THE SCIENCE TECH REVIEW
THE SCIENCE-TECH
REVIEW
Muhammad
Sheikh Ramjan Hossain
Chief Editor: S.T. Review
Cosmology
(Courtesy
of Wikipedia, Encyclopedia)
The Hubble extreme Deep Field (XDF) was
completed in September 2012 and shows the farthest galaxies ever
photographed. Except for the few stars in the foreground (which are bright and
easily recognizable because only they have diffraction spikes), every
speck of light in the photo is an individual galaxy, some of them as old as
13.2 billion years; the observable universe is estimated to contain more than 2
trillion galaxies.[1]
Cosmology (from
the Greek κόσμος, kosmos "world"
and -λογία, -logia "study of") is a branch of astronomy concerned with
the studies of the origin and evolution of the universe, from the Big Bang to today and on
into the future. It is the scientific study of the origin, evolution, and eventual fate of the universe. Physical cosmology is the
scientific study of the universe's origin, its large-scale structures and
dynamics, and its ultimate fate, as well as
the laws of science that
govern these areas.[2]
The term cosmology was
first used in English in 1656 in Thomas Blount's Glossographia,[3] and in 1731 taken up
in Latin by German philosopher Christian Wolff, in Cosmologia
Generalis.[4]
Religious or mythological
cosmology is a body of beliefs based on mythological, religious, and esoteric literature and
traditions of creation myths and eschatology.
Physical cosmology is studied by
scientists, such as astronomers and physicists, as well as philosophers, such as metaphysicians, philosophers of physics, and philosophers of space and time.
Because of this shared scope with philosophy, theories in physical
cosmology may include both scientific and
non-scientific propositions, and may depend upon assumptions that cannot be tested. Cosmology differs from
astronomy in that the former is concerned with the Universe as a whole while
the latter deals with individual celestial objects. Modern
physical cosmology is dominated by the Big Bang theory, which
attempts to bring together observational astronomy and particle physics;[5][6] more specifically, a
standard parameterization of the Big Bang with dark matter and dark energy, known as the Lambda-CDM model.
Theoretical astrophysicist David N. Spergel has
described cosmology as a "historical science" because "when we
look out in space, we look back in time" due to the finite nature of the speed of light.[7]
Big Bang
bɪɡ ˈbaŋ/
noun
1. 1.
ASTRONOMY
the rapid expansion of matter from a
state of extremely high density and temperature which according to current
cosmological theories marked the origin of the universe.
Big Bang
Courtesy of Wikipedia, the Encyclopedia)
"Big
Bang theory" redirects here. For the American TV sitcom, see The Big Bang Theory. For
other uses, see Big Bang (disambiguation) and Big Bang Theory (disambiguation).
Timeline
of the metric expansion of space,
where space (including hypothetical non-observable portions of the universe) is
represented at each time by the circular sections. On the left, the dramatic
expansion occurs in the inflationary epoch; and at the
center, the expansion accelerates (artist's
concept; not to scale).
The Big
Bang theory is the prevailing cosmological model for the universe[1] from the earliest known periodsthrough
its subsequent large-scale evolution.[2][3][4] The model describes
how the universe expanded from a very
high-density and high-temperature state,[5][6] and offers a
comprehensive explanation for a broad range of phenomena, including the
abundance of light elements, the cosmic microwave background (CMB), large scale structure and Hubble's law.[7] If the known laws of
physics are extrapolated to the highest density regime, the result is a singularity which is
typically associated with the Big Bang. Physicists are undecided whether this
means the universe began from a singularity, or that current knowledge is
insufficient to describe the universe at that time. Detailed measurements of
the expansion rate of the universe place the Big Bang at around 13.8 billion years ago, which
is thus considered the age of the universe.[8] After the initial
expansion, the universe cooled sufficiently to allow the formation of subatomic particles, and later
simple atoms. Giant clouds of these
primordial elements later coalesced through gravity in halos of dark matter, eventually forming
the stars and galaxies visible today.
Since Georges Lemaître first
noted in 1927 that an expanding universe could be traced back in time to an
originating single point, scientists have built on his idea of cosmic
expansion. The scientific community was once divided between supporters of two
different theories, the Big Bang and the Steady State theory, but a wide
range of empirical evidence has
strongly favored the Big Bang which is now universally accepted.[9] In 1929, from analysis
of galactic redshifts, Edwin Hubble concluded that
galaxies are drifting apart; this is important observational evidence
consistent with the hypothesis of an expanding universe. In 1964, the cosmic microwave background radiation was discovered, which was crucial evidence in favor of the Big Bang
model,[10] since that theory predicted the existence of
background radiation throughout the universe before it was discovered. More
recently, measurements of the redshifts of supernovae indicate that the expansion of the universe is accelerating, an observation attributed to dark energy's existence.[11]The known physical laws of nature can
be used to calculate the characteristics of the universe in detail back in time
to an initial state of extreme density and temperature.[12]
In physics, special
relativity (also known as the special
theory of relativity) is the generally
accepted and experimentally confirmed physical theory regarding
the relationship between space and time. In Albert Einstein's original
pedagogical treatment, it is based on two postulates:
1. the
laws of physics are invariant (i.e. identical)
in all inertial frames of reference (i.e.
non-accelerating frames of reference); and
2. the speed of light in a vacuum is the same for all
observers, regardless of the motion of the light source or observer.
Some of the work of Albert Einstein in special
relativity is built on the earlier work by Hendrik Lorentz.
Special relativity was originally
proposed by Albert Einstein in a paper published on 26 September 1905 titled "On the Electrodynamics of Moving Bodies".[p 1] The inconsistency of Newtonian mechanics with Maxwell's equations of electromagnetism and,
experimentally, the Michelson-Morley null result (and subsequent similar
experiments) demonstrated that the historically hypothesized luminiferous aether did
not exist. This led to Einstein's development of special relativity, which
corrects mechanics to handle situations involving all motions and especially
those at a speed close to that of light (known as relativistic
velocities). Today, special relativity is proven to be the most accurate
model of motion at any speed when gravitational effects are negligible. Even
so, the Newtonian model is still valid as a simple and accurate approximation
at low velocities (relative to the speed of light), for example, the everyday
motions on Earth.
