- #1

- 38

- 1

You are using an out of date browser. It may not display this or other websites correctly.

You should upgrade or use an alternative browser.

You should upgrade or use an alternative browser.

- Thread starter qtm912
- Start date

- #1

- 38

- 1

- #2

- 33,822

- 12,190

A null surface is a surface that has null tangent vectors; in other words, there are null vectors that lie completely within the surface. For example, the event horizon of a black hole is a null surface.

A null geodesic is just a geodesic whose tangent vector is null; for example, the worldline of a light ray traveling through a vacuum is a null geodesic. So there is indeed a close connection between null vectors and null geodesics.

- #3

- 38

- 1

- #4

WannabeNewton

Science Advisor

- 5,800

- 536

It means the vector field associated with the coordinate is null.

- #5

- 38

- 1

Ok many thanks to you both for clarifying.

- #6

WannabeNewton

Science Advisor

- 5,800

- 536

Note that for any tangent vector ##v \in T_p \Sigma##, ##v \perp \nabla r## implies that ##v## is itself null so this is equivalent to Peter's definition above.

- #7

- 38

- 1

Hi again, I am a bit unfamiliar with the notation here, how is g(del-r, del-r) defined?

- #8

- 28

- 0

That's the scalar product (the dot product) of the vector field del-r with itself.Hi again, I am a bit unfamiliar with the notation here, how is g(del-r, del-r) defined?

Share: