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I was suspicious too, until I followed the link from the Wired article, where the "loyal opposition" to the sensationalist brothers claim an article in The Register as one of their primary defenses. Since "mainstream" theoretical physicists feel they cannot trust their own journals anymore, they turn to such a respectible and knowledgable publication for their support.

I bet most nonphysics /. readers will find the original Bogdanov papers quite difficult to read, and perhaps the theses even more so since they are in French. But I can show here some very simple things that will make nonphysics reader very suspicious about the Bogdanov twin's work.

As some /. readers have pointed out already, John Baez, the UCI physics prof, criticizes a very specific passage from one thesis, involving the Foucault pendulum part. You don't have to read everything, just see that Bogdanov mentions the pendulum and topology in one breath! here I quote from Baez's webpage:

"It goes on to discuss the supposed connection between N = 2 supergravity, Donaldson theory, KMS states and the Foucault pendulum experiment, which he claims "cannot be explained satisfactorily in either classical or relativistic mechanics". If you know some physics you'll find this statement slightly odd.

After several pages he concludes: We draw from the above that whatever the orientation, the plane of oscillation of Foucault's pendulum is necessarily aligned with the initial singularity marking the origin of physical space S3, that of Euclidean space E4 (described by the family of instantons Ibeta of whatever radius beta), and, finally, that of Lorentzian space-time M4.

Zounds! He took that pendulum and rode it right off into hyperspace..."

And this Foucault pendulum quote you can obtain directly from one Bogdanov thesis.

The Foucault pendulum bit is on page 49/162 of the thesis, in French. It's easy to read and probably will parse in babelfish.

So what's the big hoopla about Foucault's pendulum and the supergravity stuff? Well, Foucault's pendulum, contrary to the Bogdanov thesis that it's not understood in classical mechanics, is really well understood, at least the regular ole' Foucault pendulum. It's basically a free-swinging pendulum, that over time, rotates its plane of swinging because of the Coriolis force. You can check it out in any decent undergrad mechanics text, such as my dusty copy of Marion/Thornton classical dynamics, page 399, where the solution is quietly sitting. Or you can read this little web tidbit.

That a PHD physics candidate would be trying to tell us there is some connection between the very earthly, understood Foucault pendulum, and the big bang (initial singularity) really stretches the imagination! But again, this just makes one suspicious, and doesn't prove anything.

John Baez has a good link filled article on the subject. Interestingly, the editors of Classical and Quantum Gravity have distanced themselves from the Bogdanovs' article.

For a collection of stuff on this subject, search google groups on ``reverse sokal hoax''. Then read the (long) thread in sci.physics.research.

I'm not a string theorist so I can't be 100% sure, but this stuff sure sounds like nonsense. The part about the Foucault pendulum aligning with the initial singularity sounds really silly. To quote John Baez, a mathmatical physicist (see below for a link)

It [one of the papers in question] goes on to discuss the supposed connection between N = 2 supergravity, Donaldson theory, KMS states and the Foucault pendulum experiment, which he claims "cannot be explained satisfactorily in either classical or relativistic mechanics". If you know some physics you'll find this statement slightly odd.

As I said, I'm not a string theorist, so I don't know for sure, but some very sharp people seem to support the contention that this is nonsense. John Baez has compiled some of the relvent stuff on his webapge, here. Jacques Distler's blog also contains some good analysis.

For a collection of stuff on this subject, search google groups on ``reverse sokal hoax''. Then read the (long) thread in sci.physics.research.

I'm not a string theorist so I can't be 100% sure, but this stuff sure sounds like nonsense. The part about the Foucault pendulum aligning with the initial singularity sounds really silly. To quote John Baez, a mathmatical physicist (see below for a link)

It [one of the papers in question] goes on to discuss the supposed connection between N = 2 supergravity, Donaldson theory, KMS states and the Foucault pendulum experiment, which he claims "cannot be explained satisfactorily in either classical or relativistic mechanics". If you know some physics you'll find this statement slightly odd.

As I said, I'm not a string theorist, so I don't know for sure, but some very sharp people seem to support the contention that this is nonsense. John Baez has compiled some of the relvent stuff on his webapge, here. Jacques Distler's blog also contains some good analysis.

AFIK particles without mass move at c. As for tachyons, I'm a chemist, not a physicist. I'm not familiar with any of the theories to know much about them. I'll refer you to what I found when googling, here.

