125 Big Questions of Science
The Top 25
1. What Is the Universe Made Of?
2. What is the Biological Basis of Consciousness?
3. Why Do Humans Have So Few Genes?
4. To What Extent Are Genetic Variation andPersonal Health Linked?
5. Can the Laws of Physics Be Unified?
6. How Much Can Human Life Span Be Extended?
7. What Controls Organ Regeneration?
8. How Can a Skin Cell Become a Nerve Cell?
9. How Does a Single Somatic Cell Become a Whole Plant?
10. How Does Earth's Interior Work?
11. Are We Alone in the Universe?
12. How and Where Did Life on Earth Arise?
13. What Determines Species Diversity?
14. What Genetic Changes Made Us Uniquely Human?
15. How Are Memories Stored and Retrieved?
16. How Did Cooperative Behaviour Evolve?
17. How Will Big Pictures Emerge from a Sea of BiologicalData?
18. How Far Can We Push Chemical Self-Assembly?
19. What Are the Limits of Conventional Computing?
20. Can We Selectively Shut Off Immune Responses?
21. Do Deeper Principles Underlie Quantum Uncertainty andNonlocality?
22. Is an Effective HIV Vaccine Feasible?
23. How Hot Will the Greenhouse World Be?
24. What Can Replace Cheap Oil -- and When?
25. Will Malthus Continue to Be Wrong?
The remain 100 problems
26. Is ours the only universe?
A number of quantum theorists and cosmologists are tryingto figure out whether our universe is part of a bigger "multiverse."But others suspect that this hard-to-test idea may be a question forphilosophers.
27. What drove cosmic inflation?
In the first moments after the big bang, the universeblew up at an incredible rate. But what did the blowing? Measurements of thecosmic microwave background and other astrophysical observations are narrowingthe possibilities.
28. When and how did the first stars andgalaxies form?
The broad brush strokes are visible, but the fine detailsaren't. Data from satellites and ground-based telescopes may soon helppinpoint, among other particulars, when the first generation of stars burnedoff the hydrogen "fog" that filled the universe.
29. Where do ultrahigh-energy cosmic rayscome from?
Above a certain energy, cosmic rays don't travel very farbefore being destroyed. So why are cosmic-ray hunters spotting such rays withno obvious source within our galaxy?
30. What powers quasars?
The mightiest energy fountains in the universe probably get their powerfrom matter plunging into whirling super-massive black holes. But the detailsof what drives their jets remain anybody's guess.
31. What is the nature of black holes?
Relativistic mass crammed into a quantum-sized object? It's a recipe fordisaster—and scientists are still trying to figure out the ingredients.
32. Why is there more matter than antimatter?
To a particle physicist, matter and antimatter are almost the same. Somesubtle difference must explain why matter is common and antimatter rare.
33. Does the proton decay?
In a theory of everything, quarks (which make up protons) should somehowbe convertible to leptons (such as electrons)--so catching a proton decayinginto something else might reveal new laws of particle physics.
34. What is the nature of gravity?
It clashes with quantum theory. It doesn't fit in the Standard Model.Nobody has spotted the particle that is responsible for it. Newton's apple contained a whole can ofworms.
35. Why is time different from other dimensions?
It took millennia for scientists to realize that time is a dimension, likethe three spatial dimensions, and that time and space are inextricably linked.The equations make sense, but they don't satisfy those who ask why we perceivea "now" or why time seems to flow the way it does.
36. Are there smaller building blocks than quarks?
Atoms were "uncuttable." Then scientists discovered protons,neutrons, and other subatomic particles--which were, in turn, shown to be madeup of quarks and gluons. Is there something more fundamental still?
37. Are neutrinos their own antiparticles?
Nobody knows this basic fact about neutrinos, although a number ofunderground experiments are under way. Answering this question may be a crucialstep to understanding the origin of matter in the universe.
38. Is there a unified theory explaining all correlatedelectron systems?
High-temperature superconductors and materials with giant and colossalmagnetoresistance are all governed by the collective rather than individualbehaviour of electrons. There is currently no common framework for understandingthem.
39. What is the most powerful laser researchers canbuild?
Theorists say an intense enough laser field would rip photons intoelectron-positron pairs, dousing the beam. But no one knows whether it'spossible to reach that point.
