Month: February 2016

Science’s First Rough Draft

It has often been said that newspapers are “history’s first rough draft.”  The same is true of science.  One could argue that journals fill the role, but historically, the vast majority of the public reads of scientific discoveries and/or events in the newspaper.  It is quite interesting to see how these events were interpreted at the time without the benefit of hindsight.  The New York Times online archive dates back to the paper’s origins in the 1850’s and represent a rich source of historical material that can be used in the class or for personal research.  Here are some historical articles pertaining to astronomy and physics.

Auroral Phenomena – September 5, 1851.  This article describes the aftermath of the Carrington Event, the most powerful magnetic storm in recorded history.  The aurora was seen across America and telegraph operators could still send messages even after disconnecting the batteries.  Below, NASA presents a computer model of the 1859 magnetic storm.

Glowing After – Sunset Skies – December 1, 1883.  Three months after the Krakatoa eruption, the skies around the world appeared deep red after sunset as a result of aerosols ejected into the atmosphere.  The cause of these sunsets were not known at the time – the article never refers to the Krakatoa eruption.

A Comet Visible by Daylight – September 20, 1882.  The Great Comet of 1882, considered the brightest comet of the past 1,000 years, is visible during the day.  The image atop this post is this comet.  In 2015, the Rosetta mission became the first to attempt a landing on a comet.

The Roentgen Discovery – February 7, 1896.  The discovery of x-rays and possible applications in the medical field.  A century later, astronomers would use the orbiting Chandra X-Ray Observatory to discover the universe to be a violent place.

Wireless Signals Across the Ocean – December 15, 1901.  Guglielmo Marconi receives radio signals in Newfoundland from London to open the era of mass communication.  Decades later, astronomers use radio telescopes to discover pulsars and peer into the center of the galaxy.

The Greatest Telescope in the World – January 27, 1907.  Plans to build a 100-inch telescope on the summit of Mt. Wilson in California.  Opened in 1917, this telescope is where Edwin Hubble discovered the universe was expanding.

Mt. Wilson 100-inch telescope. Credit: Gregory Pijanowski
Mt. Wilson 100-inch telescope. Credit: Gregory Pijanowski

Comet Gazers See Flashes –  May 19, 1910.  Report on Earth passing through tail of Halley’s Comet.  The comet tail was 100 degrees long and 10 degrees wide in the sky.  Whatever was seen that night, comet tails are much too tenuous to cause flashes in the atmosphere.

Lights All Askew in the Heavens – November 10, 1919.  Eddington Expedition proves Einstein’s General Relativity theory correct by measuring the bending of starlight during a total solar eclipse.  Relativity has passed every test since, including the recent observation of gravity waves.

Ninth Planet Discovered on Edge of Solar System – March 14, 1930.  Pluto is discovered.  Since reclassified as a dwarf planet, the New Horizons mission gave us the first close up images of Pluto in 2015.

Nebula Velocities Support Einstein – June 12, 1931.  Edwin Hubble discovers the expansion of the universe as predicted by Einstein’s relativity theory.  Actually, Einstein was originally skeptical the universe could expand.  It was Fr. Georges Lemaitre, Catholic priest and physicist, who proposed what was later called the Big Bang theory.  The word nebula in the title refers to what we now call galaxies.

Lemaitre Follows Two Paths to Truth – February 19, 1933.  Fr. Georges Lemaitre does not find a conflict between science and religion.  Einstein and Lemaitre, “Have a profound respect and admiration for each other”.  Article quotes Einstein as stating, “This is the most beautiful and satisfactory explanation of creation to which I have ever listened” regarding Lemaitre’s Big Bang theory.

Fr. Georges Lemaitre (center) and Albert Einstein, January 10, 1933. To the left is Robert Millikan who was the first to measure the charge of an electron. Credit: California Institute of Technology.