Special relativity has a wide range of
consequences. These have been experimentally verified,[1] and include length contraction, time dilation, relativistic mass, mass–energy equivalence, a universal speed limit, the
speed of causality and relativity of simultaneity. It
has, for example, replaced the conventional notion of an absolute universal
time with the notion of a time that is dependent on reference frame and spatial position. Rather
than an invariant time interval between two events, there is an invariant spacetime interval. Combined
with other laws of physics, the two postulates of special relativity predict
the equivalence of mass and energy, as expressed in the mass–energy equivalence formula E = mc2 (c is
the speed of light in a
vacuum).[2][3]
A defining feature of special
relativity is the replacement of the Galilean transformations of
Newtonian mechanics with the Lorentz transformations. Time
and space cannot be defined separately from each other (as was earlier thought
to be the case). Rather, space and time are interwoven into a single continuum known as "spacetime". Events that occur at the same time for one observer
can occur at different times for another.
Until Einstein developed general relativity, introducing
a curved spacetime to incorporate gravity, the phrase "special
relativity" was not used. A translation sometimes used is "restricted
relativity"; "special" really means "special case".[p 2][p 3][p 4][note 1]
The theory is "special" in
that it only applies in the special case where the
space time is "flat", i.e., the curvature of spacetime,
described by the energy-momentum tensor and
causing gravity, is negligible.[4][note 2] In order to
correctly accommodate gravity, Einstein formulated general relativity in 1915.
Special relativity, contrary to some historical descriptions, does accommodate accelerations as well as accelerating frames of reference.[5][6]
Just as Galilean relativity is now
accepted to be an approximation of special relativity that is valid for low
speeds, special relativity is considered an approximation of general relativity
that is valid for weak gravitational fields, i.e. at a
sufficiently small scale (for example, for tidal forces) and in conditions
of free fall. General relativity,
however, incorporates noneuclidean geometry in
order to represent gravitational effects as the geometric curvature of
spacetime. Special relativity is restricted to the flat spacetime known as Minkowski space. As long as the
universe can be modeled as a pseudo-Riemannian manifold, a
Lorentz-invariant frame that abides by special relativity can be defined for a
sufficiently small neighborhood of each point in this curved spacetime.
Galileo Galilei had
already postulated that there is no absolute and well-defined state of rest (no privileged reference frames), a
principle now called Galileo's principle of relativity. Einstein extended this principle so that it accounted for the constant
speed of light,[7] a phenomenon that had been observed in the Michelson–Morley experiment. He
also postulated that it holds for all the laws of physics, including both
the laws of mechanics and of electrodynamics.[8]
Higgs boson
Courtesy of Wikipedia, the Encyclopedia
Physicists explain the properties of
forces between elementary particles in
terms of the Standard Model – a widely
accepted framework for understanding almost everything in physics in the known
universe, other than gravity. (A separate theory, general relativity, is used for
gravity.) In this model, the fundamental forces in
nature arise from properties of our universe called gauge invariance and symmetries. The forces are transmitted by particles known
as gauge bosons.[13][14]
In the Standard Model, the Higgs
particle is a boson with spin zero, no electric charge and no colour charge. It is also very
unstable, decaying into other
particles almost immediately. The Higgs field is a scalar field, with two neutral and two
electrically charged components that form a complex doublet of the weak isospin SU(2) symmetry. The Higgs
field has a "Mexican hat-shaped"
potential. In its ground state, this causes the
field to have a nonzero value everywhere (including otherwise empty space), and
as a result, below a very high energy it breaks the weak isospin symmetry of
the electroweak interaction.
(Technically the non-zero expectation value converts the Lagrangian's Yukawa coupling
terms into mass terms.) When this happens, three components of the Higgs field
are "absorbed" by the SU(2) and U(1) gauge bosons (the "Higgs mechanism") to
become the longitudinal components of the now-massive W and Z bosons of the weak force. The remaining
electrically neutral component either manifests as a Higgs particle, or may
couple separately to other particles known as fermions (via Yukawa couplings), causing
these to acquire mass as well.[15]
History
Particle physicists study matter made from fundamental particles whose
interactions are mediated by exchange particles – gauge bosons – acting as force carriers. At the
beginning of the 1960s a number of these particles had been discovered or
proposed, along with theories suggesting how they relate to each other, some of
which had already been reformulated as field theories in which
the objects of study are not particles and forces, but quantum fields and their symmetries.[51]:150 However, attempts
to produce quantum field models for two of the four known fundamental forces – the electromagnetic force and
the weak nuclear force – and
then to unify these interactions, were
still unsuccessful.
