Saturday, November 29, 2008

What good do blogs do to the Physicists?

Blogging may be regarded as self-publicity. Is it that much or is there something beyond this too? Here is a short-nice-analysis from, which says 'Blogs add a new dimension to physics'.

Friday, November 28, 2008

Without Quantum Mechanics, ...?

What would happen if there did not exist QUANTUM MECHANICS? Here is an ANSWER (please see the page-4 of the document in the link):

Wednesday, November 26, 2008

Blogs on PHYSICS !

I had no idea that there exist so many blogs on academic fields. I Googled this morning and was astonished to find that there exist so many physics-related blogs too ! Please click on the following link to find some of them.

Tuesday, November 25, 2008

Quantum Tunneling - No Classical Analogue !

Consider a quantum particle with energy less than the potential energy barrier (that binds the particle) lying in a potential well. Is there any probability of finding the particle outside the well? Classically - NO ! The particle is always trapped by the potential and there is no chance for the particle to come out of the trap. If that is the case, there should be no chance of coming out of the alpha particle from a heavy atomic nucleus as they are bound by a strong potential barrier. George Gamow gave the theory of ALPHA DECAY saying that the alpha particles come out of the nucleus by a Quantum Phenomenon called the Tunneling. Therefore, a quantum mechanical particle trapped by a potential barrier can show up outside the barrier too ! - This is a phenomenon that can be explained ONLY by quantum mechanics !
There are broad range of phenomena of this kind that we can observe in nature everyday ! Here is a nice youtube video to explain this phenomenon:

Sunday, November 23, 2008

What is the Quantum Theory of Radiation?

The advent of the twentieth century brought a lot of exciting discoveries in the world of Physics. The dawn of the breakthroughs was from the quantum theory of radiation by Max Planck in around 1900. A hot body radiates or absorbs energy in the form of packets called quanta; the radiation or absorption is not continuous but in discrete units. Each quantum carries an energy given by the product of a constant h ( the Planck's constant) and f (the frequency of the radiation). The value of h = 6.63x10^-34 J s. Albert Einstein in 1905 wrote a famous paper on the theory of photoelectric effect applying the quantum theory of radiation, which earned him the 1921 Nobel Prize in Physics. In fact, the Quantum theory of radiation is a kind of start of a new physics - Quantum Physics !

What is a wave function?

A wave function is a mathematical tool to represent a physical system. It is usually denoted by the letter psi. It is usually complex, meaning- it has a real part and an imaginary part. It is usually a function of coordinate and time. If it is only a function of coordinate, the wave function is independent of time. A physical system is completely described quantum mechanically if its amplitude and phase at any time are known. Therefore, a wave function should consist of these two information - an amplitude and the phase. Once a well-defined wave function is assigned to a physical system, a complete information related to the system can be drawn easily. For example, the modulus squared of the wave function gives the probability density - meaning the probability of finding a particle per unit volume. If this quantity is integrated in the overall space, the result will be '1', which means that the particle is somewhere in that space. A wave function is the fundamental tool for a quantum physicists ! NO wave function -NO Qunatum Physics !

Thursday, November 20, 2008

What is SPIN?

SPIN is a special kind of angular momentum of some fundamental particles like protons, electrons and neutrons which does NOT have a classical analogue. Can we visualize the quantum mechanical spin like the spin of a rotating top in everyday life? NO ! To see this, consider an electron with uniform spherical charge distribution so that it rotates about its axis like the earth. If we calculate the rotating speed of the electron using classical electrodynamics, the speed comes to be equal to several times bigger than the speed of light, which is not possible as we know that no physical entity can have speed greater than the speed of light. Moreover, the spin of a quantum mechanical particle is a half , which is not compatible with the notion of spin in classical mechanics.
Therefore, spin exists in nature; it is always there. It can be measured, but it is different, not like the spin of a spinning top. It is purely quantum mechanical !

Sunday, November 16, 2008

When You're a KET !

Paul Dirac, a famous quantum physicist, introduced in 1930 a unique notation called a 'KET' to represent the state of a quantum system . To define a scalar product, there is another notation, called a 'BRA', so that we can define a scalar product 'BRA-KET', which gives a number. This notation greatly simplified the mathematical development of Quantum Mechanics.

What happens WHEN YOU'RE A KET? Please sing the song When You're a Ket by Prof. Paul Halpern in the following link:

Thursday, November 6, 2008

Milky Way to Quarks : Powers of TEN

If we start from viewing the Milky Way at 10 million light years from the Earth and go down by a factor of 10^-1 ( a tenth), how does the world look like in each step? Here is a very nicely programmed Java applet to answer this question. Please read the caption, while viewing the slides.

This is a quick view of a VERY BIG to a VERY SMALL world !

Sunday, November 2, 2008

Heisenberg Uncertainty Principle !

In Quantum Mechanics, nothing is certain, but probabilistic. This means that you can just say that the chance of finding a particle in a particular region of space is p% (p<100). p =" 100" p =" 0," style="color: rgb(0, 153, 0);"> Heisenberg Uncertainty Principle. According to this principle, the uncertainties of the conjugate quantities are related by the formula - delta(P)*delta(Q) greater than or equal to h divided by 4*pi, where h = 6.63*10^-34 Js is called the Planck's constant and pi = 3.1416. In this formula, delta(P) is the uncertainty of measurement in the quantity P and delta(Q) is the uncertainty of measurement in the quantity Q. This means if you measure the quantity P more accurately, the measurement of the quantity Q will be less accurate. For example, if we are making the measurements of the position and the momentum of a particle, the more accurately we measure the position, the more inaccurate or uncertain will be the momentum, always giving the product of the two uncertainties greater than or equal to h divided by 4*pi.

The following YOUTUBE video gives a nice explanation of the Heisenberg Uncertainty Principle: