Here goes my first attempt at cliche hording.
without even reading the friendly article, I can already
accurately predict (based on my education, which is mostly from
slashdot):
This means we might actually be around when Duke Nukem Forever is
released.
Each one of us has a chance with Natalie Portman... Think about
it, a nonzero probability (except for you, Cowboyneal) integrated over
an infinite time... I can dream at least...
In Soviet Russia, forever lives for YOU. Perhaps if we
reconstruct Soviet Russia we will be able to figure out what this
means.
SCO and/or Jeff Bezos already have a patent on immortality. They
blatently disregard God's prior art.
Think infinite hot grits. Yum.
With all the time in the world, we no longer have to only "imagine a
beowolf cluster of X".
Sounds like a blast to me.
Oh, wait, forgot... we can argue about BSD dying unto eternity as well
(and perhaps Apple too).
Ha ha ha... thanks but I've already got enough karma;)
I wonder though how informative the most really is... that is, how many of the people who read the post were actually informed. ANyone out there not understand what I said, can you tell me what didn't make sense to you?
I don't think most/.ers have had a course in quantum physics (seems to be many more computer geeks than physics geeks here, unlike somewhere like bottomquark).
Antiparallel... well when we think of "parallel lines", they are just lines with the same slope. But what about vectors? I mean, if they point the same direction, they are obviously parallel. But what if they point in exactly opposite directions? Clearly the lines they lay on are parallel, but they are not! That would be what "antiparallel" means. Perpendicular is about half as far away from parallel as you can get. Antiparallel is the exact opposite (as the name implies.)
FYI anisotropic means "having the property of not being the same in all directions". For instance a perfect radiating antenna would be called an "isotropic radiator". An imperfect one would be an "anisotropic radiator". Cool, eh?
Yeah sorry about that... One of the issues with science is that the precise terminology often obfuscates communication with nonexperts... Not a lot that can be done about it except the creation of (usually cheezy) analogies. As I've been very b usy with my job lately I didn't have time to really formulate the post in the best possible way.
I'm glad it made sense once you dug into it... that's what's truely important. Writing scientific explainations for a broad audience is extremely difficult and I have much admiration for those who do it successfully.
Glad you enjoyed the post.
Cheers,
Justin
BTW, if you get down to it... I avoided a lot of the jargon I could have used... Anisotropic, nth order preturbations, recoilless spontaneous emission, etc... I'm sure I could have worked a few other things in there too if I really wanted to kill some of your neurons.
Ah, sorry I forgot to mention in my plug that the newest version of SAP that can be downloaded is called "WITS for FIDO"... Don't let the acronyms fool you, it's essentially an older version of the same program, a flavor designed for "field tests" (simulated mars missions conducted out in remote locations on earth).
The site is a little odd at first but once you get used to it, it's pretty darn cool. Tell me what you guys think.
During the mission a much updated public version will be released, which should be much cooler. I haven't checked the permissions on downloading the fido version yet though, so I hope it works out for you.
Note: I work on the Mars Exploration Rovers mission, developing Ground Data Systems software used by the scientists. I'm also completing a degree in Physics.
I'm not sure exactly how they plan to fix the spectrometer but I'm sure they're not lying when they say it's an option. Remember the Galileo space probe was recently fixed from hundreds of millions of miles away. Since a Mossbauer spectrometer uses a moving radioactive source to take a spectrum I would guess it might be put through it's paces several times to try to work out a glitch(speculation).
It's really quite amazing what can be fixed remotely, or at least worked around... If there's a significant mechanical problem with the instrument, however, there's not that much that can be done.
From what I've heard, the Mossbauer on Spirit isn't currently getting data at full resolution, but they may be able to compensate for that by reprogramming the instrument remotely.
In case you don't already know, the Mossbauer spectrometer is a rediculously cool instrument. The way it works is the following:
According to elementary quantum physics, the energy levels of the nucleus are preturbed by the presence of nearby magnetic fields. Because electrons are charged fermions (and thus have nonzero spin), they have a dipolar magnetic field which can interact with the nucleus via hyperfine splitting. Hyperfine splitting is the creation of two or more distinct energy states from a single energy state via spin coupling. As an example, imagine a bar magnet which is held at the top of a one-foot drop. It has a very specific potential energy (in quantum physics energy is quantized and thus exists only in discrete amounts). Now, imagine that a uniform magnetic field is turned on in the lab room, pointing along the Z-axis (up/down). The bar magnet, if allowed to rotate, will want to minimize its energy by aligning itself antiparallel to the magnetic field (remember, opposites attract). To twist it into the "parallel" orientation, energy must be exerted, thus the single energy level of the bar magnet is now two distinct energies (in the quantum case, the difference between energy levels caused by hyperfine splitting is very small, hence the term "hyperfine"). This is a rough analogy to what's going on in the nucleus. Still with me? Good!
Now, what does this have to do with the spectrometer? Well one of the most important pieces of information we can gather about rocks on Mars is their chemical composition. Most people are aware that Mars' rusty color is due to the high concentration of iron oxides on the surface. From high school chemistry we can remember that metals have multiple valence numbers they can use to bond with other atoms... It turns out that the electron configuration of the different bonds causes the electric and magnetic field from the electrons to vary significantly.... And if the magnetic field is varied, so is the hyperfine splitting! So... the nucleus itself is slightly affected by the valence shell geometry, among other things.
So, how do we detect these differences in hyperfine splitting? That's where the Mossbauer spectrometer comes into play. The spectrometer contains two pieces of raioactive cobalt-57 (each about the size of a pencil eraser) as sources of gamma-radiation quanta. The cobalt-57 decays into an isotope of Iron with an excited nucleus. The excited nucleus quickly decays, emitting the exact gamma-quanta required to excite another iron nucleus. This gamma radiation exits the instrument and strikes a rock. Inside the rock iron nuclei absorb and re-emit the gamma radiation to be detected by the spectrometer.
The variations in the energy levels in the iron in different chemical forms are just large enough that the addition of a dopplar shift to the radiation source allows us to detect it reliably. The radiation source slides towards and away from the target at specifically varying speeds, and because the gamma rays energy levels are changed slightly by the dopplar
Well if you intended it to be a joke, I agree it's pretty funny.
Once again, a case of moderators on crack.
But the same mods modded me up... hmmm... maybe I ought not insult them?;)
As for your code suggestion, there's no objects, there's no assertions, and most importantly no over-engineering! There's no way NASA will use it like that!;)
Well the software I write (as mentioned in my previous comment) runs on ground computers, and is used by the scientists. We don't need a simulator for it, because we have the actual computers here we can test on.
But yes, the flight software is tested on simulators. My officemate wrote the motor simulations for MER for testing the flight software... He says their testing methods are almost paranoid in their coverage of possible issues... In fact, they are still testing madly right now in case they find a problem, it might be able to be worked around.
Simulations are only so good. There's no way the simulations can take every little detail into account, at least with the computers we have today. It's truely amazing how many different ways hardware can fail. And don't forget cosmic rays cause random bitflips now and then...
Yes testing can uncover a lot of issues but certainly not everything.
Dislaimer: I write software for Mars missions, including the 2007 Pheonix mission.
I hope they haven't recycled the imperial to numeric conversion code.
I must say I'm really tired of hearing about this every time there's an article about a mars misson. I mean, no one says "I hope they haven't recycled those overflow errors" every time an Ariane 5 rocket is lauched! Was it a stupid problem? Yes, however people seem to forget how rediculously hard it is to successfully launch a mission like this. Yes it's very easy to prevent a single mistake, but thousands of potential mistakes? Our track record with Mars probes is twice as good as the nearest competitor (Russia) and it's looking to continue that way.
Somebody want to contribute an open source alternative to them?
Look. The people working at NASA know how to write this stuff. That's not the problem. The problem is that on large scale projects like this, it's entirely possible for things like this to be overlooked... People tend to worry about the "hard" stuff rather than the easy stuff. And as for why they even have to convert units, as far as I understand NASA generally uses metric, it is the american aerospace companies that generally insist on using imperial units.
Also, Open Source is *NOT* the catch-all answer for everything! The development team I'm on uses linux for our development, and our software will be running on a lot of linux (and windows) boxes during the mission. We love open source, and even use some open libraries (such as castor) in our code as allowed (we are not allowed to link to GPL code of course).
However, I would cringe if the flight software was some open source deal... I mean, looking at the linux kernel sources, (some say it is the gem of open source) I wouldn't want to have to depend on anything written like *THAT* to handle flying in space. Great for on the ground where we can fix/replace/patch if there's a problem but... It's not cleanly designed and implemented like, say, QNX, etc. Few people alive have experience writing software for spaceflight systems, and I expect they they know just a little bit more about it than even the best of linux hackers do.
I guess I just don't understand why the parent post was modded insightful. Nothing personal, in7ane, but really!
There should be a variant of the GPL that prohibits all military use.
Perhaps there should also be a variant of the GPL that prohibits any use of said software by aliens during earth invasions. It would be similarly trivial to enforce.
People are better than robots at exploring a planet.
I'm not sure how valid of a claim that is. Certainly, right now our probes aren't that great, mainly because there is little actual autonomy. However, in the near future, probes will be built to handle major decisionmaking on their own. Our best hope for exploring the most of Mars is to send thousands of small autonomous probes that will do the looking around for us. This could be done for roughly the same cost as the manned mission, without the PR risk (yes, I hate it but it's very true) that manned missions currently represent.
I work at the Jet Propulsion Lab, and
many of the roboticstechnologies that are currently being persued there should give us the capability to collect huge amounts of useful data on Mars in the next 20 years or so.
Is manned flight expensive? Well not really, but the price/performance ratio isn't that great compared to what will be done in the next 20 years with robotics probles (remember economy of scale, 1000 probes isn't much more expensive to build than 1).
Actually I worked with Thomas Gold as a computer technician a year or so ago... We had many discussions of his theory. He did not forget about conservation of momentum, in fact, when I told him his theory violated it, he said, and I quote PRECISELY: "It is a silly law anyway." Needless to say, it was quite difficult to not laugh at that one.
Also he tries to use arguments tied to radiometers, despite the fact that russian experiments with better vaccuums show that the reflection happens correctly. The other physicists at Cornell that I have talked to think that Thomas Gold is dead wrong on this one, for several reasons (some of them empirical).
I love the idea of a solar sail, so here's hoping he's wrong!
I'm a student who happens to work for the head of the mission Steve Squyres (he's the Principle Investigator).
I've heard much about the politics etc that allowed this particular mission to be chosen, and it's quite an amazing story. One of the big deals about this mission is that it's a SCIENCE mission. Unlike pathfinder, whose mission was to test mars lander/rover tech, this mission is all about accomplishing as much science as possible. The mission was designed basically by looking at the pathfinder delivery system and figuring out how much rover they could cram into it.
I have much faith in the mission because the pathfinder system works, and it works well. There may be issues with the heaver weight etc, however I don't think we're going to see something like the polar lander happen to these guys.
The panoramic camera does indeed have stereo vision. I happen to be a student helping with the development of Science Activity Planner which is the primary program used by the scientists to analyse data and plan mission sequences (final analysis of data is done by other tools, but for tactical planning SAP is used).
Anyways, there is a public version planned which includes the ability to not only make 3-D images using your graphics accellerator, but also to take two 2D images taken by the pair of pancams and color them so that 3D glasses (red/blue) reveal the terrain. It's actually a very cool feature (I've tried it out while at JPL) and should hopefully be easy to use on the public version.
Not quite as good as a View-Master, but close enough.
That said, the public version of SAP should also let you create your own "missions" using the same tools the scientists do. The data distribution will be immense, however, and we are considering using bittorrent. We need a bittorrent client that Joe User can install easily however.
Any suggestions?
Re:simpons mental picture
on
Ant Farm PC
·
· Score: 1, Funny
I for one will welcome our new insect overlords.
This has got to be the only place where that comment could be modded "insightful!"
can't believe no one brought this up yet. Recently some astronomers have been using hubble to look at the middle of galaxies and have discovered Supermassive Black Holes [thehubbletelescope.com] there. In fact, they've found a bunch of 'em, and there's a relationship between the size of the galaxy and the size of the singularity, and every galaxy seems to have one, even our own! And IIRC they figured this would account for the missing stuff.
Well, as far as I understand, that's some missing mass, but not nearly enough. More importantly, it's not the right distribution to explain the velocity curves.
I did some googling (you can do some more if you like) and found this page. I'm sure theres better ones out there but it appears to be pretty accurate. This is not simply a problem of having enough mass in the galaxy, but having enough mass in the right places... The velocity curves of stars in different galaxies of the same mass provided that the mass is distributed differently. The curves we get are rather consistant with a spherical halo of dark matter (yes there's other theories but this is simple to imagine) which acts much different than a point mass at the center of the galaxy. This can be seen by the fact that anything inside a spherical shell of matter feels no net gravitational pull. for instance, if the earth was a perfect hollow sphere, on top of it you'd feel plenty of force, but go inside of it, and the forces from all directions cancel out. Same with a spherical halo of dark matter, stars only "feel" a force from the dark matter in the part of the halo that has a radius smaller than their orbital radius, the rest cancels itself out. This makes a significant difference in the measured velocity curves, and these curves do not point to dark matter simply being a point source in the center of the galaxy.
So I don't really think that discovery is that relevant to this discussion. Cool? Yes. But doesn't come close to explaining the mystery that is dark matter. (Yes, I'm aware of various modifications to gravity theory that could also explain this as well)
Cheers,
Justin
Disclaimer: I am not a physicist yet (still one more year to go before my degree). I do however have published research in astrophysics, as I do research with two respected astrophysicists here at Cornell University. If I've made a mistake anywhere in my reasoning here, someone please correct me:)
Hmm, interesting question. Let's look at it point by point...
I recall an earlier article [slashdot.org] about the universe being topologically equivolent to a torus.
Firstly, the experiment didn't prove anything by a long shot, it merely suggested that the universe may be topologically equivilent to a torus or cylander. But let's assume it is for a moment.
Consider any two stars of mass m and M. With distance r between them:
The Gravitational force of attraction is G*M*m/r^2.
Nice to see someone remembers their introductory physics:) Unfortunately that's a classical approximation to gravity's actual effect, and we don't have any proof that it works like that on the kinds of scales we are talking about (see another post in this thread about Modified Newtonian Dynamics). But even assuming this is true, there's still a few problems.
Then you could wrap around again and again and again....
Of course, generally the distance would be too huge to make difference, but when you consider how many stars there are and the infinite number of loops around the torus you could make, it would add up eventually.
Well, kinda. There's two flaws with this. Lets look at the first one, mainly the inverse r^2 dependence and wrapping. Basically the magnitude of the gravitational effect from any given object A with mas m on an object B with mas M will be:
Sum n=1->infinity of G*m*M*(-1^(n+1))/(r+n*W)^2 where W is the width of the universe. The oscillating negative 1 term reflects the fact that the object Ahas "mirror images" on BOTH sides of object B (think about pacman, if you go far enough to the left, you'll eventually reach something to your right). This series converges VERY quickly (it's 1/(n^2) not 1/n so it converges, plus it's oscillating so additional terms pretty much cancel out). Because the width of the universe W is very large, and the series oscilates, the first term (classical term for an open universe with no wraparound) completely dominates. This would be true if the only two things in the universe was a large black hole the mass of the universe, and your object B... essentially closed or open makes almost no difference on the amount of attraction you feel unless you are at a distance from the object on the order of magnitude of W. (yes I know general relativity affects things like black holes but the length scales here pretty much nullify any need to take that into account)
So already this doesn't really make much of a difference, but there's still another reason! The universe is roughly isotropic as far as we can tell from long distances away... That is, the amount of mass to one side of you in the universe is pretty much the same as the other side. This means that mass that's far away from you has little effect, because all the force vectors from all the other galaxies pretty much add up to zero (they cancel each other out). So even if this wraparound effect really did add up to a lot, it's coming from EVERYWHERE and would cancel itself out!
But wait I'm not done yet, there's yet another reason! Even assuming that the visible mass of the universe created a net force on stars in some direction because of this wraparound effect, it makes no difference to intragalactic dynamics! The length scale here is the width of the universe, so this force would not vary significantly along the width of a galaxy, and would pretty much be a uniform acceleration. This uniform acceleration does not affect the relative motions of the stars WITHIN the galaxy (intragalactic dynamics). So even if everything you speculated was completely true, it'd still never make a difference. We're looking for a source of gravity pulling things TOWARDS the center of the galaxy, not away from it or in some arbitrary direction. As far as we can tell, the only force that can do this is gravity from some hidden source within the galaxy (unless you make modifications to the fundamental theory of gravity on these
Me: There are of course downsides to this technique (what if the spacecraft drifts off the beam)
Reply:
If the spacecraft tilts, or drifts to the side, the light from the laser, hitting the underside, gets reflected in a slightly different place. In fact, the simple geometry of the craft's underbelly guarantees that the focal point shifts just enough, in the same direction as the drift, that the next energy burst will nudge the spacecraft back onto the beam. So it's sort of self-correcting.
Of course they would build a system that was dynamically stable (they would be incredibly foolish not to) but do not be fooled, any dynamically stable system has its limits! Hitting a pocket of turbulence or something may disrupt the path of the spacecraft enough that even the corrective abilities of the underbelly are not enough. Of course active tracking from the ground can help this, but a significantly large bump can still possibly put the spacecraft into a state where it is unlikely it will recover.
I've used "optical tweezers" here at Cornell that use a similar self-correcting effect to trap small particles in a laser beam (a cell for instance) and you can shake around the solution quite a bit without dislodging it, but sure enough, move things a little too fast and poof, you reach the limit. Due to constraints of geometry, in the microwave system, the corrective force is only a small fraction of the overall propulsive force, and even a small intermittent problem with the flight control surfaces could take the craft off the beam.
Just because something's "self correcting" doesn't mean it won't break.
Cheers,
Justin
Warning: I am not a physicist yet, I'll have my degree in a year:)
Correct me if i'm wrong, but doesn't using microwave radiation to heat the air consume a lot of energy than burning solid fuel?
Yes, I would imagine it does.
If so, wheres the applicable purpose?
Unfortunately when building a rocket to go into space, most of the fuel is spent CARRYING FUEL UP. That's just plain uneconomical. So when one is only lifting the actual payload (and perhaps some small reflector or whatever) there's a *HUGE* energy savings.
There's also the issue of reliability/stress. Things which are being thrown into orbit at high velocities have to be engineered very well to survive the trip. Mass must be shaved, redundancies might be cut to lower costs, etc. Building things on the ground is much easier in these respects... redundancy is much less limited, much less stress is on teh equipment, it's much easier to diagnose repair (because it doesn't have to be all micro-sized, etc). Also miniturizing things can considerably inflate their cost. So keeping as much of the equipment on the ground as you can is a good idea.
There's also safety issues... Most rockets use very dangerous explosive fuels, some of which are environmentally unfriendly. As long as a poor bird doesn't stray into the beam, this should be able as environmentally friendly as possible.
One last answer is that it allows most of the launch system to be reused between launches... Disposable rockets can't do this, and the Space Shuttle doesn't even re-use that much of it's mass... just some of the more complicated bits.
There are of course downsides to this technique (what if the spacecraft drifts off the beam, or the beam is obscured, etc) however I believe that they will eventually be overweighed by the enormous benefits.
It's a good question and not all the answers are obvious. I can't wait for the day where most of the work launching stuff into space is done from the ground.
Cheers,
Justin
Warning: I am not a physicist yet, but I almost have my degree. I also work at the Jet Propulsion Lab:-)
This should not be in the "Science" heading it's just creationist political opinion.
It's the opinion of a well-known scientist, who isn't particularly kind to the Creationist argument either (he calls it unsatisfying and unscientific in the article, if you would notice).
Man do you know anything about this guy? Check out his home page: http://aca.mq.edu.au/pdavies.html. He is a professor of Natural Philosophy. You don't seem to be familiar with this term, however it's the simply the old name for what we now call Science. It does not in any way make him a "philosophy professor". This guy has done much work (and written books about) cosmology, gravitation, and quantum field theory. He's published 25 books and over 150 papers to places like Nature and The Journal of Physics. Pretty hard core. Don't be so quick to dismiss someone because you don't understand their title.
Also, as a previous post pointed out, he hinted at a basic problem with multiverse theories: many are unfalsifiable. Unfalsifiable theorys cannot be tested, and are thus scientific. So yes, maybe some fantastic equations someone gets imply there may be other universes out there, however if they are completely separate from ours, then we cannot test whether or not they exist. It's like asking if God exists or not, no experiment can disprove his existence (or indeed prove it), and thus it's not science!
This article was his scientific opinions of a theory which deals with cosmology, which is one of his primary areas of study. Maybe you don't agree with what he has to say, but it is clear cosmology is something he knows at least a little about!
Well, in a few of my classes we have discussed electron microscopes, and while I'm certainly no expert, how they work isn't exactly voodoo.
Isn't it true that an electron microscope is not really seeing the sample? Rather, it is observing the density of states, which is then 'translated' into an image on a monitor.
"See" is a very interesting word, and I assume you mean recieving information in the visible light regime. According to that definition, no, it does not "see". It's actually a bit more like a sense of touch, as electrons are knocked off of the surface and we can take that scattering information and infer a surface topology (amoung other things) from that information. Atomic Force Microscopes are even more like a sense of touch in this way. This kind of science isn't really interested in generating "wow-golly" pictures of things, it's aimed at creating models which allow us to visualize and study the structure of small things.
BUT it doesn't seem that it will provide the same kind of image, just as an AFM doesn't do what an SEM does, which is different from a TEM.
This is what I said in my original post... It's just a tool for gathering scientific information. Spectral data is very rich and very useful, so it's not "just another" microscope, this is a big deal. Time will tell what we learn from this.
Firstly, glad to see you actually read the article. IANAP yet, but I'm close to my degree, so let me attempt to answer your questions.
First of all, they call it an optical microscope. But I couldn't find any optics. Besides, an electron microscope does have optics. So if they want to call it something, shouldn't it be a light microscope?
Blockquoth the dictionary definition (abridged):
optical - adjective:
of, relating to, or utilizing light especially instead of other forms of energy (ex. optical microscopy)
That was just one of the many definitions of "optical". Optical is one of those scientific words that can mean so many things. I took a class on Optics here at Cornell, and we almost never mentioned mirrors or lenses, it was about the fundamental nature of waves as described by the linear wave equation. A "light" microscope wouldn't really be a good technical term, as it doesn'ty even say what range the "light" is, whereas "optical" implies visible light (see the rest of the definition).
On to your second question:
Secondly, the whole context of the article was that this would let you 'see' as in with light, what something would look like. Reading the article, we find out that the photons are emitted from the sample in some way that might not at all correspond with what the thing might 'look' like.
I'm not sure where you are getting the idea that the article (or anyone else) claims that this allows us to see exactly what these structures "look" like. It very specifically states that it they are looking for specific types of information found in light, as opposed to electron scattering, etc. Quote:
With this technique we have a detailed spectrum for every point on a surface. This is very early on in the article, and the entire article uses the word "see" in quotes, hinting that we're not really seeing anything at that scale.
I'm not really sure what things would look like at that scale, but I doubt that has any revelevance to anything but aestetic curiousity. There's an awful lot of scattering which goes on at those length scales, as the objects are near the size of the light waves themselves. The human eye is a far-field optical instrument, and therefore would never see anything but a blur even with our best possible far-field optical microscopes. That's the entire point of this technology, stuff doesn't "look" like anything meaningful on that scale to our perception, however we can extract spectral and spatial data on the features from their Ramen scattering, etc.
On the other hand, our sense of vision is supposed to give us spectral and spatial information on objects we are observing, so in that sense things "look" exactly like what this microscope "sees". It's an interesting question, and it's really quite a matter of definition.
That's not possible, by information theory. In order to simulate a chaotic system, one needs perfect information (butterfly effect). Any system large enough to store info on the entire universe must have all the matter in the universe.
Another point I forgot to add last post is that you do *NOT* in any way need all the matter in the universe to store all the information in the universe. The amount of information in the universe is equal to its entropy, and until the heat death of the universe (if that is indeed what will happen) the amount of entropy in the universe is less than it could be. That means a "smaller" universe containing less mass/energy could have the same entropy and thus encode the same amount of information as is in our current universe. This is why lossless data compression works.
Another thing to consider is that if you subscribe to the copenhagen interpretation of physics, quantum information about a particle doesn't exist until it's measured, a sort of "lazy evaluation" in the way the universe works. Provided the number of observers capable of causing this collapse of the wave function was small, one could simulate the universe with far less information than actually exists.
Also, it's possible to store many many pieces of information in the wave function of a single electron, through quantum superposition. So a device that simulated the known universe could be much smaller than the universe it is simulating.
Isn't "nearly infinite" kinda like "sort of pregnant"? IANAM, but it is my understanding that the very largest number short of infinity is not significantly closer to infinity than 1.
It is true in an absolute sense, however you should know that there is a difference between how one quantifies an extremely small number of things and an extremely large number of things. A statistical description of 2 or 3 discrete objects is nearly meaningless, however if one has, say 10^100 somethings (such as discrete future universe states) then it makes sense to talk in terms of statistics (50% of the future universes have Bob being alive, rather than dead). I said nearly infinite because I was suggesting that the number was finite, but very large, large enough that for most forms of analysis, the discrete possibilities could be treated as a continuum.
I suppose that terms like "nearly infinite" are simply a matter of perspective and perhaps not as mathematically precise as I should have been. It was, however, 2:35 in the morning so I was very tired.
Cheers,
Justin
Oh, and by the way, there is no "very largest number short of infinity". Infinity is a tricky thing, there are different kinds of infinity. Given any real number x, you can apply an operator O which adds an arbitrary positive constant to x to get a new, necessarily larger number x'. Thus, if you tell me you have found this "largest number" I can apply this operator and get an even larger number, thus invalidating the idea that x was the largest number.
