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The recent below-freezing temperatures, while not the most pleasant to experience, do give us opportunities to explore some pretty interesting physics. One of my favorites is the phenomenon of supercooling a liquid.
We're used to the idea of dropping the temperature of water beneath its freezing point and it becoming ice. Normal routine so far. But if the water is especially pure then it can be cooled far lower while still maintaining is liquidy state. This is because phase transitions, when a material completely changes character, need a starting place to get the party going.
This starting point has a name, of course: the nucleation point. A tiny imperfection, like a mineral or a speck of dust, allows the water molecules to cling to something and start lining up in the familiar regimented order of a solid. Without that impurity water can stay as water.
But once the impurity is introduced the phase transition takes place as rapidly as it can (because the water is super cold) and before you know it you have a block of ice.
As the holiday festivities wind down and us in the northern hemisphere settle in for a few more months of pointing uncomfortably away from the sun, it's a good time to reflect on the scientific journey we've had in the past year. Perhaps most interesting was that of the most notable achievements and discoveries made in astronomy last year, almost all were surprises.
A family of Earth-sized exoplanets around a nearby red dwarf star; the serendipitous observation of colliding neutron stars using both gravitational waves and the more familiar electromagnetic ones; the brief encounter with an asteroid of definite interstellar origins. All unexpected, and all significant.
But then there was the Great American Eclipse. Astronomers have been able to predict solar eclipses with to-the-minute accuracy since 1715, so we pretty much knew that one was coming. And to be perfectly honest, I count August 21st as the most significant scientific moment of the year. While I personally didn't get to see totality due to an unfortunately placed cloud over Nashville, hundreds of millions of across the US, Canada, and Mexico got to enjoy at least some solar coverage.
For a brief moment, it seemed as if everyone's eyes looked skywards and all thoughts turned astronomical.
And then it was back to business as usual, as usual.
Now that everyone has seen the new Star Wars flick at least once, I can use some cheesy puns to talk about physics. Case in point: the force. We're familiar with the four known forces of nature. Electromagnetism, governing everything from light to your fridge magnets. Strong nuclear, binding quarks together to make protons and neutrons, and gluing those together to make atomic nuclei. Weak nuclear, responsible for radioactive decay. And lastly gravity, which connects all matter and energy in the universe.
Why are there four forces, not more or less? Why is gravity so weak? Why is the strong force so short-ranged? Is there any connection at all between them?
Obviously we don't have all the answers, but some intriguing hints have been discovered in the past few decades. For one, we've discovered that at very high energies the electromagnetic and weak nuclear forces merge together. Inside our particle collider experiments, there are only three forces of nature.
We have good mathematical reasons to think that at even higher energies the strong nuclear force disappears too, and based on that we suspect that at extremely high energies, like those found in the first instants of the universe, there was only a single unified force. Not The Force, but close enough.
We've all been there before. Someone asks a question about a topic we're presenting on, and we're not quite sure how to answer. Maybe we're completely stumped. Maybe we only half-remember the subject. We don't want to disappoint the audience or leave them hanging, but we don't want to say something totally wrong. What do we do?
Indeed, it's exactly that situation that prevents a lot of people, especially scientists, from engaging in public outreach. For a scientist, being correct and thorough is a key part of any communication, from an email to a conference presentation. We train for weeks on a talk, preparing ourselves for any potential question. But with the general public you never know what you're going to get...so you're better off not even trying.
Just putting yourself out there in front of an audience is a major achievement.
Mistakes are going to be made. Wrong numbers will be quoted. A simplification of a topic will leave an important aspect out. Words will get flipped around. That's life, and that's fine, as long as we're constantly challenging ourselves to do better. It's okay to say "I don't know." It's okay to admit a mistake. It's okay to go back over a topic.
Sometimes science communication requires a little risk.
We're all familiar with the annual march of the seasons, and that the usual transition from summer to winter is due to the tilt of the Earth's axis with respect to our sun - when our orbit carries us so that the Northern Hemisphere is pointed away from the sun, it's time to break out the coats and hats.
If you've ever spun a top, you know that at first it spins perfectly straight up, but as it slows down it starts to wobble. There's an extra rotation, called precession, added to the spinning of the top itself. The Earth is spinning, and it's tilted, so there should be no surprise that it too wobbles, or precesses.
This means that the north star, Polaris, isn't always the north star. It's not exactly fast: our axis of rotation takes about 26,000 years to lazily trace out a circle in the sky. But people have been around long enough to notice. The ancient Egyptians, for example, used Thuban in the constellation Draco to align themselves, and thousands of years from now the bright stars Deneb and Vega will get to take their turn.