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- [Joe] Hello, I'm Joe DalSanto professor of astronomy
at the College of DuPage
and I'd like to welcome you
to this year's virtual STEMCON.
Got a fascinating topic I'd love to share with you today,
one of the most recent,
one of the most incredible discoveries
that we've made in science, gravitational waves.
To do that I wanna start out by giving you a little bit
of background so you can fully understand
and appreciate this whole thing.
Three main questions we'll cover in this presentation.
What are gravitational waves?
How do we discover them?
Why should we care about them?
Let's begin with the first one, what are they?
To answer that question,
think about how we observe the universe,
astronomers in particular.
We use light, don't we?
Our eyes taking so much information every day
and of course astronomers supplemented that with telescopes,
some very sophisticated.
You might know that light is essentially a form of energy
and it has different wavelengths.
As you see in our images here
we can break light into a longer shorter wavelengths,
but the point of this is how do we use light?
What we see in the universe to explain the universe.
This is obviously how science works.
We'd like to understand the universe,
so how do we do that?
Well, there's many properties of the universe
that we can observe and learn about with light,
I won't take time to go into them now,
think about the sizes and distances
and appearances of stars and galaxies and planets
so much information that we've gathered over the years,
and yet now we have an entirely new way to do that,
a new way to look at the universe.
So one of our best early explanations of the universe
was produced by this gentleman here Isaac Newton,
his classic theory of physics essentially
was an experiential type of a theory.
In other words, our everyday experience
led him to develop various laws of nature.
Now, in his mind, gravity was a force
that he couldn't really explain what it was
but he knew that it acted in a certain way.
It was an attractive force and it varied with distance.
So Newton came up with a very good theory for his time,
you see, in my diagram here showing two objects
attracting each other, you might think of the moon
and the earth or the earth and the sun,
and the simple equation here describes to us
how the universe works.
So here's a good example
of the observations that were made at that time
that led us to a good explanation.
However, by the late 19th century
there were some observations being made
that were difficult to explain with Newton's idea.
In other words, his theory turned
out to be not quite so perfect.
And so the time was right for a new theory,
and you might know that this gentlemen, Albert Einstein
came up with a better theory,
we call it the general theory of relativity.
Now an Einstein's theory of relativity,
gravity is not seen so much as this mysterious force
but rather as you see in my simple diagram here
gravity is seen to be a result of matter curving space.
Kind of a very strange thought, isn't it?
Sometimes we use this two dimensional illustration here
of the sun sitting on kind of a flat plane
and the sun warps or curves the plane.
It's a little harder to imagine that three-dimensionally
but think about how that would feel
how we would experience it.
Notice for example, the earth and other planets
circle around the sun because the space is curved
and incoming comet
rather than going on a nice straight line
would also curve around the sun.
In other words, matter curve space
but space tells matter how to move,
matter must follow the curvature
and again, think of the earth orbiting the sun.
One other very important part of Einstein's theory
was this equation you see at the bottom here
e=mc squared, perhaps you've seen that or heard about that.
It's essentially telling us that matter
and energy are equivalent.
They can essentially be considered very much the same thing,
in two different forms and they can be equivalent.
Okay, so that begins to give us now
as I said, a little background a little context
in which to appreciate this momentous discovery
of gravitational waves.
As we're gonna see it turns out
that Einstein's general theory of relativity
actually predicted gravitational waves.
Here you see in our animation a first example
of how we might envision this,
we can't actually see it, of course,
but in particular two bodies orbiting around each other
will generate waves of gravity.
Now to do that they must lose energy.
What type of energy do they lose?
They lose energy from their orbit.
In other words, they will slowly,
gradually spiral closer together
and even though this takes a very long time,
it is measurable.
Notice in my graph here on the right
the sloping line is indicating that over many years
the amount of time it took for two stars
to orbit each other was decreasing.
So even though we weren't seeing them gravitational waves
we were seeing their effect.
We were seeing the object slowly
gradually getting closer together
as they gave off the gravitational waves.
Well, if they're getting closer together
you can imagine that sooner or later they're going to merge,
they're gonna meet together
and here is perhaps our best opportunity then
to find the gravitational waves to somehow detect them.
So let's go ahead and talk about that from
and how can we detect gravitational waves?
Well, what we're really we talking about here
is if a wave of gravity moves through space
it distorts it or curves it.
How could we measure the curvature distortion of space?
Scientists have come up with what is called LIGO
the Laser Interferometer Gravitational-wave Observatory,
and basically it's composed of very very long arms,
very precisely designed and built.
And in these arms, we're gonna shoot a laser beam.
That laser beam is gonna be split into two,
and as you can see in this diagram here
go down his long pass reflect off mirrors
and then come back to be recombined.
Let me put this animation to start here
as I described this further.
The idea is those two arms are identical in length
to the very highest precision we can manage.
But if a wave of gravity passes through them
they will change their length ever so slightly.
This length or distance change
is what we want to basically detect.
So again, notice here as we shoot our laser
split into two beams and then burns back
and is reflected again to a screen
notice as they exaggerate
of course the length of the arms changing,
we're gonna see now the different light waves as they travel
are gonna recombine
and the changing distance will be detectable.
So here comes Huygens model light waves
and as they bounce one more time and recombine
we see them what we would call out of phase here,
the yellow and the blue,
but notice as the arms change length now,
notice how those light waves may well be in phase.