One known problem was that gauge invariant approaches,
including non-abelian models such as Yang–Mills theory(1954), which
held great promise for unified theories, also seemed to predict known massive
particles as massless.[52] Goldstone's theorem, relating
to continuous symmetries within
some theories, also appeared to rule out many obvious solutions,[53] since it appeared to
show that zero-mass particles also would have to exist that simply were
"not seen".[54] According to Guralnik, physicists had
"no understanding" how these problems could be overcome.[54]
Particle physicist and mathematician
Peter Woit summarised the state of research at the time:
Yang and Mills work on non-abelian gauge theory had
one huge problem: in perturbation theory it has
massless particles which don’t correspond to anything we see. One way of
getting rid of this problem is now fairly well understood, the phenomenon of confinement realized in QCD, where the strong
interactions get rid of the massless “gluon” states at long distances. By the
very early sixties, people had begun to understand another source of massless
particles: spontaneous symmetry breaking of a continuous symmetry. What Philip Anderson realized
and worked out in the summer of 1962 was that, when you have both gauge
symmetry and spontaneous symmetry breaking, the
Nambu–Goldstone massless mode can combine with the massless gauge field modes
to produce a physical massive vector field. This is what happens in superconductivity, a subject
about which Anderson was (and is) one of the leading experts.[52] [text condensed]
The Higgs mechanism is a process by
which vector bosons can acquire rest mass without explicitly breaking gauge invariance, as a
byproduct of spontaneous symmetry breaking.[55][56] Initially, the
mathematical theory behind spontaneous symmetry breaking was conceived and
published within particle physics by Yoichiro Nambu in 1960,[57] and the concept that
such a mechanism could offer a possible solution for the "mass
problem" was originally suggested in 1962 by Philip Anderson (who had
previously written papers on broken symmetry and its outcomes in
superconductivity.[58] Anderson concluded in
his 1963 paper on the Yang-Mills theory, that "considering the
superconducting analog... [t]hese two types of bosons seem capable of canceling
each other out... leaving finite mass bosons"),[59][60] and in March 1964, Abraham Klein and Benjamin Lee showed that
Goldstone's theorem could be avoided this way in at least some non-relativistic
cases, and speculated it might be possible in truly relativistic cases.[61]
These approaches were quickly
developed into a full relativistic model,
independently and almost simultaneously, by three groups of physicists: by François Englert and Robert Brout in August
1964;[62] by Peter Higgs in October
1964;[63] and by Gerald Guralnik, Carl Hagen, and Tom Kibble (GHK) in
November 1964.[64] Higgs also wrote a
short, but important,[55] response published in
September 1964 to an objection by Gilbert,[65] which showed that if
calculating within the radiation gauge, Goldstone's theorem and Gilbert's
objection would become inapplicable.[k] (Higgs later described
Gilbert's objection as prompting his own paper.[66]) Properties of the model
were further considered by Guralnik in 1965,[67] by Higgs in 1966,[68] by Kibble in 1967,[69] and further by GHK in
1967.[70] The original three
1964 papers demonstrated that when a gauge theory is combined
with an additional field that spontaneously breaks the symmetry, the gauge
bosons may consistently acquire a finite mass.[55][56][71] In 1967, Steven Weinberg [72] and Abdus Salam[73]independently showed how a
Higgs mechanism could be used to break the electroweak symmetry of Sheldon Glashow's unified model for the weak and electromagnetic interactions,[74] (itself an extension
of work by Schwinger), forming what became
the Standard Model of particle
physics. Weinberg was the first to observe that this would also provide mass
terms for the fermions.[75][l]
At
first, these seminal papers on spontaneous breaking of gauge symmetries were
largely ignored, because it was widely believed that the (non-Abelian gauge)
theories in question were a dead-end, and in particular that they could not be renormalised. In 1971–72, Martinus Veltman and Gerard 't Hooft proved
renormalisation of Yang–Mills was possible in two papers covering massless, and
then massive, fields.[75] Their contribution,
and the work of others on the renormalisation group –
including "substantial" theoretical work by Russian physicists Ludvig Faddeev, Andrei Slavnov, Efim Fradkin, and Igor Tyutin[76] – was eventually
"enormously profound and influential",[77] but even with all
key elements of the eventual theory published there was still almost no wider
interest. For example, Coleman found in a study
that "essentially no-one paid any attention" to Weinberg's paper
prior to 1971[78] and discussed by David Politzer in his
2004 Nobel speech.[77] – now the most cited
in particle physics [79] – and even in 1970
according to Politzer, Glashow's teaching of the weak interaction contained no
mention of Weinberg's, Salam's, or Glashow's own work.[77] In practice,
Politzer states, almost everyone learned of the theory due to physicist Benjamin Lee, who combined the
work of Veltman and 't Hooft with insights by others, and popularised the
completed theory.[77] In this way, from
1971, interest and acceptance "exploded"[77] and the ideas were
quickly absorbed in the mainstream.[75][77]
The resulting electroweak theory and
Standard Model have accurately predicted (among
other things) weak neutral currents, three bosons, the top and charm quarks, and with great
precision, the mass and other properties of some of these.[d] Many of those involved eventually won Nobel Prizes or other
renowned awards. A 1974 paper and comprehensive review in Reviews of Modern Physics commented
that "while no one doubted the [mathematical] correctness of these
arguments, no one quite believed that nature was diabolically clever enough to
take advantage of them",[80] adding that the
theory had so far produced accurate answers that accorded with experiment, but
it was unknown whether the theory was fundamentally correct.[81] By 1986 and again in
the 1990s it became possible to write that understanding and proving the Higgs
sector of the Standard Model was "the central problem today in particle
physics".[18][19]
Symmetry breaking
By the early 1960s, physicists had realised that a given symmetry law might not always be followed under certain conditions, at least in some areas
of physics.[c] This is called symmetry breaking and was
recognised in the late 1950s by Yoichiro Nambu. Symmetry
breaking can lead to surprising and unexpected results. In 1962 physicist Philip Anderson – an
expert in superconductivity – wrote
a paper that considered symmetry breaking in particle physics, and suggested
that perhaps symmetry breaking might be the missing piece needed to solve the
problems of gauge invariance in particle physics. If electroweak symmetry was
somehow being broken, it might explain why electromagnetism's boson is
massless, yet the weak force bosons have mass, and solve the problems. Shortly
afterwards, in 1963, this was shown to be theoretically possible, at least for
some limited (non-relativistic) cases.
Symmetry breaking of the electro
```weak interaction
Below an extremely high temperature, electroweak symmetry breaking causes
the electroweak interaction to
manifest in part as the short-ranged weak force, which is carried by
massive gauge bosons. This symmetry
breaking is required for atoms and other structures
to form, as well as for nuclear reactions in stars, such as our Sun. The Higgs field is
responsible for this symmetry breaking.
Higgs mechanism
Following the 1962 and 1963 papers,
three groups of researchers independently published the 1964 PRL symmetry breaking papers with similar conclusions and for all cases, not just some limited
cases. They showed that the conditions for electroweak symmetry would be
"broken" if an unusual type of field existed throughout
the universe, and indeed, some fundamental particles would acquire mass. The field
required for this to happen (which was purely hypothetical at the time) became
known as the Higgs field (after Peter Higgs, one of the
researchers) and the mechanism by which it led to symmetry breaking, known as
the Higgs mechanism. A key
feature of the necessary field is that it would take less energy
for the field to have a non-zero value than a zero value, unlike all other
known fields, therefore, the Higgs field has a non-zero value (or vacuum
expectation) everywhere. It was the first proposal capable of
showing how the weak force gauge bosons could have mass despite their governing
symmetry, within a gauge invariant theory.
