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-------------------------------- 2365 - Mass - energy of the Universe.
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- There is some type of anti-gravity energy that is expanding the Universe and it occupies 70% of the total. Then the 30% that we call matter is 25% Dark Matter that we can not identify what it is. That means that there is 95% of the universe that is unidentified.
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- All the life that we know and think we understand resides in that remaining 5%.
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- OK, now what happens when we look closely at that 5 %. We can identify individual atoms. Atoms that make up all the elements that constitute the life and the material world we know and love.
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- The whole world is equal to the sum of its constituent parts. Right?
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- That’s how everything works, from galaxies to planets from molecules to atoms. If you take all the components of any system and look at them individually, you can clearly see how they all fit together to add up to the entire system, with nothing missing and nothing left over. The total amount you have is equal to the amounts of all the different parts of it added together.
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- All the elements are made up of atoms. All atoms are made up of electrons and protons. The electrons are fundamental particles that make up the mass. However, the protons are made up of even more fundamental particles.
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- Several decades ago we discovered that all protons are made of quarks. Every proton is made of three quarks, but if you add up the quark masses, they not only don’t equal the proton’s total mass, they don’t even come close. So, how do we get back to the whole is equal to the sum of the parts?
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- What’s happening inside protons? Why does a proton’s mass so greatly exceed the combined masses of its constituent quarks and gluons?
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- When you break atoms into protons, neutrons and electrons their combined mass are around 1% of the total. What are we missing?
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- From macroscopic scales down to subatomic ones, the sizes of the fundamental particles play only a small role in determining the sizes of composite structures. Whether the building blocks are truly fundamental or are point-like particles is still not known.
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- Like all known organisms, human beings are carbon-based life forms. Carbon atoms are made up of six protons and six neutrons, but if you look at the mass of a carbon atom, it’s approximately 0.8% lighter than the sum of the individual component particles that make it up.
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- What we are missing here is nuclear binding energy; when you have atomic nuclei bound together, their total mass is even smaller than the mass of the protons and neutrons that comprise them.
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- The way carbon is formed is through the nuclear fusion of hydrogen into helium and then helium into carbon. The energy released is what powers most types of stars in both their normal and red giant phases.
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- That “lost mass” is where the energy powering stars comes from, E = mc². As stars burn through their fuel, they produce more tightly-bound nuclei, releasing the energy difference as radiation.
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- The reason it’s harder to pull apart multiple things that are bound together is because they released energy when they were joined, and you have to put energy back in to them to free them again.
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- That’s why it’s such a puzzling fact that when you take a look at the particles that make up the proton, the up, up, and down quarks. Their combined masses are only 0.2% of the mass of the proton as a whole.
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- The way quarks bind into protons is fundamentally different from all the other forces and interactions we know of with atoms. Instead of the force getting stronger when objects get closer, like the gravitational, electric, or magnetic forces, the attractive force inside protons goes down to zero when quarks get arbitrarily close.
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- Instead of the strong force getting weaker when objects get farther away, the strong force pulling quarks back together gets stronger the farther away they get. This is how the Strong Nuclear force inside atoms works.
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- This nuclear force acts like a spring, with negligible force when unstretched but large, attractive forces when stretched to large distances. This property of the strong nuclear force is known as asymptotic freedom, and the particles that mediate this force are known as gluons.
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- Somehow, the energy binding the proton together, is responsible for the other 99.8% of the proton’s mass which comes from these gluons. The whole of matter, somehow, weighs much, much more than the sum of its parts.
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- This might sound like an impossibility at first, as the gluons themselves are massless particles. But you can think of the forces they give rise to as springs, asymptoting to zero when the springs are unstretched, but becoming very large the greater the amount of stretching.
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- The amount of energy between two quarks whose distance gets too large can become so great that it is as though additional quark-anti-quark pairs exist inside the proton.
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- The collisions performed at the Large Hadron Collider at CERN in Switzerland are perhaps the greatest test of all to learn what goes on with the internal structure of the proton. When two protons collide at these ultra-high energies, most of them simply pass by one another, failing to interact. When two internal, point-like particles collide, we can reconstruct exactly what it was that smashed together by looking at the debris that comes out.
