Black Holes

Alright, I know about the point of view from your friend standing on this side of the horizon (Bob watches you get sucked in, until you hit the horizon where it appears to him that you have stopped moving, even though you haven’t), but what would I see? Let’s pretend that I can survive all the way to the center, what would I see? Would I see all the stuff that has gotten sucked in before, or would it be invisible?

"No job’s too small, we bomb them all."
-Ace Wrecking Company

I’ve heard the same (at a certain point even photons can’t escape) and even used it in a short story once. But just on thinking about it right now it seems that the photons representing the last image that Bob sees wouldn’t freeze in space. They’d make it out and to Bob’s retina, and no more would after that. So I think you’d just fade out in his eyes.

I hope he’d take that moment to shed a tear for you, or drink a beer for you.

Down in your spaceship, if it was still intact at Bob’s last sighting, I’m WAGing that the movements of molecules of neurotransmitters and everything else would be at least as restrained as that of photons and perhaps everything would slow down until you were crushed - black out(long before reaching protoneutron status).

Perhaps I’m thinking about this incorrectly; let’s see, you have a finite mass and your reducing your distance from a close to infinite mass, so…no, there wouldn’t be any incredible lightness of being. I think your ability to move would go before your nervous system. If any of that was observable before your spacecraft imploded.

Maybe you could get some of it out to Bob before your radio transmissions are Doppler shifted to the point of incoherence.

100% WAG (as will be any or all that follow)!

Happy trails!

A black hole does not contain neutrons, protons, electrons, etc. so you would not see anything if you could survive the event horizon.

Bob would have a hard time seeing your image freeze due to the extreme doppler shift and diminishing photonic energy. You apparently slow down and fade away from Bob’s point of view.

Looking up as you go through the event horizon (given a black hole of the correct proportions such that the tidal forces are not so great that you’re squeezed to death at the e.h.), you would see the ‘outside world’ compress into a circle overhead (the light from outside does follow you in).

Looking ‘down’ or ‘forward’ into the black hole from the outside might reveal some Hawking radition (if you could detect it and if it exists), or, superheated particles emitting energy as they collide with one another on their descent. You couldn’t see past the e.h.

Once you past the e.h., looking down would reveal nothing (you’re actually not heading forward in space anymore as much as heading forward in time – thus the inescapability).

If you turned on a flashlight past the e.h., light would look like it was working normally – locally. If you kept track of the beam, it eventually gets distorted back into the ‘down’ direction you’re headed. If you measure the speed of light from your frame of reference, it travels at c. Of course, your frame of reference is severely distorted compared to those outside the e.h. In other words, your ‘straight edge’ is very non-euclidean and your ‘time’ is dilated.

As you approach the singularity, what you see of the outside is increasingly shrinking to a point overhead. Space and time gets more and more distorted. Gravitational tides rip you apart and you stop observing.

If you could survive at the singularity (which you can’t), know one knows what you would observe – all the formulas break down and give incomprehensible results at the singularity.

For more info, check out:
Now, what I want to know, which isn’t in the faq, is what you would ‘see’ when, as you pass the e.h., you look ‘sideways’ (i.e., perpendicularly) into the e.h. What whould that look like?


I believe that you would indeed fade out. You’d freeze and then fade out. The freeze would be a result of the difference in time perspective. Just as observing someone travelling at almost the speed of light makes them seem to go slower, likewise, Bob would see time slow down and then stop for you as you reached the event horizon.

That depends on which way you are looking. If you are looking towards the center of the black hole, everything will go black at the event horizon. If you twist around and look away from the center, then there is no detectable event horizon. You’ll still see stars, Bob, and whatever else might be out there, although it might be distorted.

Your experience would come to an end due to the extreme gradient of gravitation. That is, the pull on your feet will become substantially different than the pull on your head. I would guess that indeed you would first black out or have a heart attack as a result of your circulation being disrupted, and shortly thereafter you’d be ripped to pieces. this would be after the event horizon but well before reaching the singularity.

So say, you die, and now you are a ghost falling in. What would you see? That’s a hard call. :slight_smile:
You wouldn’t be able to see anything in front of you. That is clear enough. So you couldn’t see “stuff” that had fallen in before. Besides, that stuff would in theory be destroyed in the sense that any form that we think of as matter would be broken down.
So if you looked away from the center, what would you see? Hmm, I’ll make the WAG that you’d see everything get brighter, and more and more destorted. I think that you’d see a red shift of the light behind you, with a greater shift for objects farther away. In theory, mebbe everything would meld together into a single light, varying in frequency depending on what direction you look. But at this point I am totally guessing. :slight_smile:

Ok, at the risk of sounding like a moron.

