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Brian Koberlein
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Target Acquired

Now that New Horizons has zipped past Pluto, it’s main mission is to gradually transmit back all the data it gathered during the flyby. We’ve already learned some amazing things from the mission, and we’re certain to learn more as the rest of the data reaches us. But not content with just one flyby, the New Horizons team has another target in their sights.

The target they’ve chosen is known as 2014 MU69. It’s about 35 km across, and is part of the Kuiper belt, which is an icy outer region of objects similar to the asteroid belt between Jupiter and Mars. The encounter will give us an opportunity to see a Kuiper belt object up close, so we should learn a lot form a type of solar system bodies we currently know very little about.

If all goes as planned, New Horizons should make its flyby of MU69 in January 2019.
Having successfully flown past Pluto, New Horizons sets its target on an icy body in the Kuiper belt.
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It goes better if you planet ahead. :-))
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You Are Not Stupid

“So what do you do for a living?” I always cringe a bit when that question comes up among strangers, because when I reveal that I’m an astrophysics professor the response is almost always the same. “Um…wow…. You must be really smart!”

While it’s often intended as a compliment, it really isn’t. Smart didn’t allow me to become an astrophysicist. Hard work, dedication and the support of family and friends did. It’s also one of the most deeply divisive misconceptions about scientists that one can have: scientists are smarter than you. Part of this stems from the idolization of brilliant scientists. Albert Einstein was so smart that fictitious quotes are attributed to him. Media buzzes whenever Stephen Hawking says something about black holes. Any quote by Neil Tyson is a sure way to get likes on Facebook. We celebrate their genius and it makes us feel smart by association. But this stereotype of the “genius scientist” has a dark side.

For one there’s expectation that to do science you must be super smart. If you struggle with math, or have to study hard to pass chemistry, you must not have what it takes. The expectation to be smart when you don’t feel smart starts to foster a lack of self confidence in your abilities. This is particularly true if you’re a girl or minority where cultural biases presume that “your kind” aren’t smart, or shouldn’t be. Lots of talented children walk away from science because they don’t feel smart.

Then there’s the us vs. them mentality that arises from the misconception. Scientists (and fans of science) are smart. Smarter than you. You are stupid. But of course, you’re not stupid. You know you’re not stupid. The problem isn’t you, it’s the scientists. Scientists are arrogant. For example, when I criticized a particular science website for intentionally misleading readers, the most popular rebuttal was that I (as a scientist) was being elitist.

Where this attitude really raises its head is among supporters of fringe scientific ideas. Some of the strongest supporters of alternative scientific ideas are clearly quite intelligent. Presidential hopeful and evolution denier Ben Carson is a neurosurgeon. Pierre Robitaille made great advances in magnetic resonance imaging, but adamantly believes that the cosmic microwave background comes from Earth’s oceans. Physicist and Nobel laureate Ivar Giaever thinks global warming is a pseudoscience on the verge of becoming a “new religion.” None of these folks are stupid.

If there’s one thing most people know about themselves it’s that they’re not stupid. And they’re right. We live in a complex world and face challenges every day. If you’re stupid, you can quickly land in a heap of unpleasantness. Of course that also means that many people equate being wrong with being stupid. Stupid people make the wrong choices in life, while smart people make the right ones. So when you see someone promoting a pseudoscientific idea, you likely think they’re stupid. When you argue against their ideas by saying “you’re wrong,” what they’ll hear is “you’re stupid.” They’ll see it as a personal attack, and they’ll respond accordingly. Assuming someone is stupid isn’t a way to build a bridge of communication and understanding.

One of the things I love about science is how deeply ennobling it is. Humans working together openly and honestly can do amazing things. We have developed a deep understanding of the universe around us. We didn’t gain that understanding by being stupid, but we have been wrong many times along the way. Being wrong isn’t stupid.

Sometimes it’s the only way we can learn.
One of the most deeply divisive misconceptions about scientists is that they are smarter than you.
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Climbing the Ladder

A century ago, we didn’t know the size of the universe. We didn’t even know the size of our galaxy.

In 1838, Friedrich Bessel made a breakthrough in determining stellar distances by measuring the parallax of a star for the first time. While this gave us the distances to many nearby stars, it wasn’t effective beyond a few hundred light years. Even now parallax is only useful to about 1,600 light years. This is a small fraction of our galaxy, much less other galaxies and beyond.

But in the late 1800s, studies of dense, spherical clusters of stars known as globular clusters found something interesting. Most of the stars in a cluster had a constant brightness, but some (known as RR Lyrae variables) would periodically brighten quickly then slowly fade. They all have a fairly regular period of about half a day, and they all seemed to peak at about the same apparent brightness. Since stars in a globular cluster are all about the same distance away, this meant that RR Lyrae variables must have a uniform maximum brightness. By comparing the brightness of the variables in different clusters, we could then determine just how far away these clusters are.