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- The Higgs Bosons give mass to the fundamental particles; however, the proton’s mass is not due to the mass of the quarks and gluons that compose it. Under 10% of the collisions occur between two quarks; the overwhelming majority are gluon-gluon collisions, with quark-gluon collisions making up the remainder.
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- These experiments teach us an important lesson: the particles that we use to model the internal structure of protons are real. In fact, the discovery of the Higgs Boson itself was only possible because of this, as the production of Higgs Bosons is dominated by gluon-gluon collisions at the LHC.
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- Before the mass of the Higgs Boson was known, we could still calculate the expected production rates of Higgs Bosons from proton-proton collisions at the LHC.
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- It is very accurately known how large the average gluon density is inside a proton. What is not known is exactly where the gluons are located inside the proton.
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- We model the gluons as located around the three valence quarks. Then we control the amount of fluctuations represented in the model by setting how large the gluon clouds are, and how far apart they are from each other. The more fluctuations we have, the more likely this process is to happen.
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- The combination of this new theoretical model and the ever-improving LHC data better enables scientists to understand the internal, fundamental structure of protons, neutrons and nuclei in general, and hence to understand where the mass of the known objects in the Universe comes from.
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- A better understanding of the internal structure of a proton, including how the quarks and gluons are distributed, has been achieved through both experimental improvements and these new theoretical developments.
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- The difficult part with the quantum field theory that describes the strong nuclear force , quantum chromo dynamics (QCD), is that the standard approach we take to doing calculations does not work.
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- Typically, we’d look at the effects of particle couplings: the charged quarks exchange a gluon and that mediates the force. They could exchange gluons in a way that creates a particle-antiparticle pair or an additional gluon, and that should be a correction to a simple one-gluon exchange. They could create additional pairs or gluons, which would be higher-order corrections.
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- We call this approach taking a perturbative expansion in quantum field theory, with the idea that calculating higher and higher-order contributions will give a more accurate result.
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- Feynman diagrams are used in calculating every fundamental interaction spanning the strong, weak, and electromagnetic forces, including in high-energy and low-temperature condensed conditions.
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- But this approach, which relies on a perturbative expansion, is only of limited utility for the strong interactions, as this approach diverges, rather than converges, when you add more and more loops for QCD.
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- The approach, which works so well for quantum electrodynamics (QED), fails spectacularly for QCD. The strong force works differently, and so these corrections get very large very quickly. Adding more terms, instead of converging towards the correct answer, diverges and takes you away from it.
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- By treating space and time as a grid (or lattice of points) rather than a continuum, where the lattice is arbitrarily large and the spacing is arbitrarily small, we overcome this calculation problem.
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- Whereas in standard, perturbative QCD, the continuous nature of space means that you lose the ability to calculate interaction strengths at small distances, the lattice approach means there’s a cutoff at the size of the lattice spacing. Quarks exist at the intersections of grid lines; gluons exist along the links connecting grid points.
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- As our computing power increases, we can make the lattice spacing smaller, which improves our calculation accuracy. Over the past three decades, this technique has led to an explosion of solid predictions, including the masses of light nuclei and the reaction rates of fusion under specific temperature and energy conditions. The mass of the proton, from first principles, can now be theoretically predicted to within 2%.
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- As computational power and Lattice QCD techniques have improved over time, so has the accuracy to which various quantities within the proton, such as its component spin contributions, can be computed. By reducing the lattice spacing size, which can be done simply by raising the computational power employed, we can better predict the mass of the proton.
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- It’s true that the individual quarks, whose masses are determined by their coupling to the Higgs Boson, cannot even account for 1% of the mass of the proton. Rather, it is the strong force that describes the interactions between quarks and the gluons that mediate them, that are responsible for practically all of the mass.
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- The strong nuclear force is the most powerful interaction in the entire known Universe. When you go inside a particle like the proton, it is so powerful that it is primarily responsible for the total energy , and therefore mass of the normal matter in our Universe.
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- Quarks may be point-like, but the proton is huge by comparison. Confining its component particles with the binding energy of the strong force is what’s responsible for 99.8% of the proton’s mass.
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- So here you have it. All the mass returns to energy. E= mc^2. We have gone full circle. I still think it is all impossible. Einstein had no idea what he wrought. We still don’t. But it is fun to learn.
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- May 14, 2019
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