English
World Science Festival(Gravitational Waves)
Applause
Thank you.
Appreciate that thank you, I am Brian Green
co-founder with Tracy and I also
want to welcome you to day four
of the 2016 world science festival.
The program tonight
on gravitational waves
its a timely program I trust you all
heard the announcement on
February 11 through you read about it
The first direct detection
of gravitational waves.
amazing, amazing discovery.
[clapping]
and we have here tonight
a group of very individuals who made this discovery
possible
And I'm gonna bring amount just a little bit,
but just a few words at the outset
You know this discovery - to put it in context,
it's a kind of achievement that happens maybe a few times a century
in fundamental science
I mean we were thrilled some years ago for the discovery of the Higgs boson
something that was searched for - for very long period of time and finally was definitively discovered at CERN
Great discovery.
This ranks on par with that kind of experimental observational achievement
and the other side of the story that will come out in the conversation here tonight is that
we're as for the Higgs boson just about everybody was convinced that the experiments would succeed.
mean most people who are following closely the search for the Higgs boson
were saying well if it's not found that's the craziness
means that is got to work out
the theory said that all of the circumstantial evidence
suggests that the particle is out there and indeed it was found
Now with gravitational waves as we'll see
there was never really any doubt
after ... I don't know call it 1950-1960
that these ripple and the fabric of space were a real feature of Einstein's general theory of relativity
but there definitely was controversy as to whether we would ever have the capacity
to catch one of these waves and
we'll hear about why in just a moment, but what it means is
it takes a certain kind of internal fortitude
it takes a certain kind of vision,
it takes a certain kind of stubbornness
it takes a certain kind of independent spirit
to devote your life to this kind of project
and our hats are off to individuals - they now number roughly
a thousand - who made this discovery possible
OK, a little bit of a background before I bring
the panels on stage just to set the stage scientifically, right so
we're all more or less familiar by this stage of the game that Albert Einstein gave us a new theory of gravity
in 1915 the general theory of relativity
The Newtonian picture that we all learned in high school simply spoke about objects pulling on each other
through space
with some sort of
force that was described mathematically but whose mechanism of exerting its influence was
not articulated
Albert Einstein comes along and articulates a way that this force
is communicative and just to give a picture of it, we can bring up
the first little clip here
It goes like this
objects within bring like some free will
like the sun or the planet
They warp the environment
of space and time
and it is warps encurves the space
that are able to cause other objects to move along
peculiar trajectory if you weren't aware of this picture
the metaphor that we love to use, it's imperfect to be sure
but if you think about space and time as sort of like a trampoline
you put some heavy objects in the middle of it it warps
the surface and then if you roll a marble, a marble goes into orbit
much like a planet would
much the same way the sun warps the environment and then the planets go into the
orbital trajectory that we are familiar with
OK, so Einstein give this very beautiful new description
of gravity in 1915 and then the question of course is
"Is it correct?" and indeed they were very quickly to pieces of evidence that seal the deal
The first was an explanation of a puzzle have to do the motion of the planet Mercury
according to Newtonian gravity the planet should just trace out the same orbit
year after year after year
but observation shows the orbit's actually shifting a little bit
Nobody could get a good explanation of this
Einstein comes along and uses his new approach, the new picture of gravity, uses the equation of general relativity
and is able to spot on predict
this sort of procession of perihelion of Mercury
now that was kind of a post diction explaining a puzzle that was already known observationally
But then he was able to go further and make a prediction
for something that has not yet been seen
and indeed that had to do with the bending of light by the sun so
if you have a distant star, it sends like toward the earth going in night trajectory of the sort
but then later on if the earth is on the other side of the sun and you now consider that starlike
according to Einstein new picture it's going to go in a curve trajectory as it goes to the curve environment surrounding the sun
and that has the affect of making the position of the star in the sky shift
Einstein was able to use the equation of general relativity to calculate the angle
and it was just a few years later that team of astronomers went out and measured
the angle between those two positions, taking photographic place during a solar eclipse
so you could see the distant star compared with photographic place taken 6 months earlier
and indeed the data
with a little bit of
massaging, little bit of force, a little bit of knowing answer in this particular case
seem to show that Einstein ideas were correct.
Now since then these experiments have been done
over and over.
There's no doubt any longer that Einstein's theory is correct.
Now, Einstein then went further and as we'll discuss here tonight
He wrote a paper in 1916 in which he basically said
he didn't use quite this language
basically said mathematically that if space is sort of like a trampoline and it can warp and curve
well if you start to tap the trampoline, disturb the trampoline you'll send ripple going along the trampoline
Those ripples, taking away the metaphor, were the ripples in the fabric of space and that's what gravitational waves are
Now the very interesting story that we get into a little bit in just a moment with our panels is
Einstein himself he writes his paper 1916 actually made a little mistake
and maybe it's kind of weird concept - Einstein making a mistake in doing calculation of relativity.
But relativity is hard
and Einstein was the first one who's actually working on this calculation
so he was making what we now call mistakes of a beginner
Novice mistakes.
But he was the guy who plays in the trail,
so it makes perfect sense that he might have make those kind of errors.
Anyway, he corrects the error in 1918 but then he continues to have a really interesting relationship with this idea
thinks it's not quite right, writes a later paper that suggests that's not right.
Bottom line is others come along develop a very beautiful systematic framework for avoiding the pitfall
that Einstein fell into and people absolutely certain that these things are real
What would that mean? It means that if you disturb the fabric of space you should get the gravitational waves, the ripples.
and typical example might be something like this
rapidly orbiting neutron stars or black hole sending out this march of gravitational waves
and as we discuss here tonight what would that mean for somebody in the wake of these waves
the object would be stretched or squeezed according to the map. I just wanna emphasize one thing
This is not true scale
[laugh]
and that is a big deal
because when you actually do this calculation out, you will discover that the stretching and squeezing is so small that it is enormous challenge
to detect this gravitational wave and that the Ligo team has done
Alright now, lets get into the actual discussion
I gonna bring in our panelist on
and let us begin with Rai Weiss of MIT
is one of the creator of LIGO. He first proposed large scale interferometer back in 1972 and he has been scientific and engineering leader ever since
Alright next Barry Barish, many people say that Barry Barish of Caltech saved LIGO at the time it transition into big science
and built the two huge detectors in Louisiana Washington state
He joined LIGO in 1994
and was director for 1997 to 2005. Welcome
Next up, Nergis Mavalvala
I got it. I'm so proud of myself
of MIT, is an astrophysicist who was called a genius award winner for work on LIGO in 2010
She got a PhD from MIT in 1997, post-doctoral Caltech from 97 to 2002
and then joined the faculty of MIT. Welcome.
Next up, Frans Pretorius , who is professor of physics at Princeton University
His primary field of research is general relativity specializing in numerical solution through Einstein's equation
and now we'll see a vital part of this discovery
Finally, David Schoemaker, who is director of the MIT LIGO lab and was the team leader of advanced LIGO
He spent many years upgrading the technology of the observatory