Does antimatter fall up?

So, why do like electical charges repel and unlike electrical charges attract, while like mass ‘charges’ attract? How would negative mass particles behave if they exist?

According to quantum theory, forces like gravity and electromagnetism are the result of particles exchanging force carrier particles. For gravity, this force carrier is the graviton[0], and for electromagnetism, the photon. The photon is a spin-1 particle; it has 1 unit of angular momentum as a quantum mechanical property (photons don’t really spin in the classical sense). The graviton is a spin-2 particle; it has twice the angular momentum of the photon. It turns out that for forces carried by odd spin particles, such as spin-1 particles, like charges repel and unlike charges attract. So the negatively charged electron repels other electrons but attracts the positively charged proton. For forces with even spin carriers, like the spin-2 graviton, like charges attract and unlike charges repel! So, like mass ‘charges’ will be gravitationally attractive, and for normal matter that means the gravitational force is always attractive. If a negative mass object exists, it will be repelled by normal matter. But where can we find negative mass objects? We’d need some exotic form of matter.


Antimatter, composed of antiprotons and antielectrons, may have negative mass. I’ve always been curious about this, and today I found an experiment that will test antimatter to see if it is repelled by normal matter. This will answer the old question Does antimatter fall up?

AEGIS is that experiment at CERN. The idea is to make antihydrogen (composed of a positron and antiproton), taking care to keep it from annihilating on contact with ordinary matter, and measure it’s gravitational response to the Earth. No matter the answer, it will be an interesting experiment!


[0] The graviton remains unobserved in isolation, but the success of quantum field theory lends a lot of weight to the proposition that the graviton exists.

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