Heat and Its Relation to the Early Universe

Heat is what we depend on for life, warmth, and the existence of galaxies, stars, and planets. However, heat had another meaning in the very early Universe. Heat equaled movement and instability and the huge amount of heat caused particles to move around and annihilate each other causing chaos and confusion. Much of these hyperactive particles' movement happened in the first second of the Universe, creating what we know today. To encompass all temperatures, the Kelvin scale is used. Beginning at room temperature, or 293 K, we begin our journey into extreme heat, and the fascinating phenomena that occur there.

At 310 K, or 98.4 F, is the average temperature of the human body, closely followed by the boiling point of water, at 373.15 K. Note that all main states of matter of water occur naturally: solid, liquid and gas. However, the gas form, water vapor, can be attained in average temperatures by the Sun's heat and the movement of particles. At 1900 K, we reach the temperature of the nose of the Space Shuttle, during re-entry. The supercharged ionosphere (filled with ionized gas, hence the name) is a factor, along with friction, that heats the spacecraft to this temperature. As you get higher, metals start to boil, such as lead, which boils into a gas at 2022 K, or about 4000 degrees Fahrenheit.

At 3000 K, we reach our first important milestone on the backwards journey towards the Big Bang on the scale of extreme heat. The Universe had settled down to this still extreme temperature about 380,000 years after the Big Bang. It is at this time that the Cosmic Background Radiation was emitted* (see footnote below this paragraph). In fact, this is the first time that the Universe was transparent. The Cosmic Background Radiation wasn't emitted until this time, because electrons and anti-electrons (the electron's antimatter pair) were still annihilating each other and turning into photons. In the case of antimatter, there were approximately one million antiparticles for every one million and one regular particles. On contact the pairs destroyed each other and became photons. And the next second, the photons would transmit their energy into mass, and immediately create another electron and another anti-electron. This process stopped when the temperature dropped below 3000 K because the photons lost energy as the Universe expanded, and eventually, they didn't have enough energy to become electrons anymore. Gamma rays are the only waves that have enough energy to produce such particles. Overall, after this time, the net result was one particle left for every one million original particle pairs, (note that this slight amount of matter left in the Universe became everything we know today: galaxies, planets and stars) and a whole bunch of photons. These photons have been causing the Cosmic Background Radiation ever since, for the past 13.7 billion years. This also is the first time in the Universe that complete atoms existed.

*Note that I could call it the Cosmic Microwave Background Radiation as it is called today, but I will refrain from doing so due to the fact that the radiation originated as gamma and X-rays and over time, the wave lost energy and became a microwave. The different waves are distinguished by their frequency, or the distance between "crests" in the curvy line that is the wave. The frequency of the CBR (this of course being the acronym for Cosmic Background Radiation) drops as the Universe expands, and thus if the Universe continues to expand the frequency will get longer and longer, until all Cosmic Background Radiation will become radio waves.

Suddenly, we jump to 13,000,000 K, the temperature required for the proton-proton cycle and the fusion of Hydrogen nuclei into Helium nuclei. (see the post Burning Hydrogen) This is also the temperature of the Sun's core, and the temperature in the Universe about 20 minutes after its formation. This temperature in the early Universe formed the first atomic nuclei heavier than H1. (the Hydrogen nucleus consisting of one proton) The process in which the first Helium, Lithium, and Deuterium atoms were formed in this time period was called Big Bang Nucleosythesis. Big Bang Nucleosythesis lasted approximately from 3-20 minutes after the Big Bang. At this time, hyperactive electrons were still at the point where they couldn't settle down into completed atoms, and real atoms (electrons and all) weren't formed until a while after. This is because of the ongoing electron-photon reactions, see above.



The proton-proton cycle of fusion in the Sun.  Notice how neutrinos (marked v) and the positrons (anti-electrons represented by white dots) are emitted during the reaction. Also, the gamma rays are the heat and energy released from the reaction, and absorbed by the Earth. The process begins with four Hydrogen nuclei and ends with one Helium nucleus.

