Orders of magnitude (time)
Less than one second
Table:
Unit (s)

Multiple

Symbol

Definition

Comparative examples & common units

10−44

1 Planck time

tP

Presumed to be the shortest theoretically measurable time interval (but not necessarily the shortest increment of time - see quantum gravity)

10−20 ys: One Planck time tP =

ℏ
G

/

c

5

{\displaystyle {\sqrt {\hbar G/c^{5}}}}

≈ 5.39×10−44 s[1] is the briefest physically meaningful span of time. It is the unit of time in the natural units system known as Planck units.

10−24

1 yoctosecond

ys[2]

Yoctosecond, (yocto- + second), is one septillionth of a second

0.3 ys: mean lifetime of W and Z bosons

23 ys: Lifespan isotope 7 of hydrogen (Hydrogen-7)
156 ys: mean lifetime of a Higgs Boson

10−21

1 zeptosecond

zs

Zeptosecond, (zepto- + second), is one sextillionth of one second

2 zs: representative cycle time of gamma ray radiation released in the decay of a radioactive atomic nucleus (here as 2 MeV per emitted photon)
4 zs: cycle time of the zitterbewegung of an electron (

ω
=
2

m

e

c

2

/

ℏ

{\displaystyle \omega =2m_{e}c^{2}/\hbar }

)

10−18

1 attosecond

as

One quintillionth of one second

12 attoseconds: best timing control of laser pulses.[3]

10−15

1 femtosecond

fs

One quadrillionth of one second

1 fs: Cycle time for 300 nanometre light; ultraviolet light; light travels 0.3 micrometres (µm).
140 fs: Electrons have localized onto individual bromine atoms 6Å apart after laser dissociation of Br2.[4]
290 fs: Lifetime of a tauon

10−12

1 picosecond

ps

One trillionth of one second

1 ps: mean lifetime of a bottom quark; light travels 0.3 millimeters (mm)
1 ps: typical lifetime of a transition state
4 ps: Time to execute one machine cycle by an IBM Silicon-Germanium transistor

10−9

1 nanosecond

ns

One billionth of one second

1 ns: Time to execute one machine cycle by a 1 GHz microprocessor
1 ns: Light travels 30 centimetres (12 in)

10−6

1 microsecond

µs

One millionth of one second

1 µs: Time to execute one machine cycle by an Intel 80186 microprocessor
2.2 µs: Lifetime of a muon
4–16 µs: Time to execute one machine cycle by a 1960s minicomputer

10−3

1 millisecond

ms

One thousandth of one second

1 ms: time for a neuron in human brain to fire one impulse and return to rest[5]
4–8 ms: typical seek time for a computer hard disk

10−2

1

centisecond

cs

One hundredth of one second

1–2 cs (=0.01–0.02 s): Human reflex response to visual stimuli

1.6667 cs period of a frame at a frame rate of 60 Hz.

2 cs: cycle time for European 50 Hz AC electricity

10−1

1

decisecond

ds

One tenth of a second

1–4 ds (=0.1–0.4 s): Blink of an eye[6]

With reference to the provided table and the supporting text listed below.

Give the answer to the question: The smallest division of time is measured in what units ? Respond with the correct answer (omit explanations) in JSON format as {"answer": "YOUR ANSWER"}. Use only the information given.

