Eternal Tragedy: falling into a black hole

Hey everyone! The christmas season is upon us, and it’s a chance to spend some time with your friends and family.

let me share my burden with you.

Being a theoretical physicist is terribly depressing. not because of the pay. that’s depressing, but it’s not why.

Are you familiar with the Total Perspective Vortex, from the Hitchiker’s Guide to the Galaxy? Theoretical physics often involves taking a long, deep stare into it. and then afterwards, when you look at your pretty wife and happy apartment…

this is me when i’m not working. Any time you see me smile, it’s because the sand is warm around my ears.

Anyway! Merry Christmas. Today I’m going to explain what happens if you fall into a black hole. If you find it depressing, well. sorry. If you don’t find it depressing… don’t think too hard about it.

Okay, first off, the library with the colour scanner is closed right now, so i had to do my scanning in black and white. sorry.

Listen, If you want to still think about gravity in terms of little goblins with invisible ropes who pull you towards the surface of the earth, that’s fine… *brings out yo-yo* Look, here’s a toy, it goes up and down on a string. Doesn’t that look like fun?

The Truth of the matter is that Black Holes are objects in space-time. they have subtle properties that newton couldn’t imagine.

To introduce one of these properties, i’m going to preface my explanation with a little bit of Zeno (not the Stoic.) Zeno believed in Parmenides’ philosophy, which claimed that everything was One undifferentiated unchanging object, and that all differentiation or motion was a big misunderstanding. Zeno came up with a bunch of famous paradoxes to prove his point. I’m going to steal the form of one of his awesome paradoxes to help explain how falling into a black hole will ruin your day.

I don’t know why Achilles jumped off a cliff to land on a turtle. I don’t know why he does a lot of stuff.

The deal is that Achilles has to “do” an infinite number of things before he can land on the turtle.

nice diagram, ben!

What? achilles is running towards a turtle who is shooting an arrow at him? GET OUT OF MY HEAD ZENO!

Okay, back to general relativity. In past posts, i’ve explained that one of the big lessons in relativity is that time passes at different rates for different people.

the deeper in a gravity well you fall, the “slower” time passes for you, compared to people far away from the heavy mass.

Okay, so what happens to Achilles if we drop him into a black hole?

lets suppose that achilles has caught the turtle from the previous example, and taught it to read a clock.

Just as in the first Zeno example, we’re dropping Achilles. but instead of landing on a Turtle, he’s going to hit the “surface” of the black hole. There isn’t really anything *on* the surface of the black hole, it’s just the border between inside and outside the black hole.

Just like in the Zeno example, we’re going to cut his descent into 1/2’s. The deal here is that the amount of time it takes to cross each 1/2 section is DIFFERENT depending on whether we’re using Achilles’ clock, or the Turtle’s (sitting safely in a spaceship) clock.

Somehow the black hole also turned Achilles into a stickman.

Okay, so it takes an infinite amount of “turtle” time for Achilles to hit the surface; but it only takes a finite amount of Achilles’ time to hit it! (If you know a black hole scientist, and you want him to laugh, repeat this explanation and then say: “I don’t know why we’re not using tortoise coordinates for this”. they’ll laugh and laugh. )

Okay, so what does this mean?



in other news, what happens when you make it inside a black hole? Well, first you get crushed by the tidal forces. and then you hit a singularity. :(

Merry Christmas everyone!


13 Responses to Eternal Tragedy: falling into a black hole

  1. RossNo Gravatar 22 December, 2010 at 3:48 am #

    So, basically, one could say that a Dr. Who’s TARDIS is essentially a self contained gravity well where time moves at an immeasurably slow rate, but since they’re all smart and sciency-like, the Galifrayans figured out how to manipulate the time vortex through the use of a gravity well … sorta.

