Gravitational Wave Astronomy: Opening a New Window on the Universe | Martin Hendry | TEDxGlasgow
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0:15 - 0:17There's a classic urban myth
-
0:17 - 0:22which says that if everyone in China
jumps up in the air all together, -
0:22 - 0:24then the Earth
will be rocked off its axis. -
0:24 - 0:27Now, believe me, I've done
the calculations, and I can say -
0:27 - 0:29that the Earth's axis is perfectly safe.
-
0:29 - 0:32Although, as someone who grew up
in Britain in the 1980's, -
0:32 - 0:37the words 'Michael Fish'
and 'hurricane' do spring to mind. -
0:37 - 0:42Nevertheless, even a single person,
if they jump up in the air, -
0:42 - 0:45can, so to speak, make the Earth move.
-
0:45 - 0:48The trouble is, you don't
make it move very much. -
0:48 - 0:53So let's suppose we could
make a measurement, -
0:53 - 0:56not so much about jumping scientists
shaking the Earth, -
0:56 - 0:58but a measurement so precise
-
0:58 - 1:02that it could tell us something about
the change and the shape of space itself -
1:02 - 1:07produced by an exploding star
halfway across the galaxy. -
1:07 - 1:10That really does sound
like science fiction, -
1:10 - 1:13but in fact such a machine already exists.
-
1:13 - 1:16It's called a laser interferometer,
-
1:16 - 1:21and it's one of the most sophisticated
scientific instruments we've ever built. -
1:21 - 1:23And in a few years time
-
1:23 - 1:25we're confident it's going
to open up for us -
1:25 - 1:31a whole new way of looking at the universe
called gravitational-wave astronomy. -
1:31 - 1:37Now gravitational waves are not
the same thing as light; -
1:37 - 1:43they're not part of the spectrum of light
that we call the electromagnetic spectrum, -
1:43 - 1:46stretching all the way from
radio waves to gamma rays. -
1:46 - 1:48We've already got
lots of different types of light, -
1:48 - 1:51and over the last 60 years or so,
-
1:51 - 1:54we've got really rather good
at probing the universe -
1:54 - 1:56with all those different kinds of light.
-
1:56 - 1:59Whether it's building a giant radio
telescope on the surface -
1:59 - 2:02or putting a gamma ray
observatory out in space, -
2:02 - 2:05we've used these different
windows in the cosmos -
2:05 - 2:09to tell us some quite amazing things
about how our universe works. -
2:09 - 2:12We've probed the birth
and the death of stars. -
2:12 - 2:14We've explored the hearts of galaxies.
-
2:14 - 2:21We've even started to find planets
like the Earth going around other stars. -
2:21 - 2:25But the gravitational wave spectrum
will be completely different. -
2:25 - 2:27It will give us a window in the universe
-
2:27 - 2:32into some of the most violent
and energetic events in the cosmos: -
2:32 - 2:39exploding stars, colliding black holes,
maybe even the Big Bang itself. -
2:39 - 2:40Now, what will we learn
-
2:40 - 2:43from the gravitational wave window
on the universe? -
2:43 - 2:47Well, maybe the most exciting thing
is the things we don't know about yet, -
2:47 - 2:49the so-called unknown unknowns,
-
2:50 - 2:53the things that we don't even know
we don't know yet. -
2:53 - 2:56It's going to take a few more years
but we are almost there. -
2:56 - 2:59Now, before we talk
about gravitational waves, -
2:59 - 3:01let's have a think about gravity.
-
3:02 - 3:05There's another urban myth
which I'm sure everyone has heard of, -
3:05 - 3:09the one about the apple falling
on Isaac Newton's head. -
3:09 - 3:13Now, I'm not really sure if there was
any genuine fruit involved in that, -
3:13 - 3:19but wherever he got his inspiration from,
Newton came up with a very clever idea. -
3:19 - 3:23Because he worked out that
he could use the same physical law -
3:23 - 3:26to describe both
an apple falling from a tree -
3:26 - 3:28or the Moon orbiting the Earth.
