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The first image of a black hole’s event horizon. (EHT Collaboration)
SPACE
LIVE: Scientists Reveal Groundbreaking Results From Event Horizon Telescope
MICHELLE STARR & SIGNE DEAN 10 APR 2019
Folks, you’re looking at history. Astronomers have just released the very first direct image, ever, of the event horizon of a black hole.
Stop scrolling and just go back up and look at it for a second.
Before this, every image of a black hole was a simulation or an illustration. This ‘photo’ was taken of the supermassive black hole at the centre of a giant elliptical galaxy called M87, around 55 million light-years away. This thing is humungous – around 6.5 billion times the mass of the Sun. Isn’t it just glorious?
It’s the first result from the Event Horizon Telescope, a global collaboration that turned radio telescopes around the world into one giant telescope, expressly to find out what a black hole looks like, in real life.
Beautifully, it matches predictions dating back decades. This is it. We now know, for a fact, that the astrophysical objects that were just theory a mere 50 years ago are really what astronomers and physicists thought they were.
“The confrontation of theory with observations is always a dramatic moment for a theorist,” said astrophysicist Luciano Rezzolla of Goethe Universität in Germany. “It was a relief and a source of pride to realise that the observations matched our predictions so well.”
It looks a bit like a blurry orange coffee stain, but here’s what we’re looking at. In the middle is the shadow of the black hole. We can’t actually see the black hole itself, because its immense gravity doesn’t allow any detectable radiation to escape, so it appears as opaque space.
Around it is the accretion disc. M87’s supermassive black hole is active, which means it’s surrounded by a tremendous accretion disc of very hot, swirling gas and dust that is slowly falling into the black hole. That disc gives off a lot of radiation.
Because the disc is rotating, it appears brighter where it is moving towards us, and dimmer where it is moving away. This effect was predicted by Einstein’s theory of general relativity.
The image isn’t high-enough resolution at this point to measure the rotation speed, but the EHT team could tell that it’s rotating in a clockwise direction.
Future analyses of the data – which are all being made publicly available – could reveal more details, such as how closely the image matches predictions of general relativity. It could also help astrophysicists figure out the mechanisms that produce the enormous relativistic jets that shoot from active black holes.
You can read the full news story on the announcement here.
Read our live blog of the press conference unveiling the historic image below.
8:45 am EDT: It’s T-minus fifteen minutes until the announcement begins! Make sure to keep refreshing this page for all the updates as they come! Apologies in advance for any typos we make in our excitement. (If you’re watching along, best to open the livestream in a new tab.)
8:46 am EDT: Okay, so here’s what we’re waiting for.
Two black holes have been the focus of the EHT’s attention: Sagittarius A*, the supermassive black hole at the centre of the Milky Way galaxy, and the supermassive black hole at the centre of another galaxy called M87.
Sgr A* is about 4 million times the mass of the Sun, with an event horizon 44 million kilometres in diameter (about 30 times the size of the Sun), and 25,640 light-years away.
M87’s black hole is a lot bigger. It’s about 6 billion times the mass of the Sun – around 1,500 times more massive than Sgr A*. But it’s also around 2,000 times farther, at a distance of 50 million light-years, so its apparent size should be a little smaller.
Trying to image these targets is like trying to photograph a tennis ball on the Moon, through clouds of dust.
8:48 am EDT: We don’t know which black hole we might see, or what it will look like.
French astrophysicist Jean-Pierre Luminet, who gave the world the first visual simulation of a black hole back in 1978, told us last week, “I have not seen the image, but I suspect that the M87* BH image could be better than that of SgrA* because the latter could have more perturbing diffusion effects.” In other words, its stronger gravity could produce stronger effects. Neat!
8:50 am EDT: More facts while we wait!
If what we’re getting are the pictures, we won’t actually see the black hole itself, because the gravitational pull is so strong that no electromagnetic radiation can escape – not even light is fast enough for black hole escape velocity. That point of no return is called the event horizon.
We think we will see the silhouette of that event horizon, backlit by the very hot gas and dust around the black hole, bending and magnifying the spacetime around it.
8:51 am EDT: We are nervously eating snacks.
8:52 am EDT: Here’s why we’re so certain that it’s indeed a black hole we could be seeing shortly.
Theoretical astrophysicist Philip Hopkins of Caltech (who is not involved in the EHT) told us, “I don’t think you’re going to find astrophysicists who think that the thing in Sgr A* at the centre of the galaxy or at the centre of M87 is anything but a supermassive black hole, because the constraints from dynamics of stars around those systems have ruled out any other kind of compact astrophysical object that we know how to make with present physics.”
So if it ain’t a black hole, a lot of scientists are going to have… a lot of work to do!
8:55 am EDT: FIVE MINUTES TO GO!
