Subject: Black holes and light.

Background:

For years, nay, decades, I have heard or read the expression

“So dense that even light cannot escape” Or to that effect.

I have had a great deal of problem with that; visualizing some poor photon trying to struggle up the ladder of gravity, sweat dripping from the body as it struggles against the pull of gravity pulling the ladder down as fast as this desperate photon climbs the rungs in its attempt to escape.

I read a passage in a book a few years ago that caused me to have a different picture, A picture of this same photon, now happily speeding along at its relativistic speed of light, and going in a “straight line” with space.

However, as this “space” is now part of a “Black Hole”, the gravity causing space to be so bent as to be curved into a circle. So the “light” if any, inside a black hole is not trying to escape at all, but just doing its normal thing, just in the case of being inside a black hole, this light is just going around in circles from our perspective.

So, is the phrase “Light in a black hole just travels around in a circle”, any better??

Is my Mickey Mouse visualization any closer to a realistic picture than “Can’t escape” visualization?

I'm an electronic technician.

Fred Weldon

Hum,
Indeed that would be a better visualisation.

I think the light would go in circles, if those circles were lying exactly on the event horizon.

But beneath the event horizon, inside the black hole, the light would not follow a circle, but a spiral coming ever closer to the central singularity.

Yes, that's my understanding as well-- the black hole central singularity is on the "future" timeline of everything inside the event horizon, so it all gets there eventually. The "ladder" does pull the photon down after all, but it is always zipping along effortlessly at the speed of light relative to the rungs.

Somehow I really doubt it.

Hum,
Just remember that light always moves in straight lines.

(as in, a straight line drawn on a bit paper, that then is crumpled)

Space-time is curved (in a circle? - not quite; that would be another universe)

Two Suitcases
Your photons do not have a hard time getting up a gravity hill so much as the hill is actually a change of direction. Near a massive object most directions are towards the mass. Within the event horizon, what I think you meant by saying inside the black hole, all directions are toward that central mass.

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http://members.elirion.net/~maddad
There are ten kinds of people. Those that understand binary, and those that do not.

Sorry to stray. But Maddad, wouldn't that be better stated, "There are 10 kinds of people. Those that understand binary, and those that do not."?

Does light have mass? How is it that light is affected by gravity?

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I've seen things you people wouldn't believe. Attack ships on fire off the shoulder of Orion. I watched c-beams glitter in the dark near the Tanhauser Gate. All those … moments will be lost … in time … like tears … in rain. Time … to die.

Simple answer, in current theory(General Relativity), light does not have mass. Photons move along the shortest possible path through spacetime. These paths are called geodesics of spacetime. The presence of energy warps( or curves) spacetime changing the geodesics the photons move along. It's not so much that gravity affects photons as gravity changes the path photons move along.

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Some try to tell me, thoughts they cannot defend,... - Moody Blues.

Outside of a black hole, light will travel in a path that looks very bent to us, because of the bending of space time, just like the generic weights on a rubber sheet image.

Inside a black hole, Einstein's physics breaks down, so we don't know anything about the curvature of space time (if there is a space-time!) inside a black hole. One possibility is that it becomes an infinite cylendar, so the photon would zoom around on the outside of this cylendar.

I'm not sure if that cylendar would be at the event horizon though, anyone?

I am not entirely comfortable saying that Einstein's physics breaks down inside the black hole. Sure, I know it's repeated so much it must be gospel, but I don't think it's quite right. The breakdown, if it happens at all, happens at the singularity, not at or just inside the event horizon. There you can still apple Einstein's physics. Whether you can live with some of the crazy results is probably a matter of getting used to answers that do not appear to make sense at first glance.

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http://members.elirion.net/~maddad
There are ten kinds of people. Those that understand binary, and those that do not.

I'll agree with Maddad here. General relativity works fine within the event horizon (though it would admittedly be tough to test experimentally ). As a side note, horizontally moving photons won't orbit at the event horizon. At 1.5 times the Schwarzschild radius, the orbital velocity is light speed, so photons can travel in circular orbits at that radius (it's called the photon sphere because of this). Closer in than this and a photon won't orbit; it's either pointing sufficiently outward to escape entirely, or it will eventually end up inside the black hole.

We would perceive laws to work fine within the event horizon. Take a galactic black hole for instance: Its EH is located far away from the central mass. You could trespass the EH without noticing. The spacetime there would be only slightly warped. You wouldn´t be able to get out of it anymore, but everything would still seem to be alright. One of the results of the normal functioning of the laws of physics inside the black hole would be your final crunching as you approached the singularity.

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If you're careful enough, nothing bad or good will ever happen to you.

Hum,
yea that could be possible.

Though it could be possible that none of our normal physics exist there. Every thing may moves at the speed of light, they may have no mass, or they can be at different places at the same time.
We don't even know if there are just 3 macro dimensions or that the temporal dimension acts like `Time` out here...

And note, there is also the other half of the question-- if light has no mass, how can it be a source of gravity? The answer to that part is, gravity does not just come from mass, it comes from any type of energy.

And note that it doesn't even break down at the event horizon, as was wondered by Maddad, since the event horizon is only a coordinate singularity, not a true singularity. Physics doesn't break down at a coordinate singularity, any more than it doesn't work at the North pole.

That's interesting Grey, thanks. Is this the same as the "ergosphere", from which you cannot get energy, and/or the radius of the last stable orbit?

The point being, I suppose, that if we can't test it, we're asking how many angels can dance on a pin.

Yeah,
the current fad just now is the new string theories . The BH models that are envisioned are maybe wrong, but just now, they work with resolving the information problem with BHs.

Er, which is slightly better than shear speculation.

Perhaps when we can create mini black hole, we may have new information and perhaps a new theory/tools to deduce what lies within.

Interesting idea. If the loonies don't shut you down for endangering the Earth with your mini black holes!

Event horizon is something that you can define at will. Earth has an Event horizon for bodies travelling bellow certain speeds. You can cross it without noticing any change in the laws of physics. A black Hole´s EH is just the ultimate horizon. There should be no reason for expecting any physics laws breakdown upon crossing it.

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If you're careful enough, nothing bad or good will ever happen to you.

Indeed that would be the common sense view.

But as we see in quantum physics, common sense is wrong.

When we cross the event horizon all movement is in a inwards direction, effectively one-way.
http://curious.astro.cornell.edu/que...php?number=652

Inside the event horizon, time and space may change places and causality and predictability may not apply.
http://www.superstringtheory.com/blackh/blackh2a.html

Heiselberg's uncertainty principle does not seem to apply either.

And most importantly all the particles are effectivly moving at the speed of light (?)