ARMED FOR DISCOVERY: At the LIGO site in Louisiana, a pair of four-kilometer-long arms [one of which stretches toward the top of this photograph] awaits the telltale elongation or compression of a passing gravity wave. A similar observatory in Washington State is also on the case.
Image: LIGO Scientific Collaboration
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Gravity's Engines
We’ve long understood black holes to be the points at which the universe as we know it comes to an end. Often billions of times more massive than the Sun, they...
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Gravity waves spread through space and time like ripples on a pond, warping the fabric of the universe as they pass. The largest waves emanate from the most cataclysmic events in the universe: stellar explosions, mergers of black holes, and the violent first moments of cosmological history. Or so the venerable theory of general relativity goes—although many predictions of Albert Einstein's theory of gravity have been proved, only indirect evidence for gravity waves has been found.
An experiment looking for gravity waves directly has, in the course of not finding them, placed new upper limits on how noisy the universe's gravity-wave background could be. Those limits, the researchers say, can refine or even rule out cosmological models that predict large backgrounds originating from processes in the early universe, and more implications should be forthcoming as the experiment, known as the Laser Interferometer Gravitational-Wave Observatory (LIGO), ramps up in sensitivity.
The LIGO team, working with the European Virgo collaboration, presents its findings from data collected between 2005 and 2007 in a recent issue of Nature. (Scientific American is part of the Nature Publishing Group.)
Vuk Mandic, an astrophysicist at the University of Minnesota and a member of the LIGO team, says the observatory is providing a taste of things to come in the field. "This is the first time that this type of experiment, directly searching for gravitational waves, has reached the sensitivity that is sufficient to start probing cosmology and early-universe models," Mandic says.
LIGO comprises two observatory sites, in Washington State and Louisiana, each of which hosts an L-shaped laser interferometer with four-kilometer-long arms. A laser beam originating at the elbow splits into two and travels down each of the arms, before being reflected back by mirrors at the ends.
A passing gravity wave would temporarily stretch one arm of the detector while squashing the other, and the two beams, having traversed different distances, would be out of phase when recombined.
The challenge facing LIGO researchers is immense—as California Institute of Technology physicist Marc Kamionkowski noted in a commentary accompanying the new paper, gravity wave detectors "require detection of minute changes—a mere fraction of the size of an atomic nucleus—in kilometer-scale separations between free-floating masses."
In order to rule out spurious signals, LIGO has a suite of passive and active noise suppressors to counteract vibrational effects from passing pedestrians or trucks. The mirrors at the end of each arm, for instance, are suspended on pendulums to insulate them from vibrations, and a forthcoming improvement to the observatory (called Advanced LIGO) will daisy-chain four pendulums together to multiply their suppression effects, Mandic says.
Noise from seismic activity, on the other hand, can be suppressed by searching for gravity waves at relatively high frequencies—the LIGO paper sets limits on gravity waves in the band around 100 hertz, or cycles per second, whereas seismic noise is generally below 25 hertz.
By improving on LIGO's past limit by an order of magnitude, Mandic and his colleagues have further constrained the amplitude of the gravity-wave background that emerged from the universe's first moments. That background, like the cosmic microwave background—which affords cosmologists their best estimate of the age of the universe—should be packed with information about the early universe. But gravity waves have a unique value: they carry information about the all-important first minute following the big bang—farther back in time than we can currently probe.
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23 Comments
Add CommentSometimes the lack of proof means it has not yet been found.
Reply | Report Abuse | Link to thisSometimes the lack of proof means the theory is in error.
You can not find something that does not exist but with enough free grant money you can search for a long time..
"In order to rule out spurious signals, LIGO has a suite of passive and active noise suppressors to counteract vibrational effects from passing pedestrians or trucks."
Reply | Report Abuse | Link to thisI'd think that needing such sensitivity they would set up in extremely remote areas where they could start with the smallest amount of disturbance as possible...
The whole --both the design and the theory-- looks remarkable similar to the Michelson-Morley experiment, at least for a layman. I think this interferometer will not work for the very same reason.
Reply | Report Abuse | Link to thisGood observation "Uncertain"; the Michelson - Morley experiment was doomed from the start. The theory had flaws as to the behavior of ether, the design of the experiment was all wrong. The failure of the experiment discredited the experimenters and the concept of ether ( dark matter / dark energy ), set back scientific thought 100 years in that field and set us down this narrow road of quanta search with it's very strange speculations as to the facts.
