On the face of it, this might seem like a silly question. Of course we can see stars in space. We see stars more clearly from space than we do from Earth, which is why space telescopes are so useful. And yet, this question comes up again and again. Not just from moon landing skeptics and fringe science promoters, but from everyday folks who are sure they learned somewhere that stars can’t be seen in space.

When overexposed, the Moon seems to glow brilliantly. Credit: Bob King/Sky and Telescope

The origin of this misconception is usually traced back to an interview with the crew of Apollo 11, where (it is claimed) Neil Armstrong said he couldn’t see stars in space. What the crew were actually discussing at the time was the inability to see stars on the daylight side of the Moon, which is not surprising given how bright the lunar surface can be relative to the airless black of space. Even in space the stars aren’t overly bright, and our eyes can lose dark adaption pretty quickly.

An image from the ISS of stars and glowing layers of Earth’s atmosphere.

But what about all those photos of objects in space, such as the one of the international space station seen above? There’s no stars to be seen in the image. It’s actually quite common to see images of planets and other objects against a starless black background. Doesn’t that support the idea of a starless sky in space? No, since it’s no surprise that an image focused on a bright object like a planet or moon won’t have a long enough exposure to see stars clearly. There are plenty of images from space that do show stars, as well as other faint phenomena such as the green airglow of our atmosphere.

What this misconception really shows is how easily a misconception can get locked into our heads. We can all fall prey to the trap of holding misconceptions without really thinking about them. That’s part of the reason why we focus on published and verifiable evidence in science.

Which is why this isn’t such a silly question after all.

The post Can Astronauts See Stars In Space? appeared first on One Universe at a Time.

“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!”

No, Tyson didn’t say this.

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.

Dr. Ben Carson: not stupid.

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.

Actually, that’s pretty clever.

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.

The post You Are Not Stupid appeared first on One Universe at a Time.

Yesterday I got an email outlining why black hole can’t possibly exist. Those of you who are regular readers might be quick to point out that black hole most certainly exist, but the author is right. Black holes make no sense. I, and other scientists, have been lying to you all along.

As the author clearly points out:

 1. If time dilation increases the closer one approaches the event horizon of a black hole and from our perspective we see time essentially stop at the event horizon, how will a black hole ever form in our universe if nothing can ever cross the event horizon relative to us and the rest of the universe?

2. The explanation used for the creation of a black hole is that gravity increases due to an increase in the density of the material within the stellar object. Since gravity is many orders of magnitude less powerful than even the electrical forces being experienced between the nuclei of the matter in question how does the gravitational force overcome the repulsion between nuclei. I understand that the electrons will provide some neutralisation of the positive charges. However, even in standard forms of matter there are various electrical forces that occur, even though the atoms are technically neutral.

3. Thirdly, the event horizon is defined where the escape velocity is defined as being the speed of light. However, the escape velocity is defined by a specific criteria and circumstance, which is clearly understood in engineering circles does not apply to powered movement. That is the actual velocity by which you transition from from solar body to another can be as low as you like. Hence, you can cross any boundary, including an event horizon, under power at any speed (under the speed of light).

It seems very clear then that black holes defy logic, so why do we scientists keep claiming they exist? Because the arguments outlined above are based on a pack of lies.

When I say that I’ve been lying to you, this doesn’t mean I’ve intentionally tried to deceive you. It means that I’ve been intentionally feeding you information that isn’t entirely true in order to give you an understanding of what is really going on. For example, take these three points.

1. From our viewpoint, stuff takes forever to fall into a black hole, so a black hole can never form.

The position of an infalling object as seen from outside the black hole (black) and from the object itself (red).

One of the standard things said about black holes is that as material falls into a black hole it will be seen from the outside to never quite reach the event horizon. While this is true, it’s also true that from the viewpoint of the material it readily crosses the event horizon. What we often leave out in this discussion is that this is a rather simplistic description of the situation from only two vantage points. One of the central aspects of relativity is that all vantage points are valid, even when they seem contradictory. What this means is that to really describe the situation you have to look at all of spacetime as a whole. When you do this, it is clear that matter really does cross the event horizon, and black holes really do form. From the material’s vantage point you can see this, but from the exterior view you can’t. Of course to describe the whole of spacetime requires tensor calculus, so we typically omit that from the popular science tale.

