I'm also currently wearing a 24 hour analogue watch (hour goes round once a day). It's my main watch at the moment. I've a binary LED watch, a binary LCD watch, another 24 hour analogue, a digital heart rate monitor and for good measure a normal 12 hour analogue with digital 'screen' behind the hands.
The original poster might have referred to the fact that the 2012 transit is visible only from the southern hemisphere, so if you're in the north, 2004 is a once in a lifetime.
I have not been able to get onto the server since this was posted on slashdot.
Perhaps there is a solution to the slashdot effect?
When something is about to go on slashdot, the slashdot server caches a copy, images and all. When clicked from slashdot, one arrive at the cached copy, this'd have a header attached which contains a link which effectively says 'click here to get to the original'. Any HTML with relative links gets the appropriate absolute bit automagically stuck on.
Most people will be happy with the cache, and the original server does not get hammered.
The original server is available to anyone who wants it, as are all it's links.
One downside might be that the server doesn't see the page access counter go crazy, but that's life.....
The precedent for this sort of thing has been set (wayback machine, google).
This would work for most things, but slashdot types would have to have the option of the current 'link to server' - this'd be used for bigger servers (e.g. bbc, cnn)
I don't work for these people, not did I buy a DVD player from them (I gave my business to a local supplier).
They have been online for several years to my knowledge, and the site seems regularly updated.
They do their own mods, which instead of changing regions on the fly, allows you to select the region with a single keypress. This means that they tend to be slightly more pricey than a vanilla system.
They also do macrovision disabled (a technology which prohibits use in home projection systems) and they do FBI warning disabled (the point of the original question).
Codefreedvd is the site, using Google gets you exactly what you want, for example this 300 dvd sony (for UK power supply). They do ship around the world, you'll have to search for your own specs.
The magnetic field of the earth DOES change polarity every so often... but we are not due for another such switch for a great many years, and the pole does not spontaneously shift, it gradually changes, sort of "wandering" toward the other side of the planet
Whilst it does wander, my understanding is that during a switch the strength of the magnetic field drops to zero, and then increases in the other direction.
This is an important difference, as for a time it means that the background radiation will go up (charged particles are no longer deflected to make pretty patterns in the north).
This could have an effect upon mutation rates, etc.
Why use GnuCash at all? Why not just manually write down your finances in in your checkbook and do the math in your head? This is exactly the type of thing that Quicken is good for, eliminating worthless "grunt work" like manually entering numbers.
Absolutely wrong..... Use of this 'feature' means that you trust the institution to get it right. Much, much better to enter details yourself, and then use a 'reconcile' feature when the statement comes in.
Acceleration at 9.8m/s^2? Well, that's due to gravity and will only work until the center.
Actually it only 'works' at the surface.
Within the earth you only have to consider the mass inside the radius which you're at, the 'shell' at larger radii contributes nothing - this is analagous to a faraday cage.
If you assume that density is uniform (it isn't) then it's easy to show that within a solid sphere g is proportional to r. (Basically mass proportional to r cubed, g is proportional to mass divided by r squared).
( Terminal velocity? That's a product of friction, without which you wouldn't stop accelerating.
Yes you would. As soon as you're past the center you'd slow down. With no friction you'd arrive at the far side just to bob out of the hole and start falling again!
If g is proportional to (-) r then you'd get SHM, the constants in this give a time period of 90 minutes for the earth.
It can be shown that a straight frictionless tunnel between ANY two points on the surface of the Earth can be traversed in EXACTLY the same time travelling under gravity alone. That's IF you can eliminate friction. --
Murky
This is how it works (one method only, not the neatest IMO, but it's quicker than the alternative I know as more photons get through).
Have a source of entangled photons.
Send one of each pair to Alice, the other to Bob, these are send according to a clock. I.e. A and B know when to expect them.
Alice has two polaroid filters. l and /
Bob has two filters. - and \
They each use a filter at random.
The only way that they can BOTH detect a photon from th pair is if they happen to choose |\ or/-. If they choose |- or \/ then only one could detect a photon.
The next bit is done over a telephone, or radio, or TV.....
Alice says " I got photons 1, 3, 7, 8, 9, 10 etc...." (West Wing/The Sopranos, eat your heart out - THIS is drama!)
Bob says something similar.
They now have a list of the photons which they BOTH detected.
They've previously agreed that | or \ represent 1 and / or - represent 0.
This list of matched photons turns into a string of ones or zeros.
This is the key (preferably a very long key which'll be used as a one time pad).
The number of photons that get through a particular filter is 50%.
The number that get through both is 25%. So for 100 bits you'd need to send 400 bits on average.
To check for tampering, Bob would announce some of the key bits (these bits would be removed from the key - no longer secure).
I.e. Bob: "Bits 1, 3 and 72 are 101"
There is a 1 in 8 chance that these bits could have been intercepted and Alice agrees with those bits.
To reduce the chance that an undetected interception can be made, the number of check bits goes up. The chance of an interception being made undetected can be made arbitrarily small.
If a one time pad is used, this can be used to set up a TOTALLY SECURE (to cryptanalysis) system.
You'd not use the key to send a test message as this destroys the principle of a one time pad.
You'd have to send a key rather than the data itself via this method as 3/4 of the photons are not useful, and some of the rest are used for checking.
You'd also have to send (at least) four times as many photons as you need bits.
In practice, this system would be running continuously in the background, building up key data for later one time pad use.
Incidentally, if a distance through air at sea level of a few miles (single figures) can be achieved, that's equivalent to a secure data path to a satellite (density of air reduces with height).
Once you have that then the system works worldwide.....
--
Murky
hy do you assume the velocity of the Asteroid to be the earth's escape velocity? This is the velocity required to leave the earth - the relative velocity of the Asteroid and the Earth are what is important, and possibly much higher than this. The higher the velocity, the lower the mass required on the asteroid. But then, IANAAP:)
Well, IAAP....:) (APT actually)
Simply as the escape velocity is the LOWER LIMIT on the impact speed. If you throw something up at 10m/s it passes you on the way down at 10m/s (air resistance ignored) - it's much the same idea.
You're quite right in saying that the velocity could be much higher than this, but I was getting a feel for the numbers.
There will however be an UPPER limit on th velocity, which is governed by the escape velocity of the sun. Also the asteroid is not that likely to be orbitting the sun in the opposite sense to the Earth for various reasons to do with the formation of the solar system, to 11km/s, whilst low, isn't going to be that bad!
Incidentally, the velocity squared will be proportional to 1/d^3 for a given size impact, this means that if increase the velocity by 1000 you only reduce the diameter by 100. --
Murky
15 small nuclear bombs, let's say 20MT yield this gives 300MT.
1MTonne TNT=4.5x10^15 Joules IIRC.
Hence a yield of about 10^18 Joules.
Taking KE=0.5*m*v^2
This gives m = 2*KE/v^2
m= 2*10^18/(11000)^2 = 10^10kg (approx)
Using a density of about 10^4 kg/m^3, Volume is about 10^6m^3.
This means that we're talking about an asteroid of diameter 100 metres here. That's getting a bit big to be an unknown asteroid (subject, of course, to any stupidness on my part, and the usual rounding errors). This is not an infeasible size for the application though - we track a very small proportion of these objects.
However, a smaller asteroid (which are more likely not to be tracked) would still cause pretty major devastation.
The problem for any would be despots would, of course, be making an undetected launch to deflect the asteroid, rather than deflecting the thing. Also there's the problem of deflecting the object in a controlled way (the method given sounds a little hard to fine tune).
For a related weapon (this time rocks fired from the moon), read 'The Moon is a Harsh Mistress' by Heinlein. (Amazon.com/Amazon.co.uk)
--
Murky
Looks pretty much like a flat sheet would cause divergent rays to be straightened toward parallel.
Diverging rays going from air through flat glass and back to air will converge in the glass (actually diverge less quickly), and diverge again on the other side. Angle of emergence and angle of incidence would be the same.
If the light is bent the other way (e.g. glass to air layer to glass) then the rays will diverge more, then diverge less quickly. Angle of emergence and angle of incidence would be the same.
The overall effect of the layer would not be to change the angle at which the light is travelling, merely to slightly change the position from which the light appears to come.
For a flat sheet giving focussing effects one would use a fresnel lens, or conceivably one would have a material of varying refractive index. --
Murky
So if you were to say that the universe was shaped like a big doughnut then it would be a 2-dimensional manifold since we're only talking about the surface. The different paths you could travel would be any way you could draw a line on it with a pen without lifting it ( or drizzle icing to stick with the doughnut analogy). You would never bump into the edge though like if you were drawing lines inside a box.