Reply | Report Abuse | Link to thisYou are correct about ether theory having flaws from the get go. The ether should be categorized as conjecture IMO. However, Einstein equations predict gravitational waves exist and in all cases (except for extreme phenomena such as black hole singularity) his predictions were right on. Comparing conjecture to experimentally verifiable facts set forth by his genius is a fallacy. The Michaelson - Morely interferometer did a great deal by DISPROVING the existence of the ether which has lead to another revolution in Relativity and then Quantum Mechanics. LIGO, unlike Michaelson - Morley Interferometer, is backed by equations that has withstood 100 years of testing. I think the analogy is a bit polarized.
Reply | Report Abuse | Link to thisLuminiferous Aether theory proposes a model, which wasn't never tested in M-M experiment, in fact - a dense elastic fluid, which propagates energy in transversal waves. What M-M experiment disproved was sparse Aether model, which propagates energy in transversal waves, but such model cannot spread light of arbitrary energy density. And such model can explain "absence" of gravitational waves, too . In fact these waves (density fluctuations of vacuum) are forming CMB noise, which are all around us. From analogy with water surface is evident, why we cannot observe gravitational waves in common sense, i.e. like signal of audible frequency. We can observe only irregular changes in CMB noise intensity, which is actually what was observed already.
Reply | Report Abuse | Link to thisI don't think the Michelson-Morley experiment can be characterized as a failure. For one thing, it demonstrated once and for all that the speed of light was constant regardless of the motion of its source. Since this seemed counter-intuitive, it had physicists scratching their heads for a quarter of a century. Einstein was able to solve the riddle when he opined: "If the speed of light is constant, then time and space are not." And with that the great edifice of classical Newtonian physics came crashing down. (Einstein, being a thoughtful fellow, remarked, "Newton, forgive me.")
Reply | Report Abuse | Link to thisUnlike the old idea of an imaginary either in which the Earth and all astronomical bodies drifted through. or were dragged by gravity, which was finally abandoned with the advent of the "Michelson Morley" experiment in 1877, I propose that gravitational fields influence, if not provide , the means of the propagation of light, and that a gravitational field acts as a vibrating medium for light. And so within the Earth's gravitational field, which moves with the Earth, the velocity of light is actually what is measured, namely approximately 300,000 k/sec. Close to say the sun, the velocity of light would be hihger, and thus less as you move further out of the solar system. It will have a maximum value close by such objects as Quasars, and where super-density prevails, and a corresponding minimal value within the far stretches of intergalactic space.
Reply | Report Abuse | Link to thisIn a letter to a friend in 1954, the year before he died, Einstein doubted that physics could be based on the continuous field concept, in which case, quote: &Then nothing remains of my entire castle in the sky, including the theory of gravitation, but also nothing of the rest of modern physics.
Reply | Report Abuse | Link to thisThe only alternative is a discontinuous universe where a universal methodology presents itself that complements traditional approaches to the empirical evidence. Space and time are implicitly defined a posteriori by the synchronous projection of atoms as structurally distinct space frames alternating with timeless quantum frames that constitute a boundless quantum energy field that is orthogonal to the integrated fabric of space-time as we know it. Light comes to us as a series of pulses in each space frame consistent with the Planck constant, the Planck-Einstein relation and the de Broglie wave equation. External linear space is defined by light emission with respect to the internal spherical space of each atom. There is no other universal measuring rod out there. That is why light speed is universal. Where there is no light there is a black hole. Atoms are waves and particles at the same time because each oscillation defines a primary interval of time in the synchronous projection of the physical universe. All relative particulate motion occurs as relative quantum jumps between space frames, so position and momentum can not possibly be known at the same time. The integrated fabric of space time becomes warped by relative motions since they introduce relative space-frame skipping consistent with relativity effects and also with the foundations of quantum theory and wave mechanics.
The Lorentz Transformations derive directly from a unique system of historic coordinates associated with the universal methodology that complements traditional approaches to the sciences. See the website article Gravity, Quantum Relativity & System 3 at www.cosmic-mindreach.com.
In this scenario Gravity is implicitly associated with the primary projection of matter, space frame by space frame from a unified quantum energy field. It is not transmitted as a wave motion through a spacetime continuum, because there is no continuum. It is not transmitted through space and time at all, because it is associated with defining the nature of space and time. It is thus unlikely that conclusive evidence of gravity waves will be found, although there may be local anomalies in the integrated fabric of space-time in severe situations such as rapidly rotating binary pulsars.
If CERN manages to find the Higgs boson, which theoretically tells matter how much it indents the "fabric" of spacetime, does this in any way indicate what the fabric might be?