40. Can researchers make a perfect optical lens?
They've done it with microwaves but never with visible light.
41. Is it possible to create magnetic semiconductors thatwork at room temperature?
Such devices have been demonstrated at low temperatures but not yet in arange warm enough for spintronics applications.
42. What is the pairing mechanism behind high-temperaturesuperconductivity?
Electrons in superconductors surf together in pairs. After 2 decades ofintense study, no one knows what holds them together in the complex,high-temperature materials.
43. Can we develop a general theory of the dynamics ofturbulent flows and the motion of granular materials?
So far, such "non-equilibrium systems" defy the tool kit ofstatistical mechanics, and the failure leaves a gaping hole in physics.
44. Are there stable high-atomic-number elements?
A super heavy-element with 184 neutrons and 114 protons should berelatively stable, if physicists can create it.
45. Is super-fluidity possible in a solid? If so, how?
Despite hints in solid helium, nobody is sure whether a crystallinematerial can flow without resistance. If new types of experiments show thatsuch outlandish behaviour is possible, theorists would have to explain how.
46. What is the structure of water?
Researchers continue to tussle over how many bonds each H2O molecule makeswith its nearest neighbours.
47. What is the nature of the glassy state?
Molecules in a glass are arranged much like those in liquids but are moretightly packed. Where and why does liquid end and glass begin?
48. Are there limits to rational chemical synthesis?
The larger synthetic molecules get, the harder it is to control theirshapes and make enough copies of them to be useful. Chemists will need newtools to keep their creations growing.
49. What is the ultimate efficiency of photovoltaiccells?
Conventional solar cells top out at converting 32% of the energy insunlight to electricity. Can researchers break through the barrier?
50. Will fusion always be the energy source of thefuture?
It's been 35 years away for about 50 years, and unless the internationalcommunity gets its act together, it'll be 35 years away for many decades tocome.
51. What drives the solar magnetic cycle?
Scientists believe differing rates of rotation from place to place on thesun underlie its 22-year sunspot cycle. They just can't make it work in theirsimulations. Either a detail is askew, or it's back to the drawing board.
52. How do planets form?
How bits of dust and ice and gobs of gas came together to form the planetswithout the sun devouring them all is still unclear. Planetary systems aroundother stars should provide clues.
53. What causes ice ages?
Something about the way the planet tilts, wobbles, and careens around thesun presumably brings on ice ages every 100,000 years or so, but reams ofclimate records haven't explained exactly how.
54. What causes reversals in Earth's magnetic field?
Computer models and laboratory experiments are generating new data on howEarth's magnetic poles might flip-flop. The trick will be matching simulationsto enough aspects of the magnetic field beyond the inaccessible core to build aconvincing case.
55. Are there earthquake precursors that can lead touseful predictions?
Prospects for finding signs of an imminent quake have been waning sincethe 1970s. Understanding faults will progress, but routine prediction wouldrequire an as-yet-unimagined breakthrough.
56. Is there--or was there--life elsewhere in the solarsystem?
The search for life--past or present--on other planetarybodies now drives NASA's planetary exploration program, which focuses on Mars,where water abounded when life might have first arisen.
57. What is the origin ofhomochirality in nature?
Most bio-molecules can be synthesized in mirror-imageshapes. Yet in organisms, amino acids are always left-handed, and sugars arealways right-handed. The origins of this preference remain a mystery.
58. Can we predict howproteins will fold?
Out of a near infinitude of possible ways to fold, aprotein picks one in just tens of microseconds. The same task takes 30 years ofcomputer time.
59. How many proteinsare there in humans?
It has been hard enough counting genes. Proteins can bespliced in different ways and decorated with numerous functional groups, all ofwhich makes counting their numbers impossible for now.
60. How do proteins findtheir partners?
Protein-protein interactions are at the heart of life. Tounderstand how partners come together in precise orientations in seconds,researchers need to know more about the cell's biochemistry and structuralorganization.
61. How many forms of celldeath are there?
In the 1970s, apoptosis was finally recognized asdistinct from necrosis. Some biologists now argue that the cell death story iseven more complicated. Identifying new ways cells die could lead to bettertreatments for cancer and degenerative diseases.
62. What keepsintracellular traffic running smoothly?
Membranes inside cells transport key nutrients around,and through, various cell compartments without sticking to each other or losingtheir way. Insights into how membranes stay on track could help conquerdiseases, such as cystic fibrosis.
