This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Unlike electric charge, as far as we know all mass is positive, and positive masses attract one another. Could negative mass exist, and if so, what would be the ramifications?
Antigravity between a positive mass and a hypothetical negative mass has received a fair bit of attention in both physics and science fiction over the years. For example, in 1901's "First Men in the Moon" author H. Wells imagines a substance he calls "cavorite" which creates a negative force of gravity and thus acts as a gravity shield.
In Newton's theory of gravity, negative mass would effectively appear as his same equation but with the gravitational constant G replaced by -G. But Einstein's version of gravity, general relativity, is not so kind, and does not seem to consistently allow anti-gravity. In a new paper in Physics of the Dark Universe, Shin'ichi Nojiri from Japan and S.D.
Odintsovc from Spain dig deeper into the possibility of negative mass objects (NMOs) and conclude that the idea may not be as exotic as is thought. Using theoretical tools, they show that negative mass "does not always lead to any inconsistency." Mass comes from a particle's interaction with the Higgs field, and most of a particle's mass is actually binding energy (remember Einstein: m=E/c2) between its constituents. Protons, 1,836 times more massive than electrons, are composed of three quarks and gluons bound together.
The quark masses are only about 9% of the proton's mass, according to lattice gauge theories of quantum chromodynamics. The rest comes from the field energy of gluons that mediate the dynamics inside the proton. The authors begin by noting that a bubble in water effectively acts as a negative mass: "The bubble behaves as if it has a negative mass because the water around the bubble falls [away] due to gravity." They then consider a world with a positive point mass (such as a compact star) in a "fluid" with negative pressure, such as dark energy, with a negative cosmological constant. (In reality, the cosmological constant—proportional to the vacuum energy of the universe—is positive but very tiny.) The fluid alters this from a simple positive-negative mass system.
They argue that due to the negative pressure, the positive point mass pushes away the fluid. Therefore, stable regions of negative energy density would exist. A simple version of Einstein's equations of gravity, just one step beyond Newton's Universal Law of Gravity, finds that the NMO will impart a repulsive force to the positive mass object.
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