Slashdot Mirror
without even reading the friendly article, I can already accurately predict (based on my education, which is mostly from slashdot):
Sounds like a blast to me.
Oh, wait, forgot... we can argue about BSD dying unto eternity as well (and perhaps Apple too).
Cheers,
Justin
they can also predict the slashdot effect then?
;)
I can already do that. It's called The Mysterious Future. Perhaps you don't subscribe?
Can I please mod this to "+6 Informative"??
;)
/.ers have had a course in quantum physics (seems to be many more computer geeks than physics geeks here, unlike somewhere like bottomquark).
Ha ha ha... thanks but I've already got enough karma
I wonder though how informative the most really is... that is, how many of the people who read the post were actually informed. ANyone out there not understand what I said, can you tell me what didn't make sense to you?
I don't think most
Cheers,
Justin
Antiparallel... well when we think of "parallel lines", they are just lines with the same slope. But what about vectors? I mean, if they point the same direction, they are obviously parallel. But what if they point in exactly opposite directions? Clearly the lines they lay on are parallel, but they are not! That would be what "antiparallel" means. Perpendicular is about half as far away from parallel as you can get. Antiparallel is the exact opposite (as the name implies.)
FYI anisotropic means "having the property of not being the same in all directions". For instance a perfect radiating antenna would be called an "isotropic radiator". An imperfect one would be an "anisotropic radiator". Cool, eh?
BTW if jargon ever gets you down, try Google Glossary.
Cheers,
Justin Wick
SAP Developer
NASA Jet Propulsion Laboratory
Yeah sorry about that... One of the issues with science is that the precise terminology often obfuscates communication with nonexperts... Not a lot that can be done about it except the creation of (usually cheezy) analogies. As I've been very b usy with my job lately I didn't have time to really formulate the post in the best possible way.
I'm glad it made sense once you dug into it... that's what's truely important. Writing scientific explainations for a broad audience is extremely difficult and I have much admiration for those who do it successfully.
Glad you enjoyed the post.
Cheers,
Justin
BTW, if you get down to it... I avoided a lot of the jargon I could have used... Anisotropic, nth order preturbations, recoilless spontaneous emission, etc... I'm sure I could have worked a few other things in there too if I really wanted to kill some of your neurons.
Ah, sorry I forgot to mention in my plug that the newest version of SAP that can be downloaded is called "WITS for FIDO"... Don't let the acronyms fool you, it's essentially an older version of the same program, a flavor designed for "field tests" (simulated mars missions conducted out in remote locations on earth).
l /releases.
The direct link (in case you have trouble finding it) is: http://wits.jpl.nasa.gov:8080/WITS/fido/index_htm
The site is a little odd at first but once you get used to it, it's pretty darn cool. Tell me what you guys think.
During the mission a much updated public version will be released, which should be much cooler. I haven't checked the permissions on downloading the fido version yet though, so I hope it works out for you.
Cheers,
Justin
Note: I work on the Mars Exploration Rovers mission, developing Ground Data Systems software used by the scientists. I'm also completing a degree in Physics.
I'm not sure exactly how they plan to fix the spectrometer but I'm sure they're not lying when they say it's an option. Remember the Galileo space probe was recently fixed from hundreds of millions of miles away. Since a Mossbauer spectrometer uses a moving radioactive source to take a spectrum I would guess it might be put through it's paces several times to try to work out a glitch(speculation).
It's really quite amazing what can be fixed remotely, or at least worked around... If there's a significant mechanical problem with the instrument, however, there's not that much that can be done. From what I've heard, the Mossbauer on Spirit isn't currently getting data at full resolution, but they may be able to compensate for that by reprogramming the instrument remotely.
In case you don't already know, the Mossbauer spectrometer is a rediculously cool instrument. The way it works is the following:
According to elementary quantum physics, the energy levels of the nucleus are preturbed by the presence of nearby magnetic fields. Because electrons are charged fermions (and thus have nonzero spin), they have a dipolar magnetic field which can interact with the nucleus via hyperfine splitting. Hyperfine splitting is the creation of two or more distinct energy states from a single energy state via spin coupling. As an example, imagine a bar magnet which is held at the top of a one-foot drop. It has a very specific potential energy (in quantum physics energy is quantized and thus exists only in discrete amounts). Now, imagine that a uniform magnetic field is turned on in the lab room, pointing along the Z-axis (up/down). The bar magnet, if allowed to rotate, will want to minimize its energy by aligning itself antiparallel to the magnetic field (remember, opposites attract). To twist it into the "parallel" orientation, energy must be exerted, thus the single energy level of the bar magnet is now two distinct energies (in the quantum case, the difference between energy levels caused by hyperfine splitting is very small, hence the term "hyperfine"). This is a rough analogy to what's going on in the nucleus. Still with me? Good!
Now, what does this have to do with the spectrometer? Well one of the most important pieces of information we can gather about rocks on Mars is their chemical composition. Most people are aware that Mars' rusty color is due to the high concentration of iron oxides on the surface. From high school chemistry we can remember that metals have multiple valence numbers they can use to bond with other atoms... It turns out that the electron configuration of the different bonds causes the electric and magnetic field from the electrons to vary significantly.... And if the magnetic field is varied, so is the hyperfine splitting! So... the nucleus itself is slightly affected by the valence shell geometry, among other things.
So, how do we detect these differences in hyperfine splitting? That's where the Mossbauer spectrometer comes into play. The spectrometer contains two pieces of raioactive cobalt-57 (each about the size of a pencil eraser) as sources of gamma-radiation quanta. The cobalt-57 decays into an isotope of Iron with an excited nucleus. The excited nucleus quickly decays, emitting the exact gamma-quanta required to excite another iron nucleus. This gamma radiation exits the instrument and strikes a rock. Inside the rock iron nuclei absorb and re-emit the gamma radiation to be detected by the spectrometer.
The variations in the energy levels in the iron in different chemical forms are just large enough that the addition of a dopplar shift to the radiation source allows us to detect it reliably. The radiation source slides towards and away from the target at specifically varying speeds, and because the gamma rays energy levels are changed slightly by the dopplar
Well if you intended it to be a joke, I agree it's pretty funny.
;)
;)
Once again, a case of moderators on crack.
But the same mods modded me up... hmmm... maybe I ought not insult them?
As for your code suggestion, there's no objects, there's no assertions, and most importantly no over-engineering! There's no way NASA will use it like that!
