Critical Opalescence
A blog about cutting-edge physics

Are Black Holes Really Paradoxical? An Interview with David Wallace

If black holes destroy information, they create a serious conflict within otherwise well-established theories.

Today in Quanta magazine, I have an article on recent efforts to de-paradoxize black holes. Before you dive into the details, you might wonder about the framing. How paradoxical are black holes, really? Physicists and science writers throw around the word “paradox,” but do these cosmic sinkholes pose any out-and-out contradiction? I put the question […]

An Interview with Emily Adlam [Video]

Spooky influences might leap not just across space, but across time, too.

The mysteries of quantum mechanics are usually portrayed as mysteries of space: how strange that the fates of particles on opposite sides of the universe could be joined. But they are also mysteries of time. A particle you create today could be connected in some unaccountable way to one that does not exist yet. Einstein […]

Why is Quantum Physics So Freakin’ Hard to Write About? [Video]

Short answer: It’s largely a self-reinforcing expectation.

Every area of journalism presents its challenges, but quantum physics is in a molecular orbital of its own. It demands more time per word than anything else I’ve written about. Why is that? Earlier this month I offered some thoughts to fellow science journalists attending a philosophy-of-physics workshop at the University of Leeds. Although my […]

If You Think Quantum Physics Is Weird, Try These Theories

As strange as quantum entanglement is, the world would have been even stranger without it.

It’s quite a trick to picture a theory even weirder than quantum mechanics. Yet many physicists think the best way to make sense of quantum mechanics is to imagine what might have been. Within a vast radiation of conceivable theories, they look for principles that single out the quantum. In so doing, they aim to […]

Demonstrate Quantum Encryption With a Flashlight and Pair of Sunglasses

Thumb your noise at government surveillance with a highly simplified form of quantum cryptography.

“Are you telling me that this could be of practical use?” exclaimed the Irish physicist John Bell. He had shown in the 1960s that quantum entanglement burrowed deep into the foundations of physics, but even he hadn’t thought it could have real-world applications. That was the brainstorm of Artur Ekert, then a graduate student at […]

How to Demonstrate “Twisted Light” Using a Laser Pointer

A supersimple experiment endows light beams with orbital angular momentum.

In November 2003 I published a short news story in Scientific American about the orbital angular momentum of light and how you can glimpse it with a laser pointer and an overhead transparency. The article is no longer available at, so, as a service to fellow makers and citizen scientists, here are the instructions: […]

The Twelve Varieties of Consciousness

A proposed empirical scale of consciousness from dead to superhuman.

I have an essay in Aeon magazine on the possibility that machines might become conscious without our realizing it and possible ways to test for that. A huge variety of physiological and behavioral tests of consciousness might be adapted to machines, and Spanish AI researcher Raúl Arrabales Moreno and his colleagues have systematized them as […]

The Universe Is a Big Layer Cake

By thinking of nature as a hierarchy, scientists dissolve the dichotomies they have wrestled with.

Is the universe deterministic or indeterministic? A clockwork or a craps table? In this month’s issue of Scientific American, I have an essay arguing that the answer is: both. The world can be deterministic on some levels and indeterministic on others; these two categories are not mutually exclusive. To me, this is the essence of […]

Living in a World of Illusion

Stunning visual illusions from Japanese mathematicians Hitoshi and Shinobu Arai.

My favorite optical illusions are motion illusions: static images that appear to spin, shimmer, and shimmy, like Piet Mondrian’s Broadway Boogie–Woogie or the psychedelic pinwheels of Japanese psychologist Akiyoshi Kitaoka. So I was pretty pleased to come across a new class of them, known as fuyuu, or floating, illusions. I visited their co-creator, mathematician Hitoshi Arai, […]

A Hologram Shows How Space Could Pop Into Existence

The holographic principle—with a real hologram

I remember buying my first hologram as a college student in the mid-1980s. It showed a bed of nails. I came across it at a gallery in what was then the world’s capital of spacey trinkets, Haight Street in San Francisco. When I picked it up, the hologram looked like a featureless sheet of film, […]

Why Bother with Ordinary Fireworks When You Can Have Black Hole Fireworks?

