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Sunday
Feb272011

Physics at the edge... of philosophy: Lecture 2 video

Is, and is impossible not to be. from Vatche Sahakian on Vimeo.

In recent years, powerful telescopes have pushed observational cosmology into its golden age. In a span of a decade astrophysicists have successfully charted out the entire history of our universe - all 14 billion years. We can now say that we have seen the edge of the cosmos! 

Yet, in doing so, we have to accept and understand strange forms of energy – somewhat cryptically called dark matter and dark energy. We also run up against several curious and profound puzzles: the anthropic principle and the question of what time is. Driven in such a way beyond physics, we need to call upon philosophy, and are lead, strangely enough, to the Ancient Greeks, and, in particular, to Aristotle’s notion of time. We are bound to confront the concepts of entropy and chaos, and the issue of whether time flows in a certain direction.

During this lecture we will look at some of the most recent—quite remarkable—pictures of deep space, as well as discuss the questions of the grand coincidence, of the beginning of time, and of order and disorder in the universe.

Tuesday
Feb222011

Physics at the edge... of philosophy: Lecture 1 video

Lecture 1: Black Holes are Neither Black nor Holes from Vatche Sahakian on Vimeo.

In the 1920's, soon after Einstein proposed his new theory of gravity, theoretical physicists realized that this theory predicted the existence of esoteric astrophysical objects they called black holes. These are collapsed massive stars which warp time and space around them as much as they skew human imagination... Black holes push our understanding of the material world, of time, and of consciousness to its limits, driving physics into the realm of philosophy. In the past few years, we have discovered billions and billions of black holes all around us, scattered across the universe. We now know that these violent, extraordinary entities play a key role in the evolution of the universe, and of life... To understand black holes we need to go beyond traditional physics towards crazy ideas of string theory, but also those of Ancient Greek philosophy. Looking at recent photos of black holes we will discuss these strange entities and their philosophical significance.

 

Thursday
Jan272011

Retiring at 20

Here's a slideshow I prepared from some of the most amazing detailed pictures taken by the Hubble Space Telescope. In commemoration of the telescope's 20th anniversary, these images were released with associated description by hubblesite.org.

Monday
Jan242011

It's a Small World After All

Optical microscopes are familiar instruments to visualize the world of small things, like cells and bacteria. The basic principle at work in a microscope is transmission/scattering of light through a material; and the use of lenses to magnify the image. Visible light however has an inherent size, a wavelength, that limits its resolution. Think of trying to probe a small hole in a wall by throwing a basketball through it: it won't work. You need to use perhaps a tennis ball instead. In this spirit, you need a probe with a smaller size to explore smaller things. Use of visible light in an optical microscope allows one to see things about the size of bacteria, about 1 millionth of a meter, or a micrometer (one can go down to around 0.2 micrometer if things are really pushed to the limit). The same principle however can be used to build an electron microscope: replace light photons with electrons, and lenses with magnets. The wavelength of electrons is typically shorter, and hence allows one to see smaller things; about one thousand times smaller than an optical microscope.

The state of the art of visualizing the world of small things was however achieved in 1981 with the invention of the scanning tunneling microscope. This device consists of a tiny needle hovering a few nanometers above the surface of the subject of interest. A voltage difference is applied between the tip of the needle and the surface of the subject. Because of quantum mechanics, electrons in the needle can "tunnel" through the empty gap between the needle and the surface! See previous post on quantum tunneling. This creates a measurable electrical current in the needle that one can use to infer the distance between the needle's tip and the surface. As the needle scans over the surface, it can then image the topography - bumps and ditches on the surface. The resolution of this device: a fraction of a nanometer! that's the size of an atom, ten thousand times smaller than a cell! This has allowed physicists to image for the first time the fuzzy quantum world of atoms and electrons. The device can also be used to manipulate atoms individually using the needle as a tweezer! Check out the accompanying videos and photos for an amazing visual tour of the quantum world.

The first video shows the workings of a traditional electron microscope. The second one that of a scanning electron microscope. The third video describes the quantum mechanical principles underlying the workings of a scanning tunneling microscope (STM). The final video shows a portable STM in action! The last picture shows the manipulation of atoms with an STM: iron atoms on the surface of copper. The ripples are actually the copper electrons...

Saturday
Jan082011

Lecture plans...

Things will be slow with new posts in the next few weeks... as you may have noticed already. I am preparing the lecture series associated with this blog, and I am finalizing the iPhone/iPad apps. I'll try to post occasionally, but I don't think I can do one per day as before until the app is done. Meanwhile, check out the lectures web page, which I will be updating continually:

http://schrodingersdog.net/2011-lectures/

Videos of the lectures will be posted to this feed as well.

Saturday
Dec182010

Solitary Physics

In many different physical systems, complex (i.e. non-linear) and delicately balanced interactions between microscopic constituents can collude to form configurations known as solitons. This phenomenon arises in systems as disparate as fluid dynamics, superconductivity, and string theory. In all cases, solitons share common attributes and play a central role in understanding the physical system as a whole. In addition, solitons are some of the most beautiful mathematical constructs that arise in physics.

Imagine a long chain of pendulae, connected to each other by flexible springs. You may want to watch the first video attached to this post at this point to visualize the setup. If you perturb a pendulum in the chain by a small amount - say by bumping it slightly - you'll generate a small disturbance that travels along the chain. A much more interesting thing happens if you grab one of the pendulae and rotate it a full circle: this creates a twist in the chain. When you let go, the localized twist in the chain propagates along it much like a particle would (see first video). This is a soliton: a configuration arising from the strong interactions between the constituents of a system (i.e. the pendulae) - hence forming a collective entity (i.e. the twist) that propagates and behaves coherently much like a solitary particle. All solitons carry energy (or mass) inversely proportional to the strength of the interactions in the system: the stronger the interactions, the lighter or less energy the soliton would have. All solitons preserve their shape and a finite size (which is again inversely proportional to the strength of the interactions) as they propagate. In realistic scenarios like the one depicted in the videos, frictional effects eventually dissipate and unravel the soliton. But notice how long the pendulum twist lives before dissipating! All solitons have a "topological" mechanism that assure their stability. In the case of the pendulae chain, this topological element is the twist in the chain: to disentangle the soliton, you would need to untwist the entire chain which requires a rather large effort - hence the robustness and stability of the pendulum soliton. 

The second video shows a soliton propagating on the surface of water. In this case, you also can see the interactions of two solitons! The two water wave solitons repel each other, yet preserve their shapes after the collision - much like particles! Tsunamis in the ocean can be solitonic and pack a devastating blow when they hit a shoreline. The last video shows toroidal bubble solitons created by dolphins and whales, and even a smoke toroid generated by a nuclear explosion… Other examples of solitons include vortices in superconductivity (see previous post on type II superconductors), vortices in superfluids, and even D-branes in string theory (more on this later)…

Wednesday
Dec152010

Busy Times...

Been very busy lately with work and social life... But I will start catching up on the posts in the next few days. The iPhone and iPad schrodingersdog apps are still on schedule for early January release.

I'll post the next physics entry this Friday. In the meantime, have a look at the accompanying feature from NASA celebrating the shuttle with amazing video footage.