2. Gravity is weaker than electromagnetism.

Again, at a basic level this is true. Certainly if we were to put two protons close to each other, the repulsive force of their electric charge would be much, much stronger than the attractive gravitational force due to their masses. That would seem to contradict the common claim that black holes form when a star’s gravity causes it to collapse under its own weight. But gravity doesn’t cause a star to collapse. It’s the electric force that does it. Imagine a table standing in the middle of a room. The atoms and molecules of the table interact with each other through electric forces, which is what gives the table its rigidity. The table is perfectly capable of supporting its own weight, because the electric forces are much stronger than gravity. But suppose I were to start stacking books on the table. Eventually the weight of the books would cause the table to collapse.

In that case, what caused the table to collapse? Gravity? No, it’s actually the force of the books right on the table’s surface. They push on the table so strongly (with the electric forces of the atoms and molecules) that the table can’t withstand it. Granted, the lowest books can push so hard because books on top of it are pushing on them, and all of this is due to gravity giving each layer of books a little tug. But technically gravity doesn’t cause the table to collapse, gravity just helps the electric force build so that it collapses the table. The same is true with a collapsing star. It is the electric and nuclear forces pushing against each other in the interior that cause the collapse. Gravity just helps those forces work together.

But all of that is complicated, so we usually just say “gravity causes the star to collapse.”

3. The event horizon is where the escape velocity is the speed of light, but that doesn’t keep us from escaping with a slower than light rocket.

This is one of the biggest lies we tell about black holes. On one level it is true. If you calculate the escape velocity at the event horizon (according to Newtonian gravity), then it is the speed of light. It makes for a simple way to describe black holes and event horizons. The problem with the idea is that escape velocity is defined as the speed it takes to escape forever. But if I tossed a ball at just under the escape velocity, it would rise very, very high before falling back down. Using escape velocity gives the impression that a rocket could escape, just as we use rockets to escape Earth’s gravity.

Behavior of light cones near an event horizon. Credit: John D. Norton.

But in relativity, the energy of the rocket would actually work against you. To really look at the structure of a black hole, you need to look at how light behaves globally. This is often visualized using light cones to show the effects of gravity. When you look at the details you find that while the event horizon does have a light-speed escape velocity, what really makes it different is that it folds space to the point where there is no possible trajectory where you can leave. All roads lead to Rome, as the saying goes, or in this case to the singularity. So if you were really at the event horizon of a black hole, any direction you tossed a ball would be “downward,” and it would be physically impossible for you to toss the ball “up.”

So the author is right about black holes not being logical, if what we typically say about black holes were actually true. But they aren’t. And therein lies one of the dangers of popularizing science. To make things clear, we often simplify things to the point where they aren’t fully true. We lie a bit to convey the central ideas rather than getting bogged down in the details. That’s fine if you just want to get a basic understanding of things. But it’s important to keep in mind that the analogies we use shouldn’t be taken literally.

When you find contradictions in the pop-science description of an established scientific idea, it doesn’t mean the science is wrong, it means the truth is more complicated than we’ve been letting on.

The post Lies My Teacher Told Me appeared first on One Universe at a Time.

With all the news about BICEP2 and the possible detection of early inflation, there have been a lot of misconceptions about what inflation actually is.  One of the biggest is the idea that during inflation the universe expanded faster than light.  It’s a misconception that even many experts get wrong, and is so common that there’s a technical arxiv paper addressing these misconceptions.  It’s easy to see how this misconception arises.  After all, during inflation, two atoms a meter apart just before would find themselves about a light year apart within a fraction of a second.  How is that not moving faster than light?  It all has to do with the subtlety of general relativity.

Before we talk about inflation, let’s talk about a similar effect we see in the universe today, known as cosmic expansion.  When we look at distant galaxies, we see that the light of more distant galaxies is redshifted more than closer galaxies.  Now we know that light can be redshifted when objects move away from us, known as the Doppler effect.  For this reason, this effect is often described as galaxies moving away from us.  But redshift can also occur due to the expansion of space itself.  That is, space expands, but the galaxies aren’t moving through space.  The first is a property of special relativity, and is due to the motion of objects through space. The second is a property of general relativity, and is due to an expansion of space.

Supernova magnitude-redshift observations compared to GR models and SR. Credit: Davis and Lineweaver.

