Those were the headlines two weeks ago in various forms, announcing that gravity waves, a key aspect of Einstein’s General Theory of Relativity, had been detected. Rather than publish this article then, I waited to see what the scope and breadth of the reporting would be and the various reactions to it. Conspiracy theorists were out in force with this announcement with reactions to the published study spanning the entire spectrum from scholarly, insightful articles to utter nonsense. From the “It would be really funny if it weren’t so sad” or the “you can’t make this stuff up” departments, there are those who still believe the earth is flat (really, these people are out there and, what’s so sad, they have websites and a following) and that
Gravity Waves Are a Scam to Defraud the Public
There were many stories to choose from the “utter nonsense” department but this one was one of the worst (err, funniest) of all of them.
Announcements of groundbreaking discoveries in science should always be received with skepticism; witness the near apoplectic reaction of the worldwide scientific community in 2011 when it was announced by more than one group of researchers at CERN that superluminal neutrinos were observed; that is, neutrinos were observed to be traveling above light speed, something that would contradict a fundamental aspect of Special Relativity. The far-reaching implications of that experimental outcome, if it were proved to be true, can only be imagined. When it was later determined that a defect in the fiber optic cable transmitting the OPERA data was the root cause, a collective sigh of relief was breathed by all. That the discovery of gravitational waves by the LIGO Collaboration is the culmination of 40 years of work from over 1,000 scientists in 16 countries is a testament to the veracity and authenticity of the discovery and that it is above reproach; the extent of the collaboration and input from an expansive worldwide consortium of scientists unequivocally dismisses the notion that this discovery is a contrivance, a grand deception or a hoax, something that has been suggested by some.
General Relativity is Einstein’s theory of gravity, compared to Newton’s Universal Law of Gravitation. Newton’s ULG described the behavior of objects under the influence of gravity, the “how” of gravity. It perfectly describes most of the macro behavior of objects under the influence of gravity. The “why” of gravity, by his own admission, Newton was perfectly content to relegate to the “Invisible hand of God”, the “God of the Gaps” and thus, Newton made no hypothesis in that direction. So well does ULG describe and predict gravity and its effects that the unseen presence of Neptune was deduced from the orbital perturbations of Uranus. Newton’s ULG describes gravity as a mutually attractive force whose magnitude is proportional to the product of all the masses and inversely related to the square of the distances separating them. There were some (not many) observations that defied explanation using standard Newtonian dynamics; one famous example, known to Newton and defying explanation until GTR, was the precession of Mercury’s perihelion (the point in Mercury’s orbit about the sun that is closest to the sun) at a rate of 43 arc-seconds per century.
“Why” do objects gravitate to each other, an attraction that varies according to the product of their masses and inversely as the square of the distance between them? This “why” of gravity can be easily understood if we imagine space and time as a fabric with the behavior of all objects and systems subject to the curvature of that fabric with the magnitude of the local curvature dependent on the masses of the objects. For example, the earth orbits the sun because it follows the curvature of the local space in the vicinity of the sun. The greater the mass of an object, the steeper the curvature. For anything to “climb out of the gravity well” created by a black hole, to “escape its gravity”, it has to be outside the Schwarzschild radius (the “Event Horizon”) for that black hole, something that is dependent on its effective mass. All aspects of gravity, its “why”, are easily explained with GTR; for example, what of the seeming instantaneous response of one object in orbit around the other? How is it that both objects respond to changes in the relative location of one or both of the objects? In a classical sense, this would necessarily suggest some invisible force connecting the two and propagating at infinite speed affecting the change. Not if one imagines both of them moving in a mutually distorted local space, both objects moving according to the specific, local curvature; there is no need for infinite speeds, invisible forces or connections.
GTR has had fundamental implications on our understanding of the large-scale universe. The concept of a Black Hole, an entity whose gravity is so intense that not even light can escape its clutches, was first introduced in GTR. A massive star, usually in excess of ten solar masses, ends its life in a catastrophic explosion known as a Type II supernova. The “remnant” can form a rapidly rotating neutron star, known as a pulsar or, if the progenitor star was massive enough, a Black Hole. In an event known as a hypernova, the star may avoid the cataclysmic explosion of a Type II supernova entirely and collapse directly to a black hole if the the progenitor star approaches 40 solar masses.
The first modern solution to general relativity that would characterize a black hole was found by Karl Schwarzschild in 1916. In the classical sense, a wave is the transmission of energy whose velocity is the product of the wavelength and frequency with the amplitude representing the energy. As postulated in GTR, any disturbance in space-time would be propagated omnidirectionally at the speed of light in the form of “gravity waves”. Examples of such objects or systems that would disturb space-time would be the merger of two galaxies, the merger of two black holes, the close orbit and/or merger of binary white-dwarf or neutron star systems or a parasitic white-dwarf binary system, to name just a few. The published study describes the final moments in the merger of two black holes, one 36 solar masses and the other 29 solar masses, to form a black hole with a total effective mass of 60 solar masses. Detected on 14 September, 2015 and identified as GW150914, the merger occurred over 1.3 billion years ago in a distant galaxy located in an expanse of Southern sky, resulting in an equivalent energy loss of 3 solar masses. That energy loss was omnidirectionally propagated across the universe in the form of a gravity wave to be detected by both LIGO observatories in Hanford, Washington and Livingston, Louisiana. Both signals were superimposed, one upon the other, and subsequently transduced into what has become known as the “Chirp Heard Across The Universe“.