Bohr and Einstein at Odds – July 28, 1935.  The conflict between relativity and quantum mechanics.  The quest to unify the theory of relativity, which governs large objects, and quantum mechanics, which explains physics on an atomic scale, continues to this day.

Science and the Bomb – August 7, 1945.  One day after Hiroshima, nuclear fission as a weapon and the implications for humanity are explained.

Palomar Observers Dazzled in First Use of 200-inch Lens – June 5, 1948.  Delayed by World War II for five years, Mt. Palomar Observatory finally opens for business.

Palomar
Mt. Palomar 200-inch telescope. Largest in the world from 1948-97. Credit: Gregory Pijanowski

Radio Telescope to Expose Space – June 19, 1959.  Navy to build largest radio telescope in West Virginia.  The current radio observatory in Green Bank, WV is surrounded by a 13,000 square mile (slightly larger than the state of Maryland) radio quiet zone, meaning no cell phones, radio, or microwave ovens.

New Clues to the Size of the Universe – March 26, 1963.  The brightest objects in the universe, dubbed quasars, are discovered.  Located over 10 billion light years away, these objects are so bright some astronomers thought they must reside within the Milky Way.  However, further research would prove quasars to be the most distant objects observed by humans.

Signals Imply a Big Bang Universe – May 21, 1965.  The discovery of the cosmic microwave background radiation (CMB) proves the universe was born in a hot, dense state aka the Big Bang.  The CMB was most recently mapped by the ESA Planck mission.  The map shows the state of the universe when it was 380,000 years old.

*Image on top of post is the Great Comet of 1882 from the Cape of Good Hope.  Credit:  David Gill.

Vollmond, High Tides and Lunacy

When teaching astronomy to non-science majors, I try to make connections with the student’s field of study or personal interests.  Sometimes this is not difficult.  For example, I can discuss NASA budgets and cost estimating with business majors.  For art majors, the deep red sunsets that followed the Krakatoa eruption of 1883 found their way into many paintings of the era.  The most notable example of this was The Scream painted by Edvar Munch in 1893.

The Scream by Edvard Munch. National Gallery, Olso, Norway. Aerosols injected into the atmosphere by powerful volcanic eruptions can cause very deep red skies at sunset.

A while back, I talked with someone whose career was in the performing arts, specifically dance.  I was stumped at the time to think of a possible tie in between astronomy and dance.  The closest analogy I could come up with was the classic case of a figure skater demonstrating the concept of angular momentum during a spin such as below.

Angular momentum is conserved, that is, it is not created or destroyed (it can be converted to heat via friction).  Angular momentum (L) is defined as:

L = mrv

m = mass, r = radius, v = velocity

As angular momentum is conserved, the value L is constant.  In the case of the figure skater in the video, she reduces r by drawing in her arms and legs closer to herself.  As the skater’s radius decreases, velocity must increase.  Hence, the rate of spin increases as radius decreases.  You can try this at home even if you do not  know how to skate.  Just find a swivel chair and have a friend spin you around with your arms extended, then draw in your arms close to your body.  You’ll feel your spin velocity accelerate.  Not as much as the skater, but enough to notice.

The conservation of angular momentum has several applications in astronomy, in particular, pulsars.  Pulsars are the remnants of stars that went supernova.  As the outer layers of the star are dispersed in the aftermath of a supernova, its inner core compresses forming the pulsar.  In a pulsar, the gravitational force is so great that electrons merge with protons to form neutrons.  Consequently, pulsars are a sub-class of what are known as neutron stars.  As the radius of a pulsar is reduced, its spin rate greatly accelerates.

We can measure the spin rates of pulsars as they emit radio waves in the same fashion a lighthouse emits a light beam.  The most famous pulsar is located in the Crab Nebula, which is a remnant of a supernova observed by Chinese astronomers in 1054.  This pulsar spins at a rate of 30 times per second.  To put that in perspective, the skater in the video above is spinning 5 times per second.

