Why detecting nothing is really something in gravitational-wave project

Vuk Mandic and his colleagues made big headlines in scientific journals last week by finding nothing — nada, zilch, zippo — in their search for gravitational waves.

In order to comprehend why nothing can be something big in astrophysics, we need to look first at the stakes in this quest for gravitational waves.

These mysterious waves were predicted in Albert Einstein’s 1916 general theory of relativity. If mass accelerates in some way — say, you pick up a child or drive a car — you have these ripples in space and time, the theory goes. But we Earthlings are mere specks on a universal scale, so any waves we make are insignificant.

Instead, scientists are looking for the waves in connection with mega-scale cosmic events: collisions of black holes, shock waves from supernova explosions — and the granddaddy of all, the Big Bang.

Vuk Mandic
University of Minnesota
Vuk Mandic

Influence has been observed
The gravitational waves’ influence on stars has been observed. But the waves themselves never have been directly detected. If they were, it would set off a revolution in physics, opening an entirely new way of looking at the universe.

“Black holes, we can’t see at all at this point …  super nova explosions are not understood yet,” Mandic said. “So we hope that gravitational waves would allow us to open another window into astronomy.”

Scientists also believe that the Big Bang created a flood of gravitational waves that still fill the universe and carry information about the immediate aftermath of that colossal explosion. No one has ever been able to study the full fiery nature of the physics at play in the moments following the Bang. In that sense, gravitational waves would have a unique tale to tell, Mandic said.

“Gravitational waves are the only way to directly probe the universe at the moment of its birth; they’re absolutely unique in that regard. We simply can’t get this information from any other type of astronomy,” said  David Reitze, a physics professor at the University of Florida and spokesperson for the collaboration behind this research.

700 scientists, 60+ institutions
With those incentives in mind, scientists have tried for decades to directly detect the waves. In 1997, the National Science Foundation funded a project engaging 700 scientists from more than 60 institutions in 11 countries. Caltech and Massachusetts Institute of Technology designed and operated the project.

Mandic co-chairs a working group in that LIGO (Laser Interferometer Gravitational-Wave Observatory) collaboration. He was the lead author on the first major report of the collaboration’s findings, published last week in the journal Nature.

The report is based on data collected from 2005 to 2007 using instruments called interferometers. The main instruments are located in Hanford, Wash., and Livingston, La.

Interferometer in Livingston, La.
Courtesy of LIGO Laboratory

At those sites, scientists split a laser into two beams that travel back and forth down long interferometer arms. When a gravitational wave passes by, one arm should be slightly stretched while the other is compressed, according to Einstein’s theory, and the beams should reflect the difference.

Two years of research analyzed
In Minnesota, Mandic’s team analyzed data from the two years of research and explored the implications for different theoretical models.

As I said at the beginning of this post, they found nothing.

Now, finally, comes the question of why that is something.

Think of gravitational waves as if they were waves on a pond, coming in different sizes from different directions. Scientists had believed this metaphoric pond was stormy with large, crashing waves.

The findings don’t support that theory. They suggest smaller turbulence, calling for different rulers to measure gravitational waves. In other words, physicists can now rule out some models of the early universe.

“We can start learning what the universe is not like,” Mandic said.

A Hubble Space Telescope Image of Supernova 1994D in Galaxy NGC 4526.
NASA/ESA, Hubble Key Project Team, High-Z Supernova Search Team
A Hubble Space Telescope Image of Supernova 1994D in Galaxy NGC 4526.

New constraints, and parameters for future study
That in itself is a profound discovery, putting new constraints on the details of how the universe looked in its earliest moments.

And it suggests parameters for future phases of the research. Work is under way on an Advanced LIGO, which is to use instruments that are 10 times more sensitive than those available for this study.

At the end of the interview with Mandic, I said “Maybe I’ll call you back in a few years for the story of the actual detection of gravitational waves.”

Said Mandic, “That would be splendid.”

Sharon Schmickle writes about a wide range of subjects, including  science, international affairs and Greater Minnesota.