In other words, we will see a change on that screen.
And again, this is greatly simplified
but you get the general idea here.
Now this change is incredibly tiny.
The distance change of the arms
may be smaller than a typical atom
and yet we have the technology to detect the difference.
So this was a very difficult technical challenge,
required enormous energy time,
and money to construct two different as you see here
in the United States and recently another one's been added
in Italy and others are being planned along the way.
So these gravitational wave detectors
are the way that we're able to see that.
Okay, let's go back now and envision
what this may look like
as two very massive objects merge.
Let's consider probably the ideal case,
there would be two black holes, perhaps you know
the black holes are very very massive objects,
relatively small,
and as two of them would orbit each other
again we would see gravitation waves being emitted
but these are very, very weak,
it's when the gravity waves are at their maximum,
this occurs when the two objects merged
as you're gonna see here, a burst, a stronger signal
so to speak of gravitational waves.
So this is what scientists hope to capture.
This would be our opportunity
to actually detect these extremely weak gravitational waves.
Well, late summer 2015 in September
was the first direct observation.
What an exciting time that was for the team,
in less than one second two black holes merged
and they converted an enormous amount of energy
rather matter into energy.
You can see my number 10 to the 49th watts.
Imagine writing that number out with 49 zeros,
that's the equivalent of taking the mass
of our sun three times that amount
and changing that entirely into energy.
One of the most energetic events we've ever detected
and you can see here the graph showing the actual detection
and visualization down towards the bottom.
Since that time there have been over 50 other
such detections.
So the science is beginning to mature somewhat,
we're beginning to get a little greater number of them
that we can study and begin to see various masses of objects
such as black holes or even other objects
such as neutron stars causing these gravitational waves.
So it's a very exciting time,
it's very early in the study of gravitational waves,
but scientists are very excited after many years
of hard work to actually be able to do so now.
Another huge step it occurred in August of 2017
when an event it was detected
that we now think was two neutron stars merging
but amazingly this event also produced a burst
of light that was not detectable at the earlier events.
Why is this significant?
Well, this gives us the opportunity
to do what is now being called multi-messenger astronomy.
In other words, we can detect the gravitational waves
but we can also detect light of various wavelengths
as you see here visible light x-ray, ultraviolet, infrared,
this gives scientists two complimentary very powerful ways
to study these events.
This first event became known as a kilonova,
this was a anticipated event but a very rare event
and so scientists were writing.
When the first signals were received
numerous scientists throughout the earth
were notified immediately
and many telescopes were then swung towards this event
to observe it again in many different wavelengths of light
and in gravitational waves.
Would you like to see what that looks like?
This of course is just an artist's impression
but it will give you quite a sense
of the violence of this merger.
Here you see the two neutron stars spiraling closer
when they collide tremendous energy is released.
Pretty dramatic animation wouldn't you say,
showing us what that might've looked like
and I have to tell you, this was huge in another aspect,
astronomers have a very good understanding of stars,
we know much about their lives,
how they're born, how they die,
but there of course, there's some things we need
to study further.
Well, this event allowed us to do that.
This event allowed us to learn more about the deaths
of stars and as a result has greatly added to our knowledge.
So, pretty cool stuff, wouldn't you say.
But what does it all mean for you and me
for the average person?
We're probably not gonna get involved in this,
we might be interested to follow it.
Why is this even important?
Well, to answer that let me finish
with a few comments here about why we do science.
Number one, humans simply want to understand the universe,
it's as simple as that,
we've done science now for many centuries,
of course, number two there are many practical benefits,
and to do that, I sometimes use this illustration
with my students of electricity.
Go back about 200 years to the early 19th century.
Electricity was not understood very well at all,
there were a few scientists experimenting with it,
did not affect most people's lives
but little did anyone know the incredible effects
it would eventually have no one could anticipate,
where it would lead
as you see in my images at the bottom here think about it.
It first resulted in a practical sense at least,
invention of the light bulb,
after scientists began to understand it better
laws were developed.
Once the light bulb was invented
that led to further advances in technology
something called a radio.
At that time it was remarkable
to think that one person could speak into a device
and another could hear his voice many miles away.
It was a remarkable achievement at the time
a wireless communication method.
Well, you know the story as the decades went on
in the 20th century, of course, television then
was developed from that earlier technology
that also led to the development of computers
not only in industry but in everyone's home,
and today of course, we all carry around with us
a computer, a cell phones, that's far more powerful
than nearly every computer in existence a few decades ago.
And ultimately this has led now
to the incredible internet that we all love to use
so very much, don't we?
How much information can be shared earth wide?
All of this goes back to the basic research
that began almost 200 years ago into electricity.
And so my point is where will the discovery
of gravitational waves lead?
Well, we don't know,
but that's kind of the point,
we don't know what advances there may well be.
Had you asked someone 200 years ago
could they possibly envision what we have today?
No, so it would sure be interesting to stick around
for 200 more years, wouldn't it?
And see where this leads us.
So this is why I always like to say pure research
does matter.
We do want to invest in learning about
and understanding our universe.
Well, again, quite an interesting topic I think
and again you can see that in the short and longterm
there are certainly benefits to this kind of thing.
I hope you've enjoyed our brief discussion here
of gravitational waves.
Like invite you to look me up on YouTube sometimes,
I have a number of presentations out there in astronomy
that you might enjoy, but for now I like to thank you
for visiting this year's virtual STEMCOM.
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