So I've been doing some research for a while now, and yesterday came across the video of PBS space time talking about what happens to quantum information in a black hole. In the thought experiment about Bob and Alice, he does mention that when approaching the black hole, Alice doesn't get spaghettified but pancakified because of the small tidal forces of the black hole. The argument is that indeed this black hole was so big that the difference in pull, at the human scale, was not great enough for her to experience spaghettification.

So now I came with a question, maybe a dumb one at it, but why does spaghettification appear so much more frequently than pancakification? I've personally never heard of pancakification, and is very triggering since the two phenomenas are quite extreme opposites.

So I thought that maybe, for ordinary scale black holes, spaghettification is the one phenomena happening, as opposed to supermassives black holes, that would be much bigger than ordinary ones. And so, since those black holes are less frequent, would be talked about as "special cases" of black holes, making the pancakification phenomena less talked about. But since that is only a hypothesis, I don't know if it could also be tied to what black holes it is (such as kerr, Schwartzchild, [...]). I also don't quite get the pancakification phenomena either, but i'll try to do some more research on the subject and ask another question later (I'm new at this, can we have two questions in the same post?) I don't know much about the physics behind them either, I'm only in 12th grade, so I'd hope you could go easy on the mathematics, but any answer would help me a lot!

  • $\begingroup$ Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking. $\endgroup$
    – Community Bot
    Commented Jun 14 at 9:06
  • 1
    $\begingroup$ This article mentions "pancakification" as something that can happen to you once you have fallen sufficiently far into "realistic black holes, which are rotating and accreting matter." I didn't read it, so I can't say much more, but they made it sound as if you could expect be well spaghettified first, and then your spaghetti strand would be pancakified. $\endgroup$ Commented Jun 14 at 10:10
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    $\begingroup$ Pancakification seems to be a newer term. That could be why it's more rarely seen. We should probably be on the lookout now for all new research initiatives: swiss-rollification, pasta-screwification; pretzelification. There seems to be a hunger for this kind of knowledge. $\endgroup$
    – Wookie
    Commented Jun 14 at 11:46
  • $\begingroup$ @Wookie The actual reason is the official propaganda against the gravitational length contraction (“pancakification”). The gravitational equation is the Ricci tensor equals zero. This means the ttime dilation (“curvature” of time) equals the length contraction (“curvature” of space). And still the propaganda denies the obvious with the length contraction never mentioned anywhere. This makes people confused. Look at the answer of Yukterez where he mentions the time dilation instead of the length contraction. $\endgroup$
    – safesphere
    Commented Jun 15 at 16:46
  • $\begingroup$ @safesphere Right. Well, he's Viennese so it's probably wiener-breadification we're talking about now: increasingly thin layers of pastry surrounding a deliciously sticky jam hypercylinder. The link Yukterez provides to the Susskind lecture drops right in at length contraction though. Great minds think alike. $\endgroup$
    – Wookie
    Commented Jun 15 at 20:40

2 Answers 2


Susskind explains it here: the pancakification due to gravitational time dilation is only in the reference frame of Bob. In her own frame Alice gets spaghettified, not pancaked, since the local tidal forces are positive all the way.

On the left you have an infalling stream of particles with different initial velocities in ingoing Eddington-Finkelstein coordinates where you can see the local spaghettification, and on the right the same particles in the classic Schwarzschild-Droste coordinates where you can see the pancakification in the frame of the stationary coordinate bookkeeper:

enter image description here

  • $\begingroup$ The link Yukterez provides usefully covers length contraction as well as time dilation. $\endgroup$
    – Wookie
    Commented Jun 15 at 20:42
  • $\begingroup$ @Wookie No, it doesnt. See my detailed comment above. $\endgroup$
    – safesphere
    Commented Jun 16 at 3:07
  • $\begingroup$ @safesphere: in your mentioned comment above you claim that Sussind spouts some propaganda and is the source of a conspiracy to hide the gravitational depth expansion, but that's ridiculous. the real reason he focusses more on the grav. time dilation is that it is enough to explain the principle. the depth expansion is only needed quantitatively, not qualitatively, and since he didn't crunch the numbers in this video he did enough to mention it briefly. in the transverse direction you don't have gravitational expansion, and still all motions in the transverse directions also freeze at r=rs. $\endgroup$
    – Yukterez
    Commented Jun 16 at 16:55
  • $\begingroup$ @safesphere: in the animations above the depth expansion is also taken into account, those use the equations of motion that come directly from the metric. In an animation where you show the specific coordinate times you need it all, but Susskind was just drawing a cartoon image on a blackboard without any specific numbers, so he did nothing wrong when he focussed on the more important part. $\endgroup$
    – Yukterez
    Commented Jun 16 at 17:01
  • $\begingroup$ @safesphere: of course you're gonna say that the Eddington-Finkelstein coordinates on the left are crap since you want the singularity as a one dimensional line or something, but for now you have to at least accept the animation on the right, since that uses the classical coordinates, which according to you are the only ones that are real. $\endgroup$
    – Yukterez
    Commented Jun 16 at 17:09

I watched the video, and it's important to note that the term pancakification is not used anywhere else at all. However, it is interesting to see what the video tries to say. Without going too deep into general relativity, the effect can be explained purely Newtonian as well. I will keep the mathematics as simple as possible. Say we have Alice of mass $m_A$ and length $L_A$, then the Newtonian difference in force between her head and her feet will be:

\begin{equation} \Delta F = \frac{GMm_A}{r^2} - \frac{GMm_A}{(r+L_A)^2} \end{equation}

with $M$ the mass of the black hole. The idea of 'spaghettification' is now that this difference will be so large, that her head will inevitably be pulled apart from her feet. We can rewrite the force difference as: \begin{equation} \Delta F = \frac{GMm_A}{r^2}\left(1-\frac{1}{1+\frac{2L_A}{r}+\frac{L_A^2}{r^2}}\right) \end{equation} with $L_A\ll r$, so the denominator terms are almost zero. We can make a taylor expansion to estimate the behaviour. Know that for small $x$, $\frac{1}{1+x}\approx 1-x+\ldots$, so we have:

\begin{equation} \Delta F \approx \frac{GMm_A}{r^2}\left(1-1+\frac{2L_A}{r}\right) = \frac{2GMm_AL_A}{r^3} \end{equation} where I ignored quadratic terms due to being too small. Let's evaluate this approximation for the force difference at the event horizon/ Schwartzschild radius $r = \frac{2GM}{c^2}$:

\begin{equation} \Delta F \approx \frac{2GMm_AL_A}{\frac{8G^3M^3}{c^6}} = \frac{m_Ac^6L_A}{4G^2M^2} \end{equation} Even in this Newtonian approximation we can see what's going on. First of all, if Alica is longer ($L_A$ is bigger), the force difference will evidently be larger. Secondly, at the event horizon, we see that the force difference scales as $\sim 1/M^2$: the larger the black hole, the less spaghettification we have, simply because the event horizon distance is much farther away. Indeed for these super massive black holes the spaghettification process will not occur (to properly calculate the effect, you would need general relativistic calculations of course).

The idea of 'pancakification' is now that since objects seem to freeze at the event horizon, for an outside observer (Bob) Alice looks to be located in a very thin slice right before the event horizon. In some sense, she looks as a pancake, compressed into that thin slice. Bear in mind that this is only what Bob would see, from Alice's perspective she only feels a slightly stronger pull at her feet than on her head (see derivation above).


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