100 Unanswered Questions About Ourselves, Our World and Our Universe
Top Scientists were asked about 100 unsolved problems in their fields. They sent back provocations — on the origins of life, the possibilities for human progress and much more.
Bill Wasik is The Times’s science editor. This is the first of a series called Unknowns, about unanswered scientific questions.
Are you proud of your chin?
You should be. In fact, give it an appreciative rub right now, or admire it in the mirror: That bony protuberance jutting out past your teeth is a trait that distinguishes you from the rest of the animal kingdom. Even your extinct hominin cousins — those enigmatic Neanderthals and Denisovans who strode bipedally like humans and even sometimes mated with them — never belonged to the chin club.
But why just us? One human who has deep thoughts on that mystery is Daniel Lieberman, an evolutionary biologist at Harvard. It’s a question he loves to ponder in part because his students love to ponder it, too. When he poses it to them in class, he says, “it always gets them on the edge of their seat, even though it’s completely unimportant.”
Dr. Lieberman is one of 100 scientists to whom the writers and editors on The Times’s Science desk recently posed a query of their own: “What is a big unanswered question in your field?” Responses poured in from biochemists, quantum physicists, archaeologists, oceanographers, Nobel Prize-winning biologists, geoscientists, entomologists, you name it.
Scroll down and you can read the 100 questions they sent back — a list that demonstrates the fascinating range of the scientific mission and mind-set. Some questions aim at concrete, day-to-day mysteries (“How do ants work together to produce the collective behavior of colonies?” asks Deborah Gordon, a biologist). Others interrogate first principles: “What determines the laws of physics as they exist in our universe?” Katie Mack, an astrophysicist, wonders. Still others express an urgency about human problems that want solving — like “Can we make the wildlife trade sustainable?” and “Can the human aging process be safely reversed?”
And some, like Dr. Lieberman’s, express a pure curiosity for its own sake. Various hypotheses have tried to explain why chins might have helped our ancestors survive, he notes, but none really make sense. The only one left is sexual selection: Maybe chins made some hominins more attractive to the opposite sex, and the trait won out over time. But the theory is impossible to prove; testing it would entail “showing pictures of people without chins and asking if you would sleep with them,” which, Dr. Lieberman notes, is “a terrible experiment.”
In that regard, it’s one of the many big questions below that are most likely impossible to answer, at least not in our lifetimes. Still, we hope you’ll spend some time pondering them yourself. Imagine them, perhaps, as a road map for the future of science — charting long journeys of human exploration that will be well worth the trip, even if we never see the destination.
100 Scientists. 100 Questions.
1. Did time have a beginning, when our universe was very small?
Juan Maldacena, theoretical physicist, Institute for Advanced Study, Princeton University
2. What preceded the Big Bang?
Adam Riess, astrophysicist, Johns Hopkins University
3. How many dimensions does it take to describe the formation and evolution of our universe?
Andrea Ghez, astrophysicist, University of California, Los Angeles
4. When and where did the cognitive capacities that made language, mathematics and complex societies possible first emerge?
Maxime Aubert, archaeologist and geochemist, Griffith University, Australia
5. Why and how did the human brain expand so quickly during the ice age?
Sean B. Carroll, biologist, University of Maryland
6. What is curiosity?
Victor Ambros, molecular biologist, UMass Chan Medical School
7. How did the first Indigenous people enter the Americas?
Michael Waters, geoarchaeologist, Center for the Study of the First Americans, Texas A&M University
8. A million years ago, how did earlier human species colonize remote and previously uninhabited islands in Southeast Asia?
Adam Brumm, archaeologist, Griffith University, Australia
9. Why does full writing — complete sentences that can make sense to readers out of context — appear so late in human history?
Olivier Morin, cognitive scientist, Institut Jean Nicod, Paris
10. What is the form of human thought — words, pictures, something more abstract?
Evelina Fedorenko, neuroscientist, McGovern Institute for Brain Research
11. Given how much A.I. is accomplishing with relatively simple neural networks, why is the human brain so complex?
Ed Lein, neurobiologist, Allen Institute
12. How does the human brain construct meaning from language, when so much of what we understand is not expressed in the words?
