You may have heard that it’s impossible to escape from a black hole.
And it is. End of post.
However. Do you know the real reason why?
The prevailing explanation for a black hole’s event horizon being the point of no return is that gravity simply becomes too strong. As you get closer to a black hole’s centre, the force of gravity increases, so more energy is required to keep you safely away. At the event horizon, an infinite amount of energy would be required to achieve this feat. Last time I checked, physics doesn’t allow you to have literally infinite joules of energy, so, your only option is to continue falling in.
Conversely, though closely related, you might consider the escape velocity. Just as a rocket taking off from Earth requires some velocity to leave its surface (11.2 km/s to be precise), so does an unfortunate astronaut who, like Icarus, travels too close to the (dead) sun. In this case, we find that the escape velocity at the event horizon is equal to the speed of light.
Just as we’re not allowed infinite energy, a massive object cannot travel at the speed of light. It represents the maximum speed limit of the universe. Hence, this also explains our astronaut’s unfortunate future.
Whilst these explanations are true, there is a deeper way to understand the descent into a black hole. One that, rather than considering speed and energy, looks at the changes to time and space itself.
However, before we continue, it’s worth noting that falling into a black hole would be somewhat unpleasant.
Spaghettification — which is less the name of a quirky Italian restaurant and more the stretching by extreme tidal forces — would likely kill you long before you had to worry about escape. There is, however, a possibility that if you fell into a black hole that was big enough you might just make it through unscathed. Supermassive black holes that are billions of times the mass of the Sun would create a much smaller gradient of tidal force across your body. This means anyone crossing the event horizon might do so without even realising anything fundamental had changed.
As you reached the event horizon, you would experience gravitational time dilation…