Andrew Zimmerman Jones - String Theory For Dummies

One of the most unexpected and disturbing discoveries of string theory is that instead of one single model of the universe, it turns out that there may be a huge number of possible models (or, more precisely, possible solutions to the theory) — maybe as many as 10 500different solutions! (That’s a 1 followed by 500 zeroes!) While this huge number has prompted a crisis among some string theorists, others have embraced it as a virtue, claiming it means that string theory is very rich.

In order to wrap their minds around so many possible models, some string theorists have turned toward the anthropic principle, which tries to explain properties of our universe as a result of our presence in it. Others instead argue that the vast number of possible string models is to be expected — or even that it’s a feature, not a bug , so to say. For them, it’s just a matter of nailing down the particular string solution that does describe our universe.

With such a large number of theories available, the anthropic principle allows a physicist to use the fact that we’re here to choose among only those theories that have physical parameters that allow us to be here. In other words, our very presence dictates the choice of physical law — or is it merely that our presence is an observable piece of data, like the speed of light?

The use of the anthropic principle is one of the most controversial aspects of modern string theory. Even some of the strongest string theory supporters have expressed concern over its application because of the sordid (and somewhat unscientific) applications it has been used for in the past and their feeling that all that’s needed is an observation of our universe, without anything anthropic applied at all.

As anthropic-principle skeptics are quick to point out, physicists adopt the anthropic principle only when they have no other options, and they abandon it if something better comes along. It remains to be seen if string theorists will find another way to maneuver through the string theory landscape. ( Chapter 12has more details about the anthropic principle.)

In the mid-1990s, two physicists came up with an idea called the holographic principle. In this theory, if you have a volume of space, you can take all the information contained in that space and show that it corresponds to information “written” on the surface of the space. As odd as it seems, this holographic principle may be key in resolving a major mystery of black holes that has existed for more than 30 years!

Many physicists believe that the holographic principle will be one of the fundamental physical principles that will allow insights into a greater understanding of string theory. (Check out Chapter 13for more on the holographic principle.)

String theory yields many fascinating subjects for thought, but you may be wondering about the practical importance of it. For one thing, string theory is the next step in our growing understanding of the universe. If that’s not practical enough, then there’s this consideration: Your tax money goes to fund scientific research, and (a tiny fraction of) the people trying to get that money want to use it to study string theory (or its alternatives).

A completely honest string theorist would be forced to say that there are probably no practical applications for string theory, at least in the foreseeable future. This admission doesn’t look that great on either the cover of a book or at the top of a webpage, so it gets spiced up with talk about discovering parallel universes, extra time dimensions, and new fundamental symmetries of nature. They might exist, but the theory’s predictions make it seem that they’re unlikely to ever be particularly useful, so far as we know.

Better understanding the nature of the universe is a good goal in its own right — as old as humanity, some might say — but when you’re looking at funding multibillion-dollar particle accelerators or research satellite programs, you might want something tangible for your money. Unfortunately, there’s no reason to think that string theory is going to give you anything practical.

Does this mean that exploring string theory isn’t important? No, and it’s our hope that reading Part 2of this book will help illuminate the key at the heart of the search for string theory, or any new scientific truth.

No one knows where a scientific theory will lead until the theory is developed and tested.

In 1905, when Albert Einstein first presented his famous equation E = mc 2 , he thought it was an intriguing relationship, but he had no idea that it would result in something as potent as the atomic bomb. He had no way of knowing that the corrections to time calculations demanded by special relativity and general relativity would someday be required to get the worldwide global positioning system (GPS) to operate accurately (more on GPS in Chapter 6).

Quantum physics, which on the surface is about as theoretical a study as they come, is the basis for the laser and the transistor, two pieces of technology that are at the heart of modern computers and communication systems.

Even though we don’t know what a purely theoretical concept like string theory may lead to, history has shown that it will almost certainly lead somewhere profound.

For an example of the unexpected nature of scientific progress, consider the discovery and study of electricity, which was originally seen as a mere parlor trick. To be sure, you could predict some technologies from the discovery of electricity, such as the lightbulb. But some of the most profound discoveries are things that may never have been predicted — radio and television, the computer, the internet, the cell phone, and so on.

The impact of science extends into culture as well. Another by-product of electricity is rock and roll music, which was created with the advent of electric guitars and other electric musical instruments.

If electricity can lead to rock and roll and the internet, then imagine what sort of unpredicted (and potentially unpredictable) cultural and technological advances string theory could lead to!

Chapter 2

IN THIS CHAPTER

Squaring off: Gravity and quantum physics just don’t get along

Seeing four types of particle interactions

Hoping to tie all of physics into one equation with quantum gravity

Physicists like to group concepts together into neat little boxes with labels, but sometimes the theories they try to put together just don’t want to get along. Right now, nature’s fundamental physical laws can fit into one of two boxes: general relativity or quantum physics. But concepts from one box just don’t work together well with concepts from the other box.

Any theory that can get these two physics concepts to work together would be called a theory of quantum gravity. String theory is currently the most likely candidate for a successful theory of quantum gravity.