I have found AoA to be extremely useful in my understanding of Boolean Algebra, Chapter 2 covered the basic postulates, theorems, functions very well. I printed the "16 Possible Boolean Functions of Two Variables" table he included and kept it in a handy location. I first came across minterms/maxterms and how they are used to find the canonical expression, as well as k-maps for optimization. I don't particularly like Hyde's assembly library however, for me the Intel Programmers Manual Volume 1-3 dead tree book was most clear and straight-forward, unlike assembly "tutorials".

I challenge you to provide a link to a better reference than Hyde's AoA that explains boolean algebra more clearly and more comprehensively. Go ahead.

I have found AoA to be extremely useful in my understanding of Boolean Algebra, Chapter 2 covered the basic postulates, theorems, functions very well. I printed the "16 Possible Boolean Functions of Two Variables" table he included and kept it in a handy location. I first came across minterms/maxterms and how they are used to find the canonical expression, as well as k-maps for optimization. I don't particularly like Hyde's assembly library however, for me the Intel Programmers Manual Volume 1-3 dead tree book was most clear and straight-forward, unlike assembly "tutorials".

I challenge you to provide a link to a better reference than Hyde's AoA that explains boolean algebra more clearly and more comprehensively. Go ahead.

Regardless, regarding syntax, the binary infix notation is not to be ashamed of. a != b is commonplace in imperative languages; I can't speak for Lisp which you seem to be intimiately familiar with, but its well-understood in Slashdot culture at least in my limited experience. In similar vein, a = !b is also accepted, its standard C++ semantics believe it or not. The alternative, a = b' used in Randall's Art of Assembly , is no more or less favorable. Prefix or postfix, its all the same.

As I'm sure you are aware, != is what it is due to our limited rendition of mathematical binary logical operators thanks to ASCIIization of the Internet (what ASCII bytes where sent to the backbones to DDoS them? ADM, perhaps?!), and although Unicode is now a standard, 3.0 being the largest and most complete compendium ever notwithstanding Unihan CJK languages, Slashdot choses to return the same identical Content-Disposition header ignoring actual content. This forces one to write != rather than the preferred "Equal Sign With Slash Overbar", approximated /= by some, not to be confused with auto-assignment division, but you have to compromise somewhere. I would have written = U+"COMBINING SLASH" or, in canonical form U+02AF2 "NOT EQUAL/LESS THAN OR GREATER THAN", but what do I look like, a Unicode-compatible typist?

Wheels can exist without cars, everyone agrees on that. Of course, cars cannot drive without wheels--you can't go anywhere, but your kids can still fiddle in the back with the radio and color DVD players, their own XBOX, and our 802.11b-linked Home Entertainment System. If you see SSID=NACHONETWORK, I have embedded a buffer overflow in our SSID which exploites NetStumbler and is able to create a connect-back rootshell on my MacOS server. I'll show you the forest in the trees, just wait for your magic Christmas tree packet!

Now can I go?

Are you sure? This paper here attempts to discuss the physical properties in scientific terms and questions the validity of the question. is glass liquid or solid.

Look here for a discussion...Is glass liquid or solid?

The crux is that glass's structure is not clearly solid or clearly liquid. The explanation for the windows that have thicker bottoms than tops is that the old processes for making glass involved blowing a large bubble and then spinning it. The glass had non-uniform thickness, and was typically installed with the heavy end down.

Correct.

Beside the train (or on the train, looking out the window), things are foreshortened.

Both guys hold a meter stick horizontal to the ground. Each sees their own stick as being 1 meter long. Each sees the other's stick as being, say, 10cm long.

Okay, so if each guy sees the other's stick as "shorter", who's right?

And what if one guy had a tunnel 40m long, and the train was 80m long, the guy in the tunnel sees the train as being 8m long - surely he can simultaneously close a pair of doors and "catch" the 8m train in the 40m tunnel. But the guy in the train sees the barn as 4m long, and obviously an 80m train can't fit in a 4m barn. Who's right?

Answer here: A Special Relativity Paradox: The Barn and the Pole.