The second ( symbol : s , abbreviation : sec ) is the base unit of time in the International System of Units ( SI ) , commonly understood and historically defined as ​1⁄86400 of a day - this factor derived from the division of the day first into 24 hours , then to 60 minutes and finally to 60 seconds each . Analog clocks and watches often have sixty tick marks on their faces , representing seconds ( and minutes ) , and a second hand to mark the passage of time in seconds . Digital clocks and watches often have a two-digit seconds counter . The second is also part of several other units of measurement like meters per second for velocity , meters per second per second for acceleration , and cycles per second for frequency . Although the historical definition of the unit was based on this division of the Earth 's rotation cycle , the formal definition in the International System of Units ( SI ) is a much steadier timekeeper : it is defined by taking the fixed numerical value of the caesium frequency ∆νCs , the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom , to be 9192631770 when expressed in the unit Hz , which is equal to s−1 . Because the Earth 's rotation varies and is also slowing ever so slightly , a leap second is periodically added to clock time [ nb 1 ] to keep clocks in sync with Earth 's rotation . Multiples of seconds are usually counted in hours and minutes . Fractions of a second are usually counted in tenths or hundredths . In scientific work , small fractions of a second are counted in milliseconds ( thousandths ) , microseconds ( millionths ) , nanoseconds ( billionths ) , and sometimes smaller units of a second . An everyday experience with small fractions of a second is a 1-gigahertz microprocessor which has a cycle time of 1 nanosecond . Camera shutter speeds are often expressed in fractions of a second , such as ​1⁄30 second or ​1⁄1000 second . Sexagesimal divisions of the day from a calendar based on astronomical observation have existed since the third millennium BC , though they were not seconds as we know them today [ citation needed ] .
In quantum mechanics , the Planck time ( tP ) is the unit of time in the system of natural units known as Planck units . A Planck time unit is the time required for light to travel a distance of 1 Planck length in a vacuum , which is a time interval of approximately 5.39 × 10−44 s. The unit is named after Max Planck , who was the first to propose it . The Planck time is defined as :
Quantum gravity ( QG ) is a field of theoretical physics that seeks to describe gravity according to the principles of quantum mechanics , and where quantum effects can not be ignored , such as near compact astrophysical objects where the effects of gravity are strong . The current understanding of gravity is based on Albert Einstein 's general theory of relativity , which is formulated within the framework of classical physics . On the other hand , the other three fundamental forces of physics are described within the framework of quantum mechanics and quantum field theory , radically different formalisms for describing physical phenomena . It is sometimes argued that a quantum mechanical description of gravity is necessary on the grounds that one can not consistently couple a classical system to a quantum one . :11-12 While a quantum theory of gravity may be needed to reconcile general relativity with the principles of quantum mechanics , difficulties arise when applying the usual prescriptions of quantum field theory to the force of gravity via hypothesised graviton bosons . The problem is that the theory one gets in this way is not renormalizable - it predicts infinite values for some observable properties , such as the mass of particles , and therefore can not be used to make meaningful physical predictions of those properties . As a result , theorists have taken up more radical approaches to the problem of quantum gravity , the most popular approaches being string theory and loop quantum gravity . Although some quantum gravity theories , such as string theory , try to unify gravity with the other fundamental forces , others , such as loop quantum gravity , make no such attempt ; instead , they make an effort to quantize the gravitational field while it is kept separate from the other forces . Strictly speaking , the aim of quantum gravity is only to describe the quantum behavior of the gravitational field and should not be confused with the objective of unifying all fundamental interactions into a single mathematical framework . A quantum field theory of gravity that is unified with a grand unified theory is sometimes referred to as a theory of everything ( TOE ) . While any substantial improvement into the present understanding of gravity would aid further work towards unification , the study of quantum gravity is a field in its own right with various branches having different approaches to unification . One of the difficulties of formulating a quantum gravity theory is that quantum gravitational effects only appear at length scales near the Planck scale , around 10−35 meters , a scale far smaller , and equivalently far larger in energy , than those currently accessible by high energy particle accelerators .
In physics , natural units are physical units of measurement based only on universal physical constants . For example , the elementary charge e is a natural unit of electric charge , and the speed of light c is a natural unit of speed . A purely natural system of units has all of its units defined in this way , and usually such that the numerical values of the selected physical constants in terms of these units are exactly 1 . These constants are then typically omitted from mathematical expressions of physical laws , and while this has the apparent advantage of simplicity , it may entail a loss of clarity due to the loss of information for dimensional analysis . It precludes the interpretation of an expression in terms of fundamental physical constants , such as e and c , unless it is known which units ( in dimensionful units ) the expression is supposed to have . In this case , the reinsertion of the correct powers of e , c , etc. , can be uniquely determined .
