落入黑洞边界后如何延长存活时间？

Maximizing Survival Time Inside the Event Horizon of a Black Hole

Written by Fraser Cain

                               
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Here's a scenario that will face many of us in the far future. You're hurtling through the cosmos at nearly the speed of light in your spaceship when you take a wrong turn and pass into the event horizon of a black hole. Uh oh, you're dead - not yet, but it's inevitable. Since nothing, not even light can escape the pull from a black hole once it passes into the event horizon, what can you do to maximize your existence before you join the singularity as a smear of particles?


Physicists used to think that black holes were sort of like quicksand in this situation. Once you cross the event horizon, or Schwarzschild radius, your date with the singularity is certain. It will occur at some point in the future, in a finite amount of proper time. The more you try to struggle, the faster your demise will come. It was thought that your best strategy was to do nothing at all and just freefall to your doom.

Fortunately, Geraint F. Lewis and Juliana Kwan from the School of Physics at the University of Sydney, have got some suggestions that fly in the face of this stuggle = quick death hypothesis. Their paper is called No Way Back: Maximizing survival time below the Schwarzschild event horizon, and it was recently accepted for publication in the Proceedings of the Astronomical Society of Australia.

When an unlucky victim falls into the event horizon of a black hole, they will survive for a finite amount of time. If you fall straight down into a stellar black hole, you'll last a fraction of a second. For a supermassive black hole, you might last a few hours.

Due to the tremendous tidal forces, an unlucky victim will suffer spaghettification, where differences in gravity from your head to your feet stretch you out. But let's not worry about that for now. You're trying to maximize survival time.

Since you've got a spaceship capable of zipping around from star to star, you've got a powerful engine, capable of affecting your rate of descent. Point down towards the singularity and you'll fall faster, point away and you'll fall more slowly. Keep in mind that you're inside a black hole, flying a spaceship capable of traveling near the speed of light, so Einstein's theories of relativity come into play.

And it's how you use your acceleration that defines how much personal time you'll have left.

In a moment of panic, you may point your rocket outwards and fire it at full thrust, keeping the engine running until you arrive at the central singularity. However, Lewis and Kwan have demonstrated that in the convoluted space-time within the event horizon, such a strategy actually hastens your demise, and you'll actually end up experiencing less time overall. So, what are you to do? Lewis and Kwan have the solution, identifying an acceleration "sweet-spot" that gives you the maximal survival time. All you have to do, once across the event horizon, is fire your rocket for a fixed amount of time, and then turn it off and enjoy the rest of the fall.

But how long should you fire your rocket for? Lewis and Kwan show this is a simple calculation involving the mass of the black hole, how powerful your rocket is, and how fast you crossed the event horizon, easily doable on a desktop computer.

Here's another analogy from Lewis:

"Consider a race to the centre between a free faller and a rocketeer. Suppose they cross the event horizon together holding hands. As they cross, they start identical stop watches. One falls inwards, while the other accelerates towards the centre for a little, then swings their rocket round and decelerates such that the free faller and the rocketeer meet and clasp hands again just before hitting the singularity. A check on their stop watches would reveal that the free faller would experience the most personal time in the trip. This is related to one of the basic results of relativity - people in freefall experience the maximum proper time."

So now you know. Even after you've fallen into the black hole's event horizon, there are things you can do to lengthen your harrowing journey so that you get to experience more time.

Time to you can use to deal with your spaghettification problem.

人是活不了的啦

驾驶星际飞船误入黑洞，当然是必死无疑，问题是如何最大化存活时间。这里可能要用到爱因斯坦的相对论，需要进行一项“简单的计算”，它涉及黑洞的质量、飞船的动力及其穿越黑洞边界时的速度。

如何算？

假设你开着一艘宇宙飞船,那么这时你就像黑洞视界开足马力飞行,这样就可以延缓你被撕碎的时间。Stephen·Hwking说的。

呃·····只能呃了···

黑洞视界内部存活时间问题。。。好像要考虑黑洞的类型，比如克尔黑洞，是有可能在视界内部存活较长时间的。

黑洞可没有想象的那么简单（PS：其实黑洞又很简单，只有三个参量），通常科普读物上说，进入黑洞视界以后（其实视界这个地方还有点复杂，还可能有所谓的能层的东西），只有一个命运，就是掉向奇点。对无自转黑洞，情况如此。不过，对有旋转的黑洞，如Kerr黑洞，情况有点复杂，Kerr黑洞中，视界的的值有两个解，两个解形成一个空间环形区域，在该区域中，所有的物体包括光的运动方向才只能指向中心奇点。以该区域的内边界为外边界的一个环形区域，是所谓的能层（能层外面还有一个），能层中为正常时空，物体的运动方向可以由黑洞中心向外，因此，Kerr黑洞的这个区域可以存在物质，而不是一定会掉向中心奇点。（至于这一能层内边界到中心奇点处的性质，那本教材上没说，我也还没去算，不知道咋样）

另外，光速不变原理是狭义相对论SR的基本原理，但不是广义相对论GR的基本原理。在GR中（准确的说是在有引力场的非欧几何下），光速不变是有条件的，只有在时轴正交坐标系下，并且由标准钟测得的光速才是恒定的光速，在其他情况下，光速是变的。所以，在GR中，不能简单的用SR的概念说光速。

晕......OVER.....

黑洞没有体积，那么物质的存在方式是什么呢？没有质子电子了吧

14# 夜的眼睛

黑洞没有体积，这是个错误的理解。

厄。。这个。。那个

由于引力潮汐。在离黑洞很远的地方。固体物质就瓦解了。接近以后。粉末也会被继续粉碎成分子。
再接近连分子也不能成活了。只有离子存在了。

会不会从白洞出来呢