What determines the velocity of a bosonic string in string theory?

In summary, the conversation discusses the concept of superstring and the velocity of its ends. The speaker expresses doubt about the ends moving at the speed of light, as it would mean the rest of the string also has the same velocity. The other person suggests the idea of the string spinning, with the middle moving slower than the ends. However, the real solution is to fix the ends with Dirichlet boundary conditions, leading to the concept of D-branes in string physics.
  • #1
Alamino
71
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I've started to study superstring now and I have a little doubt. If you consider the open string with free ends, Polchinski's book says that the ends move with the speed of light. But if the ends move this fast, as the length of the string is fixed the rest of it must have the same velocity. If it depends only on the boundary conditions, massive states of the string will have the same velocity... It should not be this way, what am I doing wrong?
 
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  • #2
What they did was to imagine the string SPINNING, so the middle was moving slower than the ends. But I think the real answer was to remove the freedom from the ends by having them fixed with Dirichlet boundary conditions to what were at first called "walls" and are now called D-branes. This was I believe the origin of the brane idea in string physics.
 
  • #3


The velocity of a bosonic string is a fundamental concept in string theory and can be a bit confusing at first. It is important to understand that the velocity of the string is not the same as the velocity of the endpoints. The endpoints of the string are fixed and move at the speed of light due to the boundary conditions, but the rest of the string can have a different velocity.

This concept can be better understood by considering the different modes of vibration of the string. The open string with free ends has both left-moving and right-moving modes, which can have different velocities. The speed of light is the maximum velocity that any particle can travel, so the endpoint of the string must move at this speed. However, the rest of the string can have a lower velocity, depending on the specific mode of vibration.

Additionally, the velocity of a string is not a fixed value. It can change depending on the energy and momentum of the string, as well as the background spacetime it is moving through. So while the endpoints of the string may always move at the speed of light, the rest of the string can have a variable velocity depending on the circumstances.

In summary, the velocity of a bosonic string is not solely determined by the boundary conditions, but rather by the specific mode of vibration and the energy and momentum of the string. The endpoints may move at the speed of light, but the rest of the string can have a different velocity. I hope this helps clarify any confusion you may have had. Keep studying and exploring the fascinating world of superstrings!
 

What is the velocity of a bosonic string?

The velocity of a bosonic string is a fundamental quantity that describes the speed at which the string moves through spacetime. It is typically denoted by the symbol c and is equal to the speed of light in a vacuum (~299,792,458 meters per second).

How is the velocity of a bosonic string related to its tension?

The velocity of a bosonic string is inversely proportional to its tension. This means that as the tension of the string increases, its velocity decreases, and vice versa.

Does the velocity of a bosonic string change as it moves through different dimensions?

No, the velocity of a bosonic string remains constant regardless of the number of dimensions it is moving through. This is because the string is a one-dimensional object and its velocity is independent of the number of dimensions.

How is the velocity of a bosonic string affected by its energy?

The velocity of a bosonic string is directly proportional to its energy. This means that as the energy of the string increases, its velocity also increases, and vice versa.

Can the velocity of a bosonic string exceed the speed of light?

No, the velocity of a bosonic string cannot exceed the speed of light. This is a fundamental principle of the theory of relativity and is supported by experimental evidence.

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