""With the use of microwave-generated sound in a spherical flask of hot plasma, we achieved a gravity field that is 1,000 times stronger than Earth's gravity."
Sulfur gas inside the ball was heated up to a temperature of 5,000 degrees Fahrenheit (that's 2,760 degrees Celsius) to produce sound waves that acted like an extremely strong gravitational pull, generating currents in the hot, weakly ionized gas (or plasma)."
https://www.sciencealert.com/physicists-used-sound-waves-to-give-a-tiny-sun-its-own-kind-of-gravity
"Traditionally when we think of sound waves, we think of invisible vibrations moving weightless through the air - not carrying any mass.
That might be about to change. Physicists have just provided further evidence that particles of sound really can carry tiny amounts of mass."
https://www.sciencealert.com/a-new-study-backs-up-claims-that-sound-waves-really-do-have-mass-after-all
"Sound has negative mass, and all around you it's drifting up, up and away — albeit very slowly."
https://www.livescience.com/63305-sound-waves-negative-gravity-mass.html
"In basic terms, negative mass is the idea that some objects may have a mass that is opposite in sign to their normal positive mass"
https://medium.com/physics-and-machine-learning/what-is-negative-mass-e11d626edffd
"Then a negative mass would be attracted by Earth's gravity but, because of its inertial perversity, would respond to this attraction by falling upward.
Such an argument would, however, lead to a serious conflict with Einstein's general theory of relativity, the beauty and power of which derive from treating the gravitational and inertial aspects of mass, not as essentially different entities, but rather as different sides of the same cosmic coin."
https://www.daviddarling.info/encyclopedia/N/negative_mass.html
Negative Matter Propulsion | [Impossible Inventions]
"Energy is linked to mass via the formula E=mc². Negative energy would therefore also mean negative mass."
"Quantum theory, however, allows negative energy."
https://scitechdaily.com/quantum-vacuum-negative-energy-repulsive-gravity/
"If a “ring” of negative mass could be created around a spacecraft, spacetime could theoretically be contracted in front of the ship and expanded behind, allowing the spacecraft to effectively travel faster than the speed of light."
https://interestingengineering.com/science/ad-astra-the-future-of-propulsion-technology-part-ii