63. What enables cellularcomponents to copy themselves independent of DNA?
Centrosomes, which help pull apart paired chromosomes,and other organelles replicate on their own time, without DNA's guidance. Thisindependence still defies explanation.
64. What roles dodifferent forms of RNA play in genome function?
RNA is turning out to play a dizzying assortment ofroles, from potentially passing genetic information to offspring to muting geneexpression. Scientists are scrambling to decipher this versatile molecule.
65. What role do telomeresand centromeres play in genome function?
These chromosome features will remain mysteries until newtechnologies can sequence them.
66. Why are some genomesreally big and others quite compact?
The puffer fish genome is 400 million bases; onelungfish's is 133 billion bases long. Repetitive and duplicated DNA don'texplain why this and other size differences exist.
67. What is all that"junk" doing in our genomes?
DNA between genes is proving important for genomefunction and the evolution of new species. Comparative sequencing, micro-arraystudies, and lab work are helping genomicists find a multitude of genetic gemsamid the junk.
68. How much will new technologies lower thecost of sequencing?
New tools and conceptual breakthroughs are driving thecost of DNA sequencing down by orders of magnitude. The reductions are enablingresearch from personalized medicine to evolutionary biology to thrive.
69. How do organs andwhole organisms know when to stop growing?
A person's right and left legs almost always end up thesame length, and the hearts of mice and elephants each fit the proper rib cage.How genes set limits on cell size and number continues to mystify.
70. How can genomechanges other than mutations be inherited?
Researchers are finding ever more examples of thisprocess, called epigenetics, but they can't explain what causes and preservesthe changes.
71. How is asymmetry determined in theembryo?
Whirling cilia help an embryo tell its left from itsright, but scientists are still looking for the first factors that give arelatively uniform ball of cells a head, tail, front, and back.
72. How do limbs, fins, and faces develop andevolve?
The genes that determine the length of a nose or thebreadth of a wing are subject to natural and sexual selection. Understandinghow selection works could lead to new ideas about the mechanics of evolutionwith respect to development.
73. What triggers puberty?
Nutrition--including that received in utero--seems tohelp set this mysterious biological clock, but no one knows exactly what forceschildhood to end.
74. Are stem cells at theheart of all cancers?
The most aggressive cancer cells look a lot like stemcells. If cancers are caused by stem cells gone awry, studies of a cell's"stemness" may lead to tools that could catch tumours sooner anddestroy them more effectively.
75. Is cancer susceptibleto immune control?
Although our immune responses can suppress tumour growth,tumour cells can combat those responses with counter-measures. This defence canstymie researchers hoping to develop immune therapies against cancer.
76. Can cancers becontrolled rather than cured?
Drugs that cut off a tumour’s fuel supplies--say, bystopping blood-vessel growth—can safely check or even reverse tumour growth.But how long the drugs remain effective is still unknown.
77. Is inflammation amajor factor in all chronic diseases?
It's a driver of arthritis, but cancer and heart disease?More and more, the answer seems to be yes, and the question remains why andhow.
78. How do prion diseases work?
Even if one accepts that prions are just mis-foldedproteins, many mysteries remain. How can they go from the gut to the brain, andhow do they kill cells once there, for example.
79. How much dovertebrates depend on the innate immune system to fight infection?
This system predates the vertebrate adaptive immuneresponse. Its relative importance is unclear, but immunologists are working tofind out.
80. Does immunologicmemory require chronic exposure to antigens?
Yes, say a few prominent thinkers, but experiments withmice now challenge the theory. Putting the debate to rest would require provingthat something is not there, so the question likely will not go away.
81. Why doesn't a pregnantwoman reject her fetus?
Recent evidence suggests that the mother's immune systemdoesn't "realize" that the fetus is foreign even though it gets halfits genes from the father. Yet just as Nobelist Peter Medawar said when hefirst raised this question in 1952, "the verdict has yet to be returned."
82. What synchronizes an organism's circadianclocks?
Circadian clock genes have popped up in all types ofcreatures and in many parts of the body. Now the challenge is figuring out howall the gears fit together and what keeps the clocks set to the same time.