8:56 am EDT: While we wait, let’s discuss the Event Horizon Telescope itself. The EHT is a radio telescope, which means it can pick up the long, low-frequency radio wavelengths that penetrate the clouds of dust obscuring black holes.
It’s also not just one telescope, but an entire network, spanning the globe. It uses a radio astronomy technique called very-long-baseline interferometry (VLBI), in which multiple telescopes work together as one. So, the EHT is effectively one telescope the size of Earth. It has unprecedented resolution.
08:59 am EDT: One minute! We’re not counting, you’re counting.
09:00 am EDT: Okay, okay, deep breaths. We are not hyperventilating at all. Here we go!
09:00 am EDT: IT IS DEFINITELY THE PICTURE.
9:02 am EDT: The livestream has commenced, and we’re going to have a brief welcome before the simultaneous announcement starts across the globe! Speaking first is Carlos Moedas of the European Research Council. He is very emotional, and can we blame him? No!
“Einstein could not imagine what he discovered… To take a picture of something one man dreamt 100 years ago, you need people from 40 countries.”
“If there is a big moment for all of us, it is today.”
9:04 am EDT: You can follow along on Twitter with the hashtag #EHTblackhole
09:08 am EDT: Here it is! Everybody, WE HAVE RECEIVED THE PICTURE!
The first ever image of a black hole.
Taken by Event Horizon Telescope. #EUFunded.#RealBlackHole. pic.twitter.com/seOgqfkuYL
— European Commission 🇪🇺 (@EU_Commission) April 10, 2019
09:10 am EDT: Oh wow. Look at that. Look at it. That’s a BLACK HOLE’S SHADOW. That’s the accretion disc.
09:13 am EDT: “Even a child knows what a black hole is, and the best description actually came from a child – it’s just a hole you cannot fill,” says Luciano Rezzolla from Goethe University Frankfurt.
“You may wonder, how do you know it’s a black hole? The answer is that it matches extremely well what we predicted in theory.”
09:14 am EDT: We have constructed tens of thousands of predictions of black holes, Rezzolla says, and some of these come very close to the image captured by the Event Horizon Telescope.
09:15 am EDT: Eduardo Ros from the University of Granada takes the stage to tell us how the observations were taken. What was really important is that they used telescopes where the atmosphere is very thin and dry, to avoid atmospheric interference. Then they had to pay careful attention to the weather, and be ready to take observations on short notice.
09:17 am EDT: The hard discs from the Antarctica telescope had to sit in storage over winter, because a plane couldn’t get in and out easily to transport the data!
09:19 am EDT: Monika Moscibrodzka from Radboud University is explaining what we learned. Over four days’ observing time, they saw that the ring didn’t change size, and didn’t go away. That means it’s likely a permanent object.
The change in the light in the ring – it’s brighter at the front – indicates rotation. The image is not yet clear enough to measure the rotation, but we do know it’s clockwise.
09:22 am EDT: ALL THE DATA is being made public! That is awesome. Six papers are due to appear in The Astrophysical Journal Letters, and they are listed here for you to check out.
“As with all great discoveries this is just the beginning” says @EHTelescope director Shep Doeleman #EHTblackhole https://t.co/RjpPjXDt0a pic.twitter.com/ulngkjkNcz
— Physics World (@PhysicsWorld) April 10, 2019
09:26 am EDT: The picture is of M87*, but the team is confident they’re going to bag Sgr A* soon, so they ask us to “stay tuned”.
“This story is not the story of one hero. It is the story of many heroes.”
09:29 am EDT: And that’s it, that was the announcement! We are now in question time. PHEW, we still can’t believe that we’re staring at the first-ever image of a black hole. Just… look at it.
09:36 am EDT: The questions are so interesting! Meanwhile, we’re gathering up more info about the science behind this huge achievement and will publish a separate article on that soon. Thank you so much to everyone who stayed tuned into our live blog!
We are standing at the dawn of a new age of black hole science.
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The first image of a black hole’s event horizon. (EHT Collaboration)
SPACE
LIVE: Scientists Reveal Groundbreaking Results From Event Horizon Telescope
MICHELLE STARR & SIGNE DEAN 10 APR 2019
Folks, you’re looking at history. Astronomers have just released the very first direct image, ever, of the event horizon of a black hole.
Stop scrolling and just go back up and look at it for a second.
Before this, every image of a black hole was a simulation or an illustration. This ‘photo’ was taken of the supermassive black hole at the centre of a giant elliptical galaxy called M87, around 55 million light-years away. This thing is humungous – around 6.5 billion times the mass of the Sun. Isn’t it just glorious?
It’s the first result from the Event Horizon Telescope, a global collaboration that turned radio telescopes around the world into one giant telescope, expressly to find out what a black hole looks like, in real life.
