Science Blogs Physcial Sciences
"A little more persistence, a little more effort, and what seemed hopeless failure may turn to glorious success." -Elbert Hubbard I've had the great fortune in my life to see a great many wonderful things with my own eyes, including the rings of Saturn, the phases of Venus, a couple of faint, distant galaxies, and a large number of sunsets, sunrises, and lunar eclipses. But as far as solar eclipses go, I missed the only realistic opportunity I ever had to see -- as Cara Beth Satalino would say -- that
Back in 1994, an annular solar eclipse happened just 300 miles from where I was living. While I got to see the partial eclipse that resulted from being off of the ideal path, I'd never seen either a total or annular solar eclipse. But this weekend was my big chance, and I wasn't going to miss it. For the first time, I set out on an eclipse expedition, hoping to catch a glimpse of the spectacular sights that one of my former astronomy students had grabbed hours earlier from Tokyo.
(Image credit: Destiny Fox. Thanks, Destiny!)
As many of you know, I've been preparing for this for a couple of months, and that started with scouting out a prime location. The one I chose was right on the coast, for the earliest possible view from America, right in the middle of the path of maximum eclipse.
Choosing the middle of that path means that I was going to get to see -- if the conditions were ideal -- the Moon pass over the dead center of the Sun, creating a true ring of fire. The place where this was going to happen was False Klamath Cove, a rock-littered area in very northern California. But this place was "only" about 330 miles from where I live today, in Portland, Oregon, and so I made the trip down. About an hour before maximum eclipse, this was the view I had.
Yes, it was somewhat cloudy, and I knew the clouds and fog would be continuing to roll in, but it wasn't hopeless. You see, the clouds were thin enough that the "binocular trick," where you un-cap one side of a pair of binoculars and project the image of the Sun onto a white screen behind it, was still very effective.
As you can see, you were still able to see the Sun's disk, as well as the fraction of it that was obscured by the Moon. But I wasn't going to settle for a projection of the Sun's disk onto a screen; I wanted to see it with my own eyes. And so that meant bringing a little protective eyewear. In addition to my polarized sunglasses, I also brought along two wonderful pieces of equipment: a pair of shade-5 welder's goggles and a shade-10 welder's hood.
Under sunny, high-noon conditions, you need shade-14 to safely look at the Sun. Thankfully, eye protection is additive, so wearing both of these together meant that I could look at the Sun without concern for safety.
I'm not going to lie: other than a green tint, this view was spectacular. The Sun was crisp, the clouds could be seen dancing across its face, and the fraction that was obscured by the Moon was cleanly and clearly visible. I'm definitely going to be using both of these, together, to watch the Venus transit in a couple of weeks.
But for photography? That's never been a skill (or even an interest) of mine, so all I could do was experiment. Placing the shade-5 goggles in front of the camera was clearly not enough.
While the cloud cover was light, as it was in the early stages of the eclipse, it turns out that the shade-10 hood, on its own, was significantly better than the goggles.
You could see, with the camera, that part of the Sun was obscured, but the image was still greatly overexposed, making it virtually impossible to see any detail.
I tried using both the goggles and the hood together. But the combination that worked so well for my eyes was a miserable failure for the camera.
As you can see, the Sun's disk still appeared overexposed, plus now there were problems of multiple reflections between the different surfaces, ruining the image on the camera.
But as we neared the moment of maximum eclipse, and the Sun dwindled to a crescent, slowly creeping around the edges of the Moon, something both wonderful and horrifying began to happen. Thick, foggy clouds began to roll in, as they do every evening in this part of the world at this time of the year. But it meant something wonderful for my feeble photography skills.
My images were suddenly less over-exposed. And as the fog rapidly thickened, I discovered that I no longer needed shade-15 protection to watch the eclipse. I no longer needed shade-10, in fact. At the moment of maximum eclipse, I had nothing but the shade-5 welder's goggles over the lens of the camera, and this was the photo I got.
Digital cameras, of course, get outstanding resolution. So this perfect circle, this ring of fire, actually showed up like this.
There's no way to describe what it's like to see it with your own eyes, but my experience was probably extremely unique, because rather than watching the Moon move off of the Sun, I watched this ring of fire fade away behind some ever-thickening clouds, and disappear from sight.
And that's why even though there are no more pictures from my first eclipse expedition, you can bet it won't be my last!Read the comments on this post...
"But some of the greatest achievements in philosophy could only be compared with taking up some books which seemed to belong together, and putting them on different shelves; nothing more being final about their positions than that they no longer lie side by side. The onlooker who doesn't know the difficulty of the task might well think in such a case that nothing at all had been achieved." -Wittgenstein One of the most fundamental questions about the Universe that anyone can ask is, "Why is there anything here at all?"
(Image credit: Patrick at vignetted.com.)
Out beyond Earth, of course, there are trillions of other worlds within our own galaxy, and at least hundreds of billions of galaxies within just the part of our Universe that's observable to us.
