Crossing the Event Horizon: A Journey Across The Universe by Seth Shoneman There is no feeling more comforting than that of longevity: looking into the future, confident in the ability of systems to remain stable through coming struggles. No idea or body provides this comfort better than supermassive black holes, with their unfathomably long lifetimes ranging up to 10100 years (astronomy.com)1. Black holes are all-consuming areas of spacetime so dense that not even light can escape their gravitational pull. They emerge from dying stars, the mass condensing to a low enough size for the internal gravitational pull to reach infinite strengths (livescience.com)2. To fall into a black hole is not a journey to another place “on the other side”, but rather a journey through the lifetime of the universe. It’s a lengthy process, characterized by three distinct parts: the entrance into the black hole, the experience within its containment, and finally the eventual collapse. To begin, it only takes a fall of trust. Falling, a curious astronaut would rapidly accelerate towards the (nonrotating) black hole. As he approaches it, the black circle in space would look like dark emptiness silhouetted against the starry void. Moving closer, looking outward would present an odd scene of the stars all around slowly turning more blue. This is due to the gravitational pull on the photons (light particles) around the astronaut, giving them a higher energy and lower wavelength (Nemiroff)3. On the other hand, a partner still parked in a spaceship, away from the black hole, would watch their comrade fall and slowly fade into redness. The light would experience an opposite effect of gravitational redshift as a result of expending energy to escape the gravitational well, leading to a lower frequency of light reaching the ship (COSMOS)4. Closer, the astronaut falls until he reaches the black hole’s event horizon, a Schwarzschild Radius away from its center. This is what actually looks “black”: past this distance the gravitational pull is so incredibly strong that
not even light can escape to illuminate anything inside (Forbes)5. This can reasonably be called “entering” the black hole. Now the astronaut will discover what awaits him within. Inside, the experience would vary greatly based upon the magnitude of the black hole. They can range from having the mass of a large mountain and the size of a proton to being billions of times more massive than the Sun (supermassive) and comfortably able to fit within them a solar system or two (Nerdist)6. In all black holes, the gravitational pull approaches infinity as one approaches the center. The extent of this approach, however, depends upon the size. In a relatively “smaller” black hole the difference between gravitational attraction from, say, a falling astronaut's head and feet would be orders of magnitude. The falling explorer would quite literally be stretched in a process sensitively called “Spaghettification”. To avoid this gruesome fate, instead the brave astronaut falls into a supermassive black hole. The difference in gravitational pull between head and toes is negligible, leaving them to plummet in one piece towards the center (SciTechDaily)7. This “center” of the black hole is where the unimaginably strong gravitational force emanates from: the singularity. All of the mass that has been consumed by the supermassive body, in its formation and lifetime, squeezed into an infinitely small, dense point (COSMOS)8. There are theories, given the instability of Einstein’s equations about the nature of gravity at such miniscule scales, for what this point should be described as. For instance, ideas of limitations on how small they can become have arisen to fix the ‘infinite’ issues of a singularity (SPACE.com)9. These however, based upon very theoretical concepts, cannot presently be assumed to be accurate. Meanwhile, the astronaut will fall for around sixteen seconds from their perspective in a supermassive black hole towards the singularity (Hamilton)10. They will sadly reach their mortal fate in infinite condensement. Here however, for the argument of observation, it can be unspecifically guessed in this theoretical scenario that they will be kept
alive in the singularity’s warm embrace. Now is the time to wait, for as long as that embrace will hold. Supermassive black holes, both in size and mass, are inconceivable to reasonably think about in comparison to any Earthly quantity. And yet, despite this larger-than-life scale, they do eventually die. The patient escape of the lucky astronaut is only possible due to a concept called Hawking radiation, originally derived in 1974 by Stephen Hawking. He described how a black hole slowly collapses due to a gradient of curved spacetime. The gravitational curvature inside of the black hole, and its surroundings, is so strong that there is a significant difference between it and the adjacent, relatively uncurved fabric. This difference causes the emission of radiation, energy that must come from the black hole itself, resulting in shrinkage over time (Siegel)11. Thus, in the absence of material to consume, a black hole will eventually evaporate. This process can take incredible amounts of time, for instance a black hole with the mass of the Sun will evaporate in around 1067 years (Universe Today)12. At the end, when the body has had enough time to decay, it will in its final moments explode in a concluding burst of energy, leaving the astronaut once again stranded amongst the explosion’s emission of particles (Hawking)13. They will be at the end of their adventure through a black hole, and find themselves in a universe very different from what they remember. Black holes do not, literally, lead anywhere. The consumption of matter does not mean it is, to continue the analogy, digested and spit out elsewhere in space. However, that does not make going through a black hole any less of a journey. A theoretical traveler within a black hole will be treated to a trip as lengthy as one could ever expect, and will “come out” after a human eternity. It might be slow and dark, but at least it ends with a bang. 1.
https://astronomy.com/magazine/news/2021/02/the-beginning-to-the-end-of-the-universe-how-black-holes-die
2.
https://www.livescience.com/63436-llm-how-black-holes-form.html
3.
https://apod.nasa.gov/htmltest/gifcity/nslens_math.html
4.
https://astronomy.swin.edu.au/cosmos/g/Gravitational+Redshift
5.
https://www.forbes.com/sites/startswithabang/2018/01/19/what-would-you-see-as-you-fell-into-a-black-hole/?sh=7123061a8583
6.
https://nerdist.com/article/biggest-black-holes-size-comparison/
7.
https://scitechdaily.com/could-a-human-enter-a-black-hole-to-study-it-and-survive-the-event-horizon/
8.
https://astronomy.swin.edu.au/cosmos/B/Black+Hole
9.
https://www.space.com/what-happens-black-hole-center
10.
https://jila.colorado.edu/~ajsh/insidebh/schw.html
11.
https://www.forbes.com/sites/startswithabang/2020/07/09/yes-stephen-hawking-lied-to-us-all-about-how-black-holes-decay/?sh=1da1d5ab4e63
12.
https://www.universetoday.com/119794/how-do-black-holes-evaporate/
13.
https://www.nature.com/articles/248030a0