Snow vs Construction

This is one I came up with a few years ago, but with everyone in the middle of construction season, I thought I’d repost it.

Top 9 reasons Snow is better than Construction

9 – You can hire someone to remove snow.
‎8 – Snow never stops in the middle to strike.
7 – If you make a mistake, you go _faster_.
6 – Snow is edible … well sometimes 😉
5 – Snow looks pretty while its happening.
4 – Snowstorms don’t last for months.
3 – You don’t go to jail for hitting a snowflake.
2 – No one raises your taxes to pay for more snow.
1 – You can always move somewhere where there is NO SNOW.

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How to Spin like a Proton

The universe that we knew about before dark energy and dark matter is described by the Standard Model of Particles and Interactions. All of these particles have various physical properties associated with them including the following.

  • mass
  • charge (electric, weak, strong/color)
  • spin

I’m not going to worry about the mass, but I will need to discuss the other two.

If you clicked on the link above, you may have learned that the proton ,which along with the neutron makes up the nuclear matter in all atoms, is not itself a fundamental particle. It’s composed of 3 ‘valence’ quarks. I’ll describe why I add the term valence later.

Now the Standard Model describes how quarks work, but it doesn’t describe how protons work. So how do we measure the properties of quarks? By using protons, e.g. the Higgs discovery at the LHC in 2012 used the collisions of protons with protons. Why don’t we measure quarks directly? Because we can’t.

Everyone is familiar with the gravity and electromagnetic forces. Let’s take gravity for an example. On the surface of the Earth, the force of gravity on a mass m has some value F. If we move to a distance twice as far from the center of the Earth, that force would drop to F/4, three times as far, F/9, ten times as far, F/100, … In other words the further you go away, the weaker the force. In the Standard Model, forces show up through the exchange of force carrying particles, e.g. photons for electromagnetism. In an oversimplified explanation, the reason that gravity (or electromagnetism) gets weaker at larger distances is because the force carriers in the field do not interact with each other and spread uniformly around the masses involved.

Quarks carry a mass charge and an electric charge, so the electromagnetic force between two quarks does indeed mimic the example give for gravity. It falls off with distance. But quarks also carry a strong/color charge, and this is where things get different. The force carrier for a strong field is the gluon, but unlike the photon, the gluon carries a strong charge itself and interacts with other gluons. This has a curious effect in that instead of the field getting weaker at larger distances, it actually gets stronger!

So two quarks would naturally want to stay next to one another. That’s not unlike what we have with electric charges. An electron and a proton have opposite electric charges and will attract each other and try to recombine into a hydrogen atom, i.e. a final state with 0 net electric charge. This is what we normally encounter in nature, atoms and molecules with 0 net electric charge. The same thing goes for strong, or colored, matter. We encounter objects which are ‘colorless’ in nature. Nevertheless, if I want to make electrically charged matter from electrically neutral matter, I can do so by separating the charges. I’m writing this on a machine that uses that ability. But if I try to separate two colored charges, the field just goes stronger. And here is where Einstein comes in. The field energy keeps growing until one exceeds the energy needed to produce a new quark (mc^2), so that you just end up with two particles, both colorless. Consequently, producing colored matter from colorless matter becomes the paradox of creating a string with only one end. These colorless combinations of quarks are called hadrons (That’s why it’s the Large Hadron Collider).

You’re probably wondering when I’ll get to spin, so without going into further details on how quarks combine into colorless hadrons, I just wanted to assert that colorless objects primarily come (99.999999999999%) in two varieties: baryons composed of three quarks and mesons composed of a quark and an antiquark. Protons and neutrons are composed of three of the lightest quarks (up,up,down) for the proton and (down,up,down) for the neutron, modulo the binding energy which I’ll get back to.

Now we finally get to spin. Each of the quarks has the properties of a type of particle called a fermion, which just means that it obeys something called Fermi-Dirac statistics (Did that help?). Fermions have spins which are integer increments from 1/2. This means that they can have spins of …, 3/2, 1/2, -1/2, … When you combine three fermion quarks into a proton, you necessarily get something which is also a fermion. You can understand this by taking 1/2 and adding it three times with any signs, e.g. 1/2-1/2+1/2. You’ll always end up with something that’s still a fermion.