Beautifully, it matches predictions dating back decades. This is it. We now know, for a fact, that the astrophysical objects that were just theory a mere 50 years ago are really what astronomers and physicists thought they were.
“The confrontation of theory with observations is always a dramatic moment for a theorist,” said astrophysicist Luciano Rezzolla of Goethe Universität in Germany. “It was a relief and a source of pride to realise that the observations matched our predictions so well.”
It looks a bit like a blurry orange coffee stain, but here’s what we’re looking at. In the middle is the shadow of the black hole. We can’t actually see the black hole itself, because its immense gravity doesn’t allow any detectable radiation to escape, so it appears as opaque space.
Around it is the accretion disc. M87’s supermassive black hole is active, which means it’s surrounded by a tremendous accretion disc of very hot, swirling gas and dust that is slowly falling into the black hole. That disc gives off a lot of radiation.
Because the disc is rotating, it appears brighter where it is moving towards us, and dimmer where it is moving away. This effect was predicted by Einstein’s theory of general relativity.
The image isn’t high-enough resolution at this point to measure the rotation speed, but the EHT team could tell that it’s rotating in a clockwise direction.
Future analyses of the data – which are all being made publicly available – could reveal more details, such as how closely the image matches predictions of general relativity. It could also help astrophysicists figure out the mechanisms that produce the enormous relativistic jets that shoot from active black holes.
You can read the full news story on the announcement here.
Read our live blog of the press conference unveiling the historic image below.
8:45 am EDT: It’s T-minus fifteen minutes until the announcement begins! Make sure to keep refreshing this page for all the updates as they come! Apologies in advance for any typos we make in our excitement. (If you’re watching along, best to open the livestream in a new tab.)
8:46 am EDT: Okay, so here’s what we’re waiting for.
Two black holes have been the focus of the EHT’s attention: Sagittarius A*, the supermassive black hole at the centre of the Milky Way galaxy, and the supermassive black hole at the centre of another galaxy called M87.
Sgr A* is about 4 million times the mass of the Sun, with an event horizon 44 million kilometres in diameter (about 30 times the size of the Sun), and 25,640 light-years away.
M87’s black hole is a lot bigger. It’s about 6 billion times the mass of the Sun – around 1,500 times more massive than Sgr A*. But it’s also around 2,000 times farther, at a distance of 50 million light-years, so its apparent size should be a little smaller.
Trying to image these targets is like trying to photograph a tennis ball on the Moon, through clouds of dust.
8:48 am EDT: We don’t know which black hole we might see, or what it will look like.
French astrophysicist Jean-Pierre Luminet, who gave the world the first visual simulation of a black hole back in 1978, told us last week, “I have not seen the image, but I suspect that the M87* BH image could be better than that of SgrA* because the latter could have more perturbing diffusion effects.” In other words, its stronger gravity could produce stronger effects. Neat!
8:50 am EDT: More facts while we wait!
If what we’re getting are the pictures, we won’t actually see the black hole itself, because the gravitational pull is so strong that no electromagnetic radiation can escape – not even light is fast enough for black hole escape velocity. That point of no return is called the event horizon.
We think we will see the silhouette of that event horizon, backlit by the very hot gas and dust around the black hole, bending and magnifying the spacetime around it.
8:51 am EDT: We are nervously eating snacks.
8:52 am EDT: Here’s why we’re so certain that it’s indeed a black hole we could be seeing shortly.
Theoretical astrophysicist Philip Hopkins of Caltech (who is not involved in the EHT) told us, “I don’t think you’re going to find astrophysicists who think that the thing in Sgr A* at the centre of the galaxy or at the centre of M87 is anything but a supermassive black hole, because the constraints from dynamics of stars around those systems have ruled out any other kind of compact astrophysical object that we know how to make with present physics.”
So if it ain’t a black hole, a lot of scientists are going to have… a lot of work to do!
8:55 am EDT: FIVE MINUTES TO GO!
8:56 am EDT: While we wait, let’s discuss the Event Horizon Telescope itself. The EHT is a radio telescope, which means it can pick up the long, low-frequency radio wavelengths that penetrate the clouds of dust obscuring black holes.
It’s also not just one telescope, but an entire network, spanning the globe. It uses a radio astronomy technique called very-long-baseline interferometry (VLBI), in which multiple telescopes work together as one. So, the EHT is effectively one telescope the size of Earth. It has unprecedented resolution.
08:59 am EDT: One minute! We’re not counting, you’re counting.
09:00 am EDT: Okay, okay, deep breaths. We are not hyperventilating at all. Here we go!
09:00 am EDT: IT IS DEFINITELY THE PICTURE.