• Australia
  
• ftp://ftp.planetmirror.com/pub/Mandrake/iso/
• Austria
  
• ftp://gd.tuwien.ac.at/pub/linux/Mandrake/iso/ (Vienna)
• 
  Czech Republic
  
• ftp://mandrake.redbox.cz/Mandrake/iso/
• http://ftp.fi.muni.cz/pub/linux/mandrake/iso/ (Brno)
• 
  France
  
• ftp://fr2.rpmfind.net/linux/Mandrake/iso/ (Lyon)
• ftp://ftp.ciril.fr/pub/linux/mandrake/iso/ (Nancy)
• 
  United States
  
• ftp://ftp.cs.ucr.edu/pub/mirrors/mandrake/Mandrake /iso/ (California)
• ftp://ftp.cse.buffalo.edu/pub/Linux/Mandrake/mandr ake/iso (NY)
• ftp://mirror.mcs.anl.gov/pub/Mandrake/iso/ (Illinois)

Australia

ftp://ftp.planetmirror.com/pub/Mandrake/iso/

Austria

ftp://gd.tuwien.ac.at/pub/linux/Mandrake/iso/ (Vienna)
Czech Republic

ftp://mandrake.redbox.cz/Mandrake/iso/

ftp://ftp.fi.muni.cz/pub/linux/mandrake/iso/ (Brno)
France

ftp://fr2.rpmfind.net/linux/Mandrake/iso/ (Lyon)

ftp://ftp.ciril.fr/pub/linux/mandrake/iso/ (Nancy)
United States

ftp://ftp.cs.ucr.edu/pub/mirrors/mandrake/Mandrake /iso/ (California)

ftp://ftp.cse.buffalo.edu/pub/Linux/Mandrake/mandr ake/iso (NY)

ftp://mirror.mcs.anl.gov/pub/Mandrake/iso/ (Illinois)

Huh? You're trying to tell me that the earth only has a mass of 122880 kilograms(6144*20)? While simple logic can tell you that's untrue, this page can confirm it, as can this one.

Occam's razor actually says (in the context of generating hypotheses) "one should not multiply entities beyond necessity." One interpretation of that maxim is "the simplest explanation is best." A good interpretation in some contexts, but not the only interpretation.

Anyway, a soul would be an entity whose existence is postulated unnecessarily if the brain itself can reasonably be postulated as the source of the phenomenon. So, what "simpler" means in this case is fewer entities (and types of entities, such as immaterial souls) that we have to invoke in order to explain something. Not that a soul is somehow more complex than the brain (how would we know?).

A major criticism for any mix of materialistic and spiritual entities having causal relations (such as the one above where someone questioned how we know there isn't a *real* out of body experience that just happens to coincide with a particular kind of cerbral stimulation) is the lack of any means to causally relate a material thing ( even a force) with something spritual. The reverse, having a spritual thing cause things in the material world, is just as problematic.

The really-long-stick thing bugged me too for the longest time, except, I always imagined spinning the rod instead of pushing on one end.

The answer I was given is that the rod might be indestructable, but it isn't rigid. In fact, in relativity, there is no such thing as a rigid body.

This page has a pretty good explanation.

The speed of gravitational waves and "the speed of propagation" could be two different speeds, although that's just theory. http://216.239.35.100/search?q=cache:uDPNhqhck6kC: research.spinweb.com/_tp/000001fe.htm+gravity+spee d+of+light+%22gravitational+waves%22&hl=en&ie=UTF- 8

No one has been able to test that gravitational waves travel at the speed of light, it's speed is only inferred through Einstein's general relativity.

I don't know how one would go about broadcasting and receiving something over the speed of propagation, but it's interesting to think about.

The one major criticism you can make is that mechanics are covered without using the Lagrangian formalism, which is much more powerful and much more applicable to quantum mechanics. For this, you may want to check out Structure and Interpretation of Classical Mechanics. This is a very dense book but it covers a lot, and in a way geared towards programmers. Warning: uses the Scheme programming language heavily. If you don't like Scheme, you won't like this one.

For general relativity, I highly, highly recommend A First Course in General Relativity. The prerequisites are pretty minimal, and it's extremely well written.

Beyond that, check out John Baez's list of favorite books. Actually, you might want to read anything and everything Professor Baez has to say about physics, he knows a lot, explains it very well and is willing to talk to people. He's one of the few working physicists who still bothers with usenet. I'm currently working through his book on Gauge Fields, Knots and Gravity, and am enjoying it immensely.

Webster -- The Place on the Net to Learn Assembly Language Programming

See The Art of Assembly Language Programming

Webster -- The Place on the Net to Learn Assembly Language Programming

See The Art of Assembly Language Programming

The USENET sci.physics FAQ has a pretty readable explanation of some of the speculation surrounding the speed of gravity.

