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The Proton Is Lighter Than We Thought (sciencemag.org)
sciencehabit writes from a report via Science Magazine: You can't weigh the universe's smallest particles on a bathroom scale. But in a clever new experiment, physicists have found one such particle -- the proton -- is lighter than previously thought. The researchers found the mass to be 1.007276466583 atomic mass units. That's roughly 30 billionths of a percent lower than the average value from past experiments -- a seemingly tiny difference that is actually significant by three standard deviations. The result both creates and clears up mysteries, and could help explain the universe as we know it. The findings have been published in the journal Physical Review Letters.
The mass is important. Even in something like the energy levels in hydrogen. The mass of the nucleus is used to calculate the so-called reduced mass of the electron. If a sample of pure protonic hydrogen is used, that means that one is using the mass of a proton in the formula. Although at 30 billionths of a percent difference, I'm guessing the difference can't be seen in spectral lines.
Mass isn't only used for gravitational effects. It determines the inertia of bodies, so this can conceivably affect coupling constants, depending on how they are defined. Also, in electroweak theory, using the mechanism of spontaneous symmetry breaking, coupling constants are introduced to generate particle masses.
The mass doesn't turn into anything. It just turns into photons (or other particles). The photons themselves are energetic disturbances in the electro-magnetic field which carry a momentum. Think of a long, stretchy, string and the photon is just a ripple on it. Does the ripple have mass? It's just a part of the string! But if you touch the string, you'll feel the ripple moving through because the momentum interacts with you and it feels like something is there.
The speed of light is the same as the speed of sound. What limits sounds waves traveling through a medium? It's governed by the rate at which the particles in the medium can interact. The speed of light is simply the limit at which information can travel through quantum fluctuations. It's not really the speed of light, it's the speed of information propagation, of which light is a very simple example. If it were infinite, all events would be simultaneous. Anything less than infinite allows for units of time and causal order regardless of the overall rate of change because it will now take a non-zero amount of time to move through any given space.
At least that's how I think about these things...