9:02 am EDT: The livestream has commenced, and we’re going to have a brief welcome before the simultaneous announcement starts across the globe! Speaking first is Carlos Moedas of the European Research Council. He is very emotional, and can we blame him? No!
“Einstein could not imagine what he discovered… To take a picture of something one man dreamt 100 years ago, you need people from 40 countries.”
“If there is a big moment for all of us, it is today.”
9:04 am EDT: You can follow along on Twitter with the hashtag #EHTblackhole
09:08 am EDT: Here it is! Everybody, WE HAVE RECEIVED THE PICTURE!
The first ever image of a black hole.
Taken by Event Horizon Telescope. #EUFunded.#RealBlackHole. pic.twitter.com/seOgqfkuYL
— European Commission 🇪🇺 (@EU_Commission) April 10, 2019
09:10 am EDT: Oh wow. Look at that. Look at it. That’s a BLACK HOLE’S SHADOW. That’s the accretion disc.
09:13 am EDT: “Even a child knows what a black hole is, and the best description actually came from a child – it’s just a hole you cannot fill,” says Luciano Rezzolla from Goethe University Frankfurt.
“You may wonder, how do you know it’s a black hole? The answer is that it matches extremely well what we predicted in theory.”
09:14 am EDT: We have constructed tens of thousands of predictions of black holes, Rezzolla says, and some of these come very close to the image captured by the Event Horizon Telescope.
09:15 am EDT: Eduardo Ros from the University of Granada takes the stage to tell us how the observations were taken. What was really important is that they used telescopes where the atmosphere is very thin and dry, to avoid atmospheric interference. Then they had to pay careful attention to the weather, and be ready to take observations on short notice.
09:17 am EDT: The hard discs from the Antarctica telescope had to sit in storage over winter, because a plane couldn’t get in and out easily to transport the data!
09:19 am EDT: Monika Moscibrodzka from Radboud University is explaining what we learned. Over four days’ observing time, they saw that the ring didn’t change size, and didn’t go away. That means it’s likely a permanent object.
The change in the light in the ring – it’s brighter at the front – indicates rotation. The image is not yet clear enough to measure the rotation, but we do know it’s clockwise.
09:22 am EDT: ALL THE DATA is being made public! That is awesome. Six papers are due to appear in The Astrophysical Journal Letters, and they are listed here for you to check out.
“As with all great discoveries this is just the beginning” says @EHTelescope director Shep Doeleman #EHTblackhole https://t.co/RjpPjXDt0a pic.twitter.com/ulngkjkNcz
— Physics World (@PhysicsWorld) April 10, 2019
09:26 am EDT: The picture is of M87*, but the team is confident they’re going to bag Sgr A* soon, so they ask us to “stay tuned”.
“This story is not the story of one hero. It is the story of many heroes.”
09:29 am EDT: And that’s it, that was the announcement! We are now in question time. PHEW, we still can’t believe that we’re staring at the first-ever image of a black hole. Just… look at it.
09:36 am EDT: The questions are so interesting! Meanwhile, we’re gathering up more info about the science behind this huge achievement and will publish a separate article on that soon. Thank you so much to everyone who stayed tuned into our live blog!
We are standing at the dawn of a new age of black hole science.
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This New $89 Trap Finally Solves The Nigeria Mosquito Problem
Electric Mosquito Killer
Sponsored
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Canadian Visa Professionals
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International journal of high-energy physics
FEATURE
Interview: In it for the long haul
Posted on8 March 2019
We have conquered the easiest challenges in fundamental physics, says Nima Arkani-Hamed. The case for building the next major collider is now more compelling than ever.
Nima Arkani-Hamed
How do you view the status of particle physics?
There has never been a better time to be a physicist. The questions on the table today are not about this-or-that detail, but profound ones about the very structure of the laws of nature. The ancients could (and did) wonder about the nature of space and time and the vastness of the cosmos, but the job of a professional scientist isn’t to gape in awe at grand, vague questions – it is to work on the next question. Having ploughed through all the “easier” questions for four centuries, these very deep questions finally confront us: what are space and time? What is the origin and fate of our enormous universe? We are extremely fortunate to live in the era when human beings first get to meaningfully attack these questions. I just wish I could adjust when I was born so that I could be starting as a grad student today! But not everybody shares my enthusiasm. There is cognitive dissonance. Some people are walking around with their heads hanging low, complaining about being disappointed or even depressed that we’ve “only discovered the Higgs and nothing else”.
So who is right?
