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Gravitational waves: A leap towards theory of everything, a moment that rivals Galileo
Dr. David Reitze, Executive Director of the LIGO Laboratory at Caltech,
shows the merging of two black holes at a news conference to discuss
the detection of gravitational waves, ripples in space and time
hypothesized by physicist Albert Einstein a century ago, in Washington.
(Source: Reuters)
In an announcement that electrified the
world of astronomy, scientists said Thursday that they have finally
detected gravitational waves, the ripples in the fabric of space-time
that Albert Einstein predicted a century ago. Some scientists likened
the breakthrough to the moment Galileo took up a telescope to look at
the planets. Watch Video: Gravitational waves from black holes discovered The
discovery of these waves, created by violent collisions in the
universe, excites astronomers because it opens the door to a new way of
observing the cosmos. For them, it’s like turning a silent movie into a
talkie because these waves are the soundtrack of the cosmos.
LIGO scientific collaboration has confirmed discovery of gravitational waves using its detectors“Until
this moment we had our eyes on the sky and we couldn’t hear the music,”
said Columbia University astrophysicist Szabolcs Marka, a member of the
discovery team. “The skies will never be the same.” An all-star
international team of astrophysicists (including from India) used a
newly upgraded and excruciatingly sensitive $1.1 billion instrument
known as the Laser Interferometer Gravitational-Wave Observatory, or
LIGO, to detect a gravitational wave from the distant crash of two black
holes, one of the ways these ripples are created. To make sense
of the raw data, the scientists translated the wave into sound. At a
news conference, they played what they called a “chirp” — the signal
they heard on September 14. It was barely perceptible even when
enhanced. Some
physicists said the finding is as big a deal as the 2012 discovery of
the subatomic Higgs boson, sometimes called the “God particle”. Some
said this is bigger. “It’s really comparable only to Galileo
taking up the telescope and looking at the planets,” said Penn State
physics theorist Abhay Ashtekar, who wasn’t part of the discovery team.
“Our understanding of the heavens changed dramatically”. Gravitational
waves, first theorised by Einstein in 1916 as part of his theory of
general relativity, are extraordinarily faint ripples in space-time, the
hard-to-fathom fourth dimension that combines time with the familiar
up, down, left and right. When massive but compact objects like black
holes or neutron stars collide, they send gravity ripples across the
universe. Scientists found indirect proof of the existence of
gravitational waves in the 1970s — computations that showed they ever so
slightly changed the orbits of two colliding stars — and the work was
honoured as part of the 1993 Nobel Prize in physics. But Thursday’s
announcement was a direct detection of a gravitational wave. And that’s considered a big difference. “It’s
one thing to know soundwaves exist, but it’s another to actually hear
Beethoven’s Fifth Symphony,” said Marc Kamionkowsi, a physicist at Johns
Hopkins University who wasn’t part of the discovery team. “In this case
we’re actually getting to hear black holes merging.”
LIGO scientists claim that the gravitational waves originated from collision of two black holesGravitational waves are the “soundtrack of the universe”, said team member Chad Hanna of Pennsylvania State University. Detecting
gravitational waves is so difficult that when Einstein first theorised
about them, he figured scientists would never be able to hear them.
Einstein later doubted himself and even questioned in the 1930s whether
they really do exist, but by the 1960s scientists had concluded they
probably do, Ashtekar said. In
1979, the National Science Foundation decided to give money to the
California Institute of Technology and the Massachusetts Institute of
Technology to come up with a way to detect the waves. Twenty years
later, they started building two LIGO detectors in Hanford, Washington,
and Livingston, Louisiana, and they were turned on in 2001. But after
years with no luck, scientists realised they had to build a more
advanced detection system, which was turned on last September. “This is truly a scientific moonshot and we did it. We landed on the moon,” said David Reitze, LIGO’s executive director. The
new LIGO in some frequencies is three times more sensitive than the old
one and is able to detect ripples at lower frequencies that the old one
couldn’t. And more upgrades are planned.