Since both effects give a redshift to distant galaxies, how do we know that cosmic expansion is due to an expansion of space and not relative motion?  If the redshift were due to relative motion, then the light of distant galaxies would be redshifted when leaving the galaxy, and that means the light would also appear dimmer.  If the redshift is due to cosmic expansion, then light leaves a distant galaxy without being redshifted, and therefore also not dimmed.  Only later is the light redshifted due to expansion.  This means you can compare the brightness of distant supernovae with their redshift, known as the magnitude-redshift relation.  What we find is that the magnitude-redshift relation matches expansion extraordinarily well.  It doesn’t match the relative motion model at all.

So we know that space is actually expanding, but what does that actually mean?

Cosmic expansion is determined by what is known as the Hubble constant.  Currently our best measurement of the Hubble constant is about 20 km/s per million light years.  This means that two points in space a million light years apart are moving away from each other at 20 kilometers each second.  Since all of space is expanding, the greater the distance between two points in space, the faster they move apart.  So two points 10 million light years apart are moving away at 200 km/s, and so on.  Because of this, if you consider two points far enough apart, they will be moving away from each other faster than the speed of light.  The speed of light is about 300,000 km/s, which, given our current Hubble constant is the separation speed for two points 15 billion light years apart.

Now you might think then that a galaxy 16 billion light years away from us must be moving away from from us faster than light.  You could say that the the galaxy appears to be moving faster than light, but in actuality it is space that is expanding between us.  The galaxy itself isn’t moving much at all.  It’s not as if that distant galaxy is defying relativity.  After all, from that distant galaxy’s perspective we are moving away from it faster than the speed of light.  The key point to remember is that this is due to cosmic expansion, not galactic motion.  And cosmic expansion is not faster than light, even though very distant objects can appear to be moving faster than light.

Which brings us to inflation.  Many of the popular articles unfortunately state that during inflation the Universe was expanding faster than light, which isn’t true.  What is true is that during inflation the rate of spatial expansion was much larger.  This means that the distance at which objects appear to move apart faster than light is much smaller, but it does not mean that the Universe expanded faster than light.

We still don’t understand the mechanism that triggered inflation, but we do know that inflation doesn’t violate the speed of light.  During inflation the rate of expansion was tremendous, but even today space continues to expand, just at a much smaller rate.

Paper: Tamara M. Davis, Charles H. Lineweaver. Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe. arXiv:astro-ph/0310808 (2003).

The post Traveling Without Moving appeared first on One Universe at a Time.

Just how cluttered with rocks is the asteroid belt?  The answer might surprise you.

How the asteroid belt is often portrayed. Credit: Wookiepedia

You might think it is pretty packed, since it contains about 80,000 asteroids larger than a kilometer.  There are even more smaller asteroids, because the distribution of asteroids follows a power law size distribution.  For example, with a power law of 1, for every 100 meter wide meteoroid there would be 10 with a diameter of 10 meters and 100 with a diameter of 1 meter.  Based upon observations of the Spitzer telescope, asteroids follow a power law of about 2, which means there are likely about 800 trillion asteroids larger than a meter within the belt.  That’s a lot of rock.  So much that sunlight scattering off the asteroid belt and other dust in the solar system is the source of zodiacal light.

An actual image from within the asteroid belt, taken from the NEAR probe as it was heading toward Eros (center).
Credit: NASA

But there is also a lot of volume within the asteroid belt.  The belt can be said to occupy a region around the Sun from about 2.2 to 3.2 times the distance from the Earth to the Sun from the Sun (AU), with a thickness of about 1 AU.  A bit of math puts that at about 50 trillion trillion cubic kilometers.  So even though there are trillions of asteroids, each asteroid has billions of cubic kilometers of space on average.  The asteroid belt is hardly something you would consider crowded.

It should be emphasized that asteroids in the belt are not evenly distributed.  They are clustered into families and groups.  But even such clustering is not significant compared to the vast space it occupies.

You can even do a very rough calculation to get an idea of just how empty the asteroid belt actually is.  If we assumed that all the asteroids lay within a single plane, then on average there is 1 asteroid within an area roughly the size of Rhode Island.  Within the entire United States there would be about 2000 asteroids, most of them only a meter across.  The odds of seeing an asteroid along a cross-country road trip, much less hitting one, would be astoundingly small.  So you can see why we don’t worry about space probes hitting an asteroid on their way to the outer solar system.

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