SEE ALSO First Humans in Space (1961), First on the Moon (1969), Spirit and Opportunity on Mars (2004).
The International Space Station orbits about 190 miles (305 kilometers) above Earth’s surface. Assembly of the space research outpost began in 1998; this 2009 photo taken by the crew of the space shuttle Discovery shows the station’s solar panels, trusses, and pressurized modules.
2003
Human Genome Project • Clifford A. Pickover
James Dewey Watson (b. 1928), John Craig Venter (b. 1946), Francis Sellers Collins (b. 1950)
The Human Genome Project (HGP) is an international effort to determine the genetic sequence of the approximately three billion chemical base pairs in our DNA and to gain insight into its roughly 20,000 genes. Genes are units of heredity and embodied as stretches of DNA that code for a protein or an RNA molecule that has a particular function. The HGP began in 1990 under the leadership of American molecular biologist James Watson and, later, under American physician-geneticist Francis Collins. A parallel effort was conducted by American biologist Craig Venter, founder of Celera Genomics. Not only does this DNA sequence help us understand human disease, it also helps elucidate the relationship between humans and other animals.
In 2001, Collins spoke regarding the publication of a majority of the human genome: “It’s a history book: a narrative of the journey of our species through time. It’s a shop manual: an incredibly detailed blueprint for building every human cell. And it’s a transformative textbook of medicine: with insights that will give health-care providers immense new powers to treat, prevent, and cure disease.” A more complete sequence, announced in 2003, is considered to be a watershed moment in the history of civilization.
To help generate the human genetic sequence, the genome was first broken into smaller fragments, and these pieces were inserted into bacteria in order to make many copies and create a stable resource, or library, of DNA clones. Assembling the larger sequences from fragments required sophisticated computer analyses.
Except for identical twins, individual human genomes differ, and future research will continue to involve the comparison of sequences of different individuals to help scientists better understand the role of genetics in disease and differences among humans. Only about 1 percent of the genome’s sequence codes for proteins. The number of genes in humans falls between the number for grape plants (~30,400 genes) and for chickens (~16,700 genes). Interestingly, nearly half of the human genome is composed of transposable elements, or jumping DNA fragments that can move around, on, and between chromosomes.
SEE ALSO Chromosomal Theory of Inheritance (1902), DNA Structure (1953), Epigenetics (1983), Polymerase Chain Reaction (1983).
Going beyond the HGP, results from the Neanderthal Genome Project allow researchers to compare human genomes to sequences from Neanderthals, our close evolutionary relatives who became extinct around 30,000 years ago.
2004
Spirit and Opportunity on Mars • Jim Bell
More than three decades of successful orbital and landed investigations of Mars by scientists involved in the Mariner and Viking missions painted a compelling picture of major past climate changes on the Red Planet. The Martian surface today is extremely cold, bone dry, and inhospitable to life as we know it. But ancient Mars, as revealed by these missions, appears to have been a warmer, wetter, and potentially more Earthlike place. If so, then early Mars (during the first billion years or so after its formation) may have been a habitable environment where, as on our own planet, life could have thrived.
Planetary scientists wanted to move beyond photographic evidence of a potentially habitable early Mars, however, and make quantitative geologic, geochemical, and mineralogic measurements that could provide smoking-gun proof. Experience gained from the 1997 Mars Pathfinder mission proved the value of mobility in doing geologic field work with robots in distant locations, leading to the choice to embark on an even longer-range rover mission. Because of two Mars missions failures in 1999, NASA decided to reduce its risk: instead of just one rover, it would launch twin rovers—named Spirit and Opportunity—in 2003.
Both rovers landed safely in early 2004 and began their separate adventures on opposite sides of the planet: Spirit in an ancient crater named Gusev, which may once have hosted a lake, and Opportunity in the cratered area Meridiani Planum, where Mars Global Surveyor data showed evidence for water-formed minerals. After several years of virtually roving around Gusev with Spirit, mission scientists discovered evidence of water-bearing minerals in an ancient hydrothermal system that provided smoking-gun evidence for past habitability in Gusev. At Meridiani, the team immediately found other water-bearing minerals and geologic clues that provided conclusive proof of past habitability there as well. Spirit’s last data came in early 2010, but as of mid-2012 Opportunity continues to roll on and make new discoveries.
SEE ALSO First Humans in Space (1961), First on the Moon (1969), International Space Station (1998).
A computer-generated version of the NASA Mars rover Opportunity placed into an actual Opportunity Pancam mosaic of finely layered rocks inside Endurance crater. These rocks contain evidence of past liquid water on Mars, including millimeter-size iron-rich spheres (inset) called concretions.
2008
Human Cloning • Clifford A. Pickover
Science educator Regina Bailey writes, “Imagine a world where cells can be created for therapeutic treatment of certain diseases or whole organs can be generated for transplants. . . . Humans could duplicate themselves or make exact copies of lost loved ones. . . . [Cloning and biotechnology] will define our time for future generations.” In 2008, an ethical storm was already brewing when American scientist Samuel Wood became the first man to clone himself.
