Tag Archives: questions

#AdlerWall 05: Share Interesting Observations, Ask Questions

by Shane L. Larson

Apparently this creature eats quarters.

Apparently this creature eats quarters.

My wife and I just bought a new couch and when we flipped the old one over to carry it downstairs, a quarter fell out. When I was in high school, arcades were the rage and a quarter was a ticket to a nice half-hour playing Xenophobe or Blasteroids. These days, it goes in my pocket and gets spent on parking. Despite the sad evolution of my life into adulthood, the appearance of the quarter sparked an interesting thought: I don’t remember dropping a quarter in my couch, and probably no one else would either, so that must mean almost everyone’s couch likely has a loose quarter in it! That observation, sparked an interesting question: how much money in quarters is hidden in couches?

(L) How I used to spend quarters. (R) How I spend quarters now. If the place on the left still existed, I could feed the the thing on the right with my phone and put those quarters to good use! :-)

(L) How I used to spend quarters. (R) How I spend quarters now. If the place on the left still existed, I could feed the the thing on the right with my phone and put those quarters to good use! 🙂

Because you and I live in the future, information is at our fingertips. I pulled my phone out of my pocket and was quickly at the US Census site, which told me there are approximately 116,000,000 households in the United States (this page is where I landed). So if they all have a couch, and each couch has a quarter in it, that amounts to:

$0.25 * 116,000,000 = $29,000,000

There are 29 MILLION dollars in quarters hiding in couches! This observation has sparked some interesting discussions with friends that are wide ranging and varied: is there really only 1 quarter per couch? How much money disappears from circulation every year? Is there some way we could collect all that money? What could we do with $29 million?

This little exercise is something known as a “Fermi Problem,” — taking something you know (my couch has a quarter in it) and figuring out the implications based on other things you know (the number of households in the United States). Scientists use the method all the time to understand what the Universe is all about, particularly in astronomy where we don’t know much. But the interesting bit about the quarter question is not the number, it is the discussions that ensue afterward.

Just a few observations I have made and shared with friends, found on my smartphone. You most likely have a similar set!

Just a few observations I have made and shared with friends, found on my smartphone. You most likely have a similar set!

You make observations of the world around you all the time, and share those observations on social media or over coffee with friends. I know you do, because I see jillions of people everyday taking pictures of flower bushes and posting them to social media, asking friends over coffee if they noticed they way the clouds were streaked over the city that day, speculating on why the traffic was heavy or light today, or simply enjoying the spectacle of the brilliant turquoise color of the lake on a sunny day. You see the world around you and record it and talk about it, every single day.

adlerwall_questionsobservations

Given our social connectedness in modern life, this week’s exhortations from the #AdlerWall are ones that might not seem totally incongruous: “Share Interesting Observations” and “Ask Questions.” We are all good at this to some varying degree, but kids are masters. Children ask incessant questions of their parents:

“How do airplanes fly?”

“Where do frogs go in the winter?”

“Why do we say ‘bark’ to mean the sound dogs make and the skin of a tree?” 

They also share interesting observations:

“Look how you can make a loud sound by squishing your hand in your armpit!”

“If I hit my spoon right here, it flips oatmeal WAY over there!”

“The shadows from this tree look like an octopus!”

But sadly, somewhere along the pathway to adulthood, many of us lose that unbridled enthusiasm we had as children for exploring the world around us, and declaring our discoveries to the world. Sure, I’ve wondered how many gummy bears I can fit in my mouth and figured out the answer (37) — who hasn’t? It’s not that we don’t know how to ask questions and share our observations.  It has just become the societal norm to squelch the unbridled enthusiasm.

Yes, that’s right: squelch, not kill. Because in the quiet moments, we all give into the most basic impulse to ask a question, to look at the world around us and see what is going on. You might not always post a picture of the weather radar during a torrential thunderstorm, but you still made a screen capture. You have stayed up too late at night because you went to Wikipedia to find out about The Great Platte River Archway and two hours later found yourself still on your tablet, having randomly navigated through clicks until you were reading about the Toledo War. You’ve almost certainly been hanging out with your friends, when someone has asked some esoteric question about the difference between fountain pens and calligraphy pens, igniting a debate that was only resolved by asking Google or Wikipedia.

img_7696For most of us, making interesting observations and asking questions of our friends and the internet are diversions to everyday life, something we do for the sheer enjoyment of learning. But lurking just below the surface of those questions and observations is always a myriad of important ideas and applications, some of which we understand and some of which we may not. Irrespective, it points a simple and inescapable fact: we are all close to being scientists, simply by doing what we do — asking questions and making observations.

