Thursday, May 11, 2023, 16:00
WBGB/019
Jürg Dual, ETHZ
Abstract:
With the planning of new ambitious gravitational wave (GW)
observatories, fully controlled laboratory experiments on dynamic
gravitation become more and more important. Such new experiments can
provide new insights in potential dynamic effects such as gravitational
shielding or energy flow and might contribute to bringing light into the
mystery still surrounding gravity. Here we first present a
laboratory-based transmitter-detector experiment using a vibrating beam
as transmitter and a 42 Hz, high-Q bending beam resonator as detector.
Then we will focus on two rotating bars as transmitter. Using a highly
precise phase control to synchronize the rotating bars, a dynamic
gravitational field emerges that excites the bending motion with
amplitudes up to 300 nm/s or 1nm, which is a factor of 1500 above the
thermal noise. The two-transmitter design enables the investigation of
different setup configurations. The detector movement is measured
optically, using three commercial interferometers, individually
calibrated.
Acoustical, mechanical, and electrical isolation, a temperature-stable environment, and lock-in detection are central elements of the setup. The periodic moving load response of the detector is numerically calculated based on Newton's law of gravitation using three methods showing excellent agreement with measurements. We can currently determine G with an accuracy of about 10-3. The near field gravitational energy transfer is 1025 times higher than what is expected from GW analysis.
[1] Brack, T., et al. (2022). Dynamic measurement of gravitational coupling between resonating beams in the hertz regime. Nature Physics, 18(8), 952–957. doi:10.1038/s41567-022-01642-8
[2] Brack, T., et al. (2023). Dynamic gravitational excitation of
structural resonances in the hertz regime using two rotating bars.
arXiv. Retrieved from https://arxiv.org/abs/2301.01644 doi:
10.48550/ARXIV.2301.01644, in review with Communications in Physics,
2023