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Adventure to Madventure - An interview with Dr. Stanley E. Whitecomb

"Adventure to Madventure"
GRAVITATIONAL WAVE

Dr. Stanley E. Whitecomb
Chief Scientist, Laster Interferometer Gravitational Wave Observatory Laboratory

 

Dr. Stanley E. Whitcomb is currently the Chief Scientist of the Laser Interferometer Gravitational-wave Observatory (LIGO) Laboratory. The LIGO Lab is operated by Caltech and MIT through funding from the National Science Foundation.He is one of the advisory committee member for INDIGO.


Fig: Stanley E.Whitcomb


I have met Stan during my  QIP school on “Optics of Gravitational Wave Detectors” organized by Centre for lasers and Photonics, IIT Kanpur.After that I used to mail him to clear my queries and this contact enabled me to interview him for this article.

 

About Gravitational Wave

Gravitational waves are one of the best forecasts of Einstein's hypothesis of general relativity. They are swells in the ebb and flow of space-time that engender as a wave, voyaging outward from the source.In mean time Gravitational waves can't exist in the Newtonian hypothesis of gravitation, in which physical communications propagate at infinite rate. At the point when monstrous items move, the curve of space-time must change to take after their new positions. It requires significant investment for space-time to respond, as data can just proliferate at the pace of light. They are same as there would be swells on a lake if you disturb the surface. These swells in space-time are called  gravitational waves.

There is a continuous push to identify gravitational waves utilizing interferometers on the ground and in space, and through precise timing of pulsars. These perceptions can possibly change our comprehension of astronomy, cosmology and major physical science.


How Gravitational Waves are generated?

  • Galactic compact binaries
  • Black hole mergers
  • Extreme-mass-ratio in-spirals
  • Due to Neutron stars collision,etc.


Wave length of Gravitational Wave

 

Credit:NASA
The gravitational wave spectrum, sources and detectors

 

Gravitational Wave Detectors

 

Gravitational detectors around the world
Credits: IIT Madras (Photonics Department).

Gray -> Installed GWdetectors
Yellow -> Upcoming GWdetectors.

  • LIGO-USA
  • GEO-Germany
  • Virgo-Italy
  • TAMA-Japan
  • INDIGO-India

 

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1)    What is the difference between Gravity waves and Gravitational wave?
Gravitational waves are related to Einstein's General Theory of Relativity.  They are a distortion of space time that oscillate at a given frequency (determined by the particular source), and they travel at the speed of sound.  They do not need any medium (except space itself) to propagate in.

 Gravity waves are a type of wave in fluid mechanics.  They are commonly found at the surface of the ocean and in the atmosphere. They are called gravity waves because the restoring force that causes the wave action comes from the force of the earth's gravity. They travel at sub-sonic speeds (less than the speed of sound).


Q2)    Why there is disarray about gravity waves and gravitational wave among individuals?
When I first started working on gravitational waves, we made a special effort to always use the term gravitational waves, and never to call them gravity waves, for fear of creating confusion. However, as more and more people began to join the field, and as many non-scientists (for example, journalists) started to write about the field, many people became a bit sloppy about the language, and started to call gravitational waves "gravity waves".  I suspect that they felt it was a simpler term that non-scientists would understand better, or maybe they just liked that it was shorter to say or to type.

 In any event, it is now increasingly common to refer to gravitational waves as "gravity waves" in casual conversation, and to be honest, I don't think it has caused the confusion that we feared in the early days.  I personally almost never call them gravity waves, but that is mostly a long-standing habit for me.


Q3)    Can we use LIGO to detect Gravitational wave and Gravity waves?
As for the question whether you could use LIGO to detect gravity waves (the fluid mechanical ind), the answer is no, it would not be a suitable detector, but there are many other kinds of detectors that can be used depending on the medium in which the gravity waves are moving.  But you will see people who will say that LIGO will see "gravity waves" but what they really mean is gravitational waves.


Q4)    Is there is any relation between Gravitational wave and climate
The effects of gravitational waves on ordinary matter are so weak that it is safe to say that they have absolutely no effect on climate or weather on the earth.I have heard that there are people who claim that they may be connected to earthquakes, but there is no evidence to support this claim, and much evidence to reject it. 