Let me illustrate with a curious observation I just made the other day. I have a vertical glass shower door; the glass is maybe 10 mm thick. If you put your eye right up against the edge of the door, and look into the glass (not through the glass), you a mesmerizing collection of reflections inside the glass door!

The view inside a glass door, looking edge on into the glass.

The view inside a glass door, looking edge on into the glass.

I’m sure I could work out the physics of the all the reflections as to why it happens (and could probably subject some future students to the analysis of that problem), but instead I’ll just share that observation with you. The next time you walk through a glass door, take a moment and peer in through the edge, looking longways into the glass — you’ll be treated to the same awesome spectacle I discovered. Maybe you’ll show it to a friend, or you’ll sketch it in your pocket notebook, or you’ll create a new glass sculpture inspired by the sight.  Irrespective, I’ve shared my observation with you, and hopefully shown you something you haven’t see before!  You should share what you see too.

So what does that have to do with anything? Peering into the glass of your shower door produces a spectacle that is fun and pleasing to behold, like a piece of symmetric art or a kaleidoscope. But the basic physics, called internal reflection, led to many, many modern applications, not the least of which are fiber optics, and the heart of most high-speed communications networks that are likely streaming internet and movies into your home right now. Binoculars have a pair of prisms that use internal reflection to gather the images of distant objects and route them through the binoculars to make a correct, right-side up image at your eye. Internal reflection of light in a raindrop takes the light from the Sun behind you, and directs it back at you to make a rainbow. And perhaps last, but not least, internal reflection is the basic physical principle behind infinity mirrors (IMHO, one of the coolest pieces of home decor you can have — your spouse may or may not disagree…).

Everyday examples of internal reflection. (Top L) Binoculars. (Top R) Rainbow creation by raindrops. (Bottom) Light propagating through a fiber. [All images from Wikimedia Commons]

Everyday examples of internal reflection. (Top L) Binoculars. (Top R) Rainbow creation by raindrops. (Bottom) Light propagating through a fiber. [All images from Wikimedia Commons]

All of this is connected, in a simple way, to the little pane of glass on my shower door. The world is a strange and wondrous place, full of moments of giddy discovery if you take the time to notice. 🙂

So I’ll see you out in the world — I’m the guy blocking the entrance to the coffee shop as I try to snap a picture looking longways into their glass door. 🙂

—————————————-

This post is part of an ongoing series about the #AdlerWall. I encourage you to follow along with the activities, and post your adventures, questions and discoveries on social media using the hashtag #AdlerWall.  Links to the entire series are here at the first post of the #AdlerWall Series.

Advertisements

My Brain is Melting — GW150914 (Part 2)

by Shane L. Larson

It has been just more than a week since we told the world about our great discovery. It was a cold winter morning in Washington DC, the temperature hovering just below freezing. In a room at the National Press Club, the world press had gathered, and at the behest of NSF Director, Frances Córdova, LIGO Executive Director, Dave Reitze, took to the podium.

“Ladies and gentlemen. We have detected gravitational waves. We did it!” Mic drop. (Well, he should have; in the movie dramatization, he will. You can watch the moment here on YouTube, or the full press conference.)

Dave Reitze makes the announcement to the world that LIGO had detected gravitational waves.

Dave Reitze makes the announcement to the world that LIGO had detected gravitational waves. “We did it!”

So began a ninety minute press conference delivering the news of the first gravitational wave detection to the world. In the days that followed, social media and press outlets exploded in a veritable tidal wave of excitement and awestruck wonder. On twitter, the hashtags #gravitationalwaves, #LIGO, and #EinsteinWasRight have accumulated more than 70 million tweets in just one week.

Everyone has the same sense that we scientists have — this is a doorway, now open, to a Universe we have only imagined. Beyond the threshold are certainly things we have predicted and speculated about, but also many wonders yet to be found or understood.

We have done our best to explain what we are doing with LIGO, and how it works. We have made a Herculean effort to describe the astrophysical significance of the discovery. We have tried mightily to explain what Einstein’s ideas about spacetime and gravity are all about.

But this is hard stuff to think about, it is hard stuff to understand, and it is hard stuff to explain. It is well outside our normal everyday experience, so it is easy to feel like your brain is melting.

brainMelt

You shouldn’t worry that these things are hard to understand. It took physicists 41 years to even decide gravitational waves were real, and then another 59 years to build an experiment capable of detecting them. There is no doubt these are hard, brain melting matters. But the beauty of the discovery of gravitational waves is that this can be understood!

