In the first two posts in this series, I discussed the "periodic table" of particle physics
and what the Standard Model of particle physics explains
. Now, we tackle: What is wrong with the Standard Model (SM)? Two things:
- We haven't actually seen the Higgs boson yet
- It does not include gravity (General Relativity)
If the Higgs is discovered, as expected, the SM will be nearly complete in describing everything assigned to it. It will be in some sense the final validation of all the work put into the model. (There are a few small loose ends, but this is the last major gap.) However, this would actually be disappointing, as much as rewarding.
What physicists really want is to not find a Higgs! This will give them a starting hint to look for a new model of the universe.
Gravity: General Relativity
There are actually four "fundamental" forces (strong, weak, electromagnetic, and gravity) in nature, as categorized by physics theories. The SM was developed over decades by roughly a dozen Nobel-prize-winning physicists to describe three of them. The other one-fourth of the puzzle was single-handedly developed by one brilliant genius. In 1916, Einstein published his theory of general relativity (GR). This theory describes gravity perfectly; no contradictory observations have ever been made. Just as nothing disobeys Einstein and travels faster than the speed of light, nothing disobeys his theory of gravity.
Why not simply weave GR into the SM? For nearly 40 years physicists have been trying to accomplish this, and without exception, they have failed. Why? The SM describes the universe as a system of quantum-mechanical particles (the quarks, electrons, gluons, neutrinos and so on), which travel from place to place like pinballs, being emitted, absorbed and bounced around. These interactions are responsible for forces and movement.
General relativity describes the force of gravity by changing the structure of spacetime itself. Heavy (massive) objects actually bend and stretch spacetime. When gravity pulls two objects together, it is actually the bending of space between them that causes the attraction.
Imagine having four people hold the corners of a bedsheet. Put a bowling ball in the middle of the sheet. When you put a marble on the sheet, what happens? Of course it is going to roll across the sheet and fall against the bowling ball weighing down the center. General Relativity says that objects aren't pulled by an invisible gravity. They simply move along a curved spacetime. If only spacetime math were as simple as bedsheets!
New Theories Beyond the SM
If the Higgs doesn't turn up, new ways may be found to modify the SM before even trying to fit GR in. Theories for retrofitting the SM without the Higgs include "technicolor," which requires more particles and more ways for these particles to interact. Some of these particles may possibly be seen by the LHC.
An even better scenario is if new particles are discovered. This can provide clues to a greater theory, a way to combine, or unify, GR and the SM. While this new theory may well take on some unexpected form, there are several candidate theories already proposed. Most of these theories rely on something called supersymmetry -- meaning another similar particle would correspond to every particle already in the particle physics periodic table
. Some of these particles might be seen by the LHC.
String theory is the most famous of the theories that contain supersymmetry. String theory arises from the conceptually simple idea that instead of being tiny points, or pinballs, particles are actually like tiny strings when magnified far enough. It has evolved into a monstrous construct containing 11 dimensions and abstract mathematical constructs far more bizarre than the SM.
While the theory has many proponents
it also has many critics
. While Einstein changed in a profound way the view of the universe held since Galieo, his predictions are simple and hold up to be perfectly true time and time again
. String theory may never make any falsifiable predictions, or even any testable predictions at all! Whenever a new difficulty confronts the theory it grows even more baffling and complex. Why 11 dimensions? Is there a good reason to have more than four? Because of this lack of falsifiability, many physicists claim
or privately believe that the theory borders on metaphysics (or simply mathematics) and not physics.