Science Thursdays - Is Gravity an Illusion Part 1
In the inaugural Science Thursdays post, I'm tackling a very difficult question posed by Dawn. This is harder than I thought it would be, but here goes.
Dawn's question revolves around a recent article in the Times in which a scientist calls into question the existence of gravity. The original article can be found here.
Upon reviewing the article, I noted a few things. The main crux is that "Erik Verlinde, a respected string theorist and professor of physics at U. of Amsterdam" claims that "gravity is an illusion." First, the Times article is misleading, and poorly written. Second, Verlinde is a string theorist, so I was immediately skeptical. Third, the Times article states that many physicists don't understand his paper.
So, I went to the source and read the paper. Ok, I lied, I just downloaded it, and I'm reading it now. BRB.
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Wow, this is a long paper, and I'm not sure I understand it.
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The background required to understand the paper includes the holographic principal and black hole physics; thermodynamics and statistical mechanics; and quantum field theory. I think I should read it again to figure out how to distill it for the masses (and understand it myself).
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Ok, here we go. Looks like I am going to need to break this post into three parts.
Part 1 - What is "Force?"
Before we talk about wether the force of gravity is an illusion, we need to understand what a force is. So, what is a force? Glad you asked.
In Star Wars, the force is a mysterious energy that surrounds us and penetrates us (in a non-sexual way). In physics, force is a push or a pull that causes an otherwise stationary body to undergo an acceleration.
Sir Issac Newton first formalized this with the second most famous formula in physics (can you name the first?) -
F=ma, or Force equals mass times acceleration.
What Newton did was describe the relationships between mass, force, and acceleration. From F=ma, Newton derived his Law of Gravity, but it gives no explanation to what or where those forces come from.
Scientists such as Gauss, Faraday, Maxwell, and Coulomb came along and derived similar equations for the Electromagnetic forces (the attractiveness and repulsiveness of charged particles such as electrons and protons).
Some time later, the Nuclear forces (how atomic nuclei stay together and how particles decay) were formalized into formulas.
Today, it is commonly held that there are Four Fundamental Forces in the 'verse -
1. Gravity
2. Electromagnetism
3. Weak Interaction
4. Strong Interaction
So, you might be asking yourself some questions. We have some formulas that tell us how much gravity causes a certain amount of movement on some mass, or how much electrons and protons like to hang out, but what is the force making them do this? How does it work?
It's easy to understand that if you hit a bottle of water with your hand, it's going to move. But these invisible forces don't seem to make much sense intuitively. This was a problem for a long time. Enter Quantum Field Theory. QFT holds that the fundamental forces work through messenger particles called gauge bosons: one fundamental particle exerts a force on another by sending over a few these gauge bosons; just like your hand smacking or grabbing the bottle of water.
Each of the fundamental forces have their own special types of gauge bosons and over the past fifty years or so, these messenger particles have been observed in experiments for all of the fundamental forces EXCEPT gravity. This is known in physics as The Standard Model.
Einstein refined and changed our view of Newton's gravity, but it still does not fit into The Standard Model. Not only have no Gravitons (the theoretical gauge boson for gravity) been observed, but attempts to even describe the graviton in terms of Quantum Field Theory leads to cooky non-sensical answers.
One of the biggest problems in physics today is that of Quantum Gravity. It just doesn't work. Many smart people are trying to figure this out - String Theorists, Quantum Loop Gravity Theorists, etc. No one has done it yet, and this is part of the reason that Verlinde has come to believe that gravity "doesn't exist." What he REALLY means, and the Times article does not state very well, is that Gravity is not a fundamental force (as described above) at all, but a byproduct of some other property of the Universe.
Take a deep breath. Stay tuned for my follow-ups, which will cover where Verlinde thinks gravity comes from in Part 2 - Thermodynamics and Black Holes, and Part 3 - What the Hell is the Gravity is an Illusion guy really saying.