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Comments (5)

  1. Submitted by Greg Kapphahn on 09/01/2009 - 02:31 pm.

    IMHO, the miracle in this report is that the scientists did not discover what they expected to discover and, rather than lying of falsifying the data to match their expectations, they accurately reported their finding of nothing. Hence, the theories regarding the origin of the universe will change to match what we now know to be reality.

    For many folks over thousands of years, similar miracles happened as the understandings of our religious ancestors regarding the deity, by whatever name we call that deity, changed and earlier writings were reinterpreted (even within the Christian Bible itself, by the Apostle Paul and the writer of the Gospel of Matthew for instance) to match what was now better understood to be the nature of God and God’s relationship with humans.

    For those of all faiths who recognize the limitations of human understanding, the ideas and ideals of their faith change as they comprehend new ways that God is involved with the world. Science such as that described in this article has no conflict with their faith but only broadens and deepens it toward an ever-greater understanding of all that is.

  2. Submitted by Christian King on 09/01/2009 - 04:28 pm.

    Mr. Kapphahn:

    1. Please give specific examples of instances where scientists have lied about findings to match their expectations. If you read much scientific literature, you will find that scientists are skeptics by nature and aren’t prone to lying, about their own work or the work of others.

    2. You state that, “the theories regarding the origin of the universe will change to match what we now know to be reality.” If by this statement you mean that this one experiment disproves the theory of a “big bang,” you are incorrect. There is ample evidence that the big bang occurred; this data shows that it may not have occurred in a way some scientists believe it did.

    3. If your last paragraph is meant to reassure readers that science can never disprove religion, you are probably correct. Stephen Hawking, in his brilliant book “A Brief History of Time,” points out that it will be impossible to ever know what happened prior to the big bang. Future generations may prove him right or wrong. However, he says that this is where God, whatever he/she/it is, may be.

    4.Having said that, please be mindful that it is just as impossible to prove the existence of a deity having any relationship with humans now or in the past, as it is of proving one existed prior to the big bang. Faith is a powerful thing that can give people hope, strength, or meaning; but faith is not proof.

  3. Submitted by georg hausmann on 09/02/2009 - 06:45 pm.

    So far as I remember from the 80-th, we then had learned, two orbiting black holes in 30 km distance with 30 masses of Sun(?) will emitt 30 mikrowatt. ( so called 30-30-30). So arises Question number 1) who will detect 30 mikrowatt in a considerable distance? (not in the near-by galaxies). Question number 2) Remember the Michelson Experiment. The constance of “Velocity of Light” however actually performed for other theoretical questions, results in the non-detectability of gravitational waves. Time AND whatever this means “SPACE” are shuttered in such a way, so nobody can detect any change. Until today no other explanation is available. Maybe there is a deviation from General Relativity, then we will find this interesting effects.
    Yours GH

  4. Submitted by Jim Spensley on 09/02/2009 - 06:53 pm.

    The story says, as I read it, that gravitational wave is detected by LIGO becasue the laser source or a mirror at the leg ends is moved because one leg the metal tube/pathway is shortened or lengthened compaered to the other.

    I think that isn’t the case, rather the gravitational wave contracts or extends space-time, causing a small difference in the transit time and a change in the interference pattern.

  5. Submitted by Sharon Schmickle on 09/03/2009 - 07:28 pm.

    Jim, Here’s what the LIGO website says about your question:

    Gravitational waves are ripples in the fabric of space-time. When they pass through LIGO’s L-shaped detector they will decrease the distance between the test masses in one arm of the L, while increasing it in the other. These changes are minute: just 10-16 centimeters, or one-hundred-millionth the diameter of a hydrogen atom over the 4 kilometer length of the arm. Such tiny changes can be detected only by isolating the test masses from all other disturbances, such as seismic vibrations of the earth and gas molecules in the air. The measurement is performed by bouncing high-power laser light beams back and forth between the test masses in each arm, and then interfering the two arms’ beams with each other. The slight changes in test-mass distances throw the two arms’ laser beams out of phase with each other, thereby disturbing their interference and revealing the form of the passing gravitational wave.

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