In 1918, Harlow Shapley used these variable stars to determine the direction and distance of globular clusters as a way to determine the position of the Sun within the Milky Way. Shapley argued that globular clusters should orbit the gravitational center of the galaxy. By studying the distribution of globular clusters we should be able to determine the size and shape of our galaxy. He found the Milky Way was roughly pancake shaped, with a diameter of perhaps 150,000 light years, and he placed the Sun about 50,000 light years from the center (we now know it is about 27,000 light years). Shapley showed not only that the Sun was not the center of the universe, but that the Milky Way was much larger than anticipated. So large that it might comprise the entirety of creation.

By the 1920s there was a great debate over whether this was actually the case. Shapley felt it was, but others such as Heber Curtis thought otherwise. The debate centered on the distance to certain nebulae. At the time, “nebula” referred to anything (excluding comets) that appeared “fuzzy” rather than distinct like a star or planet. So things like the Orion nebula (a stellar nursery), the Crab nebula (a supernova remnant) were considered nebulae just as they are today, but what we now call galaxies were also known as nebulae. The Andromeda galaxy, for example, was known as the Great Andromeda Nebula. Curtis thought Andromeda was an “island universe” like the Milky Way, likely millions of light years away. Shapley thought Andromeda and other spiral nebula were close to the Milky Way.

The problem was that RR Lyrae couldn’t be used to settle the dispute. While they allowed us to determine the distance to globular clusters thousands of light years away, they were relatively dim and difficult to measure. But in the early 1900s Henrietta Leavitt had found a relation between another type of variable star known as Cepheid variables. Leavitt analyzed more than 1,700 Cepheids to find that their maximum brightness could be determined by the period at which their brightness varied. It became known as the period-luminosity relation. The advantage of Cepheids is that they are much brighter, and could therefore be seen in Andromeda and other spiral nebulae. It was a major breakthrough, but it took more prominent astronomers to make the relation widely known.

While Shapley began using Cepheids to better determine the distances of globular clusters, Edwin Hubble measured Cepheids in Andromeda to find that, sure enough, it was a galaxy about 2.5 million light years away. As he measured the distances to other galaxies, he began to notice a pattern. The more distant the galaxy, the greater its observed redshift. This relation became known as Hubble’s law, and it gave us another tool to determine cosmic distances. Since redshift could be measured fairly easily, Hubble’s law had the potential to measure distances across billions of light years. Hubble’s relation was not without its critics. Originally Hubble’s observations only went as far as about 8 million light years. Extrapolating the relation to a billion light years or more seemed a bit presumptuous. We needed another way to determine the distance of the farthest galaxies.

By the 1970s astronomers began to look toward supernovae as a possible solution. We had observed lots of supernovae in other galaxies by this time, and it was noticed that a particular kind of supernovae known as type Ia seemed to have a consistent maximum brightness. As such they could potentially be used as a standard candle to determine distances. By comparing a supernova’s observed brightness with its actual brightness, we could begin to measure billion light-year distances directly, rather than relying upon Hubble’s law. We found that Hubble’s relation did hold up pretty well over billions of light years, but for the most distant galaxies it didn’t hold up quite so well. In 1998 Saul Perlmutter, Brian Schmidt and Adam Riess had found that supernova distances weren’t consistent with a steadily expanding universe as Hubble’s law implied, but that the universe as a whole must be expanding at an increasing rate. This gave rise to the discovery of dark energy.

At the beginning of the 20th century, we were just beginning to map out our galaxy. By the end of the 20th century we had discovered a universe billions of light years across. The methods we now use to determine cosmic distances are known as the cosmic distance ladder. While the overview I’ve given covers the main methods, it’s important to understand that they aren’t the only methods we use. We have several ways to test one method against another, so we have a good understanding of just how accurate these methods are. There are still uncertainties in any distance measurement, and the greater the distance the greater the uncertainty. There are still debates about the strengths and weaknesses of different methods, but not about the overall scale of the cosmos.

In a very real sense we have climbed the ladder from ignorance to knowledge of just how large the universe actually is.
At the beginning of the 20th century, we were just beginning to map out our galaxy. By its end we had discovered a universe billions of light years across.
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Orion Complex

Orion is one of the more famous constellations, with its three belt stars, bright red-giant star Betelgeuse. When we observe Orion with the naked eye, we can see the bright Orion nebula (also known as M42) as a fuzzy patch within the sword of Orion. But the nebula we see is only the brightest region of a nebula that spans nearly the entire constellation, known as the Orion Molecular Cloud Complex.

The Orion complex is about 240 light years across and only about 1,500 light years away, so it spans a fairly large region of sky. It is a large molecular cloud containing regions of reflection nebulae and emission nebulae, as well as dark nebulae such as the Horsehead nebula.

