Scientific Progress Goes “Chirp”!

 
640px-Northern_leg_of_LIGO_interferometer_on_Hanford_Reservation

Northern leg (x-arm) of LIGO interferometer on Hanford Reservation. By Umptanum – wikipédia, CC BY-SA 3.0.

Ladies and Gentlemen, we have detected gravitational waves! We did it!” And with that, the Laser Interferometer Gravitational-Wave Observatory (LIGO) announced the discovery of a strange feature of General Relativity that’s been hiding since the 1960s.

Gravitational waves are ripples in the fabric of space, caused by the acceleration of mass. The bigger the mass and the faster it’s accelerated, the better, and there’s nothing that better fits that description than two black holes orbiting each other. These waves expand and compress space, which slightly changes distances between objects in their path. Two objects floating freely in deep space far from any forces, would find themselves carried a little towards each other and then a little away from each other and back and forth, as the wave passed over them. If you could measure the distance between them accurately, like with a laser range-finder, you’d detect that oscillation. But this is tough to do on the Earth, because you can’t have the two objects floating freely any more. The best you can do is to hang them from fine threads, like a swing. They’re not free to move in every direction, but they can swing back and forth.

So, how did we find them? LIGO shines laser beams down two 4-kilometer (2.5-mile) vacuum pipes, arranged in an “L” shape. At the end of each pipe is a mirror that reflects the beam back and measures its length, with an accuracy of 10^-18 m, a thousandth the width of a proton. This always amazes me, because the mirror itself is made out of atoms, which are bumpy and much larger than protons. And yet, it works because the bumps average themselves out. When a gravitational wave comes by, it shrinks the distance along one pipe while expanding the distance along the other (as they’re at right angles) and then it switches.

What they’ve announced today is the detection of gravitational waves coming from the merger of two black holes, spiraling into each other a billion light-years away from us. At 29 and 36 times the mass of the Sun, these aren’t very big for black holes: the ones in the centers of galaxies have millions or billions of solar masses. But the smaller ones are more plentiful, which means they’re more likely to collide. As the two in question orbited each other, the gravitational waves carried away more and more of their energy, making them spiral inward, until they finally collided and released massive amounts of energy (the equivalent of the mass of three Suns converted directly into energy).

Take a look at the wave patterns that LIGO felt:Gravitational waves felt by LIGO

The vibration is vertical, and time goes to the right. Early on, the waves are slow (i.e., broad) and weak (i.e., short). As the black holes spiral inward, the waves strengthen and increase in frequency until they make a loud “chirp! when they collide. Then, there’s a faint wiggling at the end, as the new, combined black hole rings like a bell until it settles down.

This pattern is so clear, you can see it without needing the computer to sort it through for you. What are the odds of detecting this? My wife — who works in numerical relativity (the computer simulation of the waves) — tells me that it was entirely possible they’d run this for decades before they heard anything. Instead, they found this within days of turning the machine on. That suggests that these black holes are colliding all over the place, and we’re going to find plenty more.

So what good is this? The press is mostly writing headlines shouting, “Einstein is proven right!” This is true in a simplified sense, but not too many of us were expecting otherwise and that’s not really why all of this was built. With more detections and better signals, we’ll get to the point where we can test theories that go beyond General Relativity, which is interesting. But I think the real value of this discovery will be observational.

Until now, astronomy has almost exclusively relied on what we can see with light: i.e, electromagnetic radiation, ranging from radio waves on one end to gamma rays on the other. We can see the gas falling into black holes — glowing x-ray hot before it disappears — and we can see supernovas from the light they emit. But there’s a lot going on down in the compact centers of these things that we can’t see with light. Gravitational waves will give us an entirely different way to probe them.

Already, the gravitational wave people and the visible light astronomers have teamed up to do joint searches for flashes of light that might accompany a gravitational wave burst. My wife, for example, is working on the computer simulations for these. This photo shows her working out the algorithm for her models.

Maria Babiuc Hamilton, working out her numerical relativity algorithm.

The discovery of gravitational waves has been a long time coming. Searches started in the 1960s, and there’s even a detector on the Moon, placed there by Apollo 17. But the evidence up to this point had always been indirect. Now, we’ve finally got something both direct and obvious.

That’s big news.

Published in Science & Technology
Like this post? Want to comment? Join Ricochet’s community of conservatives and be part of the conversation. Join Ricochet for Free.

There are 93 comments.

Become a member to join the conversation. Or sign in if you're already a member.
  1. PHCheese Inactive
    PHCheese
    @PHCheese

    It is of my opinion that a phenomenon such as this could be as much responsible for changes in the earths temperature over time as anything else.

    • #1
  2. Tim H. Member
    Tim H.
    @TimH

    While I was writing this up, I felt some literary inspiration and came up with this.  Just for fun.

