Scientists Free Laser Cavities to Embrace New Shapes

From medical technology to cat entertainment, lasers are one of the most revolutionary inventions of the last 75 years. Now, one of the key components of lasers may be in for a revolution. In new research published in the AAAS journal Science, researchers from the University of California, San Diego (UCSD) demonstrate an innovative design for the optical cavity of a laser. This development could help manufacturers pack laser components into less space on a chip, accelerating the development of light-based computing, among other applications.

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A Neutron Star Collision: Gamma Rays & Gravitational Waves

Gravitational waves have been on our radar non-stop lately, from LIGO's fourth reported detection—enhanced by data from Italy's Virgo project—to this year's physics Nobel going to three of LIGO's cofounders. But here we are again and, far from getting old, the news is more exciting than ever: we've picked up a new kind of signal, from merging neutron stars rather than black holes. That's not all, though—while black hole mergers are expected to be difficult or impossible to see, this collision produced electromagnetic waves across a broad portion of the spectrum, allowing multiple telescopes to pick up the signal and giving us our first confirmed glimpse of a binary neutron star system coalescing into a single object.

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Ask a Physicist: The Blood of a Starship

Recently, a reader by the name of Robert wrote in with a fun question that has an even more fun answer:

I'm trying to find a material that acts like a liquid under high pressures, but also acts as a solid at low pressures. I'm trying to design a kind of fictional armor for my spacecraft, I want something that will fill holes produced by impact and weapons fire. The only problem is: I don't know if something like that can exist.

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Quantifying Chaos to Understand Liquids

For those readers in regions where autumn is quickly approaching, a pumpkin spice latte might be just the thing to help you relax. As scientists like Moupriya Das and Jason R. Green from the University of Massachusetts Boston know, however, zoom in on this seasonal treat and the world is anything but relaxing.

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Texas A&M Students Make Physics Fun, With "Real Physics Live" Video Series

Have you ever seen air frozen solid? What about a tricycle with square wheels that can actually be pedaled? These oddities and more are on display in Real Physics Live, a new series of videos from physics and astronomy students at Texas A&M.


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Ecology Without Species?

Until recently, microbiology has been a science done largely in petri dishes, looking at a few million copies of one organism and asking simple questions trying to suss out how it’ll behave in the wider world. What does it eat? Does it breathe air like we do, or is it an anaerobe, to which oxygen means death? Now, however, there’s a radical new understanding sweeping the scientific world—and researchers are having to devise new tools to keep up.

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Caught in the Act: The Quick Escape of Electrons

When hit with an energetic particle of light, an electron orbiting the nucleus of an atom can break free in less than one quadrillionth of a second. Exactly what happens during this fraction of a second is difficult to capture, but there is a lot to be gained by doing so. Mapping the interactions between an escaping electron and the other particles inside of an atom will bring us closer to being able to control the behavior of an electron or other subatomic particle inside of an atom—and maybe even bring us closer to creating new states of matter.

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Ask a Physicist: Chasing the Sun

Colin, from Newfoundland, Canada wrote in this week to ask:

The Trans Canada Highway runs fairly straight. If I was to start at the border of Ontario and Manitoba and, as soon as the sun came up, began to drive west at 100km/h. How many more hours of sunlight would I be able to gain?

Colin,
Great question—and a fun idea for a roadtrip! Let's see if it's practical. There are a few ways to approach this problem; we'll look at two of them.

Standing still on the longest day of the year at the latitude of the Trans-Canadian Highway—about 50° from the equator—will net you 16 hours and 19 minutes of sunlight for starters. Let's be optimistic and take those 19 minutes for refueling, seeing as you're probably going to run down your tank at least twice, so you've got 16 hours of travel time. You've specified a speed, so that makes things relatively easy—how far can we get in 16 hours at 100 km/h? Obviously, 1600 km!

Assuming we're staying on the road and not going "as the crow flies", that's enough to get you from Whiteshell—a town along the Trans Canada Highway at the border of Manitoba and Ontario—to Canmore, just past Calgary.

Sunrise and sunset times at various longitudes and cities can be found just by googling, so let's look at Whiteshell vs. Canmore

We see here that we get an extra 29 minutes! Our original 16 hours and 19 minutes of sunlight is now 16:48. Here's where it gets interesting, though—if we're driving until sunset, the 16 hours of road-time we've calculated for isn't all we get; we can go another 29 minutes—which gets us almost 50 km farther, and buys us another few seconds of sunlight. You might wonder where this line of thinking ends—we could drive for those few extra seconds, and it would get us a few more microseconds—and the answer is that, technically, it doesn't! The problem is described by an infinite series. That doesn't mean we can drive forever, though; a series that's made up of an infinite number of ever-shrinking terms can still take on a finite value—this is known as the limit.

