Have you ever heard about gravity?
- Alexa Ines Guido
- 5 days ago
- 4 min read
Hola! I'm Alexa Guido, a young and curious woman passionate about science. Join me on an exciting journey to explore the wonders of the universe through the lens of physics.
Have you ever dropped your phone and watched it hit the ground in slow motion, only to realize it cracked the screen? That’s gravity in action. But did you know this invisible force is not only what keeps us on Earth, it also shapes galaxies, bends light, and governs the motion of everything in the universe? Or, did you know that the most familiar force in our daily lives might be the least understood at the smallest scales? Let’s take a closer look at one of nature’s most mysterious forces: gravity!
In daily life, we learn Newtonian gravity as the force of attraction between objects with mass; the more massive the object, the stronger its gravitational pull. That’s why the Earth pulls us toward its center and why the Moon orbits the Earth and the Earth orbits the Sun.
But gravity is not just a force; it’s actually a curvature of spacetime, according to Albert Einstein’s General Theory of Relativity. Imagine a bowling ball on a trampoline, this is how massive objects bend the fabric of space and time around them. Smaller objects follow this curvature, which we feel as gravity.
So, in short, Newton saw gravity as a force between objects, but Einstein saw it as the result of warped spacetime.
The Newtonian force managed everything in the universe and explained the motions of the Moon and the planets very well. Well, almost. Newtonian gravity had its triumphs. It was used to predict the location of the then-unknown planet Neptune. However, for Mercury, the closest planet to the Sun, Newton’s law was not quite as accurate in predicting the location of the planet’s perihelion (the point in its orbit where it is the closest to the Sun) as it was for the others.
This point seemed to move about the Sun, and the motion vexed astronomers until Einstein introduced his theory of general relativity in 1915, in which gravity is not a force reaching out across the universe but is a bending of space-time around a massive object. The orbits of the planets and the apples falling to the ground follow the shape of space-time. In fact, Einstein wrote four papers about general relativity in November 1915, and in the third, he accurately calculated the movement of Mercury’s perihelion.
Gravity affects everything with mass and energy, even light[1]! That’s why light bends near massive objects like black holes or even our Sun, this phenomenon is called gravitational lensing. Thanks to this effect, we can observe galaxies that lie behind others and detect mysterious things like dark matter.
Another incredible fact about gravity is that it also causes time to slow down! This isn’t science fiction, and it’s called gravitational time dilation. The closer you are to a strong gravitational field (like near a black hole), the slower time passes for you compared to someone farther away. As Einstein said, gravity literally distorts space and time!
We know that gravity is one 4 fundamental forces of the universe, but does gravity have its own particle? To keep it simple, we don’t know, but Graviton would be its name. Despite how well we understand gravity at large scales, gravity doesn’t fit into quantum mechanics.
The LHC experiments at CERN[2] have been extremely successful in verifying the Standard Model [3] of particle physics to very high precision. From the theoretical perspective, however, this model has two conceptual shortcomings.
One is that the SM appears to be an “effective field theory” that is valid up to a certain energy scale only; the other is that gravity is not part of the model. This raises the question of what a theory comprising particle physics[4] and gravity that is valid for all energy scales might look like. This directly leads to the domain of quantum gravity.
If gravitons exist, it should be possible to create them at the LHC, but they would rapidly disappear into smaller or extra dimensions. Collisions in particle accelerators always create balanced events with particles flying out in all directions. A graviton might escape the detectors, leaving an empty zone that we notice as an imbalance in momentum and energy in the event.
Physicists are on quite an intriguing quest! When they encounter a mysterious missing object, they dive deep into its properties to figure out if it might be a graviton slipping away into another dimension, or if it’s something entirely different. This method of searching for missing energy in events is also used to look for dark matter or supersymmetric particles[5].
While electromagnetism and the nuclear forces are explained by quantum field theory, gravity still resists unification. Physicists have proposed theories like string theory and loop quantum gravity, and they even hypothesize its particle, the graviton, but it hasn’t been found.
Gravity keeps your feet on the ground, but it also connects stars, curves light, and might even hold the key to unifying all forces in nature. It's a cosmic mystery still in progress, and one of the most beautiful stories science continues to explore.
[1] Learn more about photons in “Have you ever heard about photons?”
[2] For a detailed explanation of how particle accelerators work, visit “Have you heard about the CERN?”.
[3] To learn more about the Standard Model, visit “Have you heard about the Standard Model?”.
[4] Learn more about what particle physics is in “Have you ever heard about particle physics?”
[5] To learn more about the Supersymmetry theory, visit “Have you heard about the Supersymmetry?”.
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