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From The Desk of...The Chief Scientist

"The Big Crunch"

Written by Paul Sutter on Tuesday, 03 May 2016. Posted in From The Desk of...The Chief Scientist

What's the ultimate fate of the universe? Man, you guys ask some pretty heavy questions. I mean, seriously, just a few weeks ago it was fun, light stuff about how shower curtains wave around. And now we're on to subjects spanning deep space and cosmic time. You don't mess around, do you?

The crazy thing about modern physics - and especially cosmology, the branch of science dealing with the study of the whole entire universe - is that we can actually begin to answer crazy, ridiculous questions like "How will the universe end?" The answer is, of course, "we're not exactly sure". But I can tell you what the answer isn't.

We live in an expanding universe, and the amount and type of stuff in the universe affects how quickly it expands. If there's too much stuff like stars and gas and bananas the expansion will eventually slow down, stop, and reverse. Instead of spreading out the galaxies will rush towards each other. Individual objects lose their identity as they crush into the same ever-increasing volume. Temperatures and pressures rise. Atoms turn to plasma. The forces of nature meld into more exotic forms. Everything you know - everything there is - compresses into an infinitely dense point.

The opposite of the Big Bang. Behold: the Big Crunch.

...is unlikely. Almost 20 years, observations of distant supernovae revealed something surprising. Not only is the universe expanding, but it's expanding at an ever-faster rate. We don't fully understand it, but that didn't stop us from giving it a cool name: Dark Energy. It started about 5 billion years ago and doesn't look like it's going to stop. Our long-term fate isn't a Crunch, but a Rip.

"What Shape is the Universe?"

Written by Paul Sutter on Monday, 25 April 2016. Posted in From The Desk of...The Chief Scientist

Pick a friend and head down to the equator. The specific country doesn't matter; just go. Stand a few feet apart and face north (pro-tip: pack a compass). Start walking, one baby step at a time, never deviating from a northern course.

Even though the two of you start perfectly parallel, you'll eventually end up bumping into each other. The exact place where this happens has a name: the north pole.

Congratulations, you've just proved that the Earth is curved.

That is, in fact, the very definition of a curved surface: lines that start out parallel end up not being parallel. Take out a globe and look at all the lines of longitude (the up-and-down ones): they're parallel at the equator but all intersect at the poles. If the Earth were flat, those parallel lines would stay parallel forever.

Our universe, as far as we can tell, is flat. Parallel lines racing through space will always stay parallel. But like I said: that's as far as we can tell. Within our little observable bubble, everything is flat. But the actual universe is much larger than we can see, and it's shape is...well, we don't know. It's like trying to figure out the curvature of the Earth by just drawing lines in your back yard.

Here's something to bend your mind before I go. The universe can be geometrically flat, but topologically curved. Find a glass and draw parallel lines. Even though they wrap back around on themselves, they stay parallel, don't they? Cylinders are technically flat! So maybe if you rocket off into space in one direction far enough, you'll end up back where you started.

"Why does my shower curtain try to hug me when I take showers?"

Written by Paul Sutter on Friday, 22 April 2016. Posted in From The Desk of...The Chief Scientist

Someone recently asked me - and I'm paraphrasing - "Why does my shower curtain try to hug me when I take showers?" This is actually a very difficult problem to solve, without even taking into account the friendliness of plastic sheets. It turns out that showers are frighteningly complex places...at least, from the perspective of physics. I mean, think about everything that's going on: you've got thousands of hot, tiny, fast-moving water droplets, relatively cool and hard walls, a flexible barrier on one side, gaps that let air through, and steam. Oh, and a lathered-up human being.

There are a few responses floating around, invoking various explanations. Maybe the hot water causes the air to warm up and rise, leaving a partial vacuum at your feet, drawing in air from outside the stall. Maybe the fast-moving water speeds up the air, lowering its pressure on the wet side of the curtain. Maybe the natural "stickiness" of water gently tugs on the plastic. But curtains still billow when the water's cold or when it's not moving all that fast or when it's not even near the curtain.

Shoot. What's really going on? In all honesty, we're not exactly sure!

Like I said, showers are frightening. The best guess so far is based on advanced simulations. Yes, someone once took some software originally developed to study the spray of fuel in engines and made a pretend shower. The simulation was pretty fancy, going all the way to include the change in shape of the water droplets as they moved through the air.

Here's what that fancy-pants simulation revealed: the water droplets push the air around and make a sort of mini sideways tornado ("vortex" if you like awesome words). The tornado has a low pressure zone in the middle, which sucks at the curtain. Voila! But for all its sophistication, it was still a rough simulation, all the other physics stuff, like the hot air rising and the stickiness of water, also play a role. And of course things get complicated when you put a 98-degree oblong object in the middle of it all, which is why the final answer to the question is so bedeviling.
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