At 10 billion K, atomic nuclei break down and proton and anti-proton reactions occur. This temperature occurred naturally in the Universe at about one second after the Big Bang. This milestone in temperature marked the end of the hadron epoch, which lasted from one millionth of a second to one second after the Big Bang. As with electron and anti-electrons, protons and anti-protons annihilate each other on contact, forming photons. Also, since a byproduct of this reaction is the production of the tiny neutrino (a small particle possessing nearly no mass), a wave of neutrinos was released at the end of the epoch, forming the less known brother of the Cosmic Background Radiation, the Cosmic Neutrino Radiation. Since the neutrinos move at close to the speed of light, and the speed of them is known, they would probably be an even more accurate Universe clock-if they could be detected. Unlike other particles, neutrinos are so minuscule that they pass directly through ordinary matter, and barely ever make contact with other particles, such as protons. In fact, the Sun emits so many of these tiny particles that in the time that it takes to say "neutrino", 50 trillion of these particles pass through you!

At about 1,000,000,000,000 or one trillion K, the heat breaks down the hadrons themselves into the even tinier particles inside them, the quarks. The Universe dropped below this temperature at one millionth of a second after the Big Bang, at before this, from one trillionth to one millionth of a second after the creation of the Universe, was the Quark Epoch. During this epoch, the entire Universe was a sea of quarks and gluons. The gluon is the (somewhat hypothetical) particle that binds quarks together into hadrons. The substance of the Universe during this time was quark-gluon plasma, (for more info on plasma, see here) or a sea of ionized quarks mixed with gluons. Before this point however, the four forces of the Universe: gravity (the force that pulls heavy objects together), electromagnetism (the connections and effects of electricity and magnetism), the weak nuclear force (the force that causes radioactive decay) and the strong nuclear force (the force that binds protons and neutrons together in the nucleus, and, at a smaller scale, also binds together quarks within particles such as protons and neutrons) start to break down and the physics we know today start to change even at fundamental levels.



A representation of the internal structure of a proton. The quarks labeled "u" are up quarks and each have a charge of 2/3. The quark labeled "d" is a down quark and has a charge of -1/3. The wavy lines represented the strong nuclear force, carried by the gluon. Notice that the charges of the quarks, 2/3+2/3-1/3=1 add to form a charge of +1, which is the charge of a proton.

At one trillionth of a second after the Big Bang, the forces begin to unify. The first two forces to unify are the electromagnetic force and the weak nuclear force, forming what is called the electroweak force. This state only can occur at a temperature at about 1,000,000,000,000,000 K, or one million billion Kelvin. To unify these forces in theory, one must come up with a set of physical and mathematical laws that cover both forces. This has already been done for the electroweak force. The strongly hypothetical particles that carry these forces have been explained and unified, but beyond this, it gets even trickier.

At higher than 1,000,000,000,000,000,000,000,000,000 K, or one million billion trillion K, the next unification occurs, this time between the electroweak force and the strong nuclear force to form what is known as the electronuclear force. The theory connecting all three of these forces is called the Grand Unification Theory. This unites nearly all of quantum physics. This force only existed during the Grand Unification Epoch (aptly named) from 10^-43 seconds to 10^-36 seconds after the Big Bang. The electroweak and the strong nuclear force have been unified in theory, but there is still some disagreement about the force's exact nature.

Finally, we reach the hottest, densest, shortest epoch of this Universe, in which the remaining fundamentals of physics break down. This epoch is named the Planck epoch, named after Max Planck. Max Planck discovered the smallest units of length and time as well as others, and discovered the maximum possible temperature and density, as well as others. I go into detail about the Planck units in the post, The Planck Constant and Its Applications. The Universe up to 10^-43 seconds is the time when it was younger than the Planck time, a possibility not nearly explained by any modern theory. It is theorized that the electronuclear force now combines with gravity, at a soaring 14,000,000,000,000,000,000,000,000,000,000,000 K, or the Planck temperature. The theory that covers this is called (very appropriately) the Theory of Everything. This theory would unify gravitation and quantum physics into a theory that explains all phenomena that have and will occur in our Universe. The String Theory and Quantum Loop Gravity Theory have both attempted to explain this, but appear to have failed in encompassing everything. Hopefully, in the future, theories will shed light on this unknown epoch.

Therefore, extreme heat starts by boiling metal, and then breaking down particles, and finally by unifying all that there is in the Universe.