Those wishing to dig into Intel assembly language without shelling out seventy-some-odd bucks can download the PDF version of The Art of Assembly Language . IMHO, it's pretty good, and weighs in at about 1200 pages -- there's more there than you'll probably ever use. I no longer recall if there's a complete guide to the Intel instruction set in the book, but you can, unsurprisingly, get that from Intel's site.

Here's an excellent free reference - worldly reputation as one of the best from what I hear.

"I know this is going to bring up glass comparisons, so we'll head those off: glass is not a fluid."

Did the editor not read his link? :) From the article:

Conclusion
There is no clear answer to the question "Is glass solid or liquid?".

And folks complain about us posters not reading articles .... sheesh. ;)

In the reference frame of an outside observer, your objects a and b are each travelling at half the speed of light. You are correct in saying their relative velocity is c, based on how relative velocity is defined (simply the addition of two velocities) but neither of the objects is travelling faster than the speed of light.

To find out the speed of one object in the reference frame of the other object, we must use the special relativity formula for the addition of two velocities u and v:

(u + v) / (1 + uv/c^2)

If obejcts a and b are spaceships, an astronaut in spaceship a would see spaceship b travelling away from him at 0.8c, obviously not in excess of the speed of light. For a good discussion of this, see this site.

As to your second question, obviously the speed of light is not infinite speed. However, a massive object travelling at the speed of light would have to have infinite momentum. The relativistic formula for momentum is:

p = mv / sqrt (1 - v^2/c^2)

as v approaches c, p approaches infinity. It would require an infinite amount of force to accelerate anything to a state of infinite momentum (or a finite amount of force applied over an infinite time). Since neither of these things are possible, everything with mass must travel at less than the speed of light.

Also note that by definition an object's momentum cannot be greater than infinity, so just by the limit of the momentum formula we can deducde that velocities greater than the speed of light are impossible.

Offtopic reply:

I hate to be pedantic (aw, who am I kidding, I love being pedantic), but in general, saying "it's just a theory" is... well... not a good idea. (The page you referenced has a lot of bullshit new-agey stuff about higher dimensions and so on, but that's neither here nor there. Remember, "newage" rhymes with "sewage". :) )

To a scientist, a "theory" is something that explains all or most of the known evidence, is well-supported by facts, and makes testable predictions. Many well-established things like universal gravitation, aerodynamics, thermodynamics, and so forth, are all "theories".

The word you're probably looking for is "hypothesis", which means "an idea that potentially explains the facts, but isn't yet well-supported and well-tested enough to be considered a theory."

Of course, it's a pretty smooth continuum between the places where an idea is considered a "hypothesis" and where it becomes a "theory" but dismissing a scientific theory as "just a theory" is misguided at best.

Hope that helps, somehow. Check out http://phyun5.ucr.edu/~wudka/Physics7/Notes_www/no de7.html, http://www.talkorigins.org/faqs/evolution-fact.htm l, and http://www.eugeneres.org/scientificmethod.htm, for they all explain it far better than I do.

I know folks that use wwwreq and it seems to work as well as the people you have actually handling the tickets.

Also, see this page for a bigger list.

At this point we no so litle about gravity that it is difficult to make any conclusions about it.

We know quite a bit about gravity - this NASA page lists a bunch of tests of General Relativity, and doesn't even include the atomic clock measurements of gravitational redshift (The GPS satellite system works only because the approximately 40 microsecond/per day relativistic time dilation is well characterized.

Now like electromagnetism, gravity is one of the four fundamental forces.

Is it? Generations of theorists, starting with Albert Einstein himself, have attempted to draw the connection between the two, unsuccessfully to date (although String Theory research is big business these days, I know, and may eventually pay off).

It seems that gravity is actually is very different from the other forces. Those forces act on other particles & masses and subsequently cause reactive movement, but that movement is within spacetime, where gravity is due to the alteration of the spacetime
fabric itself.

You have to remember that gravity's effects go beyond just being an atractive force. The curvature of spacetime can be measured, most accurately in the time dimension; an atomic clock runs slower at sea level than it does on top
of the rockies, and way slower than one in orbit. None of the other forces come close to producing that kind of effect.

Found another one in my bookmarks i forgot to mention, Art Of Assembly

• Well, I don't know. Many scientific theories cannot be directly falsified (evolution and global warming leap to mind) but are widely regarded as the best extant explanations for the data. (...)