(Image credit: NASA, ESA, S. Beckwith (STScI) and the HUDF Team.)
Explaining where all the matter in the Universe comes from is one thing. What you traditionally think of as something -- that is, the plants, animals, elements, planets, stars, galaxies and galaxy clusters -- that's one question.
How and when all of that got here? That's something we think we can answer.
(Image credit: me, as a New Year's present to you.)
But there's an even more fundamental question than that. In order to have our Universe, you need to start with what, as a physicist, I call nothing.
You need to start with empty spacetime.
And you can start with the emptiest spacetime imaginable: something flat, devoid of matter, devoid of radiation, of electric fields, of magnetic fields, of charges, etc. All you would have, in that case, is the intrinsic zero-point energy, or the ground state, of empty space.
From a physical point of view, that's what nothing is. Only, perhaps perplexingly, that zero-point energy? It isn't zero.
(Image credit: Brian Greene's Elegant Universe.)
If it were, we wouldn't have a Universe filled with dark energy, and yet we do. Instead, spacetime has a fundamental, intrinsic, non-zero amount of energy inherent to it; that's what's causing the Universe's expansion to accelerate! What's even more bizarre than that is the fact that all the matter and energy in the Universe today came from a drop, long ago, from an even higher zero-point-energy state. That process -- reheating -- is what comes at the end of an indeterminately long phase of exponential expansion of the Universe known as cosmic inflation.
(Image credit: Ned Wright.)
The regions of space where this drop in zero-point energy occurred gave rise to regions of the Universe like ours, where matter and energy exist in abundance, and where the expansion of spacetime is relatively slow. But the regions where it hasn't yet occurred continue to have an extremely rapid rate of expansion. This is why physicists state that inflation is eternal, and this is also the physical motivation for the existence of multiverses.
In the diagram below, regions marked with red X's are regions where the drop in zero-point energy occurs, and a region of the Universe like ours comes into existence.
(Image credit: me, created especially for you last year.)
That's the physical story of where all this comes from. Of where our planets, stars, and galaxies comes from, of where all the matter and energy in the Universe comes from, of where the entire 93-billion-light-year wide section of our observable Universe comes from.
From a scientific perspective, we think we understand not only where all of this comes from, but also the fundamental laws that govern it. So when a physicist writes a book called: A Universe from Nothing, I know that some version of this story -- the scientific story of how we get our entire Universe from nothing -- is the one you're going to get told.
It's a remarkable story, it's perhaps my favorite story to tell, and it's certainly been the greatest story I've ever learned. But in at least one way, it's a dissatisfying story. Because the scientific definition of "nothing" that we use -- empty, curvature-free spacetime at the zero-point energy of all its quantum fields -- doesn't resemble our ideal expectations of what "nothing" ought to be.
(Image credit: retrieved from Universe-Review.ca.)
No one sufficiently versed in the science of physical cosmology (and being sufficiently honest with themselves about it) would argue against this: that the entire Universe that we know and exist in comes from a state like this, that existed some 13.7 billion years ago. But you may rightfully ask, "Is that truly nothing?"
This empty spacetime definition of what is physically nothing stands in contrast to what we can imagine as what I'll call pure (or philosophical) nothingness, where there's no space, no time, no laws of physics, no quantum fields to be in their zero state, etc. Just a total void.
This has been the source of much argument recently, as the answer to the physical question of where everything comes from does not necessarily answer the philosophical one. It certainly pushes it off for a while, but it still leaves unexplained the existence of spacetime and the laws of physics themselves. There has been bickering back-and-forth with a handful of physicists and philosophers arguing as to whether this physical story really explains why there is something rather than nothing?
It is a remarkable story, of course, and it explains where every galaxy, every star, and every atom in the Universe comes from, an astouding feat.
(Image credit: Don Dixon.)
But it doesn't explain, existentially, why spacetime or the laws of nature themselves exist, or exist with the properties that they have. In short, understanding how something comes from nothing does not explain how this physical state of nothing comes from an existential nothingness. This question of why, as enunciated by Heidegger, is not addressed by our physical understanding of the Universe. But is it a fair question?
Like the oft-dismissive Wittgenstein, I'm not sure. We make this inherent assumption that both spacetime and the laws inherent to our Universe come from somewhere. Yet our classical notions and intuitions about causality are violated even within our known Universe; do we have good reason to expect that this non-universal form of logic applies to the very existence of the Universe itself? Furthermore, how can something, even figuratively, come from anything else if you remove time?
One can, of course, imagine answers to these questions: an entity of some sort that exists outside of time and thus has access to all times equally, a type of hidden-variable logic that exists as part of reality but requires the knowledge of things that are presently unobservable to us, a higher-dimensional being who sees our entire Universe no differently from how an animator sees the elements of a two-dimensional cartoon, etc.
