Phenomena lacking clear scientific explanation

[edit] Cosmology and High energy physics

Accelerating universe and the Cosmological constant

Why doesn't the zero-point energy of the vacuum cause a large cosmological constant? What cancels it out? Is a non-total cancellation of the cosmological constant responsible for the observed accelerated expansion (deSitter phase) of the Universe? If it is, why is the energy density of the cosmological constant of the same magnitude as the density of matter at present when the two evolve quite differently over time; could it be simply that we are observing at exactly the right time? Or is the nature of the dark energy driving this acceleration different?

Baryon asymmetry

Why is there far more matter than antimatter in the universe?

Dark matter

What is dark matter?^[1] Is it related to supersymmetry? Do the phenomena attributed to dark matter point not to some form of matter but actually to an extension of gravity?

Electroweak symmetry breaking

What is the mechanism responsible for breaking the electroweak gauge symmetry, giving mass to the W and Z bosons? Is it the simple Higgs mechanism of the Standard Model?^[2] or does nature make use of strong dynamics in breaking electroweak symmetry, as proposed by Technicolor?

Entropy (arrow of time)

Why did the universe have such low entropy in the past, resulting in the distinction between past and future and the second law of thermodynamics?^[3]

Neutrino mass

What is the mechanism responsible for generating neutrino masses? Is the neutrino its own antiparticle?

Proton Spin Crisis

As initially measured by the European Muon Collaboration, the 3 main ("valence") quarks of the proton account for about 12% of its total spin. Can the gluons that bind the quarks together, as well as the "sea" quark pairs that are continually being created and annihilating, properly account for the rest of it?**

Quantum chromodynamics (QCD) in the non-perturbative regime

The equations of QCD remain unsolved at energy scales relevant for describing atomic nuclei, and only mainly numerical approaches seem to begin to give answers at this limit. How does QCD give rise to the physics of nuclei and nuclear constituents?

Strong CP problem and Axions

Why is the strong nuclear interaction invariant to parity and charge conjugation? Is the Peccei-Quinn theory (i.e. mechanism) the solution to this problem? What are the properties of the predicted axion?

[edit] Astronomy

Accretion disc jets

Why do the accretion discs surrounding certain astronomical objects, such as the nuclei of active galaxies, emit relativistic jets along their polar axes?

Corona heating problem

Why is the Sun's Corona (atmosphere layer) so much hotter than the Sun's surface?

Gamma ray bursts (short duration)

What is the nature of these extraordinarily energetic astronomical objects that last less than two seconds?^[4]

Hipparcos Anomaly

How far away are the Pleiades, exactly?**

Pioneer anomaly

What causes the apparent residual sunward acceleration of the Pioneer spacecraft?^[5][6] ****

Ultra-high-energy cosmic ray

Why is it that some cosmic rays appear to possess energies that are impossibly high (the so called Oh-My-God particle), given that there are no sufficiently energetic cosmic ray sources near the Earth? Why is it that (apparently) some cosmic rays emitted by distant sources have energies above the Greisen-Zatsepin-Kuzmin limit?^[7][8]

[edit] Condensed matter physics

Amorphous solids

What is the nature of the transition between a fluid or regular solid and a glassy phase? What are the physical processes giving rise to the general properties of glasses?

High-temperature superconductors

What is the responsible mechanism that causes certain materials to exhibit superconductivity at temperatures much higher than around 50 kelvins?^[9]

Sonoluminescence

What causes the emission of short bursts of light from imploding bubbles in a liquid when excited by sound?

Turbulence

Is it possible to make a theoretical model to describe the statistics of a turbulent flow (in particular, its internal structures)?^[10]

[edit] Theoretical problems

The following problems are either fundamental theoretical problems, or theoretical ideas which lack experimental evidence and are in search of one, or both, as most of them are.

Some of the following problems are strongly interrelated. For example, extra dimensions or supersymmetry may solve the Hierarchy problem. It is thought that most of these problems (not including the Island of stability problem) should be answered by a full theory of quantum gravity.

[edit] Quantum gravity and cosmology

Quantum gravity

How can gravity and general relativity be realized as a fully consistent quantum field theory? Is string theory (M-theory) the correct approach? More pressing, how much experimental information can be extracted about physics near Planck scale?

