# Light in blackhole

1. Mar 14, 2004

### darkar

U see, everything near the black hole or within event horizon will be attract towards the blackhole, even light cannot escape it.
But since light is also puuled inside, imagine u are standing on the blackhole looking outward, will u see the light? Or will the light change to mass?

2. Mar 16, 2004

### kanzure

I'm pretty sure that you'd loose your molecular structure before you even begin to care. Probably, light would go so fast into the blackhole once it reaches a certain point and continusuly accelerate into the black hole.

3. Mar 17, 2004

### darkar

Well, i know the molecular structure will change, that's why i say imagine u are they, doest mean u are really there watching. Just imagine what u can see from there.

By the way, isn't that the light is already at light speed? why will it accelerate again? U said that it will continue accelerates into black hole, so what happen when it reach there? And do light actually exist there?

I am thinking that eventually that those light will eventually being converted to mass in black hole.

Thx

4. Mar 17, 2004

Staff Emeritus
Light will follow null geodesics on its way to the black hole. That is, it won't feel any acceleration locally, but its path will look curved from far away. Light that does make it through the event horizon into the black hole will, indeed, add its energy to the gravity of the black hole. There's a theorem called the "no-hair" theorem that says everything that falls into a black hole just shows up as gravity.

Some light that doesn't quite fall into the horizon goes into orbit, and the black hole is surrounding by a shell of these orbiting photons.

5. Mar 17, 2004

### Nereid

Staff Emeritus
So if you're inside the event horizon looking out, the universe will look pretty normal? Of course, you'd notice that matter - and light - near the event horizon seems to be in grip of a very massive object (or just a very dense one?), but otherwise nothing dramatic.

You couldn't be 'standing on the black hole'; apart from anything else, we already know that our physics *cannot* correctly describe what happens there

6. Mar 17, 2004

### outandbeyond2004

One can't just sit on the event horizon. Need a rocket going at sufficient power, aimed away from the black hole center. Once it runs out of fuel, off into the hole you go.

This is a simulation of physics near the event horizon of a dust-free black hole:

blackhole sim

Last edited: Mar 20, 2004
7. Mar 21, 2004

### Tail

I think that once you're on the horizon, no rocket will help you.

8. Mar 21, 2004

### Imparcticle

Wow. Your consciousness of time would not be altered?
If you are looking inward, then everything is frozen right? Why is it that when you look outward its all "normal"?

9. Mar 21, 2004

### outandbeyond2004

Tail, I didn't mean right ON the horizon, and I was thinking of a supermassive blackhole.

10. Mar 21, 2004

### Nereid

Staff Emeritus
Come with me on a journey into a black hole. As we get closer, we both think that time goes just as fast (or slow) as it always does. We send outandbeyond2004 a series to signals to tell him (her?) that our clocks are just fine. What does he see? What do we think about the rate of rate of his clocks?

11. Mar 22, 2004

### outandbeyond2004

Nereid, have you seen the website that I linked to in a previous post?

Assuming that I am far from the event horizon, I should see you gradually fall into the blackhole with your clock getting slower and slower. You will never quite reach the event horizon from my perspective. In fact, I will die long before I see you get close. An eternally youthful Nereid.

12. Mar 22, 2004

### Tail

Well, you SAID "on the event horizon".

13. Mar 22, 2004

### Nereid

Staff Emeritus
That is a cool website! When I first visited it, I wasn't able to view it properly (browser or something problem), and hadn't realised that it contains a view of the universe from the POV of the unfortunate souls falling into the BH too.

BTW, from my perspective (falling into the BH), life is short, and I get ripped to atoms by the 'tidal force' "long" before I pass through the event horizon [b(]

14. Mar 22, 2004

### outandbeyond2004

Nereid, if it were a supermassive blackhole, the event horizon tidal forces are rather small. You would have to get close to the bh center before they get nasty, well within the eh. By the way, the universe's Schwarzschild radius (= that of the event horizon of a black hole with the same "mass" as the universe) is larger than the universe's radius. So, maybe we are in a black hole. You should be fine anyway.

15. Mar 22, 2004

### Nereid

Staff Emeritus
That's nice to know

I guess that also means that, falling into a 109 Msol BH, all those relativistic effects described in the website will shrink to invisibility (to the eye anyhow).

For the universe as BH, what test could we use, re light falling in? Where would the 'singularity' be? What would it look like?

16. Mar 22, 2004

### outandbeyond2004

Well, the observable universe could be a very small part of the black hole interior. If so, the universe would seem pretty flat, like Earth would look flat in the large to an ant. Tidal effects would not be measureable.

The apparent destination of the solar system's trajectory through space (as shown by the dipole in the CRB measurement (redshifted in one direction, blue-shifted in the other)) does not appear extraordinary.

I am close to my limits of understanding here, I think.