Big Bang… Bigger Science?

By Prof. Paul Padley
Department of Physics and Astronomy
Rice University

In order to make great scientific discoveries, it is important to build great experiments. Outside Geneva, Switzerland, the most complex experiment ever built will soon start collecting data, and it is worth asking why scientists are convinced that something new will be found with it. Let’s look at the history of Big Bang science and see what lessons we can draw from that.

In 1929, Edwin Hubble published his paper A Relation Between Distance and Radial Velocity among Extra Galactic Nebulae.

http://www.pnas.org/content/15/3/168.full.pdf+html

This is the paper which established that the universe is expanding, in a way consistent with there being a “big bang.”  What is interesting to note is that Hubble was working at one of the greatest observatories of its day, Mt. Wilson. He was using the 100-inch telescope, which was a phenomenal instrument for its day and by having access to it, was able to collect the data that established what we now call the “Hubble Constant.”

Read about the history of Mt. Wilson at:

http://www.astro.caltech.edu/palomar/history.html)

This was a revolutionary observation that changed how we understand the universe.

Measuring the Hubble Constant is one of the fundamental cosmological measurements that can be made. Refining the precision of that constant is an important goal for science and was one of the motivating goals for building the Hubble Space Telescope.  The name was no coincidence, it was a name not just in honor of Edwin Hubble, but in honor of one of its primary scientific missions — measuring the Hubble Constant.

More than just measuring the Hubble Constant, it turns out this telescope has completely upset our view of the universe.  When I was a student, I was taught that there was a Big Bang and that the universe was expanding. Gravity was acting on the matter in the universe and the expansion was slowing down. An important question was whether the universe was open or closed, that is — would gravity cause the universe to collapse back in on itself, or not? Scientists were hoping to resolve that question with the Hubble Space Telescope.

What they found was completely unexpected: It appears that the expansion of the universe is not slowing down, in fact, it is speeding up. The expansion of the universe is accelerating!  This was a completely surprising result. I remember sitting in the auditorium at CERN when Saul Perlmutter of the Supernova Cosmology Project (http://supernova.lbl.gov/) presented this result (which was  simultaneously obtained by the High-z Supernova Search team (http://www.cfa.harvard.edu/supernova//HighZ.html). The auditorium was full of skeptical scientists ready to shoot down the claim.  However, one by one, all the hostile questions were answered and the result has stood the test of time.

The accelerating expansion of the universe is now one of the greatest mysteries in science.  What is clear is that the universe is not going to collapse down on itself — it is being blown apart. What is also clear is that it took a new facility such as the Hubble Space Telescope to make this amazing discovery possible.  The scientists working on the Large Hadron Collider at CERN are anticipating that they are going to make amazing unanticipated discoveries  it’s what happens when you build tremendous new facilities.

Learn more about cosmology and the related facilities at http://www.aip.org/history/cosmology/index.htm

Take a closer look at some of the Hubble Telescopes “Greatest Hits” by clicking an image below:

[View with PicLens]

Spinning into the Future

By Prof. Paul Padley

Department of Physics and Astronomy

Rice University

Electronics works by taking advantage of one of the properties of fundamental particles: electric charge. Particles have many other properties as well, and there is a real possibility that those properties can be harnessed in order to develop new technologies. One such property is called “spin” and harnessing spin could play a key role in the future of electronics.

Nobody really understands the spin of fundamental particles, such as the electron. However, we can routinely measure it and use it. The electron, and other basic particles in nature, act as if they were spinning tops. We can do measurements in which we calculate their angular momentum — or how much they are spinning. We can put electrons in magnets and flip their spins.  Spin

So, why doesn’t anybody really understand that? There are a couple of reasons: To the best of our knowledge, the electron is an infinitely small-point particle. In our current theories, the electron has zero size and, to date, nobody has been able to measure its “size,” experimentally. How is it that something without any size can be spinning?  String-theory attempts to overcome this by postulating that particles are little bits of string in a multi-dimensional space – but, to date, there is no experimental evidence that string theory is correct. In any case, I am not sure that a 10-dimensional string is any easier to think about than an infinitely small, spinning particle.

It gets event stranger. First, I have to explain how to describe the direction of spin. If something is rotating, I can wrap the fingers of my right hand in the direction of the rotation.  If I then stick my thumb out from my hand, I say the direction of my thumb defines the spin.  So, if I am riding my bicycle forward, and I describe the rotation of my wheels in this way, my thumb points to the left.

What is strange about the spin of the electron is that when I describe it this way, my thumb will only point up or down.  It can’t point at an angle; it can’t be tilted.

Otto Stern

Walter Gerlach

[ … Why can’t the electron spin point at an angle? That is one of the mysteries of the universe. This weird spin of the electron was first measured in the 1920s (by Otto Stern and Walter Gerlach -- http://hyperphysics.phy-astr.gsu.edu/hbase/spin.html ) and has been repeatedly confirmed by experiment, ever since.  It makes my head hurt, and my students heads, too -- this exact question was being asked of me by my students last week (I teach quantum mechanics to junior physics majors).

One of the most important things that makes science different from other ways of knowing is that we have to use what we learn from experiment, whether we understand it or not. So we can write down equations that describe how electron spin will behave.  We can use those equations to predict the electron's behavior so well that we can make electronic (or spintronic) devices, using this description. But we don’t actually know how it comes about or why it is there. So I know the electron will always be measured to be spinning up or down, and not tipped at an angle, but I can’t tell you why. Wish I could (it would get me a Nobel Prize)…. ]

I always measure that the electron is spinning either up or down, no matter how I measure it. In fact, spin is predicted by relativistic quantum mechanics (the combination of quantum mechanics with Einstein’s special theory of relativity). So, perhaps I misspeak when I say nobody understands it  – we can write down the math behind it but, unfortunately, our brains can not picture what it means.

• Learn more with this fun Stern-Gerlach interactive applet that I use in Class

That spin has this property, that it can only take definite directions, is what makes it interesting for electronics. We can use spin to record information and manipulate it to do calculations. There is a whole field of electronics research called “spintronics” that is pursuing this idea. The most likely first application is in memory chips — a technology referred to as “mram,” which is approaching commercialization.  For example, IBM and Toshiba have announced that they are close to producing such chips.

• http://www.engadget.com/2008/06/02/toshiba-says-its-1gb-mram-chips-are-almost-ready-were-ready/.
• http://www.almaden.ibm.com/spinaps/
• http://www.almaden.ibm.com/spinaps/research/sd/?racetrack

There is an important lesson for the future, here. The concept of spin grew out of work in the 1920s in quantum mechanics. Without the basic science that was conducted almost 100 years ago, the new technologies being developed today would not be possible. The physicists who discovered this amazing property of fundamental particles were not  trying to develop technologies, they were just trying to understand the smallest constituents of matter. Without speculative, basic scientific research, technological progress stops. However, it can be a long time until that basic research bears fruit.

Dr. Paul Padley is professor of physics at Rice University, and a lead physicist of experimental research for the Large Hadron Collider at CERN