A large number of my colleagues in LIGO (and myself) have spent the last week collecting and responding to questions emailed to us, asked in public forums, and delivered on social media (if you have more questions, ask in the comments below, or please email question@ligo.org). All of them are thoughtful, genuine, and demonstrate a pleasing curiosity and wonder about the nature and workings of the Cosmos. I am constantly amazed by the questions people ask.

Here are a few of the more common brain-melters we have been asked, and some meager attempt to answer them. The questions are marked in red, to make them easy to find. Some responses are more complicated than others, and you may or may not want to read them all. They are here to help stem the meltdown, if you find your brain is still reeling. 🙂

What does this mean for ordinary folks?  Far and away, this is the most common question I’ve been asked, particularly from the press. What does this mean for the world? How will this help my golf game?

LIGO’s discovery is what we call “fundamental physics.” It is a discovery that tells us something about how the Universe works and why it behaves the way it does. Figuring out how to use knowledge like that to make your life better or turning it into a gadget that’s useful in your kitchen or garage takes time — we’ve only just now made the first detection of gravitational waves, and are trying to wrap our brains around it.  Scientists and engineers will have to think a long time, maybe decades, before they can make this knowledge “useful for everyday life.”  That’s always how it works with scientific discoveries. How it will impact our everyday lives is not for us to know — that is for the future.

In the modern era, many of us navigate using GPS technology, built directly into our smartphones.

In the modern era, many of us navigate using GPS technology, built directly into our smartphones.

That is not to say that there isn’t some amazing future application. We only have to look at the history of general relativity itself to know the truth of this. Einstein worked out general relativity between 1905 and 1915. This was an age before cars and electricity were mainstays in everyday life. Yet Einstein had the where-with-all to understand that gravity could be thought of as the warpage of spacetime, and that one consequence of that warpage is clocks tick at different speeds depending on how strong the gravity is.

Did you know that little, obscure fact of general relativity is used by you and most other people every, single day? It is an essential part of how the GPS in your phone works. It took nearly a hundred years for the “fundamental physics” we call general relativity to be turned into an essential piece of technology that now gets millions of us from place to place in the world every day. Without GPS and general relativity, you’d still be navigating using paper maps. Einstein had to rely on his neighbor to tell him where to find a pub; you have a smartphone.

Is it really that important? I think this is one of the most important discoveries in astronomy in the last 100 years. It is as important as discovering that there are other galaxies beyond the Milky Way, it is as important as discovering the expansion of the Universe, it is as important as discovering the Cosmic Microwave Background.

The reason I think this is just about everything you’ve ever heard about the Universe, or seen a picture of, has been discovered using LIGHT. Telescopes are just instruments that do what your eyes do (collect light), though telescopes collect much more light than your eye or collect light that your eye cannot see (like infrared or ultraviolet light).

Gravitational waves are different — none of us have a “gravitational wave detector” as part of our bodies. Gravitational waves are something that we predicted should exist, and we built an experiment that showed us our ideas were right.  The beginning of gravitational wave observations will change how we see the Universe in ways that we cannot yet imagine.

Dr. France Córdova, Director of the National Science Foundation.

Dr. France Córdova, Director of the National Science Foundation.

As a scientist and a teacher, I can appreciate the importance and utility of the collection of knowledge. But LIGO’s discovery goes far beyond the mere acquisition of yet another fact to post on Wikipedia. What the scientists and engineers working on LIGO have done was often regarded as impossible to do. But as Dr. Córdova intoned at the LIGO press conference, we took a big risk. Through a judicious application of sweat, brains, and stubbornness, we endured a decades long effort to design a machine to do the impossible. We encountered countless challenges and obstacles, and diligently overcame every single one of them to arrive at this day. That should make every person sit up a little bit straighter and prouder. That should make every single person aware that whatever challenges or problems we face on our small world, we have the means to overcome them, if we have the will to commit our time and brains and resources to them.

The black hole collision LIGO observed was more than 50 times brighter than all the stars in the Universe. How can that be?  The comparison is “the gravitational energy released by the merger is about 50 times the energy released by all the stars in the Universe during the same time.”  This is an example of a “Fermi problem” which astrophysicists use all the time to figure out if our numbers are right when we are doing complex calculations.