It boils down to what you think particle physics is really about, and what motivates you to get into this business. One view is that particle physics is the study of the building blocks of matter, in which “new physics” means “new particles”. This is certainly the picture of the 1960s leading to the development of the Standard Model, but it’s not what drew me to the subject. To me, “particle physics” is the study of the fundamental laws of nature, governed by the still mysterious union of space–time and quantum mechanics. Indeed, from the deepest theoretical perspective, the very definition of what a particle is invokes both quantum mechanics and relativity in a crucial way. So if the biggest excitement for you is a cross-section plot with a huge bump in it, possibly with a ticket to Stockholm attached, then, after the discovery of the Higgs, it makes perfect sense to take your ball and go home, since we can make no guarantees of this sort whatsoever. We’re in this business for the long haul of decades and centuries, and if you don’t have the stomach for it, you’d better do something else with your life!
Isn’t the Standard Model a perfect example of the scientific method?
Sure, but part of the reason for the rapid progress in the 1960s is that the intellectual structure of relativity and quantum mechanics was already sitting there to be explored and filled in. But these more revolutionary discoveries took much longer, involving a wide range of theoretical and experimental results far beyond “bump plots”. So “new physics” is much more deeply about “new phenomena” and “new principles”. The discovery of the Higgs particle – especially with nothing else accompanying it so far – is unlike anything we have seen in any state of nature, and is profoundly “new physics” in this sense. The same is true of the other dramatic experimental discovery in the past few decades: that of the accelerating universe. Both discoveries are easily accommodated in our equations, but theoretical attempts to compute the vacuum energy and the scale of the Higgs mass pose gigantic, and perhaps interrelated, theoretical challenges. While we continue to scratch our heads as theorists, the most important path forward for experimentalists is completely clear: measure the hell out of these crazy phenomena! From many points of view, the Higgs is the most important actor in this story amenable to experimental study, so I just can’t stand all the talk of being disappointed by seeing nothing but the Higgs; it’s completely backwards. I find that the physicists who worry about not being able to convince politicians are (more or less secretly) not able to convince themselves that it is worth building the next collider. Fortunately, we do have a critical mass of fantastic young experimentalists who believe it is worth studying the Higgs to death, while also exploring whatever might be at the energy frontier, with no preconceptions about what they might find.
What makes the Higgs boson such a rich target for a future collider?
It is the first example we’ve seen of the simplest possible type of elementary particle. It has no spin, no charge, only mass, and this extreme simplicity makes it theoretically perplexing. There is a striking difference between massive and massless particles that have spin. For instance, a photon is a massless particle of spin one; because it moves at the speed of light, we can’t “catch up” with it, and so we only see it have two “polarisations”, or ways it can spin. By contrast the Z boson, which also has spin one, is massive; since you can catch up with it, you can see it spinning in any of three directions. This “two not equal to three” business is quite profound. As we collide particles at ever increasing energies, we might think that their masses are irrelevant tiny perturbations to their energies, but this is wrong, since something must account for the extra degrees of freedom.
The whole story of the Higgs is about accounting for this “two not equal to three” issue, to explain the extra spin states needed for massive W and Z particles mediating the weak interactions. And this also gives us a good understanding of why the masses of the elementary particles should be pegged to that of the Higgs. But the huge irony is that we don’t have any good understanding for what can explain the mass of the Higgs itself. That’s because there is no difference in the number of degrees of freedom between massive and massless spin-zero particles, and related to this, simple estimates for the Higgs mass from its interactions with virtual particles in the vacuum are wildly wrong. There are also good theoretical arguments, amply confirmed in analogous condensed-matter systems and elsewhere in particle physics, for why we shouldn’t have expected to see such a beast lonely, unaccompanied by other particles. And yet here we are. Nature clearly has other ideas for what the Higgs is about than theorists do.
Is supersymmetry still a motivation for a new collider?
Nobody who is making the case for future colliders is invoking, as a driving motivation, supersymmetry, extra dimensions or any of the other ideas that have been developed over the past 40 years for physics beyond the Standard Model. Certainly many of the versions of these ideas, which were popular in the 1980s and 1990s, are either dead or on life support given the LHC data, but others proposed in the early 2000s are alive and well. The fact that the LHC has ruled out some of the most popular pictures is a fantastic gift to us as theorists. It shows that understanding the origin of the Higgs mass must involve an even larger paradigm change than many had previously imagined. Ironically, had the LHC discovered supersymmetric particles, the case for the next circular collider would be somewhat weaker than it is now, because that would (indirectly) support a picture of a desert between the electroweak and Planck scales. In this picture of the world, most people wanted a linear electron–positron collider to measure the superpartner couplings in detail. It’s a picture people very much loved in the 1990s, and a picture that appears to be wrong. Fine. But when theorists are more confused, it’s the time for more, not less experiments.
What definitive answers will a future high-energy collider give us?
