“I do not feel obliged to believe that the same God who has endowed us with sense, reason, and intellect has intended us to forgo their use.” -Galileo Galilei
Geez, Ethan, why don’t you take on a bigger question?
This question of “fundamental things” has a special meaning to scientists and natural philosophers, going all the way back to Thales of Miletus, 2600 years ago, who began asking about the arche (αρχή), which is the “element” or “prime cause” of existing things.
Of course, the scientific enterprise was just beginning, so you can’t fault Thales too much for coming up with “water”. But I totally credit him with this great idea, that’s governed all of scientific progress ever since:
This is the standard model. (Click above for a huge, poster-size image.) We have found a few different types of particles in the Universe with different masses, charges (both electrical and color), and spins (i.e., intrinsic angular momentum). As far as we know, these particles are “fundamental” in the sense that they cannot be broken down any further.
But they do more than exist. These particles also interact, which (in our language) means they exert forces on each other, and they sometimes also react in various ways, turning some fundamental particles into others. Three of the fundamental forces work by exchanging particles,
while gravity, lacking such a successful description of its force, works by mass (and other forms of energy) deforming spacetime.
So in a nutshell, that’s how everything we know works. These indivisible components of the natural world, with just a few fundamental properties (like mass, charge, and energy) and laws under which they interact, make up everything we know of in the Universe.
There are also secondary quantities that, while we don’t think of them as fundamental, play important roles in figuring out physical phenomena. I’m talking about quantities like Temperature. Heat, a form of energy, is what we think of as a fundamental quantity, but temperature is often more useful to talk about as a measurable quantity. For example, there are a number of people who get upset about the Sun’s Corona because of its temperature.
“The Sun’s Corona is at a higher temperature than the surface of the Sun. OH NO!” But the Sun’s Corona is incredibly diffuse, and would do a far worse job of, say, cooking your pizza, than the Sun’s surface would. Why? The Corona has far less heat and energy than the Sun’s surface. Looking at fundamental quantities gives us an interesting perspective here. While there’s an interesting question of “how” to be answered concerning the Corona, its high temperatures don’t represent a fundamental problem with the way we think about the Universe.
In other words, we don’t go home at night worried that our understanding of the Universe will never be complete because of the temperature of the Sun’s Corona.
But gravity is a problem, in that sense. We don’t know what causes it at a fundamental level. There are two major — seemingly unrelated — problems with it.
The first one is that general relativity is so mind-bogglingly difficult to work with. If I give you a flat, empty Universe, Einstein’s theory of gravity tells me what any particle in that Universe will do. Namely, remain in motion, unchanged by anything around it.
BOR-ING! What if we put one point mass in that Universe?
Well, now things are hard. If you’ve just got a mass, you’ve got this spacetime. If your mass is also charged, you’ve got this one. Massive and spinning? Try here. And massive, spinning, and charged? That’s this one.
You want to put a second mass in the Universe? Good luck with that analytically unsolvable problem. Our Universe, by the way, has about 1090 particles in it, so… well, in any case, that’s the first problem with gravity.
What’s the second?
We don’t even know what causes gravity, at a fundamental level. Is there such a thing as a graviton? No one’s sure. (Well, some people are sure, but those people aren’t necessarily right.) Some people hope for a theory of quantum gravity, most of whom pin their hopes on string theory.
It’s been getting a lot of press and a lot of people have been taking it up. I read the original paper and some follow-ups, and here’s my take. I want to state that there’s nothing that makes it inherently, obviously wrong. But there’s a very important assumption that one needs to make in order to take this idea seriously, that may not be based in reality.
First, there’s this idea that people throw around very frequently, known as duality. Here’s a definition from wikipedia:
If two theories are related by a duality transformation, it means that the first theory can be transformed in some way so that it ends up looking just like the second theory. The two theories are then said to be dual to one another under that kind of transformation. Put differently, the two theories are mathematically different descriptions of the same phenomena.
Here’s the deal, though. You can’t just change your variables, say “I’m the dual of gravity,” and be done with it. You need to ask yourself, “are my dual variables still physical descriptors of the same phenomenon?”
There’s an old example from general relativity, back in our “Universe with one mass” model.
If I stand a distance r away from the black hole (of Schwarzschild radius R), I can describe any point in this Universe using the parameter r/R.
But dual to that is that at any point inside the Schwarzschild radius, which can be described by R/r. There’s a huge problem with that, though.
We have no information about what goes on inside of that black hole, and whether our descriptions are accurate at all. The math looks the same, but the physics may be very, very different. In other words, what happens outside of the black hole is physically meaningful, and describes fundamental forces. The dual transformation, with the flipped variables? Not necessarily.
Verlinde’s idea hinges on his assumption of the duality between gravity and thermodynamics (or entropy) being a physically valid one.
And if he’s right, this could lead to some potentially interesting avenues of inquiry. But there’s a huge difference between two things being mathematically equivalent and being physically equivalent, and I am not yet convinced of the latter. Especially because I don’t think of entropy as being all that fundamental. If I take a physical system, I can measure its entropy, but I can measure its temperature, too. But if I give you the energy, positions, and momenta of every particle in there, you can give me the entropy. If you give me the entropy… the reverse isn’t true.
But I’ve got this old-fashioned picture of how the Universe works in my head. In this picture, particles are the most fundamental things, and something‘s got to cause the forces between them. Are they other particles? Is it a curving of spacetime? Or is it something else? At this point, all of the ideas out there are speculative and purely mathematical, because nature is slow to give her clues away. So you’ll hear more about these ideas from the news media and from scientists, because we just don’t know yet.
So there is this new idea out there, and while it isn’t necessarily crazy, it isn’t necessarily right or physically meaningful either. Hope this helps give you a little perspective!