String Theory

I received a personal message asking if I knew any online articles or if I had written a blog on string theory. I have mentioned string theory in a blog or two and have alluded to it in some responses but I have not written a blog. I made a quick reply giving the best of my understanding of string theory. After thinking about it for a while I thought it might make a good blog. So I am going to reprint my reply here.

One caveat, it is a very quick reply and I have not had a chance to fact-check everything. My wife and I are in the process of buying a new house. We close tomorrow. We are also screening renters for this house. Both my wife and I have been extremely busy at work, and we will be going to pick up our son who has been visiting relatives and checking out possible colleges. On Sunday, we leave for our vacation in Yellowstone. I am exhausted right now. So I do not expect to do much blogging for the next couple of weeks. I would very greatly appreciate anyone finding faults with this blog pointing them out, so that when things settle down for me, I can correct any errors. Thanks... Here is my reply:

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I don't know of any online articles although there almost certainly has to be some. The best books on the subject are both by Brian Greene. They are:

THE ELEGANT UNIVERSE
THE FABRIC OF THE COSMOS

I have a blog that discusses possible origin of the universe scenarios, but it does not go directly into strings.

Here is the best summary I can come up with in this short amount of time:

Physics has two theories that underlie almost all observations. Those two theories are QUANTUM MECHANICS and the GENERAL THEORY OF RELATIVITY. Each theory has been well tested and have been shown to be VERY accurate within their own domains in which we can test them.

Quantum mechanics looks at the very small. By that I mean it looks at subatomic particles and interactions that take a very short period of time. The General Theory of Relativity looks at gravity (or more precisely accelerated reference planes). It is best tested by looking at huge objects that can attract each other.

Thus, for the most part then these theories deal with separate phenomenon and do not overlap. .... well that is for the most part. There are two areas of physics where there is an overlap. (1) Black holes where a singularity (a point in which the gravitational force is infinite) may exist; and (2) the origin of the universe (which started out from an expansion of the single point). These are small areas where the force of gravity must have been huge.

So physicists want to combine these two fundamental theories into one massive THEORY OF EVERYTHING. But there is an embarrassing problem. When you mix the math of the two, you find that they are incompatible. By doing ordinary math on it you get things like where the probability of something happening is infinite (not a probability of 1 mind you, which would mean that it is certain to happen but a probability of infinity). What the hell does that mean? No one knows. There are other absurdities that come up when these two well-tested fundamental theories are tried to be united.

So something is wrong. But what?

String theory is an attempt to look at the problem from a different vantage point so that these two theories can be united. The exciting part about string theory is that if it is right it finally tells us exactly what the basic part of matter is. If it is right then ALL matter and ALL force particles are made up of tiny vibrating strings. These strings are only 1 planck's length in size (10^-35m, if my memory is correct). What would make subatomic particles different from one another is the direction that the string vibrates. In order for these strings to have enough directions to vibrate in order to create the number of subatomic particles we see in our universe, there must be more than the 3 spatial dimensions we see in our universe. There has to be at least 9 (and maybe 10) different spatial dimensions.

Now if we postulate that these strings do exist, then we can get the math to work so that it fits with the observations we see in the universe. So what does that mean? It means that we know of nothing that rules strings out. So far so good ... right? So what is the catch?

The catch is that these observations are also just as well described by quantum mechanics and the general theory of relativity and the math is easier. There is as of yet no observation that string theory has actually PREdicted.

Why hasn't it been able to predict anything yet? The reason is that the pertinent phenomena that it has a chance of predicting are phenomena that are beyond our technological capabilities of measuring.

Now, we are always improving our technologies. However, we have a LONG way to go before we can measure things in that realm. The other option is to flesh out string theory so that it can predict phenomena in the realm of the observable. But we run into problems. We can come up with 5 different string theories ALL of whom are compatible with everything we know. Which one if any is the right one? Perhaps they all are ... recently a string theorist by the name of Edward Witten came up with some new math that seems to have shown that all 5 of those string theories are just manifestations of the same theory.

I personally have a problem with that. The problem that I have is that each string theory was designed to visualize these vibrating strings differently. If they are the same then the strings they describe cannot be different (as originally proposed).

So, where does that leave us? String theory is perhaps the most worked on theory in advanced physics. But is it science? I'm a scientist. All my training and instincts says that if a theory can't actually predict something that can be tested then it isn't science, no matter how neat one may think it is. I am of the opinion that until it actually predicts something that can be tested for, it shouldn't be considered anything beyond exciting speculation.

Hope that helps,

DB