First and foremost, we go to high energies because it’s the frontier, and we look around for new things. While there is absolutely no guarantee we will produce new particles, we will definitely stress test our existing laws in the most extreme environments we have ever probed. Measuring the properties of the Higgs, however, is guaranteed to answer some burning questions. All the drama revolving around the existence of the Higgs would go away if we saw that it had substructure of any sort. But from the LHC, we have only a fuzzy picture of how point-like the Higgs is. A Higgs factory will decisively answer this question via precision measurements of the coupling of the Higgs to a slew of other particles in a very clean experimental environment. After that the ultimate question is whether or not the Higgs looks point-like even when interacting with itself. The simplest possible interaction between elementary particles is when three particles meet at a space–time point. But we have actually never seen any single elementary particle enjoy this simplest possible interaction. For good reasons going back to the basics of relativity and quantum mechanics, there is always some quantum number that must change in this interaction – either spin or charge quantum numbers change. The Higgs is the only known elementary particle allowed to have this most basic process as its dominant self-interaction. A 100 TeV collider producing billions of Higgs particles will not only detect the self-interaction, but will be able to measure it to an accuracy of a few per cent. Just thinking about the first-ever probe of this simplest possible interaction in nature gives me goosebumps.
What are the prospects for future dark-matter searches?
Beyond the measurements of the Higgs properties, there are all sorts of exciting signals of new particles that can be looked for at both Higgs factories and 100 TeV colliders. One I find especially important is WIMP dark matter. There is a funny perception, somewhat paralleling the absence of supersymmetry at the LHC, that the simple paradigm of WIMP dark matter has been ruled out by direct-detection experiments. Nope! In fact, the very simplest models of WIMP dark matter are perfectly alive and well. Once the electroweak quantum numbers of the dark-matter particles are specified, you can unambiguously compute what mass an electroweak charged dark-matter particle should have so that its thermal relic abundance is correct. You get a number between 1–3 TeV, far too heavy to be produced in any sizeable numbers at the LHC. Furthermore, they happen to have miniscule interaction cross sections for direct detection. So these very simplest theories of WIMP dark matter are inaccessible to the LHC and direct-detection experiments. But a 100 TeV collider has just enough juice to either see these particles, or rule out this simplest WIMP picture.
What is the cultural value of a 100 km supercollider?
Both the depth and visceral joy of experiments in particle physics is revealed in how simple it is to explain: we smash things together with the largest machines that have ever been built, to probe the fundamental laws of nature at the tiniest distances we’ve ever seen. But it goes beyond that to something more important about our self-conception as people capable of doing great things. The world has all kinds of long-term problems, some of which might seem impossible to solve. So it’s important to have a group of people who, over centuries, give a concrete template for how to go about grappling with and ultimately conquering seemingly impossible problems, driven by a calling far larger than themselves. Furthermore, suppose it’s 200 years from now, and there are no big colliders on the planet. How can humans be sure that the Higgs or top particles exist? Because it says so in dusty old books? There is an argument to be made that as we advance we should be able to do the things we did in the past. After all, the last time that fundamental knowledge was shoved in old dusty books was in the dark ages, and that didn’t go very well for the West.
What about justifying the cost of the next collider?
There are a number of projects and costs we could be talking about, but let’s call it $5–25 billion. Sounds like a lot, right? But the global economy is growing, not shrinking, and the cost of accelerators as a fraction of GDP has barely changed over the past 40 years – even a 100 TeV collider is in this same ballpark. Meanwhile the scientific issues at stake are more profound than they have been for many decades, so we certainly have an honest science case to make that we need to keep going.
People sometimes say that if we don’t spend billions of dollars on colliders, then we can do all sorts of other experiments instead. I am a huge fan of small-scale experiments, but this argument is silly because science funding is infamously not a zero-sum game. So, it’s not a question of, “do we want to spend tens of billions on collider physics or something else instead”, it is rather “do we want to spend tens of billions on fundamental physics experiments at all”.
Another argument is that we should wait until some breakthrough in accelerator technology, rather than just building bigger machines. This is naïve. Of course miracles can always happen, but we can’t plan doing science around miracles. Similar arguments were made around the time of the cancellation of the Superconducting Super Collider (SSC) 30 years ago, with prominent condensed-matter physicists saying that the SSC should wait for the development of high-temperature superconductors that would dramatically lower the cost. Of course those dreamed-of practical superconductors never materialised, while particle physics continued from strength to strength with the best technology available.
What do you make of claims that colliders are no longer productive?
It would be only to the good to have a no-holds barred, public discussion about the pros and cons of future colliders, led by people with a deep understanding of the relevant technical and scientific issues. It’s funny that non-experts don’t even make the best arguments for not building colliders; I could do a much better job than they do! I can point you to an awesomely fierce debate about future colliders that already took place in China two years ago: (Int. J. Mod. Phys. A 31 1630053 and 1630054). C N Yang, who is one of the greatest physicists of the 20th century and enormously influential in China, came out with a strong attack on colliders, not only in China but more broadly. I was delighted. Having a serious attack meant there could be a serious response, masterfully provided by David Gross. It was the King Kong vs Godzilla of fundamental physics, played out on the pages of major newspapers in China, fantastic!