I'm not the only one to say there needs to be a way to disprove a theory:

• There is a very important characteristic of a scientific theory or hypothesis which differentiates it from, for example, an act of faith: a theory must be ``falsifiable''.

• Direct falsification is only one particular method of testing theories. Not that this has much to do with UFOs, etc.

And proving something wrong is exactly what we're talking about. It can apply to dowsing of pictures of faeries, for example.

check out this link http://www.cert.ucr.edu/research/pubs/biodiesel-2- 20998-final.pdf if you're interested the pollution factor.

Hard drive decay is the least of our problems. Protons are decaying, the universe is flying apart at an ever-increasing rate, in a mere 10^(10^26) years there'll be nothing left but infinte, cold, dark, empty space. We're all doomed. Doomed, I say!

Gravity does not propogate at the speed of light. If the sun winks out it takes Jupiter (for example) so many minute to see this. Any EM waves traveling at light speed from the sun take time to "wink-out" so Jupiter remains "ignorant" of the suns disappearance for awhile. Except for gravity. Jupiter knows instantly that it has nothing to orbit (or at minimum 20 billion times faster than it knows there is no more EM energy coming from the sun).

If you introduce a delay in the propogation of gravity - slow it down to light speed - the solar system would fall apart. Check it out

Introducing delay into GR models is done in all celestial mechanics code that requires high precision. It is not otherwise necessary because the effects are quite small, but if you are trying to determine the state of the solar system after 1Myears, it is essential (and don't worry, contrary to your statement, these models suggest the solar system is still around on these time scales). If it falls apart in your models, you might want to check for accumulated round-off errors.

The most amazing thing I was taught as a graduate student of celestial mechanics at Yale in the 1960s ...

Expressed less technically by Sir Arthur Eddington ...

Until comparatively recently (referring to Laplace's estimation), it was thought that conclusive proof had been given that the speed of gravitation must be far higher than that of light

It amazes me that people still use a 19th century estimate done by Laplace that gravity must be at least one million times faster than light, because many (including Einstein and Eddington) have shown that Laplace was incorrect in his calculation.

Correct me if I am wrong, but do I have the pleasure of addressing Dr. Flandern? If so, then I will not comment further as I know it would be futile to argue with you given the fact that others much more knowledable than I (such as Steve Carlip at UCDavis) have entirely refuted and destroyed your general relativity objections, and yet you still make the same arguments.

O'Reilly Open Books Project
Bruce Eckel's "Thinking in..." books
Data Structures and Algorithms books
MIT's Structure and Interpretation of Programming Languages
Numerical Recipes series
Handbook of Applied Cryptography
The Art of Assembly Language Programming
Object-Oriented System Development
GTK+/Gnome Application Development
GNU Autoconf, Automake, and Libtool
Effective Perl (partial)
Programming Pearls (partial)

even though, yes, glass is a liquid technically

This is sort of a myth

Most of the evidence commonly cited to show that glass is a liquid is bogus, but an argument can be made for either case, depending on your definitions.

Look, I've already explained to you what happens several times. The FAQ goes into even more detail. Why don't you come back once you've read it and thought about it??

The acceleration will fracture the train, and the individual pieces will be length-contracted (assuming they stay on the track at .99c). A truly rigid train spanning the equator is impossible in relativity. (Rigid substances violate relativity because they would require an infinite speed of sound in the medium.)

See "rigid rotating disk" FAQ.

(I think he may have been referring to the fact that an object deeper in a static gravitational field will experience greater time dilation, and was misinterpretating the equivalence principle (loosely and incorrectly stated as "gravity = acceleration") to infer that objects experiencing greater acceleration will have greater time dilation.)

Different clock rates at the end of a journey occur when two objects travel along paths in spacetime of different lengths. Acceleration can play a role, in the sense that one's acceleration affects one's path through spacetime, but the effect is not
fundamentally due to acceleration.

In the case being discussed here, the Hafele-Keating experiment (with the clocks flown around in planes), there is no assumption that one clock is "at rest" (whatever that means) and the other is not. A difference in clock rates almost always occurs whenever two clocks are separated and brought back, unless they're done so in a very careful way to ensure that they travel along trajectories of the same spacetime length -- acceleration or not, gravity or not.