The night sky over the Pando Forest in central Utah. Pando is an 80,000 year old aspen grove -- it has seen almost 30 million nights like this one, but very little has changed. The constellations change over thousands of years, but the sky is still full of stars, and the Milky Way still arches over the sky, giving the impression that the Universe is unchanging. [Image: Shane L. Larson]

The night sky over the Pando Forest in central Utah. Pando is an 80,000 year old aspen grove — it has seen almost 30 million nights like this one, bathed in the light of the stars of the Milky Way. [Image: Shane L. Larson]

Astrophysicists measure brightness in watts, just like you are used to expressing the brightness of a light bulb in watts — the “wattage” tells you how much energy is released in a fixed amount of time. The higher the wattage, the more energy is released in a given moment, so the brighter the star (or bulb). Astronomers call this the “luminosity.” We can estimate the luminosity of all the stars in the Universe and compare it to what LIGO measured from the black holes. [[I’m going to use some scientific notation here to write some mind-bogglingly big numbers; a number like 106 means a 1 followed by 6 zeroes: 106 = 1,000,000. ]]

If you express the luminosity of the black holes (3 solar masses in just about 20 milliseconds) as a “wattage,” the brightness is about 3.6 x 1049 watts, or about 1023 times brighter than the Sun.

The Hubble Extreme Deep Field (XDF).

The Hubble Extreme Deep Field (XDF). We can use images like this to estimate the total number of stars in the Cosmos.

Now suppose we make the assumption that all the stars in the Universe are just like the Sun. This isn’t true, of course — some are brighter, some are dimmer, but on the average this is a good starting guess. There are about 100 billion stars in a galaxy like the Milky Way, and if you look at an image like the Hubble Extreme Deep Field, there are on order 100 billion galaxies in the Universe. So there are 100 billion x 100 billion = 1022 stars in the Universe. If each one of them is the brightness of the Sun, the total brightness of stars in the Universe is 1022 times the brightness of the Sun.

But we said the black hole merger seen by LIGO was 1023 times brighter than the Sun, so: 1023/1022 = 10. The black hole merger was 10x brighter than all the stars in the Cosmos. With a careful calculation, we could get the 50 number you hear from LIGO, but 10 is pretty close. This is the nature of Fermi problems — they don’t give you the exact number, but they quickly get you close to the exact number so you can understand the Universe.

What do you mean “spacetime is stretching LIGO’s arms?” What is spacetime? Spacetime is the substrate, the matrix upon which everything in the Universe is built — as we like to say, spacetime is the “fabric of the Cosmos.” It is, of course, easy to say that, but difficult to wrap your brain around. We’re used to not thinking about space at all; it is the nothing between everything. But it is exactly that nothing of which we speak — if we were not here, if nothing were here, there is still space.

Imagine a gravitational wave shooting through LIGO, directly out of the screen at you. (A) When there are no waves, the arms are at their fixed lengths. (B) When the wave first hits LIGO, the spacetime in one arm stretches and in the other arm compresses. This changes how long it takes light to go from the corner to the end of the arms and back again. (C) As the wave passes by, the arms change back and forth between stretching and compressing.

Imagine a gravitational wave shooting through LIGO, directly out of the screen at you. (A) When there are no waves, the arms are at their fixed lengths. (B) When the wave first hits LIGO, the spacetime in one arm stretches and in the other arm compresses. This changes how long it takes light to go from the corner to the end of the arms and back again. (C) As the wave passes by, the arms change back and forth between stretching and compressing.

How do you measure the length of something in space? Most of the time we use a ruler or a tape measure. You lay it down along the thing you are interested in, like LIGO’s arms, and you see how many it takes. Imagine that you put down kilometer markers along LIGOs arms, just like you see on the highway — one at 0km, 1km, 2km, 3km and 4km. When spacetime between the ends of LIGO changes, the entire arm stretches. You still think the arm is 4 kilometers long, because the markers are still evenly spaced (the spacing is just larger than it was before, though you may not be aware of it). We need a way to measure the stretching without relying on the kilometer markers.

Visualization of LIGO interferometry. (A) When no gravitational wave is present, the laser timing is set up to make a "dark fringe" at the output [square panel on the right]. (B) At the output, the light is like waves canceling each other out. (C) When a wave stretches or compresses the arms, it changes how the light is added together at the output. [Frames from video by Caltech/LIGO]

Visualization of LIGO interferometry. (A) When no gravitational wave is present, the laser timing is set up to make a “dark fringe” at the output [square panel on the right]. (B) At the output, the light is like waves canceling each other out. (C) When a wave stretches or compresses the arms, it changes how the light is added together at the output. [Frames from video by Caltech/LIGO]

A reliable way to measure the distance in a space that is changing and stretching, is to time a beam of light as it makes its way through the space you are trying to monitor. In LIGO, we use laser light. Imagine two photons, injected into LIGO at the corner, with a photon traveling down each of the two arms (in terms of the the optics, there is an element at the corner called a “beamsplitter” that splits a laser beam and sends part of it down each of the two arms). When there are no gravitational waves distorting LIGO, the two photons arrive back at the beam splitter and are combined to make an interference pattern, which is a brightness pattern that depends on how the photons arrive together. We set it up so the pattern is a “dark fringe” — the two photons cancel each other out (what physicists call “destructive interference”).