Although these ideas did not gain
much initial support or attention, by 1972 they had been developed into a
comprehensive theory and proved capable of giving "sensible" resultsthat
accurately described particles known at the time, and which, with exceptional
accuracy, predicted several other particles discovered during the following years.[d] During the 1970s these
theories rapidly became the Standard Model of particle
physics. There was not yet any direct evidence that the Higgs field existed,
but even without proof of the field, the accuracy of its predictions led
scientists to believe the theory might be true. By the 1980s the question of
whether or not the Higgs field existed, and therefore whether or not the entire
Standard Model was correct, had come to be regarded as one of the most
important unanswered questions in particle physics.
Higgs field
According to the Standard Model, a field of the necessary
kind (the Higgs field) exists throughout space and breaks certain
symmetry laws of the electroweak interaction.[e] Via the Higgs
mechanism, this field causes the gauge bosons of the weak force to be massive
at all temperatures below an extreme high value. When the weak force bosons
acquire mass, this affects their range, which becomes very small.[f] Furthermore, it was
later realised that the same field would also explain, in a different way, why
other fundamental constituents of matter (including electrons and quarks) have mass.
For many decades, scientists had no
way to determine whether or not the Higgs field existed, because the technology
needed for its detection did not exist at that time. If the Higgs field did
exist, then it would be unlike any other known fundamental field, but it also
was possible that these key ideas, or even the entire Standard Model, were
somehow incorrect.[g] Only discovering that
the Higgs boson and therefore the Higgs field existed solved the problem.
Unlike other known fields such as the electromagnetic field, the
Higgs field is scalar and has a non-zero constant
value in vacuum. The existence of the
Higgs field became the last unverified part of the Standard Model of particle
physics, and for several decades was considered "the central problem in
particle physics".[18][19]
The presence of the field, now
confirmed by experimental investigation, explains why some fundamental particles have mass, despite the symmetries controlling
their interactions implying that they should be massless. It also resolves
several other long-standing puzzles, such as the reason for the extremely short
range of the weak force.
Although the Higgs field is non-zero
everywhere and its effects are ubiquitous, proving its existence was far from
easy. In principle, it can be proved to exist by detecting its excitations, which manifest as
Higgs particles (the Higgs boson), but these are extremely
difficult to produce and detect. The importance of this fundamental question led
to a 40-year search, and the
construction of one of the world's most expensive and complex experimental facilities to date, CERN's Large Hadron Collider,[20] in an attempt to
create Higgs bosons and other particles for observation and study. On 4 July
2012, the discovery of a new particle with a mass between 125 and 127 GeV/c2 was
announced; physicists suspected that it was the Higgs boson.[21][22][23] Since then, the
particle has been shown to behave, interact, and decay in many of the ways
predicted for Higgs particles by the Standard Model, as well as having even parity and zero spin,[6][7] two fundamental
attributes of a Higgs boson. This also means it is the first elementary scalar particle discovered
in nature.[24] As of 2018, in-depth
research shows the particle continuing to behave in line with predictions for
the Standard Model Higgs boson. More studies are needed to verify with higher
precision that the discovered particle has all of the properties predicted, or
whether, as described by some theories, multiple Higgs bosons exist.[25]
Higgs boson
The hypothesised Higgs mechanism made several accurate
predictions,[d][26]:22 however to confirm
its existence there was an extensive search for a matching particleassociated with
it – the "Higgs boson".[8][9] Detecting Higgs bosons
was difficult due to the energy required to produce them and their very rare
production even if the energy is sufficient. It was therefore several decades
before the first evidence of the Higgs boson was found. Particle colliders, detectors,
and computers capable of looking for Higgs bosons took more than 30 years (c.
1980–2010) to develop.
By March 2013, the existence of the
Higgs boson was confirmed, and therefore, the concept of some type of Higgs
field throughout space is strongly supported.[21][23][6] The nature and
properties of this field are now being investigated further, using more data
collected at the LHC.[1]
Particle physics
The Higgs boson validates the Standard Model through the
mechanism of mass generation. As more
precise measurements of its properties are made, more advanced extensions may
be suggested or excluded. As experimental means to measure the field's
behaviours and interactions are developed, this fundamental field may be better
understood. If the Higgs field had not been discovered, the Standard Model
would have needed to be modified or superseded.
Related to this, a belief generally
exists among physicists that there is likely to be "new" physics beyond the Standard Model, and the Standard Model will at some point be extended or superseded.
The Higgs discovery, as well as the many measured collisions occurring at the
LHC, provide physicists a sensitive tool to parse data for where the Standard
Model fails, and could provide considerable evidence guiding researchers into
future theoretical developments
Particle mass acquisition
The Higgs field is pivotal in generating the masses of quarks and charged leptons (through Yukawa
coupling) and the W and Z gauge bosons (through the
Higgs mechanism).
It is worth noting that the Higgs
field does not "create" mass out of nothing (which
would violate the law of conservation of energy),
nor is the Higgs field responsible for the mass of all particles. For example,
approximately 99% of the mass of baryons (composite particles such
as the proton and neutron), is due instead to quantum chromodynamic binding energy, which is the sum of the kinetic energies of quarks
and the energies of the massless gluons mediating the strong interaction inside
the baryons.[27] In Higgs-based
theories, the property of "mass" is a manifestation of potential energy transferred
to fundamental particles when they interact ("couple") with the Higgs
field, which had contained that mass in the form of energy.[28]
Scalar fields and extension of the
Standard Model[edit]
The Higgs field is the only scalar (spin 0) field to
be detected; all the other fields in the Standard Model are spin ½ fermions or spin 1
bosons. According to Rolf-Dieter Heuer, director
general of CERN when the Higgs boson was discovered, this existence proof of a
scalar field is almost as important as the Higgs's role in determining the mass
of other particles. It suggests that other hypothetical scalar fields suggested
by other theories, from the inflaton to quintessence, could perhaps
exist as well.[29][30]
Practical and
technological impact
As yet, there are no known immediate technological benefits
of finding the Higgs particle. However, a common pattern for fundamental
discoveries is for practical applications to follow later, and once the
discovery has been explored further, perhaps becoming the basis for new
technologies of importance to society.[48][49][50]
The challenges in particle physics
have furthered major technological progress of widespread importance. For
example, the World Wide Web began as a
project to improve CERN's communication system. CERN's requirement to process
massive amounts of data produced by the Large Hadron Collider also led to
contributions to the fields of distributed and cloud computing[citation needed].