-
3:29 - 3:32And he called this
his universal law of gravity. -
3:32 - 3:37And it basically says that everything in
the cosmos attracts everything else. -
3:37 - 3:41It's a beautiful theory and
it's also very practically useful. -
3:41 - 3:44It lets us do all sorts of
useful things in our modern world -
3:44 - 3:47and has done for more than 300 years.
-
3:47 - 3:49It lets us fly aircraft
halfway round the world, -
3:49 - 3:53it lets fly a rocket to the Moon and back.
-
3:53 - 3:59But there is a problem with Newton's law
of gravity, a philosophical problem. -
3:59 - 4:04On a very fundamental level
it doesn't really make sense, -
4:04 - 4:08because Newton says there's a force
between the Earth and the Moon. -
4:08 - 4:12Well, how does the Moon know
it's supposed to orbit the Earth? -
4:12 - 4:15How does the force actually get
from the Earth to the Moon? -
4:16 - 4:20This was a problem which no less than
Albert Einstein puzzled over -
4:20 - 4:22in the early years of the 20th century.
-
4:22 - 4:27And Einstein came up
with a truly remarkable answer. -
4:27 - 4:32Now, Albert Einstein was probably
the first celebrity scientist. -
4:32 - 4:34Even though he died in 1955,
-
4:34 - 4:41in 1999, the editors of Time magazine
voted him the person of the 20th century. -
4:41 - 4:44Although I should mention there was
a public vote on the website -
4:44 - 4:46and they went for Elvis Presley.
-
4:46 - 4:47(Laughter)
-
4:47 - 4:50Now I'm as big a fan of
the King's music as anyone, -
4:50 - 4:53but I still have to go
with the editor's decision here. -
4:53 - 4:58In fact I even have my own action
figure of Einstein at the university. -
4:58 - 4:59(Laughter)
-
4:59 - 5:03So what exactly did Einstein do,
if he was the person of the 20th century? -
5:03 - 5:08Well, what he did, was make us rethink
what gravity really is. -
5:08 - 5:11In Einstein's picture,
gravity isn't so much a force -
5:11 - 5:15between the Earth and the Moon
or apples and trees, -
5:15 - 5:20instead it was a curving or a bending
of space and time themselves. -
5:20 - 5:22So a good metaphor here
-
5:22 - 5:25is to think of the Earth sitting
on a stretched sheet of rubber, -
5:25 - 5:27like a trampoline.
-
5:27 - 5:30The mass of the Earth,
the very great mass of the Earth, -
5:30 - 5:33will bend that rubber sheet a lot,
-
5:33 - 5:35and then you don't really need
-
5:35 - 5:39to have the Moon anymore feeling
a force reaching out from the Earth. -
5:39 - 5:43The Moon just follows
the natural curves and bends -
5:43 - 5:46of space and time around the Earth.
-
5:46 - 5:48In fact, Einstein also said
-
5:48 - 5:52that we should no longer really think of
space and time as separate things, -
5:52 - 5:56so you hear people talk about
the fabric of space-time. -
5:56 - 6:02What Einstein said was, that gravity is
a curving, a bending of space-time. -
6:02 - 6:06Or as another physicist,
John Wheeler, put it rather neatly: -
6:06 - 6:13'Space-time tells matter how to move,
and matter tells space-time how to curve.' -
6:14 - 6:17Now, all that sounds
very grand and fundamental -
6:17 - 6:18about the nature of the universe,
-
6:18 - 6:23but it's got a lot of
practical applications as well. -
6:23 - 6:26Down here on the Earth,
in the Earth's feeble gravity, -
6:26 - 6:29there's a very remarkable
prediction of Einstein's theory, -
6:29 - 6:32which you probably
have never noticed before. -
6:32 - 6:34Did you know for example
-
6:34 - 6:38that clocks run more slowly
on the surface of the Earth -
6:38 - 6:40than high above the Earth,
-
6:40 - 6:42because the gravitational
field is stronger. -
6:42 - 6:44You might remember
that scene in the movie -
6:44 - 6:46'Mission Impossible Ghost Protocol',
-
6:46 - 6:49when Tom Cruise is scaling
-
6:49 - 6:53the Burj Khalifa,
the world's tallest building. -
6:53 - 6:56But even when he was
800 metres above the ground, -
6:56 - 6:58Tom's watch, I'm sure
he was too busy to notice, -
6:58 - 7:03but Tom's watch would only be running
a few billionths of a second faster -
7:03 - 7:05than it would have done
down at ground level. -
7:05 - 7:08So what's a few billionths
of a second between friends? -
7:08 - 7:11Well, that's actually enough
to make a difference -
7:11 - 7:13to the Global Positioning System.
