Category
Physics
Explore the 26 entries currently assigned to this category. These counts describe this curated catalogue, not the size or rate of change of the field itself.
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Not a fact anymore
Neutrinos are massless.
What we know now
Neutrinos have a tiny but nonzero mass. They come in different types, called flavors, and can change from one flavor into another while traveling. That oscillation can occur only if the underlying neutrino states do not all have the same mass.
- Status
- Overturned
- Category
- Physics
- Accepted for
- ≈48 years
- Changed approximately
- 1998–2001
Not a fact anymore
Superconductivity can occur only within a few degrees of absolute zero.
What we know now
Many conventional superconductors require very low temperatures, but copper-oxide and other unconventional materials remain superconducting at far higher temperatures, including above the boiling point of liquid nitrogen.
- Status
- Overturned
- Category
- Physics
- Accepted for
- ≈75 years
- Changed approximately
- 1986–1987
Not a fact anymore
Protons and neutrons are fundamental particles with no internal structure.
What we know now
Protons and neutrons are not fundamental particles. They are composite particles built from quarks and gluons, whose interactions are governed by the strong nuclear force. Much of a proton or neutron's mass comes from the energy of this internal activity rather than simply from the masses of its quarks.
- Status
- Overturned
- Category
- Physics
- Accepted for
- ≈33 years
- Changed approximately
- 1960s–1970s
Not a fact anymore
The laws of physics always treat a process and its mirror image identically.
What we know now
The weak interaction—the force involved in radioactive beta decay—does not always treat a process and its mirror image the same way. In weak decays, nature can distinguish left from right. Electromagnetic and strong interactions still preserve this mirror symmetry.
- Status
- Overturned
- Category
- Physics
- Accepted for
- ≈32 years
- Changed approximately
- 1956–1957
Not a fact anymore
Radioactivity is an exclusively natural property and cannot be created artificially.
What we know now
Nuclear reactions can produce unstable isotopes that remain radioactive after bombardment stops. Artificial radionuclides are now made for research, medicine, industry, and energy applications.
- Status
- Overturned
- Category
- Physics
- Accepted for
- ≈38 years
- Changed approximately
- 1934–1935
Not a fact anymore
Cosmic rays are a form of electromagnetic radiation.
What we know now
Most cosmic rays are high-energy atomic nuclei and other charged particles. They produce secondary particle showers when they strike Earth's atmosphere.
- Status
- Reclassified
- Category
- Physics
- Accepted for
- ≈17 years
- Changed approximately
- 1920s–1930s
Not a fact anymore
The atomic nucleus is made of protons and nuclear electrons.
What we know now
Ordinary atomic nuclei are composed of protons and neutrons. Electrons occupy quantum states outside the nucleus, although beta decay can create and emit electrons during a nuclear transformation.
- Status
- Superseded
- Category
- Physics
- Accepted for
- ≈17 years
- Changed approximately
- 1932–1930s
Not a fact anymore
Electrons travel around an atomic nucleus in definite circular paths like planets orbiting the Sun.
What we know now
Electrons in atoms do not travel around the nucleus on fixed circular tracks. Quantum mechanics describes them with orbitals: states that tell us the probabilities of finding an electron in different regions and the energies it can have.
- Status
- Superseded
- Category
- Physics
- Accepted for
- ≈17 years
- Changed approximately
- 1920s–1930s
Not a fact anymore
Electrons are ordinary particles and cannot behave as waves.
What we know now
Electrons display both particle-like detections and wave-like interference and diffraction. Quantum mechanics describes them with quantum states rather than as classical particles or classical waves.
- Status
- Overturned
- Category
- Physics
- Accepted for
- ≈29 years
- Changed approximately
- 1924–1927
Not a fact anymore
Changes in gravity are transmitted instantaneously across any distance.
What we know now
Changes in gravity do not act everywhere at once. In general relativity, gravity is part of the structure of spacetime, and changes in the gravitational field propagate at the speed of light. Rapidly accelerating masses can produce traveling disturbances called gravitational waves.
- Status
- Superseded
- Category
- Physics
- Accepted for
- ≈265 years
- Changed approximately
- 1915 onward
Not a fact anymore
Light is purely a continuous wave and cannot behave as discrete particles.
What we know now
Light displays both wave-like and particle-like behavior. Electromagnetic radiation is quantized into photons while also producing interference, diffraction, and other wave phenomena.
- Status
- Superseded
- Category
- Physics
- Accepted for
- ≈90 years
- Changed approximately
- 1905–1920s
Not a fact anymore
Light waves require a material medium called the luminiferous ether to travel through space.
What we know now
Light can travel through a vacuum without a material carrier. Its behavior is described by electromagnetism, quantum theory, and relativity.
- Status
- Superseded
- Category
- Physics
- Accepted for
- ≈55 years
- Changed approximately
- 1880s–1910s
Not a fact anymore
Mass and energy are entirely separate conserved quantities.
What we know now
Mass and energy are related rather than completely separate. A body's rest mass corresponds to energy through E = mc², and energy stored inside a system contributes to that system's mass. Nuclear reactions make this connection large enough to measure easily.