Black holes, Black hole information, Black hole radiation and structure

Do black holes really exist? Do they radiate, as expected on theoretical grounds? Does this radiation contain information about their inner structure, as suggested by Gauge-gravity duality, or not, as implied by Hawking's original calculation? If not, and black holes can evaporate away, what happens to the information stored in it? (Quantum mechanics does not allow information to be destroyed) Or does the radiation stop at some point leaving black hole remnants? Is there another way to probe their internal structure somehow, if such a structure even exists?

Extra dimensions

Does nature have more than four spacetime dimensions? If so, what is their size? Are dimensions a fundamental property of the universe or an emergent result of other physical laws?

Cosmic inflation

Is the theory of cosmic inflation correct, and if so, what are the details of this epoch? What is the hypothetical inflaton field giving rise to inflation? Is there a natural explanation for its peculiar proposed potential? If inflation happened at one point, is it self-sustaining through inflation of quantum-mechanical fluctuations, and thus ongoing in some impossibly distant place?

Multiple universes

Are there physical reasons to believe in other universes that are fundamentally non-observable? For instance: Are there quantum mechanical "alternate histories"? Are there "other" universes with physical laws resulting from alternate ways of breaking the apparent symmetries of physical forces at high energies, possibly incredibly far away due to cosmic inflation? Is the use of the anthropic principle to resolve global cosmological dilemmas justified? ***

[edit] High energy physics

Hierarchy problem

Why is gravity such a weak force? It becomes strong for particles only at the Planck scale, around 10¹⁹ GeV, much above the electroweak scale (100 GeV, the energy scale dominating physics at low energies). Why are these scales so different from each other? What prevents quantities at the electroweak scale, such as the Higgs boson mass, from getting quantum corrections of order of the Planck scale? Is the solution supersymmetry, extra dimensions or just anthropic fine-tuning?

Island of stability

What is the largest theoretically possible stable atom?

Magnetic monopoles

Do particles that carry "magnetic charge" exist?

Proton decay and Unification

How do we unify the three different quantum mechanical fundamental interactions of quantum field theory? As the lightest baryon, are protons absolutely stable? If current theoretical ideas are correct, quarks and leptons are ultimately unified and thus nothing in principle forbids proton decay. If so, then what is the proton's half-life?

Supersymmetry

Is spacetime supersymmetry realized in nature? If so, what is the mechanism of supersymmetry breaking? Does supersymmetry stabilize the electroweak scale, preventing high quantum corrections? Does the lightest supersymmetric particle make up the dark matter?

[edit] Other problems

Emergent phenomena

Is a complete understanding of particle physics sufficient to fully understand all physical phenomena, or are there emergent phenomena in physics whose existence cannot be definitively predicted from a complete understanding of the fundamental particles and forces that govern the universe? ***

Quantum mechanics in the correspondence limit

Is there a preferred interpretation of quantum mechanics? How does the quantum description of reality, which includes elements such as the superposition of states and wavefunction collapse, give rise to the reality we perceive? ***

Physical information

Are there physical phenomena, such as black holes or wave function collapse, which irrevocably destroy information about their prior states? **

Theory of everything

Is there a theory which explains the values of all fundamental physical constants? ^[11] Do "fundamental physical constants" vary over time? Is there a theory which explains why the gauge groups of the standard model are as they are, why observed space-time has 3+1 dimensions, and why all laws of physics are as they are? Are string theory and the anthropic principle correct directions? Are there any testable consequences of that? ***

[edit] Problems solved recently

Long duration gamma ray bursts (2003)

Long-duration bursts are associated with the deaths of massive stars in a specific kind of supernova-like event commonly referred to as a collapsar.

Solar neutrino problem (2002)

Solved by a new understanding of neutrino physics, requiring a modification of the Standard Model of particle physics — specifically, neutrino oscillation.

Age Crisis (1990s)

The estimated age of the universe was around 3 to 8 billion years younger than estimates of the ages of the oldest stars in our galaxy. Better estimates for the distances to the stars and the addition of dark energy into the cosmological model reconciled the age estimates.

