Thursday, April 26, 2012

On Outreach...

In my last post, I mentioned that I recently visited Ole Miss to give a colloquium on outreach for their physics department.  Later that night, I also gave a talk at a local bakery on multi-messenger astronomy (public events like this are called "Science Cafes").  The colloquium on outreach was interesting to do since it made me organize my thoughts from my experiences here at LIGO (and this blog was featured) and I wanted to share my thoughts on engaging students and discussing religious issues in general.

The beginning of my colloquium at Ole Miss.

ENGAGING STUDENTS

I specialize in being the scientist that people talk to when they visit LIGO.  That includes taking visitors on a tour of the control room (where all the science happens).  I think everything I talk about is immensely interesting, but some of my visitors (especially the younger ones) will disagree.  So, how can I make this interesting for them?  Usually, anything that is gross (yet age appropriate) will get their attention.

One of the features of LIGO I like to point out is our outstanding vacuum system.  LIGO has 300,000 cubic feet of volume in a vacuum that is 8x better than the vacuum of space the space station is currently orbiting in (that is a trillionth of the atmospheric pressure you are sitting in now).  For some visitors, this is impressive; for others, not so much.  Then I talk about how your blood would boil if you went into our vacuum without a spacesuit.  And I put a little dramatic emphasis on the "boil" part.  Now I've got their attention!

Why would our blood boil if we were inside LIGO's vacuum?

The reason that blood would boil in our vacuum isn't because of temperature.  Rather, it is because our blood stores oxygen and carbon dioxide in solution.  How much it can store is dependent on the pressure that surrounds our body.  Going from atmospheric pressure to 1/1,000,000,000,000th that pressure would allow the oxygen and carbon dioxide to be released from solution in the form of bubble.  Hence, it "boils".  To give an example that most of us encounter in our daily lives, this "boiling" is similar to what happens when you open a 2 liter bottle of soda (or pop, or Coke depending on where you live) - you release the pressure in the bottle and the bubbles come out of the drink.  Another example that many people have heard of is deep sea divers suffering from the bends when they surface too quickly.

RELIGIOUS ISSUES

In one of my first blog posts, I stated that I don't want to argue religious issues here.  I want to make clear that I am not making any statements for or against a view, I simply want to talk about DISCUSSING religious issues when the come up.

Many people who visit LIGO have strongly held religious convictions.  Fortunately, there is very little controversy over LIGO science and religion.  The one concept that can have religious implications if the Big Bang.  This theory (and I mean a scientific theory that is supported by evidence, not a hunch) states that the Universe was once contained in a very dense, very small ball and time effectively started in a large explosion.  This is at odds with many types of creationism.  While this can yield lively debate, that is not something I am interested in doing with visitors; my goal is to talk about science and what LIGO can reveal about our Universe.

My goal when faced with situations like this is to treat everyone with respect no matter what their beliefs are.  Just like it is unlikely for them to convert me to their worldview (assuming it is different from mine), I know it is unlikely for me to change theirs.  So I define what kinds of questions science can and cannot answer: science only ever asks "How?" not "Why?".  For the "Why?" you need to turn to philosophy and religion.  With respect to the Big Bang and creationism, I point out that evidence exists to support the Big Bang in the Cosmic Microwave Background.  But, even if this is not the relic light from the Big Bang, something created it and whatever it was may have also created gravitational waves.  So, while one of our documentaries claims that we are seeking the gravitational waves from the Big Bang (and many other sources), we are really seeking the gravitational waves from whatever created the Cosmic Microwave Background.

Some have accused me of skirting the subject in the way I handle religious issues and they are mostly right.  I try to respect everyone and re-frame the contentious issue in a way that doesn't conflict with religious beliefs and is still true to the science.  But I think it is also important to make the distinction in what science can and cannot do.  Some people believe that science tries to disprove God but the truth is it can't.  Science also can never prove God.

Thursday, April 19, 2012

The Likely End to a Space-Based GW Detector

LISA...

