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2Physics Quote:
"Can photons in vacuum interact? The answer is not, since the vacuum is a linear medium where electromagnetic excitations and waves simply sum up, crossing themselves with no interaction. There exist a plenty of nonlinear media where the propagation features depend on the concentration of the waves or particles themselves. For example travelling photons in a nonlinear optical medium modify their structures during the propagation, attracting or repelling each other depending on the focusing or defocusing properties of the medium, and giving rise to self-sustained preserving profiles such as space and time solitons or rapidly rising fronts such as shock waves." -- Lorenzo Dominici, Mikhail Petrov, Michal Matuszewski, Dario Ballarini, Milena De Giorgi, David Colas, Emiliano Cancellieri, Blanca Silva Fernández, Alberto Bramati, Giuseppe Gigli, Alexei Kavokin, Fabrice Laussy, Daniele Sanvitto. (Read Full Article: "The Real-Space Collapse of a Two Dimensional Polariton Gas" )

Tuesday, February 15, 2005

The Shortest Sentence to Describe the Universe

"Four interactions among Leptons and Quarks"

That is the shortest sentence to describe all phenomenon in this
universe [Based on our current knowledge].

There are just 4 types of fundamental forces in nature. We can
present those here in increasing order of their relative strength:

(In the following, say, 10^40 means you need to put 40 zeros
after 1 to get that number)

Gravitational Force [Relative Strength: 1 ]
(That acts among all massive bodies including heavenly ones)
Weak Nuclear Force [Relative Strength: 10^29 ]
(This acts inside the nucleus of radioactive atoms, like Uranium)
Electromagnetic Force [Relative Strength: 10^40 ]
(Electric Motors and generators and lightning
are manifestations of this)
Strong Nuclear Force [Relative Strength: 10^43 ]
(This acts inside the nucleus of all stable atoms and acts among
neutrons and protons)

Note that 'strength' depends on the nature of the source of that
interaction and how far away your reference point is. So, sometimes
in other sources, you may find different numbers from the above.
But the numbers quoted here may give you an idea.

We'll describe these forces one by one more in our next postings.
But wait ... what are leptons and quarks? We'll slowly get into
those too. For the time being ... think that all matter in this
universe are made of two kinds of elementary particles: leptons
(example: electron) and Hadrons (like protons, neutrons). These
Hadrons are basically confined states of more elementary particles
called Quarks.

We know... we know... you need more and clearer explanation of
all these topics. Yes we'll do that. This is just an exposure of a few
essential information. You may not understand everything now
... but be with us.. and for the time being .. just get exposed to
some information ... and slowly you'll see a pattern is coming up in
your mind ... and before you know ... you'll find that your way of
looking at the sky and your surrounding has changed ...


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