It’s probable that you have heard the word “string theory” before on science shows, in movies, or even from Sheldon on the US sitcom, Big Bang Theory. There has been no shortage of hype about the topic, especially from those in the field of physics. You may even have looked for more information about string theory yourself, only to find the topic complicated and hard to understand.
Today we’re going to attempt to break it down in layman terms so you don’t have to be a theoretical physicist to understand it. Then you can decide for yourself if it’s deserving of the hype.
What is string theory?
In short, string theory refers to the mathematical models which seek to find a common explanation for the four main forces seen in nature. These forces are the electromagnetic force, the strong and weak nuclear force and gravity.
Doesn’t relativity and quantum mechanics already do that?General relativity is an amazing scientific theory. It explains how gravity in the world of the large works. It tells how and why planets orbit stars, and how those stars orbit the milky way. Relativity makes predictions which can be seen and verified when you look through a telescope.
Quantum mechanics is equally amazing. It explains the world of the tiny. It gives us a mathematical description of atoms, electrons and quarks and how they interact with each other. Unlike the world of the large, which could be described as serene, smooth and predictable, the quantum world is incredibly strange, weird and chaotic.
So what’s the problem?
Einstein spent the last years of his life trying to unify those 2 theories because as great as they are, problems and inconsistencies occur in some situations which show that neither theory has all the answers. They’re essentially incomplete.
One such situation is a black hole. Black holes are massive in density. They are so dense and heavy, that not even light can escape its gravitational pull. But they are also incredibly small. Gravity has compressed all that mass into a tiny point called a singularity. Do we use relativity to explain a black hole because it contains so much mass or quantum mechanics because it is so tiny?
And there exists the problem. Because the center of a black hole is both incredibly tiny, yet incredibly massive, you cannot avoid using both general relativity and quantum mechanics at the same time. When you attempt to do just that, 1+1 equals 8. They break down and give nonsensical predictions and answers that don’t make sense. It’s kind of like living in a city with 2 different sets of traffic laws that often conflict with each other. The universe is not nonsensical, 1+1=2 not 8, so something is terribly wrong.
Enter String Theory – The theory of everything?
String theory attempts to unite quantum mechanics and general relativity so we can make sense of the universe on all scales, at any place or time, large or small without breaking down.
String theory does this by throwing away the idea that subatomic particles are point-like; instead replacing that notion with tiny vibrating bits of energy, called strings. They’re so tiny that if you enlarged a single atom to the size of our solar system, a string would only be the size of a tree on earth.
These strings are said to ‘vibrate’ at different rates. These ‘notes’ or vibrational frequencies are what give rise to the different properties of quarks and atoms. Vibrations which are similar to the notes on a guitar.
One particular type of vibration (note) may give rise to a muon, while another represents an electron. By changing the vibration of the strings, you can create different particles.
By replacing those point-like subatomic particles with little vibrating strings of energy, we open up a window to the universe that relativity and quantum mechanics can not; a window which may offer us insight into gravity at the quantum scale, black holes or even the birth of our universe itself.
Are there problems or controversies?
For starters, string theory requires our universe to have a minimum of 10 dimensions. These extra dimensions are so small, they cannot be seen. They’re even smaller than quarks. Dimensions which we cannot see or feel doesn’t sit well with many people. It was partially responsible for keeping string theory on the back burner for more than 15 years because many thought the idea was ludicrous and wouldn’t take it seriously.
Another problem is testing string theory. While string theory does in fact make predictions that are testable (an absolute requirement for any serious scientific theory is being able to falsify it), many of the tests require technology that we do not possess yet and may not for hundreds, if not thousands of years from now. There are plenty of things that can be done that will be very suggestive if discovered though, (we may be able to see evidence of extra dimensions at the LHC, or evidence of cosmic strings with NASA’s LISA mission) but they wouldn’t be 100% conclusive.
So now we patiently wait while researchers and theoretical physicists try to discover new ways to test string theory.
What’s this I keep hearing about multiple universes?
One interpretation of string theory’s mathematics may suggest that we live within a brane (membrane). This brane would contain our entire universe and would exist in a higher dimension or “bulk”. In this higher dimension, other branes may exist which could contain their own universes.
In fact, many theorists propose that our brane (or universe) was completely void of matter and energy, and that it happened to collide with another brane in the bulk. The collision would have been so energetic, that it would look just like a big bang (see picture on the right).
Though, that doesn’t necessarily mean there are alternate Earths with another you in those brane universes. The laws of physics in these other dimensions or branes could be incredibly different. For instance, gravity may not exist, or the electromagnetic force may be weaker than ours which would result in stars being unable to form. That universe would be just a sea of protons and neutrons floating around, forever.
What is string theories current status in physics?
Unfortunately, directly observing strings is far beyond our current technological means. Additionally, string theory’s rich diversity makes it difficult (though not impossible) to derive unique predictions that are specific to just string theory.
Still, particle physicists at CERN’s LHC particle accelerator could connect string theory to reality. In particular, 2 discoveries, supersymmetry and extra spacial dimensions would suggest that string theory is on the right track. Stay tuned.