The Fabric of the Cosmos [Book Review]

Ahhh, Dr. Greene…. We meet again.

img_0550

Almost a decade ago, I read an intriguing book called The Elegant Universe. It talked about relativity, a bit on quantum physics, and then it dives headfirst into string theory. Almost too abruptly. During my undergraduate years, it became a forced struggle just to continue reading one sentence after another. When a book becomes a burden, you know it’s time to put that book down and really enjoy your free time.

When I was in NC last November, I picked up two books at the airport’s used book store. Please don’t ask me how a used book store survives the rent prices of an airport; I don’t know. Regardless, the purchase of two books are the only non-perishable items I’ve purchased at an airport. Programming the Universe, by Seth Lloyd, was the first book I’ve read and written about a few months ago. The other book, The Fabric of the Cosmos, written by Dr. Bryan Greene, is the topic of today’s post.

If you remove the glossary and notes section, this book is just shy of 500 pages long that span over 4 major topics. And oddly enough, there’s a lot of overlap between both of Greene’s novels. They both discuss the topics of relativity, quantum physics, and string theory. Halfway through this book, I started to wonder which book would have been better read first…… And due to the difficulty of the topic for most individuals, was the prior knowledge that I acquired from his first book REQUIRED for me to finish the second?

This book starts off on the topic of space. What is it? What is it referenced to? The scenario of “a rotating bucket of water” is the main referenced analogy. If you swirl a cup of wine in your hand, the liquid will accumulates at the edges leaving a curved shape on the surface.  While the notions of classical physics and relative motion are tossed around, this topic becomes a good point to introduce special (and general) relativity. The current theory is that the bucket is spinning in reference to “space-time,” this notion that space isn’t composed of ether, but it’s still there in the form of … something. Most likely fields…..like the Higgs Field. If you hit it hard enough, Higgs Bosons fly out!

And once you have talked about relativity, then it makes sense to bring up all the technical discoveries on quantum physics….and how it clashes with general relativity so much! While there is no equations or mathematical jargon in this book, the author does state that solutions utilizing both theories result in answers of infinity….or something implausible. Then, the history and idea(s) of string theory are introduced.

Yes, there’s multiple versions of string theory, and another one on top (M-Theory) that (supposedly) brings them all together.

You may wonder with all this scientific jargon ….. if it’s easy to get lost. And YES, you will find yourself re-reading multiple sections to make sure your thought process is in parallel with the authors. In parallel to that thought, being lost throughout this book is due to multiple reasons.

The first and most obvious is, of course, the fact that most of these topics go against your traditional mindset on how you perceive the universe’s outcomes. The fact that the speed of light is constant REGARDLESS of how fast you are going, still boggles my mind. The concept of a Higgs Field applies a sort of “resistance” to an object’s acceleration (and not velocity) is also intriguing.

To alleviate these inceptions, the author delivers A LOT of analogies. A frog in a bowl to represent the Higgs field. The crystalline nature of an ice cube to show entropy. Some topics even have multiple analogies to help visualize the same topic (even in the same paragraph). This may help some, but sometimes I had to sift through all the “comparable fluff” to stay on track with the current subject. Then again, depending on the reader’s background, it’s hard to tell how much is enough to truly get the main highlights across.

And numerous pictures all throughout the book help tremendously!

img_0551.jpg

Though, I must admit, there’s a point halfway though the third section (string theory), which I feel the author just gives up on this analogy strategy……especially when it comes to the topics of branes. What’s a brane? Umm……even the glossary doesn’t say. Let me check Wikipedia:

“A brane is a physical object that generalizes the notion of a point particle to higher dimensions. Branes are dynamical objects which can propagate through spacetime according to the rules of quantum mechanics. They have mass and can have other attributes such as charge.”

If I had to take a guess, branes are higher-order dimensional versions of strings (which are one dimensional) that the universe COULD be made of. They could connect the ends of strings? They could create universes (see Figure 13.8). It’s a whole new realm of mathematically robust possibilities…..

And the concept that our universe is just a holographic projection of a 2D brane where all of our pasts and futures are already known….. is an extremely unique, and unsettling, possibility.

ANYWAY…….

There is, in addition to your basic breakdown of these theories, a fourth section that I would call “quantum applications.” Time travel and teleportation are reviewed by utilizing previously discussed knowledge and implementing various scenarios which could arise. For example, a warp hole through space-time could be created that start in the same temporal slice of space-time. However, one side of the wormhole could be pushed farther into the future, but never backwards. This hypothetical situation demonstrates how EVEN IF we invent time travel in our future, they will never be able to travel back into the past to visit us NOW.

The second application, transportation, involves more-or-less the transportation of DATA, which is used to recreate a clone of the object that was “dismantled” during the measurement process. Thus, this brings up some philosophical questions, especially what is the meaning of an object? Does this mean that the original person is dead? They will be made with the same types of elements in the same orientation; they will act and behave the exact same way before “transportation.” However, they are not made with exact same elements, and they will not exist during that specified period of time during information transport…..or do they still? So many fun questions to ask that have no relevance to our age regardless the outcome. And don’t worry….. it’s only like two pages of the text.

Besides these topics, the author does cover a lot of additional topics to tie all the topics together, including entropy and the arrow of time, the cause and effect of the big bang, and quantum entanglement. And looking back at his older book, I found this work a lot more encompassing and approachable (instead of jumping straight into string theory only after a hundred pages of brief overview).

