Why physicists hate time

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Wait a second: What came before the big bang?

Not everyone thinks the universe had a beginning.

This story originally appeared in the print edition of the September issue of Popular Science. This week, it appeared online with enhanced graphics. The text is by PopSci editor Rachel Feltman and me; the art is by Matei Apostolescu.

Cosmologists used to think the universe was totally timeless: no beginning, no end. That might sound mind-melting, but it’s easier on the scientific brain than figuring out what a set starting point would mean, let alone when it would be. So some physicists have cooked up alternative cosmological theories that make time’s role seem a little less important. The concepts are as trippy as those black-light posters you had in college.

[read the rest at Popular Science]

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How physics and biology work together to understand cell organization

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Cells get organized

How researchers probe the physics of motion, communication and organization in cell networks, and how understanding these systems could help us tackle serious issues in medicine and biology

self-organized bacterial community

A colony of bacteria organize with each other under certain conditions to maximize nutrient intake. [Credit: Eshel Ben-Jacob]

From Physics World:

Consider this scenario: in your haste to grab the latest issue of Physics World, you scrape your hand on your postbox. It’s nothing severe, just a little scratch, but if your immune system is functioning as it should, your body will perform an amazing feat of microscopic organization. Your body assesses the level of damage and threat from infection, sending security cells to the site to hoover up intrusive bacteria and seal the wound. Within a few days you’d hardly know the scrape was ever there: your skin and blood vessels repair themselves.

Except of course there’s no mind behind this repair. Your brain isn’t required to heal a wound: there’s no local oversight from any intelligent agent, and the cells involved don’t think. Instead, cells interact with their neighbours, and a larger pattern emerges from those small-scale interactions. That’s the key to “self-organization”, whether it occurs in the human immune system, swarms of locusts, water molecules in a snowflake or electrons in a magnetic material.

For that reason, researchers studying biological self-organization draw heavily on physics. Some directly investigate the physical interactions between cells and their environments; others use theoretical models drawn or adapted from physics to understand emergent behaviours in biological systems. It’s an interdisciplinary field, involving physicists, computer scientists, biologists, mathematicians and medical doctors.

The rest of this story is in the print edition of Physics World, which you can subscribe to through membership in the Institute of Physics, which costs £15, €20, or $25 per year. You can join by clicking here. You can also get a nice mobile- and tablet-formatted version of the story using the Physics World app, available in the Google Play and iTunes stores. However, if you just want to read the rest of this article, Physics World has kindly allowed me to offer it to you as a PDF download, which looks exactly like the printed version!

The physics of dinosaurs!

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Computer model for the swing of a Stegosaurus tail-spike assembly, also known as a thagomizer from a classic Gary Larson cartoon. (Alas, we didn't get permission to reprint this cartoon.)

Computer model for the swing of a Stegosaurus tail-spike assembly, also known as a thagomizer from a classic Gary Larson cartoon. (Alas, we didn’t get permission to reprint this cartoon.)

Like many (most?) of us, I was a huge dinosaur fan as a kid. I read every horrible, outdated book I could get my hands on. I read Robert Bakker’s book The Dinosaur Heresies not long after it was published, with its often-wrong but very provocative reimagining of how dinosaurs lived, moved, and interacted with their environments. My primary scientific love was space, and so I pursued physics as a career, but I never completely forgot my dinosaur obsession. Now in the February 2017 issue of Physics World, I get to combine the two interests!

Deducing how dinosaurs moved

How did dinosaurs dash and their cousins the pterosaurs take flight? Physics-based modelling is helping to solve these mysteries of movement

For Physics World:

Jurassic Park and its sequels are best thought of as monster movies. But they do make dinosaurs look and act like real animals – which, of course, they were. For more than 100 million years, various groups of dinosaur were the largest predators and herbivores on the planet. There were many smaller species too, though we only know about a fraction of them, since fossils of them are rare, and we’re aware of many only through fragments.

Scientists have been able to answer the biggest scientific question posed by Jurassic Park in one of its most tense chase scenes: could a Tyrannosaurus rex outrun a Jeep? (Answer: no.) Knowing the top speed of an apex predator is vital as it tells us what sorts of prey it could catch. To better understand these creatures, scientists also want to know if a Stegosaurus’ fearsome spike-wielding tail could be used as a weapon, and what damage it could do. Another question is how pterosaurs (cousins of the dinosaurs) could evolve to become the largest flying animals.

Answering all of these questions involves understanding what forces and torques these creatures’ skeletons could withstand. [Read the rest at Physics World]

Seeing the invisible monster at the Milky Way center

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This is my second print magazine feature for Smithsonian Air & Space Magazine. The first was about gravitational waves, published not long before the LIGO detector found the first gravitational wave signals. The new piece is about the black hole at the center of our galaxy, published just a few months before…well, read the article to see why this is a good time to be writing about that particular black hole.

