At a conference in Washington DC this week, scientists from the European Organization for Nuclear Research, known by an acronym CERN, are presenting their results of yet another great search taking science to the crucible of creation soon after the Big Bang. As if the Higgs discovery wasn't enough, and before the immense publicity about the mechanism that gave mass to particles in the universe has died down, we are now treated to information about how the process of making a universe continued.
An experimental group called ALICE (A Large Ion Collider Experiment) -- which specializes in this era in the genesis of our universe, as well as the all-purpose groups that study a variety of phenomena and have discovered the Higgs boson, CMS (Compact Muon Solenoid) and ATLAS (A Toroidal LHC ApparatuS) -- are presenting their results of a special run of the Large Hadron Collider (LHC).
Most of the time, the LHC collides protons, which are hydrogen ions obtained from a small bottle of hydrogen gas and are then successively accelerated in a series of particle accelerators until they get into the LHC and are there accelerated far more -- at maximum energy (which has not quite been reached yet), this would be 99.9999996 per cent of the speed of light. But for a short period between proton runs, the LHC accelerates far more massive particles: lead ions (obtained from vaporizing and ionizing lead, and then accelerating these ions in the same sequence of accelerators culminating in the LHC). These particles are 207 times heavier than protons, and they are therefore accelerated to a slower speed than that of the protons. But because they are so heavy, they generate immense energies.
When the lead ions crash into other lead ions accelerated in the opposite direction inside the giant 16.5-circumference circular tube of the LHC, at speeds that -- while not as high as that of protons -- are still respectably close to that of light (well over 99 percent) they create something that physicists affectionately call "quark soup." The term originally comes from astronomy, where the fluid of particles believed to have existed soon after the Big Bang is generically described as the "primordial soup." More precisely, physicists define this medium as a plasma -- a hot, dense fluid of particles in which at least some particles are electrically charged; and this particular plasma that existed when the universe was very young is called a quark-gluon plasma.
It is an immensely hot collection of quarks (the "matter" particles that later will live inside protons and neutrons) and gluons (these are bosons, the force-carriers that later will act on quarks inside protons and neutrons, holding them in place). The new findings from CERN indicate the Collider has now created the hottest temperatures ever made by humans: between four and six trillion degrees Celsius -- a temperature that is about 300,000 times higher than that of the center of the Sun. The quark soup, dense and at this immensely high temperature, constituted our entire universe when it was roughly a trillionth of a second old and was about the size of the solar system. These estimates vary, and they also extend through time -- the quark soup existed for a tiny length of time, which is also uncertain.
The "second" in the title of this article is almost to be taken figuratively, since the actual times of various events were far shorter than a second after the Big Bang. But what I want to do here is to give you an idea, not about the exact timing of any event within this first second in the history of the universe--but about the sequence of the mysterious happenings that took place during an exceedingly small period of time and that are uniquely responsible for our being here.
First There Was A Superforce
We don't know anything about the Big Bang itself -- mathematically, the Big Bang was a singularity: a point in which space-time is so strongly curved that the laws of physics as we know them could not exist or apply. And we believe that right after this event, there existed an immense, single force of nature that governed the very young universe. We call it the superforce. The superforce was an amalgamation of the force of gravity, which holds us firmly on this planet and maintains Earth in orbit around the Sun; the strong force that now keeps quarks inside protons and neutrons, and also holds these larger particles inside the nuclei of matter; the weak nuclear force, which is responsible for some forms of radioactivity and makes the Sun shine; and the familiar electromagnetic force responsible for light, and radio waves, and cellphones, and TV, and all of chemistry.
Then something very peculiar happened: The superforce shed off the force of gravity, allowing it to go its own, separate way, while keeping the other three forces held tightly together.
The Riddle Of Inflation
At the same time that the superforce let gravity separate from it, the universe, still made of sheer energy without any mass, underwent an immense period of growth, called cosmic inflation. The inflationary process (discovered theoretically by Alan Guth of MIT) was a very short period of exponential growth in the size of the universe that, in a sense, stretched out the curvature of space, making it "flat" (as in Euclidean geometry). In the middle of this inflation, the superforce shed off yet another one of its parts and let it go its own way: the strong force that affects quarks through the action of gluons. Then suddenly, and in a way that science has not yet explained, inflation abruptly stopped and the universe continued to grow at a more moderate rate (since 1998, however, we know that the present rate of growth of our universe is now accelerating, although it is far slower than during the initial inflationary phase). At this point, our universe is believed to have been the size of an apple, and immensely hot.
Enter The Higgs
The next period in the life of the universe -- all within a fraction of its first second of existence -- was the time the Higgs boson, the so-called "God particle," did its magic. What the Higgs did was to rend asunder the last remaining two components of the original superforce: the weak force and the electromagnetic force (the latter remains united to this day as electric-magnetic). When the Higgs performed this amazing trick, it gave mass to three bosons that are responsible for the action of the weak force (called the Z, the W+, and the W-), leaving the photon (the boson that carries out the action of the electromagnetic force) massless. It is through this miracle that we believe that mass in the universe was obtained: The particles that would make up all matter, the quarks and electrons, became massive as well. (Neutrinos may have obtained their very tiny mass through another mechanism.)
The Quark Soup Era
These newly-born massive particles in our universe floated around in the fast-expanding space, constituting the quark-gluon plasma. It is this kind of fluid that the LHC has re-created--on a tiny scale, the size of a couple of lead nuclei -- and which was measured at a temperature of about 5 trillion degrees celsius. As the universe continued to cool down, all well within the first second of creation, something even more mysterious started to happen.
The Birth Of Matter As We Know It
Within a fraction of a millisecond of the Big Bang, the quark soup suddenly coagulated. The heavier quarks of higher "generations," which today we create in accelerators (charm, strange, top, and bottom) began to disappear; and with them did the muons and the taus (heavier "cousins" of the electron). The remaining quarks, of two kinds, "up" and "down," settled into triples: two "up"s and a "down" to make a proton, and two "down"s and an "up" to make a neutron. The electric charges of these quarks worked out fantastically well: an "up" quark has a charge of +2/3, while a "down" quark has a charge of -1/3 -- on a scale in which the electron's charge is exactly -1. Thus the total charge of the proton works out to be +1, identically what it must be for atoms to form when electrons join nuclei! and the charge of the neutron adds up to exactly 0 -- what it must be for the neutron to act as an electrical "buffer" between protons in all nuclei lager than hydrogen. It is only because of this incredible coincidence -- and a similar coincidence involving the masses of these particles -- that protons and neutrons could form nuclei of matter of increasing size and weight. Hydrogen, some helium, and fewer lithium nuclei would be created in the next phase of the story of the universe, extending to beyond our first second, while heavier nuclei would be "cooked" in nuclear fires inside stars over millions and billions of years. These nuclei would later capture electrons, whose properties would be perfectly matched with those of the protons in the nuclei, so that they could form stable atoms.
Thus, as the first second of creation came to an end, everything -- every force of nature, every elementary particle, as well as the composite protons and neutrons -- was in place for the universe as we know it to eventually develop. Atoms of matter would emerge, and later molecules would form -- among them a very special double-helix made of many sub-molecules that would constitute a crucial kind of code: DNA. And as life would evolve over many millions of years later, it would culminate in sentient, thinking beings determined to find out where they came from, how, and why. While the "why" part may elude us, perhaps forever, the Large Hadron Collider has over the last six weeks already supplied us with two important pieces of information about the "where" and the "how." Physicists tell us that this is just the beginning.
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