PARTICLE PHYSICS

PARTICLE PHYSICS
FUNDAMENTAL PARTICLES

शुक्रवार, 27 नवंबर 2015

How the Big Bang Theory Works ?

For centuries, humans have gazed at the stars and wondered how the universe developed into what it is today. It's been the subject of religious, philosophical, and scientific discussion and debate. People who have tried to uncover the mysteries of the universe's development include such famous scientists as Albert Einstein, Edwin Hubble and Stephen Hawking. One of the most famous and widely accepted models for the universe's development is the big bang theory.
Although the big bang theory is famous, it's also widely misunderstood. A common misperception about the theory is that it describes the origin of the universe. That's not quite right. The big bang is an attempt to explain how the universe developed from a very tiny, dense state into what it is today. It doesn't attempt to explain what initiated the creation of the universe, or what came before the big bang or even what lies outside the universe.
Another misconception is that the big bang was a kind of explosion. That's not accurate either. The big bang describes the expansion of the universe. While some versions of the theory refer to an incredibly rapid expansion (possibly faster than the speed of light), it's still not an explosion in the classic sense.
Summing up the big bang theory is a challenge. It involves concepts that contradict the way we perceive the world. The earliest stages of the big bang focus on a moment in which all the separate forces of the universe were part of a unified force. The laws of science begin to break down the further back you look. Eventually, you can't make any scientific theories about what is happening, because science itself doesn't apply.
So what's the big bang theory in a nutshell? Find out in the next section.
what is big bang theory science এর চিত্র ফলাফল

                  Particle physics

Particle physics is a branch of physics that studies the elementary constituents of matter and radiation, and the interactions between them.
particle physics এর চিত্র ফলাফল particle physics এর চিত্র ফলাফল
It is also called "high energy physics", because many elementary particles do not occur under normal circumstances in nature, but can be created and detected during energetic collisions of other particles, as is done in particle accelerators.
Modern particle physics research is focused on subatomic particles, which have less structure than atoms.
These include atomic constituents such as electrons, protons, and neutrons (protons and neutrons are actually composite particles, made up of quarks), particles produced by radiative and scattering processes, such as photons, neutrinos, and muons, as well as a wide range of exotic particles.
Strictly speaking, the term particle is a misnomer because the dynamics of particle physics are governed by quantum mechanics.
As such, they exhibit wave-particle duality, displaying particle-like behavior under certain experimental conditions and wave-like behavior in others (more technically they are described by state vectors in a Hilbert space).
All the particles and their interactions observed to date can be described by a quantum field theory called the Standard Model.
The Standard Model has 40 species of elementary particles (24 fermions, 12 vector bosons, and 4 scalars), which can combine to form composite particles, accounting for the hundreds of other species of particles discovered since the 1960s.

Big Bang

According to the Big Bang model, theUniverse expanded from an extremely dense and hot state and continues to expand.
The Big Bang theory is the prevailing cosmological model for the Universefrom the earliest known periods through its subsequent large-scale evolution.[1][2][3] The model accounts for the fact that the Universe expandedfrom a very high density and high temperature state,[4][5] and offers a comprehensive explanation for a broad range of phenomena, including the abundance of light elements, the cosmic microwave background, large scale structure and Hubble's Law.[6] If the known laws of physics are extrapolated beyond where they are valid, there is a singularity. Modern measurements place this moment at approximately 13.8 billion years ago, which is thus considered the age of the Universe.[7] 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 to form stars and galaxies.
Since Georges Lemaître first noted, in 1927, that an expanding Universe might be traced back in time to an originating single point, scientists have built on his idea of cosmic expansion. While the scientific community was once divided between supporters of two different expanding Universe theories, the Big Bang and the Steady State theory, accumulated empirical evidenceprovides strong support for the former.[8] In 1929, from analysis of galacticredshiftsEdwin Hubble concluded that galaxies are drifting apart, important observational evidence consistent with the hypothesis of an expanding Universe. In 1965, the cosmic microwave background radiation was discovered, which was crucial evidence in favor of the Big Bang model, 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.[9] 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.