(Image credit: Chuck Jones / Warner Brothers Studios.)
None of these answers are convincing or compelling, mind you, and I am not sure that the questions do even make sense as far as reality is concerned. But just because we cannot yet know the answers, or whether the questions are sensible as far as reality is concerned, doesn't mean there isn't value to asking them and thinking about them. To me, that's what philosophy is. I would encourage everyone to remember the words of my favorite philosopher, Alan Watts: The reason for it is that most civilized people are out of touch with reality because they confuse the world as it is with the world as they think about it, talk about it, and describe it. On the one hand, there is the real world, and on the other, a whole system of symbols about that world that we have in our minds. These are very very useful symbols -- all civilization depends on them -- but like all good things, they have their disadvantages, and the principal disadvantage of symbols is that we confuse them with reality. For whatever it's worth, when I think of nothing, I think about empty spacetime and the physical Universe: that's where my interests lie, and that's where I believe the knowable lies. But that doesn't mean there isn't something wonderful to be gained from philosophizing. As Alan Watts himself said:
(Video credit: dFalcStudios.)
And as well as this explanation actually describes what I think about the Universe, it didn't come from a physicist. So let's stop accusing each other -- physicists and philosophers -- of being bad at one another's disciplines, and let's work on getting it right. Education is always worth it. Read the comments on this post...
So, you find yourself living in the San Francisco Bay area, and you maybe have a dog who would like to know something about relativity, or you maybe want to someday have a dog who will want to know something about relativity, or you maybe want to know something more about relativity yourself, in case you ever find yourself cornered in a dark alley by a Rhodesian ridgeback who snarls "Explain time dilation to me, or I'll eat your face!" Well, in that case, you definitely want to be at Kepler's Books in Menlo Park on the evening of June 14th, when I'll be doing a book promotion thing for How to Teach Relativity to Your Dog.
So, here's your chance to hear me do the silly dog voice in person, and maybe get a book signed. Emmy won't be making the trip (I doubt she'd do well on a plane...), but I'm looking forward to it.Read the comments on this post...
"The Earth destroys its fools, but the intelligent destroy the Earth."
-Khalid ibn al-Walid Usually, when we talk about terraforming, we think about taking a presently uninhabitable planet and making it suitable for terrestrial life. This means taking a world without an oxygen-rich atmosphere, with watery oceans, and without the means to sustain them, and to transform it into an Earth-like world.
The obvious choice, when it comes to our Solar System, is Mars.
(Image credit: Daein Ballard.)
The red planet, after all, is not a total stranger to these conditions. On the contrary, for the first billion-and-a-half years of our Solar System, give or take, Mars was perhaps not so dissimilar to Earth. With evidence that there was once liquid water on the surface, a thicker atmosphere, and possibly even life, there's no doubt that the right type of geo-engineering could bring those conditions back.
But there's also no doubt that we couldn't, if we were sufficiently motivated, turn the Earth from this...
(Image credit: NASA / GSFC / NOAA / USGS.)
into a world where the atmosphere and the oceans were stripped away. Into a dry, nearly airless world, much like Mars.
Inspired by a recent Astronomy Picture of the Day, above, it's now time to tell you how I would, scientifically, remove the oceans from the planet. It's a process I like to call reverse terraforming, whereby you turn a world the Earth into a world like Mars.
At present, this is difficult for a number of reasons, but here's the biggest one.
(Image credit: Natalie Krivova.)
The Earth's magnetosphere! The same reason that your compass needle points towards the magnetic poles of Earth is the only thing keeping our oceans here on our world! The Sun is constantly shooting out a stream of high-energy ions, known as the solar wind, at speeds of about 1,000,000 miles-per-hour (1,600,000 km/hr).
As the solar wind runs into a world, these ions collide with particles in a planet's atmosphere, giving those molecules enough kinetic energy to escape from the planet's gravitational field.
Of course, we have a powerful magnetic shield from the solar wind thanks to our hot, dense and (partially) molten core. Our planet's magnetic field successfully bends away practically all of the solar wind particles that would be in danger of colliding with us, with the occasional exception of the polar regions, where the ions -- and hence sometimes aurorae -- get through.
(Image credit: NASA, retrieved from Cloudetal.)
Right now, our atmosphere is pretty thick: it consists of some 5,300,000,000,000,000 tonnes of material, creating the atmospheric pressure that we feel down here at the surface. There's so much pressure, in fact, that our Earth can sustain liquid water on the surface.
(Image credit: David Mogk, Montana State University.)
The ability to have liquid water is relatively rare: we need the proper temperatures and the proper pressures! That means we need at least at atmosphere of a certain thickness, a characteristic that Mars, Mercury, and the Moon totally lack. But we've got it, and hence we can have liquid water on our surface.
And do we ever! There's much more water than there is atmosphere. About 250 times as much, by mass, is the amount that the oceans outweigh the atmosphere, meaning that the oceans comprise about 0.023% of the Earth's total mass!