The three papers written in 1964 were
each recognised as milestone papers during Physical Review Letters's 50th
anniversary celebration.[71] Their six authors
were also awarded the 2010 J. J. Sakurai Prize for Theoretical Particle Physics for this work.[82] (A controversy also
arose the same year, because in the event of a Nobel Prize only up to
three scientists could be recognised, with six being credited for the papers.[83]) Two of the three PRL
papers (by Higgs and by GHK) contained equations for the hypothetical field that eventually
would become known as the Higgs field and its hypothetical quantum, the Higgs boson.[63][64] Higgs' subsequent
1966 paper showed the decay mechanism of the boson; only a massive boson can
decay and the decays can prove the mechanism.[citation needed]
In the paper by Higgs the boson is
massive, and in a closing sentence Higgs writes that "an essential
feature" of the theory "is the prediction of incomplete multiplets of scalarand vector bosons".[63] (Frank Close comments that
1960s gauge theorists were focused on the problem of massless vector bosons,
and the implied existence of a massive scalar boson was not
seen as important; only Higgs directly addressed it.[84]:154, 166, 175) In the
paper by GHK the boson is massless and decoupled from the massive states.[64]In reviews dated 2009 and
2011, Guralnik states that in the GHK model the boson is massless only in a
lowest-order approximation, but it is not subject to any constraint and
acquires mass at higher orders, and adds that the GHK paper was the only one to
show that there are no massless Goldstone bosons in the
model and to give a complete analysis of the general Higgs mechanism.[54][85] All three reached
similar conclusions, despite their very different approaches: Higgs' paper
essentially used classical techniques, Englert and Brout's involved calculating
vacuum polarisation in perturbation theory around an assumed symmetry-breaking
vacuum state, and GHK used operator formalism and conservation laws to explore
in depth the ways in which Goldstone's theorem may be worked around.[55] Some versions of the
theory predicted more than one kind of Higgs fields and bosons, and alternative "Higgsless" models were
considered until the discovery of the Higgs boson.
Discovery of candidate boson at CERN
On 4 July 2012 both of the CERN
experiments announced they had independently made the same discovery:[114] CMS of a previously unknown
boson with mass 125.3 ± 0.6 GeV/c2[115][116] and ATLAS of a boson with mass
126.0 ± 0.6 GeV/c2.[117][118] Using the combined analysis of
two interaction types (known as 'channels'), both experiments independently
reached a local significance of 5 sigma – implying that the probability of
getting at least as strong a result by chance alone is less than 1 in 3
million. When additional channels were taken into account, the CMS significance
was reduced to 4.9 sigma.[116]On 22 June 2012 CERN announced an
upcoming seminar covering tentative findings for 2012,[105][106] and shortly
afterwards (from around 1 July 2012 according to an analysis of the spreading
rumour in social media[107]) rumours began to spread
in the media that this would include a major announcement, but it was unclear
whether this would be a stronger signal or a formal discovery.[108][109] Speculation
escalated to a "fevered" pitch when reports emerged that Peter Higgs, who proposed the
particle, was to be attending the seminar,[110][111] and that "five
leading physicists" had been invited – generally believed to signify
the five living 1964 authors – with Higgs, Englert, Guralnik, Hagen
attending and Kibble confirming his invitation (Brout having died in 2011).[112][113]
The two teams had been
working 'blinded' from each other from around late 2011 or early 2012,[99]meaning they did not
discuss their results with each other, providing additional certainty that any
common finding was genuine validation of a particle.[88] This level of
evidence, confirmed independently by two separate teams and experiments, meets
the formal level of proof required to announce a confirmed discovery.
On
31 July 2012, the ATLAS collaboration presented additional data analysis on the
"observation of a new particle", including data from a third channel,
which improved the significance to 5.9 sigma (1 in 588 million chance of
obtaining at least as strong evidence by random background effects alone) and
mass 126.0 ± 0.4 (stat) ± 0.4
(sys) GeV/c2,[118] and CMS improved
the significance to 5-sigma and mass 125.3 ± 0.4 (stat) ± 0.5 (sys)
GeV/c2.[115]
The new particle tested as a possible
Higgs boson
Following the 2012
discovery, it was still unconfirmed whether or not the 125 GeV/c2 particle
was a Higgs boson. On one hand, observations remained consistent with the
observed particle being the Standard Model Higgs boson, and the particle
decayed into at least some of the predicted channels. Moreover, the production
rates and branching ratios for the observed channels broadly matched the
predictions by the Standard Model within the experimental uncertainties.