The First Sighting of a Black Hole

We know one lurks at the center of the Milky Way, but to these astronomers, seeing will be believing

For Smithsonian Air & Space Magazine:

he center of the galaxy doesn’t look like much, even if you’re lucky enough to live in a place where the night sky is sufficiently dark to see the bands of the Milky Way. In visible light, the stars between here and there blur together into a single brilliant source, like a bright beam hiding the lighthouse behind it.

But in other types of radiation—radio waves, infrared, X-rays—astronomers have detected the presence of an object with the mass of four million suns packed into a region smaller than our solar system: a supermassive black hole.

Astronomers call it Sagittarius A*, or Sgr A* (pronounced “sadge A star”) for short, because it’s located (from our point of view) in the Sagittarius constellation. Discovering the Milky Way’s black hole has helped cement the idea that the center of nearly every large galaxy harbors a supermassive black hole. But despite mounting evidence for black holes, we still haven’t seen one directly. [Read the rest at Smithsonian Air & Space Magazine]

Could gravity have mass?

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Might gravity have mass?

Click on the image to read the whole article for free, courtesy of Physics World.

Click on the image to read the whole article for free, courtesy of Physics World.

From Physics World:

When confronted with something unexplained in the data, scientists face several possibilities. Maybe there’s an error and the result is spurious. Maybe there’s a more mundane explanation they simply overlooked. Or perhaps the unexplained is a sign that a theory needs to be revised or supplanted. That last option is the rarest, at least when the theory in ques- tion is a successful one. After all, any new theory must explain all the same phenomena an old theory explained, and predict something new that can’t be handled with the old.

One unexplained result that’s been bugging physicists for more than 15 years is dark energy, which is the name we give to our ignorance. The universe is expanding at an accelerating rate, but we don’t know why. To make matters worse, dark energy comprises roughly three-quarters of the total energy content of the cosmos, so it’s not a minor thing we don’t get. For that reason, a small but dogged group of physicists thinks the existence of dark energy might be a clue that we need to revise one of the most successful theories we have: general relativity.

One way to revise general relativity is to modify the nature of the gravitational force so that it behaves as though it has mass.

The rest of this story is in the print edition of Physics World, which you can subscribe to through membership in the Institute of Physics, which costs £15, €20, or $25 per year. You can join by clicking here. You can also get a nice mobile- and tablet-formatted version of the story using the Physics World app, available in the Google Play and iTunes stores. However, if you just want to read the rest of this article, Physics World has kindly allowed me to offer it to you as a PDF download, which looks exactly like the printed version!

How standard are “standard candles”?

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Not-so-standard candles

From Physics World:

The story is already legendary. In the late 1980s and early 1990s, two groups of rival researchers set out to measure the deceleration of the expanding universe. These groups often used the same observatory, sometimes even using the same telescope on consecutive nights. And they both found the same thing, publishing their results at roughly the same time in 1998–1999: the expansion of space–time isn’t slowing down at all. In fact, it’s getting faster. The leaders of those collaborations – Saul Perlmutter and Brian Schmidt – along with Adam Riess of the latter’s group, won the Nobel Prize for Physics in 2011 for this discovery. The implication of the result was that the universe consists not only of visible matter and dark matter, but also a gravitationally repulsive substance. Known as dark energy, the nature of this weird stuff remains as mysterious today as when it was first discovered.

Both groups used certain kinds of exploding stars called type Ia supernovae for their measurements. These supernovae brighten and fade in very similar ways and the current thinking is that this is because they have a common source: the explosion of either one or two white dwarfs, which are the stellar remnants of small-to-medium-mass stars such as the Sun. This consistent brightness allows astronomers to determine how far away the object was when the light left it and for that reason, type Ia supernovae are known as “standard candles” – reliable light- houses in the measurement of cosmic distances.

Or so we all thought.

The rest of this story is in the print edition of Physics World, which you can subscribe to through membership in the Institute of Physics, which costs £15, €20, or $25 per year. You can join by clicking here. You can also get a nice mobile- and tablet-formatted version of the story using the Physics World app, available in the Google Play and iTunes stores. However, if you just want to read the rest of this article, Physics World has kindly allowed me to offer it to you as a PDF download, which looks exactly like the printed version!

I Love Q, and now you can too!

I wrote a feature story for Physics World on an interesting little discovery about neutron stars, but unfortunately the article wasn’t in their free online edition. HOWEVER, the editors have kindly let me repost the article here in PDF format for free download! (Here’s the summary I wrote a few weeks ago.)

Physics World is a glossy magazine published by the Institute of Physics (IoP) in Europe. My articles are in the print version, but you can access them online by joining IoP (US$25 per year) and see everything they publish either through the Physics World website (which also has tons of free content) or the app, available on iTunes or Google Play.