The cradle rocks above an abyss, and common sense tells us that our existence is but a brief crack of light between two eternities of darkness. -Vladimir Nabokov
Last Friday, I posed a question to you, and you kindly responded by voting as to whether, when you crossed the event horizon of a black hole, the lights would stay on or go off. The results so far?
What do I have to say? Good for you! Just because no light gets out doesn't mean that you can't see the light that comes in! When you're in your spaceship, very few things matter.
You could be in a strong gravitational field, like exists near a black hole. Or, you could be accelerating due to your engines. Or -- if you like your science with a little more fiction in it -- you could be accelerating because you're caught in a tractor beam.
No one doubts that the lights would stay on if you were simply accelerating, do they? Well, is crossing into the event horizon of a black hole any different?
Why don't we ask Al. In 1907, two years after publishing his special theory of relativity, Einstein had what he would later call, "my happiest thought." He had an insight that all accelerations were equivalent to an observer, regardless of what caused them and regardless of how fast the accelerations were.
He called this the principle of equivalence, and this is where we find our answer to the question.
It doesn't matter how big your acceleration is or what causes it. It doesn't matter what direction you accelerate in or how hostile your environment is. And, to give you the final answer, it doesn't matter whether you're inside of a black hole or not. As long as you still physically exist (i.e., you can neglect the tidal forces trying to tear you and your spaceship apart), the lights stay on!
And oddly enough, once you do cross the event horizon, if you want to maximize the time it takes for you to reach the center of the black hole, do you know what you should do to your ship's engines? Turn them off completely! Any extra acceleration you put out, even if it's directed perfectly away from the center of the black hole, will actually pull you in faster than if you turned all of your engines off. That's, umm... a survival tip that could buy you precious extra seconds to get to the end of The Count of Monte Cristo. (Spoiler alert.)
All human wisdom is contained in these two words -- wait and hope.
He that hath a beard is more than a youth, and he that hath no beard is less than a man. -Shakespeare
Far be it from me to take advice from Shakespeare, though. I prefer my advice from bluegrass musicians. If you want beards, you can't do much better than Jerry Garcia and David Grisman. Here's their version (along with Tony Rice) of House of the Rising Sun, which may be the best version of this song I've ever heard. By a lot.
Why the talk about beards? Well, many of you participated in my charity challenge and got me to shave my head. That worked so well as a motivator that I decided to issue a challenge to my intro to astronomy class:
You all have a paper to write. It's an astronomy research paper, and it's due on November 19th. Whoever writes the best paper -- as chosen by me -- gets something extra, in addition to an A. You get to choose what facial hair I should grow. And I'll start over Thanksgiving, and I promise I'll keep it until the start of the Spring Semester, at least.
Well, November 19th was this past Thursday, and when all is said and done, I'll have 63 papers to grade. After that, the beard growing starts. What would you choose if you had the option to pick for me?
Of course, this got me thinking that if there's an idea that's good enough, I may just run with it. And I may run with it so hard that I could shoot for the World Beard & Moustache Championships. For those of you who don't know, have a look at this video from the 1991 championships. The show-stopper happens at 0:21.
That is a tall order to live up to, but a man can dream!
The most well-known one is that nothing -- not even light -- can ever escape once it falls in. Well, my question is, if you fell in to a black hole, as you crossed the event horizon in your sturdy, well-lit spaceship, would the lights stay on or would they go out as you crossed into the black hole? (Ignoring the tidal forces that would rip you and the spaceship apart.)
In other words, you've read the first 1497 pages of the Count of Monte Cristo as you cross the event horizon; will you be able to finish your book with your last remaining moments?
What do you think? Feel free to discuss below; I'll post the answer with an explanation on Monday!
Why it is that of all the billions and billions of strange objects in the Cosmos -- novas, quasars, pulsars, black holes -- you are beyond doubt the strangest? -Walker Percy
When you watch someone fall into a black hole, what you actually see is pretty surprising. You see, a black hole's gravity distorts the space around it, and it does so without providing any light of its own, giving you a unique perspective on the Universe.
Well, if you watch someone else fall in, you'd see them approach the black hole normally, and then the bizarreness starts. As they go deeper and deeper into the gravitational field of the black hole, a few super bizarre things all start to happen simultaneously.
The light coming from the person gets redshifted; they'll start to take on a redder hue and then, eventually, will require infrared, microwave, and then radio "vision" to see.
The speed at which they appear to fall in will get asymptotically slow; they will appear to fall in towards the event horizon at a slower and slower speed, never quite reaching it.