(The video below is large [~44 MB] and dated, but gives good background on the motivation and specifics of a space-based gravitational-wave detector:)

video


About this time last year, I wrote a blog post about the NASA withdrawal from being a full partner in the LISA (Laser Interferometer Space Antenna) with the ESA (European Space Agency).  At that time, it meant that US scientists would still be able to receive funding to develop research programs and contribute to the LISA effort but the ESA would be responsible for the bulk of the work.  This withdrawal by NASA was caused by the poor state of the agency's funding and the cost of the James Webb Space Telescope.  For all of us in doing research in gravitational waves, it was a horrible setback; LISA was once a flagship mission of NASA's Physics of the Cosmos program and the best hope we had of detecting low frequency gravitational waves (< 10 Hz). 

This then led the ESA to redevelop their plans for a new version of LISA (that is referred to as eLISA but is officially known as NGO [New Gravitational-wave Observatory]) in order to lower the cost of the mission by at least 20% and preserve as much of the science as possible.  This new design was published in their "Yellow Book" at the beginning of the year which included, among other things, only 2 arms in a triangular formation (previously there were 3 arms and each corner pair of arms could function as an independent detector), reduced distance between satellites (1 million kilometers instead of 5 million), and a new orbit which is similar to the LISA orbit (in orbit around the Sun about 20o behind Earth in its orbit) but will allow the detector to drift away into the solar system over time.  Below is a short movie illustrating a few orbits - the "drift away" is not noticeable:


video


The newly designed eLISA/NGO received the highest science ratings of the projects up for funding at the ESA.  However, the ESA Science Programme Committee has concerns about the technological readiness of eLISA/NGO to fly in the 2020 time frame and has passed it over to recommend the JUICE (JUpiter ICy moons Explorer)This is likely the last nail in the coffin for a space-based gravitational-wave detector in the foreseeable future.  (Note:  NGO can be considered for future launch opportunities but that is way down the road.)  There is a slight chance that the recommendation could be rejected in favor of gravitational waves when the 19 member states of the ESA make the final decision on May 2.  However, I heard the news of this recommendation from a friend who specializes in LISA science and he didn't seem hopeful for the 11th hour pardon.

I wonder what will happen to the LISA Symposium that is supposed to take place in Paris at the end of May...  Or for that matter, the LISA Pathfinder mission (which will demonstrate the basic abilities that LISA would have needed to have) which is scheduled to launch on June 30.

UPDATE:  I've heard from a LISA colleague that LISA Pathfinder is still a go!  Thanks!

***

On a more uplifting front, I had the wonderful opportunity to speak at Ole Miss (this link will take you to their gravity research group - they do great work!) about the importance of outreach, useful skills for it, and different ways to do outreach (and this blog was featured!).  That night, I also got to demonstrate my points by giving one of their monthly public science cafes.  This experience gave me the chance to really consider what it is that I have been doing professionally for the last 5 years...  What have I learned?  What mistakes did I make?  What surprised me?  What ideas can I pass along on how to do outreach to those who are expected to do it but aren't afforded the extra time like I am?  I'm thinking about posting a summary of my thoughts and speaking points in next week's post (unless something else newsworthy happens in the mean time)!

Thursday, April 12, 2012

Q: How do we know gravitational waves really exist if we've never directly detected one?

Today's question is one that has been asked of me repeatedly while giving tours of LIGO and talks on the science we do:
How do we know gravitational waves really exist if we've never directly detected one?
One question I often get while discussing LIGO science with others is, "How many gravitational waves has LIGO detected?"  Well, the answer to that is none - yet.  But, we also didn't expect to detect any yet.  During our last science run, we were able to detect gravitational waves that change the length of LIGO's arms about 10,000x smaller than the diameter of a proton.  Even though this is almost an unthinkably small distance, this is considered a big gravitational wave at Earth (where these gravitational waves are produced in the depths of the Universe, they are incredibly strong - strong enough to rip you apart) and therefore a rare one - so rare that we statistically didn't expect to see one in the amount of data we collected.  (Of course, the Advanced LIGO upgrade will change that!)

