crossing the event horizon for a short distance?

[Neil9327]

I understand that it is not possible for light to escape a black hole because the escape velocity is higher than the speed of light, which it cannot achieve of course.

 

But if you are, for an instant, just inside the event horizon, say a millameter, then light shone out WILL cross the event horizon, albeit perhaps to only a millameter or so outside it. I say this because a craft may not have sufficient velocity to escape the earth's gravity, but launched upwards it WILL go up for some distance before falling to earth.

 

So could you not have a chain of devices, a camera on the first. The camera takes a photo inside the event horizon, sends the data out to the next device just outside the event horizon, and so on up back to earth. Thus allowing us to see what it looks like inside a black hole.

 

I'm just curious. Don't please go to great lengths to answer this!

 

 

Edit: Just to re-emphasize my point: If you have a space ship that is launched from earth it might have insufficient velocity to escape the earth's gravity, but it WILL be able to go up some distance.

Thereby by analogy, surely if a light beam launched from within the event horizon may not be able to escape from the black hole under its own steam, then can it not go up some distance - a few meters perhaps, analogous to the space ship.

After all, the event horizon is an arbitrary barrier - it is only the point at which light cannot under its own steam leave the black hole completely, it does not say anything about travel local to itself.

Or does it?

[insane_alien]

sorry dude, doesn't work for a number of reasons.

 

1/ all light emitted within the escape horizon will head towards the singularity

2/since things are held together with the electro magnetic force, the moment a part crosses the event horizon, it will stop interacting with the rest of the object as the virtual photons can nolonger reach the rest of the object.

 

this means it will fall off, no matter how strong the material is.

 

its a nice idea but it sadly doesn't work.

 

one of our physicists will probably explain this in greater detail.

[Spyman]

At the Event Horizon one could say that space itself is flowing towards the singularity with the speed of light.

 

Any object placed there will be forced towards the Singularity, like a boat in a very current river.

 

If a flashlight is pointed outwards when it passes the Event Horizon, then the light will move outwards with the speed of light, but space itself is moving with the same speed in the opposite direction. The photons will be brought back by space, just like the boat with a too small engine, struggling to get upstream but actually goes downstream.

 

If the flashlight is in freefall towards the Black Hole it will continue to interact with itself and keep on shining until it breaks from the strong tidal forces.

[Neil9327]

At the Event Horizon one could say that space itself is flowing towards the singularity with the speed of light.

 

Any object placed there will be forced towards the Singularity, like a boat in a very current river.

 

If a flashlight is pointed outwards when it passes the Event Horizon, then the light will move outwards with the speed of light, but space itself is moving with the same speed in the opposite direction. The photons will be brought back by space, just like the boat with a too small engine, struggling to get upstream but actually goes downstream.

 

If the flashlight is in freefall towards the Black Hole it will continue to interact with itself and keep on shining until it breaks from the strong tidal forces.

 

 

Interesting. But is this true?

With some supermassive black holes they say that the event horizon is far out from the black hole itself, such that the amount of gravity at the event horizon is not actually all that strong, but that the distance between it and outer space where the gravity is small, is much larger than for other black holes (so that the gravity * this huge distance > speed of light escape velocity).

So if you are falling through the event horizon and are holding a torch in front of you, then before you fall through you will see the light from the torch of course. Are you really suggesting that as the torch passes through the horizon first, the light will suddenly stop being visible to you?

And then once you are through, does the light reappear, to you?

 

To quote Wikipedia on Supermassive black holes:

"The tidal forces in the vicinity of the event horizon are significantly weaker. Since the central singularity is so far away from the horizon, a hypothetical astronaut travelling towards the black hole center would not experience significant tidal force until very deep into the black hole. "

So if you do not experience significant tidal forces, does the light really experience the event horizon as a true barrier to you, being right next to it?

[Spyman]

1) A supermassive Black Hole has lower tidal forces at the Event Horizon, so you could survive there, but the definition of the Event Horizon is still where the escape velocity is c.

 

2) When you are falling towards the Black Hole, you have a different Event Horizon than the rest of us.

(You would be able to see the light when you fall through our Event Horizon, but we won't.)

 

You might like to read this thread with links: http://www.scienceforums.net/forum/showthread.php?t=26710