However, the experimental uncertainties currently still left room for
alternative explanations, meaning an announcement of the discovery of a Higgs
boson would have been premature.[119] To allow more
opportunity for data collection, the LHC's proposed 2012 shutdown and 2013–14
upgrade were postponed by 7 weeks into 2013.[120]
In
November 2012, in a conference in Kyoto researchers said evidence gathered
since July was falling into line with the basic Standard Model more than its
alternatives, with a range of results for several interactions matching that
theory's predictions.[121] Physicist Matt
Strassler highlighted "considerable" evidence that the new particle
is not a pseudoscalar negative parity particle
(consistent with this required finding for a Higgs boson),
"evaporation" or lack of increased significance for previous hints of
non-Standard Model findings, expected Standard Model interactions with W and Z bosons, absence of
"significant new implications" for or against supersymmetry, and in general
no significant deviations to date from the results expected of a Standard Model
Higgs boson.[122] However some kinds
of extensions to the Standard Model would also show very similar results;[123] so commentators
noted that based on other particles that are still being understood long after
their discovery, it may take years to be sure, and decades to fully understand
the particle that has been found.[121][122]
These
findings meant that as of January 2013, scientists were very sure they had
found an unknown particle of mass ~ 125 GeV/c2, and had not been
misled by experimental error or a chance result. They were also sure, from
initial observations, that the new particle was some kind of boson. The
behaviours and properties of the particle, so far as examined since July 2012,
also seemed quite close to the behaviours expected of a Higgs boson. Even so,
it could still have been a Higgs boson or some other unknown boson, since
future tests could show behaviours that do not match a Higgs boson, so as of
December 2012 CERN still only stated that the new particle was "consistent
with" the Higgs boson,[21][23] and scientists did
not yet positively say it was the Higgs boson.[124] Despite this, in
late 2012, widespread media reports announced (incorrectly) that a Higgs boson
had been confirmed during the year.[o]
In January 2013, CERN director-general Rolf-Dieter Heuer stated
that based on data analysis to date, an answer could be possible 'towards'
mid-2013,[130] and the deputy chair
of physics at Brookhaven National Laboratory stated
in February 2013 that a "definitive" answer might require
"another few years" after the collider's 2015 restart.[131] In early March 2013, CERN Research
Director Sergio Bertolucci stated that confirming spin-0 was the major
remaining requirement to determine whether the particle is at least some kind
of Higgs boson.[132]
Confirmation of existence and current
status
On 14 March 2013 CERN confirmed that:
"CMS and ATLAS have compared a
number of options for the spin-parity of this particle, and these all prefer no
spin and even parity [two fundamental criteria of a Higgs boson consistent with
the Standard Model]. This, coupled with the measured interactions of the new
particle with other particles, strongly indicates that it is a Higgs boson."[6]
This also makes the particle the
first elementary scalar particle to be
discovered in nature.[24]
Examples of tests used to validate
that the discovered particle is the Higgs boson:[122][133]
|
Requirement |
How tested / explanation |
Current status (As of
July 2017) |
|
Zero spin |
Examining
decay patterns. Spin-1 had been ruled out at the time of initial discovery by
the observed decay to two photons (γ γ), leaving spin-0 and spin-2
as remaining candidates. |
Spin-0
confirmed.[7][6][134][135] The
spin-2 hypothesis is excluded with a confidence level exceeding 99.9%.[135] |
|
Even
(Positive) parity |
Studying
the angles at which decay products fly apart. Negative parity was also
disfavoured if spin-0 was confirmed.[136] |
Even
parity tentatively confirmed.[6][134][135] The
spin-0 negative parity hypothesis is excluded with a confidence level
exceeding 99.9%.[134][7] |
|
Decay channels (outcomes
of particle decaying) are as predicted |
The
Standard Model predicts the decay patterns of a 125 GeV Higgs boson. Are
these all being seen, and at the right rates? Particularly
significant, we should observe decays into pairs of photons (γ
γ), W and Z bosons (WW
and ZZ), bottom quarks (bb),
and tau leptons (τ
τ), among the possible outcomes. |
bb,
γ γ, τ τ, WW and ZZ observed. All observed signal strengths are
consistent with the Standard Model prediction.[137][1] |
|
Couples to mass (i.e., strength of interaction with Standard Model particles
proportional to their mass) |
Particle
physicist Adam Falkowski states that the essential qualities of a Higgs boson
are that it is a spin-0 (scalar) particle which also couples
to mass (W and Z bosons); proving spin-0 alone is insufficient.[133] |
Couplings
to mass strongly evidenced ("At 95% confidence level cV is within
15% of the standard model value cV=1").[133] |
|
Higher
energy results remain consistent |
After
the LHC's 2015 restart at the higher energy of 13 TeV, searches for multiple Higgs
particles (as predicted in some theories) and tests targeting other versions
of particle theory continued. These higher energy results must continue to
give results consistent with Higgs theories. |
Analysis
of collisions up to July 2017 do not show deviations from the Standard Model,
with experimental precisions better than results at lower energies.[1] |
The Big Bang theory is the prevailing
cosmological model for the universe from the earliest known periods through its
subsequent large-scale evolution. Wikipedia
CERN
(Courtesy of Wikipedia, Encyclopedia).
Coordinates:
|
European Organization |
|
|
CERN's main site, from Switzerland looking towards France |
|
|
Member states |
|
|
Formation |
September 29,
1954; 64 years ago[1] |
|
Headquarters |
|
|
Membership |
22 countries[show] |
|
Official languages |
|
|
Council President |
Sijbrand
de Jong[2] |
|
Website |
|
The European Organization for Nuclear
Research (French: Organisation européenne pour la recherche nucléaire), known as CERN (/sɜːrn/; French pronunciation: [sɛʁn];
derived from the name Conseil européen pour la recherche nucléaire),
is a European research organization that operates the largest particle physics laboratory in the world. Established in
1954, the organization is based in a northwest suburb of Geneva on the Franco–Swiss border, and has 22 member states.[3] Israel is the only non-European country granted full
membership.[4] CERN is an official United Nations Observer.[5]
The acronym CERN is also used to refer to the laboratory,
which in 2016 had 2,500 scientific, technical, and administrative staff
members, and hosted about 12,000 users. In the same year, CERN generated 49 petabytes of data.[6]
CERN's main function is to provide the particle accelerators and other infrastructure needed
for high-energy physics research – as a result, numerous experiments have been
constructed at CERN through international collaborations. The main site at Meyrin hosts a large computing facility, which is
primarily used to store and analyse data from experiments, as well as simulate events. Researchers need remote access to these facilities,
so the lab has historically been a major wide area network hub. CERN is also the birthplace of
the World Wide Web.[7][8]
|
CERN's main site, from Switzerland looking towards France |
|
|
Member states |
|
|
Formation |
September 29,
1954; 64 years ago[1] |
|
Headquarters |
|
|
Membership |
22 countries. |
|
Official
languages |
|
|
Council
President |
Sijbrand de Jong[2] |
|
Website |
|
The 12 founding member states of CERN in 1954[1] (map borders from 1954–1990)
The convention establishing CERN was
ratified on 29 September 1954 by 12 countries in Western Europe.[1] The acronym CERN originally represented the French
words for Conseil Européen pour la Recherche Nucléaire (European
Council for Nuclear Research), which was a provisional council for building the
laboratory, established by 12 European governments in 1952. The acronym was
retained for the new laboratory after the provisional council was dissolved,
even though the name changed to the current Organisation Européenne
pour la Recherche Nucléaire (European Organization for Nuclear
Research) in 1954.
