How to create gravity

Einstein’s theory of relativity has taught us that gravity is a force created deformities in a fabric known as ‘space-time’, and that individual objects do not contain ‘gravity particles’ but rather exert a force on each other via this attraction. This implies that one cannot artificially create gravity. Or can we?

In a new paper (published December 2015), Andre Fuzfa of the University of Belgium shows that by using superconducting magnetic coils, a slight phase shift in light could be observed. As this shift occurs in the presence of gravitational waves, Fuzfa’s idea would essentially create gravityHow?

I would like to stress that this paper follows the principle of the gedanken, or thought experiment. Einstein loved this idea and used it very frequently when trying to decipher complex scientific problems. For example, the equivalence principle– which states that one cannot distinguish physical effects between gravity and acceleration in a closed system- was formed when Einstein considered a person inside an elevator in free fall. This person wouldn’t be able to know whether gravity was pulling him down or not. The equivalence principle also hinted that light would be affected by gravity in a similar way- indicating that gravity was a geometric phenomenon, rather than an attractive one.

elevator_photon
Diagram of equivalence principle. Since in a closed system, an accelerating frame and a gravitational field are indistinguishable, similarly light does not travel in a straight line. Source: University of Oregon

Fuzfa actually used the equivalence principle to show that with a large enough magnetic field, light experiences a phase shift when passing through. These shifts, as mentioned earlier, are the result of curves in space-time, which arise from gravitational waves. The key lies in the geometry of the device generating the magnetic fields- Fuzfa’s idea involves arbitrary large (10^4 A) currents flowing through finite loops/solenoids. The space-time curvature largely occurs along the inside of the loop, and interestingly longer solenoids lead to greater space-time deformation.

The key, of course, is the experimental setup. The difficulties mainly lie in, as you probably guessed, the detection of the tiny phase shift. Fuzfa suggests that with many passes of light through the superconducting solenoid, the phase shift actually accumulates and becomes noticeable for modern detectors. Breaking down the numbers:

Proposed experiment

  • 10 stacked Helmholtz coils
    • Each with two superconducting solenoids, length of 2.5 m and opposing current of 20 kA and separated by 2.5 m.
  • Michelson interferometer (laser) arm of 50 m
  • 20T magnetic field at center of the external solenoids
  • Light phase shift: ΔΦ/round trip ~ -1.56*10^-25
  • Accumulated ΔΦ over 200 days ~ -1.08*10^-11 -> detectable by grav-wave observatories

So after 200 days, one can expect to finally observe a detectable phase shift in light caused by gravitational waves. Not to mention the fact that a very long interferometer would need to be powered for this time period, and that the light needs to be trapped inside the device long enough for detection. But hey, the prospect of controlling gravity itself is exciting to test it out. Any takers, world?

Equivalence principle

IBT: Original link to article

 

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