... There seems to be a good amount of "they-are-all-out-to-get-us" sentiment in the parent's remark. Let's put some things in perspective here:
You see, courts in Europe have this strange idea that they are there to enforce the law and protect consumers. To make matters more absurd, they choose to stick to their principles even if large companies are involved. Strange, huh?;)
And now the facts: the EU will, and has done so numerous times in the past, also punish European companies if they break antitrust laws. A complete list of antitrust cases from 1964 is here. And to give a nice example: in the cases so far in 2004, all of the listed companies are European.
Why is it that left-wing people in the US are called liberals? At least here in the Netherlands, liberals are considered to be slightly to the right of the political centre.
Now, most (Western-) European political spectra are more "leftish" than the US spectrum, so actually our two definitions of "liberal" might refer to about the same ideas.
Funny though: if in the Netherlands you make an arrogant remark about the amount of taxes you have to pay (42%), of about immigrants or the like, you stand the change of being called a dirty liberal. Strange to see that the subjective meanings of "liberal" are so different in our countries.
There's a common theme in this forum of people getting all uppity about "stupid users". But users aren't stupid. They just don't have time to learn everything. And given that we have the technology to help them, why don't we?
Again, as I stated in my original comment, I understand the frustration, which is also why I said that using black boxes is ok. My point was not to say that black boxing is wrong: on the contrary, it's the best solution that technology can provide us with in most cases.
However, even when we have black boxes, it pays to actually know a bit more than the black shiny cover of that box. I'm not saying that everybody should know this, but you do have a (fair!) advantage if you do know a bit more.
The point I was trying to make is that while using black boxes is ok, and not knowing what's actually going on is ok most of the time, actually denying that the piece of equipment you're operating is complex does seem very strange to me: if you use a black box, you should at least be aware of the fact that the thing is complex (even if you don't know how it actually works).
The problem I have with this denial is, like I said, people operating the equipment purely from their simple model (that does not reflect how the equipment works), and not even knowing, or acknowledging, that the device is more complex (regardless of the fact that they don't understand the complex device, but like I said, that doesn't matter so much).
I understand your frustration, but also disagree with it. Allow me to explain.
The concept you're bringing up is black boxing: a simple (or standardized) user-interface that hides a complex system.
The pros of black-boxing are obvious: black boxing makes it possible for many people to operate complex equipment (think cars, phones, computers). There is also a psychological factor at play here: as many people seem to suffer from self-learned helplessness when dealing with technology, black-boxing (e.g. think nice-and shiny i-POD, or automatic-transmission lady-car) helps them to overcome their physological aversion and acutally use the device.
Now, as already stated by another user, the main con of black-boxing is what happens when something goes wrong: black-boxing provides a very poor way of dealing with failure-conditions!. There is also another con, which is public perception: black-boxing makes people believe that the equipment they are operating is simple, while in reality it's very complex. But because they reason from their internal "simple make-believe model', they can make mistakes that they wouldn't have made, had they known a bit more about the equipment.
To provide an example: Here in Europe, most cars are manual transmission (typically 5 forward and 1 reverse). When driving 80 kph in a flat country like holland, it really doesn't matter that much whether you drive in 3rd gear of 5th gear. However, when some Dutch people drive through Switzerland during the summer holidays (with a big trailer behind the car), they persist in driving in 5th gear up-hill, their argument being: "Hey, don't worry man, the car maintains speed uphill, so what's the problem". Of course, had they known a bit more about how an engine works, they would have switched back to 4th (or even 3rd) gears, to allow the engine to run at a higher specific torque, and to allow the cooling fluids to be pumped around more quickly to cool the engine better. Our black-boxing people usually end up overheating their engine (and blocking traffic and creating big jams in the Alps, grumble!;) You see: it pays to know at least a bit about what's under the black cover of your black box!
In the same way, your shiny XP thingy makes your computer seem a simple device. But of course, it is still a really complex device. We've all seen people do stupid things because they persisted in acting according to how they believed the computer works (their simple model), rather than basing their actions on how the computer actually works. Knowing a bit about the latter, however small, enables you to do better in times of failure, but also in general.
On a personal account: I learned C after I learning assembly. I experienced this as a big bonus, because after using asm, you know what pointers actually are and how they work. I've seen people program Java and doing stupid memory allocation things, because they had no clue about what happens when you do "new bla" or "delete bla".
