Friday, November 4, 2011

2 Questions: "Can there be a gravitational wave detection before Advanced LIGO?" & "What does it mean if gravitational waves aren't detected with aLIGO?"

Sorry for being away from the blog for as long as I have.  What has been keeping me away from you, you say?  Well, I got sick :(  The one thing that I am very susceptible to is sinus infections (ever since I was a kid) and autumn is prime time for me to catch one.  That kept me basically in bed for about 4 days with a few days before and after still feeling miserable but ambulatory.  My waterfall of post-nasal drip has begun to slow down but my coughing is starting to taste funny again.  I'm off to the after-hours clinic tonight to see if I need antibiotics to clear this up.

There was also a meeting at the LIGO Livingston Observatory where I work that brought astronomers and LIGO scientists together to discuss what data of ours they would like to have access to and what is the best way for them to get the data.  This is all in an effort to make the data the the American taxpayer has paid for available to other scientists.  This is an interesting topic because most of us here at LIGO have neuroses about making a detection claim that later turns out to be false.  Because of that, we tend to keep our data close to the vest until we are certain what is in it.  Anyway, I will talk about this more in a later blog post.

Now, back to answering reader questions!  Since I have been away so long I figured I would answer 2:

QUESTION #1

@AstroGuyz asked:

You know the question on every science bloggers' mind is the Big One; "When will LIGO discover gravity waves?"  Are the prospects for gravitational wave detection good before AdLIGO goes online?  Think we'll nab it before the Higgs?
First off, there is very little probability of detecting gravitational waves before Advanced LIGO is ready.  Notice I didn't say it was impossible.  There are 2 situations that could produce a pre-Advanced LIGO detection.

The first possibility is a joint run between two or more detectors outside of the United States.  This happened over this past summer when GEO and Virgo were both operational and while we are still looking at this data, we haven't seen anything yet.  Now that Virgo has commenced its upgrade efforts in earnest, there isn't really another chance for a joint run until Advanced LIGO is ready.  (FYI: you can see what gravitational wave detectors are operating right now on the GWIstat page, which is always displayed under my "Interesting Links" to the right.  Note that not all of these are interferometric (laser) detectors.)

The second chance for detection is going to rely on a single detector, mainly GEO, to be operating when a significant astronomical event is observed using other astronomy observations.  For example, if a supernova is detected in the sky at the same time a very strong event is detected in GEO, then chances are that these two events are related and there is a real gravitational wave detection.  That is why GEO is continually running while LIGO and Virgo undergo their upgrades - so that we don't miss something that is basically obvious.

So, unless one of these two situations happens, we will all need to wait for Advanced LIGO to be done.  And I wouldn't expect a detection as soon as we turn it on either...  It will take a while for us to get all of the new equipment "tuned-up" to the point that it is working to the best of its abilities.  Don't quote me on this, but I wouldn't expect anything until 2016-2017.

As far as detecting gravitational waves before the Higgs particle, I can't say but I am thinking about writing a post about what all the excitement over this particle is about in another post!

QUESTION #2

@EclipseMaps asked:

What are consequences for theory of gravity/relativity if null results for gravitational waves after extended observations?
From my last question, I mentioned not to expect a detection of gravitational waves until about 2016-2017.  Even if that time comes and goes, I still wouldn't get too worried.  However, if 2020 or so comes by (remember, this is just my opinion and not that of LIGO) and we firmly see no evidence of a detection, then this does have some implications.

The first thing most people would think is that LIGO has been a failure.  Actually, that is very far from the truth.  I, along with over 800 scientists in the LIGO Scientific Collaboration, have dedicated our careers to this as well as used taxpayer dollars to search for gravitational wave and we haven't done this on a hunch.  The 1993 Nobel Prize in Physics was awarded for proof that gravitational waves exist by observing their affects on an astronomical system.  We simply want to detect them affecting our own detectors so that we can do astronomy with them.

Not detecting gravitational waves after we have detectors that clearly should be detecting them tells us that there is something we don't understand about general relativity (the theory where gravitational waves originate) or that we don't understand enough about the composition of our universe, namely how many of those things we expect to produce detectable gravitational waves exist.  This would be extraordinarily interesting (although a bit disappointing to me).  So much so, that there would be whole conferences of physicists and astronomers debating the populations of gravitational wave sources to exotic interference such as gravitational waves leaking into separated universes (see my discussion about how gravitons behave in string theory here).

PICTURE FOR THE DAY:

My "Lucky Yen"
This is my "Lucky Yen".  There really isn't anything special about it other than it was given to me by my first physics professor in college, Dr. Plitnik, who gave this to me on my birthday in 1997.  It was just after the Fall semester started.  I know it is kind of dumb, but it meant a lot to me and I have carried it in whatever bag I used through college, grad school and now.  It has even earned its own coin case (which has a higher market value than the coin).

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