- 2585 - ATOMS - massless particles control the Universe? Massless particles are the smallest particles that we can think of. What could they possible have to do with astronomy? These massless particles are completely stable they do not lose their energy decaying into pairs of less massive particles. Because all their energy is kinetic, they always travel at the speed of light. Traveling at the speed of light don't actually age. A photon is actually not aging relative to us. It is timeless.
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-------------------- 2585 - ATOMS - massless particles control the Universe?
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- How can you have a particle with no mass? Sometimes the word “mass” is used interchangeably with the word “weight.” That’s not entirely wrong. The mass of an object is measured by its resistance to a force.
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----------------------------------------- F = m*a
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--------------------------------- Force equals mass times acceleration.
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- When you pick something up to test its weight, it is resisting the Earth’s gravity, so an everyday object’s weight on Earth is indeed one measurement of its mass.
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- But there’s more to mass than just a resistance to gravity, especially on the scale of the smallest pieces of matter. So physicists’ definition of mass gets a more complicated.
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- Most fundamental matter particles, such as electrons, muons and quarks, get their mass from their resistance to a field that permeates the universe called the Higgs field. The more the Higgs field pulls on a particle, the more mass it has.
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- When it comes to composite particles like protons and neutrons, which are made up of quarks, most of their mass comes from the pull of the “strong force” that holds the quarks together.
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- Photons and gluons, two force-carrying particles, are fundamental, so they don’t host the internal tug-of-war of a composite particle. They are also unaffected by the Higgs field. Indeed, they seem to be without mass.
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- Massless particles are purely energy. These quanta of energy don’t have edges, and they don't have surfaces. A better way to think of particles is as ripples on a quantum field. A quantum field has vibration modes like the harmonics on a guitar string. Pluck it with the right frequency and you get a “particle“.
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- The two particles physicists know to be approximately massless, photons and gluons, are both force-carrying particles, also known as “gauge bosons“. Photons are associated with the electromagnetic force, and gluons are associated with the strong force.
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- The graviton, a gauge boson associated with gravity, is also expected be massless, but its existence hasn’t been confirmed yet.
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- These massless particles have some unique properties. They are completely stable, so unlike some particles, they do not lose their energy decaying into pairs of less massive particles.
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- Because all their energy is kinetic, they always travel at the speed of light. And thanks to special relativity, things traveling at the speed of light don't actually age. So a photon is actually not aging relative to us. It is timeless.
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- To return to the topic of gravity: Gravity affects anything with energy, even a particle that has no mass at all. That is why the gravitational attraction of objects like galaxies and clumps of dark matter curves the path of light passing by them in space.
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- It could be that the photon and the gluon are not the only massless particles in the universe. There could be a lot of massless things out there that either there’s no way to look for them, or rather we haven’t figured out how to look for them. It could be that there’s this whole other world out there.
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- Maybe it is not just “out there’ Maybe it is inside every atom?
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- No one really knows what happens inside an atom. Maybe looking inside will tell us what is going on with “massless particles?
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- Here is what we know for sure: Electrons whiz around "orbitals" in an atom's outer shell. Then there's a whole lot of empty space. And then, right in the center of that space, there's a tiny nucleus, a dense knot of protons and neutrons that give the atom most of its mass.
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- Those protons and neutrons cluster together, bound by what's called the “strong force“. And the numbers of those protons and neutrons determine whether the atom is iron or oxygen or xenon, and whether it's radioactive or stable.
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- Still, no one knows how those protons and neutrons behave inside an atom. Outside an atom, protons and neutrons have definite sizes and shapes. Each of them is made up of three smaller particles called quarks, and the interactions between those quarks are so intense that no external force should be able to deform them, not even the powerful forces between particles in a nucleus.
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- But for decades, researchers have known that the theory is in some way wrong. Experiments have shown that, inside a nucleus, protons and neutrons appear much larger than they should be.
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- Since at least the 1940s, physicists have known that nucleons move in tight little orbitals within the nucleus. The nucleons, confined in their movements, have very little energy. They don't bounce around much because they are restrained by the strong force.
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- In 1983, physicists at the European Organization for Nuclear Research (CERN) noticed something strange: Beams of electrons bounced off iron in a way that was very different from how they bounced off free protons. That was unexpected; if the protons inside hydrogen were the same size as the protons inside iron, the electrons should have bounced off in much the same way.
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- For some reason, protons and neutrons inside heavy nuclei act as if they are much larger than when they are outside the nuclei. This phenomenon is called the EMC effect. It violates existing theories of nuclear physics.
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- While quarks, the subatomic particles that make up nucleons, strongly interact within a given proton or neutron, quarks in different protons and neutrons can't interact much with each other. The strong force inside a nucleon is so strong it eclipses the strong force holding nucleons to other nucleons.
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- As long as nucleons stay in their orbitals, that's the case. However, recent experiments have shown that at any given time, about 20% of the nucleons in a nucleus are in fact outside their orbitals. Instead, they're paired off with other nucleons, interacting in "short range correlations."
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- Under these circumstances, the interactions between the nucleons are much higher-energy than usual. That's because the quarks poke through the walls of their individual nucleons and start to directly interact, and those quark-quark interactions are much more powerful than nucleon-nucleon interactions.
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- These interactions break down the walls separating quarks inside individual protons or neutrons. The quarks making up one proton and the quarks making up another proton start to occupy the same space. This causes the protons to stretch and blur. They grow a lot, albeit for very short periods of time. That skews the average size of the entire cohort in the nucleus producing the EMC effect.
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- QCD stands for quantum chromodynamics, this is the system of rules that govern the behavior of quarks. Shifting from nuclear physics to QCD is a bit like looking at the same picture twice. The fields operate at such tiny distances that they're of negligible magnitude outside the nucleus, but they're powerful inside of it.
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- These force fields, called "mean fields" actually deform the internal structure of protons, neutrons and pions (a type of strong force-carrying particle). This is just like if you take an atom and you put it inside a strong magnetic field, it will change the internal structure of that atom.
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- As you can see we have a lot more to learn what goes on inside the atom. The other wonder is we need that knowledge to learn what goes on inside stars. The atom controls the Universe, or, vice versa. The more we learn the more insignificant we become and our knowledge seems miniscule.
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- January 14, 2019 2585
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