CERN's first president was Sir Benjamin Lockspeiser. Edoardo Amaldi was the general secretary of CERN at its
early stages when operations were still provisional, while the first
Director-General (1954) was Felix Bloch.[10]
The laboratory was originally devoted
to the study of atomic nuclei, but was soon applied to higher-energy physics, concerned mainly with the study of
interactions between subatomic particles. Therefore, the laboratory operated by
CERN is commonly referred to as the European laboratory for
particle physics (Laboratoire européen pour
la physique des particules), which better describes the research being
performed there.
Scientific
achievements
Several important achievements in particle physics have
been made through experiments at CERN. They include:
· 1973:
The discovery of neutral currents in the Gargamelle bubble chamber;[12]
· 1983:
The discovery of W and Z bosons in the UA1 and UA2 experiments;[13]
· 1989:
The determination of the number of light neutrino families at the Large Electron–Positron Collider (LEP) operating on the
Z boson peak;
· 1995:
The first creation of antihydrogen atoms in the PS210 experiment;[14]
· 1999:
The discovery of direct CP violation in the NA48 experiment;[15]
· 2010:
The isolation of 38 atoms of antihydrogen;[16]
· 2011:
Maintaining antihydrogen for over 15 minutes;[17]
· 2012:
A boson with mass around 125 GeV/c2 consistent with
the long-sought Higgs boson.[18]
In September 2011, CERN attracted
media attention when the OPERA Collaboration reported the detection of possibly faster-than-light neutrinos.[19] Further tests showed that the results were flawed
due to an incorrectly connected GPS synchronization cable.[20]
The 1984 Nobel Prize for Physics was awarded to Carlo Rubbia and Simon van der Meer for the developments that resulted in
the discoveries of the W and Z bosons. The 1992 Nobel Prize for Physics was
awarded to CERN staff researcher Georges Charpak "for his invention and development
of particle detectors, in particular the multiwire proportional chamber". The 2013 Nobel Prize
for physics was awarded to François Englert and Peter Higgs for the theoretical description of the Higgs
mechanism in the year after the Higgs boson was found by CERN experiments.
Computer science
History of the World Wide Web (www.com)
This NeXT Computer used by British scientistSir Tim Berners-Lee at CERN became the firstWeb server.
This Cisco Systems router at CERN was one of the first IP routers deployed in Europe.
A plaque at CERN commemorating the invention of the World Wide Web by Tim Berners-Lee andRobert Cailliau
The World Wide Web began as a CERN project namedENQUIRE, initiated by Tim Berners-Lee in 1989 and Robert Cailliau in 1990.[21] Berners-Lee and Cailliau were jointly honoured by
the Association for Computing Machinery in 1995 for their
contributions to the development of the World Wide Web.
Based on the concept of hypertext, the project was intended to facilitate the sharing
of information between researchers. The first website was activated in 1991. On
30 April 1993, CERN announced that the World Wide Web would be free to
anyone. A copy[22] of the original first webpage, created by Berners-Lee, is still
published on the World Wide Web Consortium's website as a historical document.
Prior to the Web's development, CERN
had pioneered the introduction of Internet technology, beginning in the early
1980s.[23]
More recently, CERN has become a
facility for the development of grid computing, hosting projects including the Enabling Grids for E-sciencE (EGEE) and LHC Computing Grid. It also hosts the CERN Internet Exchange Point (CIXP), one of the two main internet exchange points in Switzerland.
Particle
accelerators
|
CERN accelerator complex |
|
|
List of current particle |
|
|
Accelerates protons |
|
|
Accelerates ions |
|
|
Accelerates
negative hydrogen ions |
|
|
Decelerates antiprotons |
|
|
Collides protons
or heavy ions |
|
|
Accelerates ions |
|
|
Accelerates
protons or ions |
|
|
Accelerates
protons or ions |
|
|
Accelerates
protons or ions |
|
Map of the Large Hadron Collidertogether with the Super Proton Synchrotron at CERN.
CERN operates
a network of six accelerators and a decelerator. Each machine in the chain
increases the energy of particle beams before delivering them to experiments or
to the next more powerful accelerator. Currently active machines are:
· Two linear accelerators generate low energy particles. LINAC 2 accelerates protons to 50 MeV for injection into the Proton Synchrotron Booster
(PSB), and LINAC 3 provides heavy ions at 4.2 MeV/u for injection into the Low Energy Ion Ring (LEIR).[24]
· The Proton Synchrotron Booster increases the energy of
particles generated by the proton linear accelerator before they are transferred
to the other accelerators.
· The Low Energy Ion Ring (LEIR) accelerates the ions from the
ion linear accelerator, before transferring them to the Proton Synchrotron(PS). This accelerator was commissioned in 2005, after having been
reconfigured from the previous Low Energy Antiproton Ring(LEAR).
·
· The
28 GeV Proton Synchrotron (PS), built during 1954—1959 and
still operating as a feeder to the more powerful SPS.
· The Super Proton Synchrotron (SPS), a circular accelerator
with a diameter of 2 kilometres built in a tunnel, which started operation in
1976. It was designed to deliver an energy of 300 GeV and was gradually
upgraded to 450 GeV. As well as having its own beamlines for fixed-target
experiments (currently COMPASS and NA62), it has been operated as a proton–antiproton collider (the SppS collider), and for accelerating high
energy electrons and positrons which were injected into the Large Electron–Positron Collider (LEP). Since 2008, it
has been used to inject protons and heavy ions into the Large Hadron Collider (LHC).
· The On-Line Isotope Mass Separator (ISOLDE), which is used
to study unstable nuclei. The radioactive ions are produced by the
impact of protons at an energy of 1.0–1.4 GeV from the Proton Synchrotron
Booster. It was first commissioned in 1967 and was rebuilt with major upgrades
in 1974 and 1992.
· The Antiproton Decelerator (AD), which reduces the velocity
of antiprotons to about 10% of the speed of light for research of antimatter.
· The Compact Linear Collider Test Facility, which studies
feasibility for the future normal conducting linear collider project.
· The AWAKE experiment, which is a proof-of-principle plasma wakefield accelerator.
Large Hadron Collider
Many activities at CERN currently involve operating the Large Hadron Collider (LHC) and the experiments for it.
The LHC represents a large-scale, worldwide scientific cooperation project.