It is also a stellar nursery. Many of the stars seen in the constellation of Orion have their origins in the Orion complex. Most prominently, the three bright belt stars (Alnitak, Alnilam, and Mintaka) were formed within the cloud. The complex is one of the most active star production regions in the sky, and because of its proximity it gives us an excellent view of the process. When we view the region in infrared, we’ve found over 2,000 protoplanetary disks, where planets are likely forming around young stars.

There’s a lot going on in the region. But when we look at it with the naked eye, we simply see a bright, easy to find constellation. You could say the region is more complex than it seems.
The constellation of Orion is easy to see in the night sky. But around it is the fainter Orion Molecular Cloud Complex.
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Could We Ever Build A Time Machine?

In fiction there are lots of ways to travel through time, from reaching 88 miles per hour in a DeLorean to walking through a circle of ancient Scottish stones. While the idea of time travel is centuries old, it had no basis in reality. But when Einstein developed his gravitational theory of general relativity, some physicists began to wonder if time travel might actually be possible.

One of the central ideas of general relativity is that there is no cosmic clock. While we always experience time at a normal rate, our rate can seem faster or slower relative to another observer. The relations between space and time are distorted by the presence of mass, and for objects such as black holes that distortion can be extreme. So could time be warped in such a way that it loops back on itself? In the 1970s, some physicists began to study this question in a serious way. Not as a serious effort to build a time machine, but as a way to explore the broader aspects of relativity.

One of the we can study the behavior of space and time is through what are known as light cones. Imagine a flash of light at a single point. The light would travel away from that point in all directions, so that the flash of light is an expanding sphere. Since nothing can travel faster than the speed of light, then that expanding sphere marks the limit of your influence. In general, you can’t move outside that sphere, because you can’t travel faster than light. Since it’s difficult to visualize 4-dimensional spacetime, we often imagine space as a two-dimensional surface, like a sheet of paper, and time as being the third dimension. You can imagine it as a stack of paper, with a cartoon drawing on each page, then flipping through the drawings would make them appear to move. Each sheet of paper would be a moment in time, and different pages in the stack of paper would be different moments in time. The only difference is that time is a continuum rather than discrete instants. In this visualization, an expanding sphere of light would start at a point, and with each higher page would be a larger and larger circle. If you flipped through the pages you would see an expanding circle of light. If instead you could see through the paper and just look at the circles, then you would see they form a cone starting at a particular point. This is known as a light cone, and it defines the limit of influence of an object at the point. An object at the starting point cannot influence anything outside of that light cone, nor can it ever move beyond the limit of that light cone.

The path of an object that stays within the light cone is called “timelike,” since it follows the motion of the object through time. Relativity requires that the path of all objects be timelike. So in general relativity the question becomes whether light cones can be warped in such a way that the timelike path of an object connects with its own past. If you found yourself in such a wibbly-wobbly spacetime it would be possible to meet your younger self. Such a loop is known as a closed timelike curve (CTC), and would be an actual time machine.

Interestingly, CTCs are absolutely possible within the theory of general relativity. One place where CTCs appear is in a solution to Einstein’s gravity equations known as the Gödel universe. This is a general relativistic description of a universe with an inherent rotation to it. Of course we know observationally that our universe doesn’t have such an inherent rotation, so the Gödel model doesn’t match reality. CTCs also appear inside a rotating black hole. A rotating mass causes space and time to swirl around it a bit (an effect known as frame dragging). Once you are within the event horizon of the black hole this swirling becomes strong enough there are CTCs. But this is only true if there is a singularity within the black hole, and its most likely that quantum physics prevents such a singularity from forming.

It doesn’t look like time machines occur naturally, so what about creating an artificial one? In the 1980s, Kip Thorne proposed using a wormhole as a time machine. Wormholes are purely hypothetical, and if they did exist they would collapse before you could travel through one. But Thorne found that if you could magically prevent a wormhole from collapsing, it could be used to create a time machine. Thorne’s model was simply a “what-if” scenario intended to test the limits of general relativity, but others such as Ron Mallett think it might be possible. Mallet has found a solution to general relativity that allows for CTCs without an event horizon. What Mallett has shown is that light can curve space and time in the same way as mass. By creating a rotating ring of laser light it is possible to distort space and time in a way similar to the way it is distorted by the rotating mass of a black hole, but without the black hole. This, he argues, opens the door to the possibility of creating a time loop. Critics have pointed out that Mallet’s solution still contains a singularity, so it isn’t a valid physical solution, but Mallett argues the singularity in his solution is an artifact that doesn’t affect the physics.

As for who’s right, time will tell. It’s easy to create a theoretical time machine within general relativity, the physics of matter and energy seem to prevent the creation of a real time machine. So could we ever build a time machine? Almost certainly not.

But that’s not a no.