But we could get rid of all that liquid water, eventually, by letting the solar wind in.
(Image credit: NASA / Themis mission.)
When the Earth and Sun's magnetic field align, something like 20 times as many particles as normal make it through. Charged particles are bent by magnetic fields in very predictable ways, and if we could control those fields, we could control how much of the solar wind made it through.
In other words, if we could create a large enough magnetic field on Earth, we could poke a hole in the magnetosphere and allow the solar wind to strip our atmosphere away!
(Image credit: NASA, retrieved from futurity.org.)
Something similar happened to Mars about 3 billion years ago, when its core stopped producing that powerful magnetosphere shield, and its atmosphere got stripped away. When the pressure at the surface dropped below a certain level, the liquid oceans there could only exist as frozen ice or boiled off as water vapor. (And once they're water vapor, they become part of the atmosphere, where it, too, can be stripped away by the solar wind!)
It may not be fast enough for the most supervillainous among you, but one thing's for sure.
(Image credit: flickr user Ole C. Salomonsen.)
If we do poke a hole in the magnetosphere and allow the solar wind in, I'll definitely be enjoying the auroral show!Read the comments on this post...
"The doctors realized in retrospect that even though most of these dead had also suffered from burns and blast effects, they had absorbed enough radiation to kill them. The rays simply destroyed body cells - caused their nuclei to degenerate and broke their walls." -John Hersey Everyone (well, almost everyone) recognizes that radiation is bad for you. And the higher the energy of the radiation, the worse it is for you. The reason is relatively straightforward.
(Image credit: Environmental Protection Agency.)
When high energy particles (or photons) come into contact with normal matter, they knock the electrons off of atoms, ionizing them. This action breaks apart bonds, disrupting the structure and function of cells on a molecular level. And, as you might expect, the higher the energy, the more extensive is the damage that the ionizing radiation can do.
Targeted radiation -- at cancer cells, for instance -- is useful for this exact reason: it destroys the cancer cells. Sure, some of your cells are in the way, too, but radiation therapy is designed to kill the cancer faster (and more effectively) than it kills you.
But too much ionizing radiation will cause too much damage to your body, and spells doom for any human.
(Image credit: CERN / LHC, retrieved from here.)
Here on Earth, the most intense sources of energetic particles are those that come from the world's most powerful particle accelerators: at present, that's the Large Hadron Collider.
But the thing is, you don't know whether a particle accelerator is on just by looking at it. There are few enough high-energy particles even in the most powerful accelerators that the particles themselves are -- and hence the entire beam is -- invisible to the naked eye.
(Image credit: KEK e+/e- LINAC.)
You can't even feel is, much like getting X-rays at the dentist. But, as you may have guessed, there is a trick. An awful, terrible, do-not-try-this-at-home trick. You see, you already know that nothing can move faster than the speed-of-light in a vacuum.
But the speed of light decreases, often quite dramatically, if you're not in a vacuum.
(Image credit: Grimsmann and Hansen.)
This is actually the reason why light bends when it passes through a prism, or a straw/pencil appears bent when you immerse it in a glass of water.
(Image credit: Richard Megna - Fundamental Photographs.)
The relationship between how much an object appears to bend and the speed-of-light in that medium is actually very simple, and tells you that the speed-of-light in water is only about 75% of what it is in a vacuum.
And in many real-world cases, such as from particle accelerators, nuclear reactors, and radioactive decays, we make particles that -- while not faster than light-in-a-vacuum -- can travel faster than the speed of light in a medium!
(Image credit: Matt Howard, Idaho National Laboratory / Argonne.)
And when that happens, when a particle moves faster than the speed-of-light in a medium, light is produced! That's what's going on inside this nuclear reactor and causing this blue glow: the radioactive particles (electrons, in this case) are moving faster than the speed-of-light in water, and hence the particles are emitting Čerenkov Radiation!
What's Čerenkov Radiation?
(Image credit: Cherenkov Telescope Array in Argentina.)
The charged particles, passing through this medium at such great speeds, electrically polarize the medium, which then transitions back down rapidly to the ground state. The polarizing of the medium costs the fast-moving particle some energy, slowing it down, while the transition causes the particles in the medium to emit radiation, and that's where your light -- the Čerenkov Radiation -- comes from!
So how do you tell if the beam is on?
(Image credit: flickr user ohrfeus.)
Horrifically, you stick your closed eye in there!!!
With your eye closed, you should see blackness under normal circumstances. But with the beam on, the high-energy particles entering your eye will see that nice, aqueous fluid that fills your eyeball. And since they're passing through at -- you guessed it -- greater than the speed-of-light in your vitreous eye-fluid, they're going to emit Čerenkov Radiation.
(Image credit: The Gale Group, retrieved from science clarified.)