The amount of light coming from them gets less and less. In addition to getting redder, they also will appear dimmer, even if they emit their own source of light!
But if you think that's bizarre, here's where it gets really weird: the person falling in notices no difference in how time passes or how light appears to them. They would continue to fall in to the black hole and cross the event horizon as though nothing happened.
What would you see if you fell into this black hole? Luckily, Andrew Hamilton and his group at Colorado have created a video (and an accurate video at that) to illustrate this:
And that's not even counting what the tidal forces would do to you as you fell in, which includes (in chronological order):
Tearing your extremities (head, arms, legs) from your torso,
tearing the individual muscles, tendons, ligaments, etc., apart from your body,
tearing individual cells apart from one another,
tearing the organelles inside each cell apart, destroying cells themselves,
tearing the individual molecules apart into atoms,
tearing your atoms apart into nuclei and electrons, and finally
tearing the individual nuclei apart into, eventually, quarks and gluons.
Fun stuff, yes? Perhaps someday, "death by black hole" will be commonplace, although it will take an infinite amount of time for you to see someone else experience it!
In the comments on one of my posts, someone pointed me towards Stephen Crothers, who gives the following argument (in a nutshell) as to why black holes cannot possibly exist:
General Relativity is our theory of gravity, which relates the curvature of space to the gravitational acceleration of objects.
This theory only works in certain regimes; it breaks down at the point of singularities.
A black hole, as predicted by Schwarzschild, is a singularity.
Therefore, since singularities are forbidden by General Relativity, there is no reason to think that black holes exist.
(You can watch his video here, or read his full argument here.) Therefore, he argues, astronomers are wasting their time looking for black holes, since their existence isn't even a physical prediction.
Talk about not seeing a forest for the trees. The "singularity" is not essential for a black hole to exist. Honestly, it isn't important at all whether there's a singularity or not. All that matters, in the real world, is that something is both massive and compact enough so that, within a certain radius, light cannot escape from it. That is the astrophysical definition of a black hole.
So, do they exist? Definitely. Where do you look for incontrovertible proof? The center of the galaxy! There are no two ways around it; there is definitely a black hole there.
How am I so sure? The above image shows the center of our galaxy. There are many, many stars orbiting the central point where the arrows are pointing. We have tracked these orbits over more than a decade, thanks to the UCLA Galactic Center Group. Here's a screenshot of their results.
From the motion of these orbits, we can figure out what the mass of the object they orbit around is. It turns out to be over 2 million times as massive as our Sun. And yet, we don't see any light coming from that point. We don't see a white dwarf, we don't see a neutron star, we don't see any object at all.
For a mass that large, you will have a black hole if that mass is confined to a sphere of a diameter of about ten million kilometers. That isn't hard, considering we have many, many stars that we know of where an entire solar mass is confined to a diameter of about ten kilometers. (These are neutron stars.) If you up the mass, the neutrons at the core will eventually collapse under the tremendous pressures, and collapse farther. There's a well-known upper limit to how massive a neutron star can be, and it's less than three solar masses, much less two million.
So you can argue about whether singularities violate General Relativity or not until you're blue in the face. It doesn't have a damned thing to do with whether any light gets out of your ultra-dense, massive object. And that's what we call a black hole, and it exists. Don't believe it? Then tell me what's going on at the galactic center.
Some meteor showers are spectacular, while most are mundane. If you sit around during a typical shower, you might see anywhere from 50 to 100 meteors an hour, if the Moon isn't out.
If you take a time-lapse photograph and look for meteors, you will, sometimes, get a great view of what's going on. Although it isn't immediately clear what's a meteor and what's a passing satellite or airplane, you can tell them apart in this video by looking for the "instant" streaks, which are meteors, versus the ones that streak for many frames, which are satellites or aircrafts.
Well, the Leonids peak tonight, and they are spectacular. Instead of getting one or two meteors a minute, we should get -- on average -- a meteor every five to ten seconds! What's more? The peak, tonight, is at around 3 AM Eastern Standard Time (Midnight Pacific Standard Time).
Even better? The Moon is practically new tonight.
This means that only a tiny crescent will be in the sky, and it'll be gone by an hour or two after sunset. Which means, if you get clear skies, you'll have ideal meteor shower conditions!
So where should you look on the sky? Near the constellation Leo; the meteors will emanate from there. (Ignore Saturn in the image below; it was there in 2006, but isn't in 2009. The stars are still in the same place, though.)