Construction of the CMSdetector for LHC at CERN.
The LHC tunnel is located 100 metres
underground, in the region between the Geneva International Airport and the nearby Jura mountains. The majority of its length is on the French
side of the border. It uses the 27 km circumference circular tunnel
previously occupied by the Large Electron–Positron Collider (LEP), which was shut
down in November 2000. CERN's existing PS/SPS accelerator complexes are used to
pre-accelerate protons and lead ions which are then injected into the LHC.
Seven experiments (CMS, ATLAS, LHCb, MoEDAL,[25] TOTEM, LHC-forward and ALICE) are located along the collider; each of them studies
particle collisions from a different aspect, and with different technologies.
Construction for these experiments required an extraordinary engineering
effort. For example, a special crane was rented from Belgium to lower pieces of the CMS
detector into its underground cavern, since each piece weighed nearly 2,000
tons. The first of the approximately 5,000 magnets necessary for construction
was lowered down a special shaft at 13:00 GMT on 7 March 2005.
The LHC has begun to generate vast
quantities of data, which CERN streams
to laboratories around the world for distributed processing (making use of a
specialized grid infrastructure, the LHC Computing Grid). During April 2005, a trial successfully
streamed 600 MB/s to seven different sites across the world.
The initial particle beams were
injected into the LHC August 2008.[26] The first beam was circulated through the entire
LHC on 10 September 2008,[27] but the system failed 10 days later because of a
faulty magnet connection, and it was stopped for repairs on 19 September 2008.
The LHC resumed operation on 20 November
2009 by successfully circulating two beams, each with an energy of 3.5 teraelectronvolts (TeV). The challenge for the engineers was
then to try to line up the two beams so that they smashed into each other. This
is like "firing two needles across the Atlantic and getting them to hit
each other" according to Steve Myers, director for accelerators and
technology.
On 30 March 2010, the LHC successfully
collided two proton beams with 3.5 TeV of energy per proton, resulting in a 7
TeV collision energy. However, this was just the start of what was needed for
the expected discovery of the Higgs boson. When the 7 TeV experimental period ended, the
LHC revved to 8 TeV (4 TeV per proton) starting March 2012, and soon began
particle collisions at that energy. In July 2012, CERN scientists announced the
discovery of a new sub-atomic particle that was later confirmed to be the Higgs boson.[28] In March 2013, CERN announced that the measurements
performed on the newly found particle allowed it to conclude that this is a
Higgs boson.[29] In early 2013, the LHC was deactivated for a
two-year maintenance period, to strengthen the electrical connections between
magnets inside the accelerator and for other upgrades.
On 5 April 2015, after two years of
maintenance and consolidation, the LHC restarted for a second run. The first
ramp to the record-breaking energy of 6.5 TeV was performed on 10 April 2015.[30][31] In 2016, the design collision rate was exceeded for
the first time.[32] A second two-year period of shutdown is scheduled
to begin at the end of 2018.
Enlargement
Associate Members, Candidates:
· Serbia became a candidate
for accession to CERN on 19 December 2011, signed an association agreement on
10 January 2012 [54][55] and became an associate member in the pre-stage to
membership on 15 March 2012.[45]
· Turkey signed an
association agreement on 12 May 2014 [56] and became an associate member on 6 May 2015.
· Pakistan signed an
association agreement on 19 December 2014 [57] and became an associate member on 31 July 2015.[58][59]
· Cyprus signed an
association agreement on 5 October 2012 and became an associate Member in the
pre-stage to membership on 1 April 2016. [46]
· Ukraine signed an
association agreement on 3 October 2013. The agreement was ratified on 5
October 2016. [51]
· India signed an association
agreement on 21 November 2016. [60] The agreement was ratified on 16 January 2017.[52]
· Slovenia was approved for
admission as an Associate Member state in the pre-stage to membership on 16
December 2016. [47] The agreement was ratified on 4 July 2017.[48]
· Lithuania was approved for
admission as an Associate Member state on 16 June 2017. The association agreement
was signed on 27 June 2017 and ratified on 8 January 2018. [61][53]
International
relations
Three countries have observer status:[62]
· Japan – since 1995
· Russia – since 1993
· United States – since 1997
Also observers are the following
international organizations:
· UNESCO – since 1954
· European Commission – since
1985
· JINR - since 2014
Non-Member States (with dates of
Co-operation Agreements) currently involved in CERN programmes are:[63]
· Albania
· Algeria
· Argentina – 11 March 1992
· Armenia – 25 March 1994
· Australia – 1 November 1991
· Azerbaijan – 3 December 1997
· Bangladesh
· Belarus – 28 June 1994
· Bolivia
· Brazil – 19 February 1990
& October 2006
· Canada – 11 October 1996
· Chile – 10 October 1991
· China – 12 July 1991, 14
August 1997 & 17 February 2004
· Colombia – 15 May 1993
· Croatia – 18 July 1991
· Ecuador
· Egypt – 16 January 2006
· Estonia – 23 April 1996
· Georgia – 11 October 1996
· Iceland – 11 September 1996
· Iran – 5 July 2001
· Jordan - 12 June 2003. [64] MoU with Jordan and SESAME, in preparation of a cooperation agreement signed in
2004.[65]
· Lithuania – 9 November 2004
· Macedonia – 27 April 2009
· Malta – 10 January 2008 [66][67]
· Mexico – 20 February 1998
· Mongolia
· Montenegro – 12 October 1990
· Morocco – 14 April 1997
· New Zealand – 4 December
2003
· Peru – 23 February 1993
· Saudi Arabia – 21 January
2006
· South Africa – 4 July 1992
· South Korea – 25 October
2006
· United Arab Emirates – 18
January 2006
· Vietnam
CERN also has
scientific contacts with the following countries:[63]
· Cuba
· Ghana
· Ireland
· Latvia
· Lebanon
· Madagascar
· Malaysia
· Mozambique
· Palestine
· Philippines
· Qatar
· Rwanda
· Singapore
· Sri Lanka
· Taiwan
· Thailand
· Tunisia
· Uzbekistan
International research institutions,
such as CERN, can aid in science diplomacy.[68]
Associated
institutions
· European Southern Observatory
· Swiss National Supercomputing Centre
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