Black Holes

Jillian's Guide to Black Holes: Forming - Types - Outside - Inside - Finding - References - Websites

Shutting off the engines to make your last few moments as comfortable as possible

Ah, you chose to do the freefall thing. Very wise. This means you get a great view before you are torn apart by the tidal forces of the black hole. Briefly, tidal force is what happens when your feet are accelerating faster than your head --- you get stretched! Normally, we deal with gravitational fields weak enough that this doesn't happen on a small scale (small meaning the size of humans and rockets). It does happen on the scale of the Earth in response to the gravity of the Moon. That's why it's called 'tidal,' as in 'pertaining to tides.' The gravitational attraction of the Moon on the Earth's water deforms the water into an oval so that the water bulges out from the rock in two places: one at the side that is closest to the Moon, and one on the side that is furthest from the Moon. As the different parts of the Earth pass through this water bulge, they experience higher water, or high tide.

Next to a black hole the tidal force on something the size of a human or a rocket is no longer weak at all. That deformation is happening to you and your rocket. It gets worse as as you fall further. In fact the effect is so strong that, eventually, your body will be stretched like an image on silly putty until it breaks.

As if this isn't bad enough, there is one more relativistic effect of falling past the horizon that I have yet to mention: the blue sheet. I explain it in depth in Inside section, but I'll also give a brief description here. Recall how I told you that light redshifts due to gravity? Well, the opposite happens inside the event horizon --- the light blueshifts. It's just like redshifting except it's in the opposite direction. Redshifting decreases the frequency of a light ray, blueshifting increases it. Inside the event horizon, a light ray blueshifts until it becomes what scientists call a gamma ray, the most high-energy form of light there is. Gamma rays are much more powerful than ultra-violet light, which most folks consider nasty because it raises the chances of getting cancer due to its high energy. Imagine what gamma rays would do to ya!

Heh, so, not only are you stretched by the tidal forces, you are also irradiated by gamma rays! It's a good thing that the time you have left is only about the same time it would take a light ray to cross 2Rs.

Where's the great view?!?

I was quite sneaky when I mentioned the "blue sheet." That light that got blueshifted wasn't light that fell in the event horizon from your universe! It did fall through the (same?) event horizon, but it came from another universe. It all has to do with the spacetime diagram of a static black hole, which I detailed in the Inside section, the section dealing with multiple universes and the three types of black holes.

If you just want to take my word for it that light from another universe can reach you as you freefall past the event horizon, okay; I shall just tell you this: after crossing the event horizon, you see a small area which contains light from the other universe---a small area very much like the small area that your universe became just before you crossed the event horizon. The difference between the two is that, when you see the light from the other universe, it has this black band around it --- that's the black hole. The longer you fall, the larger the other universe appears and the closer the black band seems to be. Eventually, the tidal forces tear you apart, but for that brief time, you saw the other universe. If someone had fallen through the event horizon from that side, you could wave to each other before the black hole stretched you apart.


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