Overview

History of the Universe - gravitational wavesare hypothesized to arise from cosmic inflation, an expansion just after the Big Bang.
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Hubble observed that the distances to faraway galaxies were strongly correlated with their redshifts. This was interpreted to mean that all distant galaxies and clusters are receding away from our vantage point with an apparent velocity proportional to their distance: that is, the farther they are, the faster they move away from us, regardless of direction.[17] Assuming theCopernican principle (that the Earth is not the center of the Universe), the only remaining interpretation is that all observable regions of the Universe are receding from all others. Since we know that the distance between galaxies increases today, it must mean that in the past galaxies were closer together. The continuous expansion of the Universe implies that the Universe was denser and hotter in the past.
Large particle accelerators can replicate the conditions that prevailed after the early moments of the Universe, resulting in confirmation and refinement of the details of the Big Bang model. However, these accelerators can only probe so far into high energy regimes. Consequently, the state of the Universe in the earliest instants of the Big Bang expansion is still poorly understood and an area of open investigation and indeed, speculation.
The first subatomic particles included protonsneutrons, and electrons. Though simple atomic nuclei formed within the first three minutes after the Big Bang, thousands of years passed before the first electrically neutral atoms formed. The majority of atoms produced by the Big Bang were hydrogen, along with heliumand traces of lithium. Giant clouds of these primordial elements later coalesced through gravity to form stars and galaxies, and the heavier elements were synthesized either within stars or during supernovae.
The Big Bang theory offers a comprehensive explanation for a broad range of observed phenomena, including the abundance of light elements, the cosmic microwave backgroundlarge scale structure, and Hubble's Law.[6] The framework for the Big Bang model relies on Albert Einstein's theory of general relativity and on simplifying assumptions such ashomogeneity and isotropy of space. The governing equations were formulated by Alexander Friedmann, and similar solutions were worked on by Willem de Sitter. Since then, astrophysicists have incorporated observational and theoretical additions into the Big Bang model, and its parametrization as the Lambda-CDM model serves as the framework for current investigations of theoretical cosmology. The Lambda-CDM model is the standard model of Big Bang cosmology, the simplest model that provides a reasonably good account of various observations about the Universe.

What is Kinetic Energy?

Many problems in physics require an application of kinetic energy. Kinetic energy is a form of energy that represents the energy of motion. It is a scalar quantity, which means it has a magnitude but not a direction. It is, therefore, always positive (as will be evident when we see the equation that defines it).

Deriving Kinetic Energy

Kinetic energy is closely linked with the concept of work, which is the scalar product(or dot product) of force and the displacement vector over which the force is applied.
Using some basic kinematics equations, we obtain an equation for the acceleration of an object which changes speed. (In the following equation, the term x - x0 has been replaced by s, a term which represents the total distance of displacement.)
v2 = v02 + 2as
therefore,
a = ( v2 - v02 ) / 2s
Applying Newton's Second Law of MotionF = ma, we get:
F = ma = m ( v2 - v02 ) / 2s
and, multiplying by the distance s (for work) and breaking it apart, we get:
W = Fs = 0.5mv2 - 0.5mv02
 The kinetic energy, K (or sometimes Ek) is, therefore, defined as:
K = 0.5mv2
It should be noted that, as mentioned before, this quantity will always be a non-zeroscalar quantity. If the object has mass and is moving, it will always be positive. It will be zero in the case of a massless object or an object at rest (zero velocity). Thekinetic energy equation, therefore, gives us no information about the direction of the motion, only about the speed.

Work-Energy Theorem

The work-energy theorem comes from the above derivation, and indicates that the work done by an external force on a particle is equal to the change in kinetic energy of the particle. Mathematically, then, you get:
Wtot = K2 - K1 = delta-K

Using Kinetic Energy

In addition to obtaining the work done, the kinetic energy equation is used frequently in conjunction with other forms of energy. Due to the law of conservation of energy,we know that the total energy in a closed system will remain constant. Therefore, analyzing the kinetic energy along with, say, gravitational potential energy allows us to figure out certain factors of the motion. (For an example of this, see the Free Falling Body problem.)

मंगलवार, 24 नवंबर 2015