July 4th Bang
Topic: Physics
So remember the Comet Crater Contest? Well yesterday Deep Impact collided with Comet Temple 1 and hopefully soon we'll have a look at the inside of a comet!

Follow this link to NASA's Jet Propulsion Laboratory to see pics and movies of the big event.

Stellar Collision
Topic: Physics
New data from NASA's Goddard Space Flight Center indicates that the two white dwarfs, of the double star system RX J0806, are set to collide in the distant future. These stars rotate around each other every 5.4 mins and are separated by about 50 000 miles. Since the observers measured that the rotational speed is increasing by 1.2 millisecs every year, this would imply that the two objects are approaching each other at a rate of one inch every hour.

This event will be one of the prime focuses of LISA (Laser Interferometer Space Antenna), which will be launched in 2012. This space probe will be able to detect and measure gravitational waves imparted by colliding and collapsing stars - these waves being predicted by Einstein's General Theory of Gravity.

Article from Space.com.

The Pioneer Anomaly
Topic: Physics
Apparently this is an old issue, but it remains unresolved. There is a small unexplained force experienced by all space probes launched from earth (like Pioneer 10 - left). From a January edition of Physics Web:

Indeed, the spacecraft move as if they were subject to a new, unknown force pointing towards the Sun. This force imparts the same constant acceleration, ap, of about 10^-7 cm s^-2 to all three spacecraft, about ten orders of magnitude less than the free-fall acceleration on Earth. Such a finding, if it were not explained away by some mundane effect, would be a major break with accepted physics.

Are these cracks in the mighty edifices of General Relativity or perhaps even the Standard Model?

So how can this tiny extra force be explained?

Some theories are covered in a more recent Physics Web article. These include the effects of "dark matter", a modification of general relativity, and forces that may be explained by string theory. From the second article:

String theory and/or supersymmetry, for example, involve higher dimensions of space that introduce new degrees of freedom and possible violations of space-time symmetries such as Lorentz symmetry. This could result in very weak forces that act on the scale of the solar system, although different theories make different predictions of the precise corrections to the spacecraft trajectories.


Another more mundane theory as reported in the New Scientist is that there is another unseen object out there tugging Pioneer 10 off course.

This "Pioneer Anomaly" is such an important issue that conferences have been held to figure out what's going on.

Recent article by the Planetary Society.

Images from our Galaxy
Topic: Physics
So in the latest Nature there are nice time lapses of dust devils taken by by NASA's Mars rovers. In addition the European Southern Observatory group has a neat image of a newly discovered planet (the first ever directly photographed?). For more info visit Bil's blog.

Speaking of our Galaxy, just saw Hitchhiker's Guide to the Galaxy ... and well ... it missed the mark. The spirit of Douglass Adam's books (and radio series, TV series, RPG and website ...), is that of a zany adventure taken by witty intellectual characters that caricature all the little activities of daily life. Into this mix, the movie throws in a love romance that basically kills the Monty Pythonesque aspect of the stories. Oh well at least their conception of Deep Thought (right) was kind of cool.

Comet Crater Contest
Topic: Physics

On July 4th, the NASA probe Deep Impact will land (... or more precisely crash ...) on to Comet Temple 1 (see image on the left) in order to investigate the size, shape and composition of this 8-mile-long extra-planetary object.

How big will the impact crater be? Well you can enter your best guess in the Planetary Society's contest ... the Great Comet Crater Contest.

The latest from the Planetary Society.

Quantum Mechanics, Relativity & The Uncertainty Principle
Topic: Physics
Well this year is the 100 anniversary of the publication of Einstein's two greatest ideas ...

The photoelectric effect, where he described how photons are energy in quantum (little packet) form.

And relativity, which states that the speed of light is a constant irrespective of your frame of reference. A big consequence of this assumption is that time, size and mass vary with each frame of reference.

Besides atoms and photons, one outcome of quantum theory (aka quantum mechanics) is the uncertainty principal (see Heisenberg), which sets a limit to the accuracy of our measurements. Bellow this limit our knowledge of the position and momentum of a single entity is defined by probability. In fact the act of measuring position obliterates our knowledge of momentum and vice versa.

This interference of the observer was very disconcerting to Einstein. He spent a great deal of his career trying to disprove quantum mechanics. At an annual conference of leading physicist, Einstein would challenge the proponents of quantum mechanics with a problem that would potentially reveal a flaw in the theory. Bohr and company each year solved the problem except once in 1935. This was the famous Einstein-Podolsky-Rosen (EPR) paradox.

Here's an abridged version of their thought experiment ...

Imagine there is one particle that decays into two daughter particles. These two daughter particles must have opposite parameters (spin state, velocity etc ...). Now the two particles are traveling in opposite directions at the speed of light. If you were to measure one variable (say the spin in the X axis) by symmetry the second particle must have the opposite spin in that axis. Now the tricky part. If one was to measure another variable of the second particle (say the y axis spin) you would know two variables (in this example the x and y spins) for each particle. This violates one formulation of the uncertainty principle.

Years later the experiment was performed and guess what? You can never measure the properties of the second particle! This phenomena, known as entanglement, is one of the weirdest aspects of reality ever documented. The act of measuring one particle can affect whether a second "entangled" particle can be measured.

Nice article in today's NYTimes by Brian Green on Einstein and the uncertainty principle.

Other nice descriptions of the EPR experiment Link1 , Link2.

Debate on Black Holes
Topic: Physics
So do black holes, a staple of modern day SciFi, really exist? Not so, says George Chapline, a physicist at the Lawrence Livermore National Laboratory.

Here is an instance of two main paradigms clashing. Black holes stem from modern concepts cosmology and relativity, but according to quantum mechanics black holes cannot occur.

This is no April fools joke (I couldn't resist) but the machinations of science in action. Ideas being chalenged, various inteligent proposals and arguments being made.

Link to the article from the Nature News site.

Link to the abstract in Astrophysics.

Short bio on George F Chapline.