To conclude: black boxing is ok, but you need to keep in mind that you are still operating a complex device!
Here in Holland, a PhD-studentship is a normal job, and not so much "student"-like, as portrayed in Piled Higher and Deeper.
First-year students make about EUR 23500,- a year, and that goes up to about EUR 28500,- in the fourth year. When viewing this numbers, do take into account that the price-level in Holland (and the EU as a whole) is lower than in the US.
E.g.: as a M.Sc., you can expect a starting salary of about EUR 25000-27500,- a year. If you're in engineering, that is.
A technique like the one you mention is very common in many measuring applications: it's called oversampling followed by lowpass filtering.
Essentially, you're trading bandwidth for accuracy: the lower you make your lowpass bandwidth, the more you "average out" the noise, and the more accurate your measurement can become. However, the downside is that your bandwidth is very small, which causes your measuring time to be very large (you'll have to wait for your lowpass filter to complete at least a reasonable portion of its step-response).
The above implies that there is a limit on low tight you can make your lowpass filter: the characteristic timescale of your lowpass filter must be larger than that of your actual phenomenon (not: noise) related signal, or else the process itself it "too fast" and the actual signal is also filtered out by your lowpass filter.
Example: if you have a small amount of atoms that you want to weight, then having a too-large measuring time to obtain a 0.1% (or whatever) accuracy on the mass doesn't make sense if on the timescale of your measurement more than 0.1% of the material evaporates.
The parent is right in that we see the explosion in our definition of now: remember, in relalivistic situations (i.e. anything happening either at speeds that are nonnegligible compared to the speed of light, or at distance scales that are large enough for propagation time to be nonneglibible on our time-scale of perception), there is no universal definition of "now": it's relative to each observer.
It poured out more energy in three hours than the sun does in 100 years
Given that the sun produces about 3.8e+26 Watt, and that a year contains about 3.15e+7 seconds, the explosion comes down to a total energy release of about 1.1e+36 Joules.
Still, this is puny compared with a gamma-ray burst: in 60 seconds, that yields about 10e+45 Joules.
I fully agree with you that there should be a Europe section on./. After all, although./ is US-centric, it's not that US-centric: about
a quarter of the readers are Europeans.
I do also agree with you that not separating the communities is a good idea: sure, we could start slashdot.eu (or slashdot.nl, since most of Europe's internet connectivity to the US seems to pass through the big relays in Amsterdam), but that would make two different communities.
OTOH, I also think that the "Europe" section should be confined to, say, yro-europe, since most other subjects are pretty international.
I can put a nice multiple-frame face-detection demo here, but that would destroy my research group's net-connection. If someone can offer a high-bandwidth spot, mail me: I'll then make a movie available.
IAACVPS (I Am A Computer Vision Ph.D. Student), and I'd like to add some general remarks concerning this application, and concerning computer vision in general.
Although the article mentions a nice application of computer vision, it is shockingly sparse in details. This in itself is not so strange for a news-site, but the fact that they didn't include a link to a more detailed description is a pity.
Some ideas:
First, the article doesn't make sufficiently clear whether one looks at the net, full of fish, or that one looks at the fish all spread out on a flat surface. If one looks at a full net, one can only see the fish on the outside, i.e., only a small fraction: that doesn't provide any information on the fish on the inside. If one looks at the fish spread out on a flat surface, one can see all the fish, but there are a number of issues here:
Orientation-variance: if a fish is lying head-down (e.g. because it is crammed a bit too tightly between other fish), it's hard to measure its size.
Occlusion: Even on a flat surface, on fish' tail might cover part of another fish' body. This makes measuring difficult.
Lighting-variance: Fish are shiny reflective critter. So some parts of the image might have very white spots in them. This makes the application of automated algorithms difficult. Make no mistake: we as humans can recognize objects almost irrespective of the intensity and color of the light, but computer vision algorithms have severe difficulties doing this!
Determination of number: How, exactly, do they count the fish, given all the difficulties listed above? So: what does that 90-something% accuracy mean?
Given the speed at which they process, it's most likely that they determine fish-size based on general statistical properties in different regions of the image. In that case, the 90-something% accuracy really doesn't mean that much, because in all honesty, I don't see how they can either measure or guarantee that. Looks like marketing optimism to me.
