Debunking: Black Holes

By: Christopher Hartland

Black holes are, in my personal opinion, one of the most fascinating objects in our universe. It is perhaps, the mystery surrounding them that makes them so interesting. As with many scientific concepts, there are multiple common misconceptions about black holes spread by popular science fiction and various misinterpretations of the facts.


What is a black hole?

When stars come to the end of their lives, the resulting object is determined by how massive the star is. A star with a mass greater than 25 times that of the sun will eventually collapse under its own weight, creating a black hole – an object with an ‘event horizon’ within which the gravitational pull is so strong that nothing, not even light, can escape. Due to this gravitational pull, we cannot see into a black hole, and are only aware of their existence due to their effect (through gravity) on the objects and light around them.

Common misconceptions

The most common misconception about black holes seems to be that they act like giant vacuum cleaners – sucking everything in and not allowing anything to orbit them. It is a mistake that can often be seen in science fiction; one such example being a 2006 episode of Doctor Who, in which a planet is described as ‘impossible’ because it is in orbit around a black hole. This is something that even I, admittedly, used to believe. However, when you think carefully about this idea, it is actually quite easy to see that it is incorrect.

Our planet is not spiralling towards the sun and our galaxy, which has a black hole at its centre, is not shrinking. A strong gravitational pull does not necessarily prevent one object from orbiting another. It is entirely possible for a planet, or any other object, to orbit a black hole. In fact, black holes are surrounded by discs of hot gas – accretion discs – that orbit around the event horizon. If an object in orbit were to be ‘nudged’ off of its orbit and towards the black hole, then once beyond the event horizon it would not be able to escape the pull of the black hole and would be ‘sucked in’. However, as long as it remains in orbit, this will not occur.

Our lack of an ability to see inside a black hole lends itself to speculation about what may happen if a person were to fall inside. One common theory is that anyone who falls into a black hole would exit it in another location entirely (be that another part of space or a parallel universe, a scenario depicted in numerous fictional works such as Event Horizon, Doctor Who and Star Trek). This could well be the result of people confusing black holes with wormholes (an entirely theoretical concept of a sort of gateway from one point in space to another). Of course, no one truly knows what is inside a black hole; perhaps they do form some sort of interdimensional portal, but this seems unlikely and falling into a black hole would be a rather brutal experience in which a person would be stretched by the gravitational pull in a process known as spaghettification. It’s hard to imagine the possibility of someone surviving such a journey, much less finding themselves on an interdimensional adventure.

Perhaps drawn from the ‘vacuum cleaner’ perception of black holes, a conclusion that some people come to is that black holes grow in size as they consume material. The truth is that over time black holes shrink. The theory, proposed by Stephen Hawking, is that black holes ‘evaporate’ by losing mass and energy through Hawking radiation. The idea of radiation escaping a black hole may seem contradictory to the very definition of a black hole, but it is visible in numerous ways. While it is true that no matter can leave the black hole once it is within the event horizon, radiation can be emitted from outside of it. For example, jets of plasma can be flung from the accretion disc due to an electric field generated by a magnetic field within the disc (quasars are thought to be black holes that do this).

Are black holes still interesting if the myths are untrue?

To the best of our knowledge, at the centre of a black hole is a singularity – a single point with infinite density. Singularities violate the accepted laws of physics, meaning that either the ‘invisible’ part of a black hole does not contain a singularity, or that the laws of physics need to be adjusted. ( The fact that there is so much yet to understand about the universe leaves us with a lot of potential; how can anything that we don’t understand not be interesting? Even when it comes to science fiction, an accurate representation of black holes can be just as good, if not better, than an overly-fictionalised version. Take the 2014 film Interstellar as an example of a successful film with a scientifically accurate representation of a black hole (barring the climax of the movie which strays into speculation).

While they may not be giant vacuum cleaners or portals to other universes, black holes remain incredibly intriguing.

Extra exploring:
Black holes and worm holes: physics of the universe
HubbleSite’s awesome “create a black hole” app

Deciphering the Notion of Alternate Universes

By: Nathan Simpson

 

The concept of alternate universes may seem like a science fiction, but it is a very real concept. In fact, it is a genuine hypothetical solution to some real-world problems. The fledgling idea of the “multiverse” has been around for only a decade or so, but it could be true that we are just one of many universes each with its own set of physical laws.