The pulsar in the Crab Nebula emits high energy x-rays. Red is lowest energy and blue highest energy x-rays. Credit: NASA/CXC/SAO

Is there any sort of analogy in the world of dance?  Ballet dancers use the same method as figure skaters to increase their spin.  However, as there is more friction from a wood floor than there is from ice, the effect is not as pronounced.  Looking around I found a different approach when it came to this and found a connection, albeit allegorical, to the dance performance Vollmond.

Translated from German, Vollmond means Full Moon.  Choreographed by Pina Bausch, the performance centers on two themes addressed in my class.  One is scientific, how the full Moon increases tides, the other not so scientific, how a full Moon affects human behavior.

During a full (and new) Moon, the difference between high and low tides are at their greatest.  During these two phases, the Earth, Moon, and Sun are aligned with each other.  At this time, the effect of the Sun and Moon’s gravity is greatest on the oceans as can be seen below.

Full Moon Tides
Credit: Wikipedia

The gravity from the Sun amplifies the lunar tides.  During a full Moon, high and low tides occur twice a day.  Tides during the full and new phases are referred to as spring tides.  This has nothing to do with the season of Spring.  In a way, it is during this time when the tides spring to life.  When the Moon and Sun are at a right angle relative to Earth, the Sun’s gravity partially offsets the Moon’s gravity and modulates the tides so low and high tidal differences are not as great as the spring tide.  These are referred to as neap tides.  Local conditions can also amplify the tides.  The most dramatic example of this is the Bay of Fundy where high and low tide can differ by 56 feet.

Spring tides at the Bay of Fundy Credit: Samuel Wantman/Wiki Commons.

So, if you live by the ocean, you’ll associate high tides with a full (and new) Moon.  How about the Great Lakes?  Not so much.  The lakes greatest tide is only 5 cm, not enough to be noticed with the naked eye.  The earth you stand on also feels the tidal pull from the Moon.  Like the lakes, it is not noticeable at 25 cm.  As the landmarks rise up and down with the ground, your eye cannot detect ground tides.  We can say, quite confidentially, that the full Moon affects tidal motions.  Can we say the same regarding human behavior?

The words lunar and lunatic have their roots in the Latin word luna.  In ancient Rome, Luna was the goddess of the Moon.  Lunatic means to be moon struck.  We are all familiar with the phrase, “It must be a full Moon.”  Meaning that the full Moon provides an explanation for an increase in bizarre/criminal behavior.  Does the empirical evidence support this?  The short answer is no.  Studies have indicated no change in criminal behavior during a full Moon, or even a scientific model to explain why that would happen.  This highlights the key difference between science and mythology.

Statue of the Roman Goddess Luna. Credit: Wiki Commons

Whenever a student writes the phrase, “I believe” in a science paper, I advise them to take pause and ask yourself why do you believe that?  Science is not about beliefs, but about investigation of the nature and causes of phenomena we observe around us.  If you want to assert something as being true in science, you need a model to explain why it happens, empirical evidence it actually does happen, and independent verification of the original results.  Sometimes you might have a model you think is reasonable, but the empirical evidence does not back it up.  One such case is in economics, where demand and supply curves indicate a minimum wage set above the market rate creates unemployment.  The evidence does not support that meaning a newer, more sophisticated model is required to explain what is happening.

The purpose of this exercise was to find ways to connect a student’s personal interest to a scientific topic.  If that can be accomplished, the chances of building the student’s interest and motivation in the class increases.  In this case, we can use two situations to discern between what passes for science and what does not.  For the teacher, it provides the opportunity to explore areas that were previously unknown.  I would have never learned of the Vollmond dance performance without attempting to match my specialty with the student’s.  It’s a good experience to reach out of your comfort zone to find common ground with your students.  Often, in the classroom, who is the teacher and who is the learner can be a fluid situation.  You have to permit yourself enter your current student’s world of interests.  I have found that as a teacher, that prevents my lessons from going stale over the years.