Putting on the serious face:
I'm unsure about this bit, but I think you'll find that we couldn't have the equivalent of a doughnut (with a hole) due to the topology of the situation. (I.e. the hole has to be there the whole time, this leads to problems with the big bang which I don't understand). We could have the equivalent of a doughnut (with the jam) though.
Of course, we would not perceive the jam as we're only using the doughnut as a 2 dimensional analogue of our universe and considering it's surface only.
In this kind of universe you could look at the back of your head if you had a powerful enough telescope.
Except for the Cosmic Background Radiation (the icing sugar?), and also Inflation (the size of the doughnut?). Because of Inflation the light hasn't had time to go round yet). You'd also have to be very long lived (the doughnut would go stale).
There's a nice George Gamow story about Mr. Tompkins which looks at all this stuff.
What -- Penguin is offering PC's pre-loaded from major manufactures? Funny, none of my local computer stores carry them. Walk into CompUSA and you see Windows everywhere (except for the solid little 200 sq feet of Mac in a 20,000 sq foot store).
I don't know about the retail side, but penguin seem to doing okay from this end by looking at the www, and I'm unaware of even that facility here. Of course I realise that Linux boxes will be negligable in retail compared to Windows PCs, but I've seen US online retailers (e.g. penguin, off the top of my head) offering to supply preconfigured Linux PCs, but only in the US.
Linux does have a presence in the software isles -- spend 50 to 100 US and you can walk out with the latest box of your favorite distribution as long as it's RedHat (ok, ok, they have a few other options on the shelf as well).
By 'box' I meant 'box containing processor hard drive etc'... whilst many people will like to configure their own computer, many others will, at least the first time out, like to play on a Linux system they know will work! Especially with drivers and so forth. This combined with the getting people on to Linux in the first place prompted the (possibly poorly put) question about whether RedHat has considered promoting 'Linux Inside' options from the PC manufacturers.....
Anyhow, if I'm wrong about preconfigured Linux PCs being available in the states, even if you have to seek them out, (and I accept I probably am wrong, it's just an impression) it doesn't change the point that it might be a nice idea to have Linux Inside PCs to get people started. (Also it might keep the Win only hardware at bay by creating a wider market).
Me? I'd LOVE to play with Linux, but can only afford one machine, and I can't afford downtime if I mess up! Soon I'll get a second (cheap) machine.... and away I go. I've been saying that for.. oh, years now.
Now.... will I be able to take a windows laptop to and from work and be able to happily plug it into a Mac ethernet there and my (forthcoming) Linux network at home....? La de dum.....
What a reverse index of refraction means is that the substance they are refracting light through is simply less dense than air.
The article actually talks of a negative refractive index.
Refractive index is defined as c/v where c is speed of light in vacuo, and v is speed of light in material.
A negative refractive index implies that when light hits the boundary from one side, it is also approaching the boundary from the other. Needless to say that this would have all sorts of problems with causality.
What's probably implied is that the refractive index is less than 1. This is actually fine, but it does not imply the signal in the material is faster than light.
Sound odd?
Refractive index is based upon the 'phase velocity' which does not have to be the same as the 'group velocity'. Imagine a little packet of waves. The group velocity is the speed of the packet - this can't be greater than c. The phase velocity is the speed of the wave peaks within that packet.
If you imagine travelling along with that packet of waves, the waves would appear at the back of the packet, grow, and die away at the front. The peaks travel faster than the group, but no information beats the group.... Einstein can rest easy. (This only happens in summat called a dispersive medium by the way, i.e. anything where wave speed depends upon freq, and it happens because a wave packet, being other than a pure sine wave contains a range of frequencies which travel at different speeds giving a sort of beating effect)
Materials with a refractive index of less than 1 are well known. For example, there is a famous Pink Floyd Album with a prism on the cover.....
--
Murky
Certainly on this side of the great pond (UK), it is difficult to find anyone selling Linux boxes 'off the shelf'. Indeed, it is rare to find a PC without windows preloaded on it.
