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### String Theory: Science as Symmetry

The principle of symmetry is crucial to the study of physics and has special implications for string theory in particular. *S**ymmetry* exists when you can take something, transform it in some way, and nothing [more…]

### String Theory Makes More Time Dimensions Possible

Because relativity showed time as one dimension of space-time and string theory predicts extra space dimensions, a natural question would be whether string theory also predicts [more…]

### String Theory: Sending Messages through Time

The original string theory, bosonic string theory, contained a massless particle called the tachyon, which travels faster than the speed of light. These particles are usually a sign that a theory has an [more…]

### String Theory and Loop Quantum Gravity: the Same?

One viewpoint is that both string theory and loop quantum gravity may actually represent the same theory approached from different directions. The parallels between the theories are numerous: [more…]

### String Theory and Other Roads to Quantum Gravity

Though string theorists like to point out that theirs is the most developed theory to unite general relativity and quantum physics (at times they even seem clueless that alternatives exist), sometimes [more…]

### String Theory and Causal Dynamical Triangulations

Causal dynamical triangulations’ biggest flaw in comparison to string theory is that it doesn’t tell us anything about where matter comes from, whereas matter arises naturally in string theory from the [more…]

### String Theory: The Perimeter Institute

Many of the prominent critics of string theory who are working on other approaches — Lee Smolin, John Moffat, Fotini Markopoulou, and others — call the Perimeter Institute for Theoretical Physics home, [more…]

### String Theory and Variable Speed of Light

Physicists Elias Kiritsis and Stephon Alexander independently developed variable speed of light (VSL) models that could be incorporated into string theory, and Alexander later worked with Magueijo on refining [more…]

### String Theory and Twistor Theory

As with string theory, the brilliant physicist Sir Roger Penrose’s twistor theory has provided some mathematical insights into the existing theories of physics, including some that lie at the heart of [more…]

### Ten Questions String Theory Should Answer

Any “theory of everything” — whether it be string theory or something else — would need to answer some of the most difficult questions that physics has ever asked. These questions are so difficult that [more…]

### Ten Notable String Theorists

No new theory can develop without dedicated scientists working hard to refine and interpret it. Throughout this book, you read about some of the pioneering work in string theory. Now it’s time to find [more…]

### Ten String Theory Skeptics

String theory may be the dominant theory to reconcile quantum physics and general relativity, but not all physicists have embraced it. In fact, some have become specifically marked by speaking out against [more…]

### The String Wars: Outlining the Arguments

As long as it’s been around, string theory has contended with criticisms. Some of string theory’s critics are among the most respected members of the physics community, including Nobel laureates such as [more…]

### String Theory: The Skeptic’s Point of View

Even now, with criticism on the rise, it doesn’t appear that the study of string theory has dropped. To understand why physicists continue to study string theory, and why other physicists believe it isn’t [more…]

### String Theory: A Rise of Criticisms

There seemed to be some growth in criticisms in string theory after evidence of dark energy was discovered in 1998 and the 2003 work increased the number of known solutions. [more…]

### String Theory: Hundreds of Physicists Can’t Be Wrong

One of the major criticisms of string theory has to do not with the theory so much as with theorists. The argument is that they are forming something of a “cult” of string theorists, who have bonded together [more…]

### String Theory Appeals to Authority

In the case of string theory, of course, the authority figures aren’t just popular, they are experts in physics, and string theory in particular, so listening to their opinion on string theory is a bit [more…]

### A String Theory Rebuttal

In the light of all of the recent criticisms of string theory, many of which have some measure of validity or logic to them, you may be wondering how anyone could continue working on string theory. How [more…]

### How Finite is String Theory?

One criticism that has arisen largely since Smolin’s *The Trouble with Physics* is the notion that string theory isn’t necessarily a finite theory. Remember that this is one of the key features in support [more…]

### String Theory: Space-Time Should Be Fluid

One of the hallmarks of modern physics is general relativity. The clash between general relativity and quantum physics is part of the motivation for looking for a string theory, but some critics believe [more…]

### Does String Theory Describe Our Universe?

Now comes the real science question related to string theory: Does it describe our universe? The short answer is that no, it does not. It can be written in such a way to describe some idealized worlds [more…]

### String Theory and the Academic Kingdom

The theoretical physics and particle physics communities in many of the major physics departments, especially in the United States, lean heavily toward string theory as the preferred approach to a quantum [more…]

### String Theory and Loop Quantum Gravity

Loop quantum gravity is string theory’s biggest competitor. It gets less press than string theory, in part because it has a fundamentally more limited goal: a quantum theory of gravity. Loop quantum gravity [more…]

### String Theory's Competition: What is Looping?

String theory's biggest competitor, loop quantum gravity's key insight is that you can describe space as a *field**;*instead of a bunch of points, space is a bunch of lines. The [more…]

### String Theory versus Loop Quantum Gravity

Loop quantum gravity makes some definite predictions, which may mean that it could be tested well before string theory can be. As string theory’s popularity is being brought into question, the amount of [more…]