Black holes might be explosions occuring in extremely slow motion, says theoretical physicist Carlo Rovelli.

Theoretical physicist Carlo Rovelli, one of the creators of loop quantum gravity, and his collaborator Hal Haggard have just come out with a new paper on black holes. Ever attuned to puns, Rovelli calls it the “fireworks” model, alluding to the firewall argument that has consumed black-hole theorists over the past two years. As if […]

Physicists Look Beyond the Large Hadron Collider, to the Very Large Hadron Collider

Now that the world’s premier particle smasher has reached its maximum energy, physicists are planning new machines to follow up its discoveries.

In 1954 the renowned physicist Enrico Fermi did a simple but depressing calculation about future particle accelerators. To create particles with an energy of 3 teraelectron-volts, he estimated, you’d have to build a ring 8,000 kilometers in radius at a cost of $170 billion. It was a rare instance of Fermi being wrong. The Large […]

Gravitational Waves Reveal the Universe before the Big Bang: An Interview with Physicist Gabriele Veneziano

The BICEP2 discovery of primordial gravitational waves was premature, but got theorists wondering about what came before the big bang.

It’s not usually put like this, but the discovery of primordial gravitational waves two weeks ago has given us our first direct glimpse of a period before the big bang. [The discovery was later retracted, but I’ll keep this post here to show why theorists at the time found it so exciting.] The term “big […]

What Happens to Google Maps When Tectonic Plates Move?

Consumer GPS now achieves an accuracy of a few meters, good enough to spot mapping errors and geological changes.

A couple of weeks ago, I was writing up a description of Einstein’s general theory of relativity, and I thought I’d compare the warping of spacetime to the motion of Earth’s tectonic plates. Nothing on Earth’s surface has fixed coordinates, because the surface is ever-shifting. Same goes for spacetime. But then it struck me: if […]

The Wholeness of Quantum Reality: An Interview with Physicist Basil Hiley

David Bohm's longtime collaborator explains why he thinks quantum physics describes a holistic reality.

VIENNA—One night in 1952, Richard Feynman and David Bohm went bar-hopping in Belo Horizonte. Louisa Gilder reconstructs the night in her brilliant book on the history of quantum mechanics, The Age of Entanglement. Feynman was on a sabbatical in Rio and, ever exuberant, raved about local beers, drumming lessons, and Brazilian girls. Bohm, teaching at […]

Does Some Deeper Level of Physics Underlie Quantum Mechanics? An Interview with Nobelist Gerard ’t Hooft

Is the notorious randomness of quantum mechanics just a front?

VIENNA—Over the past several days, I attended a fascinating conference that explored an old idea of Einstein’s, one that was largely dismissed for decades: that quantum mechanics is not the root level of reality, but merely a hazy glimpse of something even deeper. A leading advocate is Gerard ’t Hooft of Utrecht University, who shared […]

When the Large Hadron Collider Is Too Small

Four times the circumference, seven times as much energy: Is that really what it’ll take to test multiverse theories?

The Large Hadron Collider has only just begun its explorations, so it might seem a little premature to begin thinking about what new particle projects might come next. But given how long these things take to plan, is it ever too soon? This summer, particle physicists held a huge planning retreat in Minneapolis, which Peter […]

What Would It Mean for Time to Come to an End? [Video]

A TEDx talk in 2013

Could time come to an end? What would that even mean? In April 2013 I gave a talk about this strange physics idea at a TEDx event in Trento, Italy, based on a Scientific American article I wrote in 2010. My conceit was that time’s end poses a paradox that might be resolved if time […]

George and John's Excellent Adventures in Quantum Entanglement, Part 2 [Video]

Here’s what an entanglement experiment actually looks like.

The first time I ever saw quantum entanglement for myself was in August 2011 on a road trip to Colgate University. Goodness knows how many blog posts and magazine articles have been written about the quantum realm, invariably describing it as weird. But I’d never actually seen this supposed mind-blowingness with my own eyes, which […]

How to Build Your Own Quantum Entanglement Experiment, Part 2 (of 2)

The cheapest and easiest way to do the famous Einstein-Podolsky-Rosen experiment.