    • #2
  3. BrentB67 Inactive
    BrentB67
    @BrentB67

    This is great stuff, I think.

    Now for the smart aleck question of the day.

    We can have lasers in L-shaped vacuum tubes shone on mirrors measuring distance a thousandth of the width of a proton and prove gravitational waves, but we have to work the math out on a blackboard?

    Are there no whiteboards? Just sayin’.

    • #3
  4. Hank Rhody Contributor
    Hank Rhody
    @HankRhody

    BrentB67:This is great stuff, I think.

    Now for the smart aleck question of the day.

    We can have lasers in L-shaped vacuum tubes shone on mirrors measuring distance a thousandth of the width of a proton and prove gravitational waves, but we have to work the math out on a blackboard?

    Are there no whiteboards? Just sayin’.

    Now for the smart aleck answer:

    Racist.

    • #4
  5. Larry Koler Inactive
    Larry Koler
    @LarryKoler

    anonymous: Today’s publication was of an event precisely as expected from astrophysics and general relativity.

    Isn’t that convenient for them. What are the chances?

    Confirmation bias is hard to watch, isnt’t it? Oh yes, but Einstein, Larry. And math, Larry.

    • #5
  6. Hank Rhody Contributor
    Hank Rhody
    @HankRhody

    Tim H.: My wife tells me that it was entirely possible they’d run this for forty years before they heard anything at all. Instead, they found this within days of turning the machine on.

    A decade ago when I was studying physics at the University of Wisconsin Milwaukee I heard a lot about this thing. We were an associated school. I remember seeing a presentation where they had a lovely blank graph of the results so far, but not to worry! here’s what the simulation produced. I remember a grad student chortling about how the theorists had proposed the thing, and built it, without taking into account the thermal properties of the string you had to use to suspend the weights.

    I said they talked about it a bunch, I didn’t say I listened.

    • #6
  7. Lidens Cheng Member
    Lidens Cheng
    @LidensCheng

    That chirp was amazing to hear this morning in the press conference. On top of the already great plots.

    • #7
  8. Carey J. Inactive
    Carey J.
    @CareyJ

    Do we have any clue as to the propagational speed of gravitational waves? Is it equal to the speed of light? Is it slower? Is it faster? If it is different, and you have a way to identify an EM-observable event that created them, you can determine the distance to the event. Kind of like timing the lag between a lightening strike and its thunder.

    • #8
  9. Midget Faded Rattlesnake Contributor
    Midget Faded Rattlesnake
    @Midge

    BrentB67:This is great stuff, I think.

    Now for the smart aleck question of the day.

    We can have lasers in L-shaped vacuum tubes shone on mirrors measuring distance a thousandth of the width of a proton and prove gravitational waves, but we have to work the math out on a blackboard?

    Are there no whiteboards? Just sayin’.

    What I was told is that whiteboards are allegedly better for any computers occupying the room.

    But there’s something about a blackboard… maybe it’s a tactile thing…

    • #9
  10. BrentB67 Inactive
    BrentB67
    @BrentB67

    Midget Faded Rattlesnake:

    BrentB67:This is great stuff, I think.

    Now for the smart aleck question of the day.

    We can have lasers in L-shaped vacuum tubes shone on mirrors measuring distance a thousandth of the width of a proton and prove gravitational waves, but we have to work the math out on a blackboard?

    Are there no whiteboards? Just sayin’.

    What I was told is that whiteboards are allegedly better for any computers occupying the room.

    But there’s something about a blackboard… maybe it’s a tactile thing…

    When I saw the picture I was trying to think of the last time I used a blackboard. I would think the dust in laboratory setting would be bad, but maybe we have dustless chalk.

    • #10
  11. BrentB67 Inactive
    BrentB67
    @BrentB67

    As these waves propagate through space would it be possible to ‘catch’ one, ride it, or in any way augment space travel?

    • #11
  12. Tom Meyer, Ed. Contributor
    Tom Meyer, Ed.
    @tommeyer

    Many, many thanks to Tim for writing this.

    Tim H.: As the two in question orbited each other, the gravitational waves carried away more and more of their energy, making them spiral inward, until they finally collided and released massive amounts of energy (the equivalent of the mass of three Suns converted directly into energy).

    I can’t really wrap my head around how little I can wrap my head around that.

    That’s just an insane amount of energy.

    • #12
  13. Mark Wilson Member
    Mark Wilson
    @MarkWilson

    Tim H.: What they’ve announced today is the detection of gravitational waves coming from the merger of two black holes, spiraling into each other a billion light-years away from us.

    I also do modeling, prediction, and data matching in my job.  I’m curious about the signals called “Prediction”.  Is that a prediction based on two known black holes we knew were going to collide, then measured and saw the data matched?  Or as often happen, did they see some data and then try to create a post-event “prediction” by finding the right parameters to populate the model and get it to match the data?

