On the first day of Physics 135-2, right after Dr. Brown started us on our journey into Electricity and Magnetism, we solved an example showing us that the electronic force between particles in atoms is far stronger than the gravitational force. How can it be then, that gravity can both be so anemic and shape the universe on a cosmic scale?
Electromagnetism, the strong nuclear force, the weak nuclear force and gravity are the four fundamental forces of the universe. Gravity is one of the least understood and seems to possess an inexplicable ability to reach across interstellar distances and assert its presence.
The works of notable scholars like Aristotle and Galileo have led us to a qualitative understanding of the effects of gravity, which was then quantified though Newton’s universal law of gravity. Despite this, all we could do was predict what would happen, not why it happened. It took Einstein’s General Theory of Relativity, in which he introduces the concept of space-time, for us to understand the ‘why’ behind gravity.
In short, space-time acts like a fabric that is warped by the presence of a mass. Gravity is a consequence of the resulting curvature. Objects in space-time will move such that they follow the path of least resistance. This is why planets rotate their star system: the star warps space-time and thus, the planets maintain a trajectory over time that is stable given the curvature of space time in their immediate vicinity.
Mass grips space by telling it how to curve, space grips mass by telling it how to move. – John Wheeler, renowned physicist
However, this is all a rather qualitative take on Einstein’s work. In reality, it involves a lot of math. One of the pieces of math — an equation, if you will, — makes an odd prediction that even Einstein doubted: much like electromagnetic waves, there are gravitational waves (i.e. ripples in the fabric of space-time).
Physicists have since been looking for such waves, though no conclusive results have been obtained (however, there were a whole host of disputed and then discredited claims). In response to the seeming untenability of the gravitational wave concept, LIGO, which stands for Laser Interferometer Gravitational-Wave Observatory, was founded in 1992 as a collaborative effort between researchers at multiple universities, including Northwestern. On September 14th 2015, three days after the detectors were turned on after a five-year renovation/upgrade hiatus, LIGO finally detected something.
LIGO found gravitational waves corresponding to a rather interesting, if somewhat cataclysmic in nature, event: two black holes merge to form a massive rotating black hole. To date, this is the highest energy event that has ever been recorded.
Vicky Kalogera, a Northwestern professor and one of LIGO’s most senior astrophysicists, is ecstatic about the discovery.
“Almost everything we currently know about the universe has been discovered with light of some kind, such as X-rays, infrared radiation and radio waves,” said Kalogera.
“Gravitational waves carry completely new information about black holes and other cosmic objects, and they will unlock a new part of the universe.”
Another Northwestern professor involved with LIGO, Shane Larson, was “astounded,” and expects that this newfound proof of gravitational waves will lead to a method through which we can detect black holes directly.
Even though we cannot sense them using conventional electromagnetic radiation dependent means, black holes will create gravitational waves. While the benefits of this discovery may not be immediately realized, it’s crucial to remember that the benefits of a scientific discovery might not materialize for a few decades. As Kalogera eloquently puts it,
That’s the beauty of basic science. Basic science pursued by us humans, by those who have an innate, almost inexplicable curiosity about figuring out how nature works. The technology of today is rooted in the basic science discoveries of the past.
photo source: NASA