From DOE’s Fermi National Accelerator Laboratory: “Science of Matter, Energy, Space and Time”

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From DOE’s Fermi National Accelerator Laboratory , an enduring source of strength for the US contribution to scientific research world wide.

05/01/2014 [Brought forward today-always useful]

What is the world made of?

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The building blocks

Physicists have identified 13 building blocks that are the fundamental constituents of matter. Our everyday world is made of just three of these building blocks: the up quark, the down quark and the electron. This set of particles is all that’s needed to make protons and neutrons and to form atoms and molecules. The electron neutrino, observed in the decay of other particles, completes the first set of four building blocks.

For some reason nature has elected to replicate this first generation of quarks and leptons to produce a total of six quarks and six leptons, with increasing mass. Like all quarks, the sixth quark, named top, is much smaller than a proton (in fact, no one knows how small quarks are), but the top is as heavy as a gold atom!

Although there are reasons to believe that there are no more sets of quarks and leptons, theorists speculate that there may be other types of building blocks, which may partly account for the dark matter implied by astrophysical observations. This poorly understood matter exerts gravitational forces and manipulates galaxies. It will take Earth-based accelerator experiments to identify its fabric.

The forces

Scientists distinguish four elementary types of forces acting among particles: strong, weak, electromagnetic and gravitational force.

The strong force is responsible for quarks “sticking” together to form protons, neutrons and related particles.
The electromagnetic force binds electrons to atomic nuclei (clusters of protons and neutrons) to form atoms.
The weak force facilitates the decay of heavy particles into smaller siblings.
The gravitational force acts between massive objects. Although it plays no role at the microscopic level, it is the dominant force in our everyday life and throughout the universe.

Particles transmit forces among each other by exchanging force-carrying particles called bosons. These force mediators carry discrete amounts of energy, called quanta, from one particle to another. You could think of the energy transfer due to boson exchange as something like the passing of a basketball between two players.

Each force has its own characteristic bosons:

The gluon mediates the strong force; it “glues” quarks together.
The photon carries the electromagnetic force; it also transmits light.
The W and Z bosons represent the weak force; they introduce different types of decays.

Physicists expect that the gravitational force may also be associated with a boson particle. Named the graviton, this hypothetical boson is extremely hard to observe since, at the subatomic level, the gravitational force is many orders of magnitude weaker than the other three elementary forces.

Table of particle discoveries: who, when, where?

The Higgs boson

The Higgs boson is a particle associated with the Higgs field, the mechanism through which elementary particles gain mass. Without the Higgs field, or something similar, atoms would not form, and there would be no chemistry, no biology and no life.

The Higgs field is like a giant vat of molasses spread throughout the universe. Most of the known types of particles that travel through it stick to the molasses, which slows them down and makes them heavier. The Higgs boson is a particle that helps transmit the mass-giving Higgs force field, similar to the way a particle of light, the photon, transmits the electromagnetic field.

The ATLAS and CMS experiments at CERN’s Large Hadron Collider in Geneva, Switzerland, announced the discovery of the Higgs particle in July 2012.

CERN CMS Higgs Event May 27, 2012.


CERN ATLAS Higgs Event
June 12, 2012.

Antimatter

Although it is a staple of science fiction, antimatter is as real as matter. For every particle, physicists have discovered a corresponding antiparticle, which looks and behaves in almost the same way. Antiparticles, though, have the opposite properties of their corresponding particles. An antiproton, for example, has a negative electric charge while a proton is positively charged.

In the mid-1990s, physicists at CERN (1995) and Fermilab (1996) created the first anti-atoms. To learn more about the properties of the antimatter world, they carefully added a positron (the antiparticle of an electron) to an antiproton. The result: antihydrogen.

CERN map

FNAL/Tevatron map

Storing antimatter is a difficult task. As soon as an antiparticle and a particle meet, they annihilate, disappearing in a flash of energy. Using electromagnetic force fields, physicists are able to store antimatter inside vacuum vessels for a limited amount of time.

WIMPS and Dark Matter

No one has ever directly observed dark matter, but two clues led astronomers to suspect its existence. First, when researchers measured the masses of all the stars and planets that make up galaxies, they discovered that the gravity of those objects alone would not be great enough to hold them together. Something they could not see must have been contributing mass and therefore gravitational pull. Second, they observed in space the kind of distortions of light usually caused by large masses in areas that seemed empty.

The composition of dark matter is unknown, and its existence shows that the Standard Model of particle physics is incomplete.

Several theories of particle physics, such as supersymmetry, predict that weakly interacting massive particles, WIMPs, exist with properties suitable for explaining dark matter.

Standard Model of Supersymmetry via DESY (DE).

Dark Matter Background
Fritz Zwicky discovered Dark Matter in the 1930s when observing the movement of the Coma Cluster., Vera Rubin a Woman in STEM denied the Nobel, did most of the work on Dark Matter.

Fritz Zwicky from http:// palomarskies.blogspot.com.

Coma cluster via NASA/ESA Hubble.

In modern times, it was astronomer Fritz Zwicky, in the 1930s, who made the first observations of what we now call dark matter. His 1933 observations of the Coma Cluster of galaxies seemed to indicated it has a mass 500 times more than that previously calculated by Edwin Hubble. Furthermore, this extra mass seemed to be completely invisible. Although Zwicky’s observations were initially met with much skepticism, they were later confirmed by other groups of astronomers.

