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Monday, February 09, 2004

Stellamedusa ventana  


"Researchers have discovered a new species of jellyfish so different from its fellow creatures that it merits a new subfamily." Read all about it in Nature

Friday, December 12, 2003

Cold molecules 

"Using a method usually more suitable to billiards than atomic physics, researchers from Sandia National Laboratories and Columbia University have created extremely cold molecules that could be used as the first step in creating Bose-Einstein molecular condensates." in Physlink.com

Tuesday, December 02, 2003

History of the 2.7 K temperature prior to Penzias and Wilson 

I've found an article ( Apeiron 2, 79 (1995)) by A. K. T. Assis and M. C. D. Neves that reveals the history of the prediction of the temperature of the Universe. I'll try to give some main points:

1879 - Stefan found experimentaly that the total bolometric flux of radiation emitted by a black body is proportional to the 4th power of its temperature.

1884 - Boltzmann derived theoretically Stefan's law.

1896 - Guillaume estimated the temperature of "space" to be between 5 K and 6 K. This estimate is restricted to the effect due to stars belonging to our own galaxy.

1924 - Hubble established that the nebulae are stellar systems outside the Milky Way.

1926 - Eddington, also restricting himself to stars belonging to our own galaxy, estimated a temperature of 3.18 K

1928 - R. A. Millikan and Cameron found that the total energy of cosmic rays at the top of the atmosphere was one-tenth of that due to starlight and heat.
They also infered that the major part of the cosmic rays components originated from outside our galaxy.

1928 - Walther Nernst developed the idea of an Universe in a stationary state: " The Universe is in a stationary condition, that is, the present fixed stars cool continually and new ones are being formed".

1929 - Hubble obtained his redshift-distance law

1933 - Regener estimated that the charateristic temperature of the intergalatic space would be 2.8 K.

1937 - Nernst developed his model of a Universe in a stationary state and proposed a tired light explanation of the cosmological redshift.

1938 - Nernst discusses the radiation temperature in the Universe arriving at a temperature in intergalatic space as 0.75 K.

1941 - Herzberg based on the observations made by A. McKellar found a temperature of 2.3 K characterizing the observed degree of excitation of the cyanogen molecules if they were in equilibrium in a heat bath.

1953 - Gamow, using the Big Bang model, predicted that the temperature of the Universe should be 7 K.

1953-1954 - Finlay-Freundlich proposed a tired light model to explain the redshift of solar lines and some anomalous redshifts of several stars, as wel as the cosmological redshift. According to his theory the redshift is proportional to the 4th power of the temperature and inverselly proportional to the length of path traversed through the radiation field. By proposing an alternative to the Doppler interpretation of the cosmological redshift he arrived at 1.9K < T < 6.0K for the temperature of the intergalatic space.

1954 - Max Born discussing Finlay-Freundlich's proposal that this new effect might be due to a photon-photon interaction predicted that the resulting radiation should be of the order of radar waves.

1961 - Gamow in his book The Creation of the Universe predicts a present temperature of the Universe of 50 K.

1965 - Penzias and Wilson discovered the Cosmic Background Radiation using a horn reflector antenna built to study radio astronomy. They found a temperature of 3.5+/- 1.0K observing background radiation at 7.3 cm wavelength.

Friday, November 14, 2003

Want to know more about String Theory? 

For those that want to have a simple view of what String Theory is, go to NOVA and watch the program hosted by Brian Greene, an expert on the subject. You can believe the theory or not, but i'm sure you will be eager to search for more info. The movies are in QuickTime and RealOne format. I'm not sure if those using Linux are able to watch these.

The little things that we sometimes forget ... 

We are all humans (hopefully). And as humans we may forget some small details. Here are some i found importante to revise. I first start to state two "laws".

Weak Law of Action and Reaction (Also known as Newton's 3rd law of motion): the forces that two particles exert on each other are equal and opposite.

Strong Law of Action and Reaction(Central forces): The forces that two particles exert on each other are equal, opposite and lie along the line joining the particles.

Now for the details one must keep in mind (and i'm sure that all of you that do physics have these in mind):

(1) The conservation of the linear momentum of a system of particles is only valid if all internal forces are in agreement with the weak law.

(2) The conservation of the total angular momentum is only valid if all internal forces are in agreement with the strong law, i.e. if internal forces are central forces.

The conditions on external contributions were assumed to be known.

Tuesday, November 11, 2003

The top 30 problems with the Big Bang (featuring the first 10) 

In a work published last year (Apeiron 9, 72 (2002)) Tom van Flandern points out a list of problems with the Big Bang. In order to avoid violation of the copyrights of the article i will just point out the problems and if you are interested in justification i suggest you download the article at Apeiron. The problems that van Flandern points out are:

(1) "Static universe models fit the observational data better than expanding universe models"

(2)"The microwave 'background' makes more sense as the limiting temperature of space heated by starlight than as the remnant of a fireball."

(3)"Element abundance predictions using the Big Bang require too many adjustable parameters to make them work."

(4)"The universe has too much large scale structure (interspersed 'walls' and voids) to form in a time as short as 10-20 billion years."

(5)"The average luminosity of quasars must decrease with time in just the right way so that their average apparent brightness is the same at all redshifts, which is exceedingly unlikely."

(6)"The ages of globular clusters appear older than the universe."

(7)"The local streaming motions of galaxies are too high for a finite universe that is supposed to be everywhere uniform."

(8)"Invisible dark matter of an unknown but non-baryonic nature must be the dominant ingridient of the entire universe."

(9)"The most distant galaxies in the Hubble Deep Field show insufficient evidence of evolution, with some of them having higher redshifts (z=6-7) than the highest-redshift quasars."

(10)"If the open universe we see today is extrapolated back near the beginning the ratio of the actual density of matter in the universe to the critical density must differ from unity by just a part in 10^59. Any larger deviation would result in a universe already collapsed on itself or already dissipated."

Monday, November 10, 2003

Big Bang or Big Fantasy? 

In this blog you can find a minipoll about the Big Bang. Please state your opinion. The subject will be dealt with in the near future. Thanks! :)

Wednesday, November 05, 2003

The influence of disclinations in crystals 

"There is a class of topological defects analogous to twist and bend distortions ... that involve rotations of the lattice..."; they "...are called disclinations." These topological defects "...are energetically very costly and accur only under special circumstances in the solid phase."

Nonetheless, they "... play a very important role in determining the strength of materials."

" Freely mobile dislocations reduce the strength of a material. To make a material strong, one needs either to reduce the density of disclinations or inhibit dislocation motion. This can be accomplished by pinning dislocations to impurity sites or by putting in so many dislocations that they inhibit each other's motion. The latter process is called work hardening."