Well now we know where the proton spin comes from. It comes from the three quarks. Well, not quite. Here’s where that binding energy comes into play. A proton has a mass of around 1 GeV (GeV is a unit of energy and if one sets c=1 and reverses Einstein’s equation E=mc^2, then it’s a unit of mass, i.e. ‘natural’ units). But the up and down quarks have masses which are much less than 1/3 GeV, in the range of 0.001 GeV. Where does the extra mass come from? The binding energy of the color charges! Also, this means that that binding energy can produce lots of up and down quarks by itself, so that a proton at any one time could be (up,up,antiup,up,down) or (up, down, antidown, up, down) or … In fact, the next heaviest quark at ~0.5 GeV, the strange quark, can also be made relatively easily, i.e. (up, up, strange, antistrange, down). This is why I used the term ‘valence’ quark earlier. They’re the quarks left over after removing the quark-antiquark pairs in the gluon field forming the binding energy. Also the gluons making up the field of this binding energy also have spin, but since they are bosons their spin is 1. Consequently, a proton is not simply a colorless 3 quark state. It is a colorless 3 quark state in a massive, colorless swarm of gluons.

Well this all sounds very complicated, but why should I expect this swarm of gluons or gluons with quark-antiquark pairs to have any net spin rather than simply sum to zero, i.e. (1-1-1+1-1+1-…=0)? Put in as many binding energy particles as you want, one can make simple symmetry arguments that the spin contributions should cancel. If fact, a simple test of this is to measure the magnetic moments of the proton and neutron. The magnetic moments of the proton and neutron are related to the spins of the electrically charged particles inside them. One can then compare the measurement to the value if one sums the magnetic moments of the three valence quarks. The result is that there is very good agreement for multiple decimal places.

So why did I bother you with this. Well, there’s the rub. Magnetic moments are good, but that’s still a global, summed type of measurement. An attempt to measure what the individual quarks were actually doing was finally attempted in the 1980’s at Stanford and at CERN. Both of these scattered electrons (SLAC) or muons (CERN) off of polarized protons which really meant scattering polarized photons off of supposedly polarized quarks within the proton since electrons and muons interact with quarks only electromagnetically. This allowed them to probe a separate parameter which was the fraction of the proton’s momentum carried by the quarks. I won’t bother you with that explanation, other than to say that when one integrates over this variable, the integral is what is related to the fraction of the proton spin carried by the quarks. As you might expect, since I’m explaining it, the result was not consistent with the simple model used for the magnetic moments. In fact, the result was consistent with none of the proton spin coming from the quarks.

All of a sudden, this became a sexy topic, and several new experiments (including the one I worked on, the SMC) were started and took data during the 1990’s. The result was that the zero contribution changed to a 50% contribution from the valence quarks with the other 50% still a mystery, even to this day. The problem comes from the complications at low momentum fraction where the simple valence model (up, up, down) becomes exceedingly complex (up, up, down, antiup, down, antidown, up, antidown, up, down, antiup, …) for reasons that I will not delve into in further detail here.

But if you’d really like to go into the gory details, here’s a good link.

That’s My Battleship!

I’m a fan of military history, especially naval history. So today I thought I’d write up a little about the origin of the idea of a battleship.

Although it remains part of the public consciousness, battleships had a relatively short lifetime as the major naval unit. The first one appeared in 1906 and by 1940 they had more or less succumbed to the supremacy of air power, both sea and land based.

But let’s not get ahead of ourselves. Let’s go back to the beginning, and I think the best place to begin is the US Civil War. On two calm days in Virginia in March 1862, the naval world changed radically. On the first day, iron decisively overcame wood, and all of the naval vessels in the world were rendered obsolete. On the second day the broadside approach to naval gunfire was decisively overruled by the introduction of turreted big guns. Combined with the already occurring change to steam power, these two changes were the revolutionary factors which were incorporated into all ships of the line for the rest of the 19th century.

Image of the Battle of Hampton Roads between the CSS Virginia and the USS Monitor

On the other hand, one thing that did not change radically was speed. Sailing vessels could sail at speeds around 10 knots, and the bigger ones, like the clippers could reach 20 knots. Steam did not really change this. It simply made it more predictable. On the other hand it also gave the ships shorter legs. The key for ships of the line or ‘battleships’, though, was that it could give those speeds for vessels coated with armor.