What is the “multiverse”?

The word multiverse is quite a general term because its definition can vary depending on the context in which it is used. The most famous example of the multiverse lies in the Many-Worlds interpretation of quantum mechanics proposed by Hugh Everett in 1957 which states that there are many worlds which exist in parallel in spacetime with our own, and what we observe is just one of many possible results of reality. This allows for the removing of all randomness from physics because every possible outcome of every possible event would happen –  though not necessarily in the same universe.

Swedish-American cosmologist Max Tegmark has created a taxonomy to classify the types of multiverse. It is arranged using a levels system, such that each level builds on the understanding of the previous one. There are 4 levels to date which are summarised below: 

Level 1: This is a relatively simple model that simply states there are many, possibly infinite volumes, or bubbles, like our observable universe. Each of these bubbles occupy space and have the same set of physical laws and constants. That would mean there are an infinite number universes exactly like ours, and hence an infinite number of yous reading this article right now! 

Level 2: This type of multiverse is a set of universes much like in Level 1, but the laws and physical constants are different, i.e. pi could be 200 and E=mc etc. In fact, due to the theory of chaotic inflation and the fact that the multiverse is expanding, there are regions in this space that would stop expanding and form bubble universes just like the ones in Level 1, a bit like bubbles being trapped in soap. The number of universes formed in this way has been calculated – which is an incredible feat – to be 1010^10,000,000.

Level 3: Now, this is where things get really interesting. Here, we are reacquainted with the Many-Worlds theory from earlier. The only dissimilarity between Level 3 and Level 1 is where the alternate outcomes to different events occur. In Level 1, they occurred in the same 3D space, just very, very far away. However, in the mysterious world of a quantum mechanical multiverse of Level 3, these events happen in an infinite dimensional space on something called a quantum branch (search for “Hilbert Space” if you want to try and get your head around it). 

Level 4: If the concept of infinite dimensions wasn’t complicated or mind-boggling enough for you; have no fear, Tegmark is here to solve that. Tegmark himself termed Level 4 of the Multiverse system to be the Ultimate Ensemble, and for very good reasons: it contains within it the set of all mathematically possible universes, such that it is impossible to generalise further to a Level 5.

 Even though you now have a general idea of what a multiverse is (or could be), the idea that they could be possible, real explanations for the world we live in might still be a faraway concept. If you’re still skeptical, don’t worry! The validity of the multiverse as an actual scientific idea is a hot topic in the scientific community, with many reputable physicists in opposition to the idea. The argument against the multiverse theory as a valid scientific idea stems from the fact that it directly contradicts the scientific method, as it has no testable elements to it or outcomes we can predict.

 On the other hand, there is serious scientific research trying to prove the theory right. You might have recently seen headlines along the lines of “Scientists Claim Proof of Alternate Universes”. These articles stem from the work of Ranga-Ram Chary, who claims that he has found an anomaly whilst looking at the cosmic background radiation, or the afterglow of the big bang. He says could be attributed to a collision with another universe that has a baryon to proton ratio about 65 times larger than that of our universe. However, he also states that there is a 30% chance this could be attributed to noise fluctuations, so there isn’t anything to conclude as of yet besides news agencies are capable of creating very suggestive headlines.

Professor Jeff Forshaw of the University of Manchester, who has written about quantum mechanics and the multiverse, had this to say:

“The world could have features about it that we can’t prove. It may be that we can’t do experiments to ascertain this or that about the universe. In the case of the multiverse, it hasn’t been proven that there isn’t some sort of decent experimental evidence that would demonstrate that we are living in a multiverse, so there’s no mathematical proof that we can’t make some observations at some point in the future that demonstrates we are living in a multiverse. In that sense, it remains an interesting idea. It doesn’t have to be testable at the moment. I would make a stronger statement and say that even if you can’t prove that there is no possibility to do an experiment so that an idea can be proven to be true or false, that idea could still be the case. There could be things that we will never be able to prove about the universe that are true.”

There is much research to be done in the field of multiverse theory. Whether it is true and provable, true and not provable or not true at all, rest assured: if it is true, there are infinitely many people researching it at this instant, and if not, then why bother?