Black Hole Merger
That both observatories detected the phenomenon speaks to the observation’s veracity as an authentic detection of gravity waves. Using the same technique as current GPS technology to determine location, the location of the merged black hole was determined to be in the southern sky through the slightly different arrival times of the two signals received at Hanford and Livingston, respectively. Gravity waves are ripples in the curvature of space-time but others would characterize them as whispers heard across the universe. According to CalTech’s Kip Thorne, a world renowned theoretical astrophysicist whose group at CalTech was instrumental in the development of LIGO and its theoretical underpinnings, they represent a storm in space-time. Caused by perturbations in the fabric of space, they radiate outward from the source as gravitational waves transporting energy in the form of gravitational “radiation”. Einstein himself stipulated that the amplitude of any gravity wave would be vanishingly small and beyond detection and thus, sidestepped any discussion regarding their detection. That we have detected them is a testament to just how far we’ve advanced technologically in the intervening 100 years since he published his General Theory of Relativity.
Up until this month, the electromagnetic spectrum provided the only portal through which we could “see” or “observe” the universe around us. Outside of our ability to “hear” sound waves, the electromagnetic spectrum provides the only means by which we can sense and interact with our surroundings, be they local or across the universe. Whether we observe in the radio, infrared, ultraviolet, infrared, optical or any other region of the electromagnetic spectrum, it was always through that broad spectrum, albeit quite expansive, that we could “see” the object of interest. Now, with the successful detection of gravity waves, that has changed and a brand new ability to “see” or “sense” the universe is available; a new “window” has opened.
The LIGO (“Laser Interferometer Gravitational-Wave Observatory”) project consists of two identical observatories in Hanford, Washington and Livingston, Louisiana with major collaborative centers at CalTech (home of the late theoretical physicist Richard P. Feynman) and MIT (Advanced LIGO and The LIGO Group) as well as other institutions nationally and internationally. To minimize vibrations and interference, the “observatories” are remotely located far away from any major urban centers. Each supports an optical interferometer whose perpendicular legs are each 4 km in length. In order to detect and magnify the inconceivably small amplitude of a gravity wave and its effect on the shape of the earth, the laser beam is reflected along each 4 km leg of the interferometer 200 times; with each pass of the beam, the minute phase shift [of the beam] is amplified to the point where the change in earth’s shape (from the gravity wave) can be detected. The LIGO Interferometers are the most precise rulers ever engineered. They need to be as the sensitivity required has to detect perturbations in space-time caused by GW150914 as ripples whose gravitational-wave phase shifts changed the 4-km length of each LIGO leg by one ten thousandth the width of a proton (1×10^-18 meters), a change proportionally equivalent to changing the distance to the nearest star outside the Solar System by one hair’s width.
For those who would like to contribute to the ongoing research into gravity waves, a brand new and exciting window on nature and the universe, can do so by participating in Einstein at Home, a member project of BOINC (Berkeley Open Infrastructure for Network Computing). By installing the BOINC project manager on your computer (versions available for mobile, Mac, PC and Linux), freely downloadable from the University of California at Berkeley, then choosing the Einstein at Home project among the many others available, you can lend your idle computer time to data crunching and reduction so essential for the project and an important aspect to any ongoing research project. After an initial configuration, all BOINC projects are fully automatic with minimal interaction required by the user.
LIGO, Advanced LIGO and the discovery of Gravitational Waves were made possible through funding by and support of the US National Science Foundation (NSF). Many have questioned the benefits of detecting gravitational waves outside the strictly academic aspects of the discovery. Those same kinds of questions arose during the second half of the twentieth century with regard to cutting edge scientific research, the manned landing on the moon, manned space flight and the exploration of space in general. The answer to those questions was the same then as it is now: you can’t put a price on discovery, innovation and the growth of new technology, necessarily brought forth by a specific goal or requirement. The technology required to detect gravitational waves is cutting edge and will eventually be deployed across all sectors of society, the benefits of which can only be imagined now. You cannot and should not put a price on imagination, inspiration and innovation; the inspired mind and soul of a young person is the best gift we can give to the next generation, the future and to all of humanity and should never be diminished. There is nothing more exciting and rewarding than the discovery of something new for yourself and the inspiration that brings to others when you share it with them. This discovery will inspire generations of students and provide research opportunities for decades to come.
Along with representatives from the NSF, representatives of the LIGO scientific collaborations from CalTech (Dr. David Reitze), Louisiana State University (Dr. Gabriella Gonzalez, originally from Cordoba, Argentina) and MIT (Dr. David Shoemaker) appeared yesterday (24 February, 2016) before the US House Committee on Science, Space and Technology: https://science.house.gov/legislation/hearings/full-committee-hearing-unlocking-secrets-universe-gravitational-waves
Their remarks can be watched in their entirety at https://www.youtube.com/watch?v=mrvnnMQsUck
“Imagination is more important than knowledge”
An index of all articles in this blog can be found here.