    • #13
  14. Mark Wilson Member
    Mark Wilson
    @MarkWilson

    anonymous: The fact that the same waveform was observed in Hanford, Washington and Livingston, Louisiana, with precisely the speed of light offset expected for propagation of the wave between the two detectors

    I’ve always been curious about the distant clocks used in large scale physics experiments.  I assume they use GPS as a time source, but what do they do about the vastly different iono- and tropo- delays with different climates, different solar exposure, and different constellation visibility to get such a precise degree of synchrony?

    • #14
  15. Tom Meyer, Ed. Contributor
    Tom Meyer, Ed.
    @tommeyer

    At a friend’s suggestion, we once drove along WA-240, which skirts Hanford. It’s the kind of place you expect to run into Mulder and Scully.

    • #15
  16. drlorentz Member
    drlorentz
    @drlorentz

    Hank Rhody: I remember a grad student chortling about how the theorists had proposed the thing, and built it, without taking into account the thermal properties of the string you had to use to suspend the weights.

    To be fair to these guys, the effect they are seeking is so small that they need to worry about all kinds of issues that could normally be neglected. For example, the test masses (mirrors in the case of LIGO) have to be extremely uniform and pure because otherwise they will have greater thermal motions that mask the signal. A former colleague did her Ph.D. thesis on minimizing the losses at the attachment points to suspend the masses.

    No one person can be expert in all these areas, so it’s hardly surprising that the theorists you heard didn’t think of everything. These are not simply engineering problems. To even know what to look for you need to understand things like the fluctuation-dissipation theorem, which most engineers have never heard of.

    • #16
  17. drlorentz Member
    drlorentz
    @drlorentz

    Mark Wilson:

    I’ve always been curious about the distant clocks used in large scale physics experiments. I assume they use GPS as a time source, but what do they do about the vastly different iono- and tropo- delays with different climates, different solar exposure, and different constellation visibility to get such a precise degree of synchrony?

    The two LIGO detectors are separated by 10 milliseconds. GPS clock signals are accurate to tens of nanoseconds, about a factor of a million smaller. Differential time-of-flight delays through the ionosphere are on the order of nanoseconds.

    As an aside, GPS must account for General Relativity corrections to be accurate. This is weak-field relativity, which is considered to be well verified. The waves LIGO detected were probably the first strong-field test of relativity.

    Edit: The actual time difference between the two arrival times was about 7 ms according to the paper.  The arrival times have to be within the 10 ms spacing of the two detectors but can be less depending on the angle of arrival of the wave. The paper says that the data acquisition systems are synchronized to within 10 μs using GPS.

    • #17
  18. James Lileks Contributor
    James Lileks
    @jameslileks

    Stupid question from a layman: “Smaller black holes are more plentiful”  made me wonder if that might be where the missing mass is. I’m sure it’s occurred to them, but is there any solid refutation of the possibility?

    There’s a pretty good chance I won’t be around to witness the end of the cosmos by Heat Death, but I just hate that idea. Much prefer that there’s sufficient mass so everything comes back home, compacts, the explodes again, over and over, regular as respiration.

    I’m fine with the multiverse, though.

    • #18
  19. Z in MT Member
    Z in MT
    @ZinMT

    Larry, as I told a colleague this morning I don’t trust the astronomers. Most astronomers I know are happy to calculate something to a factor of pi. However, I do trust the scientists and engineers at LIGO. Many of them have a background in time and frequency metrology, and you will never meet a more cautious bunch of perfectionists.

    • #19
  20. Randy Webster Member
    Randy Webster
    @RandyWebster

    BrentB67:This is great stuff, I think.

    Now for the smart aleck question of the day.

    We can have lasers in L-shaped vacuum tubes shone on mirrors measuring distance a thousandth of the width of a proton and prove gravitational waves, but we have to work the math out on a blackboard?

    Are there no whiteboards? Just sayin’.

    And just look at that piece of chalk she’s using!

    • #20
  21. drlorentz Member
    drlorentz
    @drlorentz

    Z in MT:Larry, as I told a colleague this morning I don’t trust the astronomers. Most astronomers I know are happy to calculate something to a factor of pi. However, I do trust the scientists and engineers at LIGO. Many of them have a background in time and frequency metrology, and you will never meet a more cautious bunch of perfectionists.

    Years ago, the joke was that precision cosmology was an oxymoron. I had the same feeling about astronomy in general This changed when good measurements of the Hubble constant were made in the 1990s. They’re doing better now. Anyway, as you noted, many of the people are working on this are optical physicists anyway.

    • #21
  22. Dustoff Inactive
    Dustoff
    @Dustoff

    I’m pretty much with James Lileks on this one.

    • #22
  23. Peter Meza Member
    Peter Meza
    @PeterMeza

    OK, I get that Einstein predicted gravitational waves.