So if the beam is on, you'll see that light -- that Čerenkov light -- on the back of your eye. And if it's off, you won't.
If that makes you squirm, it should. Physicists used to die from cancer from lack of safety when it came to radiation at alarming rates, and we are no longer (thankfully) allowed to test whether the beam is on or not via methods like this. But this is an interesting bit of history of particle physics that I couldn't not share with you.
And now, in a life-or-death situation, you know how to tell whether the beam is on or not, consequences be damned!Read the comments on this post...
Today is the anniversary of the discovery, by John Tebbutt of New South Wales, Australia, of the Great Comet of 1861. Tebbutt was an astronome.
The comet was initially visible only in the southern hemisphere, but then became visible in the northern hemisphere on about June 29th. I find it interesting that word of the commet spread slowly enough that it was sen in the north before it was heard of.
It has been suggested that this comet had been previously sighted in April of 1500 (that comet is now known as C/1500 H1). The comet will return during the 23rd century.Read the comments on this post...
"I tell you, we are here on Earth to fart around, and don't let anybody tell you different." -Kurt Vonnegut Kurt Vonnegut may have it right for most of us, but not all of us spend all of our time on Earth. A select dozen of us, in fact, have made it to, as Cat Power would sing, to
(Image credit: Apollo 15, Dave Scott, NASA.)
Back in 1971, the Apollo 15 astronauts made huge strides in space exploration, making use of the first manned lunar rover and spending over 18 hours on activities outside of the spacecraft. But two (of the three) crew members experienced heartbeat irregularities on the mission, and the cause was unknown. This was the first time such irregularities were observed in Apollo astronauts, and NASA was, understandably, unhappy about this. Their biomedical research team initially concluded (incorrectly) that it was likely due to a potassium deficiency, and so some modifications were made to the astronauts' diets for the next mission.
A modification, mind you, that would change the place in history of one astronaut forever.
(Image credit: NASA, Apollo 10 official astronaut photo.)
Astronaut John Young is one of the most decorated astronauts in history. With an astronaut career spanning more than 40 years, he flew twice, each, on Gemini, Apollo, and Space Shuttle missions, including the inaugural STS-1 shuttle flight.
But John Young also was a crew member aboard Apollo 16, where he would become the ninth person to walk on the Moon. Oh, and where he was compelled to indulge in a diet very, very high in potassium. In particular, in the form of orange juice.
(Image credit: NASA / Science Source / Science Photo Library.)
Now, John Young had a history with particularities about food. He became something of an astronaut folk hero for smuggling a corned beef sandwich on board Gemini-3 in 1965, but was wholly unprepared for the ingestion of such tremendous quantities of orange juice.
Or, rather, for the effect that said orange juice would have on his body. And NASA was duly unprepared for the effect that would have on John Young's language.
(Video credit: NASA audio; YouTube user jude4021.)
While I imagine that there are few astronaut experiences worse than dutch ovening yourself inside your own spacesuit, you can also imagine that the governor of Florida was not too pleased at a mic'd up diatribe against the signature crop of his state. Words, in fact, that John Young would have to answer for in an official Apollo 16 press conference:
I don't know whatever happened to the gases released by astronaut Young (and others), but if there's any methane on the Moon, you can be sure that this is where it comes from! Read the comments on this post...
"They say 'A flat ocean is an ocean of trouble. And an ocean of waves... can also be trouble.' So, it's like, that balance. You know, it's that great Oriental way of thinking, you know, they think they've tricked you, and then, they have." -Nigel Tufnel Black holes* are some of the most perplexing objects in the entire Universe. Objects so dense, where gravitation is so strong, that nothing, not even light, can escape from it.
(Image credit: Artist's Impression from MIT.)
But there are a number of very counterintuitive things that happen as you get near a black hole's event horizon, and a very, very good reason why once you cross it, you can never get out! No matter what type of black hole you had, not even if you had a spaceship capable of accelerating in any direction at an arbitrarily large rate.
It turns out that General Relativity is a very harsh mistress, particularly when it comes to black holes. It goes even deeper than that, mind you, and it's all because of how a black hole bends spacetime.
(Image credit: Adam Apollo.)
When you're very far away from a black hole, spacetime is less curved. In fact, when you're very far away from a black hole, its gravity is indistinguishable from any other mass, whether it's a neutron star, a regular star, or just a diffuse cloud of gas.
The only difference is that instead of a gas cloud, star or neutron star, there will be a completely black sphere in the center, from which no light will be visible. (Hence the "black" in the moniker "black holes.")
(Image credit: Astronomy/Roen Kelly, retrieved from David Darling.)
This sphere, known as the event horizon, is not a physical entity, but rather a region of space -- of a certain size -- from which no light can escape. From very far away, it appears to be the size that it actually is, as you'd expect.
(Image credit: Cornell University.)