    • benNo Gravatar 22 December, 2010 at 6:47 am #

      kind of. apparently, there is no cohesive explanation or mechanism that the writers all refer to. but the doctor’s tardis works like a little pocket gravity well, attached to the rest of the universe by a wormhole. and he can move the mouth of the wormhole wherever he wants. … it looks like additional spatial dimensions get used, too. and i’ve been speculating that the galifrayan’s society is evolving along a 2nd time dimension. *oh god i’ve just come out of the nerd closet*

  2. DustinNo Gravatar 22 December, 2010 at 7:30 am #

    You physics guys. There’s no way the Flames win the Stanley Cup prior to the heat death of the universe, unless you invoke “quantum mechanics” in the same way that homeopaths try to use it. ;)

    • benNo Gravatar 22 December, 2010 at 7:38 am #

      listen closely, i’m going to explain this once. the lets suppose the odds that one player will die of a heart attack during a hockey game is… 1/1,000,000, thus, the odds of a whole team of people dying during a hockey game are 10E-120. and the odds of each consecutive team between the flames and the cup dying will be about 10E-3600 .

      now, most hockey teams would probably NOT accept the stanley cup after every other team in the NHL died of heart attacks. because most people have a sense of shame. but the flames are from calgary, so they would probably even have a stupid parade.

      so the odds are very low that it would happen, but in infinite time, anything can happen.

      • benNo Gravatar 22 December, 2010 at 7:41 am #

        it’s clear at this point that one of my favourite things is to say “listen closely” or someother pedantic phrase, and then to utter a bunch of silly nonsense.

        • DustinNo Gravatar 22 December, 2010 at 8:09 am #

          My bad. I didn’t realize that your calculations also included the possibility of every other team dying. I suppose the odds actually go up if we include other medical issues, as well as funny ways of dying (I’m thinking tiger attacks, rogue stars, zombie plagues and/or epic zambonie accidents…)

          with all of that hitting the universal fan, yes, Virginia, there is a Santa Claus, and yes, he may give the Stanley Cup to the Flames…

          • benNo Gravatar 22 December, 2010 at 8:13 am #

            the odds go up dramatically if we look at the odds that calgary will end up being the seat of some despotic empire, where the dictator will give the flames the cup every year to increase his own popularity.

            given the character of calgary, this seems inevitable.

  3. SophieNo Gravatar 16 January, 2011 at 10:12 am #

    So, Benjamin….
    The (non Rosen and Eistein people, because they weren’t actually trying to discuss the creation but rather explain the idea of electrons as space tunnels) people who try and theorise how one would build an Einstein-Rosen bridge (cough *stargate* cough) are even stupider than they sound, because when you exited one end of the bridge the universe would not exist for you to exit into. Yes?
    I asked my grade 11 phys teacher, and he sent me into the hallway. So.

    • benNo Gravatar 16 January, 2011 at 10:36 am #


    • benNo Gravatar 16 January, 2011 at 11:41 am #

      erm ok, though. lets see.

      well, einstein rosen bridges usually bridge the inside of a white-hole with the inside of a black hole. so if you fell into it, by the time you crossed into the adjacent universe, your universe would have died of old age. whatever that means.

      you can, theoretically, make wormholes that aren’t on the inside of black holes. shortcuts through the universe, as it were. which don’t require an infinite amount of time for you to “enter”.

      there are a bunch of asterisks next to me saying that. chances are, if such a wormhole were to exist, it’d get swallowed up by a black hole; unless a sufficient amount of “exotic matter” were used to prevent this from happening.

      the long and the short of it though is that you are essentially correct for the specific (and most popular) case.

  4. deeNo Gravatar 28 January, 2011 at 4:32 am #

    I wouldn’t say that the surface of a black hole is the event horizon, it’s just the point where the escape velocity reaches the speed of light. The event horizon is the “visual” or informational border of a black hole.

    • benNo Gravatar 28 January, 2011 at 9:07 am #

      the definition of the event horizon is that it is the boundary within which no information traveling at or slower than the speed of light can escape to observers far outside. in dynamic black holes (where the radius is growing because mass is flowing into it), the black holes’ event horizon is a little bit farther out than just the place where photons sit still.

      so if that’s why you mean by informational border, then you’re correct.

      my point to writing this article though was that you can’t just think about black holes in terms of a 3-dimensional surface, where the escape velocity is just “such-and-such” a value at each point. that it’s actually a 4-dimensional object with counterintuitive properties that result from it.

      I’m less precise with my language than i could be in my descriptions because it’s easier to tell someone how to replace a windshield wiper on their car than to tell them how to disassemble and reassemble their car in it’s entierty. i hope no one will be writing a thesis based on this blog post.

      • benNo Gravatar 28 January, 2011 at 9:09 am #

        that said, i’ve got a good explanation of the difference between an event horizon and the “apparent horizon” (where the escape velocity is the speed of light). it involves beavers and fish and glaciers or something. or maybe squirrels and woodpeckers.

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