Another chapter of Brian Greene's, The Fabric of the Cosmos. My first eight summaries are at the bottom.1. Another good chapter. This one has to do with early universe and speculation about how particles obtained mass. I thought Greene did a very good job of picturing the issue by talking about how ice melts at 0 degrees Celsius and evaporates at 100. You don't observe much change and then at these crucial points, water changes states.
So he suggests that at 1015 Kelvin, about 10-11 seconds after the beginning of the universe, the Higgs field cooled enough to take on a stable value. The result, according to the current theory, is that particles began to take on mass.
So prior to this point, nothing had any mass. Every particle was like the massless photon, the theoretical basis of light. Electrons had no mass. Quarks had no mass. There was a kind of symmetry because all these particles waiting to happen stood on the same massless ground.
2. So what are these particles? Greene divides these particles into two groups: fundamental particles (like electrons and quarks) and force particles (like gravitons, gluons, the W and the Z). Current theory identifies four basic forces in nature. There is the electromagnetic force (which Maxwell unified in the 1800s). There is the strong nuclear force, which holds the nucleus of atoms together. There is the weak nuclear force, which relates to certain atomic decay processes. Then of course there is gravity, which may not actually be a force at all. It really has to do with the curvature of space.
Current theory sees particles behind these forces. No one has discovered a graviton, but it is a proposed particle as a basis for gravity as a force. There is the gluon, which is thought to be the basis for the strong nuclear force (has been observed). W and Z particles are thought to underlie the weak force (have been observed). And photons (light particles) are the basis for the electromagnetic force (some are helping me read right now).
3. Mass is basically the property of a particle that resists a change in its motion (261). The theory has been for some time that there is a Higgs field permeating the whole universe consisting of Higgs particles. This field as it were obstructs the movement of these other particles on various levels. The ones with lighter mass are those that are not obstructed much by the Higgs. Those with heavier masses are so because the Higgs gets more in the way. Photons are not affected by the Higgs field at all, which is why they are massless.
When Greene wrote this book (2004), the Higgs had not yet been discovered. As of 2012, at least a "Higgs-like" boson has been discovered.
In the fractions of a second after the beginning of the universe but before the Higgs field stabilized into what Greene calls the "Higgs ocean," all these particles were in symmetry. That is, they were not hindered to move in any direction whatsoever. Then when the Higgs stablized, symmetry was broken and all these particles took on mass.
4. In particular, whereas the electromagnetic fields and the weak nuclear fields were identical before that point, now they became distinct because the W and Z particles took on mass. In the late 60s, Steven Weinberg and others developed the "electroweak" theory that demonstrated how these two forces would have been unified prior to the Higgs stabilization at 1015 degrees.
So the theory was expanded by Greene's professor Howard Georgi to propose that at 1028 degrees and 10-35 seconds, the electroweak force (the combined weak and electromagnetic forces) and the strong force may also have been symmetrical and "uncondensed," so to speak. If the Higgs field that locked into place mass is called the "electroweak" Higgs. Georgi proposed a "grand unified Higgs."
However, after 25 years, key evidence for this theory has not appeared.
Reality's Arena
1. Overview
2. Spinning Space Buckets
3. Relativity and the Absolute
4. Particles Separated at Birth
Time and Experience
5. Does time flow?
6. Does time have an arrow?
7. Quantum crazy
Spacetime and Cosmology
8. Universal symmetry
No comments:
Post a Comment