For a black hole the mass of the Earth, it'd be a sphere about 1 cm in radius, while for a black hole the mass of the Sun, the sphere would be closer to 3 km in radius, all the way up to a supermassive black hole -- like the one at our galaxy's center -- that would be more like the size of a planetary orbit!
From a great distance away, geometry works just like you'd expect. But as you travel, in your perfectly equipped, indestructible spacecraft, you start noticing something strange as you approach this black hole. Unlike all the other objects you're used to, where they appear to get visually larger in proportion to the distance you are away from them, this black hole appears to grow much more quickly than you were expecting.
(Image credit: Ute Kraus, Physics education group Kraus, Universität Hildesheim.)
By time the event horizon should be the size of the full Moon on the sky, it's actually more than four times as large as that! The reason, of course, is that spacetime curves more and more severely as you get close to the black hole, and so the "lines-of-light" that you can see from the stars in the Universe that surround you are bent disastrously out of shape.
Conversely, the apparent area of the black hole appears to grow and grow dramatically; by time you're just a few (maybe 10) Schwarzschild radii away from it, the black hole has grown to such an apparent size that it blocks off nearly the entire front view of your spaceship.
As you start to come closer and closer to the event horizon, you notice that the front-view from your spaceship becomes entirely black, and that even the rear direction, which faces away from the black hole, begins to be subsumed by darkness. The entirety of the Universe that's visible to you begins to close off in a shrinking circle behind you.
Again, this is because of how the light-paths from various points travel in this highly bent spacetime. For those of you (physics buffs) who want a qualitative analogy, it begins to look very much like the lines of electric field when you bring a point charge close to a conducting sphere.
(Image credit: J. Belcher at MIT.)
At this point, having not yet crossed the event horizon, you can still get out. If you provide enough acceleration away from the event horizon, you could escape its gravity and have the Universe go back to your safely (asymptotically) flat spacetime. Your gravitational sensors can tell you that there's a definite downhill gradient towards the center of the blackness and away from the regions where you can still see starlight.
But if you continue your fall towards the event horizon, you'll eventually see the starlight compress down into a tiny dot behind you, changing color into the blue due to gravitational blueshifting. At the last moment before you cross over into the event horizon, that dot will become red, white, and then blue, as the cosmic microwave and radio backgrounds get shifted into the visible part of the spectrum for your last, final glimpse of the outside Universe.
(Image credit: ZetaPrints.com.)
And then... blackness. Nothing. From inside the event horizon, no light from the outside Universe hits your spaceship. You now think about your fabulous spaceship engines, and how to get out. You recall which direction the singularity was towards, and sure enough, there's a gravitational gradient downhill towards that direction.
But your sensors tell you something even more bizarre: there's a gravitational gradient that's downhill, towards a singularity, in all directions! The gradient even appears to go downhill towards the singularity directly behind you, in the direction that you knew is opposite to the singularity! How is this possible?
(Image credit: Cetin Bal.)
Because you're inside the event horizon, and even any light beam (which you could never catch) you now emitted would end up falling towards the singularity; you are too deep in the black hole's throat! What's worse is that any acceleration you make will take you closer to the singularity at a faster rate; the way to maximize your survival time at this point is to not even try to escape! The singularity is there in all directions, and no matter where you look, it's all downhill from here.
Like I said, General Relativity is a harsh mistress, particularly when it comes to black holes.
(* -- This is all done for a non-rotating, or Schwarzschild black hole. Other forms of black holes are similar, but slightly different, and much more complicated, quantitatively.) Read the comments on this post...
There's been a bunch of discussion recently about philosophy of science and whether it adds anything to science. Most of this was prompted by Lawrence Krauss's decision to become the Nth case study for "Why authors should never respond directly to bad reviews," with some snide comments in an interview in response to a negative review of his latest book. Sean Carroll does an admirable job of being the voice of reason, and summarizes most of the important contributions to that point. Some of the more recent entries to cross my RSS reader include two each from 13.7 blog and APS's Physics Buzz.
I haven't commented on this because I haven't read Krauss's book (and I'm not likely to), and because my interest in philosophy generally is at a low ebb at the moment (I oscillate back and forth between thinking it's kind of a fun diversion, and thinking I have better things to do with my time). I've been thinking about a new project that's kinda-sorta on the edge of philosophy-of-science type things, though, which has involved a bit of time thinking about why my regard for the subject is at a low ebb at the moment. And seeing the title of Jason Rosenhouse's "The Reason for the Ambivalence Toward the Philosophy of Science" in the "most active" sidebar widget (the post itself isn't so interesting to me, but the framing of the title made me think of something useful), combined with the second Physics Buzz post, combined with what I was writing last week made a bunch of pieces fall into place.
My realization was this: I'm down on philosophy of science type things at the moment because an awful lot of the conversation reminds me of interminable arguments within science fiction fandom.Read the rest of this post... | Read the comments on this post...