Now, on the general state of computer vision: If you're expecting terminator-like all-seeing computer in the near future, don't hold your breath! It might take some time:
At the moment, some object classes that don't vary too much in structure within the class (e.g., faces, cars, people), can be found reasonably quickly and moderately reliably in an image. To give an example, the detection of human faces in 800x600 images can be done in about a second, with about a 90-95% detection rate, but with about 1-10 false positive detections per image. That effectively means that if you find a face, there still is only a 30% change that it's actually a face.
In order to understand what you see, you rely on high-level semantics. These include the geometrical arrangement of objects (e.g., your head stands on top of your body, there is a hierarchy body->limbs->extremities, etc.) and general relations (e.g. finding faces at eye-level, so e.g. near the horizon). Research on these higher-level semantics is really in its infancy: the main problem is that it's very hard to get enough "world-knowledge" into the computer for it to make all the relations.
I can put a nice multiple-frame face-detection demo here, but that would destroy my research group's net-connection. If someone can offer a high-bandwidth spot, mail me: I'll then make a movie available.
Good comment. The confusion comes down to my sloppiness in notation: with "v", I meant the maximum speed that is attained at the midpoint of the trip, not v(t) (i.e. the speed as a function of time).
So, you first need to get to that speed (takes once that amount of energy), and then back to speed zero (or to Mars' orbital speed, which is very much smaller than the ~1000 km/s max-speed, so I took the liberty to neglect that residual speed in the energy calculations).
Now, in ideal conditions, the actual time-path you use to get to the max speed doesn't matter: the amount of energy required is the same.
And as a quick check for validity of Newtonian calcs, assume constant speed travel in this time over this distance, and check what velocity would be roughly. Calc with 1. v=d/t; 2. v=(1.8e11 m) / (1.355e5 s); 3. v=1.3284e6 m/s. Compared to speed of light (c=3.0e8 m/s), this is, as you said, less than 1%. Newton rules here.
True (at least in order of magnitude, I do acknowledge the difference between your result and that of your parent post).
Just to play the devil's advocate here: the problem is the amount of energy required to reach these speeds:
Let's first make an approximation here: Earth's orbital velocity is about 30 km/s, and the extra speed to reach Mars' orbit works out to something in the O.O.M. of some 10s km/s. The energy related to this orbital difference can safely be ignored when compared to the top-speed of ~1000 km/s you list.
When assuming a space-probe of around 1000 kg, the energy to reach the top speed is about E=0.5 * m * v^2 = 8.8e14 Joules. Now that is a rather large amount of energy: it's equivalent to about 20 kilotons of TNT (say, a Nagasaki bomb). Plus, you need (about) the same amount of energy to deccelerate when arriving at Mars.
I fully agree with you that it should not be necessary. However, I assume that you are from a country using a latin charset (being Dutch, I am). However, even though we as "westerners" might still be in the majority (are we still?), this might not always be like this.
For example: the number of Chinese internet users went from roughly 600 thousand to 80 million in the timespan 1997-2003. So there will be lots more. And that's only China. I can only imagine that these people want domains in their own charset (at least we have lots of domain names in Dutch here in Holland, but of course we have the advantage of using a Latin charset).
In that case, a general "block" on multilingual domains in the address bar won't work.
Although this article on the insecurities of IE (or in a more general
sense, Windows' URL handling) is fitting for./, the advice to type URL
into the address bar may be one that we should all take to heart in the
future.
As pointed out here,
the advent of multilingual (Unicode) domain names gives rise to a new
possibility for attacks: the Homograph attack.
Example: one could replace the o's in http://www.microsoft.com with Greek
omicrons, Cyrillic o's or characters from other charsets, as long as
they are rendered by our browser as something resembling an "o". The
users won't notice the difference, but they might be redirected to
another site, even though they visually inspected the URL.
A more serious example: my bank, the Dutch Rabobank, features internet banking.
It specifically displays a warning before logging in: Make sure that
the address in the address bar starts with https://www.rabobank.nl/,
then you are sure you're communicating with us.
Now, with a homograph attack, even that might not be certain again: it
looks the same, and users are reassured even though reassurance is not due! And it's not limited to using IE or Windows either.
A comment is in order here: we're not that far yet, as most clients
require special (non-default) DNS clients to access Unicode domain
names. But it might become a big problem in the future.
Are there any people from countries using non-latin domain names that
might want to comment on this?