*Image on top of post is the full Moon, or Vollmond in German.  Credit:  Katsiaryna Naliuka/Wiki Commons.

Gravitational Waves – A New Window to the Universe

Some 1.3 billion years ago, as plant life was making its first appearance on Earth, two black holes 29 and 36 times the mass of our Sun, collided.  The result of this collision was a single black hole 62 times the mass of the Sun.  The remaining mass, equal to three Suns, was expelled as energy.  This energy created a ripple in the space-time fabric referred to as gravitational waves.  These waves, which emanated from the colliding black holes like pond waves formed by a rock tossed into it, were detected by the LIGO team on September 14, 2015.  The announcement made today, culminates a 100 year effort by physicists to confirm Albert Einstein’s prediction of gravitational waves.

What are gravitational waves?

Issac Newton’s theory postulates that gravity acts as an instantaneous force throughout the universe.  That is, the gravitational force from the Sun, Earth, even your body, is felt immediately on every other body everywhere.  As Einstein worked up his theory of relativity, he knew there was a problem with this.  According to relativity, there is a firm speed limit in the universe, this limit being the speed of light.  As nothing, whether it is matter or energy, could travel faster than this, it would not be possible for the effect of gravity to travel faster than light as well.  Clearly, a new way of explaining gravity was required.

Einstein found this explanation in the form of gravitational waves.  If there was to be some sort of perturbation in the Sun’s gravitational field, we would not sense it right away on Earth.  Instead, the disturbance would radiate from the Sun at the speed of light in the form of gravitational waves.  It takes light eight minutes to reach Earth.  Thus, a time lag of eight minutes would occur before we would feel the gravitational disturbance on Earth.  In the same manner, there was a 1.3 billion year lag to detect the gravitational waves from colliding black holes located 1.3 billion light years away.  Had Newton’s theory of gravity been correct, the gravitational effect of the colliding black holes, however faint, would have reached Earth instantly 1.3 billion years ago rather than last September.

I want to emphasize that Newton’s theory of gravity works in most situations.  Newton’s predictions deviate from Einstein’s predictions in two key situations.  One is when a body is located very close to a large mass, such as Mercury is to the Sun.  The other is when a body is traveling near the speed of light.  In other situations, Newton’s and Einstein’s equations yield the same result.  In fact, NASA engineers will use Newton’s version of gravity when they can as it is easier to work with than relativity.  The Apollo program, for example, sent humans to the Moon using Newton as a guide.  Replicating Newton’s results where they are accurate was a key stepping stone for Einstein when devising relativity theory.

Another key stepping stone for relativity was making successful predictions where Newton could not.  One such example is the orbit of Mercury.  The perihelion (spot closest the Sun) of Mercury’s orbit advances 43 seconds of arc per century (43/3600th of a degree) more than predicted by Newton.  This advance is visualized in exaggerated form below.

Credit: Wikipedia/Rainer Zenz

When Einstein found out that his theory’s solutions predicted Mercury’s orbit perfectly, he was so excited he experienced heart palpitations.  As opposed to being a force, general relativity views gravity as a bending of space-time.

Earth bends space-time. Credit: NASA

As an object bends the space around it, another object will travel along the path of that curvature.  Also, electromagnetic radiation such as light will follow the curvature as well.  If an object accelerates, as when happens when black holes are colliding, it will generate ripples in space time.  And it is these ripples that LIGO detected.