Reply | Report Abuse | Link to thisI am also at a loss to understand Lisa Randall's idea of gravity leaking over from other dimensions (much weakened) when general relativity really tells us that gravity is not a force at all, but a description of the path that an object possessing mass must follow when it passes other concentrations of mass,
In fact, in following this geodesic a particle never feels acted upon by a force, although it may decelerate and accelerate considerably in either tracing out an orbital ellipse or a drive-by hyperbola, nor is it attracted or repelled. What it is doing is moving as it must move. Our moon has been "attracted" for eons, yet it escapes our planet. Artificial satellites fall into the atmosphere only because scant traces of outer atmosphere rob them of orbital energy. Similarly, objects fall into black holes only because other matter has jostled them in there and certainly for every particle that "falls" into a BH another must be propelled outward never to return.
Indeed, it has always been the case that spacetime somehow knows how much matter has fallen into a BH previously else it (spacetime) would not know how much and how quickly to curve in the presence of a BH. But how does this value get communicated to spacetime from the BH, when no other information can escape it? Does spacetime have 'memory' concerning what has fallen into a BH?
So what "leaks" over from another dimension? Why don't other, stronger forces in other dimensions leak over? Why don't forces leak over in virtual fashion in little chunks of quanta that can only stay for an instant of borrowed time? If that's what they, indeed, do, how does that leaking compose a field through which ripples might pass?
Mike Cook wonders: Indeed, it has always been the case that spacetime somehow knows how much matter has fallen into a BH previously else it (spacetime) would not know how much and how quickly to curve in the presence of a BH. But how does this value get communicated to spacetime from the BH, when no other information can escape it? Does spacetime have 'memory' concerning what has fallen into a BH?
Reply | Report Abuse | Link to thisThe answer to this question, I believe, has to do with the violence done to space and time by the intense graviational field created as a star collapses into a black hole. We believe that matter falling into a black hole quickly reaches the center and is crushed out of existence. However, from our perspective it takes an infinite amount of time for this to happen. Thus the gravitational field of a black hole can be said to be frozen in space and time (spacetime). Consider if a hapless astronaut were to fall into a black hole. From his point of view he would not notice anything unusual happening and would quickly reach the center. However as he passed the event horizon and plunged toward the center billions of years of time would pass on earth. From your vantage point, if you could watch him, he would seem to hang motionless at the event horizon while you would seem to be moving incredibley fast to him.
This does sound a bit preposterous, but black holes also seem preposterous which is why, initially, Einstein rejected the existence of such things.
jayarezed1943 said: Close to say the sun, the velocity of light would be hihger, and thus less as you move further out of the solar system. It will have a maximum value close by such objects as Quasars, and where super-density prevails, and a corresponding minimal value within the far stretches of intergalactic space.
Reply | Report Abuse | Link to thisActually this is not so; at least there is no observational evidence to support it. The speed of light can be slowed down if it passes through a medium such as water or a dense gas, but in the vacuum of space the speed is always 300,000 kps whether or not a gravitational field is present. Gravity can bend a light ray and will alter its wavelength but it can never slow it down.
i think your comment is creative .i 'd like to communicate with you about the physics ideas on universe.I'd like read more about it.could you give me some more detailed passage about this.
Reply | Report Abuse | Link to thisE-mail:wdp1860@126.com.
thank you.
Creative ideas!I am a undergraduate student,I appreciate your comment very much and want to read more.so could you sent me some passages about your universe theory.
Reply | Report Abuse | Link to thismy email:wdp1860@126.com
thank you!
Andy
Some points about black holes at galactic centers in a discontinuous universe:
Reply | Report Abuse | Link to thisThe relative rotational motion of galaxies with respect to one another requires external space frame skipping defined by light at the galactic center with respect to the periphery. This reaches a limit at the black hole where there is no light. If a star is accreted only quantum energy equivalents of its mass remains associated with the black hole via the timeless quantum energy field namely the Void. The externally specific atomic constituents of the star cease to physically exist only at the limit. Nevertheless an orthogonal energy equivalent remains in the Void which is the conjugate reciprocal of physical matter.
There is physical X-ray and infrared evidence that old dense stars are most concentrated near the galactic center and evidence of some being accelerated in an apparent accretion disc. If this has been going on for billions of years one would expect a wall of stars approaching infinite density at the event horizon according to the spacetime continuum perspective of General Relativity. There is no evidence of this.