In particle physics and physical cosmology , Planck units are a set of units of measurement defined exclusively in terms of five universal physical constants , in such a manner that these five physical constants take on the numerical value of 1 when expressed in terms of these units . Originally proposed in 1899 by German physicist Max Planck , these units are also known as natural units because the origin of their definition comes only from properties of nature and not from any human construct . Planck units are only one system of several systems of natural units , but Planck units are not based on properties of any prototype object or particle ( that would be arbitrarily chosen ) , but rather on only the properties of free space . Planck units have significance for theoretical physics since they simplify several recurring algebraic expressions of physical law by nondimensionalization . They are relevant in research on unified theories such as quantum gravity . The term Planck scale refers to the magnitudes of space , time , energy and other units , below which ( or beyond which ) the predictions of the Standard Model , quantum field theory and general relativity are no longer reconcilable , and quantum effects of gravity are expected to dominate . This region may be characterized by energies around 1.22×1019 GeV ( the Planck energy ) , time intervals around 5.39×10−44 s ( the Planck time ) and lengths around 1.62×10−35 m ( the Planck length ) . At the Planck scale , current models are not expected to be a useful guide to the cosmos , and physicists have no scientific model to suggest how the physical universe behaves . The best known example is represented by the conditions in the first 10−43 seconds of our universe after the Big Bang , approximately 13.8 billion years ago . There are two versions of Planck units , Lorentz-Heaviside version and Gaussian version . The five universal constants that Planck units , by definition , normalize to 1 are :
Yocto ( symbol y ) is a unit prefix in the metric system denoting a factor of 10−24 or 0.000000000000000000000001 . It was adopted in 1991 by the General Conference on Weights and Measures . It comes from the Latin/Greek octo ( οκτώ ) , meaning eight , because it is equal to 1000−8 . Yocto- is the smallest official SI prefix . It can be used to state a subatomic particle 's mass , for example :
This article lists and discusses the usage and derivation of names of large numbers , together with their possible extensions . The following table lists those names of large numbers that are found in many English dictionaries and thus have a claim to being real words . The Traditional British values shown are unused in American English and are obsolete in British English , but their other-language variants are dominant in many non-English-speaking areas , including continental Europe and Spanish-speaking countries in Latin America ; see Long and short scales . Indian English does not use millions , but has its own system of large numbers including lakhs and crores . English also has many words , such as zillion , used informally to mean large but unspecified amounts ; see indefinite and fictitious numbers .
A quantity is subject to exponential decay if it decreases at a rate proportional to its current value . Symbolically , this process can be expressed by the following differential equation , where N is the quantity and λ ( lambda ) is a positive rate called the exponential decay constant :
The W and Z bosons are together known as the weak or more generally as the intermediate vector bosons . These elementary particles mediate the weak interaction ; the respective symbols are W+ , W− , and Z0 . The W± bosons have either a positive or negative electric charge of 1 elementary charge and are each other 's antiparticles . The Z0 boson is electrically neutral and is its own antiparticle . The three particles have a spin of 1 . The W± bosons have a magnetic moment , but the Z0 has none . All three of these particles are very short-lived , with a half-life of about 3×10−25 s. Their experimental discovery involved what is now known as the Standard Model of particle physics . The W bosons are named after the weak force . The physicist Steven Weinberg named the additional particle the Z particle , and later gave the explanation that it was the last additional particle needed by the model . The W bosons had already been named , and the Z bosons were named for having zero electric charge . The two W bosons are verified mediators of neutrino absorption and emission . During these processes , the W± boson charge induces electron or positron emission or absorption , thus causing nuclear transmutation .
Hydrogen ( 1H ) has three naturally occurring isotopes , sometimes denoted 1H , 2H , and 3H . The first two of these are stable , while 3H has a half-life of 12.32 years . There are also heavier isotopes , which are all synthetic and have a half-life less than one zeptosecond ( 10−21 second ) . Of these , 5H is the most stable , and 7H is the least . Hydrogen is the only element whose isotopes have different names in common use today : the 2H ( or hydrogen-2 ) isotope is deuterium and the 3H ( or hydrogen-3 ) isotope is tritium . The symbols D and T are sometimes used for deuterium and tritium . The IUPAC accepts the D and T symbols , but recommends instead using standard isotopic symbols ( 2H and 3H ) to avoid confusion in the alphabetic sorting of chemical formulas . The ordinary isotope of hydrogen , with no neutrons , is sometimes called protium . ( During the early study of radioactivity , some other heavy radioactive isotopes were given names , but such names are rarely used today . )