As some of the other posters have remarked, the major problems are:
Battery chemistry: the upcoming Martian winter features both short days (less light for the panels) and low temperatures (affecting the battery's performance. In addition, the batteries start to give out after many charge cycles.
Dust on the panels: over time, dust builds op on the panels, making them less efficient. And there aren't any wiper to take to dust off.
Weather: dust and wind will gradually damage the rover.
Note that the above has already been mentioned. However, an idea that I haven't heard yet is continued limited operation: The Voyager probes lost most of their nifty features along the way (see here for some details):
First the science boom wouldn't deploy properly, then the primary radio receiver failed, leaving NASA with a backup receiver that also was a bit flakey, and along the way more things started to go awry (like to camera-platform movement started to become really limited at a certain point).
Nonetheless, the Voyagers are still used as science intruments: currently, they are taking measurements of the interplanetary magnetic field, plasma, and charged particle environment while searching for the heliopause. They function as mankind's most distant sensors in this respect.
In fact, this kind of limited operation isn't strange to NASA: many probes first serve an extended mission after the primary mission has ended, and then limited operation may continue until the probe fails altogether (e.g. ca. 2015 for the Voyagers).
So in fact, when Spirit isn't able to drive anymore, we may still use its camera and other instruments to gather as much data on the surrounding soil as possible. Still later, when available power has dwindled to such an extent that even the advanced camera's can't be used anymore, we could still use the temperature sensors. Finally, when the high gain antenna fails, the mission might be over altogether, or they might still use the low gain antenna, until, finally, Spirit reaches the end of its agony and dies a slow electronic death.
I do agree fully with the parent on that we should organize a Q&A on this. How do we set this in motion?
Really, astronomical grammer is pretty simple. Some counter-intuitive examples:
We see the moon as it is/was...
We see the sun as it is/was...
We see the center of the Milkyway galaxy as it is/was...
Mostly, you hear people give answers to these three questions as "about 1.5 second", "about 8.5 minutes" and "about 30000 years" respectively. But guess what the correct answer is:
We see all these events in our definition of NOW, or "now" from our reference frame.: what you should keep in mind is that there is no "now", there are many many "nows" from many many different reference frames.
Let me explain: when (when from our reference frame) we see sunlight, then (assuming interplanetary space is vacuum), nothing could have reached us earlier than that light. Indeed, not a single piece of information could have reached us earlier. Moreover, because no information could have reached us earlier, no event in our world could have been caused by "something earlier" from the sun, because of causality.
So really, it is of no use to talk about seeing the sun "as it was 8.5 minutes ago", since nothing in those "8.5 minutes" could possibly have affected anything here on earth.
We see the sun as it is "our-now".
And to answer your question: the collision will happen 85 million years from "our-now".
The first part of your argument (Hawking) is a commonly heard one, but I'm glad you also mention the second part.
You see, we've decided to cut short natural selection. In a way, we've created a filter for which people are going to survive. And as always when you filter, you'll have false positives and false negatives; that's inherent to filtering, selecting or detecting.
To be more exact, if we call a survivor a positive:
True positive: Someone who is fit for survival, either because of his genes or his contribution to humanity, and indeed survives because of our techniques. (i.e. most people)
True negative: Somone who was not meant to survive, and didn't even though we applied our techniques. Somebody born with oxygen allergy is a good example.
False positive: Somebody unfit for survival, who did survive anyway because of our techniques. Hawking is a good example here.
False negative: Somebody fit for survival (either because of genes or contribution to humanity), who didn't survive because of our techniques. These are more rare.
Now consider the following: given that the minority of people would be "negavites" if natural selection was to have its was (say 1%), our decision to cut short natural selection doesn't yield that many false positives, because the negative rate was small to start with. On the other hand, this only goes for one generation, because after a few generations the intrinsic negative rate will rise because of us cutting short natural selection.
To conclude: helping "unfits" to survive doesn't matter much for one generation, but does matter over many generations. I think we should not cut short natural selection, even if that means we loose a few good false positives like Hawking; it's better for humanity on the long run.