    I get that the LIGO detector captured an event.

    I also see a “predicted wave” superimposed on the discovered wave.

    In what sense where the waves we see in the graph “predicted”.  How where they predicted?  You mean this exact event had a predicted signature?  As in this predicted wave signature was in the computer a couple of years ago, and now the signal was actually detected and jeez look at how similar they are?

    I am missing something.

    • #23
  24. Mark Wilson Member
    Mark Wilson
    @MarkWilson

    Peter Meza: In what sense where the waves we see in the graph “predicted”. How where they predicted?

    My suspicion is that they retroactively used a simulation and fiddled with the inputs until the simulation could generate a “prediction” that matched the data.  If so, it’s not a prediction in the traditional prescient sense, but in the model-agrees-with-reality sense.

    • #24
  25. drlorentz Member
    drlorentz
    @drlorentz

    Mark Wilson:

    Peter Meza: In what sense where the waves we see in the graph “predicted”. How where they predicted?

    My suspicion is that they retroactively used a simulation and fiddled with the inputs until the simulation could generate a “prediction” that matched the data. If so, it’s not a prediction in the traditional prescient sense, but in the model-agrees-with-reality sense.

    Yes, it’s a loose use of the term predicted, but not out of line with common usage in physics. It’s reasonable since the signature correspond to the kind of event they were looking for. There are some adjustable parameters but not too many.

    Put it this way, there’s a family of waveforms that can be simulated for events of this kind. They all look similar. You can’t predict the exact parameters for some signal that hasn’t arrived yet but you can make the prediction that it’s going to be a member of that family. I think that’s a reasonable use of the word predicted.

    Edit: The paper does not use the word predicted in the graphs. The figures in the OP must have been from somewhere else. The paper says,

    It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole.

    and

    to recover signals from the coalescence of compact objects, using optimal matched filtering with waveforms predicted by general relativity.

    figs

    • #25
  26. Z in MT Member
    Z in MT
    @ZinMT

    Peter Meza:I also see a “predicted wave” superimposed on the discovered wave.

    In what sense where the waves we see in the graph “predicted”. How where they predicted? You mean this exact event had a predicted signature? As in this predicted wave signature was in the computer a couple of years ago, and now the signal was actually detected and jeez look at how similar they are?

    I am missing something.

    Predicted is a misnomer. Gravitational wave theorists have been making signal predictions for LIGO under a number of different scenarios for years. One of the most likely signals they expected to see was this type of signal from two black holes orbiting and collapsing into each other. So the overall shape was a prediction, but the exact frequency, chirp rate, and amplitude of the expected signal vary based on the masses of the black holes. So the predicted curves are based on models are then used to fit the data to extract the masses and distance from earth etc.

    If you look at the time scale of the signal it boggles the mind. If I understand it right, each period of the waveform represents an orbital period of the two black holes which is in the millisecond regime. These are objects with masses about 30 times that of our sun. To think that for a brief moment they are revolving around each other faster than the blades of turbo-prop engine at full speed is just crazy.

    • #26
  27. J. D. Fitzpatrick Member
    J. D. Fitzpatrick
    @JDFitzpatrick

    Z in MT: If you look at the time scale of the signal it boggles the mind. If I understand it right, each period of the waveform represents an orbital period of the two black holes which is in the millisecond regime. These are objects with masses about 30 times that of our sun. To think that for a brief moment they are revolving around each other faster than the blades of turbo-prop engine at full speed is just crazy.

    Is it just the singularities that are rotating around each other at that point or something larger?

    • #27
  28. drlorentz Member
    drlorentz
    @drlorentz

    J. D. Fitzpatrick:

    Is it just the singularities that are rotating around each other at that point or something larger?

    Around each other. They eventually coalesce.

    • #28
  29. J. D. Fitzpatrick Member
    J. D. Fitzpatrick
    @JDFitzpatrick

    drlorentz:

    J. D. Fitzpatrick:

    Is it just the singularities that are rotating around each other at that point or something larger?

    Around each other. They eventually coalesce.

    What I meant was, how big are the orbits that the two black holes are describing as they rotate around each other? If it’s just the infinitely dense singularities rotating around each other, then you could have a huge amount of mass describing very small, very fast rotations.

    If we’re talking about something more like bubbles rotating around each other in a drain before they combine–in other words, objects with a larger diameter–then yes, it is surprising how fast the rotation is.

    • #29
  30. Randy Webster Member
    Randy Webster
    @RandyWebster

    drlorentz:

    J. D. Fitzpatrick:

    Is it just the singularities that are rotating around each other at that point or something larger?

    Around each other. They eventually coalesce.

    Is “coalesce” just a fancy term for “crash into each other?”

    • #30
Become a member to join the conversation. Or sign in if you're already a member.