LHC Black Holes

I have also heard the idea that we are not /in/ a black hole, but on the /surface/ (event horizon) of a black hole of more dimensions.

I suspect that theory will be even harder to verify than Hawking radiation!

If I am not mistaken, what spaghettifies matter falling into a black hole is the delta in gravitational force or the gradient in other words. With a very large black hole wouldn't the gradient be a lot less and so less spaghettification forces? Or is this more an issue of approaching the event horizon where the actual gradient doesn't matter?

I know from the inside the event horizon doesn't appear noticeable in any way. I believe crossing the event horizon would be noticeable from the outside since that it the point where even light can't make headway against gravity. Until then you can see things between you and the event horizon. After crossing that you can only see other things crossing behind you.

I think this pretty clearly shows it is impossible for the universe to exist inside a black hole. We observe the universe expanding, but inside a black hole everything falls inward. Even light can't make headway against gravity.

My understanding is also that it is the gradient of the gravitational

the centre of mass, and the gradient is then going to be proportional to

very big for something like a stellar black hole where you can get close before reaching the event horizon. For tiny black holes, the low mass means that there is very little gravitational force until you are extremely close - it doesn't really count as "speghettification" if it only affects a water molecule on the surface of your skin. And for supermassive black holes, the gradient will be low because you can't get close before reaching the event horizon.

Inside the black hole, light can't escape to get out. Within it, it may be a different matter. "Falling inward" is not in itself a problem - remember, the moon is continually falling inward towards the earth, and the earth is continually falling inward towards the sun. But I don't know enough about the insides of black holes to go on - I could speculate and have Phil or others correct me, but it is perhaps best to let those that know more answer this point without me getting it wrong first :-) All I can say for sure is that since serious physicists have done serious maths regarding these theories, it is /not/ "pretty clearly impossible".

I think inside the event horizon there is no place where light will behave remotely normally. Regardless of how fast you are falling, the light leaving you can't make any headway directly toward the event horizon. I'm pretty sure it makes no sense to try to say you are falling faster than the light.

But then they say that nothing actually crosses the event horizon, or is that only from the perspective of an outside observer?

The whole concept of an event horizon is fallacious, anyway. There are no singularities in nature. It would imply that an object falling into a black hole would reach c, and therefore have infinite kinetic energy. However, the mass of the BH is and remains finite, so we have a contradiction.

A bit of renormalization is needed. There are lots of places in physics where that need arises. As a simple example, the electrostatic energy of an electron --considering it as a point charge-- is infinite too, but we know it's really finite, at about 511keV. That gives us a size estimate for the electron, too. It should be possible to do something similar for a BH. I'd be surprised if it was the same as the basic Newtonian r=2GM/c^2 which we see everywhere.

I didn't attempt to do it.

Jeroen Belleman

You can't observe an object crossing the event horizon--the light coming from such an object fades out because it takes longer and longer to reach you the closer the object gets to the horizon.

From the object's point of view nothing very remarkable happens when it crosses the horizon. If the hole is massive enough, you wouldn't even notice. Of course then you intersect the singularity after a finite amount of time.

I haven't been through the math myself--I decided that I'd rather take quantum field theory than GR in grad school, and then my study partner flaked on me so I had to drop that too, about 2/3 of the way through. A pity.

Cheers

Phil Hobbs

Huh, you couldn't find some other grad student to help? My memory of grad school is that I was always pestering older grad students to help me with problem sets... Badut, genius-type guy in the lab next door, would help me, but then give me some other problem to solve as sorta payment. Wonderful time!

George H.

s to

Yeah, but I was already working on my thesis, had a wife and child, and non e of my other friends was in the class, so I bailed too. I was really only taking it for interest, since I'm not a theorist or high-energy type. I did do a bunch of Feynman diagrams and stuff though. ;)

Cheers

Phil Hobbs

On Wednesday, January 11, 2017 at 9:26:48 AM UTC-5, snipped-for-privacy@gmail.com wrote :

nts to

one of my other friends was in the class, so I bailed too. I was really onl y taking it for interest, since I'm not a theorist or high-energy type. I d id do a bunch of Feynman diagrams and stuff though. ;)

Fair enough. I audited a Solid State theory class, (full of these renormalized electrons and such.).. by the end of it I wasn't even treading water.. but slowly sinking into the deep end.

George H.

No--the event horizon is only one way. Light falling in after you will reach you. IIRC the only really odd thing that happens inside the BH is that the time axis and the radial coordinate change identities, so that there's no way to avoid hitting the singularity in a finite time.

Cheers

Phil Hobbs