## Physics in a Nutshell

#### The top quark (what’s that?) turns 25

The top quark is the heaviest known elementary particle, as small as an electron but 340,000 times more massive! We don’t know how small those particles are, only that they are smaller than 1/1000th the size of a proton which itself is 1/100,000th the size of the smallest atom, hydrogen. Millionths, billionths, … soon we’re talking small numbers!

#### What is time?

“What’s done cannot be undone.” Look to Shakespeare for a great quote. He had Lady Macbeth murmur these simple but profound words to herself. Who does not wish they had done something differently? But the past is past. A broken teacup will not put itself back together. A dissolved sugar cube will not reassemble itself.

#### The biggest ice cube in the world

January’s column was about snowflakes; this is about an ice cube, but a huge one called – wait for it – IceCube. Each side is 1 kilometer, 1,000 meters, so the volume is one billion cubic meters, and it weighs a billion tons. Scientists wanted a massive block of clear ice to detect mysterious neutrinos coming from far away in the universe. These particles interact with matter so rarely that 99.9999% pass right through that block leaving no trace. But one in a million hits a quark, much smaller than a proton, creating a shower of new particles, which make flashes of light in the ice.

#### Stardust in the snow

As I write this in mid-December there is no snow here – probably a trend – but people around me are singing “Let it Snow” and dreaming of a white Christmas. Snow is wonderful stuff, considering that it is “just” frozen water, but when you examine snowflakes you see beautiful crystalline forms usually with six-fold symmetry, and each one looks different.

#### The sparkles on the roof

One night in 1939, Professor Pierre Auger’s daughter asked him, “Papa, what are you doing?” In French, of course. “I’m studying the sparkles on the roof,” he said, with a twinkle in his eye. He had discovered that very energetic subatomic particles coming from outer space, cosmic rays, smash into atoms in the upper atmosphere making huge showers of particles that reach the ground.

#### Hydrogen, helium, lithium — energy!

Lithium is in the news. The 2019 Nobel Prize for chemistry was awarded to three scientists for transforming our lives and helping to save our climate. Our three Nobel laureates invented ways of making batteries using lithium, with metal and later with compounds.

#### Nothing does not exist

That title is another way of saying: “There’s no such thing as an empty box.” Let’s try to make one with a “thought experiment.” Einstein did these; they do not have to be practical, just imaginable. He came up with the theory of relativity when thinking about overtaking a light beam.

#### Welcome to the dark side

There’s something strange out in space. Scientists know it’s there, but not what it is. We know about visible stars and planets, gas and dust, swirling around our beautiful spiral galaxy. The stars are all rotating about the center. It takes a long time. The last time the Solar System was in this part of its orbit was at the time of the Triassic-Jurassic extinction, 200 million years ago, at the beginning of the 50 million-year reign of the dinosaurs. But the rotation is puzzling. Something more is pulling us in and stopping the galaxy flying apart.

#### The miracle of carbon

Carbon is necessary for all life. If the element carbon did not exist, scientists believe the universe would be sterile, no life anywhere. Among more than a hundred different chemical elements, only carbon has the atomic structure, with six electrons surrounding a nucleus with six protons, necessary to serve as the basis for such complex organisms. We take carbon for granted, but it is miraculous that it exists.

#### One small STEM for a man, 50 years ago

“Thousands upon thousands of years ago, at the dawn of human history, Stone Age men gazed at the moon and wondered just what it was.” Now we know. I can spell step, but it was STEM, namely science, technology, engineering and mathematics, that took Neil Armstrong and Buzz Aldrin to the moon’s surface and back 50 years ago this month.