Are there any plans for Redhat to enter into agreements with PC manufacturers to provide preconfigured, supported, possibly dual boot, 'Redhat Inside' computers, in much the same way that Penguin operates in the US? --
Murky
Imagine a rubber sheet (ah, good ol' rubber sheets... what would cosmologists or incontinent physicists do without 'em?. Shape it into a balloon. This has no boundary, but it's surface can expand.
The rubber sheet is the boundary in this case. The region enclosed by the sheet not including the sheet has no boundary (but it is bounded).
No. Let me try and make my meaning clear. Imagine a 2 dimensional creature, which lives in this two dimensional world of the balloon surface. That creature will have no conception of inside or outside the balloon, but we, as 3 dimensional beings can see the balloon is really curved. The 2D Creature could determine if their space was curved by making measurements, such as checking to see if the angles in a triangle add up to 180 degrees. (For a small triangle they do, for a large trangle they don't). This creature could travel and never reach a boundary of their 'space' - though the space is finite and could expand. It is not a meaningful question for that creature to ask 'What is my space enclosing?' as they have no conception of a third dimension.
By analogy, the curvature of space refers to a bending in 4 dimensions, but we as 3 dimensional beings cannot see it. Our space could be finite, but this does not imply a boundary we could ever reach (a brick wall at the edge of space).
Anyhow, that was an aside to the original point, and probably highly irrelevant. --
Murky
Closed = expands up to a certain point, then contracts
That's fine...
Open = expands forever
So's that....
Flat = reaches a ceratin size then stops expanding but stays that size forever
Not so. It expands forever but with a speed asympotically approaching zero (and a size asymptotically approaching a maximum).
I know I'm being pedantic.... what the hell.
Oh, for anyone who is wondering: Yes, you can have a finite size without an edge. For ease of thought, consider a 2 dimensional example. Imagine a rubber sheet (ah, good ol' rubber sheets... what would cosmologists or incontinent physicists do without 'em?. Shape it into a balloon. This has no boundary, but it's surface can expand.
Back to the point. One of the articles (Chronicle?) said:
By measuring the supernova's red shift, the Berkeley astronomers determined that it is as far away -- and as bright -- as it should be if one assumes that it existed at a time when the cosmos was decelerating under gravitational tug, soon after the Big Bang.
The key here is that they used the red shift to give distance. This relies upon Hubble's constant, Hubbles constant has HUGE errors on it (of the order of 60% if I recall.....
Therefore, I'd like to see a more detailed explanation of how a supernova of an unusual luminosity implies that Einstein's stab in the dark (the Cosmological Constant) was not such a blind guess...
... after all, it's nice that he was wrong from time to time. At least we still have the Einsteinian reliance upon hidden variables to show us that he was fallable. --
Murky
As has been pointed out elsewhere, this can be no substitute for taking a course - but such an initiative is invaluable for people who are studying from home, researching a topic or whatever.
One issue though: Funding. The page says that they're seeking partners for the funding.... How would this work exactly? This engineering course was brought to you today by..?
It'd be interesting if this was extended into an 'Open University' model, which would allow distance learning. Especially if other Universities jumped on the bandwagon (as Mordred indicated), Harvard, Yale, Oxbridge - or even my old Uni, Birmingham, UK.
--
Murky
Slashdot Mirror
I have one of those myself.
:)
I'm also currently wearing a 24 hour analogue watch (hour goes round once a day). It's my main watch at the moment. I've a binary LED watch, a binary LCD watch, another 24 hour analogue, a digital heart rate monitor and for good measure a normal 12 hour analogue with digital 'screen' behind the hands.
I like my timepieces
The original poster might have referred to the fact that the 2012 transit is visible only from the southern hemisphere, so if you're in the north, 2004 is a once in a lifetime.
I have not been able to get onto the server since this was posted on slashdot.
Perhaps there is a solution to the slashdot effect?
When something is about to go on slashdot, the slashdot server caches a copy, images and all. When clicked from slashdot, one arrive at the cached copy, this'd have a header attached which contains a link which effectively says 'click here to get to the original'. Any HTML with relative links gets the appropriate absolute bit automagically stuck on.
Most people will be happy with the cache, and the original server does not get hammered.
The original server is available to anyone who wants it, as are all it's links.
One downside might be that the server doesn't see the page access counter go crazy, but that's life.....
The precedent for this sort of thing has been set (wayback machine, google).
This would work for most things, but slashdot types would have to have the option of the current 'link to server' - this'd be used for bigger servers (e.g. bbc, cnn)
Any drawbacks?