The Higgs boson is an elementary particle in the Standard Model of particle physics , produced by the quantum excitation of the Higgs field , one of the fields in particle physics theory . It is named after physicist Peter Higgs , who in 1964 , along with five other scientists , proposed the Higgs mechanism to explain why particles have mass . This mechanism implies the existence of the Higgs boson . The boson 's existence was confirmed in 2012 by the ATLAS and CMS collaborations based on collisions in the LHC at CERN . On December 10 , 2013 , two of the physicists , Peter Higgs and François Englert , were awarded the Nobel Prize in Physics for their theoretical predictions . Although Higgs 's name has come to be associated with this theory ( the Higgs mechanism ) , several researchers between about 1960 and 1972 independently developed different parts of it . In mainstream media the Higgs boson has often been called the God particle , from a 1993 book on the topic , although the nickname is strongly disliked by many physicists , including Higgs himself , who regard it as sensationalism .
Zepto ( unit symbol z ) is a unit prefix in the metric system denoting a factor of 10−21 or 0.000000000000000000001 . Adopted in 1991 , it comes from the Latin septem , meaning seven , since it is equal to 1000−7 . Examples of its use :
This article lists and discusses the usage and derivation of names of large numbers , together with their possible extensions . The following table lists those names of large numbers that are found in many English dictionaries and thus have a claim to being real words . The Traditional British values shown are unused in American English and are obsolete in British English , but their other-language variants are dominant in many non-English-speaking areas , including continental Europe and Spanish-speaking countries in Latin America ; see Long and short scales . Indian English does not use millions , but has its own system of large numbers including lakhs and crores . English also has many words , such as zillion , used informally to mean large but unspecified amounts ; see indefinite and fictitious numbers .
A gamma ray , or gamma radiation ( symbol γ or γ { \displaystyle \gamma } ) , is a penetrating electromagnetic radiation arising from the radioactive decay of atomic nuclei . It consists of the shortest wavelength electromagnetic waves and so imparts the highest photon energy . Paul Villard , a French chemist and physicist , discovered gamma radiation in 1900 while studying radiation emitted by radium . In 1903 , Ernest Rutherford named this radiation gamma rays based on their relatively strong penetration of matter ; in 1900 he had already named two less penetrating types of decay radiation ( discovered by Henri Becquerel ) alpha rays and beta rays in ascending order of penetrating power . Gamma rays from radioactive decay are in the energy range from a few kiloelectronvolts ( keV ) to approximately 8 megaelectronvolts ( ~8 MeV ) , corresponding to the typical energy levels in nuclei with reasonably long lifetimes . The energy spectrum of gamma rays can be used to identify the decaying radionuclides using gamma spectroscopy . Very-high-energy gamma rays in the 100-1000 teraelectronvolt ( TeV ) range have been observed from sources such as the Cygnus X-3 microquasar . Natural sources of gamma rays originating on Earth are mostly as a result of radioactive decay and secondary radiation from atmospheric interactions with cosmic ray particles . However , there are other rare natural sources , such as terrestrial gamma-ray flashes , which produce gamma rays from electron action upon the nucleus . Notable artificial sources of gamma rays include fission , such as that which occurs in nuclear reactors , and high energy physics experiments , such as neutral pion decay and nuclear fusion . Gamma rays and X-rays are both electromagnetic radiation , and since they overlap in the electromagnetic spectrum , the terminology varies between scientific disciplines . In some fields of physics , they are distinguished by their origin : Gamma rays are created by nuclear decay , while in the case of X-rays , the origin is outside the nucleus .
The atomic nucleus is the small , dense region consisting of protons and neutrons at the center of an atom , discovered in 1911 by Ernest Rutherford based on the 1909 Geiger-Marsden gold foil experiment . After the discovery of the neutron in 1932 , models for a nucleus composed of protons and neutrons were quickly developed by Dmitri Ivanenko and Werner Heisenberg . An atom is composed of a positively-charged nucleus , with a cloud of negatively-charged electrons surrounding it , bound together by electrostatic force . Almost all of the mass of an atom is located in the nucleus , with a very small contribution from the electron cloud . Protons and neutrons are bound together to form a nucleus by the nuclear force . The diameter of the nucleus is in the range of 1.7566 fm ( 1.7566×10−15 m ) for hydrogen ( the diameter of a single proton ) to about 11.7142 fm for the heaviest atom uranium . These dimensions are much smaller than the diameter of the atom itself ( nucleus + electron cloud ) , by a factor of about 26,634 ( uranium atomic radius is about 156 pm ( 156×10−12 m ) ) to about 60,250 ( hydrogen atomic radius is about 52.92 pm ) . [ a ] The branch of physics concerned with the study and understanding of the atomic nucleus , including its composition and the forces which bind it together , is called nuclear physics .