So, if we have yet to make a direct (meaning measured with our own instruments) detection of gravitational waves, how do we know that they really exist?  After all, this is a lot of effort and resources going into the search!  Well, we have seen the effects of gravitational waves on astrophysical systems in the Universe.

In the early 1970's, a pulsar (a very dense star that has beams of radio waves coming out of the magnetic poles) was discovered in the constellation Aquila at the Arecibo radio telescope in Puerto Rico.  The beam of radio waves passed over the Earth 17 times every second.  After observing this star for a while, it was discovered that some of the radio pulses came a little late and others a little early.  The periodicity of these arrival times indicated that the pulsar had a companion star and they orbited around each other (together, this system is known as PSR B1913+16 [referring to its sky coordinates]).  After further observation, it was found that the orbit of these stars around each other was gaining speed indicating that the stars are getting closer together (this is just like how a figure skater starts spinning with their arms extended at their sides and then, as they pull their arms to their body, they spin faster).  This can only happen if energy is being carried away from this system of stars.

The only energy loss that matched what the researchers, Taylor and Hulse, observed was the energy carried away by gravitational waves.  After about 20 years of making observations on this system, their measurements consistently matched the energy loss caused by gravitational waves.

This plot shows the change in the periodic time of closest approach (periastron) of this pulsar system compared to when the first observations were made in the early 1970's.  The red dots are observational measurements and the blue curve is the prediction from general relativity given the emission of gravitational waves.

This provided evidence of the existence of gravitational waves and won them both the 1993 Nobel Prize in physics.  Unfortunately, LIGO will not be sensitive to this particular pulsar system for about 300 million years even with upgrades to the detector.

Now that we know that gravitational waves really are out there, we want to detect them affecting our own instruments so that we can learn more about the sources that made them (after all, we know exactly what is going on for the source above).  Gravitational waves have encoded in them information about what made them very much like how radio waves can have music encoded on them.  Just like without a radio you can't hear the music, without detectors like LIGO, we can't learn more about what made these sources.  Gravitational waves can be emitted by things that don't produce light, like black holes, so we will be able to see them in ways traditional astronomy (astronomy using light) never can.  On top of all that, gravitational waves can travel through matter and emerge unchanged - basically, there is no such thing as a gravitational wave shadow!  So we will be able to observe things in the Universe that will forever be obscured to traditional astronomy.

***

Note that I have added 2 new pages (listed just below the blog banner): "Ask a Question!" and "Contact".  If you have a question you would like to ask, please fill out the form in "Ask a Question!".  If you would like to contact me, please fill out the "Contact" form.  Of course, you are more than welcome to leave comments to any blog post and start conversations with other readers!

Thursday, April 5, 2012

No "Faster Than Light" Neutrinos

SCIENCE AS A PROCESS

Most people see science as purporting itself to be infallible and they can twist this perception for many reasons (e.g. "See, they didn't see what they thought they saw so science cannot be trusted.").  The truth is that science is a process.  It must be reproducible by others.  Sometimes, an experiment comes around that seems to defy the current understanding of science and people are quick to jump and accuse science of being unreliable.  Really, when results like this come to light, it is the duty of other scientists to scrutinize the results: to try to reproduce them and, if they cannot, try to find where the errors in the original experiment occurred.  Most of the time, radical findings are disproved.  When they are not, this is an exciting time for science to learn more about the world around us!  We scientists often spend as much time trying to disprove things as we spend trying to prove them.  Truly revolutionary results often exploit a subtlety in a theory (which in science means a highly tested and verified description of how something works and NOT a hypothesis or guess as it is sometimes used in everyday language) or law that opens the way to a deeper understanding.  Science is not created or invented by scientists - the Universe has its properties and we simply pursue the discovery of them so we can understand better how it works.

