Imagine you are sitting in a big symphony hall, listening to an orchestra play, for the first time. You’ve never been to see a live orchestra, but you decided to go anyway. There’s a first time for everything, right? The orchestra is performing a Violin Concerto by Beethoven. As the soloist runs her hands and fingers along the neck of the violin, she produces different notes or pitches. Every note the violin produces has a different sound, pitch, and vibration. With each note comes a different possible direction for the music being created. This concept can be applied to quantum physics as well, within string theory.
QUANTUM BASICS:
As you may know, everything is made up of small particles. Matter is made from atoms, which are in turn made of three basic components: electrons, neutrons, and protons. The electron is fundamental, but neutrons and protons are made of even smaller particles, known as quarks. Quarks are, as far as we know, truly elementary.
What we know about the subatomic composition of the universe is known as the Standard Model of Particle Physics. It describes the fundamental building blocks out of which the world is made, and the forces through which these blocks interact. There are twelve basic building blocks. Six of these building blacks are quarks. They go by the names: up, down, charm, strange, bottom and top. (A proton, for instance, is made of two up quarks and one down quark.) The other six are leptons. These include the electron and its two heavier siblings, the muon and the tauon, as well as three neutrinos.
Within the universe there are four fundamental forces: gravity, electromagnetism, and weak and strong nuclear forces. Each of these four forces is produced by particles that act as carries of the force. The behavior of all of these particles and forces is described by the Standard Model, with one notable exception: gravity.
STRING THEORY:
In the past ten years, string theory has emerged as the most promising candidate for a quantum explanation for gravity. But there is more to string theory than just explaining gravity on a molecular level; string theory is, essentially, the theory of everything.
The idea behind string theory is that each fundamental particle in the Standard Model is made up of tiny strings. These strings manifest in different ways to produce the different particles that we observe. For example, if a string ‘loops’ up a certain way, it will produce a photon. If it loops up another way it will form a neutrino. Another way, a quark… so on and so on. So, if string theory is correct, the entire universe is made up of strings. And to make it even more complicated and mind boggling, string theory works in ten dimensions!
MULTIPLE DIMENSIONS:
In one theory called M-theory, there are eleven dimensions rather than the three space-time dimensions we are used to and can perceive. The original version of string theories from the 1980s stated that the eleventh dimension would be a very small circle or a line. If these formulations are fundamental, then string theory requires ten dimensions. The idea of space-time dimension is not fixed in string theory; it is best thought of as different in different circumstances (Polchinski 1998).
MULTIPLE UNIVERSES:
Now, this is where things get really interesting. Like I said, each string can oscillate in different ways to form different particles. If you relate what I’ve already said to the violinist, you can get a simplified version of string theory that is easy to explain and comprehend. Just like the different notes on a violin, each different vibration of the string is a different fundamental particle. You play one note and you get a quark. A different note and you get a photon. So, every different note is a different possible particle. And every different chord and harmony within the music, is a different outcome. By different outcomes, I am talking about different universes. If string theory is correct and every different vibration of the string produces a different ‘something,’ then there should be hundreds of billions of different universes. Maybe even more universes than there are stars in the known universe.
A COSMIC CONCERTO:
Now, let’s return to the idea that the strings of string theory are like the notes played by our violinist. Each vibration of the strings creates the fundamental particles and to the forces of nature, which make up everything in the universe. Just as the orchestra and violinist are playing Beethoven, they could just as well be playing a different piece of music, with different notes and different vibrations.
Mathematically, that different piece of music, would produce different notes or vibrations, which would, in turn, create different particles and different forces of nature… meaning, a different universe. So, just as there are an endless number of possible pieces of music the orchestra could play, so our universe must be one of billions of other universes.
We can’t see these different strings because they are outside of our own universe. They have a different history and background than the strings in our universe. Some universes are unstable and collapse back to where they came from, a big crunch. Others, may not produce gravity, and would never be able to produce stars and would be dark and cold. Others will go on to produce stars, galaxies and planets, just like our universe.
According to Stephen Hawking, “we should not be surprised to find ourselves in a universe that is perfect for us. Our very presence means our universe must be just right” (Stephen Hawking’s Grand Design 2010). If string theory is correct, there may be a universe in which someone, exactly like you, decided not to go see the orchestra play. So, they would never be able to relate string theory to the beautiful music that you heard.
So, the next time you listen to a piece of music, regardless of the genre, try to think outside the box, or in this case, outside the universal box.
