Gravity, Light & Black holes

Gravity is one of the four fundamental forces of nature, it is responsible for holding galaxies together and for keeping our planet in a stable orbit around the sun, another such force is the electromagnetic force and governs the radiation of light in the cosmos. In this entry we will discuss the incongruence of gravity and its ability to distort electromagnetic fields, thus putting into question our perceptions of the universe as seen through Gravity's lens, a theory first proposed by Albert Einstein in 1915.

What is electromagnetism?

Electromagnetism has two components. The first is the magnetic force, which I'm sure you've encountered when trying to overcome the force of repulsion or attraction between two magnets. Second is the electric force, sometimes called voltage or more correctly electromotive force (EMF) and is responsible for making current flow through electrical circuitry and gives us such wonders as the electric kettle and the humble toaster.

So the electromagnetic force is the combination of electric and magnetic components and gives us a thing called light, which I'm sure you're all quite familiar with. The light in this room is in the visible part of electromagnetic spectrum but not all light is visible. Your mobile phone is emitting and absorbing light in the form of radio waves to provide you with good coverage, a microwave emits light to heat your food and an x ray machine shoots light at you so you can see your skeletal structure. In short, light is pretty incredible. What is even more incredible is that no matter how much energy a light source has, that is, no matter how much energy a packet of light has, it will always travel at the same speed. That's because light is our cosmic speed limit and only one method of exceeding this limit exists, called the Alcubierre drive, which would only be possible with the invention of a device capable of controlling gravity (plus it's not really faster than light, it's kind of cheating to be honest.) It works like a jet engine, contracting air in front of it and expanding air behind it to generate thrust. The only difference is the Alcubierre drive contracts and expands space time to generate thrust.

The components of the electromagnetic wave

So why is gravity so special?

Gravity is incredibly weak, how do I know that? Well, stand up. So then you might say "Well hang on, you just told me that gravity holds the cosmos together" and it does, because gravity depends entirely on mass. Anything that has a mass has gravity. The bigger the mass, the bigger it's gravity. What's peculiar about gravity is that it has no associated particle, for example in the electromagnetic spectrum the associated particle is the photon and as discussed it can come in a number of shapes and sizes, but gravity has no such particle. In fact of the four fundamental forces of nature, it is the only one without an associated particle, at least not one we have proven to exist. More questions arise when you think "well, if there was an associated particle, would it have a mass and thus be affected by the very force that governs it?" To that question I have no answer and is the reason gravity has remained an elusive and mysterious force in nature.

So what does gravity have to do with light?

To understand how light can be distorted by gravity we will use black hole theory. So, every mass that exists has gravity, that gravity distorts time space. To visualize this imagine you have a blanket held rigidly at four corners. This represents time space and a few pieces of fruit that represent mass in the universe. As you add fruit to the blanket the shape of the blanket begins to distort and the amount of distortion depends on the mass of the fruit, this is in essence what gravity is, the amount of distortion in the shape of time and space. So what is a black hole? Well, when a star of a sufficient size reaches the end of its life it usually undergoes a massive coronal mass ejection called a supernova and if it meets certain criteria it can implode on itself and start to form a very small, very dense ball that we call a singularity. This singularity has an infinite mass, and thus, creates an infinitely large distortion of time space called a black hole. So a black hole isn't actually a hole, it's an infinite bend in space and time. So what does that mean for our friend light? Well, nothing can escape the massive gravity created by a black hole, not even light, and thus black holes are almost entirely invisible. So let's think about something, if black holes can absorb light, and a black hole is in essence just a large mass, then how do we know that the light from a distant star is not in fact being bent out of shape by the presence of massive stars and planets before it reaches our eyes? This creates a massive uncertainty in the position of celestial objects. It's akin to walking through a mirror maze and colliding with all the walls before finally finding the path you were supposed to be following. Thus the term gravity's lens.

The effect of gravity on space time

The black hole camera

Another wonderful thing about black holes is that should a telescope survive the trip inside the event horizon of a black hole, all the light in the universe would be falling on the singularity and like a giant celestial lens, would allow the telescope to observe the entire universe. The only problem then would be getting that information back out of a black hole for interpretation, but as nothing can escape the massive gravity, the information would be trapped inside. Thus spawning an idea. If one could move a black hole to the site of another black hole thus creating a binary system, should one black hole have larger gravity than the other, quantum information could be extracted from the weaker black hole as it was consumed by the larger one. There are problems with this idea; as discussed the large mass creates a bend in space and time, so time would travel much more slowly near the black hole, meaning it would take thousands of years to record a few moments worth of data, not to mention moving black holes across the universe would be a logistical nightmare.

To conclude

I hope this piece (like all my work) has made you think about our perception of the world around us. I hope it puts more questions than answers into your head, I hope it provokes thought and I hope you have enjoyed reading it. Gravity and light are only two of the fundamental forces. There exist two more, the strong and weak nuclear forces. These govern the very very small, while the others govern the very very large. In my next piece I will talk about these other forces and their implications on the world around us. Until then, may the force be with you.

A video of me delivering this piece at Cave writings in the Ink Factory in Dublin City