# How does a photon's event horizon look like?

1. Jan 30, 2008

### EnumaElish

2. Jan 30, 2008

### pervect

Staff Emeritus
I don't understand the question. Are you perhaps interested in the Rindler horizon experienced by an accelerated observer? (Sorry if this is NOT what you're interested in, but I'm having difficulty in interpreting your question).

3. Jan 30, 2008

### EnumaElish

I assumed that the shape of the event cone would depend on the velocity with which point E is traveling along the t axis. Is that not right?

4. Jan 30, 2008

### chroot

Staff Emeritus
I don't understand the question either. "Event horizon" of a photon? "Event cone?"

- Warren

5. Jan 30, 2008

### DaveC426913

Isn't he showing a Minkowski diagram?

6. Jan 31, 2008

### EnumaElish

pervect & Warren, thank you for your responses and patience with a non-physicist. Your reply prompted me to take another look at the Wikipedia diagram.

BTW, I noticed that the first link in my OP has become nonfunctional. The new link is: http://upload.wikimedia.org/wikipedia/commons/1/1d/Event-horizon-particle.svgIf you click on it you will see the diagram represented as a spacetime diagram on the Wikipedia page entitled "event horizon."

The caption applicable to this diagram (click on: http://en.wikipedia.org/wiki/Event_horizon) reads: "event E [] is outside the particle [P]'s event horizon."

My questions:
1. Can anyone see the diagram, or is there a broken link?

If you can see the diagram:

2. Which object on the diagram represents P's event horizon?
a. Does the the red curve represent P's event horizon?
b. Do the boundaries of the hourglass-shaped yellow area represent P's event horizon?
c. Does the entirety of the hourglass-shaped yellow area represent P's event horizon?

3. What does the entirety of the hourglass-shaped yellow area represent?

4. What do the boundaries of the hourglass-shaped yellow area represent?

5. The Wiki article states "As the particle [P] accelerates, it approaches, but never reaches, the speed of light with respect to its original reference frame. On the spacetime diagram, its path is a hyperbola, which asymptotically approaches a 45 degree line (the path of a light ray)."
5.1. Would this diagram be different if the particle P was traveling at the speed of light?
5.2 How would it be different?
a. Would the red curve be different? How?
b. Do the boundaries of the yellow area be different; how?

Let me know if you need additional information or explanation about any of the questions above and I'll try my best to provide it.

Last edited: Feb 1, 2008
7. Feb 5, 2008

### EnumaElish

Partly due to a lack of responses on the PF, I put the question to Cornell University's "Curious? Ask an Astronomer!" website, and I got an answer in about a week. I decided to post it here for general information and any reactions from the community.

It says (with reference to the Minkoswki diagram on the Wiki page "Event Horizon"):
Admittedly this answers a different question than my original, which I can best state as "If Minskowski was a photon, would there be a diagram? How would it look?" So my original question did evolve under this thread, hopefully for the better.

[Further edit (now this is beginning to look like a blog): Rarely the one to give up, I put my original question to the exceedingly helpful staff of Cornell's Ask An Astronomer website. Their quick response was:
Excellent website & great staff, Ezra!]

Last edited: Feb 5, 2008