Quasars (1980s)

The nature of quasars was not understood for decades. They are now accepted as a type of active galaxy where the enormous energy output results from matter falling into a massive black hole in the center of the galaxy.

Natural science

From Wikipedia, the free encyclopedia

• •

The Michelson–Morley experiment was used to disprove that light propagated through a luminiferous aether. This 19th century concept was then superseded by Albert Einstein's special theory of relativity.

In science, the term natural science refers to a rational approach to the study of the universe, which is understood as obeying rules or laws of natural origin. The term natural science is also used to distinguish those fields that use the scientific method to study nature from the social sciences, which use the scientific method to study human behavior and society, and from the formal sciences, such as mathematics and logic, which use a different methodology.

Contents [hide] 1 Overview 2 History 3 Disciplines of natural sciences 3.1 Astronomy 3.2 Biology 3.3 Chemistry 3.4 Earth science 3.5 Physics 3.6 Cross-disciplines 4 See also 5 External links

Overview

Natural sciences form the basis for the applied sciences. Together, the natural and applied sciences are distinguished from the social sciences on the one hand, and from the humanities, theology and the arts on the other. Mathematics, statistics and computer science are not considered natural sciences, but provide many tools and frameworks used within the natural sciences.

Alongside this traditional usage, the phrase natural sciences is also sometimes used more narrowly to refer to its everyday usage, that is, related to natural history. In this sense "natural sciences" may refer to the biological sciences and perhaps also the earth sciences, as distinguished from the physical sciences, including astronomy, physics, and chemistry.

Within the natural sciences, the term hard science is sometimes used to describe those sub-fields that rely on experimental, quantifiable data or the scientific method and focus on accuracy and objectivity. These usually include physics, chemistry and many of the sub-fields of biology. By contrast, soft science is often used to describe the scientific fields that are more reliant on qualitiative research, including the social sciences.

History

Prior to the 17th century, the objective study of nature was known as natural philosophy. Over the next two centuries, however, a philosophical interpretation of nature was gradually replaced by a scientific approach using inductive methodology. The works of Sir Francis Bacon popularized this approach, thereby helping to forge the scientific revolution.

By the 19th century the study of science had come into the purview of professionals and institutions, and in so doing it gradually acquired the more modern name of natural science. The term scientist was coined by William Whewell in an 1834 review of Mary Somerville's On the Connexion of the Sciences. However the word did not enter general use until nearly the end of the same century.

According to a famous 1923 textbook Thermodynamics – and the Free Energy of Chemical Substances by the American chemist Gilbert N. Lewis and the American physical chemist Merle Randall, the natural sciences contain three great branches:

Aside from the logical and mathematical sciences, there are three great branches of natural science which stand apart by reason of the variety of far reaching deductions drawn from a small number of primary postulates – they are the mechanics, electrodynamics, and thermodynamics.

Disciplines of natural sciences

Astronomy

Main article: Astronomy

Space missions have been used to image distant locations within the Solar System, such as this Apollo 11 view of Daedalus crater on the far side of the Moon.

This discipline is the science of celestial objects and phenomena that originate outside the Earth's atmosphere. It is concerned with the evolution, physics, chemistry, meteorology, and motion of celestial objects, as well as the formation and development of the universe. Astronomy includes the examination, study and modeling of stars, planets, comets, galaxies and the cosmos. Most of the information used by astronomers is gathered by remote observation, although some laboratory reproduction of celestial phenomenon has been performed (such as the molecular chemistry of the interstellar medium.)

While the origins of the study of celestial features and phenomenon can be traced back to antiquity, the scientific methodology of this field began to develop in the middle of the seventeenth century. A key factor was Galileo's introduction of the telescope to examine the night sky in more detail. The mathematical treatment of astronomy began with Newton's development of celestial mechanics and the laws of gravitation, although it was triggered by earlier work of astronomers such as Kepler. By the nineteenth century, astronomy had developed into a formal science with the introduction of instruments such as the spectroscope and photography, along with much improved telescopes and the creation of professional observatories.

A fragment of DNA, the chemical sequence that contains genetic instructions for the development and functioning of living organisms.