Hundreds of years ago, a young Isaac Newton was vexed with problems like this one. To address them, and to calculate things like the exact amount of time between sunrise and sunset for a westward traveler without computing an infinite number of terms, he developed calculus. Here, of course, the first few terms in the series—i.e. the 16 hours plus a second-order term to account for the daylight gained—provides a close enough approximation for our purposes.

Treating this explicitly as a calculus problem would require us to know the function describing the curviness of the road, which we don't have. However, we can get there by knowing a little algebra and making a simplifying assumption.

Say we're heading straight west, as the crow flies, rather than following the Trans-Canadian Highway. Now we can treat this like a "two trains leaving their stations" algebra problem, where your car is one train, and the "terminator"—the line of sunset—is the other.

Although if it helps to picture Arnold Schwarzenegger as the other train, I don't see why not.

On the longest day of the year at 50° latitude, there's 16 hours and 19 minutes of sunlight.  This tells us that, at that latitude, it's daytime across 68% of Earth's surface at your latitude, with the remaining 32% in night—which tells us where the terminator is when the sun rises at your location. To figure out how fast the terminator is moving, we need to know the circumference of the earth at your latitude. Fortunately, this is pretty simple—just the cosine of your latitude, multiplied by Earth's circumference at the equator.

Dividing that number by 24 hours, since that's how long it takes the terminator to reach the same point on Earth's surface from one day to the next, gives us a linear speed of 1073.33 km/hr.

Now, to find out how much of a head start we have over the sunset line, we can multiply the circumference by 68%, or 0.68, to find out how far "behind" you the terminator is at sunrise—yielding a result of 17,516.8 km. Just to check our math, we can see how long it would take a line moving at 1073.3 km/hr to cover a distance of 17,516.8 km, and we find:

which is pretty exactly the length of the day we found earlier—a sign that we're on the right track.

Now, we just need to set this up as an algebra problem, to figure out how much daylight we gain by traveling west at 100 km/hr. We've got a 17,516.8 km head start, and putting that into an equation looks something like this:

taking out the units, to clean things up, we get:

which simplifies, after a step or two of algebra, to:

Dividing out both sides and simplifying, we get a surprisingly clean answer:

It's significantly more than you get driving on the road, almost remarkably so, but it checks out intuitively. Google's over-the-road distance measurements mean that, in addition to the road's lateral curvature—winding north and south rather than going straight east-to-west—there's also vertical distance to take into account; all the little hills and dips add up.

All in all, while this is a great question, you're not likely to gain enough sunlight in your day to make this roadtrip worth it; sixteen hours in the car with half an hour of stopping time doesn't sound like much fun.  It's interesting to note, though, that a fast jet at the right latitude could keep pace with the sun, effectively outrunning the night indefinitely.

Thanks for writing in!
—Stephen Skolnick

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The Shape of Randomness

We often rely on shapes and patterns when navigating the world. Poison ivy or an innocent plant? A nasty rash or the imprint of the textured wall you were leaning against? Similarly, scientists often use shapes and patterns to interpret datasets. Do the points follow a straight line? Appear in clusters? On the street and in the lab, shapes help us organize information, interpret data, and even make predictions.

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Physics in the Autumn Sunrise

The sun is an hour over the horizon. It's the first week of October in Maryland, and there's something uniquely enchanting in how the light catches the tips of the trees. What is it that makes this morning sunlight so spectacularly yellow-gold? As with most things, the answer—at some level—comes down to physics.


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Gravitational Waves Catch 2017 Nobel

A long time ago in a galaxy far, far away...two monstrously large black holes, perhaps as old as the universe itself, collided. Nearly a billion years later, in late 2015, the Advanced LIGO detectors in Hanford, WA and Livingston, LA came online—just in time to catch the signal as it went by. The men who masterminded this enormous endeavor, observing a warping of spacetime smaller than a proton over a scale of several miles, were recognized this morning for their efforts with the announcement that they would receive the 2017 Nobel prize in physics.

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Nobel Week 2017: Physics—Three Guesses Who

It's here, ladies and gentlemen! The biggest week of the year for the recognition of "boons to mankind"—the annual announcement of the Nobel prizes—kicked off today with the awarding of the medal for physiology/medicine.

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