Well the software I write (as mentioned in my previous comment) runs on ground computers, and is used by the scientists. We don't need a simulator for it, because we have the actual computers here we can test on.
But yes, the flight software is tested on simulators. My officemate wrote the motor simulations for MER for testing the flight software... He says their testing methods are almost paranoid in their coverage of possible issues... In fact, they are still testing madly right now in case they find a problem, it might be able to be worked around.
Simulations are only so good. There's no way the simulations can take every little detail into account, at least with the computers we have today. It's truely amazing how many different ways hardware can fail. And don't forget cosmic rays cause random bitflips now and then...
Yes testing can uncover a lot of issues but certainly not everything.
Good question though.
Dislaimer: I write software for Mars missions, including the 2007 Pheonix mission.
I hope they haven't recycled the imperial to numeric conversion code.
I must say I'm really tired of hearing about this every time there's an article about a mars misson. I mean, no one says "I hope they haven't recycled those overflow errors" every time an Ariane 5 rocket is lauched! Was it a stupid problem? Yes, however people seem to forget how rediculously hard it is to successfully launch a mission like this. Yes it's very easy to prevent a single mistake, but thousands of potential mistakes? Our track record with Mars probes is twice as good as the nearest competitor (Russia) and it's looking to continue that way.
Somebody want to contribute an open source alternative to them?
Look. The people working at NASA know how to write this stuff. That's not the problem. The problem is that on large scale projects like this, it's entirely possible for things like this to be overlooked... People tend to worry about the "hard" stuff rather than the easy stuff. And as for why they even have to convert units, as far as I understand NASA generally uses metric, it is the american aerospace companies that generally insist on using imperial units.
Also, Open Source is *NOT* the catch-all answer for everything! The development team I'm on uses linux for our development, and our software will be running on a lot of linux (and windows) boxes during the mission. We love open source, and even use some open libraries (such as castor) in our code as allowed (we are not allowed to link to GPL code of course).
However, I would cringe if the flight software was some open source deal... I mean, looking at the linux kernel sources, (some say it is the gem of open source) I wouldn't want to have to depend on anything written like *THAT* to handle flying in space. Great for on the ground where we can fix/replace/patch if there's a problem but... It's not cleanly designed and implemented like, say, QNX, etc. Few people alive have experience writing software for spaceflight systems, and I expect they they know just a little bit more about it than even the best of linux hackers do.
I guess I just don't understand why the parent post was modded insightful. Nothing personal, in7ane, but really!
There should be a variant of the GPL that prohibits all military use.
Perhaps there should also be a variant of the GPL that prohibits any use of said software by aliens during earth invasions. It would be similarly trivial to enforce.
People are better than robots at exploring a planet.
I'm not sure how valid of a claim that is. Certainly, right now our probes aren't that great, mainly because there is little actual autonomy. However, in the near future, probes will be built to handle major decisionmaking on their own. Our best hope for exploring the most of Mars is to send thousands of small autonomous probes that will do the looking around for us. This could be done for roughly the same cost as the manned mission, without the PR risk (yes, I hate it but it's very true) that manned missions currently represent.
I work at the Jet Propulsion Lab, and many of the robotics technologies that are currently being persued there should give us the capability to collect huge amounts of useful data on Mars in the next 20 years or so.
Is manned flight expensive? Well not really, but the price/performance ratio isn't that great compared to what will be done in the next 20 years with robotics probles (remember economy of scale, 1000 probes isn't much more expensive to build than 1).
Actually I worked with Thomas Gold as a computer technician a year or so ago... We had many discussions of his theory. He did not forget about conservation of momentum, in fact, when I told him his theory violated it, he said, and I quote PRECISELY: "It is a silly law anyway." Needless to say, it was quite difficult to not laugh at that one.
Also he tries to use arguments tied to radiometers, despite the fact that russian experiments with better vaccuums show that the reflection happens correctly. The other physicists at Cornell that I have talked to think that Thomas Gold is dead wrong on this one, for several reasons (some of them empirical).
I love the idea of a solar sail, so here's hoping he's wrong!
I'm a student who happens to work for the head of the mission Steve Squyres (he's the Principle Investigator).
:)
I've heard much about the politics etc that allowed this particular mission to be chosen, and it's quite an amazing story. One of the big deals about this mission is that it's a SCIENCE mission. Unlike pathfinder, whose mission was to test mars lander/rover tech, this mission is all about accomplishing as much science as possible. The mission was designed basically by looking at the pathfinder delivery system and figuring out how much rover they could cram into it.
I have much faith in the mission because the pathfinder system works, and it works well. There may be issues with the heaver weight etc, however I don't think we're going to see something like the polar lander happen to these guys.
I hope at least
The panoramic camera does indeed have stereo vision. I happen to be a student helping with the development of Science Activity Planner which is the primary program used by the scientists to analyse data and plan mission sequences (final analysis of data is done by other tools, but for tactical planning SAP is used).
Anyways, there is a public version planned which includes the ability to not only make 3-D images using your graphics accellerator, but also to take two 2D images taken by the pair of pancams and color them so that 3D glasses (red/blue) reveal the terrain. It's actually a very cool feature (I've tried it out while at JPL) and should hopefully be easy to use on the public version.
Not quite as good as a View-Master, but close enough.
That said, the public version of SAP should also let you create your own "missions" using the same tools the scientists do. The data distribution will be immense, however, and we are considering using bittorrent. We need a bittorrent client that Joe User can install easily however.
Any suggestions?
I for one will welcome our new insect overlords.
/.
This has got to be the only place where that comment could be modded "insightful!"
Gotta love ol'
can't believe no one brought this up yet. Recently some astronomers have been using hubble to look at the middle of galaxies and have discovered Supermassive Black Holes [thehubbletelescope.com] there. In fact, they've found a bunch of 'em, and there's a relationship between the size of the galaxy and the size of the singularity, and every galaxy seems to have one, even our own! And IIRC they figured this would account for the missing stuff.
:)
Well, as far as I understand, that's some missing mass, but not nearly enough. More importantly, it's not the right distribution to explain the velocity curves. I did some googling (you can do some more if you like) and found this page. I'm sure theres better ones out there but it appears to be pretty accurate. This is not simply a problem of having enough mass in the galaxy, but having enough mass in the right places... The velocity curves of stars in different galaxies of the same mass provided that the mass is distributed differently. The curves we get are rather consistant with a spherical halo of dark matter (yes there's other theories but this is simple to imagine) which acts much different than a point mass at the center of the galaxy. This can be seen by the fact that anything inside a spherical shell of matter feels no net gravitational pull. for instance, if the earth was a perfect hollow sphere, on top of it you'd feel plenty of force, but go inside of it, and the forces from all directions cancel out. Same with a spherical halo of dark matter, stars only "feel" a force from the dark matter in the part of the halo that has a radius smaller than their orbital radius, the rest cancels itself out. This makes a significant difference in the measured velocity curves, and these curves do not point to dark matter simply being a point source in the center of the galaxy.