They have been online for several years to my knowledge, and the site seems regularly updated.
They do their own mods, which instead of changing regions on the fly, allows you to select the region with a single keypress. This means that they tend to be slightly more pricey than a vanilla system.
They also do macrovision disabled (a technology which prohibits use in home projection systems) and they do FBI warning disabled (the point of the original question).
Codefreedvd is the site, using Google gets you exactly what you want, for example this 300 dvd sony (for UK power supply). They do ship around the world, you'll have to search for your own specs.
Whilst it does wander, my understanding is that during a switch the strength of the magnetic field drops to zero, and then increases in the other direction.
This is an important difference, as for a time it means that the background radiation will go up (charged particles are no longer deflected to make pretty patterns in the north).
This could have an effect upon mutation rates, etc.
Of course, I could be mistaken.
Why use GnuCash at all? Why not just manually write down your finances in in your checkbook and do the math in your head? This is exactly the type of thing that Quicken is good for, eliminating worthless "grunt work" like manually entering numbers.
Absolutely wrong..... Use of this 'feature' means that you trust the institution to get it right. Much, much better to enter details yourself, and then use a 'reconcile' feature when the statement comes in.
Actually it only 'works' at the surface.
Within the earth you only have to consider the mass inside the radius which you're at, the 'shell' at larger radii contributes nothing - this is analagous to a faraday cage.
If you assume that density is uniform (it isn't) then it's easy to show that within a solid sphere g is proportional to r. (Basically mass proportional to r cubed, g is proportional to mass divided by r squared).
( Terminal velocity? That's a product of friction, without which you wouldn't stop accelerating.
Yes you would. As soon as you're past the center you'd slow down. With no friction you'd arrive at the far side just to bob out of the hole and start falling again!
If g is proportional to (-) r then you'd get SHM, the constants in this give a time period of 90 minutes for the earth.
It can be shown that a straight frictionless tunnel between ANY two points on the surface of the Earth can be traversed in EXACTLY the same time travelling under gravity alone. That's IF you can eliminate friction.
--
Murky
Have a source of entangled photons.
Send one of each pair to Alice, the other to Bob, these are send according to a clock. I.e. A and B know when to expect them.
Alice has two polaroid filters. l and /
Bob has two filters. - and \
They each use a filter at random.
The only way that they can BOTH detect a photon from th pair is if they happen to choose |\ or /-. If they choose |- or \/ then only one could detect a photon.
The next bit is done over a telephone, or radio, or TV.....
Alice says " I got photons 1, 3, 7, 8, 9, 10 etc...." (West Wing/The Sopranos, eat your heart out - THIS is drama!)
Bob says something similar.
They now have a list of the photons which they BOTH detected.
They've previously agreed that | or \ represent 1 and / or - represent 0.
This list of matched photons turns into a string of ones or zeros.
This is the key (preferably a very long key which'll be used as a one time pad).
The number of photons that get through a particular filter is 50%.
The number that get through both is 25%. So for 100 bits you'd need to send 400 bits on average.
To check for tampering, Bob would announce some of the key bits (these bits would be removed from the key - no longer secure).
I.e. Bob: "Bits 1, 3 and 72 are 101"
There is a 1 in 8 chance that these bits could have been intercepted and Alice agrees with those bits.
To reduce the chance that an undetected interception can be made, the number of check bits goes up. The chance of an interception being made undetected can be made arbitrarily small.
If a one time pad is used, this can be used to set up a TOTALLY SECURE (to cryptanalysis) system.
You'd not use the key to send a test message as this destroys the principle of a one time pad.
You'd have to send a key rather than the data itself via this method as 3/4 of the photons are not useful, and some of the rest are used for checking.
You'd also have to send (at least) four times as many photons as you need bits.
In practice, this system would be running continuously in the background, building up key data for later one time pad use.
Incidentally, if a distance through air at sea level of a few miles (single figures) can be achieved, that's equivalent to a secure data path to a satellite (density of air reduces with height).
Once you have that then the system works worldwide.....
--
Murky
Well, IAAP.... :) (APT actually)
Simply as the escape velocity is the LOWER LIMIT on the impact speed. If you throw something up at 10m/s it passes you on the way down at 10m/s (air resistance ignored) - it's much the same idea.