Q5)    Does any of Gravitational wave detectors identified the wave?
To date, none of the experiments to detect GWs (including LIGO) have made a direct detection that has been accepted by the general scientific community.  LIGO has not seen anything that we believe is a GW, though we are hopeful that this will happen in the next 2-3 years.


In the late 1960's, a scientists named Joseph Weber made a claim that he had detected GWs using a type of detector known as a "bar detector".  This announcement excited a lot of people, who tried to reproduce his results, but even with more sensitive detectors, they were unable to do so, and the scientific community concluded that he had made errors in his experiments and in the way he analyzed his data.


More recently an experiment called BICEP2 made an announcement that they had observed  GWs from the Big Bang in the pattern of polarization of the Cosmic Microwave Background.  However, more work has revealed that they did not take into account all of the experimental  factors, and their result has been widely discounted.

  LIGO credit :www.sciencemag.org on March13,2015


There is one convincing observation of GWs.  Joseph Taylor and Russell Hulse discovered the Binary Pulsar (a system of 2 neutron stars orbiting each other).  By careful monitoring of the orbit, they have seen that the system is losing energy at exactly the rate that General relativity predicts due to GWs.  This is a very strong evidence for GWs, but it is usually called an "indirect detection" because it relies on observing the energy balance of the system rather than directly observing the effects of the GWs.  Hulse and Taylor won the Nobel prize for their discovery.


Q6)     On the off chance that it totally identified will some effectively proposed  hypothesis will go wrong or what is the ticket behind to build such sort of gravitational identifiers in distinctive parts of earth.
The impact of the detection, when it comes, will depend on what is measured.  It is possible that the characteristics of the waves which are measured by the LIGO detectors will not match the predictions of General Relativity (for example the polarization or the speed of the waves), and this would be a strong indicator that General Relativity is wrong in some way.

 The more likely outcome is that the properties of the waves will match what is predicted by General Relativity, which would make the observation of GWs a strong confirmation of General Relativity.

 The main reason for having detectors in different parts of the earth is to identify where the waves are coming from and measuring their polarization more completely.  In the same way that a larger astronomical telescope has better resolution than a small one, a larger GW detector network provides better resolution in locating the sources than a smaller one.

Q7)    How can satellites be used to identify Gravitational Waves in Space?
There have been several proposals for space-based gravitational wave detectors.  The one at the moment which shows the greatest promise is called eLISA.  It involves 3 satellites in orbit around the sun, and would be sensitive to gravitational waves at lower frequencies than LIGO.  It is still under development, with a tentative launch date of 2034.


Fig:2 Various Gravitational Wave detectors around the world credit:IITMadras(Photonics Department)

Q8)    What is the Significance to install Gravitational Wave detectors in India
The main importance of the LIGO-India detector is to increase the usefulness of GW observations, as I discussed in the answer to question 6 above.

However, there are several other benefits.  GWs is one of the fast growing areas of astrophysics, and participating in it will help Indian physicists and astronomers to be a part of a world-leading area of astrophysics.  It will increase the visibility of Indian science in the world community, and could help to foster future scientific collaborations in other areas.  By raising the profile of the Indian science community, it will help Indian students who want to study abroad and help India to attract foreign researchers to India.

 The technology behind LIGO is at the cutting edge of experimental physics, and the participation of Indian scientists in LIGO will increase their skills in lasers, optics, precision mechanics, servo-control systems and many other areas.  These technologies can be applied to many areas outside of pure research, and thus may boost the Indian economy.

Q9)    What are all the new technology in Indigo compared to other detectors
The plan for LIGO-India is that the LIGO Laboratory (in the US) will provide all of the components needed to build an Advanced LIGO detector.  Thus the LIGO detector will be identical to the ones in the US, and will not require the development of any new technology--it will be new for India, but shared with the other LIGO detectors.

 

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Author
Ms. Kokila
Amrita University, Coimbatore
Intern, Indian Space Station

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