(Basically that means: we should increase the false negative rate to prevent pollution of the gene-pool by false positives)
Slashdot Mirror
...are you talking about? http://www.freenetproject.org
... There seems to be a good amount of "they-are-all-out-to-get-us" sentiment in the parent's remark. Let's put some things in perspective here:
You see, courts in Europe have this strange idea that they are there to enforce the law and protect consumers. To make matters more absurd, they choose to stick to their principles even if large companies are involved. Strange, huh? ;)
And now the facts: the EU will, and has done so numerous times in the past, also punish European companies if they break antitrust laws. A complete list of antitrust cases from 1964 is here. And to give a nice example: in the cases so far in 2004, all of the listed companies are European.
That goes to show you.
Why is it that left-wing people in the US are called liberals? At least here in the Netherlands, liberals are considered to be slightly to the right of the political centre.
Now, most (Western-) European political spectra are more "leftish" than the US spectrum, so actually our two definitions of "liberal" might refer to about the same ideas.
Funny though: if in the Netherlands you make an arrogant remark about the amount of taxes you have to pay (42%), of about immigrants or the like, you stand the change of being called a dirty liberal. Strange to see that the subjective meanings of "liberal" are so different in our countries.
A comprehensive list can also be found here.
There's a common theme in this forum of people getting all uppity about "stupid users". But users aren't stupid. They just don't have time to learn everything. And given that we have the technology to help them, why don't we?
Again, as I stated in my original comment, I understand the frustration, which is also why I said that using black boxes is ok. My point was not to say that black boxing is wrong: on the contrary, it's the best solution that technology can provide us with in most cases.
However, even when we have black boxes, it pays to actually know a bit more than the black shiny cover of that box. I'm not saying that everybody should know this, but you do have a (fair!) advantage if you do know a bit more.
The point I was trying to make is that while using black boxes is ok, and not knowing what's actually going on is ok most of the time, actually denying that the piece of equipment you're operating is complex does seem very strange to me: if you use a black box, you should at least be aware of the fact that the thing is complex (even if you don't know how it actually works).
The problem I have with this denial is, like I said, people operating the equipment purely from their simple model (that does not reflect how the equipment works), and not even knowing, or acknowledging, that the device is more complex (regardless of the fact that they don't understand the complex device, but like I said, that doesn't matter so much).
I understand your frustration, but also disagree with it. Allow me to explain.
The concept you're bringing up is black boxing: a simple (or standardized) user-interface that hides a complex system.
The pros of black-boxing are obvious: black boxing makes it possible for many people to operate complex equipment (think cars, phones, computers). There is also a psychological factor at play here: as many people seem to suffer from self-learned helplessness when dealing with technology, black-boxing (e.g. think nice-and shiny i-POD, or automatic-transmission lady-car) helps them to overcome their physological aversion and acutally use the device.
Now, as already stated by another user, the main con of black-boxing is what happens when something goes wrong: black-boxing provides a very poor way of dealing with failure-conditions!. There is also another con, which is public perception: black-boxing makes people believe that the equipment they are operating is simple, while in reality it's very complex. But because they reason from their internal "simple make-believe model', they can make mistakes that they wouldn't have made, had they known a bit more about the equipment.
To provide an example: Here in Europe, most cars are manual transmission (typically 5 forward and 1 reverse). When driving 80 kph in a flat country like holland, it really doesn't matter that much whether you drive in 3rd gear of 5th gear. However, when some Dutch people drive through Switzerland during the summer holidays (with a big trailer behind the car), they persist in driving in 5th gear up-hill, their argument being: "Hey, don't worry man, the car maintains speed uphill, so what's the problem". Of course, had they known a bit more about how an engine works, they would have switched back to 4th (or even 3rd) gears, to allow the engine to run at a higher specific torque, and to allow the cooling fluids to be pumped around more quickly to cool the engine better. Our black-boxing people usually end up overheating their engine (and blocking traffic and creating big jams in the Alps, grumble! ;) You see: it pays to know at least a bit about what's under the black cover of your black box!
In the same way, your shiny XP thingy makes your computer seem a simple device. But of course, it is still a really complex device. We've all seen people do stupid things because they persisted in acting according to how they believed the computer works (their simple model), rather than basing their actions on how the computer actually works. Knowing a bit about the latter, however small, enables you to do better in times of failure, but also in general.
On a personal account: I learned C after I learning assembly. I experienced this as a big bonus, because after using asm, you know what pointers actually are and how they work. I've seen people program Java and doing stupid memory allocation things, because they had no clue about what happens when you do "new bla" or "delete bla".
To conclude: black boxing is ok, but you need to keep in mind that you are still operating a complex device!