A 3-D visualization of gravitational waves generated by colliding black holes. Credit: Henze, NASA

The universe is not very pliable and it took a tremendous amount of energy to create these waves which are very small, only 1/1000th the size of a atomic nucleus.  How much energy?  Matter in the amount of 3 solar masses was converted into energy in the collision.  Using Einstein’s famous equation:

E = mc2

E = 3(1.99 x 1030 kg)(3.0 x 108 m/s)2

E = 1.79 x 1039 J  where J = Joules

The Hiroshima atomic bomb released about 1014 J of energy.  This means the black hole collision detected by LIGO released 1.79 x 1025 times the amount of energy as the 1945 atomic bomb.  When you see the amount of energy involved, and how small the gravitational waves detected were, its easy to understand how difficult it is to observe these waves.  In fact, Einstein was doubtful gravitational waves could ever be detected as they are so faint.  The announcement today is a result of an effort started in the 1980’s to build the LIGO facility.

LIGO’s two gravitational wave detectors. Credit : LIGO

In 1992, the NSF granted funding for the LIGO project to commence.  It consists of two facilities, one in Livingston, LA, and the other in Hanford, WA.  As a sidenote, Hanford was the site of a key plutonium production plant during the Manhattan project.  Each facility has two 4 km tubes where a laser is sent through.  The mirrors in the interferometer are calibrated so when the two light beams reach their final destination, they cancel each other out so no light is recorded at the photodetector.  This is known as destructive interference and is pictured below.

Credit: NASA

If a gravity wave passes through LIGO, the ripple in space-time moves the mirrors just enough to cause the laser to captured by the photodetector.  This movement is much too slight to be felt by humans and thus the need for sophisticated equipment to catch it.

Credit: LIGO

LIGO has been operational since 2002.  During its first run, no gravitational waves were detected.  LIGO underwent a recent $220 million overhaul to increase its sensitivity.  As mentioned in the press conference today, LIGO is only at a third of its final expected resolution capability.  This bodes very well for more discoveries at LIGO over the next decade.  In all, LIGO has cost $650 million since its inception in 1992.  That is 1/10th the cost to rebuild the San Francisco-Oakland Bay Bridge.  This discovery has the potential to open a new window of observation for astronomers.

To the general public, astronomy for the most part means the classic image of an astronomer peering through an optical telescope or the famous imagery from the Hubble Space Telescope.  What is not as well known are telescopes that observe other forms of radiation.  This includes Earth-bound radio telescopes and space telescopes such as the infrared Spitzer Space Telescope and the Chandra X-ray Observatory.  Why bother with these other forms of radiation?  Think of it this way, imagine a tower located a mile away on a foggy day.  The tower has both a light beacon and radio transmitter.  The fog blocks out the light, making it invisible.  However, if you have a radio receiver, you’ll be able to pick up the radio transmission as fog is transparent to radio waves.  In this manner, astronomers use different types of radiation to detect objects not visible in the optical range.

Besides the continuing upgrade at LIGO, there are future gravitational wave observatories anticipated in India, Japan, and it is hoped, in space.  Today’s result overcomes the most important hurdle.  When LIGO was funded, many scientists were skeptical it could actually detect gravitational waves.  Now that we know it can be done, that clears a major obstacle for funding.  The opening of the radio window allowed the discoveries of pulsars and the cosmic microwave background radiation.  The x-ray window allowed us to view accretion disks around black holes.  The next decade should provide us with additional surprises about the universe as the gravitational wave window opens up.

Credit: LIGO

Above is the LIGO gravitational wave detection result announced today.  The strain is the distance space-time was stretched during the event.  At 10-21 m this is, as mentioned before, about 1/1000th the size of an atomic nucleus.  What gives the LIGO team confidence this is not a false detection as the one produced by the BICEP team two years ago is the gravitational wave was detected by both the Livingston and Hanford observatories.  You’ll also note how closely the observed wave matches with the predicted wave.  The hallmark of progress in science is when theoretical prediction matches observation.  If Einstein were around to see this, I suspect he may have had heart palpitations just as when he found a match between relativity and the orbit of Mercury 100 years ago.

*Image on top of post displays how the colliding black holes produced the gravitational waves discovered by LIGO.  Credit:  Credit: LIGO, NSF, Aurore Simonnet (Sonoma State U.)