In physics , an electronvolt ( symbol eV , also written electron-volt and electron volt ) is the amount of kinetic energy gained ( or lost ) by a single electron accelerating from rest through an electric potential difference of one volt in vacuum . When used as a unit of energy , the numerical value of 1 eV in joules ( symbol J ) is equivalent to the numerical value of the charge of an electron in coulombs ( symbol C ) . Under the 2019 redefinition of the SI base units , this sets 1 eV equal to 1.602176634×10−19 J . Historically , the electronvolt was devised as a standard unit of measure through its usefulness in electrostatic particle accelerator sciences , because a particle with electric charge q has an energy E = qV after passing through the potential V ; if q is quoted in integer units of the elementary charge and the potential in volts , one gets an energy in eV . It is a common unit of energy within physics , widely used in solid state , atomic , nuclear , and particle physics . It is commonly used with the metric prefixes milli- , kilo- , mega- , giga- , tera- , peta- or exa- ( meV , keV , MeV , GeV , TeV , PeV and EeV respectively ) . In some older documents , and in the name Bevatron , the symbol BeV is used , which stands for billion ( 109 ) electronvolts ; it is equivalent to the GeV .
The photon is a type of elementary particle . It is the quantum of the electromagnetic field including electromagnetic radiation such as light and radio waves , and the force carrier for the electromagnetic force ( even when static via virtual particles ) . The invariant mass of the photon is zero ; it always moves at the speed of light in a vacuum . Like all elementary particles , photons are currently best explained by quantum mechanics and exhibit wave-particle duality , exhibiting properties of both waves and particles . For example , a single photon may be refracted by a lens and exhibit wave interference with itself , and it can behave as a particle with definite and finite measurable position or momentum , though not both at the same time as per Heisenberg 's uncertainty principle . The photon 's wave and quantum qualities are two observable aspects of a single phenomenon - they can not be described by any mechanical model ; a representation of this dual property of light that assumes certain points on the wavefront to be the seat of the energy , is not possible . The quanta in a light wave are not spatially localized . The modern concept of the photon was developed gradually by Albert Einstein in the early 20th century to explain experimental observations that did not fit the classical wave model of light . The benefit of the photon model is that it accounts for the frequency dependence of light 's energy , and explains the ability of matter and electromagnetic radiation to be in thermal equilibrium . The photon model accounts for anomalous observations , including the properties of black-body radiation , that others ( notably Max Planck ) had tried to explain using semiclassical models . In that model , light is described by Maxwell 's equations , but material objects emit and absorb light in quantized amounts ( i.e. , they change energy only by certain particular discrete amounts ) . Although these semiclassical models contributed to the development of quantum mechanics , many further experiments beginning with the phenomenon of Compton scattering of single photons by electrons , validated Einstein 's hypothesis that light itself is quantized .
Zitterbewegung ( trembling motion in German ) is a predicted rapid oscillatory motion of elementary particles that obey relativistic wave equations . The existence of such motion was first proposed by Erwin Schrödinger in 1930 as a result of his analysis of the wave packet solutions of the Dirac equation for relativistic electrons in free space , in which an interference between positive and negative energy states produces what appears to be a fluctuation ( up to the speed of light ) of the position of an electron around the median , with an angular frequency of 2mc2/ℏ , or approximately 1.6×1021 radians per second . For the hydrogen atom , zitterbewegung can be invoked as a heuristic way to derive the Darwin term , a small correction of the energy level of the s-orbitals .
The electron is a subatomic particle , symbol e− or β− , whose electric charge is negative one elementary charge . Electrons belong to the first generation of the lepton particle family , and are generally thought to be elementary particles because they have no known components or substructure . The electron has a mass that is approximately 1/1836 that of the proton . Quantum mechanical properties of the electron include an intrinsic angular momentum ( spin ) of a half-integer value , expressed in units of the reduced Planck constant , ħ . Being fermions , no two electrons can occupy the same quantum state , in accordance with the Pauli exclusion principle . Like all elementary particles , electrons exhibit properties of both particles and waves : they can collide with other particles and can be diffracted like light . The wave properties of electrons are easier to observe with experiments than those of other particles like neutrons and protons because electrons have a lower mass and hence a longer de Broglie wavelength for a given energy . Electrons play an essential role in numerous physical phenomena , such as electricity , magnetism , chemistry and thermal conductivity , and they also participate in gravitational , electromagnetic and weak interactions . Since an electron has charge , it has a surrounding electric field , and if that electron is moving relative to an observer , said observer will observe it to generate a magnetic field . Electromagnetic fields produced from other sources will affect the motion of an electron according to the Lorentz force law . Electrons radiate or absorb energy in the form of photons when they are accelerated . Laboratory instruments are capable of trapping individual electrons as well as electron plasma by the use of electromagnetic fields .