What are you working on now?
About a decade ago, after a few years of thinking about the cosmology of “eternal inflation” in connection with solutions to the cosmological constant and hierarchy problems, I concluded that these mysteries can’t be understood without reconceptualising what space–time and quantum mechanics are really about. I decided to warm up by trying to understand the dynamics of particle scattering, like collisions at the LHC, from a new starting point, seeing space-time and quantum mechanics as being derived from more primitive notions. This has turned out to be a fascinating adventure, and we are seeing more and more examples of rather magical new mathematical structures, which surprisingly appear to underlie the physics of particle scattering in a wide variety of theories, some close to the real world. I am also turning my attention back to the goal that motivated the warm-up, trying to understand cosmology, as well as possible theories for the origin of the Higgs mass and cosmological constant, from this new point of view. In all my endeavours I continue to be driven, first and foremost, by the desire to connect deep theoretical ideas to experiments and the real world.
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NASA’s InSight Mission Triumphantly Touches Down on Mars
After enduring a high-tension descent from orbit, the spacecraft will now begin its quest to peel back the profound mysteries of the Red Planet’s interior
By Ian O’Neill on November 26, 2018
An artist’s rendition of NASA’s InSight lander moments before its successful touchdown on the Martian surface. Credit: JPL-Caltech and NASA
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A new space robot now calls Mars “home.”
PASADENA, Calif.—NASA’s InSight lander completed its seven-month interplanetary journey of nearly 500 million kilometers in dramatic style on Monday, slamming into the Martian atmosphere at a speed of nearly 20,000 kilometers per hour. Only six-and-a-half harrowing minutes later, after ejecting its heatshield, deploying a supersonic parachute and firing retrorockets, its speed had dramatically slowed to a jogging pace after traversing the 130 kilometers between Mars’s upper atmosphere and the planet’s arid surface.
According to mission controllers here at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, InSight’s entry, descent and landing (EDL) phase was completed without a hitch and the $850 million lander touched down shortly after 2:50 P.M., Eastern time. The mission’s twin relay CubeSat companions, Mars Cube One (MarCO), which have been flying alongside InSight during its interplanetary cruise phase, also successfully fulfilled their mission, transmitting signals from Mars during InSight’s EDL back to Earth in near real-time. Minutes after landing, InSight transmitted its first color image from Mars, via the MarCO relay, showing a bleak landscape through a veneer of dust that had accumulated on its camera’s protective cover. Now that the dust has settled, NASA can focus on the lander’s future as a scientific gold mine that will give Mars an unprecedented internal examination to better understand heretofore hidden details of the world’s origins and history.
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The lander safely touched down on its dusty landing site of Elysium Planitia, near the Red Planet’s equator, a region scientists refer to as “vanilla”—not because it is boring per se but because it is flat and free of rocky obstacles that could damage the lander. And besides, InSight cares little for the superficialities on the surface; its interest lies far deeper.
InSight, which stands for “Interior Exploration using Seismic Investigations, Geodesy and Heat Transport,” is a stationary science platform with a suite of instrumentation that will work in concert to give the planet an “ultrasound.” Unlike its more mobile brethren, such as NASA’s Curiosity and Opportunity rovers, it will do all of its investigations where it landed, in situ. Its ultra-sensitive seismometer (Seismic Experiment for Interior Structure, or SEIS, experiment) will detect seismic waves rippling through Mars and, by measuring their propagation through the subsurface, will assemble a detailed picture of Mars’s interior for the first time. Using its robotic arm, InSight will pluck SEIS from the lander’s top deck to place it carefully on the dusty surface. Another instrument (the Heat Flow and Physical Properties Package, or HP3, experiment) will also be placed on the surface, deploying a thermal probe that will drill itself several meters into the surface to measure heat percolating through the planet. InSight also has an experiment (Rotation and Interior Structure Experiment, or RISE) that will precisely measure the planet’s “wobble” to reveal the size and density of the Martian core.
Until now, all Mars missions have focused on the planet’s surface and atmosphere. Although InSight will also have an onboard weather station and suite of cameras, the mission’s focus is on peeling back the profound mysteries of the Martian interior.
“The main goal of InSight is to understand what the fundamental makeup is of Mars, as in how large the core is, how large the mantle is and how large the crust is,” says Tom Hoffman, project manager for InSight at JPL. “We’re doing that largely with a seismometer detecting ‘marsquakes.’”