One final thought on the Big Science/ Space Chronicles stuff from last week. One of the things I found really frustrating about the book, and the whole argument that we ought to be sinking lots of money into manned space missions is that the terms of the argument are so nebulous. This is most obvious when Tyson or other space advocates talk about the need for "inspiring" people, but it shows up even in what ought to be relatively concrete discussions of actual science.
Take, for example, the argument over humans vs. robots. Given the success of the robotic missions to Mars and other bodies, many people ask why we should bother to send people to any of those places. Tyson himself estimates the cost of sending a human to be around fifty times the cost of sending a robot, and says that "if my only goal in space is to do science, and I'm thinking strictly in terms of the scientific return on my dollr, I can think of no justification for sending a person into space." But then, he turns around and tries to justify it on fairly standard grounds: that humans are more flexible, while a robot can only "look for what it has already been programmed to find." Having humans on the scene would enable faster and more "revolutionary" discoveries.
This is an argument that sounds fairly convincing on a surface level, but on closer inspection it breaks down in two ways: it's too generous to humans, and too hard on the robots.Read the rest of this post... | Read the comments on this post...
This post was written by Brookhaven Lab science writer Justin Eure.
With nanotechnology rapidly advancing, the sci-fi dream of a Star Trek replicator becomes increasingly less fantastic. But such radical technology would, in theory, require the kind of subatomic manipulation that far exceeds current capabilities. Scientists lack both the equipment and the fundamental knowledge of quantum mechanics (the Standard Model, for all its elegance, remains incomplete) to build items from the raw stuff of quarks, gluons, and electrons . . . but what about alchemy?
Even Isaac Newton, credited with the dawn of the Age of Reason, felt the mystical draw of alchemy, working in secret to transform one element into another. Centuries later we still can't conjure gold from lead, sure, but what if it was possible to combine a handful of elements to very closely mimic gold? What if scientists engineered a synthetic Midas Touch that tricked base metals into performing like gold, thereby conquering the hurdles of rarity and price?
Now forget the alchemist's dream of gold and consider the equally precious noble metal platinum - hovering right around $50,000 per kilogram - which may be the key to building a sustainable energy future. Now, using advanced technology and elements that cost 1000 times less, researchers at Brookhaven National Lab have created a high-performing pauper's platinum from nanoscale building blocks.Read the rest of this post... | Read the comments on this post...
"There's nothing that cleanses your soul like getting the hell kicked out of you."
-Woody Hayes There's no doubt that we lucked out when it came to the formation of our Solar System.
(Image credit: Michael Pidwirny, retrieved from here.)
Our inner Solar System, where temperatures are ideal for liquid water and life-as-we-know-it, is full of rocky planets and devoid of any gas giants for many hundreds of millions of miles. But, as we know all too well from the last twenty years of finding exoplanets, this isn't the only way it could have turned out.
In fact, of the some 2,300 planets found around other stars so far, the vast majority of them are either very, very hot, very, very large, or both.
(Image credit: Jer Thorp and John Underkoffler.)
This could just be due to the fact that those types of planets are the easiest ones to find with the technology and techniques we have available to us right now, and we may wind up finding more solar systems like ours. What seems most important, at least as far as the search for extraterrestrial life (or possibly habitable exoplanets) goes, is looking for rocky planets where the temperature is right for liquid water.
And every star has a region around it where that's possible.
But although we've found a small but important number of stars with rocky planets that live in their habitable zones, there's one type of exoplanet system that never has a rocky planet in their habitable zones.
Not only that, but they -- at least so far -- never have any other planets in their solar systems! What gives?
(Image credit: NASA / GSFC, retrieved from Softpedia.)
Over in our Solar System, we've got our rocky worlds interior to all of our gas giants, with an asteroid belt interior to the giant planets, and a kuiper belt exterior to our four Jovians. But in systems where there's a Hot Jupiter, or a gas giant very close to its parent star, we don't find any other planets anywhere near the star itself.
Why is that?
(Image credit: European Southern Observatory/L. Calcada, retrieved here.)
When you bring a large-mass planet into close quarters with a much smaller one, something's got to give. Because of the way gravitation works, you're going to have a three-body gravitational interaction, which is one of the most difficult theoretical problems in all of physics.
But universally, what's going to happen is that there's going to be a transfer of momentum and angular momentum, and one of three things is going to happen. Either:
- The large planet will gravitationally capture the smaller one, turning it into a moon,
- The large planet will fling the small planet either violently into its Sun or violently out of the Solar System, or
- The large planet will collide with the small one, effectively eating it.
(Image credit: BoredofStudies.org.)
In other words, these Hot Jupiters are like the psychotic eldest child that murders its younger siblings! We see that there are no rocky planets among the gas giants in our Solar System for exactly this reason. But how does this work, and why does this prevent solar systems with Hot Jupiters from having habitable planets outside of them? This is not obvious, so let me first set up the situation for you to help you get a handle on it.