THE "FASTER THAN LIGHT" NEUTRINOS

While at the APS April Meeting this past week, there was a lot of excitement (see the talk abstracts in this session) about the "faster than the speed of light" neutrinos that the OPERA collaboration claimed to have observed.  There was extra excitement since there was a final resolution at the beginning of the meeting along with a little drama.  There were even talks on how to use this new coverage as a great outreach opportunity to illustrate science as a process (don't think of the scientific method that you were taught in school - science almost never follows that prescription but it is a good starting point).  I've had many people bring this up to me when I talk about how gravitational waves are expected to travel at the speed of light but could travel slower - never faster.  Then there is usually someone who asks about the new neutrino results and this is when I get to talk about how science is a process.  So, I've decided that I would dedicate today's blog post to the subject matter.  Spoiler alert: there are NO "faster than light" neutrinos!  If you are interested in a very good discussion of these results, disproof, and aftermath, read more about it here.

***  What is a neutrino?  ***

A neutrino is a virtually massless particle that interacts so weakly with matter that it can travel right through any matter with only a few (of billions and billions) interacting with matter.  The neutrino has never been directly detected but we know when one interacts with matter because it produces other subatomic particles or radiation.  Every second, about 10,000,000,000,000 (that's 10 trillion) neutrinos from our Sun pass through every square foot when the Sun is directly overhead.  Those neutrinos pass right through you and, since they so rarely interact with anything, you don't notice a thing. 

Because neutrinos are virtually massless (I say virtually because there is evidence they they do indeed have mass, but it is so small that it hasn't been accurately measured) they can travel at or so near the speed of light that we haven't measured evidence of them traveling slower.  This agrees with special relativity: only massless particles can travel the speed of light and massive particles can only travel slower (there are theoretical particles called tachyons that can only travel as slow as the speed of light and travel faster otherwise - these have never been observed).

***  What is the OPERA experiment?  ***

The OPERA experiment used a beam of neutrinos created at CERN on the Franco-Swiss border to send to the OPERA detector in Gran Sasso, Italy.  That's right, the beam of neutrinos was shot right through the intervening earth between these 2 sites.  Since the distance is known to high precision, the time it takes the neutrinos to arrive at OPERA is directly related to their speed.  It appeared that they were measuring their arrival about 60 nanoseconds (0.00000006 seconds) before they should have if they traveled at the speed of light. 

***  What did we know about the speed of neutrinos before OPERA?  ***

There have been many experiments that have observed neutrinos traveling at the speed of light.  These experiments have been both Earth-sourced (where we create and then detect the resulting neutrinos) and Universe-sourced.  A spectacular example of using neutrinos from space was the detection of neutrinos that preceded the supernova 1987a.  They arrived 3 hours before the light from the stellar explosion did.  This is what is expected because neutrinos are created when the matter in the star collapses before the supernova explosion.  If neutrinos traveled as fast as the OPERA collaboration claimed to have observed them traveling, then after traveling the more than 160,000 light years to Earth they would have arrived 4 years before the accompanying light we observed.

***  Should OPERA have published their result?  ***

So, was the OPERA collaboration wrong to publish their observations?  Absolutely not (in my opinion at least)!  Nowhere in their paper did they claim that they have found a fault with the current understanding of the physics - they simply couldn't disprove their own observations so they opened their experiment up to the scrutiny of the scientific community.  They even recognize the controversial results and their desire for scrutiny of their experiment in their paper (which can be read in full here):
"Despite the large significance of the measurement reported here and the stability of the analysis, the potentially great impact of the result motivates the continuation of our studies in order to investigate possible still unknown systematic effects that could explain the observed anomaly. We deliberately do not attempt any theoretical or phenomenological interpretation of the results. "
THE RESOLUTION TO THE CONTROVERSY AND THE FALLOUT

In the end, it was found that a loose fiber optic cable and an error in their timing produced the superluminal (fancy way of saying 'faster than the speed of light') observations.  THERE IS NO EVIDENCE TO SUPPORT THAT NEUTRINOS CAN TRAVEL FASTER THAN THE SPEED OF LIGHT.  Also, the ICARUS experiment (located in Gran Sasso with OPERA) independently reproduced the experiment and found no faster than light neutrinos.

The heads of the collaboration resigned their post on March 30 (just a few days ago) after a vote of no confidence.  There were scientists in the collaboration who felt the publication of the results was premature, and that not everything that was done was good experimental procedure.  It seems that the resignations were the result of their rush to publish the paper, more than what they published.