Physics

Three American scientists have been awarded the Nobel Prize in physics for their discovery that the universe is expanding at an accelerating rate. Saul Perlmutter will share the prize with Brian Schmidt and Adam Riess.

The discovery of the accelerating expansion of the universe followed an unexpected observational discovery in 1998. Astronomers in two different groups — the Supernova Cosmology Project (Perlmutter) and the High-z Supernova Search Team (Schmidt and Riess) — were observing the characteristic light signature of a certain type of supernova, called a Type 1a supernova, to probe the expansion history of the universe.

Let’s pause the story for a moment to explore the significance of these objects. Type 1a supernovae are a special subclass of exploding stars. Other types of supernovae occur when a massive star runs out of fuel, causing the core to collapse; their intrinsic brightness depends on a variety of factors, including the mass of the progenitor star. Type 1a supernovae occur when a white dwarf — the exposed core of a dead less-massive star — reaches a mass limit, called the Chandrasekhar limit. The mass limit can be reached if a white dwarf siphons matter from a companion star (see the header image above) or if two white dwarfs in a binary system collide. Since the resulting explosion always occurs at roughly the same mass, these supernovae always have roughly the same intrinsic brightness. This predictable brightness makes Type 1a supernovae excellent probes of distance and cosmic history.

Back to our story. The astronomers were using Type 1a supernovae to test the idea that the universe was slowing down in its expansion. If their idea was right, then the supernovae would appear to be brighter than expected, meaning they would be closer to the Earth than they would be if the universe had been expanding at a uniform rate. But they found the opposite: the supernovae appeared significantly dimmer than expected, meaning these exploding stars were further away than they would be for a uniform expansion. The astronomers concluded that the expansion of the universe was not slowing down, but rather speeding up. This conclusion was further supported by discoveries from other cosmological experiments, including mapping of the cosmic microwave background.

These discoveries led to the hypothesis that a mysterious force, called dark energy, is driving the accelerated expansion. Very little is currently known about this force, but several experiments, including HETDEX, Destiny, and SNAP, are underway to hopefully shed some light (as it were) on the subject.

Chemistry

Israeli scientist, Dan Schechtman, has been awarded the Nobel Prize in chemistry for his discovery of quasicrystals. What makes this award particularly interesting is the degree to which Schechtman persisted to make his discovery known. He worked for years in the face of skepticism and ridicule — two-time Nobel laureate, Linus Pauling, evidently referred to Schechtman as a “quasi-scientist” — before he managed to convince the scientific community that his observations overturned the prevailing model for how atoms and molecules can be arranged in solids.

A crystal is a type of material in which the arrangement of atoms is ordered and periodic. Scientists have probed crystalline structures using electron diffraction experiments in which beams of electrons are passed through crystal layers, producing an interference pattern. When Schechtman performed similar experiments on a different type of material, he found a peculiar interference pattern that seemed to defy the known laws of nature, since it indicated an ordered but non-periodic pattern in the arrangement of atoms. This is similar to the mosaic tile patterns found in medieval Islamic shrines.

Since Schechtman’s discovery, many quasicrystals have been synthesized and studied, and a naturally-occurring quasicrystal was discovered in Russia in 2009. Quasicrystals possess some useful properties, including a non-stick surface, low heat conduction, and hardness, that make them useful material for many products, from frying pans to surgical instruments.

In spite of his vindication and receiving the highest of accolades, Schechtman remains endearingly modest:

“The main lesson that I have learned over time is that a good scientist is a humble and listening scientist and not one that is sure 100 percent in what he read in the textbooks.”

Just as it’s difficult to be a devoted Christian in the face of skepticism, mockery, and exclusion, it’s difficult to be a devoted scientist under such conditions, as well. Schechtman deserves his award all the more for his determination and perseverance.