-
7:13 - 7:18The GPS satellites,
their data has to be adjusted -
7:18 - 7:21for time running faster
at the altitude of the satellites. -
7:21 - 7:25And that's a whopping
40 microseconds a day. -
7:26 - 7:29Now the radio signals and
microwave signals from those satellites -
7:29 - 7:33can travel about 10 kilometres
in 40 microseconds. -
7:33 - 7:37So just think how bad
your SatNav would be, -
7:37 - 7:39if it were only good to 10 kilometres.
-
7:39 - 7:42We'd all get lost pretty damn quick.
-
7:42 - 7:46So Einstein's theory of gravity,
his General Theory of Relativity, -
7:46 - 7:51really does have everyday
practical effects on our daily lives. -
7:51 - 7:55But it's out there in deep space
where you really see it to the max. -
7:55 - 7:58In fact, if gravity is all
about bending space-time, -
7:58 - 8:00we can do a kind of thought experiment.
-
8:00 - 8:05We can imagine that if you could put
enough matter into a small enough space, -
8:05 - 8:08eventually you would bend
space-time so much -
8:08 - 8:12that even light couldn't escape
the clutches of gravity. -
8:12 - 8:15You've got yourself a black hole.
-
8:15 - 8:19Now black holes were imagined
around the time of Einstein. -
8:19 - 8:23In fact, in 1916, just after
Einstein had published his theory, -
8:23 - 8:26there was a wonderful paper
written by a young scientist, -
8:26 - 8:29who was at the front
in the First World War at the time, -
8:29 - 8:31Karl Schwarzschild.
-
8:31 - 8:34And it sets out
the theory of a black hole. -
8:34 - 8:39Black holes really do sound as if they
belong in the realms of science fiction. -
8:39 - 8:42But we do think that
black holes actually exist, -
8:42 - 8:45and that for even light
to escape from a black hole -
8:45 - 8:48truly would be Mission Impossible.
-
8:48 - 8:51We find black holes
in the remnants of exploded stars, -
8:51 - 8:54we even seem to find
them in supermassive form -
8:54 - 8:58in the hearts of virtually
every galaxy in the universe. -
8:58 - 9:03Imagine you could take a black hole
and move it close to the speed of light. -
9:03 - 9:05That would shake up space-time a lot,
-
9:05 - 9:09like dropping a cannonball
on that fabric of a trampoline. -
9:09 - 9:11It would send ripples spreading out,
-
9:11 - 9:15and those ripples are
what we call gravitational waves. -
9:15 - 9:19So gravitational waves would be
produced by things like black holes, -
9:19 - 9:22or their slightly less extreme
gravitational cousins -
9:22 - 9:24called neutron stars.
-
9:24 - 9:26And if you could get two of them
to collide together -
9:26 - 9:28close to the speed of light,
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9:28 - 9:30that would really make some waves.
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9:30 - 9:32That's what we're looking for
-
9:32 - 9:37as we embark on this new field of
gravitational-wave astronomy. -
9:38 - 9:39If only it were that easy.