Gravitational waves: an astrophysicist answers your questions – as it happened
Folks, we’re going to call it a day now. But don’t forget that if you are awake at 01.00 AEDT (14.00 GMT), then CERN physicist Jon Butterworth will be here, trying to answer all your questions again! What a day! Katie Mack did an amazing job explaining the ins and outs of what she described as a bigger discovery than the Higgs boson. She reassured us that gravitational waves weren’t going to hurt anyone and that – coincidence or not – there was definitely no conspiracy behind the discovery. Katie explained that they’re a whole new window into the universe, allowing us to study the very fabric of reality, and that although it turned out Einstein was right – and they do travel at the speed of light – it wasn’t necessarily so. Thanks
again to everyone for all the fabulous questions and, of course, to
Katie Mack for spending so much time lending us her expertise. You can read all about the discovery below, and be sure to check back soon as we publish more about the exciting news.
One commenter asked: The
short answer is “yes”! Mass was lost when the two black holes
collapsed. One of the black holes was 36 times the mass of our sun and
the other was 29 times its mass. When they collapsed, the resulting
black hole was only 62 solar masses. That means that a mass three times
the mass of the sun was lost! That mass was turned into energy,
which caused the ripples in spacetime – gravitational waves – that LIGO
detected 1.3 billion years later.
A
massive thanks to Dr Katie Mack from the University of Melbourne for
answering all our questions. We’ve had to let her get back to her life
(which I’m guessing means talking about this stuff with other people!) In about 11 hours time (14:00GMT), CERN physicist Jon Butterworth will be doing something very similar! But before we wrap up here, there are a couple of questions
from the comments and Twitter that I’ll be able to help you out with. So
stay with me a little longer!
There’s been lots of amazing questions. Some of them have been very complex! One
such complex question, which quite a few people have asked, is whether
this discovery could help physicists get closer to squaring our two best
theories in physics, which currently conflict with each other. Quantum
mechanics (which is roughly about very small things) and general
relativity (roughly about very big things!) are both superbly accurate. But
they conflict with each other. They can’t both be right. So physicists
have been trying to break them both for decades but they always come out
of tests unscathed. You can read all about that here: Katie says studying gravitational waves could potentially help unify the two theories. “I
think that’s definitely a possibility,” she says. The trick to solving
the problem could be to observe how gravity works in very extreme
environments – which is exactly what LIGO just did when it observed the
gravity wave: That’s difficult to study otherwise, and so it
gives us a lot more information about how gravity works outside of our
everyday experience of it. We are already pretty sure that general relativity has to break down somewhere
because it doesn’t play nicely with quantum mechanics... So far,
everything we’ve seen is completely consistent with general relativity,
but the more we learn about it from experiments like LIGO the better
idea we’ll have of where the edges of the theory might be.
Here’s another question about how we might be able to use the discovery in technology. Katie
says she’s not quite sure how a machine running on gravitational work
would work. But then again, it’s not impossible, she says: So
far all we’ve been able to get a gravitational wave to do for us is move
a mirror suspended in an extremely well seismically isolated vacuum by a
tiny fraction of the diameter of a proton. And it took decades of
planning and construction to be able to do that. But, in a
sense, that little mirror wiggle was a machine running on gravitational
waves! It’s conceivable that we could someday find a way to extract the
energy from gravitational waves to do something useful, but it’s hard
to imagine a scenario in which some other energy source wouldn’t be more
efficient.
Thanks
so much for your thoughtful (and in some cases very informed!)
questions in comments – we’ve done our best to put as many as we can to
Katie, and apologies to those of you who didn’t get a response. Obviously,
a text Q&A isn’t the best way of digging deep into “spacetime”, but
the enormity of this discovery means we’ll be publishing more on it in
the days and weeks to come. So we’ll be wrapping up soon. But I think there’s time for maybe two more questions before we let Katie get back to her life!