As far as we understand it, all solar systems start out the same way in the very early stages: there's a central region where a star forms, accompanied by a proto-planetary disk, which will coalesce and form into planets.
(Image credit: NASA, retrieved here.)
But over time, planets clear the space around them. They do this, believe it or not, in the same way that star clusters all eventually end up dissipating: simple gravity. Watch this simulation of a star cluster to see what I'm talking about, and pay particular attention to the first 25 seconds of the video.
(Video credit: Simon Portegies Zwart (U. of Amsterdam) and Frank Summers (STScI).)
Notice how an occasional star just sped off from the star cluster in a random direction, even early on in the simulation? That's what gravitational encounters between more than 2 bodies do, pretty much all of the time! The physical process is called violent relaxation, which is a wonderful term that (somehow) no enthusiast has created a wikipedia entry for!
Just as the structure of the star cluster changes because of these gravitational ejections, the structure of the young solar system changes because of its gravitational interactions. These large planets can migrate, depending on how they absorb or remove each tiny mass they encounter. Some encounters move them closer towards their parent star, others move them farther away. In the case of Jupiter and Saturn, they were once significantly closer to the asteroid belt than they are today; in the case of Hot Jupiters, they clear out at least the entire habitable zone!
(Image credit: NASA, ESA, and G. Bacon (STScI).)
According to research led by Eric Ford, the reason we haven't found any of these habitable, rocky planets around stars with Hot Jupiters -- even though we've found 63 of them around other stars -- is because Hot Jupiters perturb the orbits of these planetesimals in the young solar systems sufficiently so as to completely clean them out, leaving no possible rocky worlds behind!
(Image credit: NASA / JPL-Caltech.)
In our Solar System, our four gas giants completely cleared out the regions between about 4 Astronomical Units and about 30 Astronomical Units, where one of them is the distance between the Earth and the Sun. But if you put a Jupiter-sized planet anywhere in the inner Solar System, then all of the rocky planets wouldn't be here!
And that's why systems with exoplanet bullies in them -- Hot Jupiters, to be specific -- have no Earth-like planets in them, or rocky worlds with the proper temperatures for water. That's just one more example of the power of gravity!Read the comments on this post...
I go back and forth about the whole question of scientific accuracy in tv shows and movies. On the one hand, I think that complaining "Explosions don't make noise in space!" is one of the worst forms of humorless dorkitude, and I'm generally happy to let bad science slide by in the service of an enjoyable story. On the other hand, though, I am a professional physicist, and it's hard to turn that off completely.
Weirdly, one thing that tends to push me toward complaining about the science is when people start doing "The Science of ______" pieces, as both MSNBC and io9 did for The Avengers, and when movie people start patting themselves on the abck for having consulted with scientists. Because, you know, if you're going to talk up the fact that there's science behind the movie, you're asking to be held to a higher standard.
And, really, most of the recent spate of comic-book movies have had scenes of technobabble that are every bit as dumb as anything produced in the days before consulting scientists. One of the worst was an exchange in The Avengers, where the team's scientists, Bruce Banner and Tony Stark, are trying to help S.H.I.E.L.D. track down Loki and his stolen energy source:
BANNER: How many spectrometers do you have?
SHIELD GUY: We have the cooperation of every university in the country.
BANNER: Tell them to put the spectrometers on the roof, and set them to detect gamma radiation.
(That's paraphrased a bit from memory.) This is one of the stupidest science-type lines I've heard in any recent movie. To give you an idea of how stupid it is, here's an analogue in more everyday terms:Read the rest of this post... | Read the comments on this post...
Continuing the blog recap series, we come to the "split year" of 2005-2006. The blog was initially launched in late June, so that's when I'm starting the years for purposes of these recaps, but ScienceBlogs launched in January 2006, so this year was half Steelypips and half ScienceBlogs. This post will cover the Steelypips half, June-January; I'll do the ScienceBlogs stuff in a second post, once I figure out the best way to go through those posts (the ScienceBlogs archives aren't set up well for reading straight through).
In reading through this, I was amused to discover this pan of Seed's relaunch, in which I call the magazine "Maxim for science geeks." Not quite three months later, they were paying me to write a blog... I remembered writing that, but didn't remember how close it was to the launch of ScienceBlogs.
So, what was on the blog in the second half of 2005?Read the rest of this post... | Read the comments on this post...
Some time back, I reviewed a cool book about Fermi problems by Aaron Santos, then a post-doc at Michigan. In the interim, he's taken a faculty job at Oberlin, written a second book on sports-related Fermi problems, and started a blog, none of which I had noticed until he emailed me. Shame on me.
Anyway, his new book is just out, and he's running an estimation contest with a signed copy as the prize. So, if you're the sort of person who enjoys Fermi problems, read his post then grab a convenient envelope and start estimating on the back. You have until June 1.Read the comments on this post...