83. How do migrating organisms find theirway?
Birds, butterflies, and whales make annual journeys ofthousands of kilometres. They rely on cues such as stars and magnetic fields,but the details remain unclear.
84. Why do we sleep?
A sound slumber may refresh muscles and organs or keepanimals safe from dangers lurking in the dark. But the real secret of sleepprobably resides in the brain, which is anything but still while we're snoringaway.
85. Why do we dream?
Freud thought dreaming provides an outlet for ourunconscious desires. Now, neuroscientists suspect that brain activity duringREM sleep--when dreams occur--is crucial for learning. Is the experience ofdreaming just a side effect?
86. Why are there criticalperiods for language learning?
Monitoring brain activity in young children--includinginfants--may shed light on why children pick up languages with ease whileadults often struggle to learn train station basics in a foreign tongue.
87. Do pheromones influence human behaviour?
Many animals use airborne chemicals to communicate,particularly when mating. Controversial studies have hinted that humans too usepheromones. Identifying them will be the key to assessing their sway on oursocial lives.
88. How do general anesthetics work?
Scientists are chipping away at the drugs' effects onindividual neurons, but understanding how they render us unconscious will be atougher nut to crack.
89. What causesschizophrenia?
Researchers are trying to track down genes involved inthis disorder. Clues may also come from research on traits schizophrenics sharewith normal people.
90. What causes autism?
Many genes probably contribute to this baffling disorder,as well as unknown environmental factors. A biomarker for early diagnosis wouldhelp improve existing therapy, but a cure is a distant hope.
91. To what extent can westave off Alzheimer's?
A 5- to 10-year delay in this late-onset disease wouldimprove old age for millions. Researchers are determining whether treatmentswith hormones or antioxidants, or mental and physical exercise, will help.
92. What is the biologicalbasis of addiction?
Addiction involves the disruption of the brain's rewardcircuitry. But personality traits such as impulsivity and sensation-seekingalso play a part in this complex behaviour.
93. Is morality hardwiredinto the brain?
That question has long puzzled philosophers; now someneuroscientists think brain imaging will reveal circuits involved in reasoning.
94. What are the limits of learning bymachines?
Computers can already beat the world's best chessplayers, and they have a wealth of information on the Web to draw on. Butabstract reasoning is still beyond any machine.
95. How much ofpersonality is genetic?
Aspects of personality are influenced by genes;environment modifies the genetic effects. The relative contributions remainunder debate.
96. What is the biologicalroot of sexual orientation?
Much of the "environmental" contribution tohomosexuality may occur before birth in the form of prenatal hormones, soanswering this question will require more than just the hunt for "gaygenes."
97. Will there ever be a tree of life thatsystematists can agree on?
Despite better morphological, molecular, and statisticalmethods, researchers' trees don't agree. Expect greater, but not complete,consensus.
98. How many species are there on Earth?
Count all the stars in the sky? Impossible. Count all thespecies on Earth? Ditto. But the biodiversity crisis demands that we try.
99. What is a species?
A "simple" concept that's been muddied byevolutionary data; a clear definition may be a long time in coming.
100. Why does lateral transfer occur in somany species and how?
Once considered rare, gene swapping, particularly amongmicrobes, is proving quite common. But why and how genes are so mobile--and theeffect on fitness--remains to be determined.
101. Who was LUCA (the last universal commonancestor)?
Ideas about the origin of the 1.5-billion-year-old"mother" of all complex organisms abound. The continued discovery ofprimitive microbes, along with comparative genomics, should help resolve life'sdeep past.
102. How did flowers evolve?
Darwin calledthis question an "abominable mystery." Flowers arose in the cycadsand conifers, but the details of their evolution remain obscure.
103. How do plants make cell walls?
Cellulose and pectin walls surround cells, keeping waterin and supporting tall trees. The biochemistry holds the secrets to turning itsbiomass into fuel.
104. How is plant growth controlled?
Redwoods grow to be hundreds of meters tall, Arcticwillows barely 10 centimetres. Understanding the difference could lead tohigher-yielding crops.
105. Why aren't all plants immune to alldiseases?
Plants can mount a general immune response, but they alsomaintain molecular snipers that take out specific pathogens. Plant pathologistsare asking why different species, even closely related ones, have differentsets of defenders. The answer could result in hardier crops.