So I don't really think that discovery is that relevant to this discussion. Cool? Yes. But doesn't come close to explaining the mystery that is dark matter. (Yes, I'm aware of various modifications to gravity theory that could also explain this as well)
Cheers,
Justin
Disclaimer: I am not a physicist yet (still one more year to go before my degree). I do however have published research in astrophysics, as I do research with two respected astrophysicists here at Cornell University. If I've made a mistake anywhere in my reasoning here, someone please correct me
Hmm, interesting question. Let's look at it point by point...
:) Unfortunately that's a classical approximation to gravity's actual effect, and we don't have any proof that it works like that on the kinds of scales we are talking about (see another post in this thread about Modified Newtonian Dynamics). But even assuming this is true, there's still a few problems.
I recall an earlier article [slashdot.org] about the universe being topologically equivolent to a torus.
Firstly, the experiment didn't prove anything by a long shot, it merely suggested that the universe may be topologically equivilent to a torus or cylander. But let's assume it is for a moment.
Consider any two stars of mass m and M. With distance r between them: The Gravitational force of attraction is G*M*m/r^2.
Nice to see someone remembers their introductory physics
Then you could wrap around again and again and again.... Of course, generally the distance would be too huge to make difference, but when you consider how many stars there are and the infinite number of loops around the torus you could make, it would add up eventually.
Well, kinda. There's two flaws with this. Lets look at the first one, mainly the inverse r^2 dependence and wrapping. Basically the magnitude of the gravitational effect from any given object A with mas m on an object B with mas M will be:
Sum n=1->infinity of G*m*M*(-1^(n+1))/(r+n*W)^2
where W is the width of the universe. The oscillating negative 1 term reflects the fact that the object Ahas "mirror images" on BOTH sides of object B (think about pacman, if you go far enough to the left, you'll eventually reach something to your right). This series converges VERY quickly (it's 1/(n^2) not 1/n so it converges, plus it's oscillating so additional terms pretty much cancel out). Because the width of the universe W is very large, and the series oscilates, the first term (classical term for an open universe with no wraparound) completely dominates. This would be true if the only two things in the universe was a large black hole the mass of the universe, and your object B... essentially closed or open makes almost no difference on the amount of attraction you feel unless you are at a distance from the object on the order of magnitude of W. (yes I know general relativity affects things like black holes but the length scales here pretty much nullify any need to take that into account)
So already this doesn't really make much of a difference, but there's still another reason! The universe is roughly isotropic as far as we can tell from long distances away... That is, the amount of mass to one side of you in the universe is pretty much the same as the other side. This means that mass that's far away from you has little effect, because all the force vectors from all the other galaxies pretty much add up to zero (they cancel each other out). So even if this wraparound effect really did add up to a lot, it's coming from EVERYWHERE and would cancel itself out!
But wait I'm not done yet, there's yet another reason! Even assuming that the visible mass of the universe created a net force on stars in some direction because of this wraparound effect, it makes no difference to intragalactic dynamics! The length scale here is the width of the universe, so this force would not vary significantly along the width of a galaxy, and would pretty much be a uniform acceleration. This uniform acceleration does not affect the relative motions of the stars WITHIN the galaxy (intragalactic dynamics). So even if everything you speculated was completely true, it'd still never make a difference. We're looking for a source of gravity pulling things TOWARDS the center of the galaxy, not away from it or in some arbitrary direction. As far as we can tell, the only force that can do this is gravity from some hidden source within the galaxy (unless you make modifications to the fundamental theory of gravity on these
Me: There are of course downsides to this technique (what if the spacecraft drifts off the beam)
:)
Reply: If the spacecraft tilts, or drifts to the side, the light from the laser, hitting the underside, gets reflected in a slightly different place. In fact, the simple geometry of the craft's underbelly guarantees that the focal point shifts just enough, in the same direction as the drift, that the next energy burst will nudge the spacecraft back onto the beam. So it's sort of self-correcting.
Of course they would build a system that was dynamically stable (they would be incredibly foolish not to) but do not be fooled, any dynamically stable system has its limits! Hitting a pocket of turbulence or something may disrupt the path of the spacecraft enough that even the corrective abilities of the underbelly are not enough. Of course active tracking from the ground can help this, but a significantly large bump can still possibly put the spacecraft into a state where it is unlikely it will recover.
I've used "optical tweezers" here at Cornell that use a similar self-correcting effect to trap small particles in a laser beam (a cell for instance) and you can shake around the solution quite a bit without dislodging it, but sure enough, move things a little too fast and poof, you reach the limit. Due to constraints of geometry, in the microwave system, the corrective force is only a small fraction of the overall propulsive force, and even a small intermittent problem with the flight control surfaces could take the craft off the beam.
Just because something's "self correcting" doesn't mean it won't break.
Cheers,
Justin
Warning: I am not a physicist yet, I'll have my degree in a year
Correct me if i'm wrong, but doesn't using microwave radiation to heat the air consume a lot of energy than burning solid fuel?
:-)
Yes, I would imagine it does.
If so, wheres the applicable purpose?
Unfortunately when building a rocket to go into space, most of the fuel is spent CARRYING FUEL UP. That's just plain uneconomical. So when one is only lifting the actual payload (and perhaps some small reflector or whatever) there's a *HUGE* energy savings.
There's also the issue of reliability/stress. Things which are being thrown into orbit at high velocities have to be engineered very well to survive the trip. Mass must be shaved, redundancies might be cut to lower costs, etc. Building things on the ground is much easier in these respects... redundancy is much less limited, much less stress is on teh equipment, it's much easier to diagnose repair (because it doesn't have to be all micro-sized, etc). Also miniturizing things can considerably inflate their cost. So keeping as much of the equipment on the ground as you can is a good idea.
There's also safety issues... Most rockets use very dangerous explosive fuels, some of which are environmentally unfriendly. As long as a poor bird doesn't stray into the beam, this should be able as environmentally friendly as possible.
One last answer is that it allows most of the launch system to be reused between launches... Disposable rockets can't do this, and the Space Shuttle doesn't even re-use that much of it's mass... just some of the more complicated bits.
There are of course downsides to this technique (what if the spacecraft drifts off the beam, or the beam is obscured, etc) however I believe that they will eventually be overweighed by the enormous benefits.
