Warp Drives: The Limitless Future
Learn more about how humanity can become the architects of space and time
Light Speed!Shaun Fell
When weak overcomes strong
Suppose you are holding two magnets that are stuck together. You grab one of them and twist it around. No matter which way you hold it, the other magnet stays firmly attached, even when it is upside down. This is incredible for a very simple reason: The entire Earth, which weighs a trillion trillion kilograms, is pulling with all its might on the magnet, yet the magnetic force between the two tiny magnets is enough to resist the Earth's gravity. This is a simple experiment to gauge the immense gap between the magnetic pull (electromagnetic force) and the earths pull (gravitational force). These two forces are fundamental in the universe. Besides these two, there are two more fundamental forces which go by the name the strong force and the weak force. Combined together, they comprise the four fundamental forces we know of in the universe.
However, there is a huge problem. The electromagnetic, strong, and weak force are all described by a single model called the Standard Model of Particle Physics, while gravity is solely described by General Relativity. Moreover, the gravitational force as you just saw is vastly weaker than any of the other fundamental forces. What makes it so special? We still do not know the answer to this question, however there have been a sea of theories hypothesized to explain it. However, there is another peculiarity. If the other three fundamental forces are so much stronger than gravity, why aren't they the most ubiquitous forces we see out in the universe? Why isn't the electromagnetic or strong force responsible for keeping planets in orbit? Why are black holes a purely gravitational phenomena and not because of the weak force? Why is it the weakest force in the universe also the one that holds planets, solar systems, entire galaxies together?
There are reasons for each of these questions and it is simpler than you think. The electromagnetic force only acts on things with electric charge and thankfully most things are electrically neutral (they contain about equal amounts of positive and negative charge), which is obvious when you think about it or else magnets would stick to everything! The weak force is responsible for radioactive decay, which is how nuclear reactors work, and well we do not see everything around us suddenly decaying into different elements. So the weak force is usually only relevant at the atomic level and definitely cannot keep a planet in orbit. Finally the strong force is responsible for holding atomic nuclei together. Moreover, it has a very short range. It does not even affect the electrons orbiting the nucleus!
Hence, when all is said and done, gravity is the only thing left over on distances relevant to our daily lives and it keeps being dominant up to the scale of the entire universe! Gravity is the force that holds planets together, keeps them in orbit, binds stars to form galaxies, creates black holes, and governs the birth-life-death of the whole universe! It completely dominates the other forces when it comes to the motion of things in our universe.
We're wrong about gravity
The theory of general relativity has passed crucial tests time and time again and affirms itself as our theory of gravity. Then how come we know it to be wrong, despite it being right time and time again? Quantum mechanics.
Quantum mechanics (really quantum field theory) lay at the heart of the electromagnetic, weak, and strong forces. It is a complicated theory whose predictions evade seemingly all logic. Yet, the quantum nature of the electromagnetic force is one of the most accurate and precise theories ever written down. The predictions of the theory have been scrutinized and more and more precise experiments have been conducted which continue to confirm the theory. Quantum field theory is the ruler of the microscopic.
How can we reconcile gravity, which describes the very large, to quantum field theory, which describes the very small? The answer is simple: We try to use gravity to describe the very small. However, when you do this, things go horribly wrong. The math completely breaks down! You get singularities, divergences, horrible non-sensical mathematical answers. General relativity cannot be pushed to this small scale, it cannot be quantized (in practice, this is called non-renormalizable, but do not worry about the jargon). Hence, we know that general relativity cannot be a complete theory or else it would be able to describe the very big and the very small. It must be wrong.
Is there hope?
What could we possibly do? After all, the holy grail of physics is a unified theory of all fundamental forces. A theory that describes all scales at all times: the big, the small, the ancient, the future. There must be some answer. However, we have yet to find it. But there have certainly not been a lack of proposals. Many theorists, most of them extremely smart, have put forth their idea of a unified theory. Many of them fall in the category of quantum gravity, where one tries to find an alternative theory to general relativity that describes both the big and small. Such examples include:
- string theory
- loop quantum gravity
- casual dynamical triangulation
However, all of these theories make predictions about the very, very small, way, way beyond the scales reachable with our current technology. It will likely be many, many years before we know what the true nature of gravity on subatomic scales truly is. We will have to wait until technology catches up to the theorists.
Until then, the universe remains split in two between the ultra small and the dominatingly large.
Black holes and their immense beauty
Learn more about black holes and how the darkest things in the universe are simultaneously the brightest.
Cross the event horizon