Paper: Ronald L. Mallett. The Gravitational Field of a Circulating Light Beam. Foundations of Physics, Vol. 33, No. 9 (2003).
When Einstein developed his gravitational theory of general relativity, some physicists began to wonder if time travel might actually be possible.
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I think we need to stop trying to build a time machine, and start using the one that we already have. The most powerful and oldest machine known to mankind: the universe.
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The Shoulders of Giants

“If I have seen further, it is by standing on the shoulders of giants.” It’s a quote often attributed to Isaac Newton, though similar statements were made as far back as the 1100s. The sentiment behind the idea is that great scientists don’t live in a vacuum. They build upon the ideas of their predecessors and peers. Take, for example, the curious case of Roger Bacon.

Bacon lived in the 1200s, in the heart of what is sometimes referred to as the “dark ages.” It’s easy to see Bacon as a man centuries ahead of his time. He advocated experimental approaches over appeals to authority, saying “Plato is my friend, but truth is a better friend.” Like Newton he studied optics, and found that light could be split into a rainbow of colors by water. He proposed a model based upon the reflection of light to explain this effect. He also studied astronomical calendars, and noted that the Georgian year of 365.25 days was slightly off. He studied alchemy, which is something Newton spent a great deal of time studying as well.

Bacon’s rejection of the blind following of earlier authorities and his view of personal experiments as the ideal seems to be much more in tune with Newton’s era than the medieval world, but Bacon was truly a product of his times. In 1178 there were reports of a bright light appearing on the Moon, which some think could have been due to a meteor collision. Gervase of Canterbury saw the event, but also collected the observations of five monks who also witnessed the event. Gervase didn’t simply trust his own eyes, but gathered data to confirm his observations. In the early 1200s, Vincent of Beauvais wrote about the Earth as a spherical globe, and noted that gravity pulled everywhere toward its center. He even speculated on what would happen if you dropped a stone into a hole going through the globe.

The science of these medieval scholars wasn’t exactly the same as the methods we use today. They were deeply rooted in the philosophical and theological scaffolding of the time. However it is clear that their ideals of a search for truth was much like our own, and their rudimentary methods did show how knowledge could be gained through experimental tests and thought experiments. Later scholars such as Newton refined their methods, just as we have built upon Newton’s.

We often think of science as a specific tool that stands objectively outside our own worldview. But science has evolved over the centuries. It’s become an increasingly powerful tool as a result. So that today by standing on the shoulders of giants, we can see very far indeed.
Scientists don't live in a vacuum. They build upon the ideas of their predecessors and peers. Take, for example, the curious case of Roger Bacon.
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Black Holes Tell No Tales. Or Do They?

You’ve just committed the perfect crime. No one saw you do the crime, and you left no trace. The perfect crime. The only way anyone could prove you did it is by finding the journal of your master plan. Get rid of the journal, and you are scot free. You want to be absolutely, 100% certain that the information it contains is permanently destroyed. Suppose you toss your journal into a black hole. Would that destroy all traces of your plan?

The answer to this hypothetical scenario lies at the heart of the information paradox. Stated more generally, the paradox raises the question: can information be destroyed? The question is important because it strikes at the very heart of what science is. Through science we develop theories about how the universe works. These theories describe certain aspects of the universe. In other words they contain information about the universe. Our theories are not perfect, but as we learn more about the universe, we develop better theories, which contain more and more accurate information about the universe. Presumably the universe is driven by a set of ultimate physical laws, and if we can figure out what those are, then we could in principle know everything there is to know about the universe. If this is true, then anything that happens in the universe contains a particular amount of information. For example, the motion of the Earth around the Sun depends on their masses, the distance between them, their gravitational attraction, and so on. All of that information tells us what the Earth and Sun are doing.

In the last century, it’s become clear that information is at the heart of reality. For example, the second law of thermodynamics. In its simplest form it can be summarized as “heat flows from hot objects to cold objects”. But the law is more useful when it is expressed in terms of entropy. In this way it is stated as “the entropy of a system can never decrease.” Many people interpret entropy as the level of disorder in a system, or the unusable part of a system. But entropy is really about the level of information you need to describe a system. An ordered system (say, marbles evenly spaced in a grid) is easy to describe because the objects have simple relations to each other. On the other hand, a disordered system (marbles randomly scattered) take more information to describe, because there isn’t a simple pattern to them. So when the second law says that entropy can never decrease, it is saying that the physical information of a system cannot decrease. What began as a theory of heat has become a theory about information.

Is Information Conserved?

It’s generally thought that information can’t be destroyed because of some basic physical principles. The first is a principle known as determinism. If you throw a baseball in a particular direction at a particular speed, you can figure out where it’s going to land. Just determine the initial speed and direction of the ball, then use the laws of physics to predict what its motion will be. The ball doesn’t have any choice in the matter. Once it leaves your hand it will land in a particular spot. Its motion is determined by the physical laws of the universe. Everything in the universe is driven by these physical laws, so if we have an accurate description of what is happening right now, we can always predict what will happen later. The future is determined by the present.