If he really thinks he's doing physics, his propositions will be testable, and it's up to him to provide a test that would show him right and his detractors wrong. Running a simulation is Mathematica is not a physics experiment. You would get the same results no matter what the universe was really like. Until I hear some novel predictions about blackbody radiation or the microwave background radiation or the distribution of galaxies or some such thing, I will continue to think that this "theory" is physically untestable, and no better than astrology or Freud's theory of the self.

Now, please notice that Wolfram makes no claim that this will ever produce testable resutls. This is the first sign of a sham. For more, consult the Crackpot Index and take note that this book scores higher than Pons & Fleischman.

From the Crackpot Index (http://math.ucr.edu/home/baez/crackpot.html)

33. 50 points for claiming you have a revolutionary theory but giving no concrete testable predictions.

Sounds pretty right on to me. Many of his "ideas" can be attributed to others several years ago. Mandelbrot comes to mind. If he has all of these "new" ideas, I'd really have liked to see him DO something with them over the past 20 years (Yes, I know he was enlightened but a few years ago).

But then again, I bought the book

Very true. Airplanes and trains have to be designed within certain jerk limits for operation. Rollercoasters shouldn't be an exception.

Jerk - Third Derivitive of Position

Speed never killed anyone. It's the jerk that hurts.

If the theory is that they were created from the "big bang", then they were all oriented most likely in some spherical pattern and moved out from there.

There is no "center of the universe". (See also here.)

But how does this theory counter the current thought among almost all physicists that there is 10 times too little mass to cause the universe to implode?

Furthermore, how does it respond to the other theory that even if it were to collapse, the result would be an enormous black hole out of which nothing could ever come?

There are a few good links

http://www.ualberta.ca/~bderksen/florin.html
http://math.ucr.edu/home/baez/physics/General/Glas s/glass.html
http://www.spectrumglass.com/Library/ScoreArticles / itAboutGlass.html

from google to the issue of classification of glass as liquid, solid, or none of the two. I guess I was wrong. Good to learn something from slashdot. hehe

Secondly, Newton's demonstration that white light was composed of many colours of light using two prisms. Very neat, and very simple.

Very well, read this and jump to the Conclusions at the bottom. I'm pretty sure that a platter can get 250 Celsius transients (at which point it becomes a supercooled liquid) upon head crash (platter irregularity or pinpoint contamination causing high friction) or a long read over the same track (e.g. reading then re-reading then dual-ECC then quad-ECC on yet another pass).

We* are doing it too. When I looked at the prototype reactor today, they were just about to start leak testing.

* Bourns College of Engineering - Center for Environmental Research and Technology (CE-CERT) at the University of California, Riverside.

The University has a press release (including a schematic) at:
http://www.info.ucr.edu/cgi-bin/display.cgi?id=217

We can see the same with cars, they are most likely to fail just after you buy them (manufacturing defect - lemon), then become unlikely to fail, and then gradually become more likely to fail after 10 years or so (because of age). Of course in the real world it won't be so extreme - half hard disks failing in 3 years, half after 22 years. It'll be more of a high-low manufacturing not perfect P(failure) = 1/exponential(t) within 10 years then slowly increasing P(failure) = log(t) rising to 100% failure after 500 years or so.

I seriously think it's possible for hard disks to (perhaps) go over 300 years because well in a car the components are rubbing => finite life, whereas in hard disks:

The heads barely touch the platter,
Servo actuators are so reliable they're used in car braking systems,
Brushless motors have no frictional brushes,
The SCSI electronics within the drive are cooled by the whirlwind generated by the fast platter rotation. IDE electronics on the drive's underside aren't.
Rust or dust? Ahh, that's why its made in a clean room.
Oil bearing technology might have high reliability soon.

Perhaps the head assembly would weaken or become brittle as the metal ages, sagging and causing the head to scrape against the platter after a couple of decades,
Maybe the fast air rushing over the head would sharpen it same as a waterfall sharpens rock over thousands over years. This sharpening would over decades wreck the aerodynamics of the head causing it to lose lift and scrape against the platters, making a groove,
Perhaps running your hard drive too cool can cause head scrapage against the platters - if the head assembly is cool then the metal will be less flexible and the head would ride closer to the platter, perhaps scraping against it,
New Glass Platter technology might limit life because glass flows like a liquid, cuasing a warping effect in old windows. Under the high centrifugal forces in a 15,000 RPM hard disk it might shatter or start liquid flow within a few years.

I wonder if the engineers have factored these failure conditions into the manufacturing process. Maybe now in this recession I should switch to career in science fiction, or science fact?