Forging dark matter in the Big Bang

[ This blog is dedicated to tracking my most recent publications. Subscribe to the feed to keep up with all the science stories I write! ]

The origins of dark matter

Theorists think dark matter was forged in the hot aftermath of the Big Bang

For Symmetry Magazine:

Transitions are everywhere we look. Water freezes, melts, or boils; chemical bonds break and form to make new substances out of different arrangements of atoms. The universe itself went through major transitions in early times. New particles were created and destroyed continually until things cooled enough to let them survive.

Those particles include ones we know about, such as the Higgs boson or the top quark. But they could also include dark matter, invisible particles which we presently know only because of their gravitational effects.

In cosmic terms, dark matter particles could be a “thermal relic,” forged in the hot early universe and then left behind during the transitions to more moderate later eras. One of these transitions, known as “freeze-out,” changed the nature of the whole universe. [Read the rest at Symmetry Magazine]

The search for magnetic monopoles, the truest north

[ This blog is dedicated to tracking my most recent publications. Subscribe to the feed to keep up with all the science stories I write! ]

The hunt for the truest north

Many theories predict the existence of magnetic monopoles, but experiments have yet to see them

For Symmetry Magazine:

If you chop a magnet in half, you end up with two smaller magnets. Both the original and the new magnets have “north” and “south” poles.

But what if single north and south poles exist, just like positive and negative electric charges? These hypothetical beasts, known as “magnetic monopoles,” are an important prediction in several theories.

Like an electron, a magnetic monopole would be a fundamental particle. Nobody has seen one yet, but many—maybe even most—physicists would say monopoles probably exist. (Read the rest at Symmetry Magazine…)

Confused about the Big Bang? Start here

[ This blog is dedicated to tracking my most recent publications. Subscribe to the feed to keep up with all the science stories I write! ]

The Big Bang is the central concept in cosmology — the study of the whole universe — but it can be confusing to a lot of people. In fact, it’s a little unfair: some of the confusion comes from us cosmologists. In my latest for Symmetry, I try to sift out some of the important concepts and hopefully clear up some of the confusion.

Five facts about the Big Bang

It’s the cornerstone of cosmology, but what is it all about?

For Symmetry Magazine:

Astronomers Edwin Hubble and Milton Humason in the early 20th century discovered that galaxies are moving away from the Milky Way. More to the point: Every galaxy is moving away from every other galaxy on average, which means the whole universe is expanding. In the past, then, the whole cosmos must have been much smaller, hotter and denser.

That description, known as the Big Bang model, has stood up against new discoveries and competing theories for the better part of a century. So what is this “Big Bang” thing all about? [Read the rest at Symmetry Magazine]

Finding all the matter in the cosmos — even the invisible stuff

[ This blog is dedicated to tracking my most recent publications. Subscribe to the feed to keep up with all the science stories I write! ]

“Weak Lensing” Helps Astronomers Map the Mass of the Universe

By making galaxies a little bit brighter, it points the way to elusive galaxies and lets us detect that most mysterious of substances: dark matter

For Smithsonian Magazine:

In ordinary visible light, this cluster of galaxies doesn’t look like much. There are bigger clusters with larger and more dramatic-looking galaxies in them. But there’s more to this image than galaxies, even in visible light. The gravity from the cluster magnifies and distorts light passing near it, and mapping that distortion reveals something about a substance ordinarily hidden from us: dark matter.

This collection of galaxies is famously called the “Bullet Cluster,” and the dark matter inside it was detected through a method called “weak gravitational lensing.” By tracking distortions in light as it passes through the cluster, astronomers can create a sort of topographical map of the mass in the cluster, where the “hills” are places of strong gravity and “valleys” are places of weak gravity. The reason dark matter—the mysterious substance that makes up most of the mass in the universe—is so hard to study is because it doesn’t emit or absorb light. But it does have gravity, and thus it shows up in a topographical map of this kind.

The Bullet Cluster is one of the best places to see the effects of dark matter, but it’s only one object. Much of the real power of weak gravitational lensing involves looking at thousands or millions of galaxies covering large patches of the sky. [Read the rest at Smithsonian Magazine]

BICEP3: Revenge of the telescope

[ This blog is dedicated to tracking my most recent publications. Subscribe to the feed to keep up with all the science stories I write! ]

Dusting for the fingerprint of inflation with BICEP3

A new experiment at the South Pole picks up where BICEP2 left off

For Symmetry Magazine:

When researchers with the BICEP2 experiment announced they had seen the first strong evidence for cosmic inflation, it was front-page news around the world. Inflation is the extremely rapid expansion of space-time during its first split second of existence, proposed to explain a number of puzzling properties of the universe, making the BICEP2 results a really big deal. Over the following months, though, the excitement evaporated: After combining their data with other experiments, the BICEP2 team showed that most or all of the signal attributed to inflation was likely produced by galactic dust inside the Milky Way.

But traces of inflation could still be hiding in the data, and that’s why scientists haven’t given up yet. BICEP3, the upgraded version of BICEP2, began collecting data yesterday. The first observations using the fully updated equipment will run through November. [Read the rest at Symmetry Magazine]

How standard are “standard candles”?

[ This blog is dedicated to tracking my most recent publications. Subscribe to the feed to keep up with all the science stories I write! ]

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!

Traces of particles from the first second after the Big Bang

[ This blog is dedicated to tracking my most recent publications. Subscribe to the feed to keep up with all the science stories I write! ]

Signs of neutrinos from the dawn of time, less than a second after the Big Bang

First unambiguous observation of the cosmic neutrino background

From Ars Technica:

The first 400,000 years after the Big Bang are inaccessible to us by using light; the material that filled the entire cosmos made it opaque. However, neutrinos interact very little with ordinary matter, so they could travel right through the opaque mess. Lots of these low-mass, fast-moving particles were formed in the first second after the Big Bang, so they could provide a sensitive probe of some of the very earliest moments in the Universe.

Unfortunately, these primordial neutrinos have never been detected directly, and they may have too little energy for us to ever detect them. But a new paper published in Physical Review Letters showed an unambiguous indirect detection using measurements of the cosmic microwave background light. This article marks the first clear measurement of the cosmic neutrino background, which is a significant confirmation of one of the major predictions of the Big Bang model. [Read the rest at Ars Technica…]