106. What is the basis of variation in stresstolerance in plants?
We need crops that better withstand drought, cold, andother stresses. But there are so many genes involved, in complex interactions,which no one has yet figured out which ones work how.
107. What caused mass extinctions?
A huge impact did in the dinosaurs, but the search forother catastrophic triggers of extinction has had no luck so far. If moresubtle or stealthy culprits are to blame, they will take considerably longer tofind.
108. Can we prevent extinction?
Finding cost-effective and politically feasible ways tosave many endangered species requires creative thinking.
109. Why were some dinosaurs so large?
Dinosaurs reached almost unimaginable sizes, some in lessthan 20 years. But how did the long-necked sauropods, for instance, eat enoughto pack on up to 100 tons without denuding their world?
110. How will ecosystems respond to globalwarming?
To anticipate the effects of the intensifying greenhouse,climate modellers will have to focus on regional changes and ecologists on theright combination of environmental changes.
111. How many kinds of humans coexisted inthe recent past, and how did they relate?
The new dwarf human species fossil from Indonesiasuggests that at least four kinds of humans thrived in the past 100,000 years.Better dates and additional material will help confirm or revise this picture.
112. What gave rise tomodern human behaviour?
Did Homo sapiens acquire abstract thought, language, andart gradually or in a cultural "big bang," which in Europeoccurred about 40,000 years ago? Data from Africa,where our species arose, may hold the key to the answer.
113. What are the roots ofhuman culture?
No animal comes close to having humans' ability to buildon previous discoveries and pass the improvements on. What determines thosedifferences could help us understand how human culture evolved.
114. What are theevolutionary roots of language and music?
Neuroscientists exploring how we speak and make music arejust beginning to find clues as to how these prized abilities arose.
115. What are human races,and how did they develop?
Anthropologists have long argued that race lacks biologicalreality. But our genetic makeup does vary with geographic origin and as suchraises political and ethical as well as scientific questions.
116. Why do some countries grow and othersstagnate?
From Norwayto Nigeria,living standards across countries vary enormously, and they're not becomingmore equal.
117. What impact do large government deficitshave on a country's interest rates and economic growth rate?
The United States could provide a test case.
118. Are political and economic freedomclosely tied?
China mayprovide one answer.
119. Why has poverty increased and lifeexpectancy declined in sub-Saharan Africa?
Almost all efforts to reduce poverty in sub-Saharan Africahave failed. Figuring out what will work is crucial to alleviating massive humansuffering.
Seven outstanding mathematics problems
(Selected by the Clay Mathematics Institute, the seventh problem isdiscussed on 19thproblem. For more details, go towww.claymath.org/millennium)
120. Is there a simple test for determining whether anelliptic curve has an infinite number of rational solutions?
Equations of the form y2 = x3 ax b are powerful mathematical tools. TheBirch and Swinnerton-Dyer conjecture tells how to determine how many solutionsthey have in the realm of rational numbers--information that could solve a hostof problems, if the conjecture is true.
121. Can a Hodge cycle be written as a sum of algebraiccycles?
Two useful mathematical structures arose independently in geometry and inabstract algebra. The Hodge conjecture posits a surprising link between them,but the bridge remains to be built.
122. Will mathematicians unleash the power of theNavier-Stokes equations?
First written down in the 1840s, the equations hold the keys tounderstanding both smooth and turbulent flow. To harness them, though,theorists must find out exactly when they work and under what conditions theybreak down.
123. Does Poincaré's test identify spheres infour-dimensional space?
You can tie a string around a doughnut, but it will slide right off asphere. The mathematical principle behind that observation can reliably spotevery sphere-like object in 3D space. Henri Poincaré conjectured that it shouldalso work in the next dimension up, but no one has proved it yet.
124. Do mathematically interesting zero-value solutionsof the Riemann zeta function all have the form a + bi?
Don't sweat the details. Since the mid-19th century, the "Riemannhypothesis" has been the monster catfish in mathematicians' pond. If true,it will give them a wealth of information about the distribution of primenumbers and other long-standing mysteries.
125. Does the Standard Model of particle physics rest onsolid mathematical foundations?
For almost 50 years, the model has rested on "quantum Yang-Millstheory," which links the behaviour of particles to structures found ingeometry. The theory is breathtakingly elegant and useful--but no one hasproved that it's sound.