It's a good question and not all the answers are obvious. I can't wait for the day where most of the work launching stuff into space is done from the ground.
Cheers,
Justin
Warning: I am not a physicist yet, but I almost have my degree. I also work at the Jet Propulsion Lab
This should not be in the "Science" heading it's just creationist political opinion.
It's the opinion of a well-known scientist, who isn't particularly kind to the Creationist argument either (he calls it unsatisfying and unscientific in the article, if you would notice).
Man do you know anything about this guy? Check out his home page: http://aca.mq.edu.au/pdavies.html. He is a professor of Natural Philosophy. You don't seem to be familiar with this term, however it's the simply the old name for what we now call Science. It does not in any way make him a "philosophy professor". This guy has done much work (and written books about) cosmology, gravitation, and quantum field theory. He's published 25 books and over 150 papers to places like Nature and The Journal of Physics. Pretty hard core. Don't be so quick to dismiss someone because you don't understand their title.
Also, as a previous post pointed out, he hinted at a basic problem with multiverse theories: many are unfalsifiable. Unfalsifiable theorys cannot be tested, and are thus scientific. So yes, maybe some fantastic equations someone gets imply there may be other universes out there, however if they are completely separate from ours, then we cannot test whether or not they exist. It's like asking if God exists or not, no experiment can disprove his existence (or indeed prove it), and thus it's not science!
This article was his scientific opinions of a theory which deals with cosmology, which is one of his primary areas of study. Maybe you don't agree with what he has to say, but it is clear cosmology is something he knows at least a little about!
Well, in a few of my classes we have discussed electron microscopes, and while I'm certainly no expert, how they work isn't exactly voodoo.
Isn't it true that an electron microscope is not really seeing the sample? Rather, it is observing the density of states, which is then 'translated' into an image on a monitor. "See" is a very interesting word, and I assume you mean recieving information in the visible light regime. According to that definition, no, it does not "see". It's actually a bit more like a sense of touch, as electrons are knocked off of the surface and we can take that scattering information and infer a surface topology (amoung other things) from that information. Atomic Force Microscopes are even more like a sense of touch in this way. This kind of science isn't really interested in generating "wow-golly" pictures of things, it's aimed at creating models which allow us to visualize and study the structure of small things.
BUT it doesn't seem that it will provide the same kind of image, just as an AFM doesn't do what an SEM does, which is different from a TEM.
This is what I said in my original post... It's just a tool for gathering scientific information. Spectral data is very rich and very useful, so it's not "just another" microscope, this is a big deal. Time will tell what we learn from this.
Cheers,
Justin
First of all, they call it an optical microscope. But I couldn't find any optics. Besides, an electron microscope does have optics. So if they want to call it something, shouldn't it be a light microscope?
Blockquoth the dictionary definition (abridged):
That was just one of the many definitions of "optical". Optical is one of those scientific words that can mean so many things. I took a class on Optics here at Cornell, and we almost never mentioned mirrors or lenses, it was about the fundamental nature of waves as described by the linear wave equation. A "light" microscope wouldn't really be a good technical term, as it doesn'ty even say what range the "light" is, whereas "optical" implies visible light (see the rest of the definition).
On to your second question:
Secondly, the whole context of the article was that this would let you 'see' as in with light, what something would look like. Reading the article, we find out that the photons are emitted from the sample in some way that might not at all correspond with what the thing might 'look' like.
I'm not sure where you are getting the idea that the article (or anyone else) claims that this allows us to see exactly what these structures "look" like. It very specifically states that it they are looking for specific types of information found in light, as opposed to electron scattering, etc. Quote: With this technique we have a detailed spectrum for every point on a surface. This is very early on in the article, and the entire article uses the word "see" in quotes, hinting that we're not really seeing anything at that scale.
I'm not really sure what things would look like at that scale, but I doubt that has any revelevance to anything but aestetic curiousity. There's an awful lot of scattering which goes on at those length scales, as the objects are near the size of the light waves themselves. The human eye is a far-field optical instrument, and therefore would never see anything but a blur even with our best possible far-field optical microscopes. That's the entire point of this technology, stuff doesn't "look" like anything meaningful on that scale to our perception, however we can extract spectral and spatial data on the features from their Ramen scattering, etc.
On the other hand, our sense of vision is supposed to give us spectral and spatial information on objects we are observing, so in that sense things "look" exactly like what this microscope "sees". It's an interesting question, and it's really quite a matter of definition.
That's not possible, by information theory. In order to simulate a chaotic system, one needs perfect information (butterfly effect). Any system large enough to store info on the entire universe must have all the matter in the universe.
Another point I forgot to add last post is that you do *NOT* in any way need all the matter in the universe to store all the information in the universe. The amount of information in the universe is equal to its entropy, and until the heat death of the universe (if that is indeed what will happen) the amount of entropy in the universe is less than it could be. That means a "smaller" universe containing less mass/energy could have the same entropy and thus encode the same amount of information as is in our current universe. This is why lossless data compression works.
Another thing to consider is that if you subscribe to the copenhagen interpretation of physics, quantum information about a particle doesn't exist until it's measured, a sort of "lazy evaluation" in the way the universe works. Provided the number of observers capable of causing this collapse of the wave function was small, one could simulate the universe with far less information than actually exists.
Also, it's possible to store many many pieces of information in the wave function of a single electron, through quantum superposition. So a device that simulated the known universe could be much smaller than the universe it is simulating.
Cheers,
Justin
Isn't "nearly infinite" kinda like "sort of pregnant"? IANAM, but it is my understanding that the very largest number short of infinity is not significantly closer to infinity than 1.
It is true in an absolute sense, however you should know that there is a difference between how one quantifies an extremely small number of things and an extremely large number of things. A statistical description of 2 or 3 discrete objects is nearly meaningless, however if one has, say 10^100 somethings (such as discrete future universe states) then it makes sense to talk in terms of statistics (50% of the future universes have Bob being alive, rather than dead). I said nearly infinite because I was suggesting that the number was finite, but very large, large enough that for most forms of analysis, the discrete possibilities could be treated as a continuum.
I suppose that terms like "nearly infinite" are simply a matter of perspective and perhaps not as mathematically precise as I should have been. It was, however, 2:35 in the morning so I was very tired.
Cheers,
Justin
Oh, and by the way, there is no "very largest number short of infinity". Infinity is a tricky thing, there are different kinds of infinity. Given any real number x, you can apply an operator O which adds an arbitrary positive constant to x to get a new, necessarily larger number x'. Thus, if you tell me you have found this "largest number" I can apply this operator and get an even larger number, thus invalidating the idea that x was the largest number.