An attosecond is 1×10−18 of a second ( one quintillionth of a second ) . For context , an attosecond is to a second what a second is to about 31.71 billion years . The word attosecond is formed by the prefix atto and the unit second . Atto- was derived from the Danish word for eighteen ( atten ) . Its symbol is as . An attosecond is equal to 1000 zeptoseconds , or ​1⁄1000 of a femtosecond . Because the next higher SI unit for time is the femtosecond ( 10−15 seconds ) , durations of 10−17 s and 10−16 s will typically be expressed as tens or hundreds of attoseconds : Times which can be expressed in attoseconds :
A femtosecond is the SI unit of time equal to 10−15 or 1/1,000,000,000,000,000 of a second ; that is , one quadrillionth , or one millionth of one billionth , of a second . For context , a femtosecond is to a second as a second is to about 31.71 million years ; a ray of light travels approximately 0.3 μm ( micrometers ) in 1 femtosecond , a distance comparable to the diameter of a virus . The word femtosecond is formed by the SI prefix femto and the SI unit second . Its symbol is fs . A femtosecond is equal to 1000 attoseconds , or 1/1000 picosecond . Because the next higher SI unit is 1000 times larger , times of 10−14 and 10−13 seconds are typically expressed as tens or hundreds of femtoseconds .
The nanometre ( international spelling as used by the International Bureau of Weights and Measures ; SI symbol : nm ) or nanometer ( American spelling ) is a unit of length in the metric system , equal to one billionth ( short scale ) of a metre ( 0.000000001 m ) . The name combines the SI prefix nano- ( from the Ancient Greek νάνος , nanos , dwarf ) with the parent unit name metre ( from Greek μέτρον , metrοn , unit of measurement ) . It can be written in scientific notation as 1×10−9 m , in engineering notation as 1 E−9 m , and as simply 1/1000000000 metres . When used as a prefix for something other than a unit of measure ( as in nanoscience ) , nano refers to nanotechnology , or phenomena typically occurring on a scale of nanometres ( see nanoscopic scale ) . The nanometre is often used to express dimensions on an atomic scale : the diameter of a helium atom , for example , is about 0.06 nm , and that of a ribosome is about 20 nm . The nanometre is also commonly used to specify the wavelength of electromagnetic radiation near the visible part of the spectrum : visible light ranges from around 400 to 700 nm . The ångström , which is equal to 0.1 nm , was formerly used for these purposes , but is still used in other fields . Since the late 1980s , in usages such as the 32 nm and the 22 nm semiconductor node , it has also been used to describe typical feature sizes in successive generations of the ITRS Roadmap for miniaturization in the semiconductor industry .
Ultraviolet ( UV ) is electromagnetic radiation with wavelength from 10 nm ( with a corresponding frequency of approximately 30 PHz ) to 400 nm ( 750 THz ) , shorter than that of visible light but longer than X-rays . UV radiation is present in sunlight , and constitutes about 10% of the total electromagnetic radiation output from the Sun . It is also produced by electric arcs and specialized lights , such as mercury-vapor lamps , tanning lamps , and black lights . Although long-wavelength ultraviolet is not considered an ionizing radiation because its photons lack the energy to ionize atoms , it can cause chemical reactions and causes many substances to glow or fluoresce . Consequently , the chemical and biological effects of UV are greater than simple heating effects , and many practical applications of UV radiation derive from its interactions with organic molecules . Short-wave ultraviolet light damages DNA and sterilizes surfaces with which it comes into contact . For humans , suntan and sunburn are familiar effects of exposure of the skin to UV light , along with an increased risks of skin cancer . The amount of UV light produced by the Sun means that the Earth would not be able to sustain life on dry land if most of that light were not filtered out by the atmosphere . More energetic , shorter-wavelength extreme UV below 121 nm ionizes air so strongly that it is absorbed before it reaches the ground . However , ultraviolet light is also responsible for the formation of bone-strengthening vitamin D in most land vertebrates , including humans ( specifically , UVB ) . The UV spectrum thus has effects both beneficial and harmful to life . The lower wavelength limit of human vision is conventionally taken as 400 nm , so ultraviolet rays are invisible to humans , although some people can perceive light at slightly shorter wavelengths than this .
Bromine is a chemical element with symbol Br and atomic number 35 . It is the third-lightest halogen , and is a fuming red-brown liquid at room temperature that evaporates readily to form a similarly coloured gas . Its properties are thus intermediate between those of chlorine and iodine . Isolated independently by two chemists , Carl Jacob Löwig ( in 1825 ) and Antoine Jérôme Balard ( in 1826 ) , its name was derived from the Ancient Greek βρῶμος ( stench ) , referencing its sharp and disagreeable smell . Elemental bromine is very reactive and thus does not occur free in nature , but in colourless soluble crystalline mineral halide salts , analogous to table salt . While it is rather rare in the Earth 's crust , the high solubility of the bromide ion ( Br− ) has caused its accumulation in the oceans . Commercially the element is easily extracted from brine pools , mostly in the United States , Israel and China . The mass of bromine in the oceans is about one three-hundredth that of chlorine . At high temperatures , organobromine compounds readily dissociate to yield free bromine atoms , a process that stops free radical chemical chain reactions . This effect makes organobromine compounds useful as fire retardants , and more than half the bromine produced worldwide each year is put to this purpose . The same property causes ultraviolet sunlight to dissociate volatile organobromine compounds in the atmosphere to yield free bromine atoms , causing ozone depletion . As a result , many organobromide compounds - such as the pesticide methyl bromide - are no longer used .