In my last post, I scrounged the parts for a very crude, but very cool, experiment you can do in your basement to demonstrate quantum entanglement. To my knowledge, it’s the cheapest and simplest such experiment ever done. It doesn’t give publishable results, but, to appropriate a line from Samuel Johnson, a homebrew entanglement experiment […]

How to Build Your Own Quantum Entanglement Experiment, Part 1 (of 2)

The cheapest and easiest way to do the famous Einstein-Podolsky-Rosen experiment.

Quantum-entanglement experiments are not exactly something you can buy in the science kit aisle at Toys ’R Us. The cheapest kit I know of is a marvel of miniaturization, but still costs 20,000 euros. In the past month, though, I’ve put together a crude version for just a few hundred dollars. It’s unbelievably simple—so simple […]

Physicists Find a Backdoor Way to Do Experiments on Exotic Gravitational Physics

Who’d have thought viscous fluids would act like gravitational waves caroming off a black hole?

The whole point of an explanation is to reduce something you don’t know to something you do. By that standard, you don’t gain much by explaining anything in terms of black holes. Appealing to the most mysterious objects known to science as an explanation sounds like using one mystery to explain another. Yet this is […]

When You Fall into a Black Hole, How Long Have You Got?

Maybe not long at all, if black holes are ringed by “firewalls.”

In chatting with colleagues after a talk this week, Joe Polchinski said he’d love to fall into a black hole. Most theoretical physicists would. It’s not because they have some peculiar death wish or because science funding prospects are so dark these days. They are just insanely curious about what would happen. Black holes are […]

Hacking the Quantum: A New Book Explains How Anyone Can Become an Amateur Quantum Physicist

Quantum physics is becoming the next maker revolution.

For years I’ve been thinking and hoping that quantum physics would become the next hacker revolution. DIYers in their basements, garages, and hackerspaces have already pioneered radio communications, PCs, household robots, and cheap 3-D printers—why not quantum entanglement, cryptography, computers, and teleportation? In recent years, physics educators have streamlined quantum experiments to the point where […]

How to Build the World's Simplest Particle Detector

Foil tray, plastic tumbler, and rubbing alcohol make for a simple cloud chamber, without any dry ice.

In about 10 minutes, using stuff you probably already have lying around your house, you can watch atomic nuclei and elementary particles for yourself using a diffusion cloud chamber—a rudimentary particle detector. There are lots of websites and YouTube videos giving step-by-step instructions to build such a chamber, but all require some component that’s hard […]

How Do You Count Parallel Universes? You Can't Just Go 1, 2, 3, ...

Introducing a whole new breed of number, the p-adics.

Cosmologists have been thinking for years that our universe might be just one bubble amid countless bubbles floating in a formless void. And when they say “countless,” they really mean it. Those universes are damned hard to count. Angels on a pin are nothing to this. There’s no unambiguous way to count items in an […]

String Theory in 26 Seconds [Video]

A weird little video, done on a dare.

SANTA BARBARA—Someone once asked me to describe string theory in 26 seconds, so, a couple of months ago, I went down to Goleta Beach with my iPhone and recorded this little video. It’s kind of spacey, I admit. Soundtrack and dog were entirely unintentional.

As If One Giant Black Hole Weren’t Enough, What’s a Galaxy Doing with Three?

Standard formation models can’t account for this triplet.

Last Thursday, my colleague John Matson described a truly amazing galaxy known, somewhat unromantically, as BX442. It has a majestic spiral pattern while hundreds of its galactic contemporaries were gawky and misshapen—a peculiar and special anomaly which suggests to many astronomers that cosmic pinwheels are ephemeral art forms, like Tibetan sand mandalas. John’s piece spurs […]

Does It Matter If Black Holes Are Popping into Existence Around Us All the Time?

Black holes are not just distant cosmic monsters. Microscopic ones may exist all around us, with potentially momentous consequences.

It may well have been the liveliest hour and a half I’ve ever spent in the company of theoretical physicists. In April, during a workshop I was attending on black holes, Bill Unruh gave a talk that challenged his colleagues on a point almost all of them thought had been settled in the mid-1980s. His […]

What Is the Higgs Boson? [Video]

In 2 1/2 minutes, you, too, can break the symmetry of the electroweak interactions.

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