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Comment by lqdc13 | Hacker News Reader

Wait what? What about sending "quantum data" back from the black hole? The point is that no information can leave.

Also, from what I learned in high school physics, the body of a human would completely fall apart if it's falling to the black hole, because of the difference in gravity between proximal and distal parts.

These are just the 2 things I noticed and I'm far from a physicist. Basically, it got a couple of things right and a bunch of things wrong. There was a clear preference of emotion over science. It just seemed like "The Core" Version 2.0, but here love and reading books conquers all and is beyond the forces of nature.

I liked Europa Report a lot more even though they didn't invest nearly as much into special effects.

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That's an interesting point! The fact that our current theories suggest that no information can ever leave a black hole entails a paradox which is known as the "Black hole information paradox" (https://en.wikipedia.org/wiki/Black_hole_information_paradox). In the movie they resolve this by resorting to gravitational waves, which can "permeate" through space and time by a mechanism not explained in the film. In real physics, there is actually an ongoing debate in the community about whether information can escape from black holes or not, which resulted in a famous bet between Stephen Hawking and Kip Thorne on one side and John Preskill on the other. The fact that Thorne suggests that information can be sent out from a black hole might therefore be a small stab at John Preskill ;)

Concerning the second point, there is actually a pretty fascinating explanation: For a small black hole, the "tidal force" when entering the black hole (i.e. the force difference between your feet and your head) would be so enormous that you'd probably get ripped apart (so-called "Spaghettification" - https://en.wikipedia.org/wiki/Spaghettification). However, the Schwarzschild radius (or event horizon) increases linearly with the mass of a black hole, whereas the gravitational force declines with the square of the radius. Hence, for a supermassive black hole with 10 million solar masses, the tidal force is not bigger than the one you experience here on Earth (https://en.wikipedia.org/wiki/Supermassive_black_hole), and you would probably not even notice when you cross the event horizon. Fascinating stuff.

They glossed over the tidal force in the movie and I assumed it was a deus ex of sorts (in fact, I assumed the whole final act of the movie was more concerned with resolution of the story than with proper Physics). Thank you for this explanation, this is fascinating stuff.

It's still a gloss over, but one of the characters does mention it early on, which I took as indication that it was going to end up being important.

I remember having a similar thought process to all of the above, but they even explicitly call it out as "gentle" with maybe a single really simple sentence on why it was. I don't remember if they made the direct connection to it being supermassive (like they did with its rotation), but it was in the same bit of dialog.

Maybe black holes are nature's true-random-number-generator (via hawking radiation). Energy comes in, energy eventually comes out, but there's no relation as far as wavelength, direction etc.

No idea, I'm an EE not an astronomer, just guessing out of my back end.

I don't know why you're being downvoted, so I'm going to give you a proper reply instead.

Actually, the 2 things you noticed are not that hard to resolve:

- The quantum data was most likely never going to get out of the black hole. They executed the plan on the off chance that TARS was able to figure out how to do it if he had the quantum data. It's not impossible that there is a way to do it, we just don't know it yet.

- Your concern about spaghettification is valid, but the risk of that happening also decreases with the size and mass of the black hole. A stellar mass black hole would rip you apart instantly, but around a supermassive black hole the gravity gradient is a lot gentler. It wouldn't be comfortable per sé, but definitely survivable. You would get ripped apart inside the event horizon, but you could cross it pretty safely.

There is actually a much bigger problem than the spaghettification: every black hole has a shell of light orbiting it at the event horizon. It's light that came in tangentially, and doesn't have enough speed to escape, but is fast enough to keep orbiting. In a black hole of considerable age (like the one in Interstellar), that shell would be very very energetic. I don't know if the ships they were in would be able to survive a blast of radiation that intense, let alone the human and robot inside.

I don't think it's fair to say that they went for emotion over science. They tried to do both, and wanted at least an inclination of accuracy from the start. That's laudable in itself, in a time where most wouldn't bother with that.

Wouldn't spaghettification happen anyway, but at a later point? Maybe everything after he fell in was a dream of his? This would actually make it much more interesting for me although many people probably wouldn't like this sort of ending.

It would happen, but for a black hole massive enough, that point would be well inside the event horizon. We don't know how deep they actually went into the black hole, or even whether or not the 4D structure was inside the black hole or somewhere else entirely. Everything inside the event horizon is essentially unknown to us, both as scientists and as movie-goers, but the trip up to that point is survivable.

That was what bothered me, there would be a zone of high energy particles that you could not pass without severe damage to your ship and your tissues.

They did show his ship being shredded by a bunch of glowing particles...

I'm not going to comment on the "cosmic censorship" hypothesis of black holes since that's actually an incredibly difficult topic, but regarding the tidal forces that would rip you apart, there are certainly large enough black holes that would allow you to comfortably enter the event horizon without being ripped apart. But just to give you a taste of how counter-intuitive this subject can be, consider that despite the fact that light cannot escape a black hole it is conjectured (by Hawking no less) that black holes can emit radiation! (The mystifying mechanism of this involves, very roughly, quantum fluctuations at the event horizon spontaneously giving rise to particle/anti-particle pairs, with one particle of negative mass falling into the horizon and the other of positive mass going out.)

The event horizon is only the "point of no return" insofar as it's the imaginary boundary inside of which even the forward light cones are oriented towards the center of the sphere (so that light cannot escape no matter what direction it's emitted in). It's not the point at which the tidal forces are so strong that matter is ripped apart (or even just your macroscopic body).

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