Reproductive human cloning refers to the production of a person who is essentially genetically identical to another. This may be accomplished by somatic cell nuclear transfer (SCNT), a process in which the nucleus of a donor adult cell is inserted into an egg cell whose nucleus has been removed, which may result in a developing embryo implanted in a womb. A new organism can also be cloned by splitting the early embryo, so that each portion becomes a separate organism (as happens with identical twins). With therapeutic human cloning, the clone is not implanted, but its cells serve a useful purpose, such as growing new tissues for transplantation. These patient-specific tissues do not trigger the immune response.
In 1996, Dolly, a sheep, became the first mammal to be successfully cloned from an adult cell. In 2008, Wood successfully created five embryos using DNA from his own skin cells, which might have been a source of embryonic stem cells used to repair injuries and cure diseases. Embryonic stem cells are capable of becoming any kind of cell in the human body. For legal and ethical reasons, the five embryos were destroyed. Following the news of human cloning, a Vatican representative condemned the act, stating, “This ranks among the most morally illicit acts.” Other methods for collecting stem cells do not require cloning of embryos. For example, skin cells can be reprogrammed to create induced pluripotent stem cells (iPS), with no embryo needed, which might serve as possible sources for various replacement tissues destroyed by degenerative diseases.
SEE ALSO Discovery of Sperm (1678), Cell Division (1855), DNA Structure (1953), Gene Therapy (2016).
Long discussed in science fiction, human cloning may become relatively easy to accomplish in the future. A Vatican representative condemned early experiments as ranking “among the most morally illicit acts.”
2009
Large Hadron Collider • Clifford A. Pickover
According to Britain’s The Guardian newspaper, “Particle physics is the unbelievable in pursuit of the unimaginable. To pinpoint the smallest fragments of the universe you have to build the biggest machine in the world. To recreate the first millionths of a second of creation you have to focus energy on an awesome scale.” Author Bill Bryson writes, “Particle physicists divine the secrets of the Universe in a startlingly straightforward
way: by flinging particles together with violence and seeing what flies off. The process has been likened to firing two Swiss watches into each other and deducing how they work by examining their debris.”
Built by the European Organization for Nuclear Research (usually referred to as CERN), the Large Hadron Collider (LHC) is the world’s largest and highest-energy particle accelerator, designed primarily to create collisions between opposing beams of protons (which are one kind of hadron). The beams circulate around the circular LHC ring inside a continuous vacuum guided by powerful electromagnets, the particles gaining energy with every lap. The magnets exhibit superconductivity and are cooled by a large liquid-helium cooling system. When in their superconduction states, the wiring and joints conduct current with very little resistance.
The LHC resides within a tunnel 17 miles (27 kilometers) in circumference across the Franco-Swiss border and allows physicists to gain a better understanding of the Higgs boson (also called the God particle), a particle that explains why particles have mass. The LHC may also be used to find particles predicted by supersymmetry, which suggests the existence of heavier partner particles for elementary particles (for example, selectrons are the predicted partners of electrons). Additionally, the LHC may be able to provide evidence for the existence of spatial dimensions beyond the three obvious spatial dimensions. In some sense, by colliding the two beams, the LHC is re-creating some of the kinds of conditions present just after the Big Bang. Teams of physicists analyze the particles created in the collisions using special detectors. In 2009, the first proton–proton collisions were recorded at the LHC.
SEE ALSO Superconductivity (1911), String Theory (1919), Standard Model (1961).
Installing the ATLAS calorimeter for the LHC. The eight toroid magnets can be seen surrounding the calorimeter that is subsequently moved into the middle of the detector. This calorimeter measures the energies of particles produced when protons collide in the center of the detector.
2016
Gene Therapy • Clifford A. Pickover
William French Anderson (b. 1936)
Many diseases result from defects in our genes, which are our units of heredity that control traits ranging from eye color to our susceptibility to cancer and asthma. For example, sickle-cell anemia, which produces abnormal red blood cells, arises from a single deleterious change in the DNA sequence of a gene.
Gene therapy is a young discipline that involves the insertion, alteration, or removal of genes in human cells to treat disease. One form of gene therapy involves the use of a virus that is engineered to contain a useful human gene. The virus inserts this gene into a defective human cell (usually at a random location in the host’s DNA), and this new gene manufactures a properly functioning protein. If a sperm or egg were modified, the change would be passed to offspring, with profound ethical implications for the human race.
The first approved gene therapy procedure in the United States occurred in 1990, to treat a four-year-old girl who was suffering from a rare immune disorder known as adenosine deaminase (ADA) deficiency that made her vulnerable to infections. American researcher W. French Anderson and colleagues treated white blood cells withdrawn from her body with the gene she lacked, returned the cells to her body, and hoped the cells would produce the enzyme she needed. Although the cells safely produced the enzyme, the cells failed to give rise to healthy new cells. Gene therapy was later used to successfully treat ADA deficiency, other forms of severe immune deficiency (e.g., “bubble boy” disease), AIDS (by genetically altering T cells to resist HIV viruses), and Parkinson’s disease (by reducing symptoms). Nevertheless, the procedure carries risks in some cases. Several of the children in an immune deficiency study contracted leukemia, since viral insertion of genes into a host cell can sometimes disrupt normal gene function. Also, the viral carriers of the genes (or the cells that harbor the newly implanted gene) may be attacked by the host immune’s system, rendering the treatment ineffective. At worst, a strong immune attack can kill a patient.
