Prof. Claudia de Rahm's theory of 'Massive Gravity' to explain Dark Energy is getting a lot of press as of late. So let's dig into it. (thread: 1/n)https://www.theguardian.com/science/2020/jan/25/has-physicists-gravity-theory-solved-impossible-dark-energy-riddle …
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Before getting to gravity, recall that forces are transmitted by a 'mediator' which are always bosons EM: the photon, strong force: gluon, weak force: W± & Z. When the symmetry corresponding to the force carrier is unbroken the force carriers are massless (m=0). (2/n)pic.twitter.com/7Y38aPPQOa
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What about Gravity? The symmetry corresponding to gravity is the most respected symmetry in all physics & goes by many names It's the one underlying Einstein's General Theory of Relativity: General Covariance/Gauge-Lorentz Symmetry/ Diffeomorphism Invariance (3/n)pic.twitter.com/Y5DyRN2qMg
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Because this symmetry (General Covariance) has never been observed to be violated, physicists were convinced that the gauge field corresponding to gravity corresponded to an exact, unbroken symmetry I would then immediately follow, then, that the graviton is massless
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But wait!, says de Rahm.. Perhaps Lorentz symmetry could just be an *approximate* symmetry of nature This would happen if the graviton (hμν) has a mass--mass terms for gauge fields always break gauge invariance But!.. look at the first tweet.. (5/n)pic.twitter.com/cgEyMtE73l
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Boom! We see that the graviton (metric; hμν) contains the exponential potential we expected! TL;DR: If the graviton has a mass~hubble rate (H), then large scale gravity can act repulsive and reproduce the Dark Energy observations, with no Dark Energy at all! (n/n)pic.twitter.com/bN8NKU4jAp
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it's probably a cutoff or a regularization factor or something, i'm not sure
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