After the Civil War, the navies of the world adapted to these two radical changes, but this did not give us the battleship we have grown to know. This gave us what is now called the predreadnought (for reasons explained later). What characterized a ‘predreadnought’? Well, as previously noted, the retirement of wooden warships led to ships with armor, more and more armor. The advent of turrets was also incorporated, but in a somewhat opportunistic and haphazard way. There tended to be two large caliber turrets, one fore and one aft, and a whole slew of smaller caliber weapons in turrets or sponsons placed in various positions. This type of battleship tended to have four large caliber weapons of 10″ or so in bore. The ships were steam powered, but their speeds were still in the range of 10-20 knots, i.e. no faster than what was common for unarmored sailing vessels. In fact, the steam engines were of the reciprocating type, so top speeds could not be maintained for long (typically less than one hour). Consequently, the cruising speed was around 10 knots.

Typical predreadnought battleship Displacement: 10000-15000 tons, Speed: 10-20 knots

Nevertheless, they were the standard and performed brilliantly in a variety of battles between the Civil War and WWI including the Spanish-American War of 1898 and the Russo-Japanese War of 1904.

Then at the beginning of the 20th century, two technological innovations again came together to provide a quantum leap in naval technology which finally gave us what we would recognize as a battleship.

The first of these innovations was the steam turbine. The steam turbine for marine propulsion as we encounter it here was the brainchild of the British industrialist Charles Parsons, who demonstrated it in dramatic fashion at the naval review for Queen Victoria’s Diamond Jubilee in 1897 where he literally ran circles around every other ship. This was still a steam engine, but rather than pushing a piston, the steam turned a turbine. The advantage was that the stop and start of a piston produces dramatic amounts of noise and damage to the engine at high speeds, whereas a turbine could just turn faster. In fact, this form of propulsion is still the primary means of propelling naval vessels today.

The second innovation was to specialize the armament and go with an almost exclusively high caliber armament which more than doubled the weight of shot in a single salvo. The result was the HMS Dreadnought, launched in 1906. With an armament of 10 12-inch guns, and the ability to steam for hours at 21 knots, the Dreadnought could outgun any ship it encountered and outrun any ship or fleet that outmatched it. Again, in a single stroke, all previous ‘battleships’ were rendered obsolete and given the appropriate moniker of ‘pre-dreadnoughts’.

HMS Dreadnought Displacement: 18000 tons, Speed: 21 knots

I’m going to stop here and recommend a couple of books on the subject which make very nice reads by Robert K. Massie: Dreadnought and Castles of Steel. In them you will find details on the technical stories I’ve described as well as the intriguing cast of characters who created the battleship as we know it and fought them in WWI. I hope you enjoy them.

Footnote: All images were derived from public web sources as far as I know.

Silence is Golden

I was thinking about all the talking heads that badger us in our 24 hr news and Twitter world. Here are some nice quotes about silence I found on brainyquote.com.

“Silence is the sleep that nourishes wisdom.”

Francis Bacon

“We need to find God, and he cannot be found in noise and restlessness. God is the friend of silence. See how nature – trees, flowers, grass- grows in silence; see the stars, the moon and the sun, how they move in silence… We need silence to be able to touch souls.”

“I have learned silence from the talkative, toleration from the intolerant, and kindness from the unkind; yet, strange, I am ungrateful to those teachers.”

Khalil Gibran

“In the End, we will remember not the words of our enemies, but the silence of our friends.”

The last one is a nice reminder that one also needs to know when to speak out.

A Marriage by Any Other Name

If one starts a discussion about the definition of marriage, then one should be prepared for a long discussion. Recently this has made the news through the Supreme Court with a general rejection of the definition in the Defense of Marriage Act.

Now the union described by marriage can be used in various contexts. Unfortunately, if one takes popular usage as a guide, then marriage is primarily, and unavoidably, a religious term. A simple example is Catholicism where it is a sacrament of the Church. Therefore, any attempt to legally define marriage is inherently going to rub up against freedom of religion.

The simplest way to solve this would be to clearly separate legal and religious activities, preferably with a different term. I don’t want to be too cynical, but much of the debate seems to center around money, or property, or other wealth issues that we’ve tied to the state of marriage in our laws. If we take marriage out of our laws (for everyone), then we can relegate marriage to a purely religious ceremony.

Oddly enough, the defeats in the Supreme Court have made the proponents of defining marriage as purely a heterosexual union work on removing marriage from the legal framework. I don’t know if they realize it, but this is what they should have done to begin with. It reminds me of the quote from Churchill: “We can always count on the Americans to do the right thing, after they have exhausted all the other possibilities.”