Femtochemistry is the area of physical chemistry that studies chemical reactions on extremely short timescales ( approximately 10−15 seconds or one femtosecond , hence the name ) in order to study the very act of atoms within molecules ( reactants ) rearranging themselves to form new molecules ( products ) . In 1999 , Ahmed Hassan Zewail received the Nobel Prize in Chemistry for his pioneering work in this field showing that it is possible to see how atoms in a molecule move during a chemical reaction with flashes of laser light . Application of femtochemistry in biological studies has also helped to elucidate the conformational dynamics of stem-loop RNA structures . Many publications have discussed the possibility of controlling chemical reactions by this method , [ clarification needed ] but this remains controversial . The steps in some reactions occur in the femtosecond timescale and sometimes in attosecond timescales , and will sometimes form intermediate products . These reaction intermediates can not always be deduced from observing the start and end products .
The tau ( τ ) , also called the tau lepton , tau particle , or tauon , is an elementary particle similar to the electron , with negative electric charge and a spin of 1/2 . Together with the electron , the muon , and the three neutrinos , it is a lepton . Like all elementary particles with half-integer spin , the tau has a corresponding antiparticle of opposite charge but equal mass and spin , which in the tau 's case is the antitau ( also called the positive tau ) . Tau particles are denoted by τ− and the antitau by τ+ . Tau leptons have a lifetime of 2.9×10−13 s and a mass of 1776.86 MeV/c2 ( compared to 105.66 MeV/c2 for muons and 0.511 MeV/c2 for electrons ) . Since their interactions are very similar to those of the electron , a tau can be thought of as a much heavier version of the electron . Because of their greater mass , tau particles do not emit as much bremsstrahlung radiation as electrons ; consequently they are potentially highly penetrating , much more so than electrons . Because of their short lifetime , the range of the tau is mainly set by their decay length , which is too small for bremsstrahlung to be noticeable . Their penetrating power appears only at ultra-high velocity and energy ( above petaelectronvolt energies ) , when time dilation extends their path-length . As with the case of the other charged leptons , the tau has an associated tau neutrino , denoted by ντ .
A picosecond is an SI unit of time equal to 10−12 or 1/1,000,000,000,000 ( one trillionth ) of a second . That is one trillionth , or one millionth of one millionth of a second , or 0.000 000 000 001 seconds . A picosecond is to one second as one second is to approximately 31,689 years . Multiple technical approaches achieve imaging within single-digit picoseconds : for example , the streak camera or intensified CCD ( ICCD ) cameras are able to picture the motion of light . The name is formed by the SI prefix pico and the SI unit second . It is abbreviated as ps . One picosecond is equal to 1000 femtoseconds , or 1/1000 nanoseconds . Because the next SI unit is 1000 times larger , measurements of 10−11 and 10−10 second are typically expressed as tens or hundreds of picoseconds . Some notable measurements in this range include :
The bottom quark or b quark , also known as the beauty quark , is a third-generation quark with a charge of −1/3 e. All quarks are described in a similar way by electroweak and quantum chromodynamics , but the bottom quark has exceptionally low rates of transition to lower-mass quarks . The bottom quark is also notable because it is a product in almost all top quark decays , and is a frequent decay product of the Higgs boson .
The transition state of a chemical reaction is a particular configuration along the reaction coordinate . It is defined as the state corresponding to the highest potential energy along this reaction coordinate . It is often marked with the double dagger ‡ symbol . As an example , the transition state shown below occurs during the SN2 reaction of bromoethane with a hydroxyl anion :
SiGe ( /ˈsɪɡiː/ or /ˈsaɪdʒiː/ ) , or silicon-germanium , is an alloy with any molar ratio of silicon and germanium , i.e . with a molecular formula of the form Si1−xGex . It is commonly used as a semiconductor material in integrated circuits ( ICs ) for heterojunction bipolar transistors or as a strain-inducing layer for CMOS transistors . IBM introduced the technology into mainstream manufacturing in 1989 . This relatively new technology offers opportunities in mixed-signal circuit and analog circuit IC design and manufacture . SiGe is also used as a thermoelectric material for high temperature applications ( > 700 K ) .
A nanosecond ( ns ) is an SI unit of time equal to one billionth of a second , that is , 1/1,000,000,000 of a second , or 10−9 seconds . The term combines the prefix nano- with the basic unit for one-sixtieth of a minute . A nanosecond is equal to 1000 picoseconds or ​1⁄1000 microsecond . Time units ranging between 10−8 and 10−7 seconds are typically expressed as tens or hundreds of nanoseconds . Time units of this granularity are commonly found in telecommunications , pulsed lasers , and related aspects of electronics .