But despite the fascination that these topics can bring to mind, I’m done reading books on particle and deep theoretical physics. It’s a great mental exercises, attempting to grasp theoretical concepts that picture a stark contrast to our perceived environment. But in the end, there are a lot of theoretical guess and a lot more unknowns, all with a minimal impact on our personal lives.

Advertisements

Introduction to Microelectronic Fabrication

This isn’t a book review, per se. I don’t even know if this “textbook” is still available, as I found at my university’s library book sale stuffed with out-of-date textbooks. But I wanted to highlight some of the technologies written in the book.

Note: I just got done with an interview with Sandia National Labs, and this book actually helped a lot with understanding more of the fabrication capabilities and equipment they possess.

img_0433

 

Microfabrication, for me personally, is a very fascinating topic. By manipulating atoms, electrons, and photons in such a controlled way, one can create extremely practical devices that power the electronic needs of our everyday lifestyles. There isn’t much in terms of design theory in this book (that’s what Volume I-IV are for). However, despite being quite small (~150 pages or so), this paperback gives a precise overview of each possible process in microfabrication and the practical limitations for each. Additionally, the book is littered with (extremely beneficial) images from concept visualizations to experimental graphs to explain both procedures and parameter controls respectively.

To the fabrication methods!

Lithography

This is the general term for the method that creates a desired pattern on the wafer. By applying a thin film of radiation-sensitive polymer, one can expose the material and change its properties. Exposure is typically done with UV light, but it can also be conducted through alternative means including electron and atom beams. When exposed to an appropriate liquid (solvent), one part is removed (washed away) while the rest of the material stays. If the exposed material is dissolved, the material is known as a “positive” resist. In contrast, a “negative” resist becomes resistant to solvents when it’s exposed to radiation.

Of course, these patterns are never useful on their own. However, they create “windows” that additional processes now have access to the wafer below.

 

Etching

Etching is when you want to remove material in the lithography windows. Etching can either be done either using wet (liquid) or dry (gas/plasma) methods. The majority of etching methods are driven through chemical reactions, which allows for chemical selectivity during the etching process. Alternatively, one can create an ion beam for a pure “physical” etch that removes material through atomic bombardment, though this method is typically slower than preferred chemical etching methods.

It’s interesting to note that some etching methods (wet or dry) are directional (anisotropic) and can be used to create novel or deep trenches in your design. For example, a directional beam of atoms will remove material in the beam’s path. Other methods will selectively attack the crystal lattice row-by-row and allow unique shapes in your design.

 

Film Deposition

To add material, numerous methods are utilized to apply layers either on the atomic scale to create crystalline (epitaxial growth) layers or in “bulk” (poly-crystalline or amorphous) films (the latter being the easier and faster method). These methods include chemical vapor deposition (CVD), material sputtering, e-beam evaporation, and many others that result in thin film coatings to be applied the entire wafer.

 

Ion Diffusion & Implantation

In the making of microelectronic circuits, one wants to change the conductive properties of the Si wafer underneath all these films. That is where doping comes in, which allows for the creation of p and n doped materials necessary for diodes and transistor technology.

The easier method is to heat up the wafer environment and allow for material (vapor) to come into contact in your “window” regions of interest. Material accumulates on the surface and slowly makes it way into the wafer beneath the surface. Smaller and less interactive atoms will, of course, diffuse into the material at a faster rate.

The one thing with dopants is that they will still move around whenever the wafer is heated up in processing steps farther down the manufacturing line. Thus, one has to take into account ALL the high temperature manufacturing steps to make sure material diffusion does not get out of hand.

 

Oxidation

Sometimes, all you want to do is just change the chemical composition of the surface. The most common method is the oxidation of silicon (Si) to silicon dioxide (SiO2). SiO2 is an insulator and is a simple, yet robust barrier to many manufacturing methods. When photoresists used in lithography are not resilient enough for the required microfabrication processes, a layer of SiO2 can be grown underneath and etched to create more chemically “inert” windows.

The visually interesting aspect of growing SiO2 on Si wafers is that the wafer will change color based on the final SiO2 thickness. Thus, one can easily verify if the process went smoothly just by comparing the wafer color to a “look-up table” (but precision measurements are still used to understand your fabrication precision and consistency).

This is one of the easiest methods in a microfabrication setup, as it only involves heating up the wafers in an oven. No plasmas, no fancy chemicals. Of course, the gases present in the chamber are highly controlled as undesired chemicals can fuse to the surface and diffuse inwards when heated at such high temperatures.

Contacts & Packaging:

Finally, semiconductor chips have to be connected to the outside world and easily handled through macroscopic manufacturing processes (like being placed on a circuit board). One is typically familiar with standard processors and integrated circuits (ICs) being a black plastic box with metal leads coming out the sides or underneath. The semiconductor chip is connected to these leads typically through wire bonds “stitched” to both surfaces before the final device is completely confined in black plastic.

 

This is just a basic overview of the processes in microfabrication in this book. There are also a few additional topics on specific methods and insights for building specific designs, including BJTs (current-controlled switches) and MOSFETs (voltage-controlled switches). The last chapter details various methods on the design for MEMs (MicroElectroMechanical Systems). This is a fascinating area of research where microscopic gears, levers, springs, bridges, and many more unique shapes can be created using standard microfabrication capabilities.

After completing my 10 hour long on-site interview with Sandia, I realize that I do have a soft-spot for microfabrication. It’s a career area that I should pursue to fulfill my long-term career desires. But until then, someone has to be the sales engineer for LEDs!