You're quite right in saying that the velocity could be much higher than this, but I was getting a feel for the numbers.
There will however be an UPPER limit on th velocity, which is governed by the escape velocity of the sun. Also the asteroid is not that likely to be orbitting the sun in the opposite sense to the Earth for various reasons to do with the formation of the solar system, to 11km/s, whilst low, isn't going to be that bad!
Incidentally, the velocity squared will be proportional to 1/d^3 for a given size impact, this means that if increase the velocity by 1000 you only reduce the diameter by 100.
--
Murky
let's work out the sums:
Impact speed : 11km/s (minimum) - escape velocity.
15 small nuclear bombs, let's say 20MT yield this gives 300MT.
1MTonne TNT=4.5x10^15 Joules IIRC.
Hence a yield of about 10^18 Joules.
Taking KE=0.5*m*v^2
This gives m = 2*KE/v^2
m= 2*10^18/(11000)^2 = 10^10kg (approx)
Using a density of about 10^4 kg/m^3, Volume is about 10^6m^3.
This means that we're talking about an asteroid of diameter 100 metres here. That's getting a bit big to be an unknown asteroid (subject, of course, to any stupidness on my part, and the usual rounding errors). This is not an infeasible size for the application though - we track a very small proportion of these objects.
However, a smaller asteroid (which are more likely not to be tracked) would still cause pretty major devastation.
The problem for any would be despots would, of course, be making an undetected launch to deflect the asteroid, rather than deflecting the thing. Also there's the problem of deflecting the object in a controlled way (the method given sounds a little hard to fine tune).
For a related weapon (this time rocks fired from the moon), read 'The Moon is a Harsh Mistress' by Heinlein. (Amazon.com/Amazon.co.uk)
--
Murky
Diverging rays going from air through flat glass and back to air will converge in the glass (actually diverge less quickly), and diverge again on the other side. Angle of emergence and angle of incidence would be the same.
If the light is bent the other way (e.g. glass to air layer to glass) then the rays will diverge more, then diverge less quickly. Angle of emergence and angle of incidence would be the same.
The overall effect of the layer would not be to change the angle at which the light is travelling, merely to slightly change the position from which the light appears to come.
For a flat sheet giving focussing effects one would use a fresnel lens, or conceivably one would have a material of varying refractive index.
--
Murky
Putting on the serious face:
I'm unsure about this bit, but I think you'll find that we couldn't have the equivalent of a doughnut (with a hole) due to the topology of the situation. (I.e. the hole has to be there the whole time, this leads to problems with the big bang which I don't understand). We could have the equivalent of a doughnut (with the jam) though.
Of course, we would not perceive the jam as we're only using the doughnut as a 2 dimensional analogue of our universe and considering it's surface only.
In this kind of universe you could look at the back of your head if you had a powerful enough telescope.
Except for the Cosmic Background Radiation (the icing sugar?), and also Inflation (the size of the doughnut?). Because of Inflation the light hasn't had time to go round yet). You'd also have to be very long lived (the doughnut would go stale).
There's a nice George Gamow story about Mr. Tompkins which looks at all this stuff.
It doesn't use doughnuts.
--
Murky
I don't know about the retail side, but penguin seem to doing okay from this end by looking at the www, and I'm unaware of even that facility here. Of course I realise that Linux boxes will be negligable in retail compared to Windows PCs, but I've seen US online retailers (e.g. penguin, off the top of my head) offering to supply preconfigured Linux PCs, but only in the US.
Linux does have a presence in the software isles -- spend 50 to 100 US and you can walk out with the latest box of your favorite distribution as long as it's RedHat (ok, ok, they have a few other options on the shelf as well).
By 'box' I meant 'box containing processor hard drive etc'... whilst many people will like to configure their own computer, many others will, at least the first time out, like to play on a Linux system they know will work! Especially with drivers and so forth. This combined with the getting people on to Linux in the first place prompted the (possibly poorly put) question about whether RedHat has considered promoting 'Linux Inside' options from the PC manufacturers.....
Anyhow, if I'm wrong about preconfigured Linux PCs being available in the states, even if you have to seek them out, (and I accept I probably am wrong, it's just an impression) it doesn't change the point that it might be a nice idea to have Linux Inside PCs to get people started. (Also it might keep the Win only hardware at bay by creating a wider market).