The second principle is known as reversibility. Given the speed and direction of the ball as it hits the ground, we can use physics to trace its motion backwards to know where it came from. By observing the ball now, we can know from where the ball was thrown. The same applies for everything in the universe. By observing the universe today we can know what happened billions of years ago. The present is predicated by the past.

These two principles are just a precise way of saying the universe is predictable, but it also means information must be conserved. If the state of the present universe is determined by the past, then the past must have contained all the information of the present universe. Likewise, if the future is determined by the present, then the present must contain all the information of the future universe. If the universe is predictable, then information must be conserved.

Now you might be wondering about quantum mechanics. All that weird physics about atoms and such. Isn’t the point of quantum mechanics that things aren’t predictable? Not quite. In quantum mechanics, individual outcomes might not be predictable, but the odds of those outcomes are predictable. It’s kind of like a casino. They don’t know which particular players will win or lose, but they know very precisely what percentage will lose, so the casino will always make money. The baseball example was one of classical, everyday determinism. To include quantum mechanics we need a more general, probabilistic determinism known as quantum determinism, but the result is still the same. Information is conserved.

So what about black holes?

At first glance it would seem that black holes destroy information. If you toss an object into a black hole, the object (and all its physical information) is lost forever. It is as if the information of the object was erased, which would violate the basic principle that information cannot be destroyed. Now you might argue that being trapped is not the same thing as being destroyed, but for information it is. If you cannot recover the information, then it has been destroyed. So it would seem that black holes “eat” information, even though the laws of physics say that shouldn’t be possible. This is known as the black hole information paradox.

But it turns out things are actually more subtle. In general relativity, once a black hole forms it exists forever. If more matter is thrown into it, it can grow larger, but it never goes away. This is important, because if black holes live forever they don’t actually destroy information. Since time is relative things get a bit strange. For example, if you were to toss your crime journal into a black hole, how long would it take to reach the event horizon? From the journal’s perspective, it will cross the event horizon and enter the black hole in a finite amount of time, but from the outside observer’s view the event horizon is never reached. Instead the journal appears to get ever closer at an ever slower pace. Any outside observer will see the time of the falling journal get slower and slower as the black hole warps spacetime more and more. From the outside it appears that the journal never quite enters the black hole, and so its information is never lost.

But suppose we took an object and compressed it into a black hole.  According to general relativity, a black hole has three measurable properties: mass, rotation (angular momentum), and charge. That’s it. If you know those three things, you know all there is to know about the black hole. So a black hole is much simpler than other massive objects such as planets, stars and the like. It would therefore seem to have less information. If you think about an object like the Sun, it has a certain chemical composition, and it’s giving off light with different wavelengths having varying intensities. There are sunspots, solar flares, convection flows that create granules, and the list goes on. The Sun is a deeply complex object that we have yet to fully understand. The Sun contains a tremendous amount of information. And yet, if our Sun were compressed into a black hole, all that information would be reduced to mass, rotation and charge. All that information is lost forever.

But perhaps information can be saved by quantum theory. In the 1970s Stephen Hawking showed that one of the consequences of quantum theory is that black holes cannot hold matter forever. Instead, black holes can leak mass in the form of light and particles through a process known as Hawking radiation. While Stephen Hawking’s clever bit of mathematics describing this effect is pretty straightforward, interpreting the mechanism is less clear. One way of looking at it is that the Heisenberg uncertainty principle (which gives quantum theory its fuzzy behavior) means that virtual quantum particles can briefly appear in the vacuum of space, then then quickly disappear. In the normal, everyday world, these particles average out to zero, so we never notice them. But near the event horizon of a black hole, some of these virtual particles could cross the event horizon before disappearing, which decreases the mass (energy) of the black hole and allows other virtual particles to become “real” and radiate energy away. Another view is that the inherent fuzziness of quantum particles means you can never be absolutely certain that it is inside the event horizon. Although a particle cannot escape the black hole by crossing the event horizon, it could find itself outside the black hole through a kind of quantum tunneling.

Since a “quantum” black hole emits heat and light, it therefore has a temperature. This means black holes are subject to the laws of thermodynamics. Integrating general relativity, quantum mechanics and thermodynamics into a comprehensive description of black holes is quite complicated, but the basic properties can be expressed as a fairly simple set of rules known as black hole thermodynamics. Essentially these are the laws of thermodynamics re-expressed in terms of properties of black holes. As with regular thermodynamics, the entropy of a black hole system cannot decrease. One consequence of this is that when two black holes merge, the surface area of the merged event horizon must be greater than the surface areas of the original black holes. But remember that thermodynamics and entropy are a way to describe the information of a system. Because black holes have entropy, they also contain information beyond the simple mass, rotation, charge. Perhaps the information isn’t destroyed after all!