A simple demonstration of how sensitive interference can be to small shifts in space. These interference patterns are made with regular circles (as opposed to moving waves) and create Moiré patterns. The difference between the left and right image is a shift of only 0.05 inches, but the pattern difference is easy to see, indicating the shift happened.

A simple demonstration of how sensitive interference can be to small shifts in space. These interference patterns are made with overlapping patterns of regular circles (as opposed to moving waves) and create Moiré patterns. Here the horizontal dark region in the left image is analogous to LIGO’s “dark fringe.” The difference between the left and right image is a shift of only 0.05 inches, but the pattern difference is easy to see. What was a “dark fringe” now has a sliver of white, indicating the shift happened. [Image: S. Larson]

When a gravitational wave goes through LIGO it stretches the spacetime in one arm, and compresses the spacetime in the other arm. That means the photon in the stretched arm arrives back at the beam splitter LATE (it had farther to travel) and the photon in the compressed arm arrives at the beam splitter EARLY (it had less distance to travel). The result is the brightness pattern CHANGES. The changing pattern of brightness is exactly in tandem with the passing gravitational wave, telling us about the shape of the wave as it passes by.

They said the stretching that LIGO measured was a fraction of the width of a proton. But I remember from Chemistry that atoms are always moving, so how can you make such a precise measurement? Remember that LIGO is not measuring the distance shift in single atoms — it is watching the mirror, which is comprised of many atoms, each of which is moving exactly as you remember from Chemistry.

Everyone on a boat is doing their own thing, but they are all moving together as the boat moves on the waves.

Everyone on a boat is doing their own thing, but they are all moving together as the boat moves on the waves.

When we make our measurements, we are looking at the behaviour of many, many photons that have travelled down the arm together, hit the mirrors, and made the return journey. Sure — some of the atoms are going one way, and some are going some other way, but overall they are all moving together, going wherever gravity is pushing the center of mass of the mirror. When we read out the light, we are looking at all of those photons that hit the mirror at the same time and using that information to determine where the mirror is.

It’s a bit like having a big gravitational wave discovery party on a boat. If you are on the shore, watching all the physicists and engineers having a good time, you see they are all going every which way on the deck. But they are all on the boat, which moves them all together in response to the underlying waves of the sea.

Will this help with time travel? quantum gravity?  Einstein’s great discovery with general relativity was the idea that gravity can be described as the interaction of mass with the shape and warpage of spacetime. The unification of space and time into a single entity — spacetime — is a huge conceptual leap that is sometimes hard to come to grips with because of the way we think about space and time.

In our everyday lives we measure space with rulers and car odometers, and we measure time with wristwatches and calendars. If they are the same thing, why don’t we measure them the same way? The idea that the two are connected takes some getting used to, though as I like to remind people: when you go somewhere, you are usually comfortable saying your destination is “25 minutes” away or saying “20 miles” away!

You think about travel as travelling through space or travelling through time without even noticing! You are used to being a "spacetime traveller."

You think about travel as travelling through space or travelling through time without even noticing! You are used to being a “spacetime traveller.”

Since gravitational waves are moving ripples, propagating warpage in spacetime, it is natural to ask: can this discovery can help us understand space and time? Can we understand “time travel” and “warp drive?

Time itself, despite being part of general relativity, is still a great mystery to us. But what we often forget is that we are time travelers. Even as you are reading this, you are traveling through time from this moment, heading toward next Tuesday. It is not possible, so far as we know, to go backward toward last Friday, and that is a great mystery. It appears to be true based on experimental evidence, but we don’t yet understand how the laws of Nature — general relativity — tell us that. So in as much as gravitational waves will dramatically improve our understanding of how spacetime works and behaves, that deeper understanding could lead us down a path of thinking that will ultimately give us more insight into the mystery of time.

In a similar way, the LIGO detection does not address the enduring questions about the microscopic, quantum nature of gravity. The gravitational waves are a “big world” phenomenon, created by strongly gravitating astrophysical objects. But based on our experience with other quantum physics, we expect that there will be a clear (though not now obvious) connection between quantum gravity and general relativity. The more we expand our understanding of general relativity, it becomes more likely we will stumble on the deep connections that would lead to ultimately understanding quantum gravity.

—————————————

I encourage you to continue asking your favorite physicist your questions and share what you learn. Also, send questions to: question@ligo.org

Remember: no question is a dumb question. If you are wondering something, I’ll bet you a jelly donut someone else has the exact same question!