Let’s
take a bit of a step back. There are lots of advanced questions in the
comments, which we’ll try to get to. But someone just asked: “Remind me
again what spacetime is?” That seems pretty important since remember, gravity waves are ripples in it. So here’s what Katie said: Spacetime
is what we call the combination of the three dimensions of space and
one dimension of time. It’s not a “stuff” exactly, but it sometimes
behaves that way, stretching and curving and bending in response to the
way mass is distributed in the Universe. Relativity says
that we need to treat time like it’s a dimension, similar to space,
because of how we travel through it. And it turns out that when you have
a big mass somewhere, it not only warps space, but also changes how
things around it experience time. Time moves more slowly when you’re
close to a massive object, for example. So mathematically
it makes sense to link up space and time together as one thing –
spacetime – that gets warped by mass and energy. It’s a bit hard to
conceptualize, I’m afraid!
My colleague Elle Hunt is getting into this. She wants to know if gravitational waves might help the search for extraterrestrial life. Katie’s response was roughly “maybe”: I
don’t see a way for gravitational waves to directly help us find
extraterrestrial life, but it could tell us more about how black holes
and stars form and die, which could in turn tell us about the kinds of
conditions some alien planet might on average expect. For
example, it can tell us more about the rate of gamma-ray bursts in the
Universe, and gamma-ray bursts are the sorts of things that an alien
planet probably should stay away from if it wants to harbour life. And then Katie had another thought: If
you want to get REALLY sci-fi about it, you can imagine some
super-advanced civilisation manipulating massive objects in a way that
could let them modulate gravitational waves to carry a message. But in general it would be a lot easier to just send radio waves.
A few people in the comments asked this: A few people answered saying “the speed of light”. And they’re right. But Katie explains that it wasn’t necessarily so: According
to Einstein’s theory, gravitational waves travel at exactly the speed
of light. And, in fact, in this observation, one of the things that the
scientists were testing was exactly that. In some alternatives to
general relativity, gravity can travel at different speeds for different
frequencies of gravitational waves. LIGO didn’t see that at all – as
far as we can tell so far, it looks like Einstein was right about the
speed of gravity too!
(By the way, make sure you hit the refresh button every now-and-again. Our auto-refresh function isn’t working properly.) We’ve got a great question from a reader in the comments: Katie says there’s lots of information you can get from the “chirp” signal of the black hole colliding. Oh– and if you haven’t heard the sound, here it is. Physicists took the wave they detected and interpreted it as a sound:
Katie says this sound lets physicists figure out where the wave came from: We
can compare the waveform to simulated ones we get from numerical
relativity calculations (solving Einstein’s equations in a
supercomputer) and figure out how the distance to the black hole changes
the shape. If we know the distance, we also know how long ago it
happened, because we know the speed of light, so we can figure out how
long the signal has been travelling toward us.
My colleague here in the Guardian Australia office, Elle Hunt, is wondering how this will help her. (She’s mostly joking.) Katie got a little upset with this: “IT GIVES YOU A NEW WINDOW ON THE UNIVERSE, ELLE!” (We’re doing this over instant messaging, so the capitals are all hers.) She collected herself to explain: Okay
so in all seriousness your day to day life will not change now that
astronomers can WATCH BLACK HOLES COLLIDING and study the details of the
VERY FABRIC OF REALITY. You can safely ignore it if you
want to, but omg really it’s going to be amazing. We are going to learn
so much, we are going to have a MUCH deeper understanding of the
Universe and how it changes over time, and we’re going to be able to
directly observe incredible violent events millions of light years away.
It’s mind boggling. So maybe that’s it. Maybe your mind
will be boggled, and you’ll experience the cosmic vertigo that I feel
every time I think about what’s out there, and how immense it is. Maybe
you’ll be humbled, or inspired, or just awed. Gravitational waves will
not cure cancer, but studying them can help us better understand areas
of physics that might someday connect to new treatments, just like
studying antimatter has led to PET scans, and observational methods used
in astronomy are often applied to improvements in medical imaging. Gravitational
waves are not going to be powering cars any time soon, but general
relativity is already part of GPS. And the development of the LIGO
experiment has been a massive effort in developing new ways of using
lasers and new materials science, which will have all sorts of
applications and are probably already improving lives. We don’t know yet
all the ways this kind of work will affect our lives, but it’s a good
bet we’ll find some amazing ones.
