Gravitational Radiation: Is it a Smoking Gun?

New science experiments are underway or in the prelaunch phase that seek to identify elusive gravitational radiation. Gravity doesn't just refer to our planetary variety that gives us weight and keeps us firmly attached. It refers to all the gravitational forces of the universe, which it seems are the most difficult to define because they are the weakest of the four Standard Model forces.

One of the quests of science today is to identify this universal gravitational force, or radiation, and learn its properties. This is necessary for the accomplishment of a Theory of Everything (TOE). When inflation theory was first developed, cosmic gravitational radiation was hypothesized to be the tell-tale evidence of inflation theory itself, the so called "smoking gun" proof of inflation theory. It was hypothesized that the gravitational force could be isolated and identified by its effect on the cosmic microwave background (CMB), as it would manifest itself as polarize light after intersecting with the CMB.

Now Lawrence Krauss, the Ambrose Swasey Professor of Physics and Astronomy at Case Western Reserve, along with colleagues Katherine Jones-Smith and Harsh Mathur, offers evidence that there is another mode by which this polarized light might be created, that being through the emanation of gravitational radiation from a different source other than the original inflation of the universe.

According to inflation theory, the creation of the primordial soup that eventually became a universe created of matter as opposed to antimatter (which is known to have a weight slightly less than matter), emitted a vibrational sound wave that eventually became a mere background vibration in the microwave range. This is called the cosmic microwave background, or CMB.

Inflation theory holds, in accord with Einstein's Theory of General Relativity, that when primordial pools of new mass originally moved in space, gravitational waves were formed, which were ripples in space-time that were caused by that movement. It is these gravitational waves that intersect with the CMB (which was formed after the gravitational wave background (GWB)) and produce polarized light, the signal of which can theoretically be detected with instruments like the Laser Interferometer Gravitational Wave Observatory (LIGO) in Livingston, LA. This source of gravitational radiation, the expected smoking gun of inflation theory, constitutes Scenario 1 for defining the source of polarized light.

But now, according to Krauss's research, there is more to consider in the search for the source of gravitational radiation that produces polarized light. Also at the beginning of the universe, scalar fields (energy fields that cannot be resolved into component parts) came to be aligned with disparate parts of the inflating universe. In time, as the universe slowed down and scalar fields spread out, these scalar fields came into contact with each other, each having its own angle of alignment to a portion of the universe. When two scalar fields come into contact, "symmetry breaking" occurs whereby the symmetry of the fields is interrupted and they unite as one field with a new orientation of alignment. During this process of symmetry breaking, the unifying scalar fields emit gravitational radiation that has the same properties as inflational gravitational radiation. The difference, of course, between the two gravitational radiations is the source and means by which they are produced: inflation versus scalar field symmetry breaking.

This Scenario 2 gravitational radiation can also intersect with the CMB. When it does so, it also emanates polarized light (light which in a plane exhibits different properties in different directions), just like inflational gravitational radiation does.

The scientific significance of this redundancy of polarized light is that when the Planck satellite, which is supported by European Space Agency (ESA) and set to launch in 2009, or the LIGO, which is actively searching for CMB polarized light at the present time, find polarized light produced by the intersect of the CMB and gravitational radiation from the GWB, it may no longer be viable to assume that the polarization is the result of inflational gravitational radiation. Thus the detection of polarized light may not lead to the unequivocal proof of inflation theory as was thought to be the case when these experiments were developed. Any successfully detected polarized light may be the product of scalar fields' relaxation gravitational radiation instead of inflational gravitational radiation.

A correlated question that Krauss's new research raises is whether the scalar fields as discussed have any definitive relation to inflation theory that would possibly posit two smoking guns for inflation theory instead of only one. Much about our universe may be learned through the continued and upcoming data collection of LIGO and Planck.

Resources and Further Reading:

http://www.sciencedaily.com/releases/2008/04/080415143816.htm

http://www.sciencedaily.com/releases/2002/10/021029070349.htm

http://www.sciencedaily.com/releases/2007/01/070130122115.htm

http://www.sciencedaily.com/releases/2007/01/070108145818.htm

http://www.rssd.esa.int/index.php?project=planck

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