionally ironic quote, “Knowledge is stupid.” Or the adage that people who can tell you the cost of everything, and the value of nothing.

        • OWilson

          Strawdog alert!

          Me? Against scientific research? :)

          I used the term “prioratization” above, which seems to get you lefties all wound up :)

          Best stick to your Beavis and Butthead discussions where you are more comfortable.

          • Mike Richardson

            Your priorities are politics, profit, and propaganda, in whatever order takes your fancy. You have to be one of the least intellectually curious folks who post here, which is rather odd, considering the topics of discussion. For all of your talk of low info folks, you frequently and regularly bemoan the increase of information that seems to get you “wound up.” You’ve really come to the wrong place to sell anti-intellectualism. Better head to a political blog where you might be comfortable and have a more gullible and receptive audience. :)

          • OWilson

            That nonsense is all in you own low info head.

            My only goal is to keep my beloved science from the routine abuse of people like you, and the unscrupulous politicians you bring to power.

            As long as the majority (10,000 at last count) of my readers like what I write, I will continue for as long as it pleases me, and them.

            Do the math, you have a less than 50% approval rating on your Disqus posts, in spite of the fact that you consistently toe your party line, and post mostly, “me too” lame fawning posts.

            At last count I had a 2 to 1 approval rating with over 4,000 posts submitted.

            I know you live in a different world, but you have to face reality. Figure it out!

            In spite of your lame and unsuccessful attempts at trolling, and now even. trying to moderate this blog, I will not be going anywhere, thank you.

            Nobody gave you that power. Get it?

            The readers and the moderators will get to decide, not you :)

          • Mike Richardson

            I love being lectured on trolling by the master. Please, teach me more. And yes, there are some loud speakers out there that like what you have to say, but unfortunately they tend to be the low information types you lament. Like Trump, you must love the poorly educated, as many of them clearly love you, my friend. Oh, and you have Odin and a couple of others who can be counted on regardless of what you post. But, whatever boosts your ego. It’s funny that in most cases, you like to point out the futility of popularity contests, except of course when it favors you. We have learned that consistency isn’t your strong point, though, so it isn’t surprising. Actually, Wilson, I encourage you to post, because you truly do more damage to the positions you espouse with your partisanship and irrationality than anyone else could. I’m the last person who wants to see you stop. 😉

          • OWilson

            Well, make up,your mind then :) That’s not quite what you said earlier, but now you are just down to ranting.

            But we ( and 10,000 others) understand. We are used to it. :)

            It’s Ok.


          • OWilson

            I would also apologize to our moderator who posted a thought provoking scientific article, only to have it deteriorate.

            That’s what trolls intend to do.

            The thread above is all the proof anyone needs.

            I submit:

            “Nobody’s knocking vaccines, but your posts here against scientific research for which you apparently have little interest are starting to remind me of an old Beavis and Butthead T-shirt I saw in college, with the intentionally ironic quote, “Knowledge is stupid.” Or the adage that people who can tell you the cost of everything, and the value of nothing”.

            Not really a mature or thoughtful response :)

          • Mike Richardson

            You, of course being blameless. Yes, a very thought provoking article, discussing the type of research many of us would like to see further supported. Knowledge about our universe gives us a better understanding of our place in it. And I do regret digressing from the topic, since it’s one I do enjoy discussing with those who actually find such research interesting.

          • OWilson

            I don’t see you “enjoying a discussion”, here on this interesting subject, with anybody on this thread.

            Just your usual trolling and stalking me!


            Caso Cerrado!

          • Mike Richardson

            Wilson, nobody’s interested in stalking you, just responding to some rather peculiar viewpoints. And I think unloading political rants and anti-science posts, and even occasional personal digs at certain moderators, on blogs advocating research and discovery, might easily be considered trolling. That old self-reflection problem, again.
            Exactly what would you prioritize for scientific research? If not theoretical physics or cosmology, aerospace research? Climate science? Paleontology? Anthropology? The funny thing about scientific research is you really can’t predict what breakthroughs in seemingly obscure fields might bring civilization within a generation or two. Einstein’s theories seemed pretty abstract, but affect everything from nuclear energy to the precise measurements of GPS satellites. It’s one thing to be a curmudgeon, but past a certain point, decrying scientific research on general principle gets a little ridiculous.

          • Mike Richardson

            Just a valid observation of posts which reflect disdain for acquiring knowledge of the universe, phrasing it as a choice of “priorities.” Trust me, your opinions on these subjects aren’t the pearls of wisdom you imagine them to be, either.
            But on topic, the proportion of the federal budget such projects as LIGO and Kepler consume is miniscule, pennies out of the annual income tax bill. Much more worthwhile than planes even the Pentagon doesn’t want, or subsidies to already profitable businesses. These projects inspire new generations of students interested in science, technology, engineering, and math. Promoting this interest in the STEM subjects in turn benefits society, as many of the students then go on to develop more practical innovations, as well as continuing the cycle of pure research. Just because the worlds they explore are discovered by gravity, mathematics, or spectroscopy, doesn’t make them any less real than the one we reside on, even if we haven’t filled in all the details yet. Just enough to whet the appetite, for those with the intellectual curiosity.

          • OWilson

            Now. That wasn’t so hard was it?

            I was going to respond to your rare on topic post, then I saw the junk you posted later, below.

            It seems you just can’t help yourself, can you?


          • Mike Richardson

            10,000 voices in your head? Or are those the ghosts of the cosmos we’re looking for? I’m sure they’re out there somewhere, Wilson. Remember, you’re popular, and that’s what’s really important. At least according to high school girls. Meanwhile, I’m off to read some more astronomy nerd news. Popularity never was my main concern.

          • jonathanpulliam

            Mike doesn’t quite rise to the Beavis or Butthead level

    • jonathanpulliam

      “That’s funny. That feller’s dusting crops where there ain’t no crops.”

  • Jason Marrow

    Not just “cosmic ghost hunting” (a cool term, by the way), but looking far back into the past, of course. I read that this signal, observed by LIGO, occurred over 1 billion light years away. That’s a pretty old ghost, among all of the others out there!

    • Tihomir Pavlovic

      Gravitational waves do not exist,…electrostatic energy does,…and in the last 20 years poor scientists do not see things further then their noses,….that is why they are producing ghost theories,…to make some money for living, without any benefit for mankind,..! Space-time, as well do not exists, since nobody can curve the space and time is subjective measure in the minds of all living beings,…filling or observing motion!

  • jonathanpulliam

    Mike Richardson is a troll.


Out There

Notes from the far edge of space, astronomy, and physics.

About Corey S. Powell

Corey S. Powell is DISCOVER's Editor at Large and former Editor in Chief. Previously he has sat on the board of editors of Scientific American, taught science journalism at NYU, and been fired from NASA. Corey is the author of "20 Ways the World Could End," one of the first doomsday manuals, and "God in the Equation," an examination of the spiritual impulse in modern cosmology. He lives in Brooklyn, under nearly starless skies.


See More


Discover's Newsletter

Sign up to get the latest science news delivered weekly right to your inbox!

Collapse bottom bar