- Status
- Superseded
- Category
- Physics
- Accepted for
- ≈205 years
- Changed approximately
- 1905 onward
Not a fact anymore
Time passes identically everywhere, and all observers can agree on one universal present.
What we know now
Elapsed time depends on relative motion and gravitational conditions. Observers can disagree about the duration and simultaneity of events while each obtains internally consistent measurements.
- Status
- Superseded
- Category
- Physics
- Accepted for
- ≈255 years
- Changed approximately
- 1905–1915
Not a fact anymore
A chemical element can never transform into another element.
What we know now
Elements can transform through radioactive decay and nuclear reactions. Changing the number of protons in a nucleus changes one element into another.
- Status
- Overturned
- Category
- Physics
- Accepted for
- ≈152 years
- Changed approximately
- 1902–1930s
Not a fact anymore
Radioactivity is a chemical or molecular property that should change when a substance is heated, cooled, dissolved, or combined.
What we know now
Radioactivity originates in unstable atomic nuclei. Ordinary changes in temperature, pressure, or chemical bonding generally have little or no effect on nuclear decay rates.
- Status
- Overturned
- Category
- Physics
- Accepted for
- ≈6 years
- Changed approximately
- 1902–1908
Not a fact anymore
Atoms are the smallest possible pieces of matter and have no internal structure.
What we know now
Atoms contain electrons and a nucleus made of protons and usually neutrons. Protons and neutrons are themselves made of quarks, while electrons are currently treated as elementary particles.
- Status
- Overturned
- Category
- Physics
- Accepted for
- ≈82 years
- Changed approximately
- 1890s–1930s
Not a fact anymore
Electricity and magnetism are fundamentally separate forces.
What we know now
Electric and magnetic fields are coupled aspects of one electromagnetic interaction. Changing electric fields generate magnetic fields, changing magnetic fields generate electric fields, and light is an electromagnetic wave.
- Status
- Superseded
- Category
- Physics
- Accepted for
- ≈215 years
- Changed approximately
- 1820–1860s
Not a fact anymore
Light travels faster in optically denser transparent media such as water than in air.
What we know now
Light travels more slowly through ordinary transparent materials such as water and glass than through vacuum or air. Their refractive index is related to that reduced propagation speed.
- Status
- Overturned
- Category
- Physics
- Accepted for
- ≈146 years
- Changed approximately
- 1850
Not a fact anymore
Heat is a weightless material fluid called caloric that flows from hotter bodies into colder ones.
What we know now
Heat is energy transferred because of a temperature difference. Temperature is related to the microscopic motion and internal energy of matter, not to the amount of a conserved heat-fluid stored inside it.
- Status
- Superseded
- Category
- Physics
- Accepted for
- ≈75 years
- Changed approximately
- 1790s–1850s
Not a fact anymore
Light travels instantaneously.
What we know now
Light propagates through vacuum at a finite speed of exactly 299,792,458 metres per second. This speed is a fundamental constant and the maximum speed for causal influence in relativity.
- Status
- Overturned
- Category
- Physics
- Accepted for
- ≈39 years
- Changed approximately
- 1676–19th century
Not a fact anymore
White light is a simple, uniform kind of light, while prisms and other transparent bodies create or modify the colors seen in a spectrum.
What we know now
White light can contain a mixture of wavelengths. A prism separates different wavelengths because the refractive index depends on wavelength; it does not manufacture the spectral colors from otherwise colorless light.
- Status
- Overturned
- Category
- Physics
- Accepted for
- Not quantified
- Changed approximately
- 1666–1672
Not a fact anymore
Air and other gases are weightless because they naturally rise or disappear.
What we know now
Gases are matter with mass. Air has weight, exerts pressure, and can be compressed, transferred, and weighed.
- Status
- Overturned
- Category
- Physics
- Accepted for
- Not quantified
- Changed approximately
- 17th–18th centuries
Not a fact anymore
Heavier objects naturally fall faster than lighter objects in direct proportion to their weight.
What we know now
When air resistance is negligible, objects near the same location fall with essentially the same acceleration regardless of their mass.
- Status
- Overturned
- Category
- Physics
- Accepted for
- ≈1,988 years
- Changed approximately
- 16th–17th centuries
Not a fact anymore
A thrown projectile continues moving after release because the surrounding air rushes around it and supplies the continuing external push.
What we know now
A projectile does not require a continuing forward-moving agent. Inertia carries it forward while gravity, aerodynamic drag, and other forces change its motion.
- Status
- Superseded
- Category
- Physics
- Accepted for
- Not quantified
- Changed approximately
- 14th-century impetus mechanics
Not a fact anymore
Vision occurs because visual rays or a visual power travels outward from the eyes to the object being seen.
What we know now
Light from external sources is emitted or reflected by objects, enters the eye, is focused onto the retina, and is converted by photoreceptors into neural signals processed by the visual system.
- Status
- Superseded
- Category
- Physics
- Accepted for
- Not quantified
- Changed approximately
- 13th-century European optics after the Latin reception of Ibn al-Haytham
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