How's that in the US?
Here in Holland, a PhD-studentship is a normal job, and not so much "student"-like, as portrayed in Piled Higher and Deeper.
First-year students make about EUR 23500,- a year, and that goes up to about EUR 28500,- in the fourth year. When viewing this numbers, do take into account that the price-level in Holland (and the EU as a whole) is lower than in the US.
E.g.: as a M.Sc., you can expect a starting salary of about EUR 25000-27500,- a year. If you're in engineering, that is.
I wonder how the lander is going to stay on the comet once the comet gets closer to the sun and starts ejecting mass.
The lander will fire a harpoon into the comet to ensure it doesn't bounce off again.
A technique like the one you mention is very common in many measuring applications: it's called oversampling followed by lowpass filtering.
Essentially, you're trading bandwidth for accuracy: the lower you make your lowpass bandwidth, the more you "average out" the noise, and the more accurate your measurement can become. However, the downside is that your bandwidth is very small, which causes your measuring time to be very large (you'll have to wait for your lowpass filter to complete at least a reasonable portion of its step-response).
The above implies that there is a limit on low tight you can make your lowpass filter: the characteristic timescale of your lowpass filter must be larger than that of your actual phenomenon (not: noise) related signal, or else the process itself it "too fast" and the actual signal is also filtered out by your lowpass filter.
Example: if you have a small amount of atoms that you want to weight, then having a too-large measuring time to obtain a 0.1% (or whatever) accuracy on the mass doesn't make sense if on the timescale of your measurement more than 0.1% of the material evaporates.
The parent is right in that we see the explosion in our definition of now: remember, in relalivistic situations (i.e. anything happening either at speeds that are nonnegligible compared to the speed of light, or at distance scales that are large enough for propagation time to be nonneglibible on our time-scale of perception), there is no universal definition of "now": it's relative to each observer.
Please see my other comment on this.
Ah crap: that's supposed to be 1e+45 Joules...
From the article:
It poured out more energy in three hours than the sun does in 100 years
Given that the sun produces about 3.8e+26 Watt, and that a year contains about 3.15e+7 seconds, the explosion comes down to a total energy release of about 1.1e+36 Joules.
Still, this is puny compared with a gamma-ray burst: in 60 seconds, that yields about 10e+45 Joules.
Ok, see my earlier reply to this message:
Let's start the initiative then: sign this petition and add it to your sig.
I'll try to keep you posted on the progress.
I fully agree with you that there should be a Europe section on ./. After all, although ./ is US-centric, it's not that US-centric: about
a quarter of the readers are Europeans.
I do also agree with you that not separating the communities is a good idea: sure, we could start slashdot.eu (or slashdot.nl, since most of Europe's internet connectivity to the US seems to pass through the big relays in Amsterdam), but that would make two different communities.
OTOH, I also think that the "Europe" section should be confined to, say, yro-europe, since most other subjects are pretty international.
My EUR 0.02
Ok, there goes:
Face Detection .torrent.
Ok, PLEASE leave your client open: I don't want my connection killed! ;)
IAACVPS (I Am A Computer Vision Ph.D. Student), and I'd like to add some general remarks concerning this application, and concerning computer vision in general.
Although the article mentions a nice application of computer vision, it is shockingly sparse in details. This in itself is not so strange for a news-site, but the fact that they didn't include a link to a more detailed description is a pity.
Some ideas:
First, the article doesn't make sufficiently clear whether one looks at the net, full of fish, or that one looks at the fish all spread out on a flat surface. If one looks at a full net, one can only see the fish on the outside, i.e., only a small fraction: that doesn't provide any information on the fish on the inside. If one looks at the fish spread out on a flat surface, one can see all the fish, but there are a number of issues here:
Given the speed at which they process, it's most likely that they determine fish-size based on general statistical properties in different regions of the image. In that case, the 90-something% accuracy really doesn't mean that much, because in all honesty, I don't see how they can either measure or guarantee that. Looks like marketing optimism to me.
Now, on the general state of computer vision: If you're expecting terminator-like all-seeing computer in the near future, don't hold your breath! It might take some time:
At the moment, some object classes that don't vary too much in structure within the class (e.g., faces, cars, people), can be found reasonably quickly and moderately reliably in an image. To give an example, the detection of human faces in 800x600 images can be done in about a second, with about a 90-95% detection rate, but with about 1-10 false positive detections per image. That effectively means that if you find a face, there still is only a 30% change that it's actually a face.