-
9:39 - 9:42That's the plan, but to do it is tough,
-
9:42 - 9:44because even though
the gravitational waves -
9:44 - 9:47shake up space-time colossally
where the black holes are, -
9:47 - 9:51just like ripples in a pond,
if they spread out through the universe, -
9:51 - 9:53they get weaker and weaker.
-
9:53 - 9:55By the time they arrive at the Earth,
-
9:55 - 9:58the shaking of space-time
that we're trying to measure -
9:58 - 10:02is roughly speaking about a millionth
of a millionth of a millionth of a metre. -
10:02 - 10:04That's pretty tough to measure.
-
10:04 - 10:06So how do you do it?
-
10:06 - 10:09Well, at the risk of sounding like
one of those Las Vegas magic shows, -
10:09 - 10:12it's all done with mirrors and lasers.
-
10:13 - 10:17What you do, is you take a laser beam,
you shine that laser beam at a mirror, -
10:17 - 10:21you split it into two beams that
go at right angles to each other, -
10:21 - 10:24bounce them off a mirror,
recombine them, -
10:24 - 10:26and then have a look at what you've got.
-
10:26 - 10:30If the two beams have travelled
exactly the same distance, -
10:30 - 10:34then what you get back is the beams
in perfect step with each other. -
10:34 - 10:37They're light waves just like
all those other forms of light, -
10:37 - 10:39so the wave trains will be matched up.
-
10:39 - 10:42But if they've travelled
a different distance, -
10:42 - 10:45they'll be out of step with each other,
they'll interfere with each other - -
10:45 - 10:48we call this phenomenon interference,
-
10:48 - 10:53so that's why these things
are called laser interferometers. -
10:53 - 10:57So a laser interferometer
is a cool thing to have -
10:57 - 11:00if you want to try and
catch a gravitational wave. -
11:00 - 11:03But remember they're
incredibly minute signals, -
11:03 - 11:08so it's going to be a huge
engineering challenge to build one. -
11:08 - 11:11So Einstein said that
when a gravitational wave goes by, -
11:11 - 11:16it will stretch and squeeze
the space-time in our vicinity, -
11:16 - 11:18but by this incredibly tiny amount.
-
11:18 - 11:22So we're trying to use the laser beam
and its interference pattern -
11:22 - 11:25to tell us if a gravitational wave
has gone past. -
11:25 - 11:29But you've really got to scale up
the experiment and go large. -
11:29 - 11:32And that is where LIGO comes in.
-
11:32 - 11:37LIGO stands for Laser Interferometer
Gravitational-Wave Observatory. -
11:37 - 11:40And it's the most ambitious
and sophisticated -
11:40 - 11:45scientific project ever undertaken by
the National Science Foundation in the US. -
11:45 - 11:47In fact, there are two LIGO's.
-
11:47 - 11:52There's one in Louisiana and there's
another one in Washington State. -
11:52 - 11:54And together with
two other interferometers, -
11:54 - 11:59one called GEO in Germany
and Virgo in Italy, -
11:59 - 12:02this is our early warning system
for gravitational waves. -
12:02 - 12:05Now, they're built
in quite remote locations, LIGO, -
12:05 - 12:08and I think the locals
don't really get what they're for. -
12:08 - 12:12One of my LIGO colleagues
was flying over the Livingston site -
12:12 - 12:16and a fellow passenger on the flight
was looking down at the detector and said, -
12:16 - 12:18'I have a theory what that's for.
-
12:18 - 12:21It's actually a secret
government time machine.' -
12:21 - 12:24He wasn't quite sure
how to respond, -
12:24 - 12:27but well he sort of said,
'OK then, why the L-shape?' -
12:27 - 12:29And she said, 'Ah, they have to
come back again.' -
12:29 - 12:31(Laughter)
-
12:31 - 12:34Time travel really is science fiction,
-
12:34 - 12:37but finding gravitational waves,
we very much hope, -
12:37 - 12:39in a few years time, will be science fact.