Unfortunately there’s a snag. Just like any quantum process, Hawking radiation is probabilistically determined. But it’s determined by the basic properties of the black hole. According to Hawking’s original theory, when a black hole evaporates, it evaporates into a random mix of light and matter. Not just “kind of” random, like tossing a dice, but truly random. This eliminates any possibility of recovering information from a black hole. So it would seem Hawking radiation also destroys information.

But several people have looked at modifications to Hawking’s model that would allow information to escape. For example, because Hawking’s quantum particles appear in pairs, they are “entangled” (connected in a quantum way). Perhaps you can used this quantum connection to give the information a way to escape. It turns out that to allow Hawking radiation to carry information out of the black hole, the entangled connection between particle pairs must be broken at the event horizon, so that the escaping particle can instead be entangled with the information-carrying matter within the black hole. This breaking of the original entanglement would make the escaping particles appear as an intense “firewall” at the surface of the event horizon. This would mean that anything falling toward the black hole wouldn’t make it into the black hole. Instead it would be vaporized by Hawking radiation when it reached the event horizon. This is known as the firewall paradox.

It would seem then that either the physical information of an object is lost when it falls into a black hole (information paradox) or objects are vaporized before entering a black hole (firewall paradox). Basically these ideas strike at the heart of the contradiction between general relativity and quantum theory.

Can Hawking save us?

This brings us to Stephen Hawking, and all the hullabaloo about his announcement that he’s solved the information paradox. Has he? The truth is we don’t know, but probably not. Hawking knows his stuff, but so do lots of other folks who have been working on this problem for years with less media attention. So far no one has been able to crack this nut. Hawking also hasn’t released a formal paper yet. So not only is his idea not peer reviewed, it’s not even public. Until we see the details there will be more speculation than facts.

But we do know a few things about the idea, and one interesting aspect is the fact that it’s not a quantum model. It actually draws upon the ideas of thermodynamics. Time for a little history.

In the late 1800s Ludwig Boltzmann proposed that the properties of a gas, such as its temperature and pressure, were due to the the motion and interactions of atoms and molecules. This had several advantages. For example, the hotter a gas, the faster the atoms and molecules would bounce around, therefore temperature was a measure of the kinetic (moving) energy of the atoms. The pressure of a gas is due to the atoms and molecules bouncing off the walls of the container. If the gas is heated, the atoms move faster and bounce off the container walls harder and more frequently. This explains why the pressure of an enclosed gas increases when you heat it.

Boltzmann’s kinetic theory not only explained how heat, work and energy are connected, it also gave a clear definition of entropy. The pressure, temperature and volume of a gas is known as the state of the gas. Since these are determined by the positions and speeds of all the atoms or molecules in the gas, Boltzmann called these the microstate of the gas (the state of all the microscopic particles). For a given state of the gas, there are lots of ways the atoms could be moving and bouncing around. As long as the average motion of all the atoms is about the same, then the pressure, temperature and volume of the gas will be the same. This means there are lots of equivalent microstates for a given state of the gas.

But how do equivalent microstates relate to heat flowing from hot to cold? Imagine an ice cube in a cup of warm water. The water molecules in the ice cube are frozen in a crystal structure. This structure is pretty rigid, so there aren’t a lot of ways for the water molecules to move. This means the number of equivalent microstates is rather small. As the ice melts the crystal structure breaks down, and the water molecules are much more free to move. This means there are many more equivalent microstates for water than for ice. So heat flows into the ice, which increases the number of equivalent microstates, so the entropy of the system increases. The second law of thermodynamics applies both ways.

The idea of equivalent microstates can be applied to general relativity through an idea known as degenerate vacuua. The region outside a black hole (the vacuum) is the same for a black hole with a particular mass, rotation and charge. But lots of things could have gone into making the black hole, from stars to old issues of National Geographic. A black hole made of hydrogen, or neutrons, or iron all look the same from the outside, so we could say that each type of black hole is a microstate, and thus all the different ways we could make a black hole are therefore equivalent microstates. Or in general relativity terms, their exteriors are degenerate vacua.

These different vacua are related by a type of symmetry relation known as BCS symmetry, or supertranslations. What Hawking seems to be saying is that these supertranslations can be used to connect the information inside a black hole with the outside world. Basically, these degnenerate vacua bias the Hawking radiation so that it isn’t random. That way the information can escape without creating a firewall. If the idea works, then it might solve the information paradox. But even the little information released about the work has raised some serious doubts from other experts. It seems to be based upon an idealized black hole that doesn’t match real black holes, and it might not work even then. Either way, it’s up for Hawking and his colleagues to prove their case.

So we still don’t know whether black holes tell no tales.