In order to understand what you see, you rely on high-level semantics. These include the geometrical arrangement of objects (e.g., your head stands on top of your body, there is a hierarchy body->limbs->extremities, etc.) and general relations (e.g. finding faces at eye-level, so e.g. near the horizon). Research on these higher-level semantics is really in its infancy: the main problem is that it's very hard to get enough "world-knowledge" into the computer for it to make all the relations.
I can put a nice multiple-frame face-detection demo here, but that would destroy my research group's net-connection. If someone can offer a high-bandwidth spot, mail me: I'll then make a movie available.
Good comment. The confusion comes down to my sloppiness in notation: with "v", I meant the maximum speed that is attained at the midpoint of the trip, not v(t) (i.e. the speed as a function of time).
So, you first need to get to that speed (takes once that amount of energy), and then back to speed zero (or to Mars' orbital speed, which is very much smaller than the ~1000 km/s max-speed, so I took the liberty to neglect that residual speed in the energy calculations).
Now, in ideal conditions, the actual time-path you use to get to the max speed doesn't matter: the amount of energy required is the same.
And as a quick check for validity of Newtonian calcs, assume constant speed travel in this time over this distance, and check what velocity would be roughly. Calc with 1. v=d/t; 2. v=(1.8e11 m) / (1.355e5 s); 3. v=1.3284e6 m/s. Compared to speed of light (c=3.0e8 m/s), this is, as you said, less than 1%. Newton rules here.
True (at least in order of magnitude, I do acknowledge the difference between your result and that of your parent post).
Just to play the devil's advocate here: the problem is the amount of energy required to reach these speeds:
Let's first make an approximation here: Earth's orbital velocity is about 30 km/s, and the extra speed to reach Mars' orbit works out to something in the O.O.M. of some 10s km/s. The energy related to this orbital difference can safely be ignored when compared to the top-speed of ~1000 km/s you list.
When assuming a space-probe of around 1000 kg, the energy to reach the top speed is about E=0.5 * m * v^2 = 8.8e14 Joules. Now that is a rather large amount of energy: it's equivalent to about 20 kilotons of TNT (say, a Nagasaki bomb). Plus, you need (about) the same amount of energy to deccelerate when arriving at Mars.
I fully agree with you that it should not be necessary. However, I assume that you are from a country using a latin charset (being Dutch, I am). However, even though we as "westerners" might still be in the majority (are we still?), this might not always be like this.
For example: the number of Chinese internet users went from roughly 600 thousand to 80 million in the timespan 1997-2003. So there will be lots more. And that's only China. I can only imagine that these people want domains in their own charset (at least we have lots of domain names in Dutch here in Holland, but of course we have the advantage of using a Latin charset).
In that case, a general "block" on multilingual domains in the address bar won't work.
Although this article on the insecurities of IE (or in a more general sense, Windows' URL handling) is fitting for ./, the advice to type URL
into the address bar may be one that we should all take to heart in the
future.
As pointed out here, the advent of multilingual (Unicode) domain names gives rise to a new possibility for attacks: the Homograph attack.
Example: one could replace the o's in http://www.microsoft.com with Greek omicrons, Cyrillic o's or characters from other charsets, as long as they are rendered by our browser as something resembling an "o". The users won't notice the difference, but they might be redirected to another site, even though they visually inspected the URL.
A more serious example: my bank, the Dutch Rabobank, features internet banking. It specifically displays a warning before logging in: Make sure that the address in the address bar starts with https://www.rabobank.nl/, then you are sure you're communicating with us. Now, with a homograph attack, even that might not be certain again: it looks the same, and users are reassured even though reassurance is not due! And it's not limited to using IE or Windows either.
A comment is in order here: we're not that far yet, as most clients require special (non-default) DNS clients to access Unicode domain names. But it might become a big problem in the future.
Are there any people from countries using non-latin domain names that might want to comment on this?