Biology

Main article: Biology

This field encompasses a set of disciplines that examines phenomena related to living organisms. The scale of study can range from sub-component biophysics up to complex ecologies. Biology is concerned with the characteristics, classification and behaviors of organisms, as well as how species were formed and their interactions with each other and the natural environment.

The biological fields of botany, zoology, and medicine date back to early periods of civilization, while microbiology was introduced in the 17th century with the invention of the microscope. However it was not until the 19th century that biology became a unified science; once scientists discovered commonalities between all living things it was decided they were best studied as a whole. Some key developments in the science of biology were the discovery of genetics; Darwin's theory of evolution through natural selection; the germ theory of disease and the application of the techniques of chemistry and physics at the level of the cell or organic molecule.

Modern Biology is divided into sub-disciplines by the type of organism and by the scale being studied. Molecular biology is the study of the fundamental chemistry of life, while cellular biology is the examination of the cell; the basic building block of all life. At a higher level, Physiology looks at the internal structure of organism, while ecology looks at how various organisms interrelate.

Chemistry

Main article: Chemistry

This structural formula for molecule caffeine shows a graphical representation of how the atoms are arranged.

Constituting the scientific study of matter at the atomic and molecular scale, chemistry deals primarily with collections of atoms, such as gases, molecules, crystals, and metals. The composition, statistical properties, transformations and reactions of these materials are studied. Chemistry also involves understanding the properties and interactions of individual atoms for use in larger-scale applications. Most chemical processes can be studied directly in a laboratory, using a series of (often well-tested) techniques for manipulating materials, as well as an understanding of the underlying processes. Chemistry is often called "the central science" because of its role in connecting the other natural sciences.

Early experiments in chemistry had their roots in the system of Alchemy, a set of beliefs combining mysticism with physical experiments. The science of chemistry began to develop with the work of Robert Boyle, the discoverer of gas, and Antoine Lavoisier, who developed the theory of the Conservation of mass. The discovery of the chemical elements and the concept of Atomic Theory began to systematize this science, and researchers developed a fundamental understanding of states of matter, ions, chemical bonds and chemical reactions. The success of this science led to a complementary chemical industry that now plays a significant role in the world economy.

Earth science

Main article: Earth science

This short section requires expansion.

Earth science (also known as geoscience, the geosciences or the Earth Sciences), is an all-embracing term for the sciences related to the planet Earth, including geology, geophysics, hydrology, meteorology, physical geography, oceanography, and soil science.

Physics

Main article: Physics

This free body diagram illustrates the different forces acting on a projectile.

Physics embodies the study of the fundamental constituents of the universe, the forces and interactions they exert on one another, and the results produced by these interactions. In general, the physics is regarded as the fundamental science as all other natural sciences utilize and obey the principles and laws set down by the field. Physics relies heavily on mathematics as the logical framework for formulation and quantification of principles.

The study of the principles of the universe has a long history and largely derives from direct observation and experimentation. The formulation of theories about the governing laws of the universe has been central to the study of physics from very early on, with philosophy gradually yielding to systematic, quantitative experimental testing and observation as the source of verification. Key historical developments in physics include Isaac Newton's theory of universal gravitation and classical mechanics, an understanding of electricity and it's relation to magnetism, Einstein's theories of special and general relativity, the development of thermodynamics, and the quantum mechanical model of atomic and subatomic physics.

The field of physics is extremely broad, and can include such diverse studies as quantum mechanics and theoretical physics to applied physics and optics. Modern physics is becoming increasingly specialized, where researchers tend to focus on a particular area rather than being "universalists" like Albert Einstein and Lev Landau, who worked in multiple areas.

Cross-disciplines

The distinctions between the natural science disciplines is not always sharp, and they share a number of cross-discipline fields. Physics plays a significant role in the other natural sciences, as represented by astrophysics, geophysics, physical chemistry and biophysics. Likewise chemistry is represented by such fields as biochemistry and astrochemistry.

A particular example of a scientific discipline that draws upon multiple natural sciences is Environmental science. This field studies the interactions of physical, chemical and biological components of the environment, with a particular regard to the effect of human activities and the impact on biodiversity and sustainability. This science also draws upon expertise from other fields such as economics, law and social sciences.