Thirty years later, astronomer Vera Rubin provided a huge piece of evidence for the existence of dark matter. She discovered that the centers of galaxies rotate at the same speed as their extremities, whereas, of course, they should rotate faster. Think of a vinyl LP on a record deck: its center rotates faster than its edge. That’s what logic dictates we should see in galaxies too. But we do not. The only way to explain this is if the whole galaxy is only the center of some much larger structure, as if it is only the label on the LP so to speak, causing the galaxy to have a consistent rotation speed from center to edge.

Vera Rubin, following Zwicky, postulated that the missing structure in galaxies is dark matter. Her ideas were met with much resistance from the astronomical community, but her observations have been confirmed and are seen today as pivotal proof of the existence of dark matter.

Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science).


Vera Rubin measuring spectra, worked on Dark Matter (Emilio Segre Visual Archives AIP SPL).


Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970. https://home.dtm.ciw.edu.

Dark Energy

In the 20th century, astronomers first discovered that the universe was getting bigger. They found this by observing something similar to the Doppler effect in the light coming from distant galaxies. The Doppler effect is what causes a car horn to change in pitch from high to low as it approaches and passes. This happens because the sound waves are compressed as the car moves toward you, resulting in a higher pitch, and are stretched as it recedes, resulting in a lower pitch. As an object approaches you, the light waves coming from it compress. Astronomers call this blueshift. When light waves stretch as an object moves farther away, astronomers call it redshift.

By measuring the spectrum of an astronomical object, astronomers can tell how much the space between the object and observer has stretched as the light traveled through it. When astronomer Vesto Slipher measured light coming from other galaxies, he found that almost all were redshifted, or moving away. He found that those that seemed dimmer and farther away had even higher redshifts. The universe was expanding. This led astronomers to the idea of the big bang.

Astronomers assumed, however, that the force of gravity from all of the matter in the universe would slow the expansion. They were in for a surprise in 1998 when they discovered that the expansion was actually speeding up. Astronomers discovered this when they measured the brightness of the light coming from a certain type of supernova that always explodes with roughly the same energy. The dimmer the light from the supernova, the farther the distance it had traveled to Earth. They discovered that the supernovae were farther away than their redshift measurements predicted. The universe was expanding at an accelerating rate.

Some particle astrophysicists think this is happening because a force with a repulsive gravity is pushing the universe apart. They call this force Dark Energy.

Dark Energy Survey


Dark Energy Camera [DECam], built at FNAL


NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam at an altitude of 7200 feet

Timeline of the Inflationary Universe WMAP

The Dark Energy Survey (DES) is an international, collaborative effort to map hundreds of millions of galaxies, detect thousands of supernovae, and find patterns of cosmic structure that will reveal the nature of the mysterious dark energy that is accelerating the expansion of our Universe. DES began searching the Southern skies on August 31, 2013.

According to Einstein’s theory of General Relativity, gravity should lead to a slowing of the cosmic expansion. Yet, in 1998, two teams of astronomers studying distant supernovae made the remarkable discovery that the expansion of the universe is speeding up. To explain cosmic acceleration, cosmologists are faced with two possibilities: either 70% of the universe exists in an exotic form, now called dark energy, that exhibits a gravitational force opposite to the attractive gravity of ordinary matter, or General Relativity must be replaced by a new theory of gravity on cosmic scales.

DES is designed to probe the origin of the accelerating universe and help uncover the nature of dark energy by measuring the 14-billion-year history of cosmic expansion with high precision. More than 400 scientists from over 25 institutions in the United States, Spain, the United Kingdom, Brazil, Germany, Switzerland, and Australia are working on the project. The collaboration built and is using an extremely sensitive 570-Megapixel digital camera, DECam, mounted on the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory, high in the Chilean Andes, to carry out the project.

Over six years (2013-2019), the DES collaboration used 758 nights of observation to carry out a deep, wide-area survey to record information from 300 million galaxies that are billions of light-years from Earth. The survey imaged 5000 square degrees of the southern sky in five optical filters to obtain detailed information about each galaxy. A fraction of the survey time is used to observe smaller patches of sky roughly once a week to discover and study thousands of supernovae and other astrophysical transients.

The Standard Model

Standard Model of Particle Physics via http://www.plus.maths.org .

Standard Model of Particle Fever via “Particle Fever” movie.

Physicists call the theoretical framework that describes the interactions between elementary building blocks (quarks and leptons) and the force carriers (bosons) the Standard Model. Gravity is not yet part of this framework, and a central question of 21st-century particle physics is the search for a quantum formulation of gravity that could be included in the Standard Model.

Though still called a model, the Standard Model is a fundamental and well-tested physics theory. Physicists use it to explain and calculate a vast variety of particle interactions and quantum phenomena. High-precision experiments have repeatedly verified subtle effects predicted by the Standard Model.

So far, the biggest success of the Standard Model is the unification of the electromagnetic and the weak forces into the so-called electroweak force. The consolidation is a milestone comparable to the unification of the electric and the magnetic forces into a single electromagnetic theory by J.C. Maxwell in the 19th century. Physicists think it is possible to describe all forces with a Grand Unified Theory.

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