And at its peak, we should get about 500 meteors per hour, which is huge. If you get to see it remember to thank Comet Tempel Tuttle for coming through in 1998 and leaving this beautiful debris trail for us.
All of it makes for a beautiful sight this night! So go out and enjoy it, and know that I'll be jealous here in cloudy Portland!
I thought I should consult you first before I went ahead with my plan to destroy the Moon. -Greg Angelone, via The Straight Dope
Last week, scientists from LCROSS announced that they had detected "a buttload" of water on the Moon. Let's go over what happened and what it means.
The Moon is very different from Earth. It has no atmosphere (literally, less than one atom thick), day-and-night lasts for two weeks apiece, and the temperature extremes are horrifically severe. But one of the biggest differences? Whereas the Earth is tilted at 23.5 degrees as it goes around the Sun, the Moon is tilted by less than two degrees.
This is hugely important. On Earth, because of the 23.5 degree tilt, every place on Earth receives a significant amount of sunlight at some point during the year. But with a tilt that tiny on the Moon, the Sun never gets more than 1.54 degrees above the horizon as seen from either the North or South Pole of the Moon!
Or, in other words, if you dug a hole that was 100 meters deep and 100 meters wide, only the top 2.7 meters of your hole would ever get illuminated by the Sunlight, and the bottom 97.3 meters would be permanently shadowed. So if you ever put water in that hole, it should freeze and remain frozen for all eternity.
Well, we don't have holes that have been dug at the poles, but we do have "natural" holes. These appear as humongous craters, like so.
So, what did we do with LCROSS? We crashed it into one of these permanently shadowed craters, and looked at the debris plume that got shot up from the impact. If we find a huge amount of water, then we can infer that pretty much all of these permanently shadowed craters on the Moon are loaded with huge amounts of water, and will be for pretty much the next billion years.
So, the fact that we found "a buttload" of water? That means the Moon's craters at the North and South poles are loaded up with reservoirs of water, and all we have to do is go there and claim it. Hooray for exploration! Hooray for space! And hooray for the Moon!
But I want you to know something... you and me, it's not gonna be a one-way street. 'Cause I don't believe in one-way streets. Not between people, and not while I'm driving. So, here's some advice I wish I woulda got when I was your age: Live every week like it's Shark Week. -Tracy Jordan, 30 Rock
And, much like Tracy, the song for you this week is simple, sweet, and good-hearted. Enjoy an old classic, Just the Two of Us by Grover Washington, Jr., and Bill Withers.
There's also an episode about Terraforming Mars, which is balanced and scientifically accurate, plus it has Robert Zubrin, whom I met back in 1999 and really respect his views on Mars exploration and colonization. (Image Credit: National Geographic Channel.)
The treatment of these subjects is entirely different from what I've come to expect from, say, the History Channel. The expeditions are riveting because the questions they're asking are riveting, and you get to journey along with the researchers, watching some of the science unfold as it unfolds. It gives me a tremendous appreciation for the level of specialization of knowledge in our society, as well as providing an accurate picture of scientific investigation.
It's something that's very rare on television these days, and I've found this to be an excellent program. So if you can watch it, enjoy it, and have a great weekend!
Can you touch your toes? Seems like an easy thing to do for those of us who have the flexibility.
Now, here's the challenge. Stand with your back and your heels pressed up against a wall, and now try to touch your toes.
You can't do it! Not without putting your hands down on the floor, you can't. There's a super-simple reason for this: center-of-mass.
For human beings, your center-of-mass is somewhere in your abdomen. It's lower down for women than men, but in the abdomen region for everyone. When you typically bend down to touch your toes, you'll notice that the upper part of your body moves forwards, while the lower part moves backwards. You do this by default, but the major reason you need to do this is so that your center-of-mass stays over a stable point: your feet!
But as soon as you prop yourself up against the wall, the lower part of your body can't move back! So as the upper part moves forward, your center of mass moves forward. It goes from being over your heels to being over your arches to your toes, and the instant it extends out beyond your toes, you know what happens?
You begin to rotate, and once that happens, you're going to fall, like so:
(Image credit: Gabrielle Varieschi.) And that's it! This is a great trick to try on children to teach them about stability. It's also great for physics teachers to introduce torque, rotation, and center-of-mass. (And on unsuspecting coworkers to teach them about falling on their faces!)
It's a remarkable phenomenon that such a simple thing as touching your toes would be off-limits with your heels against a wall, but there it is! Don't believe me? Try it yourself and see what happens, but I warned you...