Me? I'd LOVE to play with Linux, but can only afford one machine, and I can't afford downtime if I mess up! Soon I'll get a second (cheap) machine.... and away I go. I've been saying that for.. oh, years now.
Now.... will I be able to take a windows laptop to and from work and be able to happily plug it into a Mac ethernet there and my (forthcoming) Linux network at home....? La de dum.....
Regards,
--
Murky
The article actually talks of a negative refractive index.
Refractive index is defined as c/v where c is speed of light in vacuo, and v is speed of light in material.
A negative refractive index implies that when light hits the boundary from one side, it is also approaching the boundary from the other. Needless to say that this would have all sorts of problems with causality.
What's probably implied is that the refractive index is less than 1. This is actually fine, but it does not imply the signal in the material is faster than light.
Sound odd?
Refractive index is based upon the 'phase velocity' which does not have to be the same as the 'group velocity'. Imagine a little packet of waves. The group velocity is the speed of the packet - this can't be greater than c. The phase velocity is the speed of the wave peaks within that packet.
If you imagine travelling along with that packet of waves, the waves would appear at the back of the packet, grow, and die away at the front. The peaks travel faster than the group, but no information beats the group.... Einstein can rest easy. (This only happens in summat called a dispersive medium by the way, i.e. anything where wave speed depends upon freq, and it happens because a wave packet, being other than a pure sine wave contains a range of frequencies which travel at different speeds giving a sort of beating effect)
Materials with a refractive index of less than 1 are well known. For example, there is a famous Pink Floyd Album with a prism on the cover.....
--
Murky
Are there any plans for Redhat to enter into agreements with PC manufacturers to provide preconfigured, supported, possibly dual boot, 'Redhat Inside' computers, in much the same way that Penguin operates in the US?
--
Murky
The rubber sheet is the boundary in this case. The region enclosed by the sheet not including the sheet has no boundary (but it is bounded).
No. Let me try and make my meaning clear. Imagine a 2 dimensional creature, which lives in this two dimensional world of the balloon surface. That creature will have no conception of inside or outside the balloon, but we, as 3 dimensional beings can see the balloon is really curved. The 2D Creature could determine if their space was curved by making measurements, such as checking to see if the angles in a triangle add up to 180 degrees. (For a small triangle they do, for a large trangle they don't). This creature could travel and never reach a boundary of their 'space' - though the space is finite and could expand. It is not a meaningful question for that creature to ask 'What is my space enclosing?' as they have no conception of a third dimension.
By analogy, the curvature of space refers to a bending in 4 dimensions, but we as 3 dimensional beings cannot see it. Our space could be finite, but this does not imply a boundary we could ever reach (a brick wall at the edge of space).
Anyhow, that was an aside to the original point, and probably highly irrelevant.
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Murky
That's fine...
Open = expands forever
So's that....
Flat = reaches a ceratin size then stops expanding but stays that size forever
Not so. It expands forever but with a speed asympotically approaching zero (and a size asymptotically approaching a maximum). I know I'm being pedantic.... what the hell.
Oh, for anyone who is wondering: Yes, you can have a finite size without an edge. For ease of thought, consider a 2 dimensional example. Imagine a rubber sheet (ah, good ol' rubber sheets... what would cosmologists or incontinent physicists do without 'em?. Shape it into a balloon. This has no boundary, but it's surface can expand.
Back to the point. One of the articles (Chronicle?) said:
By measuring the supernova's red shift, the Berkeley astronomers determined that it is as far away -- and as bright -- as it should be if one assumes that it existed at a time when the cosmos was decelerating under gravitational tug, soon after the Big Bang.
The key here is that they used the red shift to give distance. This relies upon Hubble's constant, Hubbles constant has HUGE errors on it (of the order of 60% if I recall.....
Therefore, I'd like to see a more detailed explanation of how a supernova of an unusual luminosity implies that Einstein's stab in the dark (the Cosmological Constant) was not such a blind guess...
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Murky
One issue though: Funding. The page says that they're seeking partners for the funding.... How would this work exactly? This engineering course was brought to you today by..?
It'd be interesting if this was extended into an 'Open University' model, which would allow distance learning. Especially if other Universities jumped on the bandwagon (as Mordred indicated), Harvard, Yale, Oxbridge - or even my old Uni, Birmingham, UK.
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Murky