Interstellar : 2 scienc-y questions

[Error404brain]

I know there is an interstellar thread but I think it don't belong to it, because it's more about how stuff work than the movie

1) Does the oberth effect can explain why they use a so small ship ? (They are going fast in the first planet, so ? :-p )

2) If u go fast enough, u can make your vessel smaller. is it possible to make it so small (planck length) that it can enter the blackhole with no problem ?

[cicatrix]

1) I don't know.

2) Anything can go into a black hole, it's getting out that's tricky. And no, from what I know, anything that can get affected by gravity can never exit because, in simple words, the escape velocity exceeds the speed of light.

Ps. This raises another question, if I have supposedly a working Alcubierre Drive and go beyond the event horizon, is it theoretically possible to bend the spacetime and exit elsewhere?

Edited November 13, 2014 by cicatrix

[Error404brain]

1) I don't know.

2) Anything can go into a black hole, it's getting out that's tricky. And no, from what I know, anything that can get affected by gravity can never exit because, in simple words, the escape velocity exceeds the speed of light.

Ps. This raises another question, if I have supposedly a working Alcubierre Drive and go beyond the event horizon, is it theoretically possible to bend the spacetime and exit elsewhere?

Well, the trick is when you enter the blackhole, u are ripped apart by the gravity. So the question was, is it possible to survive. Going out is out of question.

For the alcubierre drive, I think, yes. Since it modify the spacetime, thus gravity, it normaly should be able to run away. But I am totally not a fiable source.

[cicatrix]

Well, the trick is when you enter the blackhole, u are ripped apart by the gravity. So the question was, is it possible to survive. Going out is out of question.

For the alcubierre drive, I think, yes. Since it modify the spacetime, thus gravity, it normaly should be able to run away. But I am totally not a fiable source.

You aren't immediately torn apart once you've crossed the event horizon. It's still a long way down to the singularity and you'll be torn apart quite a bit later, once the gravity differential between the force acting on your legs is greater than the force around your head. You'll can even orbit around the singularity of the black hole for quite a long time keeping as far away from it as possible.

[theend3r]

1) I don't know.

2) Anything can go into a black hole, it's getting out that's tricky. And no, from what I know, anything that can get affected by gravity can never exit because, in simple words, the escape velocity exceeds the speed of light.

Ps. This raises another question, if I have supposedly a working Alcubierre Drive and go beyond the event horizon, is it theoretically possible to bend the spacetime and exit elsewhere?

Some things obviously can exit since black holes are gradually losing mass. Definitely not ships though.

[cicatrix]

Some things obviously can exit since black holes are gradually losing mass. Definitely not ships though.

Nah,

1) The black hole evaporation (Hawking's radiation) is not not a proven fact just a theory.

2) Even if this theory is true, the evaporation comes out from quantum fluctuations immediately on the event horizon. An electron-positron pair is born out of quantum fluctuation and if this happened right on the event horizon, it is theoretically possible that one of them can appear within the Schwarzschild radius of the black hole and the other one - outside of it. As the trapped particle cannot leave the 'free' one should end up carrying 'negative' energy which is 'subtracted' from the total energy of the black hole. Assuming this, the black hole loses its energy over time, but nothing really exits its event horizon.

[Bill Phil]

I wouldn't call the ship "small". It's around a diameter that's about the height of the Space Shuttle, not just the Orbiter, but the whole thing.

[theend3r]

Nah,

1) The black hole evaporation (Hawking's radiation) is not not a proven fact just a theory.

2) Even if this theory is true, the evaporation comes out from quantum fluctuations immediately on the event horizon. An electron-positron pair is born out of quantum fluctuation and if this happened right on the event horizon, it is theoretically possible that one of them can appear within the Schwarzschild radius of the black hole and the other one - outside of it. As the trapped particle cannot leave the 'free' one should end up carrying 'negative' energy which is 'subtracted' from the total energy of the black hole. Assuming this, the black hole loses its energy over time, but nothing really exits its event horizon.