A
lot of people are saying that the discovery of gravitational waves
opens a new window on the Universe. Katie confirms that that is
completely true and not even a bit of an exaggeration. It could have
implications for theories of gravity as well as our understanding of
black holes, stars and entire galaxies, she says: It’s an
entirely new way of looking at the cosmos, using an entirely new way of
seeing (or “hearing” if you prefer that analogy, keeping in mind that
it’s not exact). We’ll be able to study things that we would never be
able to see in any kind of detail or perhaps even at all. We’ll be able
to watch as black holes (and galaxies) merge and grow, throughout an
incredibly huge volume of the Universe. We can test theories of gravity,
find out how black holes spin, learn about the formation of stars and
their deaths. It’s an immense treasure trove of information and I can’t wait to see what it will tell us.
Twitter user John Stetson asks
Katie to put the gravitational waves discovery in the context of other
recent scientific breakthroughs. How might it change how we think about
physics in future?
@guardian@mikeyslezak how many doors does this discovery open to the future of physics? Can you compare it with recent science big-deals?
In Katie’s informed opinion, it’s a bigger deal than the
detection of the Higgs boson – “because it gives us more stuff to do and
more opportunities to discover new things”: It’s probably on
par with the discovery of dark energy, though in that case, we really
weren’t expecting dark energy at all. In this case, we knew pretty well
that gravitational waves existed, but we couldn’t detect them and thus
use them to study the cosmos. Now we can.
Could gravitational waves be dangerous? Thankfully, Katie says no. They’re actually “really, really fantastically weak”: We
had to build a system that could measure a change in length of a
thousandth the diameter of a proton just to be able to detect this
signal at all. And all gravitational waves do is stretch and squeeze
things a tiny, tiny bit – so I don’t see a way for them to harm us. If
something was massive enough and close enough to produce an even
slightly non-tiny gravitational wave effect, then it would probably
obliterate us from whatever it was doing to make that wave. Uhh... phew!
Guardian Australia’s Walkley-winning marsupial correspondent First Dog On The Moon is wondering whether it is a conspiracy?! (Of course he is.) It’s
not a conspiracy, but people on Twitter have asked similar questions
about whether it was a coincidence that as soon as the LIGO machine (a
“tube with a laser shooting through it”... broadly) was turned on, it
detected a massive gravitational wave in action.
@guardian@MikeySlezak Was it purely coincidence they captured the merger of these black holes? Seems so improbable.
Here’s First Dog’s question in full (caps original...):
As I understand it, these two
black holes crashed into each other a billion years ago, a gazillion
miles away in space – and the resulting gravity waves have been hurtling
toward us ever since.
Is the arrival of these waves like a one off event? Or is it like the ocean – a constant rippling sort of thing?
Because
if it is a one-off event it is a pretty amazing coincidence that all
these scientists decided to flick the switch on the LIGO machine JUST IN
TIME FOR THESE GRAVITY WAVES FROM A BILLION YEARS AGO TO ARRIVE ON
EARTH.
THAT IS EVEN MORE OF AN AMAZING COINCIDENCE THAN PRETTY MUCH ANYTHING EVER!
Or
have these waves just been pootling through here the whole time – and
if they have, how can we then get the distinct “sound” of the two black
holes colliding?
Katie says: They crashed into each other about a billion
years ago and yeah, really far away (depending on how you measure it,
somewhere around a billion light years away). And yeah, the waves have
been coming toward us ever since (“gravitational waves”, not “gravity
waves”, as it happens). It’s a one-off for that PARTICULAR binary
system — the two black holes have merged now and they’re done. But there
are LOTS of systems like this around the Universe, and probably many
more also happening right now. And if there’s a binary system that
hasn’t yet merged, that’s sending us a kind of constant rippling. I
guess it’s a coincidence for this particular system, but we’ve missed
all the other black hole mergers that have happened since the beginning
of time – and there are lots more happening that hopefully we’ll now
see. In short: the Universe has been buzzing away with all this
gravitational radiation forever and we’ve been completely unable to
perceive it until now.
