Falling Up

An apple probably never fell on Isaac Newton’s head, but if one had he certainly would have deserved it. A notorious jerk, Newton was constantly making vicious remarks about other scientists and their work. He often took sole credit for discoveries even when it wasn’t due. Even his most famous “compliment” was actually a sarcastic insult—when he wrote, “If I have seen further it is by standing on the shoulders of giants,” it was in a letter to Robert Hooke, the inventor of the microscope, and a hunchback. Perhaps there is some consolation to be found in the fact that many historians believe Newton died a virgin, but while he may have lost that battle, he certainly won the war. He is constantly recognized as one of the most influential scientists of all time for his work on calculus, optics, and gravity.

Gravity is such a fundamental part of our understanding of the world that it is hard to imagine anyone “discovering” it. Obviously things fell down, not up, before Newton came up with his laws of motion, and they continued to do so after he published his theories. The greatest achievement of his laws is that they unified what was going on here on Earth with what happened in the sky. Newton was the first to say that gravity was responsible not only for apples falling from trees, but also for the Earth (and the rest of the planets) revolving around the sun. The idea that laws describing what happened on Earth also applied to the rest of the universe made scales beyond the human imagination accessible to human investigation.

There was one question Newton left unanswered: Why? Why does gravity exist at all? When you think about it, gravity is extremely counterintuitive. In order to push a ball up a ramp, you actually have to touch the ball. For gravity to pull the ball back down the ramp, however, nothing has to make contact with it. The Earth exerts a force on the ball without touching it, just as the sun exerts a force on the planets without ever coming into contact with them. Newton and other scientists knew this was weird and they never came up with a satisfactory explanation for it.

When that explanation finally came along, it turned out to be so radical that it forced us to re-imagine our universe. Albert Einstein, easily the most famous physicist since Newton, wrote his papers on relativity while working in the Swiss patent office (where he also found the time to patent the triangular shape of Toblerone chocolate bars). Relativity is founded on the idea that the speed of light is a constant and that nothing can travel faster than it. That simple premise unfolds into many awesomely weird implications, including the idea of gravity as the warping of space-time. Imagine that you and three friends are holding onto the corners of a sheet, and that each one of you puts a marble on your corner. When the sheet is held taut, the marbles don’t move. If you put a bowling ball in the middle of the sheet, however, the marbles would roll towards it. In relativity, the sun is the bowling ball, the marbles are the planets, and the sheet is space-time. The sun does not pull on the planets—instead, it distorts space-time in such a way that causes the planets fall into orbit.

Relativity was one of the first scientific advancements that proved the universe to be fundamentally different from what our everyday experiences taught us. Since then, things have just gotten weirder. Shortly after Einstein’s relativity revolution, quantum mechanics was introduced. Based on probability, quantum mechanics says that the universe is inherently unstable on the smallest scales. It took decades and many brilliant experiments for the counterintuitive ideas of quantum physics to be accepted by the establishment. Einstein himself was famously resistant to its idea of a random universe. But his biggest problem wasn’t philosophical. It was that relativity and quantum physics conflict with each other. Clearly, the basic ideas of quantum mechanics do not apply to the large-scale world we live in. Particles may pop in and out of existence and behave in ways we cannot predict, but we are able to live with the certainty that every apple that will ever fall from a tree will fall down, not up. In the same way, gravity has no effect on subatomic particles. Atoms and particles are governed by the much more powerful electro-magnetic force (with some help from the strong force and the weak force). A magnet sticks to your fridge because gravity is actually negligible in the face of electromagnetism.

The biggest question in particle physics is how to unify all four fundamental forces into one theory of everything. The first thing we have to do is explain why gravity is so much weaker than the other three forces. One idea is that gravitons, or the hypothesized particles that may transmit gravity, can escape into extra dimensions, thereby diluting their force and weakening the gravity we experience in our three-dimensional world. And that’s actually one of the less crazy ideas.

After over 300 years of research, one of our most basic and intuitive experiences still has yet to be fully explained. That we did not give up long ago is a testament to the willingness of science to reexamine itself. If we do ever come to understand gravity, the feat will have been so much the more impressive because it will have taken so many centuries to get there. The arc of science is long and it is easy to get lost in crazy ideas along the way. As exciting as these ideas are to talk about, we should never lose sight of the end goal: to finally be able to answer the question “why.”

Elizabeth Wade is a Barnard senior majoring in comparative literature.
Fear of Physics runs alternate Mondays.
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