I know all that but that doesn't change the fact that black holes lose mass, which is already proven I think. Then the question is what happens when it loses enough mass that it can no longer sustain its current state. If we assume that it explodes then all the things (or rather the particles they were made of) are loosed eventually. Also since they're probably accelerated to relativistic speeds inside it may even seem from their pov that it doesn't take much time for this to happen.

[Error404brain]

You aren't immediately torn apart once you've crossed the event horizon. It's still a long way down to the singularity and you'll be torn apart quite a bit later, once the gravity differential between the force acting on your legs is greater than the force around your head. You'll can even orbit around the singularity of the black hole for quite a long time keeping as far away from it as possible.

You can't orbit it. it's a blackhole. Or so I tought ? Anyways, that don't change my question, can we survive a blackhole (inside one) ? (Just asking for gravity and the time don't matter.

[Kryten]

It depends on the size. The problem isn't gravity as such, but tidal forces; the bigger the hole, the less force you'll feel.

[Error404brain]

It depends on the size. The problem isn't gravity as such, but tidal forces; the bigger the hole, the less force you'll feel.

) that's the point of going fast. so you have uniformized gravity (one planck length for the ship). I was asking if it was possible to survive by doing so ?

[Kryten]

If you were going that fast, you'd reach the centre of the hole basically instantly no matter how big it was. No surviving that.

[cicatrix]

You can't orbit it. it's a blackhole. Or so I tought ? Anyways, that don't change my question, can we survive a blackhole (inside one) ? (Just asking for gravity and the time don't matter.

It is quite a bit of distance between a point near a singularity where the tidal forces can really rip you apart and some edges WITHIN the event horizon where you can make your descent as slow as possible going in spirals. Eventually though, you will be dragged into the singularity, but with powerful enough engines and delta-v this process can take years.

As you will approach the singularity the gravity acting on different parts of your ship and later - your body will be different at different spots.

If you are standing then the gravity force acting on your legs will be much greater than the gravity acting on your head (which are only about 1.7 m apart). Thus your body will be ripped.

Here's a video:

Edited November 13, 2014 by cicatrix

[lajoswinkler]

Nah,

1) The black hole evaporation (Hawking's radiation) is not not a proven fact just a theory.

2) Even if this theory is true, the evaporation comes out from quantum fluctuations immediately on the event horizon. An electron-positron pair is born out of quantum fluctuation and if this happened right on the event horizon, it is theoretically possible that one of them can appear within the Schwarzschild radius of the black hole and the other one - outside of it. As the trapped particle cannot leave the 'free' one should end up carrying 'negative' energy which is 'subtracted' from the total energy of the black hole. Assuming this, the black hole loses its energy over time, but nothing really exits its event horizon.

In the wacky world of theoretical physics, "theory" is a raped term. Theory is something which includes empirical data and an explanation. It's consistent. There are not many theories out there, and each of them is strong in its field of work.

So you can't say "not a proven fact, just a theory". That is a meaningless statement.

Lots of stuff from theoretical physics is simply not a theory, but a hypothesis. Why are those physicists insisting on calling their scribbling theories, I don't know.

My suggestion - outside theoretical physics, consider the word "theory" to be for all intents and purposes a solid block of cast iron. Modern evolutionary theory, general & special relativity, germ theory, plate tectonic theory, ...

Inside theoretical physics... expect this:

[cantab]

1) No. It's something of a plot hole that they needed the big rocket to launch from Earth but could then use the shuttle alone to launch from the target planets. The best explanation I can come up with is that the shuttle has hyper-efficient engines but nonetheless needed to reach LEO fully fuelled, and the big rocket was the booster NASA had available to do that.

2) I think it's the other way round. From your point of view the black hole would be compressed, making matters worse.

[problemecium]

Hawking radiation is about as well proven as anything else in black hole physics. If nothing else, we have the evidence that the black holes generated by the Large Hadron Collider haven't destroyed the world - they exploded within microseconds due to Hawking radiation.

That said, I wouldn't go expecting anything lacking a warp drive to make it out intact. Even if black holes radiate mass, they remain Nature's ultimate garbage shredder. You'll come out eventually - one particle at a time, in random directions. And I wouldn't exactly call that a safe return (or really any kind of return).

