Hi, I’m Rachel. The Astronomer at the Space Centre.
Just old enough to walk, I vividly remember sitting on my brother’s toy fire truck, honking the horn and generally just having the time of my life; that is, until my brother came along, shoved me off, and I went tumbling to the ground – this was my first (memorable) experience with gravity. Since then, I’ve embraced my inner adventurer and have gone bungee jumping, skydiving, and oodles of other adrenaline-pumping activities. But the question of gravity always stuck with me. What is this invisible force that pulls me to the ground – even from great heights – and shapes both the small- and large-scale structures of our universe?
My quest to find out more about this formidable force of nature landed me in a combined physics and astronomy degree at UBC. In lectures, I followed the footsteps of great scientists: to the reasoning of Galileo as he dropped spheres of different masses from the Leaning Tower of Pisa (starting in 1589); to Newton (1687) using mass to describe gravity and his approximation of the inverse-square law of universal gravitation (I.e. the force is stronger between objects that are closer together); then finally, to the genius of Einstein’s general theory of relativity (1915) that said gravity arises from the curvature of spacetime – a pseudoforce – meaning that it walks and talks like a force, but it doesn’t arise from the (direct) interaction between objects. Instead, it arises directly from the curvature of (the fabric of) spacetime, caused by the uneven distribution of mass.
Each of these theories of gravity builds upon the last.
Anything that has mass and is accelerating will generate gravitational waves. That means, as I fell off my brother’s fire truck and accelerated towards the ground, I was making ripples in the fabric of spacetime (albeit, very tiny ones). Since the gravitational waves emitted by things on Earth are far too small for researchers to detect, they started looking out into the cosmos for merger events between the most massive objects in our universe – black holes and neutron stars.
Before the invention of the telescope (and the microscope!) during the Renaissance, astronomy was limited to observing the night sky with the naked eye alone. We did a pretty good job – the stars were used to track the seasons and trace out patterns of the Sun, Moon, and planets. Then, by the end of the 20th century, we had harnessed the power of the telescope and began studying stars and galaxies across the entire electromagnetic spectrum – all energies of light. But the universe talks to us in so many ways; every time we find a new way of listening, we uncover more about our universe. In 2015, the LIGO and Virgo collaborations had their first direct detection of gravitational waves, revealing another way of listening to our universe through both waves of light and gravity!
To help explain these concepts at every step of the way, I’ve curated a list of resources that you can try from the comfort of your own home:
Share what you learned by explaining the gravity water cup drop experiment to someone. Watch the Sci Guys video for a little help explaining the concepts.
Ask yourself: What was the hardest part of the experiment to explain to someone?
Experiment with how changing the mass of an object affects the path light takes with this Gravitational Lensing interactive. (Note: look for the Gravitational Interaction link on the web page.)
Ask yourself: How do you think this information might be useful for astronomers?