Looking at my spam-box, I find the usual stuff:
From ukKimble@mailthat.net Tue Jan 13 00:43:36 2004
X-Habeas-SWE-1: winter into spring
X-Habeas-SWE-2: brightly anticipated
X-Habeas-SWE-3: like Habeas SWE (tm)
X-Habeas-SWE-4: Copyright 2002 Habeas (tm)
X-Habeas-SWE-5: Sender Warranted Email (SWE)
(tm). The sender of this
X-Habeas-SWE-6: email in exchange for a license for this Habeas
X-Habeas-SWE-7: warrant mark warrants that this is a Habeas Compliant
X-Habeas-SWE-8: Message (HCM) and not spam. Please report use of this
X-Habeas-SWE-9: mark in spam to .
Subject: Fwd: V|@gra, Vali(u)m, X(a)n@x. Prescribed Online and Shipped
... and finally, the real information as far as I'm concerned in in the last header:
X-Spambayes-Classification: spam; 1.00
So whether the spam is "legitimate" (is there anything like that?) or not, SpamBayes doesn't seem to have much trouble with it.
As some of the other posters have remarked, the major problems are:
- Battery chemistry: the upcoming Martian winter features both short days (less light for the panels) and low temperatures (affecting the battery's performance. In addition, the batteries start to give out after many charge cycles.
- Dust on the panels: over time, dust builds op on the panels, making them less efficient. And there aren't any wiper to take to dust off.
- Weather: dust and wind will gradually damage the rover.
Note that the above has already been mentioned. However, an idea that I haven't heard yet is continued limited operation: The Voyager probes lost most of their nifty features along the way (see here for some details):First the science boom wouldn't deploy properly, then the primary radio receiver failed, leaving NASA with a backup receiver that also was a bit flakey, and along the way more things started to go awry (like to camera-platform movement started to become really limited at a certain point).
Nonetheless, the Voyagers are still used as science intruments: currently, they are taking measurements of the interplanetary magnetic field, plasma, and charged particle environment while searching for the heliopause. They function as mankind's most distant sensors in this respect.
In fact, this kind of limited operation isn't strange to NASA: many probes first serve an extended mission after the primary mission has ended, and then limited operation may continue until the probe fails altogether (e.g. ca. 2015 for the Voyagers).
So in fact, when Spirit isn't able to drive anymore, we may still use its camera and other instruments to gather as much data on the surrounding soil as possible. Still later, when available power has dwindled to such an extent that even the advanced camera's can't be used anymore, we could still use the temperature sensors. Finally, when the high gain antenna fails, the mission might be over altogether, or they might still use the low gain antenna, until, finally, Spirit reaches the end of its agony and dies a slow electronic death.
I do agree fully with the parent on that we should organize a Q&A on this. How do we set this in motion?
Really, astronomical grammer is pretty simple. Some counter-intuitive examples:
Mostly, you hear people give answers to these three questions as "about 1.5 second", "about 8.5 minutes" and "about 30000 years" respectively. But guess what the correct answer is:
We see all these events in our definition of NOW, or "now" from our reference frame.: what you should keep in mind is that there is no "now", there are many many "nows" from many many different reference frames.
Let me explain: when (when from our reference frame) we see sunlight, then (assuming interplanetary space is vacuum), nothing could have reached us earlier than that light. Indeed, not a single piece of information could have reached us earlier. Moreover, because no information could have reached us earlier, no event in our world could have been caused by "something earlier" from the sun, because of causality.
So really, it is of no use to talk about seeing the sun "as it was 8.5 minutes ago", since nothing in those "8.5 minutes" could possibly have affected anything here on earth.
We see the sun as it is "our-now".
And to answer your question: the collision will happen 85 million years from "our-now".
The first part of your argument (Hawking) is a commonly heard one, but I'm glad you also mention the second part.
You see, we've decided to cut short natural selection. In a way, we've created a filter for which people are going to survive. And as always when you filter, you'll have false positives and false negatives; that's inherent to filtering, selecting or detecting.
To be more exact, if we call a survivor a positive:
Now consider the following: given that the minority of people would be "negavites" if natural selection was to have its was (say 1%), our decision to cut short natural selection doesn't yield that many false positives, because the negative rate was small to start with. On the other hand, this only goes for one generation, because after a few generations the intrinsic negative rate will rise because of us cutting short natural selection.
To conclude: helping "unfits" to survive doesn't matter much for one generation, but does matter over many generations. I think we should not cut short natural selection, even if that means we loose a few good false positives like Hawking; it's better for humanity on the long run.
(Basically that means: we should increase the false negative rate to prevent pollution of the gene-pool by false positives)
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