The Difference Between Math and Physics

Recent headlines boast that string theory is finally testable.  If true, this would mark a significant turning point for the speculative theory.  Touted as a potential TOE, or theory of everything, string theory attempts to unite general relativity (our best theory of the very large) and quantum mechanics (our best theory of the very small).  The theory has been around for decades, but has yet to make a single, testable prediction.  The problem lies in the fact that string theory has so many independent constants, it can accommodate almost any empirical data.

Until now, argues Michael Duff of Imperial College, London.  According to a PhysOrg report, the insight came when Duff attended a “conference in Tasmania where a colleague was presenting the mathematical formulae that describe quantum entanglement: ‘I suddenly recognised his formulae as similar to some I had developed a few years earlier while using string theory to describe black holes. When I returned to the UK I checked my notebooks Continue reading “The Difference Between Math and Physics”


Is there ANYTHING we can’t explain with thermodynamics?

String TheoryPhilosophers David Albert and Barry Loewer have long argued that thermodynamics (or, more broadly, statistical mechanics) can explain the direction of time, the regularities of the special sciences, our memories, and our ability to control the future and not the past.  As if this weren’t enough, a recent article in the New York Times reports that Dutch physicist Erik Verlinde thinks thermodynamics can explain gravity too!

According to his paper, if we accept the holographic principle (very roughly: that the spatial dimensions of the universe emerge from its boundary conditions) popular among string theorists, then the motions of bodies through that emergent space Continue reading “Is there ANYTHING we can’t explain with thermodynamics?”

The Origin of Quantum Interpretation

QuantumThere is a new book I’d like to read: Quantum: Einstein, Bohr, and the Great Debate about the Nature of Reality, by Manjit Kumar.  The book is a non-technical account of the discoveries and arguments that led to the Theory of Quantum Mechanics we rely on today.  According to Graham Farmelo’s review of Quantum in the New York Times last month, the book is full of interesting anecdotes about the physicists, their ideas and their disagreements.

Early quantum mechanics is often portrayed as a battlefield from which Bohr emerges victorious while Einstein recedes into the background.  Bohr’s view is now taught to almost every undergraduate physics major and philosophers routinely refer to his view as the ‘Standard Interpretation’.  However, Continue reading “The Origin of Quantum Interpretation”

Quantum Effects are Getting Observably Bigger

Thought you were big enough to escape quantum superposition?  A recent demonstration by physicist Andrew Cleland and his colleagues at UC Santa Barbara suggests otherwise.  Tiny particles have always been subject to quantum effects, but many physicists were skeptical those effects could be reproduced in larger objects.  In an amazing leap, Cleland and his team succeeded in demonstrating quantum effects in an object with trillions of atoms, beating the previous record (fewer than 100 atoms) by a factor of over a billion!

Quantum mechanical experiments have long revealed that a particle can exist in a state of superposition, a state that seems to allow it to be in two contradictory states at once.  It seems as if a particle can pass simultaneously through two slits, or be in a ground state and an excited state at once, or even take two wildly different paths through an experiment.  There are many different explanations for such odd behavior (see below) but the important thing is that until now, these effects were unimaginably small.

According to a recent article in Nature, Cleland’s experiment Continue reading “Quantum Effects are Getting Observably Bigger”

Boundaries and Control

You probably know that traveling back in time to kill your grandfather is not only unethical, it’s also prohibited by the laws of nature.  This isn’t because the laws prohibit travel to the past (in fact, there are several speculative models of current physics that allow for it) but because killing someone who fathered your father means you aren’t born (and thus not in a position to travel back in time and do the dirty deed).  What you may not know is why this restriction on your action seems especially onerous.  In a recent Discover article, CalTech physicist Sean Carroll argues that the difference can be explained by an appeal to boundary conditions.

Why should boundary conditions matter?  The clearest answer is provided by Continue reading “Boundaries and Control”

A Chiral Universe

When the universe was newborn (just a couple of microseconds old) it displayed a handedness, or chirality, that, according to a recent article in Science, physicists are finally able to reproduce in the laboratory.  Dmitri Kharzeev and his team at the Relativistic Heavy Ion Collider at the Brookhaven National Laboratory noticed that the strong force behaves differently when things get hot enough.  At temperatures of four trillion degrees Celsius—the hottest temperature ever measured in a lab—protons and neutrons, smashed out of gold nuclei, turn into a flowing plasma of quarks and gluons.  The plasma, which behaves like a liquid, seems not to be mirror symmetric.  Continue reading “A Chiral Universe”

What Explains the Direction of Time?

Why do we experience the world as unfolding in time?  And why does it unfold toward the future rather than the past?  One hint is provided by entropy: eggs break (but never un-break), we grow older (but never younger), ice melts when we add it to a pot of boiling water (but the boiling water never gets hotter while the chunk of ice gets bigger).  Yet entropy itself requires an explanation because both entropic and anti-entropic behavior are compatible with the fundamental laws of physics.  One solution was first explained in detail by David Albert, a philosopher at Columbia University, in his book, Time and Chance (2001).  According to Albert, it is the big bang, which provides a low-entropy boundary condition, that explains the direction of time (and all of its associated puzzles).  Now, Sean Carroll, a theoretical physicist at the California Institute of Technology has taken up Albert’s idea in his new book, From Eternity to Here.  In a recent interview in Scientific American, Carroll claims “just about everything about the arrow of time—what we would think of as “how time works,” the fact that the past is set in stone while the future can still be altered—is all because of entropy.”  Carroll’s book is intended for a popular audience, and would be a worthwhile investment for any philosopher curious about physics-based approaches to the metaphysics of time.

Related Articles:

The Experience of Time and Change

By Barry Dainton , University of Liverpool
(Vol. 3, June 2008)
Philosophy Compass

Time Travel: Double Your Fun

By Frank Arntzenius , Rutgers University
(Vol. 1, October 2006)
Philosophy Compass