Sharlene Newman, psychologist, University of Alabama
13. What kind of information — about people, places and other dogs — can dogs acquire through smell?
Alexandra Horowitz, cognitive scientist, Dog Cognition Lab, Barnard College
14. How do birds migrate with such energy efficiency?
David Lentink, engineer and biologist, University of Groningen, the Netherlands
15. Why did birds survive the Cretaceous mass extinction while other dinosaurs went extinct?
Sushma Reddy, ornithologist, University of Minnesota
16. Were the first dinosaurs warm-blooded, or did different groups evolve it as separate evolutionary events?
Thomas R. Holtz, Jr., paleontologist, University of Maryland
17. How did some herbivorous dinosaurs grow to 100 feet long or more on an all-plant diet?
Mary Schweitzer, paleontologist, North Carolina State University
18. How many undiscovered animal species live in the deep sea, and do they matter?
Lisa Levin, marine ecologist, Scripps Institution of Oceanography, University of California, San Diego
19. Why do so many marine organisms glow, including some that live in burrows?
Joseph Pawlik, marine biologist, University of North Carolina, Wilmington
20. How did some animals evolve to be strictly nocturnal?
Sunday Ekesi, entomologist, International Center of Insect Physiology and Ecology
21. Why do we sleep?
Katalin Kariko, biochemist, University of Pennsylvania
22. Which other animals dream, and how similar are their dreams to ours?
Benjamin Scott, neuroscientist, Boston University
23. Why do animals that fly live longer?
Elinor Karlsson, vertebrate geneticist, UMass Chan Medical School and Broad Institute
24. Can the human aging process be safely reversed?
Dr. Eric Topol, physician-scientist, Scripps Research Translational Institute
25. Can we make the wildlife trade sustainable?
Jérôme Gippet, ecologist, University of Fribourg, Switzerland
26. Will climate change increase or reduce the ocean’s biological productivity?
Daniel Sigman, geoscientist, Princeton University
27. To what extent are the forests of North America a human-created landscape?
Cathy Whitlock, earth scientist, Montana State University
28. How does the three-dimensional structure of a forest canopy create its own climate?
Nalini Nadkarni, biologist, University of Utah
29. How does the spotted lanternfly find its preferred host, the tree of heaven?
Kelli Hoover, entomologist, Penn State University
30. Because of erosion, almost no fossils from ancient alpine environments have survived. What unknown creatures dwelled there?
Kenneth Lacovara, paleontologist, Rowan University
31. Why did the first members of our lineage start walking on two legs?
William Harcourt-Smith, paleoanthropologist, American Museum of Natural History
32. Did Neanderthals and early Homo sapiens share their lives and cultures as well as their genes?
Rebecca Wragg Sykes, archaeologist, University of Cambridge and University of Liverpool, England
33. What was life like for the Denisovans?
Jennifer Raff, anthropologist, University of Kansas
34. Why did modern humans, and not other hominins, become so numerous and develop such complex culture and technology?
Svante Pääbo, geneticist, Max Planck Institute for Evolutionary Anthropology
35. Most animals, including humans, find social encounters more attractive than other activities. How does the social brain work?
Catherine Dulac, neuroscientist, Howard Hughes Medical Institute, Harvard University
36. How do ants work together to produce the collective behavior of colonies?
Deborah Gordon, biologist, Stanford University
37. Why are humans the only species with a chin?
Daniel Lieberman, evolutionary biologist, Harvard University
38. When in our evolutionary history did the human pattern of slow childhood development emerge?
Carrie Mongle, paleoanthropologist, Stony Brook University
39. How did the building blocks of life, like proteins and nucleic acid, first organize into a living cell?
Steve Brusatte, paleontologist, University of Edinburgh
40. What is dark matter?
Ina Sarcevic, astrophysicist, University of Arizona
41. How can we understand the nature of dark matter without detecting it on Earth?
Gurtina Besla, astrophysicist, University of Arizona
42. Is dark energy — which is causing the expansion of our universe to accelerate — a constant? Or is it changing over time?