Quakes are a familiar feature of our tectonically active Earth. Continental plates shift as they float atop a hot and viscous mantle, rubbing and pushing against one another, producing earthquakes and volcanoes. Mars, however, is very different. It is not presently tectonically active, and its volcanoes have been dormant for hundreds of millions of years. Unlike earthquakes, marsquakes are a consequence of a cooling and shrinking world, says Hoffman, and hopes are high that there will be many marsquakes for InSight to detect. The seismic waves marsquakes produce will be used by InSight to create a 3-D picture of Mars’s interior—but they can also be used to study meteorites thudding into the surface.
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“Depending on how large the meteorite impacts are and how far away they are from the lander, it determines how well we can detect them or not,” adds Hoffman. “We also have orbital assets [such as NASA’s Mars Reconnaissance Orbiter] that can then show us exactly where that impact was, because we are constantly mapping the surface.”
Interestingly, meteorite impacts also had an important part to play in the selection of Elysium Planitia as InSight’s landing zone, says Suzanne Smrekar, InSight deputy principal investigator, who is also at JPL. Once deployed on the surface, the HP3 self-penetrating heat flow probe—aptly nicknamed “the mole” —will pound the ground tens of thousands of times to eventually burrow as much as 5 meters below the surface. But it can only do so if there is no hard bedrock in its way. How, though, could scientists know whether or not there are mission-scuttling rocks hidden just below Elysium Planitia’s dirt?
“An impact crater can act like a probe of the subsurface,” Smrekar explains. While surveying the landing site during the planning phase of InSight’s mission, scientists studied the ejecta from small impact craters scattered across Elysium Planitia. As a rule, meteors will gouge a hole approximately a tenth as deep as the crater’s diameter. They found that, for this region, craters as wide as 100 meters didn’t appear to throw up any large rocks, meaning the upper 10 meters of this region is composed mainly of fine material, such as small stones, sandy material and dust, that would pose no insurmountable barriers for InSight’s “mole.”
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Assuming the heat flow probe deploys successfully, the measurements it makes could transform our understanding not only of how Mars evolved, but also how other rocky planets, like Earth, came to be.
After formation, planets contain a lot of heat that slowly leaks to the surface over billions of years. Directly measuring the flow of this heat in modern Mars will help alleviate some huge uncertainties in planetary formation models. For example, planets form by slowly accreting asteroids, but the type of asteroid that clumps together greatly affects a planet’s composition and therefore its heat flow. Many indirect measurements of Mars’s heat flow have been made, but they often contradict theoretical models.
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“Some heat flow estimates are consistent with the idea that Mars, and all the rocky planets in fact, formed from a certain class of asteroids—chondritic asteroids—that have a certain amount of radiogenic material [which generates heat],” explains Smrekar. “But some of those measurements don’t agree with that; they indicate that Mars is composed of less chondritic material and its interior should be a lot colder than our models predict.”
Once InSight measures the heat flow number just below its landing site, it can be extrapolated globally, adds Smrekar. “This one crazy number will tell us so much about the history of Mars as well as the present day—that’s what I’m most excited to get.”
Beyond developing planetary evolution models, the heat flow measurements will also have implications for understanding if Mars has ever been habitable enough to support life. Some hypotheses suggest that there may be reservoirs of water just below the Martian surface, and the value of the heat flow number could help us understand whether these reservoirs are in a life-giving liquid state or are a not-so-life-giving solid ice.
InSight has another trick to decipher what’s inside Mars, but it needs a little help from the Deep Space Network (DSN) —radio antennae on Earth that maintain contact with robotic space missions throughout the solar system. By analyzing subtle frequency shifts in radio transmissions between InSight and the DSN, scientists will be able to measure just how fast the lander is moving relative to Earth. Over the two years of InSight’s primary mission, the experiment will build a picture of how much Mars wobbles as it rotates, using the lander as a fixed point on the planet’s surface.
“We’ll be able to track the location of InSight to an accuracy of about 10 inches,” says Bruce Banerdt, InSight principal investigator. “That’s phenomenal—it’s as close as you can get to magic and still be science.”
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Mars’s wobble can provide us with information about the core of the planet, says Banerdt. “If Mars’s core is liquid, it’s actually kinda sloshing around inside, and the size and speed of that wobble is related to the size of the core and the density of the core. The heavier the core, the more sloshing, the greater the effect on the wobble.”
InSight will be very different from the Mars missions that have come before it, but it’s going to fill a crucial role in humanity’s quest to understand how Mars formed and whether it has ever played host to life. Ultimately, by giving Mars an internal examination we’ll be able to compare the Red Planet’s composition with Earth’s, greatly improving our understanding of how planets in our solar system—and even exoplanets orbiting other stars—actually form.
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