-
12:39 - 12:41Now it is tough.
-
12:41 - 12:43All those tiny, tiny effects
we're trying to measure -
12:43 - 12:48could be swamped by the local effects
of disturbances from shaking the ground; -
12:48 - 12:50not because of out there in the universe,
-
12:50 - 12:54but because of very much more
mundane phenomena here on Earth. -
12:54 - 12:56So what you've got to do,
is put your mirrors -
12:56 - 12:58on very complex suspension systems
-
12:58 - 13:02that push against the limits
of materials technology. -
13:02 - 13:05And even the buffeting of the air
in the laser beam -
13:05 - 13:06could swamp our signal,
-
13:06 - 13:09so we have to send
the lasers back and forth -
13:09 - 13:12in the most ultra-high vacuum system
anywhere on Earth, -
13:12 - 13:17only one trillionth of the atmospheric
pressure that we're breathing here today. -
13:17 - 13:21So put all that together,
spend a few hundred million dollars, -
13:21 - 13:23and hope you're going to find
some gravitational waves, -
13:23 - 13:26but it takes a lot of scientists to do it.
-
13:26 - 13:30So at Glasgow we're part
of the LIGO scientific collaboration. -
13:30 - 13:33More than 900 scientists
and engineers around the world -
13:33 - 13:35looking for gravitational waves.
-
13:35 - 13:37Now we haven't found any yet,
-
13:37 - 13:41but having multiple detectors,
it's not just a 'buy one, get one free', -
13:41 - 13:47It's because if you detect a signal in
both detectors, both LIGO detectors, -
13:47 - 13:50that helps to convince you
you've really got something. -
13:50 - 13:54And if you see it in Virgo
and GEO as well, all the better. -
13:54 - 13:59So very soon we're going to have
a global network of advanced detectors -
13:59 - 14:02because the LIGO's aren't quite
sensitive enough to do the job yet. -
14:02 - 14:04But we're giving them more heavy mirrors,
-
14:04 - 14:08more powerful lasers,
better suspension systems, -
14:08 - 14:11and we expect by about 2016
-
14:11 - 14:15that we'll have a network of advanced
gravitational-wave interferometers -
14:15 - 14:17looking for gravitational waves.
-
14:17 - 14:20Now how long will we have
to wait to get a signal? -
14:20 - 14:23We don't really know,
but based on what we do know, -
14:23 - 14:25we don't think it should be more
than a few months. -
14:26 - 14:28In fact, at a conference last year,
-
14:28 - 14:31a group of us in Poland
tried to come up with a figure, a date, -
14:31 - 14:33of when we expect to see one.
-
14:33 - 14:35Now our tongues were
a little bit in our cheeks -
14:35 - 14:39when we predicted
the date of January 1st, 2017. -
14:39 - 14:42I did point out there probably
wouldn't be very many people -
14:42 - 14:43at work in Glasgow that day.
-
14:43 - 14:44(Laughter)
-
14:44 - 14:46However gravitational waves are coming.
-
14:46 - 14:49We stand on the brink of opening
this new window on the universe -
14:49 - 14:52and it's a very exciting time
to be an astrophysicist. -
14:52 - 14:54Thank you very much.
-
14:54 - 14:56(Applause)
- Title:
- Gravitational Wave Astronomy: Opening a New Window on the Universe | Martin Hendry | TEDxGlasgow
- Description:
-
This talk was given at a local TEDx event, produced independently of the TED Conferences.
Did you know that gravity can bend space and time, and that clocks run faster at the top of a skyscraper? Martin Hendry describes how Einstein's theory of gravity shapes our modern world, and how lasers, at the heart of the most sensitive scientific instruments ever built, are opening a whole new way of studying the cosmos.
- Video Language:
- English
- Team:
- closed TED
- Project:
- TEDxTalks
- Duration:
- 15:07