David Kaiser, physicist and historian of science, Massachusetts Institute of Technology
43. Are all atoms of the same element and isotope identical? Or is every atom in the universe unique?
Mark Raizen, physicist, University of Texas, Austin
44. Why are neutrinos non-trinary?
Chanda Prescod-Weinstein, physicist, University of New Hampshire
45. How do we unify small-scale quantum physics with large-scale gravitational physics?
Jim Peebles, physicist, Princeton University
46. Could we probe the interplay between quantum and gravitational physics in a laboratory setting?
Jun Ye, physicist, JILA, University of Colorado, Boulder
47. What are the practical consequences of long-distance quantum entanglements between particles?
George Schatz, chemist, Northwestern University
48. Do organisms use quantum effects, such as entanglement and superposition?
Christof Koch, neuroscientist, Allen Institute for Brain Science
49. How did the earliest genetic materials replicate before there were enzymes?
Jack Szostak, chemist, Center for the Origins of Life, University of Chicago
50. How did viruses originate?
Edward C. Holmes, virologist, University of Sydney
51. When does a cell become destined to develop into cancer?
Dr. Kimryn Rathmell, physician-scientist, The Ohio State University Comprehensive Cancer Center, The Arthur G. James Cancer Hospital
52. Can we catalog all the microbes that make us sick — including some that might be triggers of chronic disease?
Dr. Pardis Sabeti, computational geneticist, Harvard University
53. Can we decode the language of microbiomes?
Jennifer Doudna, biochemist, University of California, Berkeley
54. Will we ever decipher Linear A, Cypro-Minoan and other important ancient scripts?
Silvia Ferrara, philologist, University of Bologna, Italy
55. Can we figure out which approaches are best for preserving biodiversity in different ecosystems?
Erika Zavaleta, ecologist, University of California, Santa Cruz
56. Can we learn to predict how a work of art will look in the future based on the microscopic changes occurring inside it today?
Francesca Casadio, cultural heritage scientist, Getty Conservation Institute
57. When we invent new materials, can we learn also to predict how they age, so we can preserve the things we make with them?
Andrew Davis, chemist, Library of Congress
58. How do humans create genuinely new concepts — not just random variations or recombinations of old ideas?
Alison Gopnik, cognitive scientist, University of California, Berkeley
59. How do the smallest low-mass dwarf galaxies create multiple generations of stars?
Deidre Hunter, astronomer
60. Are deep mantle plumes the cause of important volcanic activity on Earth?
Gillian R. Foulger, geophysicist, Durham University, England
61. What would be the global impact of a supervolcanic eruption in modern times?
Wendy Stovall, volcanologist, U.S. Geological Survey Volcano Hazards Program
62. What underlying physics determines when and how earthquakes start and stop?
Vashan Wright, geophysicist, University of California, San Diego
63. Can we identify any visible sign that a major earthquake is coming?
John Vidale, geophysicist, University of Southern California
64. Venus and Earth are of similar size and are similarly close to the sun. Why are they so different?
Fran Bagenal, senior research scientist, University of Colorado, Boulder
65. Can unlocking the mysteries of our sun reveal how stars create worlds?
Nour E. Rawafi, astrophysicist, Johns Hopkins Applied Physics Laboratory
66. How many stars host planets like the Earth?
Heather Knutson, planetary scientist, California Institute of Technology
67. Why has evolution given human females a relatively narrow “Goldilocks zone” for successful reproduction?
Binyam Mogessie, reproductive biologist, Yale University
68. Where do endometriosis lesions come from, and why do only some women and girls develop them?
Linda Griffith, biological engineer, Center for Gynepathology Research, Massachusetts Institute of Technology
69. How do children learn so much from so little?
Joshua Tenenbaum, computational cognitive neuroscientist, Massachusetts Institute of Technology
70. Blue whales are the biggest animals ever to exist on Earth. Where are their babies born?
Helen Scales, marine biologist
71. Can we learn how to locate the exact breeding sites of sand flies, in order to control the diseases they cause?
Daniel Masiga, biologist, International Center of Insect Physiology and Ecology
72. What biological mechanisms cause some hosts to be superspreaders of ticks and the diseases they carry?
Abel S. Biguezoton, health ecologist, International Center of Insect Physiology and Ecology
73. Can we build protein nanomachines that patrol our bodies to repair cellular damage?
David Baker, biochemist, University of Washington
74. Most cancers are not genetic, so why do they occur?
Dr. Mehra Golshan, cancer surgeon, Yale School of Medicine
75. Why does the immune system in some people, and not others, control cancers and viruses?
Dr. Sharon Lewin, infectious diseases physician, the Peter Doherty Institute for Infection and Immunity, University of Melbourne, Australia
76. Will we learn how to use stem cells to grow new, healthy organs that can replace old or diseased ones?
Paul Knoepfler, cell biologist, University of California, Davis
77. Is there a way to predict how humans will respond to newly developed drugs without having to perform clinical trials?