More recently, CRISPR technology allows researchers to make more precise genetic changes at exact locations in an organism’s genome. In 2016, the US Food and Drug Administration approved the first human trial for CRISPR to be used in cancer therapy, involving editing patients’ T cells, which play a role in immunity.
SEE ALSO Epigenetics (1983), Polymerase Chain Reaction (1983), Human Cloning (2008).
Hemophilia is caused by a mutation in a single gene on the X chromosome. Hemophiliacs bleed profusely when cut. Show here is Queen Victoria of the United Kingdom (1819–1901), who passed this mutation to numerous royal descendants.
2016
Gravitational Waves • Jim Bell
In the view of the universe elegantly advocated by Albert Einstein in his early twentieth-century theory of general relativity, our three dimensions of space and one dimension of time are intimately linked into a continuum called “spacetime.” Furthermore, Einstein and others realized that spacetime can become warped or curved in the presence of mass or energy, and thus ripples or waves could theoretically propagate through spacetime like the waves on a pond.
At least, that is theoretically the case. The problem scientists encountered throughout the rest of the twentieth century, however, was that the magnitude of these predicted gravitational waves in the spacetime continuum was extremely small and impossible to detect with existing technology. In addition, the kinds of events or disturbances that could produce detectable gravitational waves—like the supernova explosion of an enormously massive star, or the merger of two black holes—are rare and/or extremely distant. Thus, detecting gravitational waves had to wait for technological advances.
Those advances finally arrived with the advent of two enormous detectors specially designed to search for gravitational waves: the US Laser Interferometer Gravitational-wave Observatory (LIGO) and the European Virgo Interferometer. Both facilities use lasers to search for the tiny changes in the distances between reference targets that would be caused by a passing gravitational wave. The instruments can achieve exquisite sensitivity, comparable to being able to measure the distance to the nearest stars to within an accuracy of a human hair. LIGO began operations in 2002 and Virgo in 2003, and since 2007 both facilities have jointly shared their data and analyses, helping to refute or confirm each other’s potential detections.
After more than a decade of searching, and after careful data processing and peer review of their results, LIGO and Virgo finally announced the first detection of gravitational waves (from the merger of two supermassive black holes) in February 2016, confirming the last major unproven prediction of Einstein’s theory of general relativity. More detections have been made since, and astronomers are now excited to use gravitational waves as new tools to study extremely violent and high-energy phenomena across the universe.
SEE ALSO Newton’s Laws (1687), Einstein’s “Miracle Year” (1905), Black Holes (1965), Hawking’s “Extreme Physics” (1965), Gravitational Lensing (1979).
Computer simulation of ripples in the spacetime continuum—gravitational waves—caused by the merger of two supermassive, co-orbiting black holes.
2017
Proof of the Kepler Conjecture • Clifford A. Pickover
Johannes Kepler (1571–1630), Thomas Callister Hales (b. 1958)
Imagine that your goal is to fill a large box with as many golf balls as possible. Close the lid tightly when finished. The density of balls is determined from the proportion of the volume of the box that contains a ball. In order to stuff the most balls into the box, you need to discover an arrangement with the highest possible density. If you simply drop balls into the box, you’ll only achieve a density of roughly 65 percent. If you are careful, and create a layer at the bottom in a hexagonal arrangement, and then put the next layer of balls in the indentations created by the bottom layer, and continue, you’ll be able to achieve a packing density of , which is about 74 percent.
In 1611, German mathematician and astronomer J
ohannes Kepler wrote that no other arrangement of balls has a higher average density. In particular, he conjectured in his monograph The Six-Cornered Snowflake that it is impossible to pack identical spheres in three dimensions greater than the packing found in face-centered (hexagonal) cubic packing. In the nineteenth century, Karl Friedrich Gauss proved that the traditional hexagonal arrangement was the most efficient for a regular 3-D grid. Nevertheless, the Kepler conjecture remained, and no one was sure if a denser packing could be achieved with an irregular packing.
Finally, in 1998, American mathematician Thomas Hales stunned the world when he presented a proof that Kepler had been right. Hales’s equation and its 150 variables expressed every conceivable arrangement of 50 spheres. Computers confirmed that no combination of variables led to a packing efficiency higher than 74 percent.
The Annals of Mathematics agreed to publish the proof, provided it was accepted by a panel of 12 referees. In 2003, the panel reported that they were “99 percent certain” of the correctness of the proof. Finally, in 2017, the Forum of Mathematics, Pi journal published a formal proof of the Kepler Conjecture, by a team led by Hales, resolving a problem that was unsolved for hundreds of years.
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