Philosophy and its relation to the world

As you've surely picked up by now, philosophy is about some of the very deep questions. Some of those questions have to do with purpose, morality, and free will. In this book, we will ask different kinds of questions, which focus on metaphysics, the study of the nature of reality. But we will also engage in the study of how we come to know about that reality. This is called epistemology, the study of knowledge.

There is a certain picture of a philosopher as someone who sits alone in the basement in order to ponder the world. (Indeed, Rembrandt quite literally painted this very picture!) On that picture, a philosopher engages only in elite and clever thoughts, leaving the dirty matters of observation to the poor scientists and social scientists.

This is not the picture of philosophy that you will get in this book. The type of philosophy that you will learn here makes crucial use of observed fact. We will adopt the perspective that you can only learn about the nature of the world and our knowledge of it by going out there and observing it. For this reason, you will find that philosophy very naturally draws from science, social science, and many other fields. Similarly, many other fields benefit a great deal from the study of philosophy.

Our study will draw us into some of the most exciting questions that have ever been asked. Many fields of knowledge come together to inform our answers to some of these questions, and they all remain active areas of study. Let them draw you in and consume your brain. We make progress by developing new perspectives even when the subject matter is old. So, make these subjects yours. There is much that remains to be done.

Is Time Travel Possible?

Time travel is a tantalizing possibility, and a much-loved topic among science fiction authors. But in what sense is time travel possible, if any? Is it even a meaningful concept? Is it compatible with the laws of logic? What about with the laws of physics?

These questions will first lead us to ask whether or not there might be a helpful way to visualize time travel, and what a time travel world might be like. We will then take an easy foray into some of our best theories of modern physics, in order to see why some of the world's most eminent physicists, such as Stephen Hawking, have taken the possibility of time travel very seriously.

Is it possible to complete infinitely many tasks?

The ancient Greek philosopher Zeno of Elea (490-430 BC) mounted a surprising argument, whose conclusion was that motion through space is impossible — a clear absurdity, given that the world is constantly in motion. But why?

Zeno pointed out a paradox now called Zeno's paradox. He said in particular that in order to travel any distance, say from A to B, one must first go half way. After that, one must go half way again. And then half way again. And so on. But if each of these steps takes finite time, Zeno argued, it would seemingly take an infinite amount of time to get there. Therefore, you can never get from A to B. In other words, motion is impossible.

What went wrong in this argument, if anything? Thankfully, we will learn some ways to think about it that make motion possible after all. However, the paradox emerges in other forms, which we must ask how to deal with. We will also see a surprising sense in which infinitely many tasks are not only possible, but lead to very strange consequences in physics!

Are unobservable entities like quarks and gluons real?

Descartes famously questioned whether or not his own hand was real. Sure, you can make reliable predictions about your hand, but does this mean it's really there?

With the rise of modern science, this question took a particularly sharp form. A great deal of modern science, from the subatomic quarks in your fingernail to certain features of the human brain, are unobservable. Nevertheless, modern science is successful beyond our wildest dreams, making surprising predictions with unprecedented accuracy. But does the reliability of unobservable entities imply they exist?

We will see the major arguments in favor of reality, as well as some important arguments against. Insights from science, history, and philosophy will all be required to make progress on a question as tough as this.

Do we know that the sun will rise tomorrow?

Most of us believe the sun will rise tomorrow, but to what extent do we know that it will? Is it enough to say it's because we've observed it to rise so many days before? If your cat comes back for dinner every evening thus far, you might not know that it will come back the next. Or do you?

Answers like this make use of a type of reasoning called induction. Induction is ubiquitous in science and the social sciences, where it is used with great success. But there are certain kinds of induction that don't appear to tell us very much at all. So it is of vital importance that we understand the extent to which it provides us with knowledge.

Are there natural or social laws?

We often talk about the laws of nature. But what exactly is a law? There seems to be some difference between the Newton's law of gravity, and the statement that you're reading this paragraph. One is a law, but the other is just a fact. What we would like to know is what distinguishes laws from mere facts, if anything.

Once we've settled what a law is, we can ask when they exist. People talk a great deal about laws of physics, and sometimes even biological laws. But are there laws in social sciences? In economics or anthropology? If not, why?

Why does mathematics work so darn well?

We put an extraordinary amount of confidence in mathematically correct propositions. Why is that? Think about this: suppose you were to encounter a pair of oranges, and then decide to put them with another pair of oranges. Suppose that when you count them all up, you find that you have a total of five. Is that enough to prove to you that 2+2=5?

Of course not. You would be more likely to conclude that some magician has been messing about with the oranges, or that your eyes are deceiving you. Mathematical truths seem more certain than empirical truths. But what accounts for this certainty? And how is it that we can come to know such certain truths?