Outside the black hole the inner space of atoms that constitute suns is skipped only due to their rotational motions. Their rotations maintain them in synchronicity with the synchronous projection of the universe as a whole. This inner skipping due to rotational motion is compensated by fusion processes in their centers that contract space when heavier elements and neutrons are formed. This can be calculated consistent with observations. Stars migrate in a radial direction outward or inward according to their degree of inner space-time contraction which seeks a balance with the external contraction due to the galactic revolution as a whole. The angular velocity of stars is remarkably constant across the galactic radius. Their radial velocity is not.
In this scenario inertial velocity is distinct from gravitational mass consistent with Foucaults Pendulum. The arc of its swings is governed by the fixed stars thousands of light years distant, even though they are fuelled by Earths gravity. The gyrocompass works on the same principle. A spinning top does not fall over. General Relativity equates inertial and gravitational mass but has no answer to why inertial velocity is distinct.
The article Gravity, Quantum Relativity & Cosmic Order at www.cosmic-mindreach.com uses Historic Coordinates to derive the Lorentz Transformations directly. There are four ways to interpret them depending on perspective. They illustrate that in a cosmic context a star accreted into a black hole does indeed cease to physically exist. This is not a matter of infinite regress in a discontinuous universe. Zenos arrow does reach the target. Space and time are quantized.
Nothing unreal exists.--Spock
Reply | Report Abuse | Link to thisAfter reading all the above posts I see greater and greater complexities with no improvement in real understanding.
Reply | Report Abuse | Link to thisEinstein at least tried to create simple explainations for the strange behavour of light speed and gravity.
Mass /inertia is caused by the effects of matter in relative motion within the aetheral ocean on the dark matter /dark energy of the aether.
Mass /inertia is not an internal characteristic of matter but a coupling with the fields and material of aether.
Aether is chaos, matter is organization. KISS
Except gravity does not travel. It exists everywhere instantly. That's why there has been no advance in the understanding of gravity. The approach is flawed and nobody will study, "What is the speed of gravity" even though he answer has been given, as the solar system will not hold together if there is a gravity delay between the sun and the planets.
Reply | Report Abuse | Link to thisGood Luck.
I would like to hear more about the Gravity Probe B experiment and learn if it provided any data that would be relevant to this experiment. I believe that it was supposed to provide information pertaining to curvature and fram dragging. This is a very interesting subject. Good Luck larryk
Reply | Report Abuse | Link to thisI was very intrested in the results of the Gravity Probe B experiment. Its stated perposes were to detect curvature and fram dragging. These two Einstein predictions were to be accieved as a result that was first proposed back in the fiftys. Its accomplishment had to result for the technology to accomplish this experiment. I would like to hear mose about this experiment and if it was relevent to this current endevour. Larry
Reply | Report Abuse | Link to thisthese two
"Gravity is the universal cryptic language of spacetime; a major player in unified field theory, and perhaps much more than we think.
Reply | Report Abuse | Link to thisIt is postulated that Gravitational Waves may be found on earth in addition to outer space, since humans generate frequencies just like astral objects.
In fact, planets, thought, and matter of every shape and size distort spacetime – warping it with gravitational waves that vibrate – expanding or contracting the atmosphere and ionosphere through interaction. This is the Law of Attraction in Action."
EXCERPT from: Solar Plexus: The Secret Gravitational System
ISBN: 1456300474
[Courtesy of Whiffs of Bliss]
Why don't they use three qeosychronous satellites that form a right angle. That would eliminate "noise" and increase the distance between mirrors, so the shift difference would be larger than the size of an atom.
Reply | Report Abuse | Link to thisTrying to take a precise measurement between three satellites even with interferometry could be complicated by high speed cosmic particles that are certainly energetic enough to rattle a satellite a little bit. Then there is pure dust. On Earth this type of jitteriness in the environment gets cancelled out because it comes from every direction. Maybe not so in orbit. . .
Reply | Report Abuse | Link to thisWhat I have been wondering about is the satellite that studies the cosmic microwave background radiation. In theory the CMB should be precisely the same in every direction, and in addition any roughness in it is credited to quantum fluctuations at the start of the universe. But what about a passing gravity wave causing some type of slight fluctuation in the CMB that is the equivalent of directional interference?
Of course, the present satellite on duty is undoubtedly only looking in one direction at a time. It gradually maps out the complete sphere of the edge of the universe. However, if we had multiple detectors simultaneously observing and comparing inputs from every quadrant of the CMB sphere, perhaps we could detect some interesting inconsistencies.