A lot of people on Twitter are asking whether the discovery helps in any way with time travel? Katie says – sadly – no: All
we’re doing here is listening to the disturbances in spacetime caused
by massive objects (like black holes) far away. We still don’t have any
way to manipulate spacetime ourselves (except, you know, by curving it
very very slightly by piling up rocks or something). Even if we could
manipulate spacetime easily, it’s not at all clear that time travel
wouldn’t be completely ruled out by some as-yet unknown physical law. Basically,
you’d have to loop spacetime around itself in some complicated way and
then travel through that loop and it’s so far beyond what we can even
conceive of ever doing, even theorists think it may not be possible in
principle. It’s important to remember that spacetime is
the sort of background in which everything happens, and it can be curved
and stretched and squeezed and stuff, but that stretching and squeezing
never reverses time. It can slow it down or speed it up, but that’s
about it.
You guys will have to excuse me while I get my nerd on here for a second. This is something I’ve been wondering... So as Katie just explained, they’re detecting tiny changes in the size of spacetime itself. But how can you measure that? I
mean, let’s say I try to measure the size of something with a ruler. If
spacetime itself shrinks, both the thing I’m measuring and the ruler itself will shrink – so according to my ruler, it wouldn’t have changed size. Here’s what Katie said: Great
question! To measure it we rely on another of Einstein’s great insights
– that the speed of light is constant NO MATTER WHAT. That means that
when you shoot a laser through a 4km tube (which is what the LIGO
machine does) and that tube gets a little bit longer because spacetime
is stretching, light just keeps on at its usual speed and so takes a
little longer to get to the end. So with LIGO, it’s set
up so that the laser light going through each arm comes together at the
middle and matches up perfectly (to cancel out), but when a
gravitational wave comes through, one arm gets a little longer and the
other a little shorter. So the light takes a little
longer to get down one arm than the other, and that messes up the
perfect alignment at the middle, so you can see that the perfect
cancellation has been lost. Assuming nothing else moved the mirrors,
it’s a sign spacetime itself changed shape!
@guardian@MikeySlezak what is the substance of the wave? I.e., what is it that's moving?
Katie: Spacetime! The fabric of the
Universe. Einstein’s big insight was that space and time are both tied
in together in this sort of single concept called spacetime, and it can
curve and stretch and squeeze... What we feel as gravity is just how we
experience the curvature of spacetime around massive objects.
Gravitational waves are fluctuations of curvature in spacetime. Michael: Hang on. “Fluctuations of curvature in spacetime”? Katie:
Yeah, so when you’re close to something massive, spacetime curves in
toward that mass (usual visual analogy: a bowling ball making a dent in a
rubber sheet – though you have to imagine that in a higher dimension!). As
a result, the paths of other masses and even of light get diverted a
bit toward that mass, because the spacetime they’re travelling through
is bent. A gravitational wave is when spacetime ripples happen –
the curvature of empty space gets disturbed because of the mass
accelerating in some way nearby sending ripples through the space around
it. It’s kind of like if you put a bowling ball on a trampoline
and then bounce it up and down – it sends little wobbles of disturbance
out.
So, physicists have announced the discovery of gravitational waves. You’ve
heard they’re “ripples in the fabric of spacetime”. You’ve heard they
were a prediction of Albert Einstein’s general theory of relativity. You
probably even know the waves that were detected were created when two
massive black holes circled each other and violently collapsed. You can
read all about the discovery here, and we’ve already answered a few questions here. But we know you’re still brimming with questions! So here we have Dr Katie Mack,
an astrophysicist from the University of Melbourne. She’s on hand to
answer Everything You Wanted To Know About Gravitational Waves But Were
Too Afraid To Ask. No question is too basic! Hit us up in the comments and I’ll put them to Katie, who will do her best to bring you up to speed.
Gravitational Waves Exist: The Inside Story
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— John Stetson (@ruiduarte16) February 12, 2016
@guardian @mikeyslezak how many doors does this discovery open to the future of physics? Can you compare it with recent science big-deals?— Keith Brewster (@k_brewster) February 12, 2016
@guardian @MikeySlezak Was it purely coincidence they captured the merger of these black holes? Seems so improbable.— msatonienne (@msatonienne) February 12, 2016
@guardian @MikeySlezak what is the substance of the wave? I.e., what is it that's moving?
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