What if we brought a wormhole with us into the black hole, and used it to jump out after crossing the event horizon?

[lajoswinkler]

Is a wormhole an object with mass that orbits something? I've never heard people talking about those things. "It's a hole in space" - great. Positioned relative to what?

[cantab]

A wormhole is a shortcut between two distant places. Imagine two spheres, if you fly in through one you fly out through the other. They're well-described in general relativity, but entirely hypothetical.

[lajoswinkler]

I know what an Einstein-Rosen bridge is. It's basic scientific culture to know these things. Also, even a toddler can learn it just by googling.

I'm interested in more. Is it fixed in space? What's it spatial relation to other objects?

If it's fixed in space, that causes problems with the whole relativity of motion. In the movie, it was "near Saturn". What the hell does that mean? Is it orbiting Saturn? If it's fixed, it's fixed relative to what? Nobody is talking about these things.

[cantab]

Ah, reading again I see what you're asking.

I recall reading about "towing" one end of a wormhole by using the gravity from a massive object, in order to time dilate that wormhole end and thus create a time machine. That would imply that each end of a wormhole behaves like a freely-moving object with mass, and as such it can orbit things and if the mass is enough compared to the size things can orbit it.

[YNM]

1. No, not at all. Oberth effect is all about the change in the velocity vector before and after slingshot, and transfer of angular momentum. Even comets and asteroids experiences this when coming close to the giant planets.

2. It becomes shorter to an observer that's moving wrt to that length. I think that gravitational effect doesn't change whatever speed you're moving, whatever length do you have (or others perceive). Look at photons - they don't have a length (as a boson particle, I guess) yet they experiences gravitational lensing around large-gravitational-effect bodies. I'm not sure through how does it goes when special relativity and general relativity is combined... haven't learned general relativity well.

[Rickenbacker]

You can't orbit it. it's a blackhole. Or so I tought ?

You can orbit a black hole just fine. It's just another gravity well, so orbiting it works the same as orbiting a planet or a star.

[Bill Phil]

You can orbit a black hole just fine. It's just another gravity well, so orbiting it works the same as orbiting a planet or a star.

In the sense that you can orbit. The velocities would be HUGE though.

[problemecium]

Regarding that wormhole question: first things first, a wormhole is a hypothetical construct. While possible under the known laws of physics, the scientific community has no real evidence that any exist anywhere. Thus we can only speculate as to its properties.

That said, almost certainly a wormhole should be movable through the universe like everything else, including a black hole. Unlike in video games (and bad sci-fi movies), the universe does not have any absolute coordinate system and thus no way for any entity to be "anchored" immovably in space. In order to move it, all you need to do is move yourself the other way and then claim that you are the reference point. More practically, we don't have an obvious means of making a wormhole move, but once we start making them I presume we'll figure it out. Probably it'll involve a strong magnetic field or something of the like to hold it within a solid container or frame, which can then be carried aboard a spacecraft.

and @ Bill: that all depends on your altitude. Just like orbiting Kerbin in a high orbit involves a lower velocity, so too does orbiting a black hole. Orbiting near the event horizon would require a huge velocity, but orbiting at a million miles away isn't anything spectacular.

[NERVAfan]

and @ Bill: that all depends on your altitude. Just like orbiting Kerbin in a high orbit involves a lower velocity, so too does orbiting a black hole. Orbiting near the event horizon would require a huge velocity, but orbiting at a million miles away isn't anything spectacular.

Right. If the Sun became a black hole, the Earth's orbit wouldn't change (within Kepler's laws level of approximation anyway - ignoring possible small effects from the Sun currently not being a perfect sphere etc.)

Generally the crazy stuff doesn't start happening until you get much closer to the black hole than the surface of a comparable-mass object of normal-matter densities. (You can't orbit the Earth's center closer than about 6500 km because the Earth/atmosphere is in the way, and once you get under the Earth's surface some of the mass is above you, so the gravity stops increasing... if the Earth were uniform, it would linearly decrease, but the core being denser makes things more complex.)