A microsecond is an SI unit of time equal to one millionth ( 0.000001 or 10−6 or ​1⁄1,000,000 ) of a second . Its symbol is μs , sometimes simplified to us when Unicode is not available . A microsecond is equal to 1000 nanoseconds or ​1⁄1,000 of a millisecond . Because the next SI prefix is 1000 times larger , measurements of 10−5 and 10−4 seconds are typically expressed as tens or hundreds of microseconds .
The muon ( /ˈmjuːɒn/ ; from the Greek letter mu ( μ ) used to represent it ) is an elementary particle similar to the electron , with an electric charge of −1 e and a spin of 1/2 , but with a much greater mass . It is classified as a lepton . As is the case with other leptons , the muon is not known to have any sub-structure - that is , it is not thought to be composed of any simpler particles . The muon is an unstable subatomic particle with a mean lifetime of 2.2 μs , much longer than many other subatomic particles . As with the decay of the non-elementary neutron ( with a lifetime around 15 minutes ) , muon decay is slow ( by subatomic standards ) because the decay is mediated by the weak interaction exclusively ( rather than the more powerful strong interaction or electromagnetic interaction ) , and because the mass difference between the muon and the set of its decay products is small , providing few kinetic degrees of freedom for decay . Muon decay almost always produces at least three particles , which must include an electron of the same charge as the muon and two neutrinos of different types . Like all elementary particles , the muon has a corresponding antiparticle of opposite charge ( +1 e ) but equal mass and spin : the antimuon ( also called a positive muon ) . Muons are denoted by μ− and antimuons by μ+ . Muons were previously called mu mesons , but are not classified as mesons by modern particle physicists ( see § History ) , and that name is no longer used by the physics community . Muons have a mass of 105.66 MeV/c2 , which is about 207 times that of the electron . More precisely , it is :
A minicomputer , or colloquially mini , is a class of smaller computers that was developed in the mid-1960s and sold for much less than mainframe and mid-size computers from IBM and its direct competitors . In a 1970 survey , The New York Times suggested a consensus definition of a minicomputer as a machine costing less than US $ 25,000 ( equivalent to $ 165,000 in 2019 ) , with an input-output device such as a teleprinter and at least four thousand words of memory , that is capable of running programs in a higher level language , such as Fortran or BASIC . The class formed a distinct group with its own software architectures and operating systems . Minis were designed for control , instrumentation , human interaction , and communication switching as distinct from calculation and record keeping . Many were sold indirectly to original equipment manufacturers ( OEMs ) for final end use application . During the two decade lifetime of the minicomputer class ( 1965-1985 ) , almost 100 companies formed and only a half dozen remained . When single-chip CPU microprocessors appeared , beginning with the Intel 4004 in 1971 , the term minicomputer came to mean a machine that lies in the middle range of the computing spectrum , in between the smallest mainframe computers and the microcomputers . The term minicomputer is little used today ; the contemporary term for this class of system is midrange computer , such as the higher-end SPARC , Power ISA and Itanium-based systems from Oracle , IBM and Hewlett-Packard .
A millisecond ( from milli- and second ; symbol : ms ) is a thousandth ( 0.001 or 10−3 or 1/1000 ) of a second . A unit of 10 milliseconds may be called a centisecond , and one of 100 milliseconds a decisecond , but these names are rarely used .
Higher performance in hard disk drives comes from devices which have better performance characteristics . These performance characteristics can be grouped into two categories : access time and data transfer time ( or rate ) .
A reflex , or reflex action , is an involuntary and nearly instantaneous movement in response to a stimulus . A reflex is made possible by neural pathways called reflex arcs which can act on an impulse before that impulse reaches the brain . The reflex is then an automatic response to a stimulus that does not receive or need conscious thought .
Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere . It comprises the westernmost part of Eurasia and is bordered by the Arctic Ocean to the north , the Atlantic Ocean to the west , the Mediterranean Sea to the south , and Asia to the east . The eastern border comprises a long and mixed line of mountain ranges and waterways that would normally define a subcontinent . However , Europe is generally accorded the status of a full continent because of its great physical size and the weight of history and tradition . It is the 6th largest continent in the world . Europe is commonly considered to be separated from Asia by the watershed divides of the Ural and Caucasus Mountains , the Ural River , the Caspian and Black Seas and the waterways of the Turkish Straits . Europe covers about 10,180,000 square kilometres ( 3,930,000 sq mi ) , or 2% of the Earth 's surface ( 6.8% of land area ) . Politically , Europe is divided into about fifty sovereign states of which Russia is the largest and most populous , spanning 39% of the continent and comprising 15% of its population . Europe had a total population of about 741 million ( about 11% of the world population ) as of 2018 [ update ] . The European climate is largely affected by warm Atlantic currents that temper winters and summers on much of the continent , even at latitudes along which the climate in Asia and North America is severe . Further from the sea , seasonal differences are more noticeable than close to the coast . Europe , in particular ancient Greece and ancient Rome , was the birthplace of Western civilisation .