If you’ve made it this far, congratulations. This is a deeply complex topic, and while I’ve done my best to explain what I understand about it, I won’t claim to be an authority. Fortunately lots of other scientists have written about it as well. For a few good summaries check out Sabine Hossenfelder, Ethan Siegel, and Matt Strassler.
Stephen Hawking thinks he's solved a long standing problem in physics known as the information paradox. But has he?
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Not only did I get treated to an extra-long post, but I got to enjoy an analogy that compared a black hole to an ice cube in the post and a frog-jumping analogy in the comments. Well done.
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Twin Giants

A supermassive black hole lurks in the center of our galaxy. But two supermassive black holes lurk in some galaxies.

Since most galaxies contain a black hole in their center, and galaxies have been known to collide, it’s thought that supermassive binary black holes could be relatively common in the universe. We know of some that exist, but they are difficult to confirm. But new research in the Astrophysical Journal has found a supermassive binary in the heart of a quasar.

Quasars are extremely bright sources of energy, powered by the superheated material (the accretion disk) near a black hole. They are so luminous that it’s impossible to resolve a supermassive binary directly. But a close binary black hole would clear out the region between the black holes, leaving a gap in the surrounding material. This gap would lower the overall temperature of the accretion disk, and that means less ultraviolet light should be emitted by the quasar. In this work, the team compared the visible and ultraviolet spectrum of a quasar known as Markarian 231. They found a weaker ultraviolet spectrum, just as expected for a supermassive binary.

What’s great about this research is that it allows us to find supermassive binary black holes by looking at the spectra of quasars. So it’s quite likely that the method could be used to find many more of these twin giants.

Paper: Chang-Shuo Yan et al. A Probable Milli-parsec Supermassive Binary Black Hole in the Nearest Quasar Mrk 231. ApJ 809 117 (2015)
A supermassive black hole lurks in the center of our galaxy. But two supermassive black holes lurk in some galaxies.
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+Tony Spilotro +Nick Earl Thanks!  That's some pretty awesome stuff. :)  I think I saw Kip Thorne give a talk at SIGGRAPH just a few weeks ago on how they simulated and rendered the black hole in Interstellar.  It was quite fun.
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Call of the Void

It was in the twilight of summer, when the trees begin to whisper of autumn. The wheat field outside my family’s house had been harvested a couple of days before, and the night sky was crystal clear. With blanket in hand, I trekked out to the middle of the field to look at the stars.

When you lie out in the middle of a field, all you see is stars. The tree line is at the edge of your peripheral vision, so if you keep your head still, it’s just a field of stars. At first you’ll notice the brightest stars, and then the recognition of constellations. You might notice a shooting star, or watch a satellite shine briefly across the sky.  But if you’re still, and you keep watching the sky, changes happen.

After about half an hour, your eyes become dark adapted. Faint objects such as the Milky Way become more clear, and what seems like thousands of stars begins to seem like millions. The sky deepens beyond the stars, and you see smudges and ripples of light. There’s a range of color to the sky beyond light and dark. The brightest stars gain a sparkle you hadn’t noticed before. It is a brilliance and subtlety you hadn’t noticed before.

Within an hour you’ll begin to notice the stars have shifted. A bright star has drifted above your head, or a star off to the side now dances on the edge of your vision. Once aware of the motion, you can’t help but notice it. The eternal drift of the night sky. For me, that’s usually about the time when it occurs. I was about 13 the first time it happened to me. Lying in the middle of that field on a late summer night. The stars seemed to race toward me, though not a single star moved. It hit like a physical blow, and I gripped the soil to keep from falling into the sky.

It is a feeling both wondrous and terrifying. A realization that you are clinging to a rock in motion through the cosmos, and the feeling that the pull of the world might not be enough to hold you.
It realization that you are clinging to a rock in motion through the cosmos, and the feeling that the pull of the world might not be enough to hold you.
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Jun Rae
 
Awesome
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Neutrinos From Outer Space!

Neutrinos are being detected from outer space, and that’s kind of a big deal.

Neutrinos are an elementary particle somewhat related to electrons. But unlike electrons, which have an electric charge and a measurable mass, neutrinos have no charge and a tiny difficult to measure mass. These elusive particles only interact through the weak force, and so they’re extremely difficult to detect. One way to detect them is by using large tanks of water and waiting for a neutrino to collide with a water molecule. Neutrinos strike the molecule with such energy that a small amount of light is produced, which we can detect. One of the biggest challenges comes from the fact that other energetic particles can collide with water molecules to produce light, so we shield the detectors by building them in abandoned mines, or burying them under the ice in Antarctica.