What is the difference between a “quantum singularity” and a “black hole”

Quantum singularities are fictional. The term was created by the writers of Star Trek.

Theoretically, if he was looking in, Bob would see an distorted (perhaps in pieces) image of you floating around the surface of the hole. That image would be stuck there forever.

Actually at one time there was a theory of something called a Quantum Black Hole. These were Black Holes with very small mass which were created during the Big Bang as opposed to being formed through gravitational collapse. Unfortunately, it was later discovered that Black Holes decay and any Black Hole below a certain size would have “evaporated”, so Quantum Black Holes are unstable and do not exist. (At least, they don’t exist for any reasonable period of time.)

“You can’t run away forever; but there’s nothing wrong with getting a good head start.” — Jim Steinman

Dennis Matheson —
Hike, Dive, Ski, Climb —

Always thought that, while Bob would see me apparently stop moving at the cusp of the black hole, I, looking over my shoulder, would see the end of the universe.

This seems like a good time to inject a Hawking quote

From A Brief History of Time, chapter 7.

Given the fame of this book, and the fact that they actually got Hawking to do a cameo, I’d bet that this second paragraph was a direct influence on the Star Trek TNG concept the Romulan “quantum singularity” power source.

As tanstaafl described, these “primordial” black holes could only be created in the moments shortly after the big bang. So far, none have been detected. Hawking notes that they would be very hard to detect because they are small, with a weak signal (compared to stars). Even a primordial black hole as close as Pluto would be hard to see.

Yeah, well, the end of the universe ain’t much to see. It’s rather, how should I put it? Black.

Conceptually, a black hole is in fact a localized end of time.

I had read that time actually stops at the event horizon. I’m not sure what that is about, but I would like to make a small correction.
A black hole would not actually crush you, it would rip you apart. While your in free fall towards it, all parts are accelrated towards it pretty much equally, but as you get closer and closer the parts of you body closest(your feet) to the center are pulled with more force than parts farther away(your head) creating a shearing force, that approaches infinity as you get closer to the sigularity. The gravitaion gradient is actual shallower near the event horizon for supermassive black holes than for smaller ones.

You know, if you people who posted your messages a significant amount of time after I posted mine (and thus presumably read my post) had actually taken the time to read the link to the physics faq I posted, you wouldn’t be sounding so misinformed with your wild-ass guesses. (This does not apply to Undead Dude who posted relatively simultaneously with me.)

The image of the guy falling in isn’t stuck there forever.

You don’t see the universe come to an end.

Time does not stop at the event horizon.

Now, to answer a legitimate question about the difference between a singularity and the event horizon. (Though, the physics faq answers that, too.)

The singularity is at the center of a black hole. It’s where all that matter gets crushed so densely that no known laws of physics describes adequately what’s happening in there. Neither relativity nor quantum mechanics can deal with it. It is unknown at that point.

Around this singularity, there is a strong gravitational field, to put it mildly. Here, the laws of physics do adequately describe what happens, as wierd as it may be. There is a spherical (given an ‘ideal’ black hole) region around the singularity in which neither light nor anything else (except maybe Hawking radiation) can escape. The outer most point of ‘no return’ is the event horizon. The e.h. can be quite far from the singularity if the singularity is massive enough.

The e.h. can be far enough away from the singularity so that the gravitational tidal force is not yet strong enough to kill you. So, it is possible to travel through the e.h. unharmed. As you fall through the e.h. in your space ship, you can be sitting down having tea and not even notice. Local space still seems normal to you as you are in your never-to-return free fall toward the singularity.

(Although, keep in mind that for some black holes, the gravitational tidal forces at or even outside the e.h. can be strong enough to kill you.)


No, but as his image approaches the event horizon, the image will slow down, and would appear to stop at the event horizon if it weren’t for the fact that the light from him will fade out at the same time.

Well, from Bob’s perspective, it would seem that time was going to stop when the falling person reached the even horizon. As is mentioned in the link you provided, observing an object that is close to the event horizon has a temporal effect comparable to that of observing an object that is travelling at close to the speed of light. The closer an object gets to the event horizon, the slower time appears to travel for it. The event horizon itself would represent a temporal asymptote of sorts, just as would the speed of light in special relativity.

I’ve always been intrigued by the asymptotic nature of the “pseudodiameter” of black holes of various sizes, i.e., that your million-ton black hole is microscopic, your sun-weight black hole is three miles across, and your black hole with the weight of the universe is the diameter of the universe. I suspect that that last fact explains something, though I’m not sure what.