Dr. Don Ingber, biologist and engineer, Wyss Institute for Biologically Inspired Engineering, Harvard University
78. Can we create virtual versions of human tissues and organs that truly mimic the ones in our bodies?
Robert Langer, biotechnologist and chemical engineer, Massachusetts Institute of Technology
79. What features of a virus’s genetic code might help predict whether it can infect humans, spread widely and cause severe disease?
Dr. Charles Chiu, microbiologist and infectious diseases physician, University of California, San Francisco
80. Why do the viruses that cause colds and flu spread so much more easily in winter?
Linsey Marr, environmental engineer, Virginia Tech
81. Chemical reactions have had a speed limit, described more than a century ago. Can we learn to surpass it?
Paul Dauenhauer, chemical engineer, University of Minnesota
82. Will we ever understand consciousness in a way that could apply to nonliving entities?
Edward Wasserman, experimental psychologist, University of Iowa
83. How can we learn to recognize — and communicate with — unconventional intelligences in cells, tissues and other unfamiliar substrates?
Michael Levin, developmental and synthetic biologist, Tufts University
84. Can we learn what emotions animals are experiencing?
Tom Smulders, evolutionary neuroscientist, Newcastle University, England
85. How can we give robots a great sense of touch?
Katherine J. Kuchenbecker, roboticist, Max Planck Institute for Intelligent Systems
86. How much does human taste — as opposed to other factors like food texture and smell — guide food selection and overeating?
Nirupa Chaudhari, physiologist, University of Miami Miller School of Medicine
87. When did hominids first begin to ferment foods, and what role did that invention play in human evolution?
Rob Dunn, biologist, North Carolina State University
88. Who were the Sea Peoples of the Eastern Mediterranean and what was their role in the collapse of the late Bronze Age?
Eric H. Cline, archaeologist, George Washington University
89. Did Nefertiti ever rule Ancient Egypt on her own as a sole pharaoh?
Alejandro Jiménez-Serrano, Egyptologist, University of Jaen, Spain
90. How did the ancient Egyptians build the Great Pyramid?
Mark Lehner, archaeologist, Ancient Egypt Research Associates
91. What will be the total financial cost of climate change?
Chris Gloninger, climate scientist, Woods Hole Group
92. How sensitive are the world’s ice sheets to global warming, and what will this mean for global sea levels?
Sarah Aarons, geochemist, Columbia University
93. Can environmental sustainability be achieved under capitalism?
Luis Zambrano, biologist, National Autonomous University of Mexico
94. Is humanity doomed by our nature to inequality and war?
Sarah Parcak, anthropologist, University of Alabama at Birmingham
95. Can humans figure out how to survive the space radiation environment and settle off Earth?
Lindy Elkins-Tanton, planetary scientist, UC Berkeley Space Sciences Laboratory
96. How will the universe end?
Michael Turner, cosmologist, University of California, Los Angeles, and University of Chicago
97. Why is there any matter at all in the universe?
Aaron Roodman, astrophysicist, Stanford University
98. What determines the laws of physics as they exist in our universe?
Katie Mack, astrophysicist, Perimeter Institute for Theoretical Physics
99. Are we alone in the universe?
Robert Hazen, staff scientist, Carnegie Institution for Science
100. Can we ever know everything about the universe — or must some of its mysteries always remain beyond our reach?
rk K. R.Times) Callaway, Stella Raine Chu, Carolyn Y. Johnson, Carl Zimmer, Katrina Miller, Amber Williams, Alan Burdick and Alexandra Sifferlin contributed reporting. ( With courtesy from The new York Times)