Because neutrinos are so difficult to detect, they typically come from three main sources: those produced in particle accelerators, those produced from fusion in the Sun’s core, and those produced by cosmic rays striking our atmosphere. None of these neutrinos are produced outside our solar system. The only time cosmic neutrinos were detected was during the 1987a supernova in the Large Magellanic Cloud. Supernovae produce tremendous quantities of neutrinos, and this caused small neutrino spikes at three separate neutrino observatories, which confirmed they were extra-solar neutrinos. We haven’t detected any cosmic neutrinos since.

But now the IceCube Collaboration in Antarctica has announced the discovery of cosmic neutrinos. The IceCube detector is much more sensitive than the detectors we had in 1987, so it’s not only able to detect neutrinos, it’s able to determine both the energy levels of different neutrino events and the direction from which they originate. Out of 35,000 neutrino detections over the course of 2 years, they found 21 that had very high energy levels. Higher than those typically produced by cosmic rays. They also came from the direction of the northern hemisphere, which meant they traveled through the Earth to reach the detector. Both of these facts point to the neutrinos originating from outside the solar system.

On one level, this discovery simply confirms the existence of astrophysical neutrinos, which we’ve known should exist for quite some time. But the fact that we now have the sensitivity to detect these things is pretty amazing.

Paper: M. G. Aartsen et al. (IceCube Collaboration) Evidence for Astrophysical Muon Neutrinos from the Northern Sky with IceCube. Phys. Rev. Lett. 115, 081102 (2015)
Neutrinos are being detected from outer space, and that's kind of a big deal.
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+Lord Hambone - Yep, now you're catching on!
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Judging by the Size

Most of the planets we’ve discovered around other stars have been found using the transit method. When a planet passes in front of its star, it blocks some of the starlight, making it appear slightly dimmer. It’s a great way to discover planets, but it has some serious limitations.

Given our current technology, we can’t resolve most planets directly. Earth-sized planets are far too small to be directly observed. With the transit method we can’t see a planet pass in front of its star, just a dimming in the overall brightness of the star. From the star’s temperature and spectrum we can get a pretty good idea of its size, and from the amount of dimming we have an idea of the size of the planet relative to the star. With the transit method we know the size of a planet, but that’s about it.

The problem is that planets with similar sizes can have very different physical characteristics. Take, for example, the exoplanet known as Kepler 22b. It’s radius is about 2.4 times that of Earth, and thus it’s a type of planet known as a “super Earth.” However its mass isn’t well known, and could vary significantly depending upon its composition. If it is mostly water and ice, it might be 3 – 5 Earth masses. If it is mostly rock, 30 – 50 Earth masses, and if it’s mostly iron its mass could be over 100 Earth masses. By comparison, the mass of Neptune is only 17 Earth masses, while Saturn is only 95 Earth masses.

Realistic estimates put Kepler 22b around 40 Earth masses, perhaps as an ocean world with a rocky iron core, which is hardly an Earth-like world.
The transit method is a great way to discover planets, but it has some serious limitations.
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I'd also like to mention that in addition to the transit method for detecting exoplanets, there is another called the "radial velocity" method, which gives us different information.

The way this method works is to examine the spectrum of the star over time.  The star is tugged back and forth slightly by the gravity of the planet(s) orbiting it, which shows up as a slight doppler shift -- redshifted when its being pulled away, and blueshifted when its pulled towards us.  The strength of the shift will depend on how massive the planet is in relation to the star and how far out it orbits.

Unfortunately, we can only see this shift along the pure line-of-sight between us and the star.  It doesn't show up at all if the planet's orbit happens to be face-on to us, whereas we get the full signal if it is edge-on.  So with radial-velocity detections we have to characterize the planet's mass as a function of the (unknown) angle that the orbit makes from our perspective.

However, a very nice thing happens if we are able to combine the transit method with the radial velocity.  If the planet transits, then we know exactly what the angle of the orbit is: it has to be edge on to us.  So we can then precisely measure both the planet's size and its mass -- which gives us the density -- and thus we'll have much more confidence in exactly what type of planet it is and what it is made of.

There are also the very big questions of whether an exoplanet has liquid water on its surface, or oxygen in its atmosphere, life, etc.  It is extremely difficult to tell these things now, but we're getting pretty close!  The revolution will come from being able to obtain spectra of the exoplanet's atmosphere, something we've only been able to do in a few cases thus far. 

The future of exoplanet observations should be really exciting. :)
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A Word From Our Sponsors

I'm starting to get huge spikes of drive-by readers, and as a result I've had to upgrade the webserver once again. So I'm asking for help to grow more long-term readers.
You won't find ads on this site, just articles written by me on various topics in astronomy and physics. I like it that way. I intend to keep it that way.
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Oh YES +Martino Mosna newletters are fantastic, espesually ones with links to related past stuff alteady published. 
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An astrophysicist and physics professor at Rochester Institute of Technology.  Author of "Astrophysics Through Computation" with David Meisel.  Creator of the science outreach project Prove Your World, developing a science television show for children.

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